Immunoreactivity for GAD and three peptides in somatosensory cortex and thalamus of the raccoon.

Immunocytochemical methods were used to determine the distributions of glutamic acid decarboxylase (GAD), vasoactive intestinal polypeptide (VIP), cholecystokinin (CCK), and somatostatin (SOM) in the primary somatosensory cortex and somatosensory thalamus of adult raccoons. The cortex showed extensive immunoreactivity for GAD, revealing a large population of GABAergic neurons. GAD-labeled cells were numerous in all cortical layers, but were most concentrated in laminae II-IV. The cells were nonpyramidal and of varying morphology, typically with somata of small or medium size. GAD-immunoreactive puncta, presumably synaptic terminals, were widespread and often appeared to end on both GAD-negative and GAD-positive neurons. Immunoreactivity for the peptides was much less extensive than that for GAD, with the number of labeled neurons for VIP > CCK > SOM. Peptidergic cells were preferentially located in the upper and middle cortical layers, especially laminae II and III. The cells were nonpyramidal, often bitufted or bipolar in morphology, and small to medium in size. Their processes formed diffuse plexuses of fibers with terminal-like varicosities that occasionally surrounded nonpeptidergic neurons. The thalamus showed a clearly differentiated pattern of immunoreactivity for GAD, but little or no labeling for the three peptides. Nuclei adjoining the ventral posterior lateral (VPL)/ventral posterior medial (VPM) complex--including the reticular nucleus--contained many GAD-positive neurons and fibers. In contrast, the VPL and VPM nuclei displayed considerably less GAD immunoreactivity, somewhat surprising given the raccoon's highly developed somatosensory system. However, the ventral posterior inferior (VPI) nucleus revealed rather dense GAD labeling, perhaps related to a specialized role in sensory information processing. Thus, the primary somatosensory cortex of the raccoon showed patterns of immunoreactivity for GAD and peptides that were similar to those of other species; the somatosensory thalamus revealed a distinctive profile of GAD immunoreactivity, with labeling that was light to moderate in the VPL/VPM complex and relatively extensive in VPL.

Immunoreactivity for glutamic acid decarboxylase and several neuropeptides in the spinal cord of the raccoon.

The peroxidase-antiperoxidase method was used to examine major immunohistochemical features of the spinal cord of adult raccoons. The lateral portions of the ventral horn contained many large multipolar neurons that showed cholecystokinin-like immunoreactivity, suggesting the coexistence of cholecystokinin with acetylcholine in a subset of motoneurons. The dorsal horn revealed unique but overlapping patterns of immunoreactivity for glutamic acid decarboxylase, somatostatin, substance P, vasoactive intestinal polypeptide and cholecystokinin. The data imply that some of the peptides may coexist within the same dorsal root ganglion cells and their spinal cord processes.

Projections from cortical area SmII and claustrum to two functional subdivisions of SmI forepaw digit cortex of the raccoon.

The retrograde HRP tracer method was used to study the projections from cortical area SmII and the claustrum to two electrophysiologically defined, functionally distinct subdivisions of the SmI forepaw cortex of the raccoon. Individual SmI cortical digit zones were found to receive ipsilateral projections from SmII and immediately adjoining cortical regions; the projections to the "heterogeneous" (hairy skin and claw) functional subdivision of a given digit zone were considerably more extensive than those to the glabrous skin functional subdivision of that zone. HRP-filled neurons within SmII were located primarily in layers VI and V, often formed clusters, and were distributed antero-posteriorly in a manner consistent with a loosely topographic representation of the digits. The SmI cortical digit zones received ipsilateral projections from approximately the middle 1/3 of the anterior-posterior extent of the insular claustrum; no clear difference was found in the projections to the two functional subdivisions of a given digit zone. Labeled neurons were typically scattered throughout much of the claustrum but were more numerous in its dorsal regions, tended to aggregate in clusters, and were distributed antero-posteriorly in an overlapping but roughly topographic fashion.

Thalamic connections of two functional subdivisions of the somatosensory forepaw cerebral cortex of the raccoon.

The purpose of this study was to compare the thalamic interconnectivities of 2 functionally distinct subdivisions of the somatosensory (Sml) forepaw cortex of the raccoon--the somatotopic subdivision representing the glabrous skin of the digits and the more heterogeneous subdivision representing the hairy skin and claws. Injections of HRP were made into one or the other functional subdivision of a specific digit subgyrus of Sml cortex in 10 adult raccoons. The distribution of HRP-labeled neurons and axon terminals in the thalamus revealed that the 2 sectors have different patterns of thalamic projections. The glabrous skin region of each cortical digit zone was interconnected with a specific crescent-shaped lamella of neurons that extended rostrocaudally through the ventral posterior lateral (VPL) nucleus and typically was separated from adjacent lamellae by small bundles of myelinated fibers. The VPL lamellae constituted relatively distinct digit subnuclei that were connected somatotopically with the glabrous subdivisions of the corresponding cortical digit areas. The projections were dense, topographic, and reciprocal; labeled neurons and axon terminals within a particular lamella overlapped considerably and tended to be arranged in clusters. In contrast, the heterogeneous region of each cortical digit zone was reciprocally connected with the somatotopically appropriate VPL digit subnucleus and with adjoining subnuclei as well. The projections were comparatively sparse, less topographic, and more widely distributed than those of the glabrous skin sectors; groups of HRP-positive neurons and terminals in VPL tended to straddle the borders of the appropriate lamella and extended into adjacent lamellae. Furthermore, small clusters of labeling were found in the dorsal, presumed kinesthetic region of VPL and in portions of the ventral posterior inferior nucleus and the posterior nucleus. These results indicate that the glabrous cortical subdivisions have precise, somatotopically organized connections with specific VPL subnuclei, whereas the heterogeneous cortical subdivisions have more diffuse and scattered connections with several subregions of VPL and other thalamic nuclei as well. These 2 thalamocortical projection patterns may account for many of the differing functional properties of neurons residing within the 2 cortical sectors. Finally, the convergent thalamic projections to the heterogeneous cortical regions could contribute, at least indirectly, to the functional reactivation that occurs within Sml cortex of the raccoon following peripheral nerve transection (Kelahan and Doetsch, 1984).

