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This study explores whether near-infrared (NIr) light treatment neuroprotects dopaminergic cells in the substantia nigra pars compacta (SNc) and the zona incerta-hypothalamus (ZI-Hyp) from degeneration in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice. BALB/c albino mice were divided into four groups: 1) Saline, 2) Saline-NIr, 3) MPTP, 4) MPTP-NIr. The injections were intraperitoneal and they were followed immediately by NIr light treatment (or not). Two doses of MPTP, mild (50 mg/kg) and strong (100 mg/kg), were used. Mice were perfused transcardially with aldehyde fixative 6 days after their MPTP treatment. Brains were processed for tyrosine hydroxylase (TH) immunochemistry. The number of TH(+) cells was estimated using the optical fractionator method. Our major finding was that in the SNc there were significantly more dopaminergic cells in the MPTP-NIr compared to the MPTP group (35%-45%). By contrast, in the ZI-Hyp there was no significant difference in the numbers of cells in these two groups. In addition, our results indicated that survival in the two regions after MPTP insult was dose-dependent. In the stronger MPTP regime, the magnitude of loss was similar in the two regions ( approximately 60%), while in the milder regime cell loss was greater in the SNc (45%) than ZI-Hyp ( approximately 30%). In summary, our results indicate that NIr light treatment offers neuroprotection against MPTP toxicity for dopaminergic cells in the SNc, but not in the ZI-Hyp.

In contrast to the restricted receptive field (RF) properties of the ventral posteromedial nucleus (VPM), neurons of the ventral thalamus zona incerta (ZI) have been shown to exhibit multiwhisker responses that vary from the ventral (ZIv) to the dorsal (ZId) subdivision. Differences in activity may arise from the trigeminal nuclear complex (TNC) and result from subnucleus specific inputs via certain cells of origin, axon distribution patterns, fiber densities, bouton sizes, or postsynaptic contact sites. We tested this hypothesis by assessing circuit relationships among TNC, ZI, and VPM. Results from tracer studies show that, 1) relative to ZId, the trigeminal projection to ZIv is denser and arises predominantly from the principalis (PrV) and interpolaris (SpVi) subdivisions; 2) the incertal projection from TNC subnuclei overlaps and covers most of ZIv; 3) two sets of PrV axons terminate in ZI: a major subtype, possessing bouton-like swellings, and a few fine fibers, with minimal specialization; 4) both PrV and SpVi terminals exhibit asymmetric endings and preferentially target dendrites of ZI neurons; 5) small and large neurons in PrV are labeled after retrograde injections into ZI; 6) small PrV cells with incertal projections form a population that is distinct from those projecting to VPM; and 7) approximately 30-50% of large cells in PrV send collaterals to ZI and VPM. These findings suggest that, 1) although information to ZI and VPM is essentially routed along separate TNC circuits, streams of somatosensory code converge in ZI to establish large RFs, and 2) subregional differences in ZI response profiles are attributable in part to TNC innervation density.

The anterior pretectal nucleus (APT) and the zona incerta (ZI) are diencephalic nuclei that exert a strong inhibitory influence selectively in higher order thalamic relays. The APT is also known to project to the ZI as well as the thalamus, but anatomical details of the APT-ZI projection have not been described. In the present study, the efferent pathways of the APT were examined in the APT-ZI-thalamus network by using anterograde and retrograde tracing in combination with pre- and postembedding immunocytochemical stainings and in situ hybridization. The vast majority of APT fibers selectively innervated the parvalbumin-positive, ventral part of the ZI, which contains ZI neurons with axons projecting to higher order thalamic nuclei. The APT-ZI pathway consisted of both gamma-aminobutyric acid (GABA)-negative and GABA-positive components; 38.2% of the terminals in the ZI contained GABA, and 8.6% of the projecting somata in the APT were glutamic acid decarboxylase 67 (GAD67) mRNA positive. The combination of parvalbumin immunostaining with retrograde tracing showed that strongly and weakly parvalbumin-positive as well as parvalbumin-negative neurons were all among the population of APT cells projecting to the ZI. Similar heterogeneity was found among the APT cells projecting to the thalamus. Double retrograde tracing from higher order thalamic nuclei and their topographically matched ZI regions revealed hardly any APT neuron with dual projections. Our data suggest that both ZI and the higher order thalamic relays are innervated by distinct, physiologically heterogeneous APT neurons. These various efferent pathways probably interact via the rich recurrent collaterals of the projecting APT cells. Therefore, the powerful, GABAergic APT and ZI outputs to the thalamus are apparently co-modulated in a synergistic manner via dual excitatory and inhibitory APT-ZI connections.

