JOURNALOF NEIJROPH~SIOLOGY Vol. 67, No. 1, January 1992. Printed
in U.S.A.
n in the Cat Visual C
ritic
N. W. DAW, K. FOX, H. SATO, AND D. CZEPITA Department of Cell Biology and Physiology, Washington University Medical SUMMARY
AND
CONCLUSIONS
I. Cats were monocularly deprived for 3 mo starting at 8-9 mo, 12 mo, 15 mo, and several years of age. Single cells were recorded in both visual cortexes of each cat, and the ocular dominance and layer determined for each cell. Ocular dominance histograms were then constructed for layers II/III, IV, and V/VI for each group of animals. 2. There was a statistically significant shift in the ocular dominance for cells in layers II/III and V/VI for the animals deprived between 8-9 and 1 I- 12 mo of age. There was a small but not statistically significant shift for cells in layer IV from the animals deprived between 8-9 and 1 l- 12 mo of age, and for cells in layers V/VI from the animals deprived between 15 and 18 mo of age. There was no noticeable shift in ocular dominance for any other layers in any other group of animals. 3. We conclude that the critical period for monocular deprivation is finally over at - 1 yr of age for extragranular layers (layers II, III, V, and VI) in visual cortex of the cat.
INTRODUCTION
Synaptic connections in cat and primate visual cortex are altered by abnormal visual input early in life. Several types of visual deprivation have been investigated, including closure of one eye, strabismus, rearing in lines of one orientation, and rearing in an environment continually moving in one direction (see Mitchell and Timney 1984). The resulting deficits found in the properties of single cortical cells are specific to the visual deprivation: that is, monocular deprivation affects ocular dominance, rearing in lines of one orientation affects orientation specificity, and so on. There is a critical period for the effects of visual deprivation (Hubel and Wiesel 1970; Wiesel 1982) that varies with the type of visual deprivation involved: for example, the critical period for rearing in an environment continually moving in one direction ends earlier than the critical period for monocular deprivation (Berman and Daw 1977; Daw and Wyatt 1976). It is commonly stated that the critical period for monocular deprivation in the cat lasts from 3 wk to 3 mo of age. This is based on early investigations (Hubel and Wiesel 1970; Olson and Freeman 1980; Wiesel and Hubel1963) in which results from cells in all layers of cortex were combined and the number of animals tested in each age group was small. There is convincing evidence from both cat and primate that the critical period for changes in layer IV ends earlier than the critical period for cells in other layers (LeVay et al. 1980; Mower et al. 1985). Layer IV probably becomes stabilized when the lateral geniculate afferents become segregated into eye-specific bands around 50-60 days of age (LeVay et al. 1978; Shatz and Stryker 1978). Experi-
School, St. Louis, Missouri
63110
ments that combine results from cells in all layers in animals deprived after 8 wk of age will therefore underestimate the effects of monocular deprivation, because the effects on cells in layer IV, which are small, are averaged in with the effects on cells in layers II, III, V, and VI, which may be substantial. In fact, there is good evidence that monocular deprivation has an effect in animals deprived for 1 mo at 8 mo of age, even when the results from all layers are combined (Jones et al. 1984). The question of when, or indeed if, the critical period ends for extragranular layers (the layers outside layer IV) is therefore unresolved. We decided to investigate when the critical period ends in extragranular layers, and to compare the end of the critical period in layers II and III with the end of the critical period in layers V and VI for additional reasons. First, we have shown that N-methyl-o-aspartate (NMDA) receptors are functionally effective in layers II and III in animals around 1 yr of age, whereas they are not functionally effective in other layers (Fox et al. 1989b). Several authors have suggested that NMDA receptors may be involved in the effects of visual deprivation (Bear et al. 1990; Kleinschmidt et al. 1987). The consequent implication is that the critical period should end in layers II and III later than it does in layers V and VI. Second, we have been investigating the hypothesis that hormones that may rise around the time of puberty may reduce the effects of monocular deprivation (Daw et al. 1987, 199 1). In evaluating these hypotheses, it is clearly important to know when the critical period finally ends. An abstract of these results has been presented (Fox et al. 1989a). METHODS
Monocular
deprivation
Sixteen cats were monocularly deprived for 3 mo, starting at 8-9mo(n=6), 12mo(n=4), 15mo(n=4),andseveralyears of age ( y1= 2). In each group, one-half had the left eye occluded, and one-half had the right eye occluded. The eyelids of one eye were sutured closed under ketamine anesthesia (20-30 mg/ kg im). The lid margins were cut after dropping proparacaine hydrochloride (Alcaine) onto the cornea; polymyxin b-bacitracin-neomycin (Neosporin) eye ointment was applied, then the margins were closed with 4-O thread, leaving a small aperture on the medial side for drainage.
Recordings Recordings were made from both visual cortexes, one cortex on the first day and the other cortex on the second day. In each group the ipsilateral cortex was recorded first in one-half the experiments, and the contralateral cortex first in the other half. The animal was given preanesthetic doses of acepromazine (0.1 mg/ kg
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DAW, FOX, SATO, AND CZEPITA
im) and atropine (0.04 mg/ kg im), then anesthesiawasinduced with 4% halothanein 34%oxygen-66% nitrous oxide. A tracheal tube wasinserted,an intravenousline wasplacedinto the femoral vein, the headwasplacedin a stereotaxicinstrument, and the skull and dura wereopened.Anesthesiawasmaintainedwith 0.7- 1.5% halothane, the depth being judged by reactions before paralysis and by heart rate and cortical recordingsafter paralysis.Paralysis wasinduced with Pavulon (pancuronium bromide, OS- 1.5 mg/ h). Body temperaturewasmaintainedat 365°C by a thermostatically controlled heatingpad, and end-tidal CO, at 4%by adjusting the rate and/or volume of respiration. The eyeswerefocusedon a tangent screenat 57 in. by lensesof zero power and appropriatecurvature. The nictitating membrane was withdrawn by a drop of 10%phenylephrine hydrochloride (Neo-Synephrine) and the pupils dilated with a drop or two of atropine (0.125 mg/ml). A tungstenelectrode(Hubel 1957)was insertedinto the cortex for recordingsfrom singlecells. Receptivefieldswerecharacterizedby the useof a light projector moved by hand. The preferred width and length of stimulus, preferred orientation, and velocity and direction of movement wereall determined,then the responses in the two eyeswerecompared. Two observersindependently assignedan ocular dominanceaccordingto the seven-pointscaleintroduced by Hubel and Wiesel( 1962).About four penetrationsweremadein eachcortex, spaced0.5-l mm apart betweenAPO and P4. For the first millimeter,while the electrodewasexpectedto stayin a singlecolumn, cells were sampledevery 330 pm; after that they were sampled every 166pm. The electrodewasangledat 15-20° to the vertical, to sampleas many layersand columnsaspossible.Lesionswere made every millimeter to determine the layer for each cell recorded. At the end of the secondday of recordings,surgicallevels of anesthesiawere reachedby raisingthe halothaneto 4% until the heart slowed,then the chestwasopened,and the animal wasperfusedthrough the heart with phosphate-bufferedsalinefollowed by 10%Formalin. Frozen sectionsof the visual cortex were cut at 60 ,umand stainedwith cresyl violet, then the penetrationswere reconstructed.
