318
Specialia
w i t h r e c e n t b i o a s s a y m e a s u r e m e n t s 12,1a. The slightly h i g h e r values o b t a i n e d in our e x p e r i m e n t s could be e x p l a i n e d b y a m o r e efficient e x t r a c t i o n p r o c e d u r e ~. As seen in Table I I I , chronic exercise induces a n increase in t h e t o t a l a c e t y l c h o l i n e c o n t e n t of t h e h e a r t . Also, t h e h e a r t tissue a c e t y l c h o l i n e c o n c e n t r a t i o n as e x p r e s s e d b y ~zg/g is s i g n i f i c a n t l y increased in t h e exercised animals. V e r y p r o b a b l y , a n d as show:: b y HE~RLtCV: et aI, ~ t h e increase of t h e a c e t y l c h o l i n e c o n c e n t r a t i o n of t h e auricles is m a i n l y r e s p o n s i b l e for t h e s e result. I n addition, EKSTR6M ~ r e p o r t e d r e c e n t l y t h a t in c h r o n i c a l l y exercised animals, t h e choline a c e t y l t r a n s f e r a s e a c t i v i t y of t h e auricles was significantly increased. A l t h o u g h t h e existence of a c e t y l c h o l i n e b o u n d to t h e m y o c a r d i u m a n d indep e n d e n t f r o m n e r v e t e r m i n a l s h a s b e e n reportedlY, it is t e m p t i n g t o suggest t h a t t h e a c e t y l c h o l i n e increase in t h e h e a r t reflects a n increase of t h e p a r a s y m p a t h e t i c a c t i v i t y on t h e h e a r t . W h e t h e r t h e a c t i v i t y of t h e h e a r t in chronically exercised a n i m a l s is m a i n l y i n f l u e n c e d b y t h e s y m p a t h e t i c or p a r a s y m p a t h e t i c s y s t e m is still a c o n t r o versial m a t t e r a-~
Neurotubules
: Different
Densities
in P e r i p h e r a l
40
F--'I N.gastrocnemius reed. N.saphenus Animal
3
E 20 g
~ii i l
Zg 1C
1'0
2'0
Rdsumd. L e t a u x de l ' a c e t y l c h o l i n e du m y o c a r d e a 6t6 dos6 p a r c h r o m a t o g r a p h i c en p h a s e gazeuse chez le rat. Chez l ' a n i m a I exerc4 le t a u x de l ' a c e t y l c h o l i n e ~tait plus 61ev~ que chez son h o m o l o g u e s4dentaire. C.
DE
SCHRYVER a n d J. MERTENS-STRYTHAGEN 16
Department of Physiology, Faculty o/Medicine, Facultds Universilaires Notre Dame de la Pain, Rue de Bruxelles 51, B-5000 Namur (Belgium), 77 September/97d.
1= j. VLK, S. TUCEK and V. HABERMANN,Nature, Lond. 189, 923 (1961). 13 V. BHARGAVA,Nature, Lond. 215, 202 (1967). 1~ j. 1?;KSTR6~a,Q. J1. exp. Physiol. 59, 73 (1974). ta E. CORABOEUF, G. LE DOUARI~ and G. OBRECHT-COUTRIS, J. Physiol., Paris 206, 383 (1970). 1~ The authors aknowledge the excellent technical assistance of
Mr. F.
VIGNERON.
Motor and Sensory
A c c o r d i n g to earlier f i n d i n g s in m o u s e sciatic n e r v e 8, w h i c h are s u b s t a n t i a l l y s u p p o r t e d b y o t h e r authors~, 5, a general rule of inverse r e l a t i o n s h i p b e t w e e n fibre size a n d d e n s i t y of n e u r o t u b u l e s is well established. I n a p r e v i o u s paper% e v i d e n c e was p r e s e n t e d t h a t - while t h e a b o v e m e n t i o n e d rule is fully v a l i d - t h e d e n s i t y of n e u r o t u b u l e s is s i g n i f i c a n t l y h i g h e r in v e n t r a l (motor) r o o t fibres t h a n in dorsal (sensory) r o o t fibres of c o m p a r a b l e d i a m e t e r . T h e p r e s e n t i n v e s t i g a t i o n is c o n c e r n e d w i t h t h e q u e s t i o n of w h e t h e r t h e s e differences in t u b u l a r d e n s i t y are also p r e s e n t in m o t o r a n d s e n s o r y n e r v e fibres d i s t a l to t h e spinal ganglia a n d p a r t i c u l a r l y in m o r e d i s t a n t p a r t s of the peripheral nervous system.