We have examined the general ultrastructure of the posterior thalamic (Po) and parafascicular (Pf) nuclei of the dorsal thalamus, together with the ultrastructure of afferents to these nuclei from the zona incerta (ZI). The ZI of Sprague-Dawley rats was injected with biotinylated dextran (BD) by using stereotaxic coordinates, and the brains were prepared for routine BD histochemistry. The Po and Pf were then dissected free and processed for electron microscopy by using standard methods. A survey of the general ultrastructure of Po and Pf revealed many RS profiles (small with round vesicles) making asymmetric synapses around single, small (distal; 0.5–1.5 μm in diameter) or larger (proximal; 2–4 μm in diameter) dendrites. RL (large with round vesicles) and F type (pleomorphic vesicles) profiles, although sparse, were also observed. Single RLs were seen to envelope proximal dendrites and make asymmetric synapses that usually had a perforated appearance. F type profiles were seen to make symmetric synapses on proximal and sometimes distal dendrites. There were no profiles making synapses on other vesicle-filled profiles seen, reflecting the scarcity of interneurons in the Po and Pf of rats. Finally, BD-labeled terminal profiles from the ZI formed a homogeneous population within both the Po and Pf. They were small (1.1 ± 0.2 μm in diameter; n = 238), contained round vesicles, and made asymmetric synapses with proximal (∼75%) and, to a lesser extent, distal (∼25%) dendrites; they formed part of the RS population of the Po and Pf. In conclusion, our results indicate that the ZI imparts a presumably excitatory (asymmetric synapses) input of high efficacy (preference for proximal dendrites) to the Po and Pf of the dorsal thalamus. J. Comp. Neurol. 451:33–44, 2002. © 2002 Wiley-Liss, Inc.

The afferents to the red nucleus from visual and nonvisual forebrain centers have been investigated in the lizard Podarcis hispanica by using both retrograde and anterograde transport of tracers. Because the red nucleus constitutes a key structure in the limb premotor system, these sensory afferents probably are involved in visuomotor and other forms of sensorimotor integration. After tracer injections aimed at the red nucleus, retrograde labeling was found in the reticular thalamus, the subthalamus, the nucleus of the posterior commissure, as well as in two retinorecipient nuclei, namely, the ventral lateral and pretectal geniculate nuclei, where labeled cells are especially abundant. These geniculorubral projections have been confirmed by means of anterograde tracing with dextranamine injections. On the other hand, small injections of tracers in the retina demonstrated that its projections to the ventral lateral and pretectal geniculate nuclei are organized in a point-to-point fashion. Moreover, small tracer injections into the optic tectum of Podarcis indicated that the ventral lateral geniculate nucleus also receives a precisely organized tectal afferent. Taken together, these results strongly suggest that geniculorubral projections might constitute the neuroanatomical substrate for the generation of quick locomotor responses to appropriate visual stimuli. Additional ventral thalamic, subthalamic, and pretectal afferents to the red nucleus are likely to subserve other kinds of sensorimotor integration. These results help to clarify the organization of the reptilian motor system, including the telencephalic control of motor responses, and to unravel some of the major trends in the evolution of the limb premotor network of tetrapodian vertebrates. J. Comp. Neurol. 411:35–55, 1999. © 1999 Wiley-Liss, Inc.

