158
Brain Research, 137 (1977) 158-163 © Elsevier/North-Holland Biomedical Press
Cerebellar afferents from neurons in motor nuclei of cranial nerves demonstrated by retrograde axonal transport of horseradish peroxidase
NAIPHINICH KOTCHABHAKDI and FRED WALBERG Anatomical Institute, University of Oslo, Oslo (Norway) and Laboratory of Neurobiology and Department of Anatomy, Faculty of Science, Mahidol University, Bangkok (Thailand)
(Accepted July 14th, 1977)
It is well known that, in participating in the fine coordination of movement, the cerebellum receives a wide variety of afferent inputs from direct as well as indirect central projections of ascending sensory and proprioceptive paths 2,12. More interestingly, it has been proposed that the cerebellum also receives an 'efference copy' of descending motor command impulsesLll,2L Hence, information of the on-going movements reaches the cerebellum either before the movement by collaterals of central neurons which terminate in the precerebellar relay nuclei, e.g. the pons, the inferior olive and the brain stem reticular formation, or in the form of feedback proprioceptive impulses after the intended movements have been initiated17, is. No evidence so far, however, indicates that the cerebellum might also receive afferent information directly from neurons in the motoneuronal pools. During recent investigations on cerebellar afferents from various nuclei in the brain stem of the cat 2°,22, it was observed that large motoneuron-like cells in various motor nuclei of the cranial nerves were consistently labeled with dark brown granules, typical of retrogradely labeled cells, following horseradish peroxidase (HRP) injection in certain regions of the cerebellum. Similar findings were briefly mentioned in tables in a recent publication by Chan-Palay 9 who observed HRP-labeled cells in certain nuclei of cranial nerves after H R P injection in the dentate nucleus, the nucleus interpositus anterior and posterior, and the cerebellar cortex of lobule IV overlying the interpositus nuclei in the rhesus monkey (Macaca mulatta). In this report we present preliminary evidence from detailed studies in a large number of series of brain material with H R P injections in various regions of the cerebellum in the cat. Similar findings were also obtained from preliminary studies of cerebellar afferents in primates (Macaca irus). Most of the experimental brain material from cat included in this report has also been used in other studies on cerebellar afferent systems, made in our laboratory 4-s, 13,14,16,20,22,24. A detailed description of the technique for H R P injection used in these studies has been given by Walberg et al. 25. The same method has also been employed in our experiments on monkeys. Illustrations of the injection sites in the cerebellum for most of our cases are found in recent publications2°,2L
159 Since endogenous peroxidatic activities have been reported in some nuclei in the brain of squirrel monkeys z6 and rats 19, brains from normal cats and monkeys were also perfused, processed according to the same methods and included as controls in our studies. No labeling of neurons by the H R P reaction product was observed in the motor nuclei of the cranial nerves in the normal brains under the conditions and methods used in our laboratory. The results obtained for this report come from a total of 67 series in the cat and 5 series in the monkey. Unlike afferents from the inferior olive 4-6,14,16,25, pons 8,1a,15 and the brain stem lateral reticular nucleus 7, which project to large parts of the cerebellum, afferents from neurons in the m o t o r nuclei of the cranial nerves appear to project only to certain parts of the cerebellum. Thus, in spite of detailed examinations of brain material from H R P injections in various parts of the cerebellum and the cerebellar nuclei, positive labeled cells in the motor nuclei of the cranial nerves were only found following H R P injections in the anterior lobe, the nodulus, the flocculus, and the fastigial nucleus. The largest number of labeled cells in these nuclei was observed following H R P injections which had spread from the overlying cerebellar cortex into the white matter and the adjacent part of the cerebellar peduncles. Some labeled cells in these nuclei were also observed following injections which had been limited to one or more of the cerebellar peduncles. The presence and distribution of HRP-labeled cells in the motor nuclei of the cranial nerves observed in the present report are shown in Fig. 1. Detailed description of the H R P injection sites and the findings in each positive case are summarized in Table I. The labeled cells were found bilaterally in the rostral half of the hypoglossal nuclei*, and in the region of the ambiguus nucleus (the motor nucleus of the I X and X cranial nerves)**. Some large labeled cells were also found in the facial nucleus, the motor nucleus of the trigeminal nerve, and in the nucleus of the abducent nerve. In the cat, labeled cells in the trochlear and oculomotor nuclei were found following H R P injection in the nodulus, and the flocculus. More labeled cells were found in the m o t o r nuclei of the cranial nerves in the monkey than in the cat. Although the presence of HRP-labeled cells in the m o t o r nuclei of the cranial nerves is rather consistent, such cells (see Table I) are few, probably constituting less than 5 ~ of the total population of neurons in each nucleus. However, due to the limitation of the method20,~4, 25, these numbers might not accurately represent the total number of cells which contribute to cerebellar afferents from these nuclei. Similarly, we can not totally exclude the possibility that other areas of the cerebellum might also receive afferent projections from the motor nuclei of the cranial nerves. The labeled cells in the motor nuclei of the cranial nerves after H R P injections in the cerebellum are usually large or medium-sized. As shown in Fig. 1, the cells are heavily labeled with positive granules also in their dendrites, thus making them very
* Labeled cells are also present in the dorsal motor vagal nucleus. ** In none of our series was the spinal nucleus of the accessory nerve included in the material.
