The thalamostriatal projection in the cat.

The organization of the projections from the intralaminar and other thalamic nuclei to the caudate nucleus (CD), putamen (PU), nucleus accumbens (Acc), and olfactory tubercle (TO) were examined in the cat by autoradiography after deposits of 3H-amino acids in individual thalamic nuclei and by retrograde cell labeling after intrastriatal deposits of wheat-germ-conjugated horseradish peroxidase. All of the rostral intralaminar nuclei, here considered to include the central lateral (CL), paracentral (PC), central medial (CeM), and rhomboid nuclei (Rh), project to the striatum. Projections closely associated with those of the rostral intralaminar group arise from cells of the paraventricular nucleus (PV) and a region lateral to the stria medullaris. These nuclei, which roughly form a ring around the mediodorsal nucleus, project in a highly particular, but loosely arranged topographic pattern to all parts of the striatum. The medially located cells in Rh, PV, and those alongside the stria medullaris project mainly to medial parts of Acc and CD; the dorsolaterally located cells of CL project mainly to the dorsolateral parts of CD and PU; cells in PC and CeM project to progressively more ventral and medial parts of CD and PU, and the lateral part of Acc. Superimposed on this projection from the rostral intralaminar region is the projection from the caudal intralaminar group including the centromedian (CM), parafascicular (PF), and subparafascicular nuclei (subPF). Together these nuclei project in a loosely but specifically organized topography to the entire striatum. The lateral and dorsal parts of CD and PU receive fibers mainly from CM. Ventral and medial parts of CD and PU and Acc receive fibers mainly from PF; TO receives fibers from subPF and the ventral part of PF. Several nuclei in the lateral nuclear mass of the thalamus also project to particular parts of the striatum. Thus, cells in the rostromedial part of the ventral anterior nucleus project to the head of CD and some cells in the rostral part of the ventromedial nucleus project to the head of CD and to PU. Several cells scattered in the lateral posterior complex project to lateral parts of the head of CD, and cells in the rostral extension of the medial subdivision of the posterior nuclear complex project to lateral parts of the head and body of CD. Finally, several cells of the paratenial nucleus project selectively to Acc. These data provide a detailed map of the total thalamostriatal projection in the cat and, hence, form a basis for more specific functional questions about this poorly understood system.

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. 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.

Efferent connections of the substantia nigra and ventral tegmental area in the rat.

Small injections of tritiated leucine and proline confined to the ventral tegmental area (AVT) were found to label fibers ascending: (a) to the entire ventromedial half of the striatum, but most massively to the ventral striatal zone that includes the nucleus accumbens; (b) to the thalamus: lateral habenular nucleus, nuclei reuniens and centralis medius, and the most medial zone of the mediodorsal nucleus; (c) to the posterior hypothalamic nucleus and possibly the lateral hypothalamic and preoptic region; (d) to the nuclei amygdalae centralis, lateralis and medialis; (e) to the bed nucleus of the stria terminalis, the nucleus of the diagonal band, and the medial half of the lateral septal nucleus; (f) to the anteromedial (frontocingulate) cortex; and (g) to the entorhinal area. Further AVT efferents descend to the medial half of the midbrain tegmentum including an anterior region of the median raphe nucleus, to the ventral half of the central grey substance including the dorsal raphe nucleus, to the parabrachial nuclei, and to the locus coeruleus. Similar injections centered in the pars compacta of the substantia nigra (SNC) label fibers that are distributed in the striatum in an orderly medial-to-lateral arrangement, and almost entirely avoid the nucleus accumbens and olfactory tubercle. With the exception of the lateral quarter of the substantia nigra, which apparently does not project to the extreme rostral pole of the striatum, each small SNC locus, regardless of its anteroposterior localization, distributes nigrostriatal fibers throughout the length of the striatum. Descending SNC efferents are distributed to the same general regions that receive descending AVT projections, except that no SNC fibers appear to enter the locus coeruleus. Isotope injections confined to the pars reticulata (SNR) label sparse nigrostriatal fibers, and numerous nigrothalamic fibers ascending mainly to the nucleus ventromedialis and in lesser number to the parafascicular nucleus and the paralamellar zone of the nucleus mediodorsalis. Descending SNR fibers leave the nigra as a voluminous fiber bundle that bifurcates into a large nigrotectal and a smaller nigrotegmental component, the latter terminating largely in the pedunculopontine nucleus of the pontomesencephalic tegmentum.

Afferent connections of the entorhinal area in the rat as demonstrated by retrograde cell-labeling with horseradish peroxidase.

The entorhinal cortex (EC) of the rat has been divided into medial (MEA) and lateral (LEA) subdivisions. In order to analyze its afferent connections, small deposits of horseradish peroxidase (HRP) were placed at various loci within EC. The patterns of retrograde cell-labeling charted in 18 such cases suggested that EC is projected upon by several allocortical and subcortical structures and that there are differences in the afferent connections of the two subdivisions. Thus, although HRP injection of either division of EC led to cell-labeling in the hippocampal formation, most in ammonic field CA1 and the subiculum, several cells of the presubiculum were preferentially labeled by injection of MEA. Injections of LEA, but not those in MEA, resulted in substantial cell-labeling in the anterior piriform cortex of both hemispheres. Regardless of the location of its injection site within EC, the enzyme labeled cells in the diagonal band nucleus of Broca, amygdala and claustrum. The pattern of cell-labeling in the diagonal band nucleus extended into the ventrolaterally contiguous nucleus basalis after injection of LEA and into the dorsally contiguous medial septal nucleus after injection of MEA Whereas HRP deposits in either division of EC resulted in cell-labeling in the cortical and medial nuclei of the amygdala, only those deposits which involved LEA led to cell-labeling in the posterior part of the lateral nucleus. In the thalamus, labeled cells were found in the rostral part of the paratenial, periventricular and reuniens nuclei. Finally, at midbrain levels, numerous labeled cells appeared in the dorsal raphe nucleus, a few in the median raphe and locus coeruleus, and, only after rostral EC injection, in the ventral tegmental area.