This study explores the organisation and neurochemical nature of the projections from the zona incerta (ZI) to the basal ganglia. Sprague-Dawley rats were anaesthetised with ketamine (100 mg/kg) and Rompun (10 mg/kg), and injections of cholera toxin subunit B were made into each of the following nuclei: the ZI, the substantia nigra (SN), the pedunculopontine tegmental nucleus (PpT), and the entopeduncular nucleus (Ep). Brains were aldehyde fixed, sectioned, and processed using standard methods. Tracer-labelled sections were then doubly labelled with antibodies to glutamate (Glu), nitric oxide synthase (NOS), parvalbumin (Pv), or glutamic acid decarboxylase (GAD; the latter two are markers for GABAergic cells); these neurochemicals characterise most types of ZI cells. After ZI injections, labelling was nonuniform across the different basal ganglia nuclei. The bulk of labelling, both anterograde and retrograde, was seen in the SN and PpT and, to a lesser extent, within the other nuclei of the basal ganglia (e.g., caudate-putamen, globus pallidus, subthalamus, Ep). In the SN, labelling was found in both major parts of the nucleus, the pars compacta and pars reticulata. Within the PpT, however, the bulk of labelling was limited to only one of the two sectors of the nucleus, namely, the pars dissipata (PpTd). The pars compacta of the PpT (PpTc) remained largely free of labelled profiles. After CTb injections into three basal ganglia nuclei (SN, PpT, Ep), most labelled cells in the ZI were glutamate+ and very few were NOS+ or gamma-aminobutyric acidergic. Overall, the results indicate that the ZI is in a position to influence preferentially the activity of the SN and PpTd of the basal ganglia via an excitatory, glutamatergic input.

We have shown previously that the zona incerta (ZI), a small nucleus deriving from the ventral thalamus, has extensive ipsilateral connections with the higher order and intralaminar nuclei of the dorsal thalamus and that there are many ipsilateral interconnections between the different cytoarchitectonic sectors of the ZI. In this study, we explore the contralateral connections that the ZI has with its opposing nucleus as well as with the other nuclei of the thalamus. Injections of biotinylated dextran or cholera toxin subunit B were made into each of the different ZI sectors (rostral, dorsal, ventral, and caudal) and into intralaminar and higher order dorsal thalamic nuclei of Sprague-Dawley rats by using stereotaxic coordinates. Brains were fixed in aldehyde and processed using standard methods. Our results show that, after injections limited to a given ZI sector, labelled terminal-like elements and cells were seen across the other sectors of the ZI of the contralateral side. Furthermore, after each of these ZI injections, labelling was seen in the intralaminar (e.g., parafascicular, central lateral, and central medial) and higher order (e.g., posterior thalamic, lateral posterior, and lateral dorsal) nuclei of the contralateral side. These patterns of labelling were confirmed after tracer injections into intralaminar and higher order nuclei; after such injections, labelling was seen in the contralateral ZI. In all cases, there was labelling on the ipsilateral side as well, and this was generally heavier than on the contralateral side. Overall, our results indicate that there is a network of interconnections between the ZI of both sides of the thalamus and that the ZI has contralateral connections with the intralaminar and higher order nuclei. Hence, the ZI furnishes a substrate that spreads activity to both sides of the brain.

This work is a study of the distribution pattern of calbindin-D28k, calretinin, and parvalbumin in the diencephalic alar plate of a reptile, the lizard Psammodromus algirus, by using the prosomeric model (Puelles [1995] Brain Behav Evol 46:319-337), which divides the alar plate of the diencephalon into the caudorostrally arranged pretectum (p1), dorsal thalamus plus epithalamus (p2), and ventral thalamus (p3). Calbindin and calretinin are more extensively expressed in the dorsal thalamus than in the neighboring alar regions, and therefore these calcium-binding proteins are particularly suitable markers for delimiting the dorsal thalamus/epithalamus complex from the ventral thalamus and the pretectum. Conversely, parvalbumin is more intensely expressed in the pretectum and ventral thalamus than in the dorsal thalamus/epithalamus complex. Within the dorsal thalamus, calcium-binding protein immunoreactivity reveals a three-tiered division. The pretectum displays the most intense expression of parvalbumin within the diencephalon. Virtually all nuclei in the three sectors of the pretectum (commissural, juxtacommissural, and precommissural) present strong to moderate expression of parvalbumin. We compare the distribution of calcium-binding proteins in the diencephalon of Psammodromus with other vertebrates, with mammals in particular, and suggest that the middle and ventral tiers of the reptilian dorsal thalamus may be comparable to nonspecific or plurimodal posterior/intralaminar thalamic nuclei in mammals, on the basis of the calcium-binding protein expression patterns, as well as the hodological and embryological data in the literature.