IPSIIATERAL
TO OPEN
CONTRALATERAL
EYE
LAYERS 11/111
50
TO OPEN
EYE
LAYERS ll/lll
1 4-o 30
t t
LAYER Iv
LAYERS V/b
50
LAYERS V/b
40
30 20 10 O
I L-
1
OEYE
234567
1234567 OPEN EYE
DOMINANCE
CLOSED EYE
GROUP
FIG. 1. Ocular dominance histograms from 6 animals deprived for 3 mo between 8 and 12 mo of age. Results are separated into histograms for layers II /III, IV, and V/ VI recorded from cortexes ipsilateral and contralatera1 to the open eye. Total number of cells recorded: layers II/ III, ipsilatera1 7 1, contralateral 90; layer IV, ipsilateral 6 1, contralateral 74; layers V/VI, ipsilateral 95, contralateral 94.
ence was quantified by calculating weighted ocular dominance for each animal. The results are 0.258 -t 0.085 Data analysis (mean t SD) for the contralateral cortexes and 0.625 t Weighted ocular dominance was calculated from the ocular 0.145 for the ipsilateral cortexes. These weighted ocular dominance values are significantly different (2-tailed t test, dominancehistogramsaccordingto the formula P < 0.0 1). The values in layer IV (0.402 t 0.097 contralat1/6N, + 2/6N, + 3/6N, + 4/6N, + 5/6N, + N7 eral, 0.539 t 0.198 ipsilateral) were not statistically differNl + N2 + N3 + N4 + Nj + N6 + NT ent (2-tailed t test, P > 0.2). However, the weighted ocular whereN, is the number of cellsin ocular dominancegroup i (Ka- dominances in layers V and VI were clearly and significantly different (0.237 t 0.069 contralateral, 0.645 t 0.092 samatsuet al. 1981). ipsilateral; P < 0.00 1 ), even more so than those for layers II and III. RESULTS The shift in weighted ocular dominance values in relaFor each cat the cells were grouped by layer into three tion to normal animals is about equal for both cortexes groups: layers II and III, layer IV, and layers V and VI. For (Table 1). For normal animals, we averaged published and each group the ocular dominance histograms for the cor- unpublished data from the laboratories of Shatz and texes contralateral and ipsilateral to the open eye were comStryker ( 1978) and ourselves, showing weighted ocular pared. If there is no effect of monocular deprivation, then dominances of 0.445 in layers II and III, 0.466 in layer IV, these histograms should appear the same from bilateral and 0.400 in layers V and VI. If we compare these values symmetry: any effect of monocular deprivation shows up as with those found in the present experiment, the average a difference between the histograms, and the strength of the shift in the monocularly deprived animals in layers II and effect can be measured by the extent of the difference. III was 0.188 for the contralateral cortex and 0.180 for the Six animals were deprived for 3 mo starting at 8-9 mo of ipsilateral; in layer IV, 0.064 for the contralateral and 0.073 age (4 animals had both cortexes recorded; in 2, only 1 for the ipsilateral; and in layers V and VI, 0.163 for the cortex was recorded to give 5 samples, both contralateral contralateral and 0.245 for the ipsilateral cortex. The imand ipsilateral) . The ocular dominance histograms for cells portant point to note is that there is a bias toward domiin layers II and III were clearly different (Fig. 1) . The differnance by the contralateral eye in all layers in the normal Downloaded from www.physiology.org/journal/jn by ${individualUser.givenNames} ${individualUser.surname} (129.108.009.184) on October 31, 2018. Copyright © 1992 American Physiological Society. All rights reserved.
CRITICAL
PERIOD FOR MONOCULAR
Weighted OD and OD shiftsfor animals deprived from 8-9 to 11-12 mo of age TABLE
DEPRIVATION IPSILATERAL
1.
IN CAT TO OPEN
199
EYE
CONTRAIATERAL
LAYERS 11/111
50
lAYERS
TO OPEN
EYE
ll/lll
40
Contralateral
Normal Animals
Eye Open
Layers
Weighted
OD
II/III IV V/VI
0.258 I!I 0.85 0.402 of: 0.097 0.237 -t 0.069
OD Shift 0.188 0.064 0.163
Weighted
30
Ipsilateral OD
OD Shift
0.445 0.466 0.400
I
Eye Open Weighted
0.180 0.073 0.245
0.625 0.539 0.645
OD I?I 0.145 rt 0.198 AI 0.092
Values are means + SD. OD, ocular dominance.
LAYER N
50
LAYER Iv
40 30
animal, so that a shift in weighted ocular dominance that is about the same for both cortexes will lead to a contralateral cortex that is more dominated by the contralateral eye than the ipsilateral cortex is by the ipsilateral eye. Four animals were monocularly deprived for 3 mo between 12 and 15 mo of age. The ocular dominance histograms for the cortexes ipsilateral to the open eye appeared similar to those for the cortexes contralateral to the open eye in all layers ( Fig. 2). Four animals were monocularly deprived for 3 mo between 15 and 18 mo of age. The ocular dominance histograms in layers II and III, and in layer IV for ipsilateral and contralateral cortexes, appeared similar to each other, but the histograms in layers V and VI were different (Fig. 3). The weighted ocular dominances in layers V and VI for the IPSILATERAL
TO OPEN
EYE
CONTRALATERAL
TO OPEN
EYE
40
30
1
1 I
4
40 30 I
IAYERS V/bl
LAYERS V/Vi
50
1
4-o 30 /
:J-+--J1 01
i
LAYER Iv
LAYER IV
50
10 L-J
50T
LAYERS V/!/l
LAYERS V/id
40 30 t
%Lc5LLkJ 6
CLOSED M
7
6
OPEN M
OCULAR
DOMINANCE
7
CLOSED M
GROUP
3. Ocular dominance histograms as in Fig. 1 for 4 animals deprived for 3 mo between 15 and 18 mo of age. Total number of cells recorded: layers II/ III, ipsilateral63, contralateral 7 1; layer IV, ipsilateral 78, contralateral 69; layers V/VI, ipsilateral73, contralateral 80. FIG.
LAYERS ll/lll
LAYERS ll,‘lll
50
20
1234567
1234567
CLOSED M
OPEN M
OCULAR
DOMINANCE
CLOSED EYE
cortexes contralateral to the open eye were 0.371 t 0.033, and for the cortexes ipsilateral to the open eye were 0.533 t 0.137. These were different from each other, but not at the usually accepted level of significance ( t test, P < 0.10 ) . Two adult animals, deprived for 3 mo at several years of age were also recorded, and ocular dominance histograms for ipsilateral and contralateral cortexes appeared similar in all layers (Fig. 4). These results are summarized in Fig. 5, where the mean and standard deviations for the weighted ocular dominance shifts in each group of animals are plotted as a function of age and of layer. The general conclusion is that there is substantial plasticity in extragranular layers at 8- 12 mo of age, but very little in layer IV. There is little evidence for plasticity in layers II and III after 12- 15 mo of age. There is some indication that ocular dominance shifts can occur in layers V and VI with a 3-mo monocular deprivation between 15 and 18 mo of age, but this result was not confirmed when animals deprived from 12 to 15 mo of age were recorded. The ocular dominance shift in layers V and VI for animals deprived between 8 and 12 mo of age was slightly larger than the shift in layers II and III, so layers V and VI may be more plastic than layers II and III, but the reverse is certainly not true.
