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An autoradiographic study on the terminal distribution of cerebellothalamic fibers in the cat
Brain Research, 215 (1981) 29--47 © Elsevier/North-Holland Biomedical Press
29
AN AUTORADIOGRAPHIC STUDY ON THE TERMINAL DISTRIBUTION OF C E R E B E L L O T H A L A M I C FIBERS I N T H E CAT
TETSUO SUGIMOTO, NOBORU MIZUNO and KAZUO ITOH Department of Anatomy (lst Division), Faculty of Medicine, Kyoto University, Kyoto 606 (Japan)
(Accepted November 13th, 1980) Key words,: cerebellothalamic fibers - - thalamus - - cerebellar nuclei - - autoradiography - - cat
SUMMARY Distribution of cerebellothalamic fibers was studied in the cat by the anterograde tracing method. The vast majority of cerebellothalamic fibers were distributed contralaterally. The fastigial fibers arose mostly from the caudal half of the nucleus. These ended moderately in the VM* and the most ventromedial regions of the V A - V L complex, and sparsely in the ventral portions of the CL, Pc and N C M ; a few also ended in the CM and ZI. The dentate fibers ended moderately in the medial and rostrodorsal V A - V L regions, and sparsely in the VM, CL, N C M , CM, LP and MD. The existence of the dentatopulvinar fibers was also confirmed. The posterior interpositus fibers ended heavily in the central V A - V L regions, moderately in the subparafascicular nucleus and ZI, and sparsely in the CM and the ventral lateral geniculate nucleus. The anterior interpositus fibers ended mainly in the ventrolateral V A - ¥ L regions, and additionally in the CL and CM. The ipsilateral cerebellothalamic fibers arose mainly from the fastigial nucleus, and additionally from the dentate nucleus; those arising from the interpositus nuclei were very sparse.
INTRODUCTION Direct projections from the cerebellum to the thalamus have often been the subject of studies by the anterograde degeneration methods in several mammals (for reviews, see refs. 1, 8 and 36). The general pattern of direct projections of the cerebellothalamic fibers appears to be well documented by these previous studies, but less is known about the precise topography of termination of the cerebellothalamic * For an explanation of the abbreviations, see list at the end of article.
30 fibers from each cerebellar nucleus. A n g a u t and his associates examined intensively the distribution of the cerebellothalamic fibers from each cerebellar nucleus in the cat, using the anterograde axonal degeneration method 1-3 as well as the evoked potential method4,11. It is known, however, that the degeneration methods do not always provide the most satisfactory means of studying projections from the structures which are adjacent to, or traversed by, many fibers, and that it is occasionally difficult to distinguish with certainty the degenerated fibers of passage from the so-called terminal degeneration. The interpretation o f data from the evoked potential method is also difficult because of uncertainty about the extent of current spread. The present study was performed in an attempt to shed more light on the topography of distribution o f the cerebellothalamic fibers from each cerebellar nucleus in the cat, using the autoradiographic tracing technique in which the contribution of fibers of passage at the injection site to labeling the axon terminals is k n o w n to be neglectedlZ,23. MATERIALS AND METHODS In 18 cats (body weight 2100-4700 g) anesthetized with intraperitoneal sodium pentobarbital (35 mg/kg), a single injection of 0.07-1.2/A (50-100 #Ci/#l) of equal parts of L-[3H]leucine and L-[aH]proline (New England Nuclear) was made stereotaxically with a H a m i l t o n microsyringe into either the fastigial, dentate, anterior interpositus or posterior interpositus nucleus (Table 1). Additionally, in 2 cats (Cats 4 and TABLE I Cat no.
1
3 4 5 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99
Site of injection
FN DN CBN CBN PIN FN DN X FN PIN FN DN DN AIN DN FN X DN X AIN
Amount of injected isotope (t~Ci)
30 12 60 120 30 30 18 18 30 28 40 12 40 30 40 18 20 7 20 25
CBN, all cerebellar nuclei; X, white matter.
Survival period (days)
13 l0 11 I0 10 7 8 8 23 8 7 7 10 10 20 13 8 10 8 7
31 5), all of the cerebellar nuclei were injected unilaterally at 8 points with a total of 0.6-1.2/zl (100 #Ci/#l) of the same isotope mixture. After survival periods of 7-23 days, the cats were deeply anesthetized and perfused through the ascending aorta with 2 liters of 10~ buffered formalin. The brains were removed and stored in 10~ buffered formalin. After saturation with a solution of 30 ~ sucrose in 10~ buffered formalin, serial frontal sections of 35 ,um thickness were made on a freezing microtome and mounted onto gelatinized slides. These sections were processed for autoradiography according to the standard method 13, using 40 ~ Kodak NTB-3 or Sakura NRM2 emulsion. After exposure periods of 4-8 weeks, the slides were developed with Kodak D-19 and stained with cresyl violet or neutral red. The locations of the injection sites and the radioactive labeling were charted onto enlarged outline drawings of selected sections. The thalamic nomenclature and boundaries were mostly based on the atlas of Jasper and Ajmone-Marsan 21. Establishment of fields of fiber termination was not solely on the presence of grain densities exceeding background; silver deposits on identifiable fiber systems were regarded as labeling of transit-fibers, and randomly arranged small grains were considered as terminal grains, i.e. products resulting from labeling of axon terminals. RESULTS In 2 cats injected with isotope unilaterally into all cerebellar nuclei (Cats 4 and 5), silver grains were massively distributed within the ventral, intralaminar and midline nuclei of the thalamus contralateral to the injection. Although many silver grains were seen throughout the rostrocaudal extent of the ventroanterior (VA), ventrolateral (VL) and ventromedial (VM) nuclei, terminal grains were less dense in the lateralmost regions of the VL at the levels immediately rostral to the rostral end of the posterolateral ventral nucleus (VPL) (arrow in Fig. 3b) and in the dorsal portions of the caudalmost levels of the VL (arrow in Fig. 3e). Terminal silver grains in the VM were mainly distributed in the lateral portions of the nucleus. Many terminal grains were seen in the paracentral (Pc), centrolateral (CL) and centromedial (NCM) nuclei. Terminal grains in the CL, however, were distributed only to the caudal two-thirds of the nucleus. In the caudalmost levels of the CL terminal grains were seen throughout the nucleus (Fig. 3f), and in the middle levels of the CL they were observed mainly in the regions close to the lateral margin of the CL (Fig. 3d and e). In the NCM, few terminal grains were found in the iostral one-third of the nucleus (Fig. 3b). Possible labeling of axon terminals was also observed in the centre median-parafascicular complex (CM-Pf), subparafascicular nucleus (Spf), pulvinar nucleus (Pul), and zona incerta (ZI) (Fig. 3d-f). In the CM, Spf and ZI, terminal grains were rather sparse and a moderate number of labeled fibers were seen, indicating the presence of considerable number of passing fibers (Fig. 3f). Only a few terminal grains were found in the Pf. In the Pul, terminal grains were located in a narrow region close to the lateral margin of the nucleus (Fig. 3f). Possible light labeling of axon terminals was seen in the ventral lateral geniculate nucleus (GLv), mediodorsal nucleus (MD) and thalamic reticular nucleus (R). No conclusive evidence, however, was obtained showing
32
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f A
Fig. 1. The sites of isotope injection (stippled areas) into the fastigial (a-d) and the dentate (e-h) nuclei in 5 representative cats (Cats 1, 90, 3, 86, 97). In 2 additional cats (Cats 87, 96) the injection sites are located in the white matter. Two series of projection drawings of sections (a-d and e-h) are arranged in rostrocaudat sequence.
