Bra#1 Research, 90 (1975) 313-318 :~ Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
313
Demonstration of nigrothalamic connections in the cat by retrograde axonal transport of horseradish peroxidase
ERIC R1NVIK Anatontical Institute, University of Oslo, Oslo 1 (Norway)
(Accepted March 4th, 1975)
Ever since the substantia nigra was involved in discussions concerning the pathology of Parkinson's disease, attempts have been made with a variety of methods to clarify its afferent and efferent fiber connections (for a recent review of the literature, see ref. 19). Of major significance in the last decade's research on these problems has been the discovery by Fuxe and collaborators that there is a continuous transport of dopamine from cells in the substantia nigra to axon terminals in the putamen and caudate nucleus2,3, ,~. It is known that the substantia nigra can be divided into a cell-rich pars compacta and a cell-poor pars reticulatall,17,19. The pars reticulata lies ventrally to the cell-rich pars compacta, and is particularly well developed laterallyn,lL Using fluorescing histochemical techniques, it was established early that the bulk of nigral dopamine is localized to the soma of the cells in the pars compacta. Only few fluorescing - - and presumed dopaminergic - - cells are seen in the pars reticulata 2& Furthermore, the dopamine level in the striatum is not reduced when the pars reticulata, and particularly its lateral portion, is destroyedL On the other hand, there are ample reports in the literature that degenerating fibers can be followed to parts of the thalamic nuclei following nigral lesionsl,6-s, l°. Some of these authors are actually of the opinion that this represents the main nigrofugal projection. However, selective electrolytic lesions of the substantia nigra are very difficult to obtain, and attempts to produce retrograde cell changes or cell loss in this nucleus, as a consequence of lesions of the thalamus, have not revealed detectable cellular alterations 4,16. Therefore, the question still prevails whether the anterograde degeneration studies with silver impregnation techniques demonstrate a genuine nigrothalamic pathway, or whether the degenerating fibers observed belong to other, accidentally lesioned, pathways. Furthermore, if there is a nigrothalamic pathway, from which part of the nucleus does it originate ? In order to elucidate this problem, investigations were undertaken using the recently introduced technique of retrograde axonal transport of horseradish peroxidase (HRp)14,1L Multiple (one animal) and single (7 animals) injections of H R P (Sigma Type Vl) were successfully confined within the boundaries of the thalamus.
4~
315 The concentration o f the H R P varied between 250 and 500 #g/f4, and a m o u n t s of 0.06-0.3 #1 were stereotaxically injected over a period of 20-30 rain by means of a 1 #1 H a m i l t o n syringe held in a holder m o u n t e d on a microelectrode carrier. In all experiments the tip of the injection cannula was aimed at the nucleus ventralis lateralis (VL) or at the nucleus ventralis medialis (VM) of the thalamus. The animals survived for 24-72 h and were perfused by a mixture of 0.4~o formaldehyde and 1.25 ~ glutaraldehyde in a 0.1 M phosphate buffer solution ~a. The brains were immediately dissected free and postfixed in the same fixative for 24 h before being transferred to a phosphate buffered solution containing 30 ~ sucrose for another 24 h. The brains were cut on a freezing microtome and the 50 # m thick frontal sections were transferred to a solution containing 0.05 ~/o 3,3'-diaminobenzidine tetrahydrocloride in T r i s - H C l buffer (pH 7.6) for 5 rain at r o o m temperature. They were then incubated for a further 15 rain at r o o m temperature in a similar solution but with the addition of 66 #1 of 3 0 ~ hydrogen peroxide/100 ml. Two complete series from each case were m o u n t e d and one series f r o m each case was counterstained with thionine. In animal 11660 three injections of 0.1 #1 H R P (each 500 #g/#l) were made in the left VL, and the animal survived for 72 h. The injected H R P had diffused widely t h r o u g h o u t the medial half of the thalamus, but did not appear to have trespassed the ventral borders of the thalamus (Fig. 1). In particular, no signs of diffused H R P were observed in the putamen, the nucleus caudatus and in the region o f the medial forebrain bundle where the nigrostriatal pathway runs. In the ipsilateral substantia nigra m a n y cells contained a yellow-brownish granular reaction product scattered throughout the cytoplasm and proximal dendrites (Fig. 2), The labeled cells were confined to the pars reticulata o f the substantia nigra, where they were seen t h r o u g h o u t its rostrocaudal extent, particularly abundantly in its lateral part (Fig. 2). Labeled cells were occasionally located along the ventralmost aspect o f the cell-rich pars compacta. N o labeled cells, however, were seen in pars c o m p a c t a itself. The labeled cells were of varying size and shape, but the majority were large, elongated or spindle-shaped (Figs. 2, 4, 6). N o labeled cells were seen in substantia nigra contralateral to the injection site. In the 7 other animals with single injections, the H R P was limited to VL (Fig. 5) or to the border between VL and VM (Fig. 3). Labeled cells were seen in the ipsilateral