GROUP
FIG. 2. Ocular dominance histograms as in Fig. 1 for 4 animals deprived for 3 mo between 12 and 15 mo of age. Total number of cells recorded: layers II/III, ipsilateral 38, contralateral 42; layer IV, ipsilateral 33. contralateral 28: lavers V/VI. ipsilateral66. contralateral 6 1.
DISCUSSION
These results show that the critical period for ocular dominance shifts lasts longer than meviouslv suggested. The sus-
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DAW, FOX, SATO, AND CZEPITA
200 IPSIIATERAL
TO OPEN
EYE
CONTRALATERAL
TO OPEN
EYE
LAYERS ll/lll
50 4-o 30 20
1
10
I
,
0
LAYER Iv
501
LAYER N
1
I
LAYERS VP
50
4-o
’
LAYERS V/t/l
T
30 20 10
I
‘1234567
1234567
CLOSED M
OPEN M
OCULAR
DOMINANCE
4 CLOSED M
GROUP
FIG. 4. Ocular dominance histograms as in Fig. 1 for 2 animals deprived for 3 mo at several years of age. Total number of cells recorded: layers 11/III, ipsilateral34, contralateral 29; layer IV, ipsilaterd 28, contralateral 34; layers V/ VI, ipsilateral 3 1, contralateral 27.
ceptibility of the cortex to monocular deprivation arises between 3 and 4 wk of age. Between 4 and 6 wk of age, the ocular dominance in all layers can be completely shifted by a few days of monocular deprivation (Hubel and Wiesel 1970; Movshon and Dursteller 1977; Olson and Freeman 1975 ) . The critical period then declines sharply for layer IV, and more slowly for layers II, III, V, and VI between 6 wk and 1 yr of age. It is well established that monocular deprivation affects the synapses between lateral geniculate cells and cells in the cortex. This paper shows that monocular deprivation also affects the synapses between cells in layer IV and cells in other layers of the cortex. This point was implicit in previous results showing that monocular deprivation shifts the ocular dominance histogram further in layers II, III, V, and VI than it does in layer IV for animals monocularly deprived to several months of age ( Shatz and Stryker 1978 ) and in results showing that monocular deprivation at later ages can have a substantial effect on layers II, III, V, and VI when it has very little effect on layer IV (LeVay et al. 1980; Mower et al. 1985). The general flow of information within visual cortex is from layer IV to layers II and III to layers V and VI, although the detailed picture is clearly much more complicated than this. We cannot say from our results which of the intracortical synapses are affected by monocular deprivation late in the critical period. If we had found that cells in layers II/ III were affected substantially more or substantially less than cells in layers V/VI, some conclusions on
this point would have been possible. In fact, what we found was that layers V/VI may have been affected slightly more than layers II/III, but the difference was not significant. Nevertheless, it seems very likely that the synapses between layer IV and layers II/ III are affected. This must occur by a loss of strength of the connections from cells in layer IV that are primarily driven by the closed eye. Results from different laboratories for the overall ocular dominance shifts that occur are summarized in Fig. 6. Olson and Freeman ( 1980) deprived animals for 10 days of age at various ages between 10 days and 120 days, recording one animal at each age. Jones et al. ( 1984) deprived animals for 1 mo at various ages between 1 and 8 mo, recording four animals at each age. We deprived animals for 3 mo at various ages between 8 and 18 mo of age, recording several animals at each age. Also shown in Fig. 6 are results from several different laboratories from normal animals (Albus 1975; Albus and Wolf 1984; Hubel and Wiesel 1962; Jones et al. 1984; Shatz and Stryker 1978). Because there is a bias toward dominance by the contralateral eye in normal animals, the weighted ocular dominance shift should be compared with 0.45 rather than 0.5. Why have previous authors, with a few exceptions (Cynader et al. 1980; Jones et al. 1984), not noticed that ocular dominance shifts can occur in animals up to 1 yr of age? First, most previous authors have combined the results from all layers together. As noted above, this will include cells from layer IV that are not plastic together with cells in layers II, III, V, and VI that are plastic. Second, the bias toward dominance by the contralateral eye has often been ignored. We recorded from both cortexes in each animal
““T@\ 0.0
1 .o -i-J
Layers
I I
!
II and III
1 I
T
i
Layer
IV
d 0.0
I 1
I
I 1
la0
1
Layers
V and VI
/
Conga
to Open iI
Eye
1
!1
2
Age (years) FIG. 5. Weighted ocular dominance shifts for each group of animals as a function of age and layer. Points at 4-6 wk of age come from Shatz and Stryker ( 1978), who recorded only from the cortex ipsilateral to the open eye. Results from cortexes contralateral to the open eye are plotted with open circles, results from cortexes ipsilateral to the open eye are plotted with closed circles. Means and standard deviations are shown for each group of animals. Where the standard deviation does not show, it was sufficiently small that it fell within the symbol used for plotting the mean.
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CRITICAL
.
Monocular
0.8
c
\
-y 0.6 0 ti d
PERIOD FOR MONOCULAR
IN CAT
201
to changes in NMDA receptors (Bode-Greuel and Singer 1989; Fox et al. 1989; Gordon et al. 199 1; Tsumoto et al. 1987), although the causal mechanism remains to be worked out. The second clearly is not. Very likely therefore there are at least two mechanisms involved.
Deprived
A\*/.
8
0.4 Normal
Binocular
0.2 0
DEPRIVATION
0
2
4
6
8
Age (months
10
12
14
16
18
adult
post-natal)
FIG. 6. Ocular dominance shifts from various laboratories for all layers combined. Results from Olson and Freeman ( 1980) for 10 days of deprivation ( n ), from Jones et al. ( 1984) for 1 mo of deprivation (A ), and from us for 3 mo of deprivation ( l ). Results for normal animals (o ) come from Hubel and Wiesel( 1962), Albus ( 1975), Shatz and Stryker ( 1978), Albus and Wolf ( 1984), and from unpublished data from C. J. Shatz and M. P. Stryker and from our laboratory.