L
R
~
2
,t~..~j "Sp'V
LRN ~,mb CX
"7
LRN CAUDAL
Fig. 1. A: schematic drawing from transverse sections at different levels of the brain stem and mesencephalon showing the distribution of labeled cells in the motor nuclei of the cranial nerves following HRP injections in the cerebellum. The caudalmost section (7) represents the level at the rostral half of the hypoglossal nucleus, while that in 6 represents the rostral pole of the same nucleus. B: darkfield photomicrograph from a section corresponding to level 6 in case B.St.L.721 showing a large labeled cell in the hypoglossal nucleus. Bar indicates 100/~m. C: a montage at different focal planes of interference contrast photomicrographs taken from the large hypoglossal neuron shown in B. Bar indicates 50/~m. Arrows in B point to labeled cells in the perihypoglossal nuclei. Abbreviations: Amb, ambiguus nucleus; AQ, aqueduct; BC, brachium conjunctivum; BIC, brachium of inferior colliculus; BP, brachium pontis; C, nucleus coeruleus; CN, cochlear nucleus; Cu, cuneate nucleus; CX, external cuneate nucleus; D, descending vestibular nucleus; Gr, gracile nucleus; g.VlI, genu of the facial nerve; IC, external nucleus of the inferior colliculus; Ic, nucleus intercalatus; IO, inferior olive; L, lateral vestibular nucleus; LRN, lateral reticular nucleus, internal division; M, medial vestibular nucleus; MG, medial geniculate body; P, pyramidal tract; PAG, periaqueductal gray; PG, pontine gray; Ph, perihypoglossal nuclei; PT, posterior pretectal nucleus; RN, red nucleus; S, superior vestibular nucleus; SC, superior colliculus; SM, medial nucleus of solitary tract; SN, substantia nigra; SO, superior olive; Sp.V, spinal trigeminal tract; St, solitary tract; Tb, trapezoid body; TD, dorsal tegmental nucleus; 11I, oculomotor nucleus; IIIN, oculomotor nerve; IV, trochlear nucleus; V, trigeminal nucleus; VI, abducens nucleus; VIN, abducent nerve; VII, facial nucleus; X, dorsal motor nucleus of vagus; XII, hypoglossal nucleus; XIIN, hypoglossal nerve.
161 TABLE I S u m m a r y o f the findings f r o m positive cases in which labeled cells were observed in motor nuclei o f the cranial nerves
The number indicated in the table represents the total number of labeled cells in each nucleus counted from two of every 5 consecutive sections. Abbreviations: L, left; R, right. Case
B.St.L.665 B.St.L.700 B.St.L.725 B.St.L.775 B.St.L.721 B.St.L.627 B.St.L.720 B.St.L.717 B.St.L.712 B.St.L.752 B.St.L.772 B.St.L.762 B.St.L.763 B.St.L.695 B.St.L.699 MI-3 MI-5
Injection site
Ant. lobe I-II Ant. lobe I-II Ant. lobe II-III Ant. lobe I-IV ÷ nucl. fast. L ant. lobe lat. III-V ÷ sup. cer. ped. L ant. lobe lat. II-V ÷crusIa L ant. lobe III lat. ~- rostr, nucl. fast. L ant. lobe III lat. ÷ sup. cer. ped. L sup. cer. ped. Nodulus Nodulus L flocculus L flocculus L nucl. fast. L nucl. fast. Ant. lobe I-II Lcer. ped.
