Localization of nigrostriatal, nigrothalamic and nigrotectal neurons in ventricular coordinates in macaques

The topography of the substantia nigra and its subdivisions was first analysed in macaques by using a topographic technique based on ventricular landmarks. This study shows the stability of the contours of the substantia nigra and its subdivisions in various species of macaques. The anteroposterior sequence of four subdivisions was standardized by defining eight verticotransverse levels, regularly interspaced and systemically used for each experimental case. Neurons of the substantia nigra sending axons to the striatum, thalamus and superior colliculus were identified by the technique of retrograde transport of horseradish peroxidase. The nigrostriatal labeled neurons were essentially located in the ipsilateral pars compacta but also scattered dorsally in the pars mixta and ventrally in the pars reticulata. In addition, the existence of a crossed nigrostriatal pathway was demonstrated in monkeys. Nigrothalamic labeled neurons were found in the whole pars reticulata at rostral levels and only in the medial part at more caudal levels. Comparatively, nigrotectal labeled neurons were also found in the whole pars reticulata at rostral levels, but caudally, they were confined to the lateral part of the pars reticulata and the pars lateralis. It thus appears that these three nigral components may overlap at some levels of the substantia nigra. This is discussed in relation to the existence of branched axons already documented. However, the present results underline the strong tendency of the nigrotectal neurons to be segregated from the nigrothalamic ones and to be laterally located in monkeys. In addition, two nigrotectal components have been identified on the basis of their topography and their somata size: one with large somata located in the pars lateralis, probably specific to primates, and the other with smaller somata located in the pars reticulata. These two components may indicate the existence of two different functional systems.     

The striatonigral projection and nigrotectal neurons in the rat. A correlated light and electron microscopic study demonstrating a monosynaptic striatal input to identified nigrotectal neurons using a combined degeneration and horseradish peroxidase procedure

In a light and electron microscopic study of the substantia nigra of the rat, the distribution and morphology of nigrotectal neurons and the pattern of termination of striatonigral fibres have been examined following the placement of horseradish peroxidase injections in the superior colliculus and kainic acid lesions in the dorsal striatum. In confirmation of previous findings, nigrotectal neurons which had been identified by the retrograde transport of horseradish peroxidase from the superior colliculus had mainly medium sized somata, varied from fusiform to stellate in shape and were found in mainly ventral regions of the rostral two-thirds of the substantia nigra pars reticulata. On electron microscopic examination, single and multiple (from two to six) degenerating striatonigral boutons were found in synaptic contact with the soma, proximal mainstem dendrites and small dendrites (but mainly on small dendrites) of labelled nigrotectal and unlabelled nigral neurons in the ventral region of the pars reticulata. In addition, a small number of degenerating striatonigral boutons formed axoaxonic synapses with degenerating or normal boutons which were presynaptic to nigral dendrites. Almost all of the identified striatonigral synapses were of the symmetrical type, although a few degenerating boutons established asymmetrical synaptic contacts on unlabelled dendrites. These findings provide evidence of a monosynaptic input from the dorsal striatum to nigrotectal projection neurons in the substantia nigra and thus demonstrate the existence of a bineuronal pathway from the striatum through the substantia nigra to the superior colliculus. The possible significance of the pattern of termination of striatonigral fibres in the substantia nigra is discussed with reference to the known dendritic arborization of nigral neurons.     

Early establishment of adult-like nigrotectal architecture in the neonatal cat: a double-labeling study using carbocyanine dyes