33
Fig. 2. The sites of isotope injection (stippled areas) into the posterior interpositus (a-d) and the anterior interpositus (e-h) nuclei in 4 representative cats (Cats 84, 89, 93, 99). Two series of projection drawings of sections (a-d and e-h) are arranged in rostrocaudal sequence.
o
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35 termination of cerebellar fibers in the anterior thalamic nuclei, dorsal lateral geniculate nucleus (GLd), laterodorsal nucleus (LD), submedius nucleus (Sm), posteromedial ventral nucleus (VPM) and the posteriol group of the thalamus. On the side ipsilateral to the isotope injection in the cerebellar nuclei, light labeling of axon terminals could be seen in the homologous regions of the thalamus.
Cerebellothalamic fibers from the fastigial nucleus In 6 cats injection of isotope into the fastigial nucleus (FN) was attempted unilaterally (Cats 1, 85, 87, 88, 90 and 95). The sites of injection in 3 of them (Cat 1, 87 and 90) are shown in Fig. l a d . In Cat 87 in which the isotope was injected into the a
0 b
e
LD
0 Fig. 4. Distribution of transported label in the thalamus after injecting isotope contralaterally (left side) into the fastigial nucleus in Cat 1.
36
Fig. 5. Distribution of the fastigiothalamic fibers in a VL region of Cat 1. a : low-power photomicrograph of a frontal section through the thalamus of Cat 1 at a level corresponding to that of Fig. 4a. ~ 10. b: dark-field photomicrograph of the VL region encircled with a rectangle in a, showing terminal grains seen after injecting isotope contralaterally into the fastigial nucleus. ",; 60. white matter dorsolateral to the F N (Fig. I b, c), no labeling of axon terminals was found in any thalamic nuclei. In Cat 1 and 88 the isotope injection covered nearly the whole extent o f the F N (Fig. la-d). Distribution of terminal silver grains in Cat 1 was shown in Fig. 4. A moderate number of terminal silver grains were distributed as patchy clusters in the ventrolateral portions of the VL (Fig. 5). Some clusters of terminal grains were also seen in the paralaminar or ventromedial regions of the VL. In the caudalmost levels of the VL, distribution of terminal grains was almost confined in the dorsolateral portions of the nucleus close to the VPL (arrow in Fig. 4e). In the VM, terminal grains were seen nearly the whole extent of the nucleus. The density of grains was heaviest in the dorsolateral VM portions, which were contiguous to the ventromedial VL regions distributed with terminal silver grains (Fig. 6). Light labeling of axon terminals was observed in the ventral portions o f the CL, Pc and N C M , and only a few terminal silver grains were found in the C M and ZI. Labeling in the VL, VM, CL, Pc and N C M ipsilateral to the injection was very light. The areas of distribution of terminal silver grains within these nuclei were much smaller than those within the contralateral counterparts. W h e n the isotope injection was centered on the rostral-half of the F N (Cats 90 and 95) (Fig. la-c), distribution of terminal silver grains in the VL was almost
37
Fig. 6. Dark-field photomicrograph showing distribution of terminal silver grains in the VM and VL regions after injecting isotope contralaterally into the fastigial nucleus in Cat 1. x 50. confined to its ventral regions close to the medial VPL regions (Fig. 12a). In these cats no terminal silver grains were seen in the NCM, VM or paralaminar VL regions, although light labeling was observed in the Pc.
Cerebellothalamic fibers from the dentate nucleus Isotope injection into the dentate nucleus (DN) was attempted in 8 cats. Although the injection involved more or less the D N in 6 cats, injected isotope extended into the interpositus nuclei in 3 of them (Cats 91, 92 and 94). In the remaining 2 cats (Cats 96 and 98) the injection sites were located in the white matter dorsal to the DN. The injection sites in 4 cats (Cats 3, 86, 96 and 97) are shown in Fig. le-h. In the cats injected with isotope into the dorsal-half of the D N (Cats 3 and 97) (Fig. lf-h), labeling of axon terminals of cerebellothalamic fibers was seen within the ventral (VA, VL and VM), intralaminar (CL), midline (NCM), CM, posterolateral (LP) and MD nuclei (Fig. 7). Patchy clusters of dense terminal grains were scattered in the VA and the rostral levels of the VL (Fig. 7a--c). In the VL, terminal grains were mainly distributed in the medial or paralaminar regions (Fig. 8). The density of terminal silver grains in the dersal portions of the VL was moderate. In the CL moderate labeling of axon terminals was observed in the caudal levels of the nucleus, especially in the caudodorsal CL regions adjacent to the lateral habenular nucleus (Fig. 7f), but few terminal grains were found in the caudolateral CL regions (arrow in Fig. 7f) and the rostral CL regions. In the CM many labeled fibers were observed to run through the nucleus, but only a few terminal silver grains were found. Terminal silver grains within the VM, NCM, LP and M D were rather sparse. On the side ipsilateral to the injection, light labeling of axon terminals was seen most frequently in the NCM and the medial VL regions close to the CL (Fig. 7e-e).
38 a
d C..d
b
e
/t t
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Fig. 7. Distribution of transported label in the thalamus after injecting isotope contralaterally (left side) into the dentate nucleus in Cat 3. In a cat (Cat 86) in which the isotope injection was made into the ventrolateral portions of the D N (Fig. le-g), distribution of terminal silver grains was almost confined to the dorsomedial VL regions and the adjacent VA regions (Fig. 12b). In this cat moderate labeling was noted in a narrow Pul region close to the lateral margin of the nucleus. Similar labeling was also noted in Cats 4 and 5 (Fig. 3f).
Cerebellothalamic fibers from the posterior interpositus nucleus In 2 cats (Cats 84 and 89) isotope injection was centered on the posterior interpositus nucleus (PIN) (Fig. 2a-d). In one of them (Cat 84), small caudomedial portions of the D N were also involved in the injection site. In Cat 89 (Fig. 2b-d), terminal silver grains were seen massively in the central portions of the VL at the
39
Fig. 8. Dark-field photomicrograph showing distribution of terminal silver grains in the paralaminar VL region after injecting isotope contralaterally into the dentate nucleus in Cat 3. x 50.
middle levels of the nucleus (Fig. 9b and c), and less densely in the rostromedial and caudolateral regions of the VL (Fig. 9a, d and e). A few clusters of terminal silver grains were seen in the VA, but no terminal grains were found in the VM. Terminal silver grains were also seen moderately in the Spf and ZI (Fig. 9d and e); in the ZI they were mainly distributed in its ventral and lateral portions. Light labeling of axon terminals was noted in the GLv, especially in its rostral portions (Fig. 9e). In the CM only a few terminal grains were observed, although labeling of many passing fibers was noted. On the side ipsilateral to the injection, very light labeling was found only in the restricted regions of the VL (Fig. 9c). In Cat 84 (Fig. 2a-c) the pattern of distribution of terminal silver grains was similar to that in Cat 89 described above. Terminal silver grains in the VA and VL, however, were more dense and located more dorsolateraUy than those in Cat 89 (Fig. 12c). Additionally, light labeling was found in the restricted Pul regions close to the lateral border of the nucleus. Labeling of axon terminals in the Pul and the dorsolateral-most regions of the VA and VL was considered to be due, at least partly, to the isotope injection into the ventromedial portions of the DN (Fig. 2).