Fig. 1. Maximal diffusion of HRP following 3 injections of 0.1 /d each (500 l~g HRP///I) in the left thalamus in cat 11660. Thionine-stained. x 5.5. Fig. 2. Cluster of labeled cells in the pars reticulata of the left substantia nigra. Notice the absence of labeled cells in the pars compacta (Co). Pc: cerebral peduncle. Same animal as in Fig. 1. Counterstained with thionine. Dark-field illumination, x 185. Fig. 3. Injection site in VL/VM of 0.3 I~l (250/~g/f4) HRP in cat 11677. Thionine-stained. x 6.5. Fig. 4. Labeled cell in pars reticulata of the same animal as in Fig. 3. Arrow points to 'droplets' of the reaction product probably lying in the axon which leaves a primary dendrite. The axon is directed towards the cerebral peduncle (see ref. 19). Dark-field. × 450. Fig. 5. Injection site in VL of 0.2/~I (250/~g//~l) HRP in eat 11673. Thionine-stained. ,x 6.5. Fig. 6. Labeled cell in the pars reticulata in the same animal as in Fig. 5. Notice the unlabeled cells in the dorsally situated pars compacta. Counterstained with thionine. Dark-field illumination, x 450.
316 pars reticulala of substaniia nigra, particularly in its lateral part (Figs. 4 and f~L In none of these cases were labeled cells observed in pars compacts of substantia nigra: occasionally a labeled cell was located along its ventral aspect (Fig. 6). The number of labeled cells in these animals was in each case quite inferior to that observed in cat 11660. In a few other animals the tip of the injection cannula has been located in thalamic nuclei other than VL or VM, such as the nucleus medialis dorsalis (MD), the anterior group of nuclei, and in the intralaminar nuclei. In none of these cases were labeled cells observed in substantia nigra. That this negative finding obviously was not due to technical fallacies is learnt from the finding that labeled cells were seen in other regions such as the lateral mammillary nucleus in cases with injections in the anterior group of thalamic nuclei. No injections of H R P have been made in the nucleus ventralis anterior (VAt in the present investigation. The present material does not permit conclusions to be drawn concerning a possible topographical organization in the nigrofugal projection upon VL and/or VM. It appears justified, however, to state that nigrofugal fibers at least appear to terminate in rostral parts of VL (Fig. 5). On the other hand, it cannot be concluded without reservation that V M is an area of termination of the nigrothalamic projection. The nigrofugal fibers to VL probably pass through VM, and it is not yet ascertained whether intact axons take up the extracellularly injected enzyme, or whether the axons must be damaged before uptake, thus leading to a retrograde axonal transport. The present study confirms the existence of a nigrothalamic pathway as reported by authors using anterograde degeneration techniques t,6-s,l°. Carpenter and Peter s in the monkey, and Faull and Carman 1° in the rat, conclude that the cells in pars reticulata of substantia nigra must be the major - - if not the sole .... origin of nigrothalamic fibers. This conclusion was based on a meticulous correlation between the extent of nigral lesions and the amount of fiber degeneration in the thalamus, and is completely supported by the present observations that only cells in pars reticulata are labeled following thalamic injections of HRP. Furthermore, the greatest number of labeled cells is seen in the lateral part of pars reticulata. This again concurs with the observations of Carpenter and co-workers 7 (reviewing some older material of Carpenter and McMasters s) that the heaviest degeneration in the thalamus of the monkey is seen when the lesions involve the lateral part of the substantia nigra. The fact that only the scattered cells in the nigral pars reticulata project upon tile thalamus may explain why cellular changes were not observed in the nigra following thalamic lesions 1,16. In an investigation on the monkey's substantia nigra Schwyn and Fox 19 emphasize that the spindle-shaped neurons which they observe in the pars reticulata are comparable to the large and elongated neurons that Gulley and Wood ~ describe in the rat's pars reticulata, and which they consider the cells of origin of the nigrothalamic pathway. The observations made in the present study indicate that in the cat the cells of origin in pars reticulata of the nigrothalamic axons mostly have a fusiform or spindle shape (Figs. 2, 4, 6), thus resembling the cells in pars reticulata of the two other species (rat and monkey).