Virtually nothing is known about the ontogeny of substantia nigra, pars reticulata projections to the midbrain superior colliculus, even though this pathway is critical for the basal ganglia modulation of midbrain-mediated visuomotor behaviors. The present studies used the lipophilic carbocyanine dyes 1,1'-dioctodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate and 1,1'-dioctodecyl-3,3,3',3'-tetramethylindodi, 4-chlorobenzenesulfonate salt to examine the crossed and uncrossed nigrotectal projections in neonatal cats, from parturition to 14 days postnatal (the technical limits of the tracing technique). In retrograde experiments, paired placement of the dyes in each superior colliculus produced numerous retrogradely-labeled nigrotectal neurons, with the uncrossed neurons far out numbering their crossed counterparts. No double-labeled neurons were observed, indicating that crossed and uncrossed nigrotectal neurons are segregated at birth. In anterograde experiments, dye placements into each substantia nigra, pars reticulata resulted in an iterative series of labeled patches, aligned medial-to-lateral across the intermediate and deep superior colliculus, a pattern reminiscent of the adult. Uncrossed neonatal axons had simple linear morphologies with few branch points; by contrast, crossed axons displayed more extensive terminal arbors that were distributed diffusely throughout the rostrocaudal extent of the contralateral superior colliculus In the final series of experiments, one dye was placed unilaterally in the substantia nigra, pars reticulata, while the second dye was positioned in the predorsal bundle, in order to bilaterally label superior colliculus output neurons. Although both crossed and uncrossed axons appeared to have contacted superior colliculus output neurons, crossed axons preferentially targeted the soma and proximal dendrites, whereas uncrossed terminals were distributed more distally. Throughout this early postnatal period, no significant changes in cellular morphologies or gross modification of terminal projection patterns were observed; however, the presence of growth cones in even the oldest animals studied suggests that the refinement of the nigrotectal projections extends well into postnatal life. Nevertheless, the segregation of crossed and uncrossed nigrotectal neurons into a highly organized afferent mosaic that has established synaptic contacts with superior colliculus output neurons indicates that many of the salient features characterizing nigrotectal projections are established prior to the onset of visual experience.     

Long collateral branches of substantia nigra pars reticulata axons to thalamus,superior colliculus and reticular formation in monkey and cat. Multiple retrograde neuronal labeling with fluorescent dyes

In order to gain some impressions about the degree to which individual neurons of the pars reticulata of the substantia nigra send long collateral branches to more than one of its three major targets (thalamus, superior colliculus, reticular formation), two, or all three targets were injected with fluorescent dyes (Evan's blue, granular blue, nuclear yellow, propidium iodide) in six squirrel monkeys and four cats. The best results were obtained in the monkey brain with injections of Evan's blue in the thalamus, granular blue in the colliculus and nuclear yellow in the reticular formation. Whereas nigrothalamic and nigroreticular neurons are numerous and widely scattered throughout all parts of the pars reticulata, cells projecting only to the superior colliculus are fewer in number and restricted to a rostral-lateral zone. These results are consistent with earlier data obtained with the horseradish peroxidase method.² Although double-labeled cells with projections to both the thalamus and reticular formation occur throughout the pars reticulata, such cells are somewhat more abundant at caudal levels of the nucleus. Cells containing dyes from both the superior colliculus and reticular formation are less common and restricted to the lateral part of the pars reticulata. A small number of cells near the rostral pole of the pars reticulata contain dye from both the tectal and thalamic injection. Typically, less than two dozen cells in any case can be confidently identified as containing all three dyes and these cells are located in the rostrolateral half of the pars reticulata. Fewer than 20% of the labeled nigral cells contain more than one dye.In the cat, thalamic injection of granular blue and tectal injection of nuclear yellow indicate that most nigrotectal cells are located in the middle of the mediolateral expanse of the pars reticulata in its rostral half. Nigrothalamic cells flank the nigrotectal group medially, laterally and caudally. Where these groups border one another, several cells contain both dyes indicating that they project to both the thalamus and colliculus. In both the cats and monkeys, a less extensive cell-labeling occurs in the contralateral nigra with a pattern similar to that in the ipsilateral substantia nigra.The results indicate that several neurons of the substantia nigra's pars reticulata send long collateral branches to two or even all three of the major targets. Many reticulata cells, however, appear to project either to the thalamus, or to the superior colliculus or to the reticular formation.     

