Journal of the Neurologwal Sewnces, 1977, 34 25-36
25
© Elsewer SoentJfic Pubhshmg Company, Amsterdam - Printed m The Netherlands
T H E C Y T O A R C H I T E C T U R E OF T H E I N F E R I O R C O L L I C U L U S I N T H E CAT A Stereological Approach
VINCENT MEININGER and MARIELLE BAUDRIMONT Laboratolre d'.4natomte (Pr DELMAS), Facultd de Medecme, 45, Rue des St -Pdres, F-75270 Parts Cedex 06 (France)
(Received 25 March, 1977)
SUMMARY The present study gives an hlstometric analysis of cells in the different subdivisions of the inferior colllculus The use of principles and methods of stereology allows the definition of various cellular parameters, l e nuclear and cell volume, nuclear and cell profile areas, nuclear diameter, volume proportion of perlkaryon, nuclear/cytoplasmic volume ratio and nuclear packing density Our data confirm the existence of at least 3 parts in the inferior colhculus of the cat, namely the ventral, the dorso-medlal and the lateral parts We furnish the various parameters which permit the characterlsation of cells in these different parts The dorsome&al part or region appears to be composed of numerous cells characterized by their small volume and their high nuclear/cytoplasmic volume ratio The ventral region seems to be distinguished by its scattered cells, characterized by their large volume and their low nuclear/cytoplasmic volume ratio, whereas the lateral region appears as an intermediate one with scattered cells of low volume It seems notable that these cytoarchitectonic sub&visions fit well with the functional subdlvlston since the dorsomedial region receives cortical fibres, the ventral region receives cochlear fibres and the lateral region receives both cortical and cochlear fibres
INTRODUCTION As emphasized by Genlec and Morest (1971), the inferior colhculus appears as "an ~mposJng part of the auditory system in the mldbraln tectum" An important station for the auditory pathways toward the medial genlculate nucleus, the inferior colhculus also receives the bulk of fibres from the auditory cortices (AI-AII) The integration of these ascending and descending pathways has been
26 lmphcated in a lot of complex functions, 1 e central audnory "feedback" adjustmelHs (Desmedt 1960. Massopust and Ordy 1962), elaboration of acoustic reflexes (Bu~e) St Laurent and Memm 1966) and attention and orientation functions (Lemlan and Hafter 1972, Stdlman 1972. Syka and Radlc-Welss 1973) The projections from the cochlear nuclei and from the auditory coruces have been described anatomically by numerous authors (Rasmussen 1964. Diamond, Jones and Powell 1968, Van Noort 1969. Osen 1972. Rockell and Jones 1973) From these studies it seems well estabhshed that these projections terminate m two different territories in the inferior colhculus the cochlear nuclei project on to the ventro-lateral part, the auditory cortices project on to the dorso-medml part Most authors recognize at least 3 parts m the inferior colhculus a central nucleus, w~th dorso-medtal and ventro-lateral parts, and a lateral nucleus However, a lot of d~screpanc~es exist between the various descriptions of these nuclei The central nucleus exhibits for Cajal (1911) "des cellules polygonales ou 6toll6es, de tmlle grande, moyenne ou petite" Van Noort (1969) claims that the central nucleus d~scloses 2 parts a dorso-medlal one, rich with small neurons and a ventro-lateral part w~th large neurons Rocketl and Jones (1972) dwxde the central nucleus into a dorso-medml part rich w~th large neurons and a ventro-lateral part with small and medium neurons The lateral nucleus appears for all authors to contain small and medmm neurons However, none of these studies furmshes precise quant~tatwe data about cell.~ m the different parts of the inferior colhculus The purpose of the present study ~s to define more precisely the d~fferent types of neurons m the various parts of the inferior colhculus, especmlly m the central nucleus In th~s a~m the hlstometnc properties of cells m the d~fferent parts of the inferior colhculus were stud~ed by quantitative optical macroscopy As emphasized by different authors (Welbel 1969, Elias, Hennlg and Schwartz 1971), and more pamcularly for the central nervous system by Mayhew and Momoh (1973) the apphcat~on of the principles and methods of stereology allows quant~tatwe mformat~on to be obtained from thin sections of biological materml and permits the definition of tissue and cell structures m three-dimensional terms MATERIAL AND METHODS Two adult cats (M28, M31) of 3000-3500 g body weight were anaesthetized with Ketamine (20 mg 1 m ) and Nembutal (25-30 mg/kg i.p ) and perfused by a standardized procedure This techmque ~s a shght modlficahon of that described by Baleydler, Leger and Quoex (1973) The perfusate is a phosphate-buffered (0 1 M) mixture of 1% glutaraldehyde and 4 % paraformaldehyde After thoracotomy, the solution (pH 7 4) was introduced through the left ventricle at a temperature of 20 °C, at a pressure of 160 mm Hg and with a controlled flow decreasing from 200 to 120 mt/mm Animals were previously exsangulnated by mC~slng the right atrium Immediately after perfuslon, the brain was removed and the inferior colhcuh were dissected out The inferior colhcuh were then chopped transversely into approximately four 1 mm slices Each shce was then drawn under a binocular dissecting macro-