Nucl. n. X I I
Nucl. ambig,
Nucl. n. VII
Nucl. n. VI
Nucl. n. V
Nucl. n. I V
Nucl. n. H I
L
L
L
L
L
L
L
R
R
R
R
R
8 11 4
5 4 7 1 1 11
8
3 20
8
3
3
6
18 10 27
6
12
7
16
12
6 22 14
5
16
7 23
3
R
R
12 10 4
7
13 2 20 4 2 14 4 4 1 1 4 8 7 3 3 3 1 6 2 5 3 15 8 17 3 45 39 26 22 11 - -
5 --
2
5
3 26 11
5 5 3 12 10 1
2 2 3 3 20
1
1 3 3 3 10 22 11 35 40 15 - -
3
8
1
2
2 4
3 -3 1
12 15
2 --
3
similar to the m o t o n e u r o n s in those nuclei shown in Golgi preparations by R a m 6 n y Caja123. U n f o r t u n a t e l y , in our present study, the H R P reaction p r o d u c t did n o t impregnate the axons of these n e u r o n s sufficiently to allow for a tracing. Therefore, we do n o t k n o w whether the H R P - l a b e l e d cells are m o t o n e u r o n s sending collaterals to the cerebellum a n d their m a i n axons to effector organs, or merely represent large a n d medium-sized i n t e r n e u r o n s within the m o t o r nuclei of the cranial nerves. O u r findings are, in this respect, similar to those recently made by Corvaja et al. 10, who in the cat observed large m o t o n e u r o n - l i k e cells in Rexed's l a m i n a I X of the spinal cord following H R P injections in the lateral reticular nucleus. W i t h regard to the projection areas in the cerebellum, it is extremely interesting that labeled cells in the m o t o r nuclei of the cranial nerves in the present report were f o u n d only after H R P injections in the anterior lobe, nodulus, flocculus a n d fastigial nucleus. These areas of the cerebellum have been referred to as the older region, the paleocerebellum (for references, see 2 a n d 12). However, it is i m p o r t a n t to r e m e m b e r that, in these areas o f the cerebellum, where H R P injections resulted in labeling of
162 n eu r o n s in the m o t o r nuclei o f the cranial nerves, there is a t r e m e n d o u s o v er l ap p i n g of p r o p r i o c e p t i v e inputs f r o m vestibular as well as spinal origin, and afferent inputs f r o m the m o t o r and other areas o f the cerebral cortex z,3. T h e observations m a d e in the present investigation indicate that the cerebellum plays a m o r e active m o n i t o r i n g role than hitherto assumed in the integrated c o m m a n d impulses which are sent d o w n to the m o t o n e u r o n a l pools, thus controlling the activities in the axons o f the m o t o n e u r o n s . S u p p o r t e d by the N o r w e g i a n Agency for International D e v e l o p m e n t ( N O R A D ) and a research grant f r o m The N a t i o n a l Research Council o f Thailand.