The neurons of the substantia nigra and zona incerta which project to the cat superior colliculus are GABA immunoreactive: a double-label study using GABA immunocytochemistry and lectin retrograde transport

The neurotransmitter cytochemistry of neurons in the substantia nigra and zona incerta which project to the cat superior colliculus was examined. Neurons in both structures were double-labeled with an antibody to the transmitter GABA and a retrograde tracer, [3H]n-acetylated wheat germ agglutinin, injected into the superior colliculus. All cells in the zona incerta and substantia nigra which projected to the superior colliculus were labeled by the GABA antiserum. Most other neurons within the zona incerta and virtually all within the substantia nigra pars reticulata and pars lateralis were also labeled by the GABA antibody. By contrast, neurons in the substantia nigra pars compacta were not labeled by either the GABA antibody or wheat germ agglutinin. Nigrotectal cells in the substantia nigra were of medium to large size and most had stellate-shaped cell bodies. Zona incerta cells projecting to the superior colliculus were also of medium to large size, but most had horizontal fusiform cell bodies. This study demonstrates two new findings: (1) that all nigrotectal neurons in cat are immunoreactive to a GABA antibody and probably contain the neurotransmitter GABA; and (2) that these GABA immunoreactive neurons in cat are found not only in the substantia nigra pars reticulata but also within the pars lateralis. Zona incerta cells projecting to the superior colliculus have a different morphology but are also apparently GABAergic. These data provide an anatomical substrate for the known inhibitory action of the nigrotectal pathway on superior colliculus neurons.     

Nigrotectal projections in the primate Galago crassicaudatus

Summary The pattern of the nigrotectal projection in Galago crassicaudatus was determined using retrograde and anterograde transport methods. These experiments revealed that pars reticulata and pars lateralis of the substantia nigra project to all layers of the ipsilateral and contralateral superior colliculus, except to layer I. The nigrotectal projection is not homogeneous, but is concentrated in particular collicular layers and sublayers, and the intensity and laminar distribution of the projection varies along the rostral-caudal dimension of the superior colliculus. The ipsilateral and contralateral nigrotectal projections are generally similar, except that a tier of dense label which is prominent in the ventral part of much of the ipsilateral layer IV is not obvious contralaterally; moreover, the contralateral projection is much sparser than the ipsilateral. Deposits of tracers at different medial-lateral locations within the substantia nigra did not result in different laminar patterns of anterogradely transported label in the superior colliculus. Based on the known connections and functions of the collicular layers and sublayers, the pattern and distribution of the nigrotectal projection suggests that the substantia nigra may use this pathway to gain access to particular components of vision- and visuomotor-related networks.Abbreviations Cd Caudate - CG Central gray - CP Cerebral peduncle - D Dorsal - FEF Frontal eye field - IC Internal capsule - ICo Inferior colliculus - IP Interpeduncular nucleus - L Lateral - LG Lateral geniculate - MDmf Medial dorsal nucleus, pars multiformis - MG Medial geniculate - MI Mammillary body, lateral nucleus - Mm Mammillary body, medial nucleus - MRF Mesencephalic reticular formation - nIII Oculomotor nerve - OT Optic tract - PG Pontine gray - Pg Pregeniculate nucleus - Pt Pretectal complex - Pulv Pulvinar nuclei - Put Putamen - R Red nucleus rostral - SCi,d Superior colliculus, intermediate and deep layers - SCs Superior colliculus, superficial layers - SEF Supplementary eye field - SNc Substantia nigra, pars compacta - SNr Substantia nigra, pars reticulata - SNr, 1 Substantia nigra, pars reticulata and pars lateralis - St Subthalamic nucleus - VAmc Ventral anterior nucleus, pars magnocellularis - V Cort Visual cortical areas - ZI Zona incerta - II Layer II of the superior colliculus - III Layer III of the superior colliculus - IV Layer IV of the superior colliculus - V Layer V of the superior colliculus - VI Layer VI of the superior colliculus     

Collateral projection from the substantia nigra to the striatum and superior colliculus in the rat

Our retrograde fluorescent double labeling study demonstrated the existence of divergent collateral projections from the substantia nigra to the striatum and superior colliculus in the rat. These bifurcating projection neurons were located predominantly in the ventrolateral portions of the substantia nigra pars reticulata at its rostral level, where they formed a narrow band along the boundary between the substantia nigra and cerebral peduncle. Such specific projection cells were also seen in the substantia nigra pars lateralis. However, nigral neurons did not give off axonal branches to the striatum and ventromedial thalamic nucleus. The new nigral cell population proposed here might constitute a neuroanatomical substrate for abnormal saccadic eye movements clinically manifested by many parkinsonian patients.     