and compared the results from the contralateral and ipsilatera1 cortexes. This allows each animal to be used as a control for itself, taking into account the contralateral bias, and also any variation in this bias that there may be between animals. Third, very few animals have been recorded with monocular deprivation at around 1 yr of age. Fourth, the susceptibility of the cortex to monocular deprivation has clearly declined by 8- 12 mo of age, so that deprivation for a period of at least 1 mo is required to get a substantial effect. We started this experiment partly because NMDA receptors are driven by the visual input in layers II and III, but not in layers V and VI, in adolescent and adult cats, and some authors have suggested that NMDA receptors are associated with plasticity. We found that the critical period for layers II and III ends at around the same time as the critical period for layers V and VI: if anything, layers V and VI remain plastic for ocular dominance shifts longer than layers II and III. After 1 yr of age, NMDA receptors are present in layers II and III, but ocular dominance shifts do not occur. Consequently, the presence of NMDA receptors is not an indicator of plasticity for monocular deprivation. NMDA receptors in layers II and III of adolescent and adult cat must have some other function. When we began the experiment, we wished to determine whether the critical period finally ends around puberty. Our results show that it does. Unfortunately, our experiments on the effects of hormones on ocular dominance plasticity do not confirm a simple correlation. Testosterone, which increases around puberty, has a very small effect on ocular dominance shifts (Daw et al. 1987). Cortisol reduces ocular dominance shifts substantially, but blood levels of cortisol do not increase around puberty enough to implicate it in the termination of the critical period (Daw et al. 1991). It is clear from these results that there are two phases to the decline of the critical period, one between 5 and 8 wk of age that is related primarily to events in layer IV, and another between 8 and 12 mo of age that is related primarily to events in layers II, III, V, and VI. The first may be related
We thank J. Peters and J. Watkins for help with the experiments, Drs. Nina Tumosa and Jeff Lichtman for comments on the manuscript, and Dr. Michael Ullery for consultation on the statistics. This research was supported by National Eye Institute Grant EY-00053 and a grant from the Human Frontier Science Program. K. Fox was partly supported by the McDonnell Center for Higher Brain Function. H. Sato was a Research to Prevent Blindness International Research Scholar. Address for reprint requests: N. W. Daw, Dept. of Anatomy and Neurobiology, Washington University Medical School, 4566 Scott Ave., St. Louis, MO 63110. Received 19 April 199 1; accepted in final form 2 1 August 199 1. REFERENCES K. Predominance of monocularly driven cells in the projection area of the central visual field in the cat’s striate cortex. Brain Res. 89: 341-347, 1975. ALBUS, K. AND WOLF, W. Early postnatal development of neuronal function in the kitten’s visual cortex: a laminar analysis. J. Physiol. Land. 348: 153-185, 1984. BEAR, M. F., KLEINSCHMIDT, A., Gu, Q., AND SINGER, W. Disruption of experience-dependent synaptic modifications in striate cortex by infusion of an NMDA receptor antagonist. J. Neurosci. 10: 909-925, 1990. BERMAN, N. AND DAW, N. W. Comparison of the critical period for monocular and direction deprivation in cats. J. Physiol. Lond. 265: 249-259, 1977. BODE-GREUEL, K. M. AND SINGER, W. The development of N-methyl-Daspartate receptors in cat visual cortex. Dev. Brain Res. 46: 197-204, 1989. &NADER, M. S., TIMNEY, B. N., AND MITCHELL, D. E. Period of susceptibility of kitten visual cortex to the effects of monocular deprivation extends beyond six months of age. Brain Res. 19 1: 545-550, 1980. DAW, N. W., BAYSINGER, K. J., AND PARKINSON, D. Increased levels of testosterone have little effect on visual cortical plasticity in the kitten. J. Neurobiol. 18: 141-154, 1987. DAW, N. W., SATO, H., Fox, K., CARMICHAEL, T., AND GINGERICH, R. Effect of cortisol on monocular deprivation in the cat visual cortex. J. Neurobiol. 22: 158-168, 1991. DAW, N. W. AND WYATT, H. J. Kittens reared in a unidirectional environment: evidence for a critical period. J. Physiol. Land. 257: 155-170, 1976. Fox, K., DAW, N. W., AND SATO, H. Plasticity in adult and adolescent cat visual cortex. Sot. Neurosci. Abstr. 15: 796, 1989a. Fox, K., SATO, H., AND DAW, N. W. The location and function of NMDA receptors in cat and kitten visual cortex. J. Neurosci. 9: 2443-2454, 1989b. GORDON, B., DAW, N. W., AND PARKINSON, D. The effect of age on binding of MK-80 1 in the cat visual cortex. Dev. Brain Res. 62: 6 l-68, 199 1. HUBEL, D. H. Tungsten microelectrode for recording from single units. Science Wash. DC 125: 549-550, 1957. HUBEL, D. H. AND WIESEL, T. N. Receptive fields, binocular interaction and functional architecture in cat’s visual cortex. J. Physiol. Land. 160: 106-154, 1962. HUBEL, D. H. AND WIESEL, T. N. The period of susceptibility to the physiological effects of unilateral eye closure in kittens. J. Physiol. Lond. 206: 419-436, 1970. JONES, K. R., SPEAR, P. D., AND TONG, L. Critical periods for effects on monocular deprivation: differences between striate and extrastriate cortex. J. Neurosci. 4: 2543-2552, 1984. KASAMATSU, T., PETTIGREW, J. D., AND ARY, M. Cortical recovery from the effects of monocular deprivation: acceleration with norepinephrine and suppression with 6-hydroxydopamine. J. Neurophysiol. 45: 254266, 1981. KLEINSCHMIDT, A., BEAR, M. F., AND SINGER, W. Blockade of “NMDA” ALBUS,
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receptors disrupts experience-dependent plasticity of kitten striate cortex. Science Wash. DC238: 355-358, 1987. LEVAY, S., STRYKER, M. P., AND SHATZ, C. J. Ocular dominance columns and their development in layer IV of the cat’s visual cortex: a quantitative study. J. Comp. Neurol. 179: 223-244, 1978. LEVAY, S., WIESEL, T. N., AND HUBEL, D. H. The development of ocular dominance columns in normal and visually deprived monkeys. J. Comp. Neurol. 191: l-5 1, 1980. MITCHELL, D. E. AND TIMNEY, B. Postnatal development of function in the mammalian visual system. In: Handbook of Physiology. The Nervous System. Sensory Processes. Bethesda, MD: Am. Physiol. Sot., 1984, sect. 1, vol. III, p. 507-555. MOVSHON, J. A. AND DURSTELLER, M. R. Effects of brief periods ofunilatera1 eye closure on the kitten’s visual system. J. Neurophysiol. 40: 12551265, 1977. MOWER,G. D., CAPLAN,~. J., CHRISTEN, W.G., AND Dum,F.H.Dark
rearing prolongs physiological but not anatomical plasticity of the cat visual cortex. J. Comp. Neurol. 235: 448-466, 1985. OLSON, C. R. AND FREEMAN, R. D. Progressive changes in kitten striate cortex during monocular vision. J. Neurophysiol. 38: 26-32, 1975. OLSON, C. R. AND FREEMAN, R. D. Profile of the sensitive period for monocular deprivation in kittens. Exp. Brain Res. 39: 17-2 1, 1980. SHATZ, C. J. AND STRYKER, M. P. Ocular dominance in layer IV of the cat’s visual cortex and the effects of monocular deprivation. J. Physiol. Lond. 281: 267-283, 1978. TSUMOTO, T., HAGIHARA,K.,SATO, H., ANDHATA, Y.NMDAreceptors in the visual cortex of young kittens are more effective than those of adult cats. Nature Lond. 327: 5 13-5 14, 1987. WIESEL, T. N. Postnatal development of the visual cortex and the influence of environment. Nature Lond. 299: 583-59 1, 1982. WIESEL, T. N. AND HUBEL, D. H. Single cell responses in striate cortex of kittens deprived of vision in one eye. J. Neurophysiol. 26: 1003- 10 17, 1963.