1 Allen, G. I. and Tsukahara, N., Cerebrocerebellar communication systems, Physiol. Rev., 54 (1974) 957-1006. 2 Bell, C. C. and Dow, R. S. (Eds.), Cerebellar circuitry, Neurosci. Res. Progr. Bull., 5 (1967) 520616. 3 Brodal, A., Anatomical studies of cerebellar fiber connections with special reference to problems of functional localization, Progr. Brain Res., 25 (1967) 135-173. 4 Brodal, A., The olivocerebellar projection in the cat as studied with the method of retrograde axonal transport of horseradish peroxidase. II. The projection to the uvula, J. comp. NeuroL, 166 (1976) 417426. 5 Brodal, A. and Walberg, F., The olivocerebellar projection in the cat studied with the method of retrograde axonal transport of horseradish peroxidase. VI. The projection onto longitudinal zones of the paramedian lobule, J. comp. Neurol., in press. 6 Brodal, A., Walberg, F. and Hoddevik, G. H., The olivocerebellar projection in the cat studied with the method of retrograde axonal transport of horseradish peroxidase. I. The projection to the paramedian lobule, J. comp. Neurol., 164 (1975) 449-470. 7 Brodal, P., Demonstration of a somatotopically organized projection onto the paramedian lobule and the anterior lobe from the lateral reticular nucleus. An experimental study with the horseradish peroxidase method, Brain Research, 95 (1975) 221-239. 8 Brodal, P. and Walberg, F., The pontine projection to the cerebellar anterior lobe. An experimental study in the cat with retrograde transport of horseradish peroxidase, Exp. Brain Res., in press. 9 Chan-Palay, V., Cerebellar Dentate Nucleus; Organization, Cytology and Transmitter, Springer, Berlin, 1977, 548 pp. 10 Corvaja, N., Grofov~, I., Pompeiano, O. and Walberg, F., The lateral reticular nucleus in the cat. I. An experimental anatomical study of its spinal and supraspinal afferent connections, Neuroscience, in press. l I Evarts, E. V., Bizzi, E., Burke, R. E., DeLong, M. and Thach, W. T., Jr. (Eds.), Central control of movements, Neurosci. Res. Progr. Bull., 9 (1971) 1-170. 12 Fields, W. S. and Willis, W. D. (Eds.), The Cerebellum in Health and Disease, Green, St. Louis, 1970, XV I- 557 pp. 13 Hoddevik, G. H., The pontocerebellar projection onto the paramedian Iobule in the cat: An experimental study with the use of horseradish peroxidase as a tracer, Brain Research, 95 (1975) 291-307. 14 Hoddevik, G. H. and Brodal, A., The olivocerebellar projection studied with the method of retrograde axonal transport of horseradish peroxidase. V. The projection to the flocculonodular lobe and the paraflocculus in the rabbit, J. comp. Neurol., in press. 15 Hoddevik, G. H., Brodal, A., Kawamura, K. and Hashikawa, T., The pontine projection to the cerebellar vermal visual area studied by means of the retrograde axonal transport of horseradish peroxidase, Brain Research, 123 (1977) 209-227. 16 Hoddevik, G. H., Brodal, A. and Walberg, F., The olivocerebellar projection in the cat studied with the method of retrograde axonal transport of horseradish peroxidase. III. The projection to the vermal visual area, J. comp. NeuroL, 169 (1976) 155-170. 17 Ito, M., Neurophysiological aspects of the cerebellar motor and control system, bit. J. Neurosci., 7 (1970) 162-176.
163 18 Ito, M., Neural design of the cerebellar motor control, Brain Research, 40 (1972) 81-84. 19 Keefer, D. A. and Christ, J. F., Distribution of endogenous diaminobenzidine-staining cells in the normal rat brain, Brain Research, 116 (1976) 312-316. 20 Kotchabhakdi, N., Hoddevik, G. H. and Walberg, F., Cerebellar afferent projections from the perihypoglossal nuclei: an experimental study with the method of retrograde axonal transport of horseradish peroxidase, Exp. Brain Res., in press. 21 Oscarsson, O., Functional organization of spinocerebellar paths. In A. Iggo (Ed.), Handbook of Sensory Physiology, Vol. H, Springer, Berlin, 1970, pp. 121-127. 22 Pierce, E. T., Hoddevik, G. H. and Walberg, F., The cerebellar projection from the raphe nuclei in the cat as studied with the method of retrograde transport of horseradish peroxidase, Anat. ErnbryoL, in press. 23 Ram6n y Cajal, S., Histologie du Syst~me Nerveux de l'Homme et des Vert~brds, 1/ol. 1, Instituto Ram6n y Cajal, Madrid, 1952, XV ÷ 986 pp. 24 Rinvik, E. and Walberg, F., Studies on the cerebellar projections from the main and external cuneate nuclei in the cat by means of retrograde axonal transport of horseradish peroxidase, Brain Research, 95 (1975) 371-381. 25 Walberg, F., Brodal, A. and Hoddevik, G. H., A note on the method of retrograde transport of horseradish peroxidase as a tool in studies of afferent cerebeUar connections, particularly those from the inferior olive; with comments on the orthograde transport in Purkinje cell axons, Exp. Brain Res., 24 (1976) 383-401. 25 Wong-Riley, M. T. T., Endogenous peroxidatic activity in brain stem neurons as demonstrated by their staining with diaminobenzidine in normal squirrel monkeys, Brain Research, 108 (1976) 257-277.