Dopaminergic dendrites in the pars reticulata of the rat substantia nigra and their striatal input. Combined immunocytochemical localization of tyrosine hydroxylase and anterograde degeneration

An antiserum prepared in the rabbit against bovine adrenal gland tyrosine hydroxylase has been used to identify by the immunoperoxidase method dopaminergic neurons in the rat substantia nigra. The purpose of this identification was (i) to assess the storing compartments and the release sites in the dopamine-containing processes of the pars reticulata; (ii) to determine if these processes receive a direct input from the neostriatum.Immunoreactive neurons were present in the three divisions of the substantia nigra (pars compacta, pars lateralis and pars reticulata), but they were much more numerous in pars compacta. The caudal half and the most rostral end of pars reticulata contained single and small clusters of reactive neurons, which were absent from the remaining regions. Processes emerging from the positive neurons, exhibiting also immunoperoxidase reactivity, spread throughout the whole pars reticulata. The ultrastructural study was limited to the region of the pars reticulata free of reactive perikarya, in order to analyze the processes that originate from neurons located in the pars compacta. Five hundred and eighty well-preserved immunoreactive processes were analyzed. Almost all of them (578) displayed cytological features allowing their identification as dendrites. Two of them corresponded to thin unmyelinated, non-synaptic segments of axons, probably in their way to their terminal fields outside the substantia nigra. The large majority of the reactive dendrites (82%) were postsynaptic to one or several axon terminals and did not establish direct appositions with other dendritic elements. Only 4.35% of the labeled dendrites were directly apposed to other reactive or unreactive dendrites. Two of the labeled dendrites (0.35%) contained synaptic-like vesicles. In one of them, the vesicles were clustered against a restricted area of the plasma-membrane, forming an active zone.In two animals, kainic acid was used to destroy neurons located within the central region of the main body of the neostriatum. Their projections were traced to the ipsilateral substantia nigra, in which dopaminergic neurons were visualized by the immunoperoxidase method. The axons originating from the injured neurons in the striatum established direct synaptic contacts with the immunoreactive dendrites in pars reticulata.These findings indicate that (i) there is no dopaminergic recurrent collateral axonal plexus in pars reticulata; (ii) the dopamine-storing compartment in the dendritic processes is not vesicular; the cisterns of the smooth endoplasmic reticulum might be such a compartment; (iii) The differentiation of presynaptic dendrites which establish typical junctional synaptic complexes does not occur in the dopaminergic dendrites present in pars reticulata; (iv) The proportion of presynaptic release sites observed in dopaminergic dendrites (1 active zone out of the 578 analyzed dendrites) is too low to account for the dendritic release revealed by biochemical analysis (Nieoullou, Chéramy &; Glowinski, 1977a). Therefore, the modality of transmitter release from dopaminergic dendrites must be different from that supposed in the vesicular theory; (v) combined anterograde degeneration and immunocytochemistry has allowed us to demonstrate a direct striatal input to the dopamine-containing dendrites present within the pars reticulata.     

Bilateral tectal projection of single nigrostriatal dopamine cells in the rat

Employing fluorescent retrograde double/triple labeling techniques, we found that a substantial population of substantia nigra pars reticulata cells send divergent axon collaterals to both the ipsilateral striatum and bilateral superior colliculi in the rat. These multi-collateralized neurons were localized predominantly in the ventrolateral portion of the substantia nigra pars reticulata at its rostral level. Furthermore, tyrosine hydroxylase immunofluorescence histochemistry combined with fluorescent retrograde tracing techniques showed that the vast majority (more than 85%) of such specifically branched cells are dopaminergic. This novel nigral cell population seems to be in a strategic position to evoke dopamine-mediated motor impairments (i.e. abnormal saccadic eye movements in Parkinsonism) and/or behavioral syndromes (i.e. compulsive turning behavior) through the GABA-containing nigrotectal pathway.     

Anticonvulsant role of nigrotectal projection in the maximal electroshock model of epilepsy--II. Pathways from substantia nigra pars lateralis and adjacent peripeduncular area to the dorsal midbrain.