Afferents from the zona incerta (ZI) of the ventral thalamus contribute to the dense, transient gamma-aminobutyric acid (GABA)ergic fiber plexus in layer 1 of the developing rodent somatosensory cortex. Incertocortical axons contact the distal apical dendrites of postmigratory cortical pyramidal cells. Although recent work has shown that these GABAergic incertocortical fibers are likely to provide widespread fast synaptic excitation of pyramidal cells in layers 2-6 during peak periods of cortical synaptogenesis, little is known about the mechanisms by which these axons project to the neocortex and are confined to layer 1. Here we characterize organotypic slice co-cultures in which a region of embryonic diencephalon containing the ZI is maintained adjacent to a region of embryonic somatosensory cortex. Diencephalic explants from transgenic mice expressing enhanced green fluorescent protein (EGFP) enabled direct visualization of diencephalocortical connections. Isochronic co-cultures exhibited diencephalocortical fiber ingrowth immunoreactive for both GABA and the presynaptic vesicle-associated protein synaptophysin that was restricted to neocortical layer 1. This pattern of lamina-specific diencephalocortical ingrowth occurred irrespective of placement of the afferent explant, and persisted in the absence of action potential activity and GABA(A) receptor activation. Heterochronic co-cultures containing older cortex demonstrated that the cortical explants remain permissive for lamina-specific ingrowth through the first postnatal week. Organotypic slice cocultures provide a system in which to study the mechanisms underlying the layer 1-specific ingrowth of extrinsic GABAergic inputs to the perinatal neocortex.

This study describes the organization and topography of the descending efferent projections from the monkey ventral pallidum. The main efferent projections from the globus pallidus are to the subthalamus, to the thalamus, and to the substantia nigra. Although these projections have been well established for the dorsal pallidum, the projections of the ventral pallidum have not been explored in primates. The results of this study add an important link in how information from the limbic lobe is channeled through the basal ganglia in monkeys. Anterograde tracers, Phaseolus vulgaris-leucoagglutinin, and tritiated amino acids were injected into various regions of the ventral pallidum. The descending efferent projection from the ventral pallidum in monkeys terminates primarily in the subthalamic nucleus and adjacent lateral hypothalamus, in the substantia nigra, and in the lateral habenular nucleus. Although terminals are also found in the thalamus, these are relatively sparse. The projections to the subthalamic nucleus and the lateral hypothalamus are topographically arranged, while those to the substantia nigra are not. These results suggest that pathways from distinct pallidal regions that receive specific striatal input terminate in distinct regions of the subthalamic/hypothalamic regions, thus maintaining a topographic arrangement. Projections to the substantia nigra, however, overlap extensively, suggesting convergence of terminals from different ventral pallidal regions. The relatively small projection to the thalamus raises the question that without a prominent thalamic projection, is this system parallel to that described for the dorsal globus pallidus?

Cytoarchitectonic atlas plates of the Macaca mulatta thalamus are presented in the sagittal plane of section with a revised nomenclature of the motor thalamic region. The proposed changes in nomenclature are based on the analysis of topographical relationships between nigral, pallidal, and cerebellar projections to the thalamus studied in 13 rhesus monkeys with the use of autoradiography technique. Mapping of the projection zones of these motor-related systems in serial sagittal sections revealed that they are completely segregated with each honoring cytoarchitectonic boundaries of specific nuclear subdivisions. The available data on thalamic connectivity together with the results of the present study allowed us to divide the primate “motor” thalamus into two major territories: (1) the ventral anterior region (VA) and (2) the ventral lateral region (VL). Although the designation of these two areas of the motor thalamus is the same as the classic one, the nuclear subdivisions that compose them differ significantly from those described in previous classifications. As is delineated in the maps, VA represents the basal ganglia territory of the motor thalamus where nigral projections coincide with its magnocellular part (VAmc), and pallidal projections occupy densicellular (VAdc) and parvicellular (VApc) subdivisions. VAdc corresponds closely to VLo of Olszewski; however, we prefer the new term in order to avoid possible conceptual confusions with the ventral lateral region (VL), which does not receive basal ganglia projections. The VL region is characterized as a distinct cytoarchitectonic entity of the motor thalamus that receives cerebellar projections and includes area X, VPLo, VLc, and VLps of Olszewski. The ventral medial region (VM in the present study or VLm in Olszewski terminology) is usually considered together with the basal ganglia territory on a common connectional basis. However, we did not obtain convincing data to support this view, since evidence of terminal labeling was observed only in (or around) fiber bundles passing through the nucleus with other areas free of label. Rather, in this study VM was treated as an intermediate zone between the subthalamus and motor thalamus where fiber bundles from basal ganglia and cerebellum are organized in a topographical manner before reaching their destinations in the VA and VL regions, respectively. Other major thalamic regions represented in the maps were delineated purely on cytoarchitectonic grounds and their traditional nomenclature was maintained. In this respect the present maps can be considered as a supplement to the available cytoarchitectonic atlases of the monkey thalamus since the latter lack sagittal Plates. Additionally, the present atlas is constructed within an intracerebral coordinate system that relies on anterior and posterior brain commissures as landmarks. Thus it can be used as a guide for stereotactic placements in the thalamus by means of a recently developed technique that utilizes contrast ventriculography for the visualization of these landmarks. The advantages of this stereotactic technique and its superior accuracy compared to the conventional stereotactic methods have been demonstrated earlier.