Cerebellothalamic fibers frorn the anterior interpositus nucleus In 2 cats (Cats 93 and 99) isotope injection was centered on the anterior interpositus nucleus (AIN) (Fig. 2e-h). In Cat 93, in which the site of injection involved mainly the rostral two-thirds of the AIN and slightly the adjacent PIN regions (Fig. 2e-g), terminal silver grains were observed as patchy clusters in the VL, especially in the ventrolateral regions (Figs. 10 and 11). The areas of distribution of terminal grains in the ventrolateral regions of the caudal VL appeared to extend into the most dorsolateral regions of the VPL (Fig. 10d-f). A few, small clusters of terminal grains in the central and medial portions of the VL might be due to involvement of the PIN in the site of injection.
40 Cd
~ l!l~it ..~-" / \ v /
VLS"4/" / /,',, ~ / /
b.
d
it/
e
( ¢
Fig. 9. Distribution of transported label in the thalamus after injecting isotope contralaterally (left side) into the posterior interpositus nucleus in Cat 89.
In Cat 99 in which the isotope injection involved the caudal-half of the AIN and additionally the rostromedial portions of the PIN (Fig. 2g and h), labeling of axon terminals was seen in the ventrolateral regions of the VL as in Cat 93 described above (Fig. 12d). Terminal silver grains in the dorsolateral VL regions were much sparser than those in Cat 93. In these 2 cats (Cats 93 and 99) only a few terminal grains were found in the CM and its adjacent CL regions, while no labeling of axon terminals occurred in the ZI or GLv, or in the thalamic nuclei ipsilateral to the isotope injection.
0
0
~,,~
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~gr
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42
Fig. 11. Bright- and dark-field photomicrographs of a frontal section through the thalamus of Cat 93, showing distribution of terminal silver grains in a VL region close to the ventrolateral border of the VL after injecting isotope contralaterally into the anterior interpositus nucleus. The blood vessels pointed with arrows in a are also indicated with arrows in b. The level of the section corresponds to that of Fig. 10b. a: × 10, b: × 50. DISCUSSION Topographic arrangement of the sites of termination of cerebellothalamic fibers in the V A - V L complex of the cat has been reported by Angaut et al. on the basis of the data obtained from the degeneration 1-3 and the evoked potential4,11 methods. According to their results, the terminal sites of fibers from each cerebellar nucleus appeared to overlap one another considerably. The present study, which was performed by the autoradiographic anterograde tracing method, revealed similar but more clear-cut topographic arrangement in the cerebellothalamic fiber system as summarized in Fig. 13. In the V A - V L complex, the cerebellothalamic fibers arising from the DN, PIN and A I N respectively terminated dorsomedially, centrally and ventrolaterally. Topographic arrangement in the dorsoventral direction was further found in the DN- and PIN-recipient regions in the V A - V L complex; cerebellothalamic fibers arising from dorsal portions of the DN or P I N terminated more ventrally in the V A - V L complex
43 Q
a
cd
SM
C
'
d
CL
Fig. 12. Distribution of transported label at representative levels of the thalamus in 4 cats after injecting isotope contralaterally into the fastigial nucleus in Cat 90 (a), dentate nucleus in Cat 86 (b), posterior interpositus nucleus in Cat 84 (c) and anterior interpositus nucleus in Cat 99 (d).
than those arising from ventral portions of the D N or PIN. The DN-recipient V A - V L regions appeared to cover regions where neurons were found to send their axons to the areas 5 and 7 in the parietal cortex16, ~°. The vast majority o f the fastigiothalamic fibers were found to arise from the caudal levels of the FN, as described previously in the cata,9, 2° and monkey 5. In the V A - V L complex, the fastigial fibers terminated in 2 separate regions; in the ventrolateral regions between the ventral portions of the A I N and PIN-recipient areas in the V A - V L complex, and in the ventromedial VL regions where the dentatothalamic fibers were seen to terminate. Although the termination of the fastigiothalamic fibers in the VM of the cat was reported in the degeneration studies3,24, ~4, Rinvik and Grofov~i could find no fastigioVM fibers by the autoradiographie anterograde tracing method a2. The present study, however, clearly showed the termination of fastigial fibers in the VM. According to the
44 a
'c°°
\ J
Fig. 13. Summary diagram showing the topographic relationship of sites of termination of cerebellothalamic fibers from each of the cerebellar nuclei. The sites of termination of fibers from the fastigial, dentate, posterior interpositus and anterior interpositus nuclei are marked on a series of frontal sections of the thalamus with vertical lines, horizontal lines, open circles and solid circles, respectively. The sites of termination of the fastigial fibers overlap those of the dentate fibers in the most ventromedial VL regions (cross-hatched). The sections are arranged in rostrocaudal sequence.