Lesion evidence suggests that the superior colliculus is essential for mediating the anticonvulsant properties of nigral suppression in the electroshock model of epilepsy. However, our companion paper [Redgrave et al. (1991) Neuroscience 46, 379-390] established that the region of dorsal midbrain where bicuculline was most effective in suppressing tonic hindlimb extension did not correspond well with the known distribution of nigrotectal terminals. The purpose of the present anatomical study was, therefore, to investigate in more detail ventral midbrain connections to the dorsal midbrain anticonvulsant zone in rat. Small injections (10-20 nl) of a 1% solution of wheatgerm agglutinin conjugated with horseradish peroxidase were made specifically into the region of dorsal midbrain where bicuculline was maximally effective. Numerous retrogradely labelled cells were found in substantia nigra pars lateralis and adjacent peripeduncular area but not in substantia nigra pars reticulata. Retrogradely labelled cells were also located in ventral zona incerta. When wheatgerm agglutinin-horseradish peroxidase injections were made into lateral substantia nigra, a region of anterogradely transported reaction product characteristic of nerve terminals was observed in the caudolateral deep layers and underlying reticular tissue; this area corresponded well to the dorsal midbrain anticonvulsant zone. These data suggest that, in the electroshock model of epilepsy, direct connections between substantia nigra pars lateralis and adjacent peripeduncular area and the dorsal midbrain anticonvulsant zone could be critical for mediating the anticonvulsant properties previously attributed to substantia nigra pars reticulata. During the course of this study, anterograde projections from substantia nigra pars lateralis and adjacent peripeduncular area to both superficial and intermediate layers of the ipsilateral superior colliculus were noted. Additional experiments using retrograde transport of the fluorescent tracer Fast Blue confirmed these projections.     

Topographic distribution of the axonal endings from the sensorimotor and associative striatum in the macaque pallidum and substantia nigra

The striatopallidonigral connection was studied by injecting anterograde tracers into either the associative or the sensorimotor striatum in ten macaques. The results were analyzed using a precise cartographic method. Injections into various parts of the associative striatum (caudate nucleus and ventromedial putamen) produced a labeling of axons in the dorsomedial and ventral pallidal regions. These associative regions occupied two-thirds of the lateral pallidum and one-third of the medial pallidum. Bands of labeled axons from the sensorimotor striatum (dorsolateral putamen) were found in the remaining, central part of the two pallidal nuclei. In the substantia nigra, the rostral associative striatum projected medially to the pars reticulata, while the caudal parts projected laterally. The whole pars reticulata and lateralis thus appeared to receive associative striatal inputs. The sensorimotor striatal territory projected to the central part of the pars reticulata/lateralis. It was concluded that the two functional territories remain separate in the two pallidal nuclei but overlap in the middle third of the substantia nigra. However, due to their great size, the pallidal neurons located at the border of the two territories may receive striatal inputs from both the associative and the sensorimotor components in the same way that nigral neurons do.     

Cytoarchitecture of the substantia nigra in the rat

Midbrains of ten young adult rats were sectioned serially in three planes to study the detailed cytoarchitecture of the substantia nigra. These neurons measure 8 to 17 μ in diameter. In comparison, the largest neurons in the midbrain measure 20 to 40 μ; hence, neurons are designated according to size as follows: those measuring 18 to 40 μ, large; 12 to 17 μ, medium; and 8 to 11 μ, small. The substantia nigra of the rat contains non-pigmented neurons in three divisions: pars reticulata, pars compacta, and pars lateralis. The pars reticulata is the largest division and has the longest rostrocaudal extent. It contains neurons of small size medially and of medium size laterally. This finding correlates with described differences in connections. Three-dimensionally, the pars reticulata is an oblate spheroid with the long axis in the rostrocaudal plane. The pars compacta is a triangular layer dorsal to reticulata. It is subdivided into rostral and caudal portions at the level of the fibers of the basal optic root. Neurons in both subdivisions are medium in size, but cells rostrally are darker than those caudally. The pars lateralis is a column of neurons with its long axis located in the rostrocaudal plane. It lies dorsolateral to the pars reticulata and the pars compacta, with occasional connections to both by cellular strands. The pars lateralis has rostral and caudal portions; neurons rostrally are medium in size and round; caudally, however, neurons are variable in size, dark, stellate or fusiform, and have long processes.     