Brain Research, 137 (1977) 158-163 © Elsevier/North-Holland Biomedical Press
Cerebellar afferents from neurons in motor nuclei of cranial nerves demonstrated by retrograde axonal transport of horseradish peroxidase
NAIPHINICH KOTCHABHAKDI and FRED WALBERG Anatomical Institute, University of Oslo, Oslo (Norway) and Laboratory of Neurobiology and Department of Anatomy, Faculty of Science, Mahidol University, Bangkok (Thailand)
(Accepted July 14th, 1977)
It is well known that, in participating in the fine coordination of movement, the cerebellum receives a wide variety of afferent inputs from direct as well as indirect central projections of ascending sensory and proprioceptive paths 2,12. More interestingly, it has been proposed that the cerebellum also receives an 'efference copy' of descending motor command impulsesLll,2L Hence, information of the on-going movements reaches the cerebellum either before the movement by collaterals of central neurons which terminate in the precerebellar relay nuclei, e.g. the pons, the inferior olive and the brain stem reticular formation, or in the form of feedback proprioceptive impulses after the intended movements have been initiated17, is. No evidence so far, however, indicates that the cerebellum might also receive afferent information directly from neurons in the motoneuronal pools. During recent investigations on cerebellar afferents from various nuclei in the brain stem of the cat 2°,22, it was observed that large motoneuron-like cells in various motor nuclei of the cranial nerves were consistently labeled with dark brown granules, typical of retrogradely labeled cells, following horseradish peroxidase (HRP) injection in certain regions of the cerebellum. Similar findings were briefly mentioned in tables in a recent publication by Chan-Palay 9 who observed HRP-labeled cells in certain nuclei of cranial nerves after H R P injection in the dentate nucleus, the nucleus interpositus anterior and posterior, and the cerebellar cortex of lobule IV overlying the interpositus nuclei in the rhesus monkey (Macaca mulatta). In this report we present preliminary evidence from detailed studies in a large number of series of brain material with H R P injections in various regions of the cerebellum in the cat. Similar findings were also obtained from preliminary studies of cerebellar afferents in primates (Macaca irus). Most of the experimental brain material from cat included in this report has also been used in other studies on cerebellar afferent systems, made in our laboratory 4-s, 13,14,16,20,22,24. A detailed description of the technique for H R P injection used in these studies has been given by Walberg et al. 25. The same method has also been employed in our experiments on monkeys. Illustrations of the injection sites in the cerebellum for most of our cases are found in recent publications2°,2L
159 Since endogenous peroxidatic activities have been reported in some nuclei in the brain of squirrel monkeys z6 and rats 19, brains from normal cats and monkeys were also perfused, processed according to the same methods and included as controls in our studies. No labeling of neurons by the H R P reaction product was observed in the motor nuclei of the cranial nerves in the normal brains under the conditions and methods used in our laboratory. The results obtained for this report come from a total of 67 series in the cat and 5 series in the monkey. Unlike afferents from the inferior olive 4-6,14,16,25, pons 8,1a,15 and the brain stem lateral reticular nucleus 7, which project to large parts of the cerebellum, afferents from neurons in the m o t o r nuclei of the cranial nerves appear to project only to certain parts of the cerebellum. Thus, in spite of detailed examinations of brain material from H R P injections in various parts of the cerebellum and the cerebellar nuclei, positive labeled cells in the motor nuclei of the cranial nerves were only found following H R P injections in the anterior lobe, the nodulus, the flocculus, and the fastigial nucleus. The largest number of labeled cells in these nuclei was observed following H R P injections