30
EXPERIE>ITIA 31/3
Nerve
F i b r e s ~,2
Methods. 3 albino r a t s ( S p r a g u e - D a w l e y / 3 2 0 - 4 4 0 g) were fixed b y p e r f u s i o n w i t h c a c o d y l a t e - b u f f e r e d 7% g l u t a r a l d e h y d e u n d e r n e m b u t a l a n a e s t h e s i a . In 2 a n i m a l s t h e dorsal r o o t s of L~ were excised in c o n n e c t i o n w i t h t h e spinal ganglia, each w i t h a s h o r t s t u m p of t h e spinal nerve. I n a t h i r d a n i m a l t h e s a p h e n o u s n e r v e a n d t h e n e r v e to t h e m e d i a l h e a d of t h e g a s t r o c n e m i u s muscle (MGN) were t a k e n out as e x a m p l e s of a t y p i c a l c u t a n e o u s a n d a t y p i c a l m u s c u l a r nerve. P o s t f i x a t i o n in OSO4; e m b e d d i n g in e p o n ; double s t a i n i n g of u l t r a t h i n sections w i t h u r a n y l a c e t a t e a n d lead c i t r a t e ; Zeiss E M 9S e l e c t r o n microscope. M i c r o g r a p h s of c o m p l e t e n e r v e fibre cross sections were m a d e a t s t a n d a r d m a g n i f i c a t i o n of • 5000; for m o r p h o m e t r i c m e a s u r e m e n t s p r i n t s a t • 15,000 were used. S a m p l e s of 22-50 large as well as s m a l l d i a m e t e r n e r v e fibres of e a c h s p e c i m e n were e v a l u a t e d . The following p a r a m e t e r s h a v e b e e n d e t e r m i n e d a n d s u b j e c t e d to s t a t i s t i c a l a n a l y s i s : 1. area of cross section (ACS) i n . Fm 2 ( p l a n i m e t r y of t h e micrographs), a n d 2. t o t a l c o u n t of n e u r o t u b u l e s per ACS a n d calculation of t h e i r d e n s i t y ( n u m b e r per btm~ of ACS). F o r s t a t i s t i c a l analysis t h e S t u d e n t t-test was applied. Resulls and discussion. N e r v e fibres of t h e s a p h e n o u s nerve, a c u t a n e o u s nerve, were c o m p a r e d w i t h t h o s e of t h e MGN, a m i x e d muscle n e r v e c o n t a i n i n g m o r e t h a n 50% of m o t o r n e r v e fibres. The d e n s i t y of n e u r o t u b u l e s was s i g n i f i c a n t l y h i g h e r in t h e a x o n s of s a p h e n o u s n e r v e fibres as c o m p a r e d w i t h t h o s e of t h e MGN. T h e s e differ-
3'0 pm2
Axon cross sections
Fig. 1. Comparison of the densities of axonal neurotubules in samples of small and large nerve fibres of a cutaneous nerve (black bars) and a muscle nerve (white bars) of the rat. Ordinate: number of neurotubules per square micron of axon cross section (NT/txm2); the bars give the mean and the standard deviation of the mean. Abscissa : position of the bars according to the mean cross sectional area of the axons of each sample; axon cross sections in square microns (ACS/i~m2) were determined by planimetry.
1 This investigation was supported by the 'Fonds zur F/Jrderung der wissenschaftliehen Forsehung in 0sterreich'. The authors gratefully acknowledge the excellent technical assistence of Miss E. HOHBERGand Mrs. B. STOGERMAYER. a R. L. FRIEDE and T. SAMORAJSKY, Anat. Rec. 167, 379 (1970). 4 R. MAYR,Anat. Anz. 130, 391 (1972). ~ K. H. ANDRES and M. YON DORING, in Handbook o/ Sensory Physiology, (Springer-Verlag, Berlin-Heidelberg-New York 1973), vol. 2. W. ZEXKER, R, MA'z~ and H, GRUBER,Experientia 29, 77 (1973).