27 scope, the caudal plane facing the exammer Each slice was cut into 4-6 blocks, slightly asymmetrical m shape, and each block was drawn Next, each block was fixed overnight at 4 °C m the perfusate solution, then washed twice in the phosphate buffer and post-fixed in 2 % o s m m m tetroxlde m phosphate buffer for 2 hr After dehydration in a graded series of alcohols followed by propylene oxide and infiltration with Epon, each block from a shce was gathered like the pieces of a puzzle This technique permits each block from the d~fferent shces to be set in 3 spatial dimensions before terminal embedding Next, each block was embedded in Epoxy resin About 60 blocks of embedded tissue were obtained per animal Blocks were sectioned on a O M U - 2 R E I C H E R T Ultra-Mlcrotome with glass knives Semi-thin sections (0 5 /~m) were taken for hlstometrlc analysis and stained with alkahne tolmdlne blue according to the method of Ling, Paterson, Prlvat, Morl and Leblond (1973)
Tissue samphng We decided to choose samples, as it seemed too time-consuming to study every section using hastometrlc and stereologlcal procedures As emphasized by Welbel, Straubh, Gnagl and Hess (1969) it is very important when analysing only a part of the available material to make sure that the sample is representative of the whole Following Mayhew and M o m o h (1973), a systematic samphng procedure was performed using a series of steps Step 1 The right inferior colhculus was taken through the fixation and embedding stages previously described The blocks obtained (see below) from each of 2 right inferior colhcuh provided a store of material from which samples at the other steps could be taken Step 2 For further sampling we decided to choose, from the store of blocks of step 1, only blocks belonging to the cranial and caudal planes Since the cramal and caudal planes of cat M28 were intercalated between the planes of cat M31 we obtained an orderly sequence for cats cranial (M31), cranlo-lntermed,ate (M28), caudo-mtermediate (M28) and caudal (M31) Step 3 In each plane, which furmshed 4-6 blocks, the inferior colhculus was assumed to be trmngular in shape We therefore decided to choose the blocks belonglng to each angle of the triangle, namely the dorso-medlal, the dorso-lateral and the ventral blocks Each of these blocks representatwe of an angle furnished two semi-thin sections for h~stometrJc analysis We therefore obtained 24 semi-thin sections of 2 × 2 m m in size Step 4 For each section, a low magnification mlcrograph was performed ( × 200) On each mlcrograph we superimposed at random a samphng lattice In this lattice each square was equivalent to a 9 • 10a # m 2 square, 1 e 300 # m on a side Photomicrographs of all observed neurons were taken from every other square Approximately 600 mlcrographs per animal were recorded All these mlcrographs were taken at an initial magmficatlon of × 400 With such a techmque, we ensured a systematic random sampling We decided to use this method because it was shown by Ebbesson and Tang (1967) to have the smallest standard error
28
Htstometrtc techntques As emphasized by Mayhew and M o m o h (1973) "quantltatlon of neuronal parameters requires the use of reproducible and accurate techmques which are capable of resolving biological differences from methodological ones In other words, they must allow for biological variations m neuron populations" The aim of our study was to discover if such variations exist between the different parts of the inferior colhculus In our investigation neuronal parameters were estimated using the principles of stereology (Underwood 1969, Welbel 1969) These prlnclples have already proved to be useful for the study of neuronal parameters (Mayhew and M o m o h 1973) We decided to choose for measurement all types of neuron profile within the field of view m order to avoid the "nucleolar-blaslng" of Mayhew and M o m o h (1973) As emphasized by these authors "nucleolar biasing", i e the choice for measurement of only those neurons whose nucleoh are wslble, leads to substantml overestimates of cell volume and perlkaryal volume/surface ratio and to s,gnlficant underestimates of neuronal population density, perlkaryal volume proportion and cytoplasmic volume/ nuclear volume ratio Different techniques were used