317 Particularly relevant to the present investigation are the recent studies by H6kfelt and Ungerstedt 12 in the rat. Following administration of 6-OHDA most cells in the pars compacta of substantia nigra show clear signs of degeneration ~e. One type of cell, however, with clearly defined cytological characteristics, does not show signs of being affected by the administered 6-OHDA. Judging from their illustrations 12 it appears that these unaffected cells are located in pars reticulata of the substantia nigra. This type of cell 12 has cytological characteristics similar to the cells in the rat's pars reticulata 1~. The latter authors also reported unpublished observations that this cell type did not take up [3H]noradrenaline. Summing up, the present investigation has established the existence of a nigrothalamic projection in the cat. The cells of origin are strictly located to pats reticulata of the substantia nigra, particularly to its lateral part. The nigrothalamic fibers end in VL and most probably also in VM. Other reports in the literature indicate that this nigrothalamic pathway is not dopaminergic, Experimental electron microscopical investigations are currently in progress, in order to identify and locate the boutons of the nigrothalamic fibers, and to assess their precise participation within the synaptical organization of the cat's VL is. The present investigation was supported bv a grant from Thomas Fearnley's Bidrags- og Gavefond. The author is indebted to Mrs. Evelyn Pettersen, Anatomical Institute, for skilful technical assistance. NOTE ADDED IN PROOF
After the present paper was submitted for publication, Ljungdahl et al. have published further evidence that the dopaminergic nigro-striatal neurons are mainly localized to the pars compacta of the rat's substantia nigra. (LJUNGDAHL,,~., HOKFELT, T., GOLDSTEIN,M., AND PARK, D., Retrograde peroxidase tracing of neurons combined with transmitter histochemistry, Brain Research, 84 (1975) 313-319.)
1 AFIFI, A., AND KAELBER, W. W., Efferent connections of the substantia nigra in the cat, Exp. 2
3 4 5 6
7
Neurol., 11 (1965) 474-482. ANDI~N,N.-E., CARLSSON,A., DAHLSTROM,A., FUXE, K., HILLARP,N.-~., AND LARSSON,K., Demonstration and mapping out of nigroneostriatal dopamine neurons, Life Sci., 3 (1964) 523 530. ANDEN,N.-E., DAHLSTROM,A., FOXE,K., ANDLARSSON,K., Further evidence for the presence of nigroneostriatal dopamine neurons in the rat, Amer. J. Anat., 116 (1965) 329-334, BEDARD,P., LAROCHELLE,L., PARENT,A., AND POIRIER,L. J,, The nigro-striatal pathway: a correlative study based on neuroanatomical and neurochemical criteria in the cat and the monkey, Exp. Neurol., 25 (1969) 365-377. CARPEYTER,M. B., ANDMCMASTERS,R. E., Lesions of the substantia nigra in the rhesus monkey. Efferent fiber degeneration and behavioral observations, Amer. J. Anat., 114 (1964) 293 320. CARPENTER, M. B., AND PETER, P., Nigrostriatal and nigrothalamic fibers in the rhesus monkey, J. eomp. Neurol., 144 (1972) 93-116. CARPENTER, M. B., AND STROMINGER, N. L., Efferent fibers of the subthalamic nucleus in the mon-
318
8
9
10 II 12
13
14 15 16 17 18 19
key. A comparison ol the efferent projections of the subthalamic nucleus: ~ubstamia nh,~ ~ d globus pallidus, .4m~,r. d. AH~a.. 121 (1967)41-72. COLE, M., NAUTA, W..I. I-I., .~,ND M~tU.t;R, W. H., The ascending efferent projections of the substantia nigra. In M. 1). 'r'AHR (Ed.), TraH,~. 4mer. Nem'ol. As~., Vol. 89, Springer, New ~ork~ I~}h4, pp. 74 75. DAHLSrR6M, A., AND EUXI~ K., Evidence of the existence of monoamine-containing neuron~ ~n the central nervous system. 1. Demonstration of monoamines in the cell bodies of brain s~em neurons, Actaphysiol. scwM., 62, Suppl. 