horseradish peroxidase studies in the cat, neurons in the VM send fibers to the area 6aft or 6a0 of the cerebral cortex 31,~5. Therefore, the F N of the cat can be considered to project to these cortical areas through the VM. Since the VM of the cat was also reported to receive nigral fibersl0,1G, 2~, some interactions between fastigial and nigral inputs may occur in the VM. Cerebellar fibers to the intralaminar and midline nuclei were found to arise mainly from the F N and DN. The cerebellar fibers to the N C M occurred mainly from the F N and additionally from the DN. These fibers weie distributed bilaterally, in particular, in the ventral portions of the N C M , many of them crossed the midline at the thalamic levels. The fastigiothalamic fibers were also distributed bilaterally in the Pc, particularly in its ventral and lateral portions. The cerebellar fibers to the CL arose mainly from the DN, and were distributed mainly to the caudalmost regions of the CL, especially its dorsal portions close to the lateral habenular nucleus. These DNrecipient CL regions appeared to contain neurons sending their axons to the caudate nucleus 33. No cerebellothalamic fibers, however, were found to terminate in the lateral regions of the CL where the spinothalamic fibers were known to terminatel~,XT, 26,~9. Sparse but definite termination of cerebellar fibers was seen in the CM after injecting isotope into each of the cerebellar nuclei. The terminal silver grains, however, were often intermingled with many labeled fibers of passage. This may be one of the reasons why some of the previous reports could not obtain conclusive evidence for the existence of the cerebello-CM fibers in the cat 32 as well as in the monkeyS5,27, 28. Termination of cerebellar fibers in the VPL of the cat was described in the degeneration studiesg, 36. In the present study, after the isotope injection into the AIN, terminal silver grains were seen in the ventrolateral VL regions bordering on the VPL at the levels of the stereotaxic frontal plane A --9.5 to A --9.0 (regions indicated by arrows in Fig. 10e and f). These regions appeared to correspond to those where spinothalamic fibers and fibers from the nucleus z were reported to terminate6,V, 14,22. Although in these regions no sharp line of demarcation could be drawn between the VL and the VPL, at least some terminal grains appeared to be distributed within the
45 confines of the VPL. These regions of the VPL appear to be included in the representation zone of the hindlimb (for review, see ref. 37). Fibers arising from the PIN were found to terminate in the Spf, ZI and GLv. The termination of the PIN fibers in the Spf was previously reported by Rinvik and Grofov~ia2. Labeling in the GLv appeared to be an extension of that in the ZI. The present study also confirmed the existence of the cerebellopulvinar fibers terminating in a narrow area at the extreme dorsolateral edge of the Pul around the level of the stereotaxic frontal plane A --7.018,19. ACKNOWLEDGEMENT
The photographic work of Mr. Akira Uesugi is gratefully acknowledged. LIST OF ABBREVIATIONS AD, anterodorsal nucleus; AIN, anterior interpositus nucleus; AM, anteromedial nucleus; AV, anteroventral nucleus; Cd, caudate nucleus; CL, centrolateral nucleus; CM, centre median nucleus; CP, cerebral peduncle; De, nucleus of Deiters; DN, dentate nucleus; EP, entopeduncular nucleus; FN, fastigial nucleus; GLd, dorsal lateral geniculate nucleus; GLv, ventral lateral geniculate nucleus; Hbl, lateral habenular nucleus; Hbm, medial habenular nucleus; HI, habenulo-interpedunculartract; LD, laterodorsal nucleus; LP, posterolateral nucleus; MD, mediodorsal nucleus; Mt, mammillothalamic tract; NCM, centromedial nucleus; OT, optic tract; Pc, paracentral nucleus; Pf, parafascicular nucleus; PIN, posterior interpositus nucleus; Pul, pulvinar nucleus; R, thalamic reticular nucleus; SM, stria medullaris; Sm, submedius nucleus; Spf, subparafascicular nucleus; STN, subthalamic nucleus; VA, ventroanterior nucleus; VL, ventrolateral nucleus; VM, ventromedial nucleus; VPL, posterolateral ventral nucleus; VPM, posteromedial ventral nucleus; ZI, zona incerta. REFERENCES 1 Angaut, P., The cerebello-thalamic projections in the cat. In J. Massion and K. Sasaki (Eds.), Cerebro-Cerebellar Interactions, Elsevier, Amsterdam, 1979, pp. 19-43. 2 Angaut, P., The ascending projections of the nucleus interpositus posterior of the cat cerebellum: an experimental anatomical study using silver impregnation methods, Brain Research, 24 (1970) 377-394. 3 Angaut, P. and Bowsher, D., Ascending projections of the medial cerebellar (fastigial) nucleus: An experimental study in the cat, Brain Research, 24 (1970) 49-68. 4 Angaut, P., Guilbaud, G. and Reymond, M. C., An electrophysiological study of the cerebellar projections to the nucleus ventralis lateralis of thalamus in the cat. I. Nuclei fastigii et interpositus, J. comp. NeuroL, 134 (1968) 9-20. 5 Barton, R. R. III, Jayaraman, A., Ruggiero, D. and Carpenter, M. B., Fastigial efferent projections in the monkey: an autoradiographic study, J. comp. Neurol., 174 (1977) 281-306. 6 Boivie, J., The termination of the spinothalamic tract in the cat. An experimental study with silver impregnation methods, Exp. Brain Res., 12 (1971) 331-353. 7 Boivie, J., An anatomical reinvestigation of the termination of the spinothalamic tract in the monkey, J. comp. NeuroL, 186 (1979) 343-370. 8 Chan-Palay, V., Cerebellar Dentate Nucleus. Organization, Cytology and Transmitters, SpringerVerlag, New York, 1977, 548 pp. 9 Cohen, D., Chambers, W. W. and Sprague, J. M., Experimental study of the efferent projections from the cerebellar nuclei to the brainstem of the cat, J. comp. NeuroL, 109 (1958) 233-259. 10 Cole, M., Nauta, W. J. H. and Mehler, W. R., The ascending efferent projections of the substantin nigra, Trans. Amer. NeuroL Ass., 89 (1964) 74-78. 11 Cond6, H. and Angaut, P., An electrophysiological study of the cerebellar projections to the nucleus ventralis lateralis thalami in the cat. II. Nucleus lateralis, Brain Research, 20 (1970) 107-119.
46 12 Cowan, W. M. and Cu6nod, M. (Eds.), The Use of Axonal Transportfor Studies of Neuronal Connectivity, Elsevier, Amsterdam, 1975, 365 pp. 13 Cowan, W. M., Gottlieb, D. I., Hendrickson, A. E., Price, J. L. and Woolsey, T. A., The autoradiographic demonstration of axonal connections in the central nervous system, Brain Research, 37 (1972) 21-51. 14 Grant, G., Boivie, J. and Silfvenius, H., Course and termination of fibres from the nucleus z of the medulla oblongata. An experimental light microscopical study in the cat, Brain Reserach, 55 (1973) 55-70. 15 Harding, B. N., An ultrastructural study of the termination of afferent fibres within the ventrolateral and centre median nuclei of the monkey thalamus, Brain Research, 54 (1973) 341-346. 16 Hendry, S. H. C., Jones, E. G. and Graham, J., Thalamic relay nuclei for cerebellar and certain related fiber systems in the cat, J. comp. Neurol., 185 (1979) 679-714. 17 Itoh, K. and Mizuno, N., Topographic arrangement of thalamocortical neurons in the centrolateral nucleus (CL) of the cat, with special reference to a spino-thalamo-motor cortical path through the CL, Exp. Brain Res., 30 (1977) 471-480. 18 ltoh, K. and Mizuno, N., A cerebello-pulvinar projection in the cat as visualized by the use of anterograde transport of horseradish peroxidase, Brain Research, 171 (1979) 131-134. 