Point counting For estimating various parameters, we employed a point counting method A square lattice (0 8 cm per side for each square) containing 891 point intersections was used with the apparatus described by Welbel, Klstler and Scherle (1966) Since the final magnification was × 4000, each test point represented the centre of an area of 4 # m 2 Profiles of neurons were easily identified on the basis of nuclear shape, cytoplasmic granularity and presence of Nlssl substance With the point counting method we obtained Nuclear profile areas All the observed profiles were counted, without exception, accordmg to Mayhew and M o m o h (1973) Neuronal profile areas All types of neurons, nucleated or anucleated were monitored - Nuclear volume/cellular volume ratio (Vn/Ve) This ratio is proportional to that of nuclear profile areas/cellular profile areas - Volume proportion of perlkaryon (Vvp) This parameter, obtained by point counting, defines the fractional volume of the inferior colhculus tissue occupied by the neuronal penkaryon It therefore, gives a measure of the so-called grey/cell coefficient (Mayhew and M o m o h 1973) Nuclear profile diameter (Dl,) These profiles were essentially circular In most instances the apparent long axis was nearly equal to the dimension perpendicular to this axis So in every case we defined a mean diameter Dp as equal to the mean of these dimensions Actual mean nuclear diameter Da This was derived from the Dp estimate using a correction factor 4/zc according to AbercrombIe (1946) Mean nuclear volume This was calculated using the formula -
-
-
-
-
29 7~ Vn = -~- Dap
As emphasized by Mayhew and Momoh (1975), we calculated thls volume using Dp of nucleated profiles only, without the correcting factor 4/# Nuclear area density (Nan) The number of nuclear profiles per umt area of inferior colhculus tissue is related to the number of actual nuclei per unit volume of t)ssue (Nvn) Thls value of Nvn, or nuclear numerlcal density (Weibel 1969), or packing denslty (Haddara 1956) was calculated using the formula (De Hoff and Rhmes 196 I) -
N,n
Nvn -- - -- number/mm 3 Da - Penkaryon volume The mean penkaryon volume (lip) was calculated from the estlmates of nuclear volume and Vn/Ve ratlo re=
Vn
Vn/Vo
Statistics For the various hlstometrlc parameters, we calculated the means, the standard deviations and the standard error The data so obtained permit us to calculate for each histometric parameter the value of the 2 samples t-test between our different populations i e , dorsomedlal vs ventral (DM vs V), dorsomedial vs dorsolateral (DM vs DL) and ventral vs dorsolateral (V vs DL) as expressed in Table 1 By this procedure we were able to test the null hypothesis that the 2 population means are equal The values of t and of the number of degrees of freedom were furnished by the classical formula, assuming that the different populations were normal with unequal variances Sample means were considered to differ significantly if the error probability (P) was less than 0 01 RESULTS
Neurons of the inferior colhculus (Fig 1) are easily recogmzed on the basis of their spherical nucleus, containing a large nucleolus, in a clear nucleoplasm The nuclear envelope appears dehcately stained The cytoplasm contains stained flakes and small spherical or elongated mltochondrla The cytoplasm looks lighter than the surrounding neuropil
(1) Nuclear parameters Table 1 records the various nuclear parameters, i e nuclear volume, nuclear profile areas and nuclear profile diameters m the various parts of the inferior colllculus dorso-medlal (D M ), ventral (V) and dorso-lateral (D L ) The nuclear volume appears the same in the d~fferent parts of the inferior colliculus, with a mean value for the inferior colhculus of 749 03/~m s As predicted by the nuclear volume, the nuclear profile areas and the nuclear
30 TABLE 1 RESULTS OF THE VARIOUS HISTOMETRIC PARAMETERS Parameters
Dorso-
(mean only)
medJal
P value ( D M vs V)
Ventral (V)
P value (V vs DL)
(DM)
Nuclear volume (/~ma)
Nuclear profiles
753 31
71 41
areas ( # m 2)
Nuclear profiles dmmeter (/~m)
12 47
Cellular volume (/tm a) 1674 02
Neuronal profiles areas (~m 2)
163 57
Vvp ( ~ )
4 29
Vnl Ve (,umalt~ma)
0 45
Nuclear areal
130 91
density ( n u m b e r / m m z)
Nuclear numerical density
1055809
( n u m b e r / m m a)
t 040 v 229 NS t 010 v 1138 NS t 1 89 v 1136 NS t 4 57 v 200 P -/-001 t 1160 901 P