232 (1965) 55. FAULL, R. L. M., A~D CARMAX, J. B., Ascending projections of the substantia nigra in fllc rat, J. romp. New'ol., 132 (1968) 73---92. GULL~Y, R. L., ANt) Wool), R. L., The line structure of the neurons in the rat substantia nigra, Tissue and C¢11, 3 (1971) 675 690, HOKFEt~r, T., ANt) LJNGERsrt~)r, U., Specificity of 6-hydroxydopamine induced degeneration of central monoamine neurons: an electron and fluorescence microscopic study with special reference to intracerebral injection on the nigro-striatal dopamine system, Brain Research, 60 (1973) 269 297. JONES, E. G., ant) LEAWrT. R. Y., Retrograde axonal transport and the demonstration o[" nonspecific projections to the cerebral cortex and striatum from intralaminar nuclei in the rat, cat and monkey, J. comp. Neurol., 154 (1974) 349 -378. KRiSTBNSSON, K., AND OLSSON, Y., Uptake and retrograde axonal transport of peroxidase in hypoglossal neurons, Acre nem'opath. (Bed.), 19 (1971) l-9. LAVML, J. H., ANt) LAVAn., M. M., Retrograde axonal transport in the central nervous systenl, Seiem'c', 176 (1972) 1416 1417. METTLER, F. A.. Nigrofugal connections in the primate brain, J. comp. Neurol., 138 {1970) 291-320. RINVIK, E., AND GROFOVA, I., Observations on the fine structure of the substantia nigra in the cat, Exp. Brai~, Res., 11 (1970} 229-248. RINVIK, E., AND GRomva, I., Light and electron microscopical studies of the normal nuclei ventralis lateralis and ventralis anterior thalami in the cat, Anat. Embryol., 146 (1974) 57-93. SCHW'eN, R. C., aND Fox, C. A., The primate substantia nigra: a Golgi and electron microscopic study, J. Hirt,[orsch., 15 (1974) 95-126.
313
Demonstration of nigrothalamic connections in the cat by retrograde axonal transport of horseradish peroxidase
ERIC R1NVIK Anatontical Institute, University of Oslo, Oslo 1 (Norway)
(Accepted March 4th, 1975)
Ever since the substantia nigra was involved in discussions concerning the pathology of Parkinson's disease, attempts have been made with a variety of methods to clarify its afferent and efferent fiber connections (for a recent review of the literature, see ref. 19). Of major significance in the last decade's research on these problems has been the discovery by Fuxe and collaborators that there is a continuous transport of dopamine from cells in the substantia nigra to axon terminals in the putamen and caudate nucleus2,3, ,~. It is known that the substantia nigra can be divided into a cell-rich pars compacta and a cell-poor pars reticulatall,17,19. The pars reticulata lies ventrally to the cell-rich pars compacta, and is particularly well developed laterallyn,lL Using fluorescing histochemical techniques, it was established early that the bulk of nigral dopamine is localized to the soma of the cells in the pars compacta. Only few fluorescing - - and presumed dopaminergic - - cells are seen in the pars reticulata 2& Furthermore, the dopamine level in the striatum is not reduced when the pars reticulata, and particularly its lateral portion, is destroyedL On the other hand, there are ample reports in the literature that degenerating fibers can be followed to parts of the thalamic nuclei following nigral lesionsl,6-s, l°. Some of these authors are actually of the opinion that this represents the main nigrofugal projection. However, selective electrolytic lesions of the substantia nigra are very difficult to obtain, and attempts to produce retrograde cell changes or cell loss in this nucleus, as a consequence of lesions of the thalamus, have not revealed detectable cellular alterations 4,16. Therefore, the question still prevails whether the anterograde degeneration studies with silver impregnation techniques demonstrate a genuine nigrothalamic pathway, or whether the degenerating fibers observed belong to other, accidentally lesioned, pathways. Furthermore, if there is a nigrothalamic pathway, from which part of the nucleus does it originate ? In order to elucidate this problem, investigations were undertaken using the recently introduced technique of retrograde axonal transport of horseradish peroxidase (HRp)14,1L Multiple (one animal) and single (7 animals) injections of H R P (Sigma Type Vl) were successfully confined within the boundaries of the thalamus.