15.3. 1975
319
Speeialia
Table I. Density of neurotubules in a cutaneous (N. saphenus) and a muscular (N. gastrocnemius med.) nerve branch (animal 3)
Cross sectional area of axon in [zmz (ACS) Neurotubules (number/bm~ of ACS)
Small nerve fibers (2.1-3.3 ~xm diameter)
Large nerve fibers (5.4-6.7 [zm diameter)
N. saph.
N. gastrocn, med.
Significance
N. saph.
N. gastroen, med.
Significance
50 3.66:~0.17 38.22=[_1.37
50 4.16i0.19 23.574-0.96
ns @++
35 15.07~0.41 21.84=t=0.87
35 15.544.0.55 17.73~0.63
ns -k~+
The values give the mean and the standard deviation of the mean. The values of comparable caliber classes of central and peripheral processes of spinal sensory neurons were statistically examined by the Student t-test. HS, not significant; -t-, p < 0.05; -k -t-, p < 0.01; -k -k - a p < 0.001.
40
H
30
Spinal sensory neurons IN~ centr, processes periph.processes Animal I
E
2o
,~ 10 z
l0
40
20
b)
4'0 ~Jm2
30 Axon cross sections
Spinal sensory neurons INNlcentr.processes ~periph.processes
30 Animal 2 E
mi
20
10
0, S
10
20
30
7 R. S.
4'0 }Jm2
Axon cross section
e n c e s w e r e o b s e r v e d i n l a r g e d i a m e t e r n e r v e f i b r e s a s well a s in s m a l l o n e s ( T a b l e I, F i g u r e 1). W i t h i n b o t h n e r v e s , according to the general rule, the small fibres exhibited higher tubular densities than the large ones. H o w c a n t h e s e r e s u l t s of h i g h e r t u b u l a r d e n s i t y i n a c u t a n e o u s n e r v e t h a n in a m u s c l e n e r v e b e r e c o n c i l e d w i t h o u r p r e v i o u s f i n d i n g s of h i g h e r t u b u l a r d e n s i t y i n t h e motor ventral root fibres as compared to the sensory dorsal ones ~ ? To answer this question we examined w h e t h e r t h e r e is a d i f f e r e n c e i n t u b u l a r d e n s i t y b e t w e e n sensory fibres proximal and immediately distal to the spinal ganglion. In fact, the tubular densities in nerve f i b r e s o n b o t h s i d e s of t h e s p i n a l g a n g l i o n p r o v e d t o b e unequal. We found the density of neurotubules to be s i g n i i i c a n t l y h i g h e r i n t h e p e r i p h e r a l p r o c e s s e s of s p i n a l g a n g l i o n cells t h a n in t h e c e n t r a l o n e s of c o m p a r a b l e d i a m e t e r a t t h e l e v e l of t h e d o r s a l r o o t s ( T a b l e I I , F i g u r e 2). This fact probably accounts for the invers relationship of t h e t u b u l a r d e n s i t i e s in s e n s o r y a n d m o t o r n e r v e f i b r e s between spinal roots and peripheral nerves. I n a r e c e n t s t u d y o n a m p h i b i a n s p i n a l n e r v e fibresV, a s i m i l a r d i f f e r e n c e of t u b u l a r d e n s i t y b e t w e e n s e n s o r y nerve fibres proximal and distal to the dorsal root ganglion w a s f o u n d . I n a g r e e m e n t w i t h o u r f i n d i n g s i n t h e r a t s,
SMITH,
Can. J. Physiol. Pharmac. 51, 798 (1973).
Fig. 2. Comparison of the densities of axonal neurotubules in samples of small and large sensory nerve fibres immediately distal (black bars) ar2d proximal (dotted bars) to the spinal ganglion L a of the rat. a) Animal 1; b) Animal 2. Ordinate and abscissa as in Figure 1.