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in U.S.A.
n in the Cat Visual C
ritic
N. W. DAW, K. FOX, H. SATO, AND D. CZEPITA Department of Cell Biology and Physiology, Washington University Medical SUMMARY
AND
CONCLUSIONS
I. Cats were monocularly deprived for 3 mo starting at 8-9 mo, 12 mo, 15 mo, and several years of age. Single cells were recorded in both visual cortexes of each cat, and the ocular dominance and layer determined for each cell. Ocular dominance histograms were then constructed for layers II/III, IV, and V/VI for each group of animals. 2. There was a statistically significant shift in the ocular dominance for cells in layers II/III and V/VI for the animals deprived between 8-9 and 1 I- 12 mo of age. There was a small but not statistically significant shift for cells in layer IV from the animals deprived between 8-9 and 1 l- 12 mo of age, and for cells in layers V/VI from the animals deprived between 15 and 18 mo of age. There was no noticeable shift in ocular dominance for any other layers in any other group of animals. 3. We conclude that the critical period for monocular deprivation is finally over at - 1 yr of age for extragranular layers (layers II, III, V, and VI) in visual cortex of the cat.
INTRODUCTION
Synaptic connections in cat and primate visual cortex are altered by abnormal visual input early in life. Several types of visual deprivation have been investigated, including closure of one eye, strabismus, rearing in lines of one orientation, and rearing in an environment continually moving in one direction (see Mitchell and Timney 1984). The resulting deficits found in the properties of single cortical cells are specific to the visual deprivation: that is, monocular deprivation affects ocular dominance, rearing in lines of one orientation affects orientation specificity, and so on. There is a critical period for the effects of visual deprivation (Hubel and Wiesel 1970; Wiesel 1982) that varies with the type of visual deprivation involved: for example, the critical period for rearing in an environment continually moving in one direction ends earlier than the critical period for monocular deprivation (Berman and Daw 1977; Daw and Wyatt 1976). It is commonly stated that the critical period for monocular deprivation in the cat lasts from 3 wk to 3 mo of age. This is based on early investigations (Hubel and Wiesel 1970; Olson and Freeman 1980; Wiesel and Hubel1963) in which results from cells in all layers of cortex were combined and the number of animals tested in each age group was small. There is convincing evidence from both cat and primate that the critical period for changes in layer IV ends earlier than the critical period for cells in other layers (LeVay et al. 1980; Mower et al. 1985). Layer IV probably becomes stabilized when the lateral geniculate afferents become segregated into eye-specific bands around 50-60 days of age (LeVay et al. 1978; Shatz and Stryker 1978). Experi-
School, St. Louis, Missouri
63110
ments that combine results from cells in all layers in animals deprived after 8 wk of age will therefore underestimate the effects of monocular deprivation, because the effects on cells in layer IV, which are small, are averaged in with the effects on cells in layers II, III, V, and VI, which may be substantial. In fact, there is good evidence that monocular deprivation has an effect in animals deprived for 1 mo at 8 mo of age, even when the results from all layers are combined (Jones et al. 1984). The question of when, or indeed if, the critical period ends for extragranular layers (the layers outside layer IV) is therefore unresolved. We decided to investigate when the critical period ends in extragranular layers, and to compare the end of the critical period in layers II and III with the end of the critical period in layers V and VI for additional reasons. First, we have shown that N-methyl-o-aspartate (NMDA) receptors are functionally effective in layers II and III in animals around 1 yr of age, whereas they are not functionally effective in other layers (Fox et al. 1989b). Several authors have suggested that NMDA receptors may be involved in the effects of visual deprivation (Bear et al. 1990; Kleinschmidt et al. 1987). The consequent implication is that the critical period should end in layers II and III later than it does in layers V and VI. Second, we have been investigating the hypothesis that hormones that may rise around the time of puberty may reduce the effects of monocular deprivation (Daw et al. 1987, 199 1). In evaluating these hypotheses, it is clearly important to know when the critical period finally ends. An abstract of these results has been presented (Fox et al. 1989a). METHODS
Monocular
deprivation
Sixteen cats were monocularly deprived for 3 mo, starting at 8-9mo(n=6), 12mo(n=4), 15mo(n=4),andseveralyears of age ( y1= 2). In each group, one-half had the left eye occluded, and one-half had the right eye occluded. The eyelids of one eye were sutured closed under ketamine anesthesia (20-30 mg/ kg im). The lid margins were cut after dropping proparacaine hydrochloride (Alcaine) onto the cornea; polymyxin b-bacitracin-neomycin (Neosporin) eye ointment was applied, then the margins were closed with 4-O thread, leaving a small aperture on the medial side for drainage.
Recordings Recordings were made from both visual cortexes, one cortex on the first day and the other cortex on the second day. In each group the ipsilateral cortex was recorded first in one-half the experiments, and the contralateral cortex first in the other half. The animal was given preanesthetic doses of acepromazine (0.1 mg/ kg
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DAW, FOX, SATO, AND CZEPITA
im) and atropine (0.04 mg/ kg im), then anesthesiawasinduced with 4% halothanein 34%oxygen-66% nitrous oxide. A tracheal tube wasinserted,an intravenousline wasplacedinto the femoral vein, the headwasplacedin a stereotaxicinstrument, and the skull and dura wereopened.Anesthesiawasmaintainedwith 0.7- 1.5% halothane, the depth being judged by reactions before paralysis and by heart rate and cortical recordingsafter paralysis.Paralysis wasinduced with Pavulon (pancuronium bromide, OS- 1.5 mg/ h). Body temperaturewasmaintainedat 365°C by a thermostatically controlled heatingpad, and end-tidal CO, at 4%by adjusting the rate and/or volume of respiration. The eyeswerefocusedon a tangent screenat 57 in. by lensesof zero power and appropriatecurvature. The nictitating membrane was withdrawn by a drop of 10%phenylephrine hydrochloride (Neo-Synephrine) and the pupils dilated with a drop or two of atropine (0.125 mg/ml). A tungstenelectrode(Hubel 1957)was insertedinto the cortex for recordingsfrom singlecells. Receptivefieldswerecharacterizedby the useof a light projector moved by hand. The preferred width and length of stimulus, preferred orientation, and velocity and direction of movement wereall determined,then the responses in the two eyeswerecompared. Two observersindependently assignedan ocular dominanceaccordingto the seven-pointscaleintroduced by Hubel and Wiesel( 1962).About four penetrationsweremadein eachcortex, spaced0.5-l mm apart betweenAPO and P4. For the first millimeter,while the electrodewasexpectedto stayin a singlecolumn, cells were sampledevery 330 pm; after that they were sampled every 166pm. The electrodewasangledat 15-20° to the vertical, to sampleas many layersand columnsaspossible.Lesionswere made every millimeter to determine the layer for each cell recorded. At the end of the secondday of recordings,surgicallevels of anesthesiawere reachedby raisingthe halothaneto 4% until the heart slowed,then the chestwasopened,and the animal wasperfusedthrough the heart with phosphate-bufferedsalinefollowed by 10%Formalin. Frozen sectionsof the visual cortex were cut at 60 ,umand stainedwith cresyl violet, then the penetrationswere reconstructed.