which had spread from the overlying cerebellar cortex into the white matter and the adjacent part of the cerebellar peduncles. Some labeled cells in these nuclei were also observed following injections which had been limited to one or more of the cerebellar peduncles. The presence and distribution of HRP-labeled cells in the motor nuclei of the cranial nerves observed in the present report are shown in Fig. 1. Detailed description of the H R P injection sites and the findings in each positive case are summarized in Table I. The labeled cells were found bilaterally in the rostral half of the hypoglossal nuclei*, and in the region of the ambiguus nucleus (the motor nucleus of the I X and X cranial nerves)**. Some large labeled cells were also found in the facial nucleus, the motor nucleus of the trigeminal nerve, and in the nucleus of the abducent nerve. In the cat, labeled cells in the trochlear and oculomotor nuclei were found following H R P injection in the nodulus, and the flocculus. More labeled cells were found in the m o t o r nuclei of the cranial nerves in the monkey than in the cat. Although the presence of HRP-labeled cells in the m o t o r nuclei of the cranial nerves is rather consistent, such cells (see Table I) are few, probably constituting less than 5 ~ of the total population of neurons in each nucleus. However, due to the limitation of the method20,~4, 25, these numbers might not accurately represent the total number of cells which contribute to cerebellar afferents from these nuclei. Similarly, we can not totally exclude the possibility that other areas of the cerebellum might also receive afferent projections from the motor nuclei of the cranial nerves. The labeled cells in the motor nuclei of the cranial nerves after H R P injections in the cerebellum are usually large or medium-sized. As shown in Fig. 1, the cells are heavily labeled with positive granules also in their dendrites, thus making them very
* Labeled cells are also present in the dorsal motor vagal nucleus. ** In none of our series was the spinal nucleus of the accessory nerve included in the material.
L
R
~
2
,t~..~j "Sp'V
LRN ~,mb CX
"7
LRN CAUDAL
Fig. 1. A: schematic drawing from transverse sections at different levels of the brain stem and mesencephalon showing the distribution of labeled cells in the motor nuclei of the cranial nerves following HRP injections in the cerebellum. The caudalmost section (7) represents the level at the rostral half of the hypoglossal nucleus, while that in 6 represents the rostral pole of the same nucleus. B: darkfield photomicrograph from a section corresponding to level 6 in case B.St.L.721 showing a large labeled cell in the hypoglossal nucleus. Bar indicates 100/~m. C: a montage at different focal planes of interference contrast photomicrographs taken from the large hypoglossal neuron shown in B. Bar indicates 50/~m. Arrows in B point to labeled cells in the perihypoglossal nuclei. Abbreviations: Amb, ambiguus nucleus; AQ, aqueduct; BC, brachium conjunctivum; BIC, brachium of inferior colliculus; BP, brachium pontis; C, nucleus coeruleus; CN, cochlear nucleus; Cu, cuneate nucleus; CX, external cuneate nucleus; D, descending vestibular nucleus; Gr, gracile nucleus; g.VlI, genu of the facial nerve; IC, external nucleus of the inferior colliculus; Ic, nucleus intercalatus; IO, inferior olive; L, lateral vestibular nucleus; LRN, lateral reticular nucleus, internal division; M, medial vestibular nucleus; MG, medial geniculate body; P, pyramidal tract; PAG, periaqueductal gray; PG, pontine gray; Ph, perihypoglossal nuclei; PT, posterior pretectal nucleus; RN, red nucleus; S, superior vestibular nucleus; SC, superior colliculus; SM, medial nucleus of solitary tract; SN, substantia nigra; SO, superior olive; Sp.V, spinal trigeminal tract; St, solitary tract; Tb, trapezoid body; TD, dorsal tegmental nucleus; 11I, oculomotor nucleus; IIIN, oculomotor nerve; IV, trochlear nucleus; V, trigeminal nucleus; VI, abducens nucleus; VIN, abducent nerve; VII, facial nucleus; X, dorsal motor nucleus of vagus; XII, hypoglossal nucleus; XIIN, hypoglossal nerve.