Both anatomical and physiological studies have shown that pause neurons (PNs) in the medial pontine reticular formation project to two groups of burst neurons (BNs) involved in the genesis of horizontal saccadic eye movements: The excitatory burst neurons (EBNs), which lie rostral to the abducens nucleus, and the inhibitory burst neurons (IBNs), which lie caudal to the abducens. This study is concerned with the projection from PNs to a group of vertical BNs in the nucleus of the H field of Forel (H FF) in the caudomedial subthalamus. Three anatomical methods were used to demonstrate this connection. First, intra-axonal horseradish peroxidase (HRP) injection into physiologically identified PN axons demonstrated axonal branching and axonal terminations in and around the H FF. Second, micro-injection of the tracer Phaseolus vulgaris leucoagglutinin (PHA-L) into the pontine PN region labelled terminal axons and boutons in the nucleus of the H FF. Third, extracellular pressure injection of HRP into H FF yielded retrogradely labelled pontine PN neurons. These anatomical results confirmed the termination of PNs in areas controlling rapid vertical eye movements as physiologically demonstrated by Nakao et al.: Exp. Brain Res. 70:632–636, (88). This work points to the major role of pontine PNs in the synchronization of BN activity in rapid eye movements in all directions.

Immunohistochemical methods were used to map the distribution of neurons exhibiting tyrosine hydroxylase-like immunoreactivity (TH) in the brainstem of the reptile Caiman crocodilus. The results reveal that many catecholamine systems previously described in mammalian and avian species are present in the brainstem of the caiman. Within the medulla, many immunoreactive neurons surround the central canal. This neuronal field extends rostrally to the level of the dorsal motor nucleus of the vagus. Many TH neurons overlap the region of the solitary nucleus, and an extensive system of fibers derived from these neurons extends ventrally and laterally into the region immediately bordering the descending nucleus of the trigeminal nerve Some TH neurons are also present in the ventrolateral tegmentum of the medulla at this level. A large number of TH cells are present in the pons and midbrain. These include the locus coeruleus, nucleus subcoeruleus ventralis, nucleus subcoeruleus dorsalis, substantia nigra (Brauth et al., '83), and area ventralis of Tsai. The subcoeruleus nuclei are considerably larger in the caiman than in other reptilian species including turtles and lizards and closely resemble the subcoeruleus nuclei of birds in terms of position and anterior-posterior extent. Within the diencephalon, numerous small, intensely staining, TH-immunoreactive and CSF-contacting neurons were observed within the preoptic recess and in close proximity to the ventricular wall at rostral hypothalamic and preoptic levels. Many intensely stained, immunoreactive cell bodies were observed in the medial hypothalamus similar in position to the A13 cell group of mammals. In the subthalamus, TH neurons completely surround the ventral peduncle of the forebrain bundle (which contains fibers of the ansa lenticularis) and extend into the ventromedial and ventrolateral thalamic areas. A rich plexus of TH-positive axons and terminals invests the external layer of the median eminence.