Separate neuronal populations of the rat substantia nigra pars lateralis with distinct projection sites and transmitter phenotypes.

The topographic organization of the nigral cells sending axons to the striatum, amygdala and inferior colliculus was studied in the rat substantia nigra pars lateralis by using retrograde fluorescent tracers. Nigral perikarya projecting to the inferior colliculus were located dorsolaterally within the substantia nigra pars lateralis, whereas nigral perikarya projecting to the striatum or to the amygdala were mostly situated ventromedially within the substantia nigra pars lateralis. The transmitter substances of the nigrotectal cells were examined by combining a retrograde tracing method with immunohistochemistry for tyrosine hydroxylase or glutamate decarboxylase. Nigral neurons projecting to the inferior colliculus lacked tyrosine hydroxylase immunoreactivity, but exhibited immunoreactivity for glutamate decarboxylase. The substantia nigra pars lateralis is made up of different neuronal populations: one projecting to the inferior colliculus and another directed to the striatum and amygdala. The pars lateralis pathway to the inferior colliculus utilized GABA as a neurotransmitter, whereas the previously characterized nigral cells projecting to the striatum and superior colliculus use GABA and dopamine as neurotransmitters.     

Topographical organization of the nigrotectal projection in rat: evidence for segregated channels.

Recent evidence suggests that projections from the superior colliculus to the brainstem in rat are organized into a series of anatomically segregated output channels. To understand how collicular function may be modified by the basal ganglia it is important to know whether particular output modules of the superior colliculus can be selectively influenced by input from substantia nigra. The purpose of the present study was, therefore, to examine in more detail topography within the nigrotectal system in the rat. Small injections (10-50 nl) of a 1% solution of wheatgerm agglutinin conjugated with horseradish peroxidase were made at different locations within substantia nigra and surrounding structures. A discontinuous puff-like pattern of anterogradely transported label was found in medial and caudal parts of the ipsilateral intermediate layers of the superior colliculus. In contrast, the rostrolateral enlargement of the intermediate layers contained a greater density of more evenly distributed terminal label. Injection sites associated with this dense pattern of laterally located label were concentrated in lateral pars reticulata, while the puff-like pattern was produced by injections into ventromedial pars reticulata. Retrograde tracing experiments with the fluorescent dyes True Blue and Fast Blue revealed that injections involving the rostrolateral intermediate layers were consistently associated with a restricted column of labelled cells in the dorsolateral part of ipsilateral pars reticulata. Comparable injections into medial and caudal regions of the superior colliculus produced retrograde labelling in ventral and medial parts of the rostral two-thirds of pars reticulata. Both anterograde and retrograde tracing data indicated that contralateral nigrotectal projections arise from cells located in ventral and medial pars reticulata. The present results suggest that the main ipsilateral projection from substantia nigra pars reticulata to the superior colliculus comprises two main components characterized by regionally segregated populations of output cells and spatially separated zones of termination. Of particular interest is the apparent close alignment between terminal zones of the nigrotectal channels and previously defined populations of crossed descending output cells in the superior colliculus. Thus, the rostrolateral intermediate layers contain a concentration of terminals specifically from dorsolateral pars reticulata and output cells which project to the contralateral caudal medulla and spinal cord. Conversely, the medial and caudal intermediate layers receive terminals from ventral and medial pars reticulata and contain cells which project specifically to contralateral regions of the paramedian pontine and medullary reticular formation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Direct projections from the central amygdaloid nucleus to the globus pallidus and substantia nigra in the cat.