19 Itoh, K., Mizuno, N., Sugimoto, T., Nomura, S., Nakamura, Y. and Konishi, A., A cerebellopulvino-cortical and a retino-pulvino-cortical pathways in the cat as revealed by the use of the anterograde and retrograde transport of horseradish peroxidase, J. comp. NeuroL, 187 (1979) 349-358. 20 Jansen, J. and Jansen, J., Jr., On the efferent fibers of the cerebellar nuclei in the cat, J. comp. Neurol., 102 (1955) 607-632. 21 Jasper, H. H. and Ajmone-Marsan, C., A Stereotaxic Atlas of the Diencephalon of the Cat, National Research Council of Canada, Ottawa, 1954. 22 Jones, E. G. and Burton, H., Cytoarchitecture and somatic sensory connectivity of thalamic nuclei other than the ventrobasal complex in the cat, J. comp. NeuroL, 154 (1974) 395-432. 23 Jones, E. G. and Hartman, B. K., Recent advances in neuroanatomical methodology, Ann. Rev. Neurosci., 1 (1978) 215-296. 24 Kievit, J. and Kuypers, H. G. J. M., Fastigial cerebellar projections to the ventrolateral nucleus of the thalamus and the organization of the descending pathways. In T. Frigyesi, E. Rinvik and M. D. Yahr (Eds.), Corticothalamic Projections and Sensorimotor Activities, Raven Press, New York, 1972, pp. 91-114. 25 Kultas-Ilinsky, K., Ilinsky, I. A., Massopust, L. C., Young, P. A. and Smith, K. R., Nigrothalamic pathway in the eat demonstrated by autoradiography and electron microscopy, Exp. Brain Res., 33 (1978) 481-492. 26 Mehler, W. R., Some neurological species differences - - a posteriori, Ann. N. Y. Acad. Sci., 167 (1969) 424-468. 27 Mehler, W. R., Idea of a new anatomy of the thalamus, J. psychiat. Res., 8 (1971) 203-217. 28 Miller, R. A. and Strominger, N. L., An experimental study of the efferent connections of the superior cerebellar peduncle in the rhesus monkey, Brain Research, 133 (1977) 237-250. 29 Mizuno, N., Konishi, A., Itoh, K. and Nomura, S., An electron microscopic study of spinothalamic fibers which end at the centrolateral nucleus neurons sending their axons to the motor cortex in the cat and monkey: The use of horseradish peroxidase as a neuronal marker for electron microscopy. In M. Ito et al. (Eds.), Integrative Control Functions of the Brain, Vol. 1, Kodansha, Tokyo/Elsevier, Amsterdam, 1978, pp. 106--108. 30 Mizuno, N., Konishi, A., Sato, M., Kawaguchi, S., Yamamoto, T., Kawamura, S. and Yamawaki, M., Thalamic afferents to the rostral portions of the middle suprasylvian gyrus in the cat, Exp. Neurol., 48 (1975) 79-87. 31 Nakano, K., Takimoto, T., Kayahara, T., Matsuba, H. and Takeuchi, Y., Horseradish peroxidase labeling of thalamic neurons projecting to the area 6a6 and adjacent areas in the cat cerebral cortex, Mie reed. J., 27 (1978) 119-135. 32 Rinvik, E. and Grofov~i, I., Cerebellar projections to the nuclei ventralis lateralis and ventralis anterior thalami. Experimental electron microscopical and light microscopical studies in the cat, Anat. EmbryoL, 146 (1974) 95-111. 33 Sato, M., ltoh, K. and Mizuno, N., Distribution of thalamo-caudate neurons in the cat as demonstrated by horseradish peroxidase, Exp. Brain Res., 34 (1979) 143-153. 34 Thomas, D. M., Kaufman, R. P., Sprague, J. M. and Chambers, W. W., Experimental studies of
47 the vermal cerebellar projections in the brain stem of the cat (Fastigiobulbar tract), J. Anat. (Lond.), 90 (1956) 371-385. 35 Vedovato, M., Identification of afferent connections to cortical area 6aft of the cat by means of retrograde horseradish peroxidase transport, Neurosci. Lett., 9 (1978) 303-310. 36 Voogd, J., The Cerebellum o f the Cat. Structure and Fibre Connexions, Van Gorcum, Assen, 1964, 215 pp. 37 Welker, W. I., Principles of organization of the ventrobasal complex in mammals, Brain Behav. Evol., 7 (1973) 253-336.
29
AN AUTORADIOGRAPHIC STUDY ON THE TERMINAL DISTRIBUTION OF C E R E B E L L O T H A L A M I C FIBERS I N T H E CAT
TETSUO SUGIMOTO, NOBORU MIZUNO and KAZUO ITOH Department of Anatomy (lst Division), Faculty of Medicine, Kyoto University, Kyoto 606 (Japan)
(Accepted November 13th, 1980) Key words,: cerebellothalamic fibers - - thalamus - - cerebellar nuclei - - autoradiography - - cat
SUMMARY Distribution of cerebellothalamic fibers was studied in the cat by the anterograde tracing method. The vast majority of cerebellothalamic fibers were distributed contralaterally. The fastigial fibers arose mostly from the caudal half of the nucleus. These ended moderately in the VM* and the most ventromedial regions of the V A - V L complex, and sparsely in the ventral portions of the CL, Pc and N C M ; a few also ended in the CM and ZI. The dentate fibers ended moderately in the medial and rostrodorsal V A - V L regions, and sparsely in the VM, CL, N C M , CM, LP and MD. The existence of the dentatopulvinar fibers was also confirmed. The posterior interpositus fibers ended heavily in the central V A - V L regions, moderately in the subparafascicular nucleus and ZI, and sparsely in the CM and the ventral lateral geniculate nucleus. The anterior interpositus fibers ended mainly in the ventrolateral V A - ¥ L regions, and additionally in the CL and CM. The ipsilateral cerebellothalamic fibers arose mainly from the fastigial nucleus, and additionally from the dentate nucleus; those arising from the interpositus nuclei were very sparse.
INTRODUCTION Direct projections from the cerebellum to the thalamus have often been the subject of studies by the anterograde degeneration methods in several mammals (for reviews, see refs. 1, 8 and 36). The general pattern of direct projections of the cerebellothalamic fibers appears to be well documented by these previous studies, but less is known about the precise topography of termination of the cerebellothalamic * For an explanation of the abbreviations, see list at the end of article.
30 fibers from each cerebellar nucleus. A n g a u t and his associates examined intensively the distribution of the cerebellothalamic fibers from each cerebellar nucleus in the cat, using the anterograde axonal degeneration method 1-3 as well as the evoked potential method4,11. It is known, however, that the degeneration methods do not always provide the most satisfactory means of studying projections from the structures which are adjacent to, or traversed by, many fibers, and that it is occasionally difficult to distinguish with certainty the degenerated fibers of passage from the so-called terminal degeneration. The interpretation o f data from the evoked potential method is also difficult because of uncertainty about the extent of current spread. The present study was performed in an attempt to shed more light on the topography of distribution o f the cerebellothalamic fibers from each cerebellar nucleus in the cat, using the autoradiographic tracing technique in which the contribution of fibers of passage at the injection site to labeling the axon terminals is k n o w n to be neglectedlZ,23. MATERIALS AND METHODS In 18 cats (body weight 2100-4700 g) anesthetized with intraperitoneal sodium pentobarbital (35 mg/kg), a single injection of 0.07-1.2/A (50-100 #Ci/#l) of equal parts of L-[3H]leucine and L-[aH]proline (New England Nuclear) was made stereotaxically with a H a m i l t o n microsyringe into either the fastigial, dentate, anterior interpositus or posterior interpositus nucleus (Table 1). Additionally, in 2 cats (Cats 4 and TABLE I Cat no.
1
3 4 5 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99
Site of injection
FN DN CBN CBN PIN FN DN X FN PIN FN DN DN AIN DN FN X DN X AIN
Amount of injected isotope (t~Ci)
30 12 60 120 30 30 18 18 30 28 40 12 40 30 40 18 20 7 20 25
CBN, all cerebellar nuclei; X, white matter.