IPSIIATERAL
TO OPEN
CONTRALATERAL
EYE
LAYERS 11/111
50
TO OPEN
EYE
LAYERS ll/lll
1 4-o 30
t t
LAYER Iv
LAYERS V/b
50
LAYERS V/b
40
30 20 10 O
I L-
1
OEYE
234567
1234567 OPEN EYE
DOMINANCE
CLOSED EYE
GROUP
FIG. 1. Ocular dominance histograms from 6 animals deprived for 3 mo between 8 and 12 mo of age. Results are separated into histograms for layers II /III, IV, and V/ VI recorded from cortexes ipsilateral and contralatera1 to the open eye. Total number of cells recorded: layers II/ III, ipsilatera1 7 1, contralateral 90; layer IV, ipsilateral 6 1, contralateral 74; layers V/VI, ipsilateral 95, contralateral 94.
ence was quantified by calculating weighted ocular dominance for each animal. The results are 0.258 -t 0.085 Data analysis (mean t SD) for the contralateral cortexes and 0.625 t Weighted ocular dominance was calculated from the ocular 0.145 for the ipsilateral cortexes. These weighted ocular dominance values are significantly different (2-tailed t test, dominancehistogramsaccordingto the formula P < 0.0 1). The values in layer IV (0.402 t 0.097 contralat1/6N, + 2/6N, + 3/6N, + 4/6N, + 5/6N, + N7 eral, 0.539 t 0.198 ipsilateral) were not statistically differNl + N2 + N3 + N4 + Nj + N6 + NT ent (2-tailed t test, P > 0.2). However, the weighted ocular whereN, is the number of cellsin ocular dominancegroup i (Ka- dominances in layers V and VI were clearly and significantly different (0.237 t 0.069 contralateral, 0.645 t 0.092 samatsuet al. 1981). ipsilateral; P < 0.00 1 ), even more so than those for layers II and III. RESULTS The shift in weighted ocular dominance values in relaFor each cat the cells were grouped by layer into three tion to normal animals is about equal for both cortexes groups: layers II and III, layer IV, and layers V and VI. For (Table 1). For normal animals, we averaged published and each group the ocular dominance histograms for the cor- unpublished data from the laboratories of Shatz and texes contralateral and ipsilateral to the open eye were comStryker ( 1978) and ourselves, showing weighted ocular pared. If there is no effect of monocular deprivation, then dominances of 0.445 in layers II and III, 0.466 in layer IV, these histograms should appear the same from bilateral and 0.400 in layers V and VI. If we compare these values symmetry: any effect of monocular deprivation shows up as with those found in the present experiment, the average a difference between the histograms, and the strength of the shift in the monocularly deprived animals in layers II and effect can be measured by the extent of the difference. III was 0.188 for the contralateral cortex and 0.180 for the Six animals were deprived for 3 mo starting at 8-9 mo of ipsilateral; in layer IV, 0.064 for the contralateral and 0.073 age (4 animals had both cortexes recorded; in 2, only 1 for the ipsilateral; and in layers V and VI, 0.163 for the cortex was recorded to give 5 samples, both contralateral contralateral and 0.245 for the ipsilateral cortex. The imand ipsilateral) . The ocular dominance histograms for cells portant point to note is that there is a bias toward domiin layers II and III were clearly different (Fig. 1) . The differnance by the contralateral eye in all layers in the normal Downloaded from www.physiology.org/journal/jn by ${individualUser.givenNames} ${individualUser.surname} (129.108.009.184) on October 31, 2018. Copyright © 1992 American Physiological Society. All rights reserved.
CRITICAL
PERIOD FOR MONOCULAR
Weighted OD and OD shiftsfor animals deprived from 8-9 to 11-12 mo of age TABLE
DEPRIVATION IPSILATERAL
1.
IN CAT TO OPEN
199
EYE
CONTRAIATERAL
LAYERS 11/111
50
lAYERS
TO OPEN
EYE
ll/lll
40
Contralateral
Normal Animals
Eye Open
Layers
Weighted
OD
II/III IV V/VI
0.258 I!I 0.85 0.402 of: 0.097 0.237 -t 0.069
OD Shift 0.188 0.064 0.163
Weighted
30
Ipsilateral OD
OD Shift
0.445 0.466 0.400
I
Eye Open Weighted
0.180 0.073 0.245
0.625 0.539 0.645
OD I?I 0.145 rt 0.198 AI 0.092
Values are means + SD. OD, ocular dominance.
LAYER N
50
LAYER Iv
40 30
animal, so that a shift in weighted ocular dominance that is about the same for both cortexes will lead to a contralateral cortex that is more dominated by the contralateral eye than the ipsilateral cortex is by the ipsilateral eye. Four animals were monocularly deprived for 3 mo between 12 and 15 mo of age. The ocular dominance histograms for the cortexes ipsilateral to the open eye appeared similar to those for the cortexes contralateral to the open eye in all layers ( Fig. 2). Four animals were monocularly deprived for 3 mo between 15 and 18 mo of age. The ocular dominance histograms in layers II and III, and in layer IV for ipsilateral and contralateral cortexes, appeared similar to each other, but the histograms in layers V and VI were different (Fig. 3). The weighted ocular dominances in layers V and VI for the IPSILATERAL
TO OPEN
EYE
CONTRALATERAL
TO OPEN
EYE
40
30
1
1 I
4
40 30 I
IAYERS V/bl
LAYERS V/Vi
50
1
4-o 30 /
:J-+--J1 01
i
LAYER Iv
LAYER IV
50
10 L-J
50T
LAYERS V/!/l
LAYERS V/id
40 30 t
%Lc5LLkJ 6
CLOSED M
7
6
OPEN M
OCULAR
DOMINANCE
7
CLOSED M
GROUP
3. Ocular dominance histograms as in Fig. 1 for 4 animals deprived for 3 mo between 15 and 18 mo of age. Total number of cells recorded: layers II/ III, ipsilateral63, contralateral 7 1; layer IV, ipsilateral 78, contralateral 69; layers V/VI, ipsilateral73, contralateral 80. FIG.
LAYERS ll/lll
LAYERS ll,‘lll
50
20
1234567
1234567
CLOSED M
OPEN M
OCULAR
DOMINANCE
CLOSED EYE
cortexes contralateral to the open eye were 0.371 t 0.033, and for the cortexes ipsilateral to the open eye were 0.533 t 0.137. These were different from each other, but not at the usually accepted level of significance ( t test, P < 0.10 ) . Two adult animals, deprived for 3 mo at several years of age were also recorded, and ocular dominance histograms for ipsilateral and contralateral cortexes appeared similar in all layers (Fig. 4). These results are summarized in Fig. 5, where the mean and standard deviations for the weighted ocular dominance shifts in each group of animals are plotted as a function of age and of layer. The general conclusion is that there is substantial plasticity in extragranular layers at 8- 12 mo of age, but very little in layer IV. There is little evidence for plasticity in layers II and III after 12- 15 mo of age. There is some indication that ocular dominance shifts can occur in layers V and VI with a 3-mo monocular deprivation between 15 and 18 mo of age, but this result was not confirmed when animals deprived from 12 to 15 mo of age were recorded. The ocular dominance shift in layers V and VI for animals deprived between 8 and 12 mo of age was slightly larger than the shift in layers II and III, so layers V and VI may be more plastic than layers II and III, but the reverse is certainly not true.