Employing both anterograde and retrograde axonal tracing, we investigated direct projections from the central amygdaloid nucleus to the basal ganglia in the cat. The anterograde axonal tracing of Phaseolus vulgaris-leucoagglutinin revealed that projection fibers from the central amygdaloid nucleus to the basal ganglia ended in the globus pallidus (the feline homolog to the external segment of the globus pallidus of primates) and substantia nigra. The amygdalopallidal fibers terminated chiefly in the medial most part of the globus pallidus at its caudal level. The amygdalonigral fibers terminated densely in the substantia nigra pars lateralis, and moderately in the dorsolateral part of the substantia nigra pars reticulata; none of them were found to end in the substantia nigra pars compacta. Both of the amygdalopallidal and amygdalonigral projections were ipsilateral. These neuronal connections were confirmed by retrograde axonal tracing of cholera toxin B subunit in the second set of the experiments: The cells of origin of the amygdalopallidal and amygdalonigral projections were located predominantly in the lateral part of the central amygdaloid nucleus, and additionally in the intercalated cell islands of the amygdala. Most of them were of small bipolar or multipolar type. The cells projecting to the globus pallidus were preferentially distributed at the rostral levels of the central nucleus and intercalated cell islands of the amygdaloid complex, while those projecting to the substantia nigra were mainly located at the caudal levels of these amygdaloid subdivisions. In the third set of the experiments, sequential double-antigen immunofluorescence histochemistry for transported cholera toxin B subunit and horseradish peroxidase showed that some single neurons in the lateral part of the central amygdaloid nucleus, particularly at its middle level, issued axon collaterals to both the globus pallidus and substantia nigra pars lateralis. The results of the present study indicate that the central amygdaloid nucleus sends projection fibers to the globus pallidus and substantia nigra possibly to exert a limbic influence upon forebrain motor mechanisms.     

Organization of the striatal projections from the rostral caudate nucleus to the globus pallidus,the entopeduncular nucleus,and the Pars reticulata of the substantia nigra in the cat

This study explores the organization of the striatal projections from the rostral caudate nucleus to the output nuclei of the basal ganglia in the cat. Tracer deposits were stereotaxically injected in different dorsoventral, mediolateral, and rostrocaudal sectors of the head of the caudate nucleus using horseradish peroxidase (HRP) conjugated with wheat germ agglutinin (HRP-WGA) either alone or mixed with free HRP. After the injections, a detailed analysis of the terminal labeling was carried out within the globus pallidus (GP), the entopeduncular nucleus (Ep), and the substantia nigra (SN) pars reticulata (SNR). Our findings illustrate how different dorsoventral, mediolateral, and rostrocaudal parts of the rostral caudate nucleus project primarily to similarly positioned but spatially segregated parts of GP. The striatoentopeduncular pathway was also organized topographically, but there was overlapping by projections from different parts of the rostral caudate nucleus. Areas of topographical segregation and zones of overlap were detected in the organization of the striatal projections from the rostral caudate nucleus to SNR. These results raise the possibility of distinct striatal actions upon different sectors of the output nuclei of the basal ganglia and, indirectly, upon their targets in the thalamus and brainstem. © 1994 Wiley-Liss, Inc.     

Corticonigral projections from area 6 in the raccoon

Summary The corticonigral projections from area 6 in the raccoon were investigated using the autoradiographic tracing method. Injections of tritiated proline and leucine were made into either medial or lateral area 6 subdivisions. Uniformly distributed silver grains were observed overlying the ipsilateral substantia nigra pars compacta (SNc) while more restricted foci of label indicative of fiber labeling were present in the substantia nigra pars reticulata (SNr). Autoradiographic label was also present in the substantia nigra pars lateralis (SNl), the retrorubral area and the ventral tegmental area of Tsai. The existence of corticonigral projections from area 6 may serve to modulate SNc activity as a whole and provide an important substrate for the cerebral control of movement.Abbreviations cp cerebral peduncle - IP interpeduncular nucleus - PG pontine gray - R red nucleus - RR retrorubral area - SNc substantia nigra, pars compacta - SNl substantia nigra, pars lateralis - SNr substantia nigra, pars reticularis - VTA ventral tegmental area     

Topographic projections from the basal ganglia to the nucleus tegmenti pedunculopontinus pars compacta of the cat with special reference to pallidal projections