Survival period (days)
13 l0 11 I0 10 7 8 8 23 8 7 7 10 10 20 13 8 10 8 7
31 5), all of the cerebellar nuclei were injected unilaterally at 8 points with a total of 0.6-1.2/zl (100 #Ci/#l) of the same isotope mixture. After survival periods of 7-23 days, the cats were deeply anesthetized and perfused through the ascending aorta with 2 liters of 10~ buffered formalin. The brains were removed and stored in 10~ buffered formalin. After saturation with a solution of 30 ~ sucrose in 10~ buffered formalin, serial frontal sections of 35 ,um thickness were made on a freezing microtome and mounted onto gelatinized slides. These sections were processed for autoradiography according to the standard method 13, using 40 ~ Kodak NTB-3 or Sakura NRM2 emulsion. After exposure periods of 4-8 weeks, the slides were developed with Kodak D-19 and stained with cresyl violet or neutral red. The locations of the injection sites and the radioactive labeling were charted onto enlarged outline drawings of selected sections. The thalamic nomenclature and boundaries were mostly based on the atlas of Jasper and Ajmone-Marsan 21. Establishment of fields of fiber termination was not solely on the presence of grain densities exceeding background; silver deposits on identifiable fiber systems were regarded as labeling of transit-fibers, and randomly arranged small grains were considered as terminal grains, i.e. products resulting from labeling of axon terminals. RESULTS In 2 cats injected with isotope unilaterally into all cerebellar nuclei (Cats 4 and 5), silver grains were massively distributed within the ventral, intralaminar and midline nuclei of the thalamus contralateral to the injection. Although many silver grains were seen throughout the rostrocaudal extent of the ventroanterior (VA), ventrolateral (VL) and ventromedial (VM) nuclei, terminal grains were less dense in the lateralmost regions of the VL at the levels immediately rostral to the rostral end of the posterolateral ventral nucleus (VPL) (arrow in Fig. 3b) and in the dorsal portions of the caudalmost levels of the VL (arrow in Fig. 3e). Terminal silver grains in the VM were mainly distributed in the lateral portions of the nucleus. Many terminal grains were seen in the paracentral (Pc), centrolateral (CL) and centromedial (NCM) nuclei. Terminal grains in the CL, however, were distributed only to the caudal two-thirds of the nucleus. In the caudalmost levels of the CL terminal grains were seen throughout the nucleus (Fig. 3f), and in the middle levels of the CL they were observed mainly in the regions close to the lateral margin of the CL (Fig. 3d and e). In the NCM, few terminal grains were found in the iostral one-third of the nucleus (Fig. 3b). Possible labeling of axon terminals was also observed in the centre median-parafascicular complex (CM-Pf), subparafascicular nucleus (Spf), pulvinar nucleus (Pul), and zona incerta (ZI) (Fig. 3d-f). In the CM, Spf and ZI, terminal grains were rather sparse and a moderate number of labeled fibers were seen, indicating the presence of considerable number of passing fibers (Fig. 3f). Only a few terminal grains were found in the Pf. In the Pul, terminal grains were located in a narrow region close to the lateral margin of the nucleus (Fig. 3f). Possible light labeling of axon terminals was seen in the ventral lateral geniculate nucleus (GLv), mediodorsal nucleus (MD) and thalamic reticular nucleus (R). No conclusive evidence, however, was obtained showing
32
~e
~~
I
.....
b~'~"
,7
0
c.~'~__~ ~
f A
Fig. 1. The sites of isotope injection (stippled areas) into the fastigial (a-d) and the dentate (e-h) nuclei in 5 representative cats (Cats 1, 90, 3, 86, 97). In 2 additional cats (Cats 87, 96) the injection sites are located in the white matter. Two series of projection drawings of sections (a-d and e-h) are arranged in rostrocaudat sequence.
33
Fig. 2. The sites of isotope injection (stippled areas) into the posterior interpositus (a-d) and the anterior interpositus (e-h) nuclei in 4 representative cats (Cats 84, 89, 93, 99). Two series of projection drawings of sections (a-d and e-h) are arranged in rostrocaudal sequence.
o
T-,'_.. o
8"
~o
e-~
~--'lm
\
35 termination of cerebellar fibers in the anterior thalamic nuclei, dorsal lateral geniculate nucleus (GLd), laterodorsal nucleus (LD), submedius nucleus (Sm), posteromedial ventral nucleus (VPM) and the posteriol group of the thalamus. On the side ipsilateral to the isotope injection in the cerebellar nuclei, light labeling of axon terminals could be seen in the homologous regions of the thalamus.
Cerebellothalamic fibers from the fastigial nucleus In 6 cats injection of isotope into the fastigial nucleus (FN) was attempted unilaterally (Cats 1, 85, 87, 88, 90 and 95). The sites of injection in 3 of them (Cat 1, 87 and 90) are shown in Fig. l a d . In Cat 87 in which the isotope was injected into the a
0 b
e
LD
0 Fig. 4. Distribution of transported label in the thalamus after injecting isotope contralaterally (left side) into the fastigial nucleus in Cat 1.
36
Fig. 5. Distribution of the fastigiothalamic fibers in a VL region of Cat 1. a : low-power photomicrograph of a frontal section through the thalamus of Cat 1 at a level corresponding to that of Fig. 4a. ~ 10. b: dark-field photomicrograph of the VL region encircled with a rectangle in a, showing terminal grains seen after injecting isotope contralaterally into the fastigial nucleus. ",; 60. white matter dorsolateral to the F N (Fig. I b, c), no labeling of axon terminals was found in any thalamic nuclei. In Cat 1 and 88 the isotope injection covered nearly the whole extent o f the F N (Fig. la-d). Distribution of terminal silver grains in Cat 1 was shown in Fig. 4. A moderate number of terminal silver grains were distributed as patchy clusters in the ventrolateral portions of the VL (Fig. 5). Some clusters of terminal grains were also seen in the paralaminar or ventromedial regions of the VL. In the caudalmost levels of the VL, distribution of terminal grains was almost confined in the dorsolateral portions of the nucleus close to the VPL (arrow in Fig. 4e). In the VM, terminal grains were seen nearly the whole extent of the nucleus. The density of grains was heaviest in the dorsolateral VM portions, which were contiguous to the ventromedial VL regions distributed with terminal silver grains (Fig. 6). Light labeling of axon terminals was observed in the ventral portions o f the CL, Pc and N C M , and only a few terminal silver grains were found in the C M and ZI. Labeling in the VL, VM, CL, Pc and N C M ipsilateral to the injection was very light. The areas of distribution of terminal silver grains within these nuclei were much smaller than those within the contralateral counterparts. W h e n the isotope injection was centered on the rostral-half of the F N (Cats 90 and 95) (Fig. la-c), distribution of terminal silver grains in the VL was almost
37
Fig. 6. Dark-field photomicrograph showing distribution of terminal silver grains in the VM and VL regions after injecting isotope contralaterally into the fastigial nucleus in Cat 1. x 50. confined to its ventral regions close to the medial VPL regions (Fig. 12a). In these cats no terminal silver grains were seen in the NCM, VM or paralaminar VL regions, although light labeling was observed in the Pc.