Table II. Density of neurotubules in central and peripheral processes of spinal sensory neurons Large spinal sensory fibers (8.5-10.3 [xm diameter)
Small spinal sensory fibers (3.0-4.5 ~zm diameter) Central processes
Peripheral processes
Animal 1 (n) Cross sectional area of axon in txme (ACS) Neurotubules (number/~m 2 of ACS)
30 7.24 4- 0.34 28.71 4- 1.23
30 9.22 • 0.46 34.83 4" 1.26
Animal 2 (n) Cross sectional area of axonin~xm2 (ACS) Neurotubules (number/[xme of ACS)
29 10.62 4" 0.45 21.91 4- 1.12
30 9.57 4" 0.60 33.13 • 1.04
Cf. Legend to Table I.
Significance
Central processes
Peripheral processes
Significance
-k § -F +
22 35.39 -4- 1.07 12.71 • 0.43
22 34.35 -t- 1.06 15.16 • 0.60
ns
ns + + +
31 33.63 :~ 1.10 13.33 • 0.64
29 35.57 i 1.13 17.80 • 0.27
ns
++
+++
320
Specialia
also in t h e frog t h e d e n s i t y of t h e n e u r o t u b u l e s a t t h e level of t h e spinal r o o t s p r o v e d t o b e lower in dorsal r o o t fibres t h a n in v e n t r a I root fibres. H o w e v e r , in t h e frog equal n u m b e r s of n e u r o t u b u l e s were f o u n d in m o t o r and s e n s o r y fibres i m m e d i a t e l y distal to t h e spinal ganglia. W e h a v e n o w f o u n d c o n s i d e r a b l y h i g h e r t u b u l a r densities in r a t s a p h e n o u s n e r v e fibres t h a n in M G N fibres of c o m p a r a b l e sizes. This fact suggests a n e v e n m o r e pron o u n c e d difference in t h e c o n t e n t of n e u r o t u b u l e s b e t w e e n m o t o r and s e n s o r y fibres of r a t p e r i p h e r a l nerves, w i t h lower v a l u e s for m o t o r n e r v e fibres t h a n t h o s e p r e s e n t e d for MGN in Table I; for it has to be t a k e n into a c c o u n t t h a t muscle n e r v e s like t h e MGN c o n t a i n a c o n s i d e r a b l e p e r c e n t a g e of sensory n e r v e fibres w h i c h could n o t be e x c l u d e d b y our s a m p l i n g t e c h n i q u e .
EXeEm~;NTIA 31/3
Zusamrne~c/assung. E s e r g a b sich, dass die Neurot u b u l u s d i c h t e in d e n A x o n e n eines H a u t n e r v e n ( R a t t e , N. saphenus) klar h b h e r ist als in gleich d i c k e n F a s e r n eines M u s k e l n e r v e n (N. g a s t r o c n e m i u s med.). E i n w e i t e r e r B e f u n d leistet einen B e i t r a g zt{r Erkl~Lrung dieses G e g e n s a t z e s : Die N e u r o t u b u l u s d i c h t e in d e n p e r i p h e r e n N e u r i t e n prim~irer sensibler N e u r o n e u n m i t t e l b a r distal des Spinalganglions (L~) ist s i g n i i i k a n t h 6 h e r als in d e n z e n t r a l e n N e u r i t e n in H 6 h e der H i n t e r w u r z e l W. ZENKER, R. MAYR a n d H. C-RUBER