Summary Projections from the basal ganglia to the nucleus tegmenti pedunculopontinus pars compacta (TPC) were studied by using anterograde and retrograde tracing techniques with horseradish peroxidase conjugated with wheat germ agglutinin (WGA-HRP) in the cat. Following WGA-HRP injections into the medial TPC area, a substantial number of retrogradely labeled cells were seen in the entopeduncular nucleus (EP) and medial half of the substantia nigra pars reticulata (SNr), whereas following WGA-HRP injections into the lateral TPC area, labeled cells were marked in the caudal half of the globus pallidus (GP) and lateral half of the SNr. To confirm the retrograde tracing study, WGA-HRP was injected into the EP or the caudal GP, and anterograde labeling was observed in the TPC areas. Terminal labeling was located in the medail TPC area in the EP injection case, while terminal labeling was observed in the lateral TPC area in the caudal GP injection case. Projections from the striatum to the pallidal complex (the EP and the caudal GP) were also studied autoradiographically by injecting amino acids into various parts of the caudate nucleus and the putamen. Terminal labeling was distributed over the whole extent of the EP and the rostral GP following injections into the rostral striatum (the head of the caudate nucleus or the rostral part of the putamen), while terminal labeling was distributed over the caudal GP following injections into the caudal striatum (the body of the caudate nucleus or the caudal part of the putamen). From these findings, we conclude that there exists a medio-lateral topography in the projection from the basal ganglia to the TPC: The EP receives afferent projections from the rostral striatum and projects to the medial TPC area, whereas the caudal GP receives projections from the caudal striatum and sends fibers to the lateral TPC area.Abbreviations BC brachium conjunctivum - CD caudate nucleus - CP cerebral peduncle - DBC decussation of the brachium conjunctivum - EP entopeduncular nucleus - GP globus pallidus - IC internal capsule - ICo inferior colliculus - LH lateral habenular nucleus - ML medial lemniscus - PN pontine nuclei - PUT putamen - SCo superior colliculus - SI substantia innominata - SN substantia nigra - SNc substantia nigra pars compacta - SNr substantia nigra pars reticulata - STN subthalamic nucleus - TH thalamus - TPC nucleus tegmenti pedunculopontinus pars compacta     

The distribution and some morphological features of substantia nigra neurons that project to the thalamus,superior colliculus and pedunculopontine nucleus in the monkey

Neurons of the substantia nigra's pars reticulata that send axons to the thalamus, superior colliculus and midbrain reticular formation (including the pedunculopontine nucleus) have been revealed in monkeys by the technique of retrograde transport of horseradish peroxidase. The populations of nigrothalamic, nigrotectal and nigroreticular neurons differ from one another in their number, intranigral distribution and somatodendritic size and shape. Nigrothalamic cells are the most abundant and, although scattered throughout the mediolateral expanse of the pars reticulata, their numbers progressively diminish from rostral to caudal levels. Nigrotectal cells are least numerous and are restricted almost exclusively to the lateral margin of the rostral one-half of the pars reticulata. Nigroreticular cells, like nigrothalamic, are scattered throughout the mediolateral dimension of the nucleus, but are more commonly located at middle to caudal levels. In addition to their restricted intranigral location, the nigrotectal cells are larger, polygonal and have more major dendritic processes than the smaller nigrothalamic and nigroreticular cells which are usually triangular or fusiform. A small proportion of cells of all three types appears to project contralaterally.These findings indicate that the efferent organization of the primate pars reticulata differs markedly from that of the rodent¹⁸ and the monkey's nigrotectal cells constitute a spatially and morphologically distinct subpopulation within the pars reticulata. These data should be useful in understanding the functional organization of topographic inputs to the pars reticulata such as that from the neostriatum.     

Different neuronal location of [3H]SCH 23390 binding sites in pars reticulata and pars compacta of the substantia nigra in the rat

The precise neuronal localization of D1 receptors in the substantia nigra has been studied autoradiographically in the rat by measuring the alterations of [3H]SCH 23390 binding site densities in this brain area after 6-hydroxydopamine (6-OHDA) induced destruction of nigrostriatal dopaminergic neurons and after ibotenate-induced lesion of striatal afferents. 6-OHDA-induced nigral lesion provoked a total loss of [3H]SCH 23390 binding sites in the pars compacta and pars lateralis (but not in the pars reticulata) of the substantia nigra. In contrast, ibotenate-induced striatal lesion caused a large diminution of the [3H]ligand binding site density in the pars reticulata but not in the pars compacta and pars lateralis of the substantia nigra. These results suggest that D1 receptors in the pars compacta or pars lateralis of the substantia nigra are located on the dopaminergic perikarya whereas those D1 receptors present in the pars reticulata of the substantia nigra lie on the terminals of nigral afferents of striatal origin.