Cerebellothalamic fibers from the dentate nucleus Isotope injection into the dentate nucleus (DN) was attempted in 8 cats. Although the injection involved more or less the D N in 6 cats, injected isotope extended into the interpositus nuclei in 3 of them (Cats 91, 92 and 94). In the remaining 2 cats (Cats 96 and 98) the injection sites were located in the white matter dorsal to the DN. The injection sites in 4 cats (Cats 3, 86, 96 and 97) are shown in Fig. le-h. In the cats injected with isotope into the dorsal-half of the D N (Cats 3 and 97) (Fig. lf-h), labeling of axon terminals of cerebellothalamic fibers was seen within the ventral (VA, VL and VM), intralaminar (CL), midline (NCM), CM, posterolateral (LP) and MD nuclei (Fig. 7). Patchy clusters of dense terminal grains were scattered in the VA and the rostral levels of the VL (Fig. 7a--c). In the VL, terminal grains were mainly distributed in the medial or paralaminar regions (Fig. 8). The density of terminal silver grains in the dersal portions of the VL was moderate. In the CL moderate labeling of axon terminals was observed in the caudal levels of the nucleus, especially in the caudodorsal CL regions adjacent to the lateral habenular nucleus (Fig. 7f), but few terminal grains were found in the caudolateral CL regions (arrow in Fig. 7f) and the rostral CL regions. In the CM many labeled fibers were observed to run through the nucleus, but only a few terminal silver grains were found. Terminal silver grains within the VM, NCM, LP and M D were rather sparse. On the side ipsilateral to the injection, light labeling of axon terminals was seen most frequently in the NCM and the medial VL regions close to the CL (Fig. 7e-e).
38 a
d C..d
b
e
/t t
.~,
Fig. 7. Distribution of transported label in the thalamus after injecting isotope contralaterally (left side) into the dentate nucleus in Cat 3. In a cat (Cat 86) in which the isotope injection was made into the ventrolateral portions of the D N (Fig. le-g), distribution of terminal silver grains was almost confined to the dorsomedial VL regions and the adjacent VA regions (Fig. 12b). In this cat moderate labeling was noted in a narrow Pul region close to the lateral margin of the nucleus. Similar labeling was also noted in Cats 4 and 5 (Fig. 3f).
Cerebellothalamic fibers from the posterior interpositus nucleus In 2 cats (Cats 84 and 89) isotope injection was centered on the posterior interpositus nucleus (PIN) (Fig. 2a-d). In one of them (Cat 84), small caudomedial portions of the D N were also involved in the injection site. In Cat 89 (Fig. 2b-d), terminal silver grains were seen massively in the central portions of the VL at the
39
Fig. 8. Dark-field photomicrograph showing distribution of terminal silver grains in the paralaminar VL region after injecting isotope contralaterally into the dentate nucleus in Cat 3. x 50.
middle levels of the nucleus (Fig. 9b and c), and less densely in the rostromedial and caudolateral regions of the VL (Fig. 9a, d and e). A few clusters of terminal silver grains were seen in the VA, but no terminal grains were found in the VM. Terminal silver grains were also seen moderately in the Spf and ZI (Fig. 9d and e); in the ZI they were mainly distributed in its ventral and lateral portions. Light labeling of axon terminals was noted in the GLv, especially in its rostral portions (Fig. 9e). In the CM only a few terminal grains were observed, although labeling of many passing fibers was noted. On the side ipsilateral to the injection, very light labeling was found only in the restricted regions of the VL (Fig. 9c). In Cat 84 (Fig. 2a-c) the pattern of distribution of terminal silver grains was similar to that in Cat 89 described above. Terminal silver grains in the VA and VL, however, were more dense and located more dorsolateraUy than those in Cat 89 (Fig. 12c). Additionally, light labeling was found in the restricted Pul regions close to the lateral border of the nucleus. Labeling of axon terminals in the Pul and the dorsolateral-most regions of the VA and VL was considered to be due, at least partly, to the isotope injection into the ventromedial portions of the DN (Fig. 2).
Cerebellothalamic fibers frorn the anterior interpositus nucleus In 2 cats (Cats 93 and 99) isotope injection was centered on the anterior interpositus nucleus (AIN) (Fig. 2e-h). In Cat 93, in which the site of injection involved mainly the rostral two-thirds of the AIN and slightly the adjacent PIN regions (Fig. 2e-g), terminal silver grains were observed as patchy clusters in the VL, especially in the ventrolateral regions (Figs. 10 and 11). The areas of distribution of terminal grains in the ventrolateral regions of the caudal VL appeared to extend into the most dorsolateral regions of the VPL (Fig. 10d-f). A few, small clusters of terminal grains in the central and medial portions of the VL might be due to involvement of the PIN in the site of injection.
40 Cd
~ l!l~it ..~-" / \ v /
VLS"4/" / /,',, ~ / /
b.
d
it/
e
( ¢
Fig. 9. Distribution of transported label in the thalamus after injecting isotope contralaterally (left side) into the posterior interpositus nucleus in Cat 89.
In Cat 99 in which the isotope injection involved the caudal-half of the AIN and additionally the rostromedial portions of the PIN (Fig. 2g and h), labeling of axon terminals was seen in the ventrolateral regions of the VL as in Cat 93 described above (Fig. 12d). Terminal silver grains in the dorsolateral VL regions were much sparser than those in Cat 93. In these 2 cats (Cats 93 and 99) only a few terminal grains were found in the CM and its adjacent CL regions, while no labeling of axon terminals occurred in the ZI or GLv, or in the thalamic nuclei ipsilateral to the isotope injection.
0
0
~,,~
t~
~-~ ~ °
~,1~ ~
~gr
g~'o
~
42
Fig. 11. Bright- and dark-field photomicrographs of a frontal section through the thalamus of Cat 93, showing distribution of terminal silver grains in a VL region close to the ventrolateral border of the VL after injecting isotope contralaterally into the anterior interpositus nucleus. The blood vessels pointed with arrows in a are also indicated with arrows in b. The level of the section corresponds to that of Fig. 10b. a: × 10, b: × 50. DISCUSSION Topographic arrangement of the sites of termination of cerebellothalamic fibers in the V A - V L complex of the cat has been reported by Angaut et al. on the basis of the data obtained from the degeneration 1-3 and the evoked potential4,11 methods. According to their results, the terminal sites of fibers from each cerebellar nucleus appeared to overlap one another considerably. The present study, which was performed by the autoradiographic anterograde tracing method, revealed similar but more clear-cut topographic arrangement in the cerebellothalamic fiber system as summarized in Fig. 13. In the V A - V L complex, the cerebellothalamic fibers arising from the DN, PIN and A I N respectively terminated dorsomedially, centrally and ventrolaterally. Topographic arrangement in the dorsoventral direction was further found in the DN- and PIN-recipient regions in the V A - V L complex; cerebellothalamic fibers arising from dorsal portions of the DN or P I N terminated more ventrally in the V A - V L complex
43 Q
a
cd
SM
C
'
d
CL
Fig. 12. Distribution of transported label at representative levels of the thalamus in 4 cats after injecting isotope contralaterally into the fastigial nucleus in Cat 90 (a), dentate nucleus in Cat 86 (b), posterior interpositus nucleus in Cat 84 (c) and anterior interpositus nucleus in Cat 99 (d).