2. A natomisches InsHtut der U~ziversitiit Wien, Wdhri~r 13, A-7090 Wien (Austria), # J u l y 7974.
Visual Cell Coding: Factoring Dioptric Responses from Maintained Discharge M a i n t a i n e d discharge, c o m m o n t h r o u g h o u t t h e visual s y s t e m , has tong f a s c i n a t e d a n d f r u s t r a t e d i n v e s t i g a t o r s ~-3. A l t h o u g h such a c t i v i t y is n o w generally a c c e p t e d as physiological, a n d i n d e e d vital, to t h e n o r m a l f u n c t i o n of t h a t sensory s y s t e m (see t h e c u r r e n t r e v i e w of LEvlCK ~), its v e r y p r e s e n c e c o m p l i c a t e s t h e d e c i p h e r i n g of t r a n s i e n t e v e n t signals m o v i n g in t h o s e p a t h w a y s W h i l e c o m p l e x models h a v e b e e n e x p l o r e d for t h e analysis of m a i n t a i n e d a c t i v i t y in t h e visual s y s t e m 5, c e r t a i n f o r m s of t r a n s i e n t i n f o r m a t i o n can a t t i m e s be e x t r a c t e d t h r o u g h v e r y f u n d a m e n t a l models, even in t h e p r e s e n c e of v e r y h i g h d e n s i t y 'noise' (e.g. 30 spikes/sec or more) g e n e r a t e d b y t h e c o n d u c t i n g neurone. The relative success of such r e d u c e d f a c t o r i n g models d e p e n d s , of course, on t h e r e g u l a r i t y of t h e m a i n t a i n e d discharge, a n d is i l l u s t r a t e d here in r e l a t i o n t o one of t h e m o s t f u n d a m e n t a l of t r a n s i e n t signals in t h e visual p a t h w a y s : t h e ongoing a s s e s s m e n t of i m a g e focus on t h e r e t i n a 6.
A~
~oc (~ 9OO E: LO
13-
IO
q--' ----\~9 le.
8
0
g.
76
3 400
1" . . . . . . . . . . . 4
6
8
I0
12
NetResponseDi,~arffy WithCorrectionfor MaintainedActivityDrift
~ 6
16
18 20
NetResp~eDisparity WithoutCorrechOnfor Mointained~ctlvityDrift
8O0
700
700
600
600
50C
50G
40(}
40O
1" 14
.LO
90G
800
500
C. t000
{0
700
2
(1969). 6 R. IVL HILL and H. IKEDA,Arch. Ophthal. 85, 592 (1971).
900
r,3 n," L,I O- 6 0 0 co LIJ
0
1 H. K. HARTLINIsJ. cell. comp. Physiol. 5, 229 (1934). 2 E. D. ADRIAN',J. Physiol., Loud. 91, 66 (1937). 8 R. GRANIT, Acta physiol, seand. 7, 370 (1941). 4 W. R. LEVICK,Handbook o] Sensory Physiology (Springer-Verlag, New York 1973), vol. 7, part A, p. 575. H. B. BARLOWand W. R. LEVlC~, J. Physiol., Loud. 202, 699
I000
. . . . . . . .
o 03
ResponseD~spority for ActivityDrift
Net Witho~B Correchon Mointcjiried
The r e s p o n s e s cited are f r o m a m o n g s t a c u m u l a t i v e s a m p l e of m o r e t h a n 300 nero-ones w i t h i n t h e r a b b i t m e s e n c e p h a l o n a n d visual c o r t e x n o w s t u d i e d . T h e a n i m a l s were m a i n t a i n e d u n d e r light u r e t h a n e a n e s t h e s i a (6.0 m l / k g b o d y wt. of a 20% s o l u t i o n in saline, a dosage level f o u n d f r o m earlier w o r k to be no m o r e d e t r i m e n t a l t o cell r e s p o n s i v e n e s s t h a n ' e n c @ h a l e isol6' techniques). This was s u p p l e m e n t e d w i t h 3.3 m g / k g b o d y w t . / h of gallamine t r i e t h i o d i d e to p r e v e n t eye a n d b o d y m o v e m e n t s ,
.
.
.
.
.
0
2
4
6
8
.
iO
.
12
.
14
.
16
.
.
18 20
.
5
.
.
.
.
0
2
4
8
.
6
.
.
8
I0
.
12
.
r
.
16
18 20
INDUCED RETINAL IMAGE BLUR (Dioptres)
Responses of a midbrain ceil to a black edge moviug across its receptive field once per sec, integrated over 30 sec periods. The test sets for each focal condition were spaced 90 sec apart, their order of presentation being indicated by the numbers next to the points. A) shows the actual spike totals recorded, i.e. without correction for maintained activity drift; t3) shows the same data, corrected for maintained activity drift (see text} ; and C) shows the maximum case of transient response distortion expected, calculated on the assumption that the data could have been collected in the particular order indicated.