25
© Elsewer SoentJfic Pubhshmg Company, Amsterdam - Printed m The Netherlands
T H E C Y T O A R C H I T E C T U R E OF T H E I N F E R I O R C O L L I C U L U S I N T H E CAT A Stereological Approach
VINCENT MEININGER and MARIELLE BAUDRIMONT Laboratolre d'.4natomte (Pr DELMAS), Facultd de Medecme, 45, Rue des St -Pdres, F-75270 Parts Cedex 06 (France)
(Received 25 March, 1977)
SUMMARY The present study gives an hlstometric analysis of cells in the different subdivisions of the inferior colllculus The use of principles and methods of stereology allows the definition of various cellular parameters, l e nuclear and cell volume, nuclear and cell profile areas, nuclear diameter, volume proportion of perlkaryon, nuclear/cytoplasmic volume ratio and nuclear packing density Our data confirm the existence of at least 3 parts in the inferior colhculus of the cat, namely the ventral, the dorso-medlal and the lateral parts We furnish the various parameters which permit the characterlsation of cells in these different parts The dorsome&al part or region appears to be composed of numerous cells characterized by their small volume and their high nuclear/cytoplasmic volume ratio The ventral region seems to be distinguished by its scattered cells, characterized by their large volume and their low nuclear/cytoplasmic volume ratio, whereas the lateral region appears as an intermediate one with scattered cells of low volume It seems notable that these cytoarchitectonic sub&visions fit well with the functional subdlvlston since the dorsomedial region receives cortical fibres, the ventral region receives cochlear fibres and the lateral region receives both cortical and cochlear fibres
INTRODUCTION As emphasized by Genlec and Morest (1971), the inferior colhculus appears as "an ~mposJng part of the auditory system in the mldbraln tectum" An important station for the auditory pathways toward the medial genlculate nucleus, the inferior colhculus also receives the bulk of fibres from the auditory cortices (AI-AII) The integration of these ascending and descending pathways has been
26 lmphcated in a lot of complex functions, 1 e central audnory "feedback" adjustmelHs (Desmedt 1960. Massopust and Ordy 1962), elaboration of acoustic reflexes (Bu~e) St Laurent and Memm 1966) and attention and orientation functions (Lemlan and Hafter 1972, Stdlman 1972. Syka and Radlc-Welss 1973) The projections from the cochlear nuclei and from the auditory coruces have been described anatomically by numerous authors (Rasmussen 1964. Diamond, Jones and Powell 1968, Van Noort 1969. Osen 1972. Rockell and Jones 1973) From these studies it seems well estabhshed that these projections terminate m two different territories in the inferior colhculus the cochlear nuclei project on to the ventro-lateral part, the auditory cortices project on to the dorso-medml part Most authors recognize at least 3 parts m the inferior colhculus a central nucleus, w~th dorso-medtal and ventro-lateral parts, and a lateral nucleus However, a lot of d~screpanc~es exist between the various descriptions of these nuclei The central nucleus exhibits for Cajal (1911) "des cellules polygonales ou 6toll6es, de tmlle grande, moyenne ou petite" Van Noort (1969) claims that the central nucleus d~scloses 2 parts a dorso-medlal one, rich with small neurons and a ventro-lateral part w~th large neurons Rocketl and Jones (1972) dwxde the central nucleus into a dorso-medml part rich w~th large neurons and a ventro-lateral part with small and medium neurons The lateral nucleus appears for all authors to contain small and medmm neurons However, none of these studies furmshes precise quant~tatwe data about cell.~ m the different parts of the inferior colhculus The purpose of the present study ~s to define more precisely the d~fferent types of neurons m the various parts of the inferior colhculus, especmlly m the central nucleus In th~s a~m the hlstometnc properties of cells m the d~fferent parts of the inferior colhculus were stud~ed by quantitative optical macroscopy As emphasized by different authors (Welbel 1969, Elias, Hennlg and Schwartz 1971), and more pamcularly for the central nervous system by Mayhew and Momoh (1973) the apphcat~on of the principles and methods of stereology allows quant~tatwe mformat~on to be obtained from thin sections of biological materml and permits the definition of tissue and cell structures m three-dimensional terms MATERIAL AND METHODS Two adult cats (M28, M31) of 3000-3500 g body weight were anaesthetized with Ketamine (20 mg 1 m ) and Nembutal (25-30 mg/kg i.p ) and perfused by a standardized procedure This techmque ~s a shght modlficahon of that described by Baleydler, Leger and Quoex (1973) The perfusate is a phosphate-buffered (0 1 M) mixture of 1% glutaraldehyde and 4 % paraformaldehyde After thoracotomy, the solution (pH 7 4) was introduced through the left ventricle at a temperature of 20 °C, at a pressure of 160 mm Hg and with a controlled flow decreasing from 200 to 120 mt/mm Animals were previously exsangulnated by mC~slng the right atrium Immediately after perfuslon, the brain was removed and the inferior colhcuh were dissected out The inferior colhcuh were then chopped transversely into approximately four 1 mm slices Each shce was then drawn under a binocular dissecting macro-