The ascending projections of the central gray substance and adjacent tegmentum in the rat and cat were studied with the Fink-Heimer (1967) modification of the Nauta method. Following lesions of the circumaqueductal gray, degeneration was traced along the dorsal longitudinal fasciculus of Schutz, a reciprocal association pathway between the central gray and the hypothalamus, into the dorsal and posterior hypothalamus, midline and intralaminar regions of the thalamus, and the zona incerta of the subthalamus. Another group of fibers travelled ventrally from the central grey to reach the ventral tegmental area of Tsai; some of these fibers continued rostrally to terminate in the lateral hypothalamus. Other fibers distributed to the midbrain tegmentum as components of Weisschedel's radiatio grisea tegmenti. Lesions which extended into the adjacent tegmentum produced a larger quantity of degeneration than did lesions confined to the central gray, but the patterns of degeneration were similar in both cases. The ascending projections of the central gray in the rat and cat were found to have similar distributions but were slightly more massive in the cat. No evidence of fiber degeneration was detected in the ventromedial hypothalamus. Negative results, however, must be interpreted with caution, for they may be due to an excessively small caliber of axons and/or peculiar modes of axon termination in hypothalamic tissue.

Times of final mitotic division for neurons of the epithalamic, dorsasl thalamic and subthalamic nuclei of the rat were determined with the aid of thymidine-H3 autoradiography. Intensely labelled neurons were observed in the brains of animals injected with radiochemical from days 13 to 19 of gestation. The pattern of distribution of the labelled neurons indicated that neurogenesis in these regions followed caudorostral, lateromedial and ventrodorsal neurogenetic gradients, all of which were found to operate simultaneously. Since neurogenesis in the epithalamus, subthalamus and caudolateral thalamic regions began on days 13 and 14 of gestation, the ventrodorsal and lateromedial proliferative gradients were clearly discerned only within the ventral and dorsal thalamus exclusive of the epithalamus. These directional neurogenetic gradients were apparent throughout the entire thalamus and within individual thalamic nuclei. No neurogenetic pattern based upon neuronal size was observed, i.e., large neurons were not preferentially formed earlier than smaller ones. Detailed information has also been provided on the cytological character of each thalamic nucleus.

The distribution and collateralization of ascending and descending projections from neurons in the nucleus tegmenti pedunculopontinus (PPN) were studied in the rat by using retrograde transport of HRP, HRP/WGA, and fluorescent dyes. The PPN and its two subdivisions, the subnucleus compactus (PPNc) and subnucleus dissipatus (PPNd), were delineated on sagittal Nissl-stained sections by using cytoarchitectural features as guidelines. Large bilateral pressure injections of HRP and/or fluorescent dyes into the cervical cord retrogradely labeled moderate numbers of fusiform and polygonal PPN cells which ranged in size between 65 and 390 microns2. The labeled cells were scattered throughout the PPNd and were somewhat more numerous in the medial half of the subnucleus. The PPNc contained only occasional labeled cells in its ventralmost portion. Following single unilateral HRP/WGA injections in the striatum, globus pallidus, entopeduncular nucleus, subthalamus, or the substantia nigra, the distribution of the labeled cells was similar to that of the spinal cord-projecting PPN neurons. Multiple HRP injections were then made bilaterally in the substantia nigra and the entopeduncular nucleus and/or subthalamus in order to label the entire population of PPN neurons projecting to the basal ganglia. In this case, not only the PPNd but also the PPNc contained a substantial number of retrogradely labeled cells. The rostrally projecting PPN cells outnumbered 5.4 times those projecting to the spinal cord, and their somata were somewhat larger, ranging between 114 and 472 microns2. While both fusiform and polygonal shapes were encountered, the polygonal cell somata were more numerous. In the double-labeling experiments, Granular Blue and Diamidino Yellow Dihydrochloride were injected into the cervical cord and the entopeduncular nucleus or subthalamus. In general, these experiments confirmed the extensive overlap of forebrain- and spinal cord-projecting neurons within the PPNd and the quantitative preponderance of ascending neurons. They also demonstrated that these two projection systems originate largely from separate cell populations since the double-labeled cells always composed less than 5% of the labeled neurons. The results confirm the existence of a direct PPN projection to the spinal cord. This pathway originates mainly in the PPNd and appears to be quantitatively weaker than the PPN projections to the forebrain. The spinal cord-projecting cells are not spatially segregated from the cells projecting to the basal ganglia, but they represent a separate population of the PPN projection neurons.