4~
315 The concentration o f the H R P varied between 250 and 500 #g/f4, and a m o u n t s of 0.06-0.3 #1 were stereotaxically injected over a period of 20-30 rain by means of a 1 #1 H a m i l t o n syringe held in a holder m o u n t e d on a microelectrode carrier. In all experiments the tip of the injection cannula was aimed at the nucleus ventralis lateralis (VL) or at the nucleus ventralis medialis (VM) of the thalamus. The animals survived for 24-72 h and were perfused by a mixture of 0.4~o formaldehyde and 1.25 ~ glutaraldehyde in a 0.1 M phosphate buffer solution ~a. The brains were immediately dissected free and postfixed in the same fixative for 24 h before being transferred to a phosphate buffered solution containing 30 ~ sucrose for another 24 h. The brains were cut on a freezing microtome and the 50 # m thick frontal sections were transferred to a solution containing 0.05 ~/o 3,3'-diaminobenzidine tetrahydrocloride in T r i s - H C l buffer (pH 7.6) for 5 rain at r o o m temperature. They were then incubated for a further 15 rain at r o o m temperature in a similar solution but with the addition of 66 #1 of 3 0 ~ hydrogen peroxide/100 ml. Two complete series from each case were m o u n t e d and one series f r o m each case was counterstained with thionine. In animal 11660 three injections of 0.1 #1 H R P (each 500 #g/#l) were made in the left VL, and the animal survived for 72 h. The injected H R P had diffused widely t h r o u g h o u t the medial half of the thalamus, but did not appear to have trespassed the ventral borders of the thalamus (Fig. 1). In particular, no signs of diffused H R P were observed in the putamen, the nucleus caudatus and in the region o f the medial forebrain bundle where the nigrostriatal pathway runs. In the ipsilateral substantia nigra m a n y cells contained a yellow-brownish granular reaction product scattered throughout the cytoplasm and proximal dendrites (Fig. 2), The labeled cells were confined to the pars reticulata o f the substantia nigra, where they were seen t h r o u g h o u t its rostrocaudal extent, particularly abundantly in its lateral part (Fig. 2). Labeled cells were occasionally located along the ventralmost aspect o f the cell-rich pars compacta. N o labeled cells, however, were seen in pars c o m p a c t a itself. The labeled cells were of varying size and shape, but the majority were large, elongated or spindle-shaped (Figs. 2, 4, 6). N o labeled cells were seen in substantia nigra contralateral to the injection site. In the 7 other animals with single injections, the H R P was limited to VL (Fig. 5) or to the border between VL and VM (Fig. 3). Labeled cells were seen in the ipsilateral
Fig. 1. Maximal diffusion of HRP following 3 injections of 0.1 /d each (500 l~g HRP///I) in the left thalamus in cat 11660. Thionine-stained. x 5.5. Fig. 2. Cluster of labeled cells in the pars reticulata of the left substantia nigra. Notice the absence of labeled cells in the pars compacta (Co). Pc: cerebral peduncle. Same animal as in Fig. 1. Counterstained with thionine. Dark-field illumination, x 185. Fig. 3. Injection site in VL/VM of 0.3 I~l (250/~g/f4) HRP in cat 11677. Thionine-stained. x 6.5. Fig. 4. Labeled cell in pars reticulata of the same animal as in Fig. 3. Arrow points to 'droplets' of the reaction product probably lying in the axon which leaves a primary dendrite. The axon is directed towards the cerebral peduncle (see ref. 19). Dark-field. × 450. Fig. 5. Injection site in VL of 0.2/~I (250/~g//~l) HRP in eat 11673. Thionine-stained. ,x 6.5. Fig. 6. Labeled cell in the pars reticulata in the same animal as in Fig. 5. Notice the unlabeled cells in the dorsally situated pars compacta. Counterstained with thionine. Dark-field illumination, x 450.