27 scope, the caudal plane facing the exammer Each slice was cut into 4-6 blocks, slightly asymmetrical m shape, and each block was drawn Next, each block was fixed overnight at 4 °C m the perfusate solution, then washed twice in the phosphate buffer and post-fixed in 2 % o s m m m tetroxlde m phosphate buffer for 2 hr After dehydration in a graded series of alcohols followed by propylene oxide and infiltration with Epon, each block from a shce was gathered like the pieces of a puzzle This technique permits each block from the d~fferent shces to be set in 3 spatial dimensions before terminal embedding Next, each block was embedded in Epoxy resin About 60 blocks of embedded tissue were obtained per animal Blocks were sectioned on a O M U - 2 R E I C H E R T Ultra-Mlcrotome with glass knives Semi-thin sections (0 5 /~m) were taken for hlstometrlc analysis and stained with alkahne tolmdlne blue according to the method of Ling, Paterson, Prlvat, Morl and Leblond (1973)
Tissue samphng We decided to choose samples, as it seemed too time-consuming to study every section using hastometrlc and stereologlcal procedures As emphasized by Welbel, Straubh, Gnagl and Hess (1969) it is very important when analysing only a part of the available material to make sure that the sample is representative of the whole Following Mayhew and M o m o h (1973), a systematic samphng procedure was performed using a series of steps Step 1 The right inferior colhculus was taken through the fixation and embedding stages previously described The blocks obtained (see below) from each of 2 right inferior colhcuh provided a store of material from which samples at the other steps could be taken Step 2 For further sampling we decided to choose, from the store of blocks of step 1, only blocks belonging to the cranial and caudal planes Since the cramal and caudal planes of cat M28 were intercalated between the planes of cat M31 we obtained an orderly sequence for cats cranial (M31), cranlo-lntermed,ate (M28), caudo-mtermediate (M28) and caudal (M31) Step 3 In each plane, which furmshed 4-6 blocks, the inferior colhculus was assumed to be trmngular in shape We therefore decided to choose the blocks belonglng to each angle of the triangle, namely the dorso-medlal, the dorso-lateral and the ventral blocks Each of these blocks representatwe of an angle furnished two semi-thin sections for h~stometrJc analysis We therefore obtained 24 semi-thin sections of 2 × 2 m m in size Step 4 For each section, a low magnification mlcrograph was performed ( × 200) On each mlcrograph we superimposed at random a samphng lattice In this lattice each square was equivalent to a 9 • 10a # m 2 square, 1 e 300 # m on a side Photomicrographs of all observed neurons were taken from every other square Approximately 600 mlcrographs per animal were recorded All these mlcrographs were taken at an initial magmficatlon of × 400 With such a techmque, we ensured a systematic random sampling We decided to use this method because it was shown by Ebbesson and Tang (1967) to have the smallest standard error
28
Htstometrtc techntques As emphasized by Mayhew and M o m o h (1973) "quantltatlon of neuronal parameters requires the use of reproducible and accurate techmques which are capable of resolving biological differences from methodological ones In other words, they must allow for biological variations m neuron populations" The aim of our study was to discover if such variations exist between the different parts of the inferior colhculus In our investigation neuronal parameters were estimated using the principles of stereology (Underwood 1969, Welbel 1969) These prlnclples have already proved to be useful for the study of neuronal parameters (Mayhew and M o m o h 1973) We decided to choose for measurement all types of neuron profile within the field of view m order to avoid the "nucleolar-blaslng" of Mayhew and M o m o h (1973) As emphasized by these authors "nucleolar biasing", i e the choice for measurement of only those neurons whose nucleoh are wslble, leads to substantml overestimates of cell volume and perlkaryal volume/surface ratio and to s,gnlficant underestimates of neuronal population density, perlkaryal volume proportion and cytoplasmic volume/ nuclear volume ratio Different techniques were used