161 TABLE I S u m m a r y o f the findings f r o m positive cases in which labeled cells were observed in motor nuclei o f the cranial nerves
The number indicated in the table represents the total number of labeled cells in each nucleus counted from two of every 5 consecutive sections. Abbreviations: L, left; R, right. Case
B.St.L.665 B.St.L.700 B.St.L.725 B.St.L.775 B.St.L.721 B.St.L.627 B.St.L.720 B.St.L.717 B.St.L.712 B.St.L.752 B.St.L.772 B.St.L.762 B.St.L.763 B.St.L.695 B.St.L.699 MI-3 MI-5
Injection site
Ant. lobe I-II Ant. lobe I-II Ant. lobe II-III Ant. lobe I-IV ÷ nucl. fast. L ant. lobe lat. III-V ÷ sup. cer. ped. L ant. lobe lat. II-V ÷crusIa L ant. lobe III lat. ~- rostr, nucl. fast. L ant. lobe III lat. ÷ sup. cer. ped. L sup. cer. ped. Nodulus Nodulus L flocculus L flocculus L nucl. fast. L nucl. fast. Ant. lobe I-II Lcer. ped.
Nucl. n. X I I
Nucl. ambig,
Nucl. n. VII
Nucl. n. VI
Nucl. n. V
Nucl. n. I V
Nucl. n. H I
L
L
L
L
L
L
L
R
R
R
R
R
8 11 4
5 4 7 1 1 11
8
3 20
8
3
3
6
18 10 27
6
12
7
16
12
6 22 14
5
16
7 23
3
R
R
12 10 4
7
13 2 20 4 2 14 4 4 1 1 4 8 7 3 3 3 1 6 2 5 3 15 8 17 3 45 39 26 22 11 - -
5 --
2
5
3 26 11
5 5 3 12 10 1
2 2 3 3 20
1
1 3 3 3 10 22 11 35 40 15 - -
3
8
1
2
2 4
3 -3 1
12 15
2 --
3
similar to the m o t o n e u r o n s in those nuclei shown in Golgi preparations by R a m 6 n y Caja123. U n f o r t u n a t e l y , in our present study, the H R P reaction p r o d u c t did n o t impregnate the axons of these n e u r o n s sufficiently to allow for a tracing. Therefore, we do n o t k n o w whether the H R P - l a b e l e d cells are m o t o n e u r o n s sending collaterals to the cerebellum a n d their m a i n axons to effector organs, or merely represent large a n d medium-sized i n t e r n e u r o n s within the m o t o r nuclei of the cranial nerves. O u r findings are, in this respect, similar to those recently made by Corvaja et al. 10, who in the cat observed large m o t o n e u r o n - l i k e cells in Rexed's l a m i n a I X of the spinal cord following H R P injections in the lateral reticular nucleus. W i t h regard to the projection areas in the cerebellum, it is extremely interesting that labeled cells in the m o t o r nuclei of the cranial nerves in the present report were f o u n d only after H R P injections in the anterior lobe, nodulus, flocculus a n d fastigial nucleus. These areas of the cerebellum have been referred to as the older region, the paleocerebellum (for references, see 2 a n d 12). However, it is i m p o r t a n t to r e m e m b e r that, in these areas o f the cerebellum, where H R P injections resulted in labeling of
162 n eu r o n s in the m o t o r nuclei o f the cranial nerves, there is a t r e m e n d o u s o v er l ap p i n g of p r o p r i o c e p t i v e inputs f r o m vestibular as well as spinal origin, and afferent inputs f r o m the m o t o r and other areas o f the cerebral cortex z,3. T h e observations m a d e in the present investigation indicate that the cerebellum plays a m o r e active m o n i t o r i n g role than hitherto assumed in the integrated c o m m a n d impulses which are sent d o w n to the m o t o n e u r o n a l pools, thus controlling the activities in the axons o f the m o t o n e u r o n s . S u p p o r t e d by the N o r w e g i a n Agency for International D e v e l o p m e n t ( N O R A D ) and a research grant f r o m The N a t i o n a l Research Council o f Thailand.
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