GROUP
FIG. 2. Ocular dominance histograms as in Fig. 1 for 4 animals deprived for 3 mo between 12 and 15 mo of age. Total number of cells recorded: layers II/III, ipsilateral 38, contralateral 42; layer IV, ipsilateral 33. contralateral 28: lavers V/VI. ipsilateral66. contralateral 6 1.
DISCUSSION
These results show that the critical period for ocular dominance shifts lasts longer than meviouslv suggested. The sus-
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DAW, FOX, SATO, AND CZEPITA
200 IPSIIATERAL
TO OPEN
EYE
CONTRALATERAL
TO OPEN
EYE
LAYERS ll/lll
50 4-o 30 20
1
10
I
,
0
LAYER Iv
501
LAYER N
1
I
LAYERS VP
50
4-o
’
LAYERS V/t/l
T
30 20 10
I
‘1234567
1234567
CLOSED M
OPEN M
OCULAR
DOMINANCE
4 CLOSED M
GROUP
FIG. 4. Ocular dominance histograms as in Fig. 1 for 2 animals deprived for 3 mo at several years of age. Total number of cells recorded: layers 11/III, ipsilateral34, contralateral 29; layer IV, ipsilaterd 28, contralateral 34; layers V/ VI, ipsilateral 3 1, contralateral 27.
ceptibility of the cortex to monocular deprivation arises between 3 and 4 wk of age. Between 4 and 6 wk of age, the ocular dominance in all layers can be completely shifted by a few days of monocular deprivation (Hubel and Wiesel 1970; Movshon and Dursteller 1977; Olson and Freeman 1975 ) . The critical period then declines sharply for layer IV, and more slowly for layers II, III, V, and VI between 6 wk and 1 yr of age. It is well established that monocular deprivation affects the synapses between lateral geniculate cells and cells in the cortex. This paper shows that monocular deprivation also affects the synapses between cells in layer IV and cells in other layers of the cortex. This point was implicit in previous results showing that monocular deprivation shifts the ocular dominance histogram further in layers II, III, V, and VI than it does in layer IV for animals monocularly deprived to several months of age ( Shatz and Stryker 1978 ) and in results showing that monocular deprivation at later ages can have a substantial effect on layers II, III, V, and VI when it has very little effect on layer IV (LeVay et al. 1980; Mower et al. 1985). The general flow of information within visual cortex is from layer IV to layers II and III to layers V and VI, although the detailed picture is clearly much more complicated than this. We cannot say from our results which of the intracortical synapses are affected by monocular deprivation late in the critical period. If we had found that cells in layers II/ III were affected substantially more or substantially less than cells in layers V/VI, some conclusions on
this point would have been possible. In fact, what we found was that layers V/VI may have been affected slightly more than layers II/III, but the difference was not significant. Nevertheless, it seems very likely that the synapses between layer IV and layers II/ III are affected. This must occur by a loss of strength of the connections from cells in layer IV that are primarily driven by the closed eye. Results from different laboratories for the overall ocular dominance shifts that occur are summarized in Fig. 6. Olson and Freeman ( 1980) deprived animals for 10 days of age at various ages between 10 days and 120 days, recording one animal at each age. Jones et al. ( 1984) deprived animals for 1 mo at various ages between 1 and 8 mo, recording four animals at each age. We deprived animals for 3 mo at various ages between 8 and 18 mo of age, recording several animals at each age. Also shown in Fig. 6 are results from several different laboratories from normal animals (Albus 1975; Albus and Wolf 1984; Hubel and Wiesel 1962; Jones et al. 1984; Shatz and Stryker 1978). Because there is a bias toward dominance by the contralateral eye in normal animals, the weighted ocular dominance shift should be compared with 0.45 rather than 0.5. Why have previous authors, with a few exceptions (Cynader et al. 1980; Jones et al. 1984), not noticed that ocular dominance shifts can occur in animals up to 1 yr of age? First, most previous authors have combined the results from all layers together. As noted above, this will include cells from layer IV that are not plastic together with cells in layers II, III, V, and VI that are plastic. Second, the bias toward dominance by the contralateral eye has often been ignored. We recorded from both cortexes in each animal
““T@\ 0.0
1 .o -i-J
Layers
I I
!
II and III
1 I
T
i
Layer
IV
d 0.0
I 1
I
I 1
la0
1
Layers
V and VI
/
Conga
to Open iI
Eye
1
!1
2
Age (years) FIG. 5. Weighted ocular dominance shifts for each group of animals as a function of age and layer. Points at 4-6 wk of age come from Shatz and Stryker ( 1978), who recorded only from the cortex ipsilateral to the open eye. Results from cortexes contralateral to the open eye are plotted with open circles, results from cortexes ipsilateral to the open eye are plotted with closed circles. Means and standard deviations are shown for each group of animals. Where the standard deviation does not show, it was sufficiently small that it fell within the symbol used for plotting the mean.
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CRITICAL
.
Monocular
0.8
c
\
-y 0.6 0 ti d
PERIOD FOR MONOCULAR
IN CAT
201
to changes in NMDA receptors (Bode-Greuel and Singer 1989; Fox et al. 1989; Gordon et al. 199 1; Tsumoto et al. 1987), although the causal mechanism remains to be worked out. The second clearly is not. Very likely therefore there are at least two mechanisms involved.
Deprived
A\*/.
8
0.4 Normal
Binocular
0.2 0
DEPRIVATION
0
2
4
6
8
Age (months
10
12
14
16
18
adult
post-natal)
FIG. 6. Ocular dominance shifts from various laboratories for all layers combined. Results from Olson and Freeman ( 1980) for 10 days of deprivation ( n ), from Jones et al. ( 1984) for 1 mo of deprivation (A ), and from us for 3 mo of deprivation ( l ). Results for normal animals (o ) come from Hubel and Wiesel( 1962), Albus ( 1975), Shatz and Stryker ( 1978), Albus and Wolf ( 1984), and from unpublished data from C. J. Shatz and M. P. Stryker and from our laboratory.