316 pars reticulala of substaniia nigra, particularly in its lateral part (Figs. 4 and f~L In none of these cases were labeled cells observed in pars compacts of substantia nigra: occasionally a labeled cell was located along its ventral aspect (Fig. 6). The number of labeled cells in these animals was in each case quite inferior to that observed in cat 11660. In a few other animals the tip of the injection cannula has been located in thalamic nuclei other than VL or VM, such as the nucleus medialis dorsalis (MD), the anterior group of nuclei, and in the intralaminar nuclei. In none of these cases were labeled cells observed in substantia nigra. That this negative finding obviously was not due to technical fallacies is learnt from the finding that labeled cells were seen in other regions such as the lateral mammillary nucleus in cases with injections in the anterior group of thalamic nuclei. No injections of H R P have been made in the nucleus ventralis anterior (VAt in the present investigation. The present material does not permit conclusions to be drawn concerning a possible topographical organization in the nigrofugal projection upon VL and/or VM. It appears justified, however, to state that nigrofugal fibers at least appear to terminate in rostral parts of VL (Fig. 5). On the other hand, it cannot be concluded without reservation that V M is an area of termination of the nigrothalamic projection. The nigrofugal fibers to VL probably pass through VM, and it is not yet ascertained whether intact axons take up the extracellularly injected enzyme, or whether the axons must be damaged before uptake, thus leading to a retrograde axonal transport. The present study confirms the existence of a nigrothalamic pathway as reported by authors using anterograde degeneration techniques t,6-s,l°. Carpenter and Peter s in the monkey, and Faull and Carman 1° in the rat, conclude that the cells in pars reticulata of substantia nigra must be the major - - if not the sole .... origin of nigrothalamic fibers. This conclusion was based on a meticulous correlation between the extent of nigral lesions and the amount of fiber degeneration in the thalamus, and is completely supported by the present observations that only cells in pars reticulata are labeled following thalamic injections of HRP. Furthermore, the greatest number of labeled cells is seen in the lateral part of pars reticulata. This again concurs with the observations of Carpenter and co-workers 7 (reviewing some older material of Carpenter and McMasters s) that the heaviest degeneration in the thalamus of the monkey is seen when the lesions involve the lateral part of the substantia nigra. The fact that only the scattered cells in the nigral pars reticulata project upon tile thalamus may explain why cellular changes were not observed in the nigra following thalamic lesions 1,16. In an investigation on the monkey's substantia nigra Schwyn and Fox 19 emphasize that the spindle-shaped neurons which they observe in the pars reticulata are comparable to the large and elongated neurons that Gulley and Wood ~ describe in the rat's pars reticulata, and which they consider the cells of origin of the nigrothalamic pathway. The observations made in the present study indicate that in the cat the cells of origin in pars reticulata of the nigrothalamic axons mostly have a fusiform or spindle shape (Figs. 2, 4, 6), thus resembling the cells in pars reticulata of the two other species (rat and monkey).
317 Particularly relevant to the present investigation are the recent studies by H6kfelt and Ungerstedt 12 in the rat. Following administration of 6-OHDA most cells in the pars compacta of substantia nigra show clear signs of degeneration ~e. One type of cell, however, with clearly defined cytological characteristics, does not show signs of being affected by the administered 6-OHDA. Judging from their illustrations 12 it appears that these unaffected cells are located in pars reticulata of the substantia nigra. This type of cell 12 has cytological characteristics similar to the cells in the rat's pars reticulata 1~. The latter authors also reported unpublished observations that this cell type did not take up [3H]noradrenaline. Summing up, the present investigation has established the existence of a nigrothalamic projection in the cat. The cells of origin are strictly located to pats reticulata of the substantia nigra, particularly to its lateral part. The nigrothalamic fibers end in VL and most probably also in VM. Other reports in the literature indicate that this nigrothalamic pathway is not dopaminergic, Experimental electron microscopical investigations are currently in progress, in order to identify and locate the boutons of the nigrothalamic fibers, and to assess their precise participation within the synaptical organization of the cat's VL is. The present investigation was supported bv a grant from Thomas Fearnley's Bidrags- og Gavefond. The author is indebted to Mrs. Evelyn Pettersen, Anatomical Institute, for skilful technical assistance. NOTE ADDED IN PROOF
After the present paper was submitted for publication, Ljungdahl et al. have published further evidence that the dopaminergic nigro-striatal neurons are mainly localized to the pars compacta of the rat's substantia nigra. (LJUNGDAHL,,~., HOKFELT, T., GOLDSTEIN,M., AND PARK, D., Retrograde peroxidase tracing of neurons combined with transmitter histochemistry, Brain Research, 84 (1975) 313-319.)