than those arising from ventral portions of the D N or PIN. The DN-recipient V A - V L regions appeared to cover regions where neurons were found to send their axons to the areas 5 and 7 in the parietal cortex16, ~°. The vast majority o f the fastigiothalamic fibers were found to arise from the caudal levels of the FN, as described previously in the cata,9, 2° and monkey 5. In the V A - V L complex, the fastigial fibers terminated in 2 separate regions; in the ventrolateral regions between the ventral portions of the A I N and PIN-recipient areas in the V A - V L complex, and in the ventromedial VL regions where the dentatothalamic fibers were seen to terminate. Although the termination of the fastigiothalamic fibers in the VM of the cat was reported in the degeneration studies3,24, ~4, Rinvik and Grofov~i could find no fastigioVM fibers by the autoradiographie anterograde tracing method a2. The present study, however, clearly showed the termination of fastigial fibers in the VM. According to the
44 a
'c°°
\ J
Fig. 13. Summary diagram showing the topographic relationship of sites of termination of cerebellothalamic fibers from each of the cerebellar nuclei. The sites of termination of fibers from the fastigial, dentate, posterior interpositus and anterior interpositus nuclei are marked on a series of frontal sections of the thalamus with vertical lines, horizontal lines, open circles and solid circles, respectively. The sites of termination of the fastigial fibers overlap those of the dentate fibers in the most ventromedial VL regions (cross-hatched). The sections are arranged in rostrocaudal sequence.
horseradish peroxidase studies in the cat, neurons in the VM send fibers to the area 6aft or 6a0 of the cerebral cortex 31,~5. Therefore, the F N of the cat can be considered to project to these cortical areas through the VM. Since the VM of the cat was also reported to receive nigral fibersl0,1G, 2~, some interactions between fastigial and nigral inputs may occur in the VM. Cerebellar fibers to the intralaminar and midline nuclei were found to arise mainly from the F N and DN. The cerebellar fibers to the N C M occurred mainly from the F N and additionally from the DN. These fibers weie distributed bilaterally, in particular, in the ventral portions of the N C M , many of them crossed the midline at the thalamic levels. The fastigiothalamic fibers were also distributed bilaterally in the Pc, particularly in its ventral and lateral portions. The cerebellar fibers to the CL arose mainly from the DN, and were distributed mainly to the caudalmost regions of the CL, especially its dorsal portions close to the lateral habenular nucleus. These DNrecipient CL regions appeared to contain neurons sending their axons to the caudate nucleus 33. No cerebellothalamic fibers, however, were found to terminate in the lateral regions of the CL where the spinothalamic fibers were known to terminatel~,XT, 26,~9. Sparse but definite termination of cerebellar fibers was seen in the CM after injecting isotope into each of the cerebellar nuclei. The terminal silver grains, however, were often intermingled with many labeled fibers of passage. This may be one of the reasons why some of the previous reports could not obtain conclusive evidence for the existence of the cerebello-CM fibers in the cat 32 as well as in the monkeyS5,27, 28. Termination of cerebellar fibers in the VPL of the cat was described in the degeneration studiesg, 36. In the present study, after the isotope injection into the AIN, terminal silver grains were seen in the ventrolateral VL regions bordering on the VPL at the levels of the stereotaxic frontal plane A --9.5 to A --9.0 (regions indicated by arrows in Fig. 10e and f). These regions appeared to correspond to those where spinothalamic fibers and fibers from the nucleus z were reported to terminate6,V, 14,22. Although in these regions no sharp line of demarcation could be drawn between the VL and the VPL, at least some terminal grains appeared to be distributed within the
45 confines of the VPL. These regions of the VPL appear to be included in the representation zone of the hindlimb (for review, see ref. 37). Fibers arising from the PIN were found to terminate in the Spf, ZI and GLv. The termination of the PIN fibers in the Spf was previously reported by Rinvik and Grofov~ia2. Labeling in the GLv appeared to be an extension of that in the ZI. The present study also confirmed the existence of the cerebellopulvinar fibers terminating in a narrow area at the extreme dorsolateral edge of the Pul around the level of the stereotaxic frontal plane A --7.018,19. ACKNOWLEDGEMENT
The photographic work of Mr. Akira Uesugi is gratefully acknowledged. LIST OF ABBREVIATIONS AD, anterodorsal nucleus; AIN, anterior interpositus nucleus; AM, anteromedial nucleus; AV, anteroventral nucleus; Cd, caudate nucleus; CL, centrolateral nucleus; CM, centre median nucleus; CP, cerebral peduncle; De, nucleus of Deiters; DN, dentate nucleus; EP, entopeduncular nucleus; FN, fastigial nucleus; GLd, dorsal lateral geniculate nucleus; GLv, ventral lateral geniculate nucleus; Hbl, lateral habenular nucleus; Hbm, medial habenular nucleus; HI, habenulo-interpedunculartract; LD, laterodorsal nucleus; LP, posterolateral nucleus; MD, mediodorsal nucleus; Mt, mammillothalamic tract; NCM, centromedial nucleus; OT, optic tract; Pc, paracentral nucleus; Pf, parafascicular nucleus; PIN, posterior interpositus nucleus; Pul, pulvinar nucleus; R, thalamic reticular nucleus; SM, stria medullaris; Sm, submedius nucleus; Spf, subparafascicular nucleus; STN, subthalamic nucleus; VA, ventroanterior nucleus; VL, ventrolateral nucleus; VM, ventromedial nucleus; VPL, posterolateral ventral nucleus; VPM, posteromedial ventral nucleus; ZI, zona incerta. REFERENCES 1 Angaut, P., The cerebello-thalamic projections in the cat. In J. Massion and K. Sasaki (Eds.), Cerebro-Cerebellar Interactions, Elsevier, Amsterdam, 1979, pp. 19-43. 2 Angaut, P., The ascending projections of the nucleus interpositus posterior of the cat cerebellum: an experimental anatomical study using silver impregnation methods, Brain Research, 24 (1970) 377-394. 3 Angaut, P. and Bowsher, D., Ascending projections of the medial cerebellar (fastigial) nucleus: An experimental study in the cat, Brain Research, 24 (1970) 49-68. 4 Angaut, P., Guilbaud, G. and Reymond, M. C., An electrophysiological study of the cerebellar projections to the nucleus ventralis lateralis of thalamus in the cat. I. Nuclei fastigii et interpositus, J. comp. NeuroL, 134 (1968) 9-20. 5 Barton, R. R. III, Jayaraman, A., Ruggiero, D. and Carpenter, M. B., Fastigial efferent projections in the monkey: an autoradiographic study, J. comp. Neurol., 174 (1977) 281-306. 6 Boivie, J., The termination of the spinothalamic tract in the cat. An experimental study with silver impregnation methods, Exp. Brain Res., 12 (1971) 331-353. 7 Boivie, J., An anatomical reinvestigation of the termination of the spinothalamic tract in the monkey, J. comp. NeuroL, 186 (1979) 343-370. 8 Chan-Palay, V., Cerebellar Dentate Nucleus. Organization, Cytology and Transmitters, SpringerVerlag, New York, 1977, 548 pp. 9 Cohen, D., Chambers, W. W. and Sprague, J. M., Experimental study of the efferent projections from the cerebellar nuclei to the brainstem of the cat, J. comp. NeuroL, 109 (1958) 233-259. 10 Cole, M., Nauta, W. J. H. and Mehler, W. R., The ascending efferent projections of the substantin nigra, Trans. Amer. NeuroL Ass., 89 (1964) 74-78. 11 Cond6, H. and Angaut, P., An electrophysiological study of the cerebellar projections to the nucleus ventralis lateralis thalami in the cat. II. Nucleus lateralis, Brain Research, 20 (1970) 107-119.
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