and compared the results from the contralateral and ipsilatera1 cortexes. This allows each animal to be used as a control for itself, taking into account the contralateral bias, and also any variation in this bias that there may be between animals. Third, very few animals have been recorded with monocular deprivation at around 1 yr of age. Fourth, the susceptibility of the cortex to monocular deprivation has clearly declined by 8- 12 mo of age, so that deprivation for a period of at least 1 mo is required to get a substantial effect. We started this experiment partly because NMDA receptors are driven by the visual input in layers II and III, but not in layers V and VI, in adolescent and adult cats, and some authors have suggested that NMDA receptors are associated with plasticity. We found that the critical period for layers II and III ends at around the same time as the critical period for layers V and VI: if anything, layers V and VI remain plastic for ocular dominance shifts longer than layers II and III. After 1 yr of age, NMDA receptors are present in layers II and III, but ocular dominance shifts do not occur. Consequently, the presence of NMDA receptors is not an indicator of plasticity for monocular deprivation. NMDA receptors in layers II and III of adolescent and adult cat must have some other function. When we began the experiment, we wished to determine whether the critical period finally ends around puberty. Our results show that it does. Unfortunately, our experiments on the effects of hormones on ocular dominance plasticity do not confirm a simple correlation. Testosterone, which increases around puberty, has a very small effect on ocular dominance shifts (Daw et al. 1987). Cortisol reduces ocular dominance shifts substantially, but blood levels of cortisol do not increase around puberty enough to implicate it in the termination of the critical period (Daw et al. 1991). It is clear from these results that there are two phases to the decline of the critical period, one between 5 and 8 wk of age that is related primarily to events in layer IV, and another between 8 and 12 mo of age that is related primarily to events in layers II, III, V, and VI. The first may be related
We thank J. Peters and J. Watkins for help with the experiments, Drs. Nina Tumosa and Jeff Lichtman for comments on the manuscript, and Dr. Michael Ullery for consultation on the statistics. This research was supported by National Eye Institute Grant EY-00053 and a grant from the Human Frontier Science Program. K. Fox was partly supported by the McDonnell Center for Higher Brain Function. H. Sato was a Research to Prevent Blindness International Research Scholar. Address for reprint requests: N. W. Daw, Dept. of Anatomy and Neurobiology, Washington University Medical School, 4566 Scott Ave., St. Louis, MO 63110. Received 19 April 199 1; accepted in final form 2 1 August 199 1. REFERENCES K. Predominance of monocularly driven cells in the projection area of the central visual field in the cat’s striate cortex. Brain Res. 89: 341-347, 1975. ALBUS, K. AND WOLF, W. Early postnatal development of neuronal function in the kitten’s visual cortex: a laminar analysis. J. Physiol. Land. 348: 153-185, 1984. BEAR, M. F., KLEINSCHMIDT, A., Gu, Q., AND SINGER, W. Disruption of experience-dependent synaptic modifications in striate cortex by infusion of an NMDA receptor antagonist. J. Neurosci. 10: 909-925, 1990. BERMAN, N. AND DAW, N. W. Comparison of the critical period for monocular and direction deprivation in cats. J. Physiol. Lond. 265: 249-259, 1977. BODE-GREUEL, K. M. AND SINGER, W. The development of N-methyl-Daspartate receptors in cat visual cortex. Dev. Brain Res. 46: 197-204, 1989. &NADER, M. S., TIMNEY, B. N., AND MITCHELL, D. E. Period of susceptibility of kitten visual cortex to the effects of monocular deprivation extends beyond six months of age. Brain Res. 19 1: 545-550, 1980. DAW, N. W., BAYSINGER, K. J., AND PARKINSON, D. Increased levels of testosterone have little effect on visual cortical plasticity in the kitten. J. Neurobiol. 18: 141-154, 1987. DAW, N. W., SATO, H., Fox, K., CARMICHAEL, T., AND GINGERICH, R. Effect of cortisol on monocular deprivation in the cat visual cortex. J. Neurobiol. 22: 158-168, 1991. DAW, N. W. AND WYATT, H. J. Kittens reared in a unidirectional environment: evidence for a critical period. J. Physiol. Land. 257: 155-170, 1976. Fox, K., DAW, N. W., AND SATO, H. Plasticity in adult and adolescent cat visual cortex. Sot. Neurosci. Abstr. 15: 796, 1989a. Fox, K., SATO, H., AND DAW, N. W. The location and function of NMDA receptors in cat and kitten visual cortex. J. Neurosci. 9: 2443-2454, 1989b. GORDON, B., DAW, N. W., AND PARKINSON, D. The effect of age on binding of MK-80 1 in the cat visual cortex. Dev. Brain Res. 62: 6 l-68, 199 1. HUBEL, D. H. Tungsten microelectrode for recording from single units. Science Wash. DC 125: 549-550, 1957. HUBEL, D. H. AND WIESEL, T. N. Receptive fields, binocular interaction and functional architecture in cat’s visual cortex. J. Physiol. Land. 160: 106-154, 1962. HUBEL, D. H. AND WIESEL, T. N. The period of susceptibility to the physiological effects of unilateral eye closure in kittens. J. Physiol. Lond. 206: 419-436, 1970. JONES, K. R., SPEAR, P. D., AND TONG, L. Critical periods for effects on monocular deprivation: differences between striate and extrastriate cortex. J. Neurosci. 4: 2543-2552, 1984. KASAMATSU, T., PETTIGREW, J. D., AND ARY, M. Cortical recovery from the effects of monocular deprivation: acceleration with norepinephrine and suppression with 6-hydroxydopamine. J. Neurophysiol. 45: 254266, 1981. KLEINSCHMIDT, A., BEAR, M. F., AND SINGER, W. Blockade of “NMDA” ALBUS,
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receptors disrupts experience-dependent plasticity of kitten striate cortex. Science Wash. DC238: 355-358, 1987. LEVAY, S., STRYKER, M. P., AND SHATZ, C. J. Ocular dominance columns and their development in layer IV of the cat’s visual cortex: a quantitative study. J. Comp. Neurol. 179: 223-244, 1978. LEVAY, S., WIESEL, T. N., AND HUBEL, D. H. The development of ocular dominance columns in normal and visually deprived monkeys. J. Comp. Neurol. 191: l-5 1, 1980. MITCHELL, D. E. AND TIMNEY, B. Postnatal development of function in the mammalian visual system. In: Handbook of Physiology. The Nervous System. Sensory Processes. Bethesda, MD: Am. Physiol. Sot., 1984, sect. 1, vol. III, p. 507-555. MOVSHON, J. A. AND DURSTELLER, M. R. Effects of brief periods ofunilatera1 eye closure on the kitten’s visual system. J. Neurophysiol. 40: 12551265, 1977. MOWER,G. D., CAPLAN,~. J., CHRISTEN, W.G., AND Dum,F.H.Dark
rearing prolongs physiological but not anatomical plasticity of the cat visual cortex. J. Comp. Neurol. 235: 448-466, 1985. OLSON, C. R. AND FREEMAN, R. D. Progressive changes in kitten striate cortex during monocular vision. J. Neurophysiol. 38: 26-32, 1975. OLSON, C. R. AND FREEMAN, R. D. Profile of the sensitive period for monocular deprivation in kittens. Exp. Brain Res. 39: 17-2 1, 1980. SHATZ, C. J. AND STRYKER, M. P. Ocular dominance in layer IV of the cat’s visual cortex and the effects of monocular deprivation. J. Physiol. Lond. 281: 267-283, 1978. TSUMOTO, T., HAGIHARA,K.,SATO, H., ANDHATA, Y.NMDAreceptors in the visual cortex of young kittens are more effective than those of adult cats. Nature Lond. 327: 5 13-5 14, 1987. WIESEL, T. N. Postnatal development of the visual cortex and the influence of environment. Nature Lond. 299: 583-59 1, 1982. WIESEL, T. N. AND HUBEL, D. H. Single cell responses in striate cortex of kittens deprived of vision in one eye. J. Neurophysiol. 26: 1003- 10 17, 1963.
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