1 AFIFI, A., AND KAELBER, W. W., Efferent connections of the substantia nigra in the cat, Exp. 2
3 4 5 6
7
Neurol., 11 (1965) 474-482. ANDI~N,N.-E., CARLSSON,A., DAHLSTROM,A., FUXE, K., HILLARP,N.-~., AND LARSSON,K., Demonstration and mapping out of nigroneostriatal dopamine neurons, Life Sci., 3 (1964) 523 530. ANDEN,N.-E., DAHLSTROM,A., FOXE,K., ANDLARSSON,K., Further evidence for the presence of nigroneostriatal dopamine neurons in the rat, Amer. J. Anat., 116 (1965) 329-334, BEDARD,P., LAROCHELLE,L., PARENT,A., AND POIRIER,L. J,, The nigro-striatal pathway: a correlative study based on neuroanatomical and neurochemical criteria in the cat and the monkey, Exp. Neurol., 25 (1969) 365-377. CARPEYTER,M. B., ANDMCMASTERS,R. E., Lesions of the substantia nigra in the rhesus monkey. Efferent fiber degeneration and behavioral observations, Amer. J. Anat., 114 (1964) 293 320. CARPENTER, M. B., AND PETER, P., Nigrostriatal and nigrothalamic fibers in the rhesus monkey, J. eomp. Neurol., 144 (1972) 93-116. CARPENTER, M. B., AND STROMINGER, N. L., Efferent fibers of the subthalamic nucleus in the mon-
318
8
9
10 II 12
13
14 15 16 17 18 19
key. A comparison ol the efferent projections of the subthalamic nucleus: ~ubstamia nh,~ ~ d globus pallidus, .4m~,r. d. AH~a.. 121 (1967)41-72. COLE, M., NAUTA, W..I. I-I., .~,ND M~tU.t;R, W. H., The ascending efferent projections of the substantia nigra. In M. 1). 'r'AHR (Ed.), TraH,~. 4mer. Nem'ol. As~., Vol. 89, Springer, New ~ork~ I~}h4, pp. 74 75. DAHLSrR6M, A., AND EUXI~ K., Evidence of the existence of monoamine-containing neuron~ ~n the central nervous system. 1. Demonstration of monoamines in the cell bodies of brain s~em neurons, Actaphysiol. scwM., 62, Suppl. 232 (1965) 55. FAULL, R. L. M., A~D CARMAX, J. B., Ascending projections of the substantia nigra in fllc rat, J. romp. New'ol., 132 (1968) 73---92. GULL~Y, R. L., ANt) Wool), R. L., The line structure of the neurons in the rat substantia nigra, Tissue and C¢11, 3 (1971) 675 690, HOKFEt~r, T., ANt) LJNGERsrt~)r, U., Specificity of 6-hydroxydopamine induced degeneration of central monoamine neurons: an electron and fluorescence microscopic study with special reference to intracerebral injection on the nigro-striatal dopamine system, Brain Research, 60 (1973) 269 297. JONES, E. G., ant) LEAWrT. R. Y., Retrograde axonal transport and the demonstration o[" nonspecific projections to the cerebral cortex and striatum from intralaminar nuclei in the rat, cat and monkey, J. comp. Neurol., 154 (1974) 349 -378. KRiSTBNSSON, K., AND OLSSON, Y., Uptake and retrograde axonal transport of peroxidase in hypoglossal neurons, Acre nem'opath. (Bed.), 19 (1971) l-9. LAVML, J. H., ANt) LAVAn., M. M., Retrograde axonal transport in the central nervous systenl, Seiem'c', 176 (1972) 1416 1417. METTLER, F. A.. Nigrofugal connections in the primate brain, J. comp. Neurol., 138 {1970) 291-320. RINVIK, E., AND GROFOVA, I., Observations on the fine structure of the substantia nigra in the cat, Exp. Brai~, Res., 11 (1970} 229-248. RINVIK, E., AND GRomva, I., Light and electron microscopical studies of the normal nuclei ventralis lateralis and ventralis anterior thalami in the cat, Anat. Embryol., 146 (1974) 57-93. SCHW'eN, R. C., aND Fox, C. A., The primate substantia nigra: a Golgi and electron microscopic study, J. Hirt,[orsch., 15 (1974) 95-126.