Point counting For estimating various parameters, we employed a point counting method A square lattice (0 8 cm per side for each square) containing 891 point intersections was used with the apparatus described by Welbel, Klstler and Scherle (1966) Since the final magnification was × 4000, each test point represented the centre of an area of 4 # m 2 Profiles of neurons were easily identified on the basis of nuclear shape, cytoplasmic granularity and presence of Nlssl substance With the point counting method we obtained Nuclear profile areas All the observed profiles were counted, without exception, accordmg to Mayhew and M o m o h (1973) Neuronal profile areas All types of neurons, nucleated or anucleated were monitored - Nuclear volume/cellular volume ratio (Vn/Ve) This ratio is proportional to that of nuclear profile areas/cellular profile areas - Volume proportion of perlkaryon (Vvp) This parameter, obtained by point counting, defines the fractional volume of the inferior colhculus tissue occupied by the neuronal penkaryon It therefore, gives a measure of the so-called grey/cell coefficient (Mayhew and M o m o h 1973) Nuclear profile diameter (Dl,) These profiles were essentially circular In most instances the apparent long axis was nearly equal to the dimension perpendicular to this axis So in every case we defined a mean diameter Dp as equal to the mean of these dimensions Actual mean nuclear diameter Da This was derived from the Dp estimate using a correction factor 4/zc according to AbercrombIe (1946) Mean nuclear volume This was calculated using the formula -
-
-
-
-
29 7~ Vn = -~- Dap
As emphasized by Mayhew and Momoh (1975), we calculated thls volume using Dp of nucleated profiles only, without the correcting factor 4/# Nuclear area density (Nan) The number of nuclear profiles per umt area of inferior colhculus tissue is related to the number of actual nuclei per unit volume of t)ssue (Nvn) Thls value of Nvn, or nuclear numerlcal density (Weibel 1969), or packing denslty (Haddara 1956) was calculated using the formula (De Hoff and Rhmes 196 I) -
N,n
Nvn -- - -- number/mm 3 Da - Penkaryon volume The mean penkaryon volume (lip) was calculated from the estlmates of nuclear volume and Vn/Ve ratlo re=
Vn
Vn/Vo
Statistics For the various hlstometrlc parameters, we calculated the means, the standard deviations and the standard error The data so obtained permit us to calculate for each histometric parameter the value of the 2 samples t-test between our different populations i e , dorsomedlal vs ventral (DM vs V), dorsomedial vs dorsolateral (DM vs DL) and ventral vs dorsolateral (V vs DL) as expressed in Table 1 By this procedure we were able to test the null hypothesis that the 2 population means are equal The values of t and of the number of degrees of freedom were furnished by the classical formula, assuming that the different populations were normal with unequal variances Sample means were considered to differ significantly if the error probability (P) was less than 0 01 RESULTS
Neurons of the inferior colhculus (Fig 1) are easily recogmzed on the basis of their spherical nucleus, containing a large nucleolus, in a clear nucleoplasm The nuclear envelope appears dehcately stained The cytoplasm contains stained flakes and small spherical or elongated mltochondrla The cytoplasm looks lighter than the surrounding neuropil
(1) Nuclear parameters Table 1 records the various nuclear parameters, i e nuclear volume, nuclear profile areas and nuclear profile diameters m the various parts of the inferior colllculus dorso-medlal (D M ), ventral (V) and dorso-lateral (D L ) The nuclear volume appears the same in the d~fferent parts of the inferior colliculus, with a mean value for the inferior colhculus of 749 03/~m s As predicted by the nuclear volume, the nuclear profile areas and the nuclear
30 TABLE 1 RESULTS OF THE VARIOUS HISTOMETRIC PARAMETERS Parameters
Dorso-
(mean only)
medJal
P value ( D M vs V)
Ventral (V)
P value (V vs DL)
(DM)
Nuclear volume (/~ma)
Nuclear profiles
753 31
71 41
areas ( # m 2)
Nuclear profiles dmmeter (/~m)
12 47
Cellular volume (/tm a) 1674 02
Neuronal profiles areas (~m 2)
163 57
Vvp ( ~ )
4 29
Vnl Ve (,umalt~ma)
0 45
Nuclear areal
130 91
density ( n u m b e r / m m z)
Nuclear numerical density
1055809
( n u m b e r / m m a)
t 040 v 229 NS t 010 v 1138 NS t 1 89 v 1136 NS t 4 57 v 200 P -/-001 t 1160 901 P