Anterograde tracers (tritiated leucine, proline, fucose; WGA-HRP) were injected into sites within the frontal eye fields (FEF) of nine macaque monkeys. Low thresholds (less than or equal to 50 microA) for electrically evoking saccadic eye movements were used to locate injection sites in four monkeys. Cases were grouped according to the amplitude of saccades evoked or predicted at the injection site. Dorsomedial prearcuate injection sites where large saccades were elicited were classified as lFEF cases, whereas ventrolateral prearcuate sites where small saccades were evoked were designated sFEF cases. One control case was injected in the medial postarcuate area 6. We found five descending fiber bundles from FEF; fibers to the striatum, which enter the caudate nucleus at or just rostral to the genu of the internal capsule; fibers to the claustrum, which travel in the external capsule; and transthalamic, subthalamic, and pedunculopontine fibers. Our results indicate that transthalamic and subthalamic pathways supply all terminal sites in the thalamus, subthalamus, and tegmentum of the midbrain and pons, whereas pedunculopontine fibers appear to terminate in the pontine and reticularis tegmenti pontis nucleus exclusively. Frontal eye field terminal fields in the striatum were topographically organized: lFEF projections terminated dorsal and rostral to sFEF projections. Thus, lFEF terminal fields were located centrally in the head and body of the caudate nucleus and a small dorsomedial portion of the putamen, whereas sFEF terminal fields were located in ventrolateral parts of the caudate body and ventromedial parts of the putamen. In the claustrum, lFEF projections terminated dorsal and rostral to sFEF projections. Projections from FEF terminated in ventral and caudal parts of the subthalamic nucleus without a clear topography. By comparison, terminal fields from medial postarcuate area 6 were located more caudally and laterally in the striatum and claustrum than projections from FEF, and more centrally in the subthalamic nucleus. In the thalamus, FEF terminal patches in some thalamic nuclei were also topographically organized. Projections from lFEF terminated in dorsal area X, dorsolateral medial dorsal nucleus, pars parvicellularis (MDpc), and the caudal pole of MDpc, whereas projections from sFEF terminated in ventral area X, medial dorsal nucleus, pars multiformis, and caudal medial dorsal nucleus pars densocellularis.(ABSTRACT TRUNCATED AT 400 WORDS)

The organization and projections of the presumed homologue of the mammalian corpus striatum, the ventrolateral area (VLA) of the telencephalon, were investigated in the reptile Caiman crocodilus. The caiman VLA was divided into two major cell fields on the basis of cytoarchitectonic criteria: a rostromedial small celled field (VLA s.c.) and a large celled field occupying the dorsal, lateral and ventrocaudal portions of the VLA (VLA l.c.). Histochemical results indicate that the VLA s.c. contains high levels of both cholinesterase and catecholamine (CA) activity. An intense lacy plexus of CA-containing axons and terminals was found in the VLA s.c. Far less CA activity was found within the VLA l.c. CA activity within the VLA appears to be derived primarily from axons of cells located within a large field of the midbrain tegmentum which is called in this report nucleus tegmenti pedunculo pontinus (TP). In the caiman the VLA also receives projections from the CA-positive cells of the locus ceruleus and from serotonin containing cells of the midline raphe system. Anatomical experiments indicate that the VLA L.C. receives projections from neurons in the VLA S.C. and projects upon these subtelencephalic cell groups: the anterior and posterior entopeduncular nuclei (ENa and ENp), the ventral lateral and ventral medial thalamic areas (Avl and Avm), the dorsal nucleus of the posterior commissure (nDCP), and TP. The VLA s.c. projects upon TP. ENa neurons project upon cells in the VLA l.c. Cells of Avl and Avm receive both paleostriatal and cerebellar projections; Avl neurons project upon portions of the rostral telencephalon external to the VLA. NDCP neurons project upon the optic tectum. The organization and projections of the VLA in Caiman crocodilus are compared to the organization and projections of the paleostriatal complex of the pigeon (Karten and Dubbeldam, '73; Brauth, Ferguson and Kitt, '78) and to the mammalian basal ganglia. The following paleostriatal characteristics appear to be common features in these species and may represent retained characteristics derived from the common ancestor: (1) an ascending catecholaminergic system derived from neurons in the midbrain tegmentum; (2) projections from the basal striatum upon the catecholamine containing neurons of the midbrain tegmentum; (3) an intrinsic cholinergic system; (4) projections upon thalamic cell groups which are also in receipt of cerebellar projections and which project upon telencephalic regions external to the paleostriatum; (5) reciprocal connections between the paleostriatum and the ventral or subthalamus; and (6) projections upon cell groups which project to the optic tectum. The results are discussed in terms of the overall role of the basal ganglia in the neural control of behavior.

Retinal projections to the thalamus and midbrain were studied by the Nauta-Laidlaw technique. After unilateral enucleation, degeneration was found in five areas: dorsal lateral geniculate nucleus (LGNd, thalamus), ventral lateral geniculate nucleus (LGNv, subthalamus), nucleus of optic tract (NOT, pretectum), superior colliculus (S.C., tectum), and accessory optic nuclei (AON, tegmentum). Degeneration after focal lesions in nasal retina made by photocoagulation is found in four areas of the contralateral LGNd: Laminae A and B, nucleus interlaminaris centralis (NIC), and the medial part of nucleus interlaminaris medialis (NIM). Temporal lesions lead to degeneration ipsilaterally in three areas: lamina A1, NIC, and the lateral part of NIM. Central lesions are followed by bilateral projections; the area of degeneration on each side is greater than that of peripheral lesions of comparable size. Focal degeneration is found in NIM after either central or peripheral retinal lesions. Each retina projects to both NOT and both S.C. In NOT, degeneration following nasal lesions is strictly contralateral while after temporal lesions is mainly ipsilateral. A bilateral projection of temporal retina to NOT constitutes an exception to theories of chiasmal decussation. Both nasal and temporal projections to AON are wholly crossed, thus constituting another example of projection of temporal retina to the contralateral side, Nasal fibers project contralaterally and nearly all temporal fibers ipsilaterally to S.C.

Fiber projections from the main sensory trigeminal nucleus and the supratrigeminal region (reticular formation dorsal and rostrodorsal to the motor trigeminal nucleus) in the cat and monkey have been studied by the Nauta, Fink-Heimer and Marchi methods. Following experimental lesions in the main sensory trigeminal nucleus and its vicinity, the crossed ventral and the uncrossed dorsal trigeminal tracts were traced rostrally to the posteromedial ventral nucleus of the thalamus. The uncrossed dorsal trigeminal tract ascended through Forel's tegmental fascicle (tractus fasciculorum tegmenti Foreli). However, Forel's tegmental fascicle was composed mainly of the ascending reticular fibers terminating in the intralaminar nuclei of the thalamus and in the subthalamus. Commissural components distributing chidfly to the motor trigeminal nucleus of the opposite side appeared to arise from the supratrigeminal region as well as from the main sensory trigeminal nucleus. A fiber bundle, arising from the reticular zones surrounding the motor trigeminal nucleus, descended through the lateral reticular formation immediately ventromedial to the spinal trigeminal nucleus down to lower levels of the medulla oblongata. The functional significance of the supratrigeminal region as an interneuron system intercalated between the trigeminal sensory and the cranial motor systems is discussed.

The central gustatory pathways of the albino rat have been traced using a combined electrophysiological-neuroanatomical technique. Gustatory responses in the medulla were recorded in the region of the solitary nucleus which receives the seventh nerve primary afferents. Fibers traced from lesions of these recording sites did not cross as expected into the medial lemniscus, but instead travelled rostrally to terminate ipsilaterally in a small celled area dorsal and ventral to the brachium conjunctivum as it enters the pons. Since gustatory responses could be recorded in this region it represents a previously undescribed secondary “pontine taste area.” Lesions of PTA result in degeneration of a bilateral ascending pathway travelling in the dorsomedial tegmentum to terminate in the classical gustatory nuclei of the thalamus. Other fibers in this pathway continue rostrally and distribute in the subthalamus, dorsolateral hypothalamus and subpallidal gray in the ventral forebrain. These findings in a mammal resemble those established nearly three quarters of a century ago by Herrick ('05) in the carp, and confirm his prediction that “broad lines of similarity [would be found] between both the peripheral and central gustatory paths in all vertebrates”.