Intracortical connections of two functional subdivisions of the somatosensory forepaw cerebral cortex of the raccoon.

The aim of this study was to compare the intrinsic intracortical connectivities of 2 functionally distinct subdivisions of the somatosensory (Sml) forepaw cortex of the raccoon--the somatotopic glabrous skin representation and the more heterogeneous, hairy skin and claw representation of the digits. HRP was injected into one or the other functional subdivision of a particular digit subgyrus of Sml cortex in 10 adult raccoons. The distribution of HRP-labeled neurons and axon terminals in the cortex showed that intrinsic "horizontal" connections exist within and between individual cortical digit zones; the labeling tended to have an oval-shaped configuration that was longer in the mediolateral than in the anteroposterior curvilinear plane. The 2 cortical sectors were found to have different patterns of intracortical projections. The connections of the glabrous skin region of each cortical digit zone were primarily local and confined to that same digit representation. HRP-filled neurons were concentrated near the injection site and decreased in density within the banks and fundi demarcating the injected digit subgyrus; few labeled cells were found in adjoining digit zones. Longer projections to the glabrous subdivision of a particular digit area typically originated from neurons in the heterogeneous subdivision of that same digit area. In contrast, the connections of the heterogeneous region of each digit zone were much more extensive and usually included projections from nonadjacent, as well as neighboring digit zones. The density of HRP-positive neurons declined more gradually with distance from the injection site, and considerable labeling was present in the heterogeneous sectors of adjacent digit zones. The intracortical projections of both functional subdivisions were often, but not always, reciprocal, and the cells of origin tended to be distributed in clusters. The laminar distributions of labeled neurons were similar for both sectors; HRP-filled cells were concentrated more in the supragranular layers, especially in layer III; fewer were found in the infragranular layers, mainly in layer VI and rarely in layer V. These results show that the intrinsic connections of the glabrous cortical subdivisions are fairly localized, whereas those of the heterogeneous cortical subdivisions are more diffuse and highly convergent. The differing intracortical connectional patterns of the 2 sectors are consistent with their contrasting thalamocortical projection patterns and may contribute to the unique functional properties of neurons located within each sector.(ABSTRACT TRUNCATED AT 400 WORDS)

An investigation of collateral projections of the dorsal lateral geniculate nucleus and other subcortical structures to cortical areas V1 and V4 in the macaque monkey: a double label retrograde tracer study.

Previous anterograde studies in the macaque monkey have shown that, in addition to the projection to striate cortex (V1), the dorsal lateral geniculate nucleus (DLG) has a sparse, horizontally segregated projection to layers IV and V of prestriate cortex (V4). However, the distribution and degree of axon collateralization of DLG cells which give rise to these projections are unknown. This study was designed to answer these questions. The DLG (along with the pulvinar and other subcortical regions) was examined for the presence of single- or double-labeled cells after injections of two different (fluorescent or HRP) retrograde tracers into corresponding retinotopic points in visual cortical areas V1 and V4. In the DLG, it was found that cells projecting to V4, which reside in or near the tectorecipient interlaminar zones of the DLG, do not project to V1 and thus represent a separate population of cells. The organization of the macaque geniculo-prestriate projection thus seems quite different from that of carnivores. Both single- and double-labeled cells were found in other subcortical areas, e.g., single-labeled cells were found in the claustrum, hypothalamus and lateral pulvinar, and a double-labeled cell population was found in the inferior pulvinar.

Histochemical and architectonic differentiation of zones of pretectal and collicular inputs to the pulvinar and dorsal lateral geniculate nuclei in the macaque.

The pattern of acetylcholinesterase (AChE) reactivity was studied in the pulvinar and dorsal lateral geniculate nucleus (DLG) of the adult macaque monkey. Discrete islands of AChE reactivity were found that correlated precisely in location with the pattern of projections from the superior colliculus and pretectum. Specifically, AChE overlies terminal fields of superior colliculus projections in the DLG, in four foci in the medial and lateral pulvinar, and in several foci in the inferior pulvinar. All of these tectal projection areas have very high AChE reactivity such that they are easily distinguished. In addition, the pretectum projects to a specific focus in the lateral pulvinar that also has a very dense AChE histochemical reaction. A number of these AChE foci could be further distinguished from other areas in the pulvinar by myeloarchitectonic characteristics. Some of the foci in the lateral and inferior pulvinars could also be distinguished by unique cytoarchitectonic features (as seen with both Nissl and Golgi stains). In an attempt to determine the possible origin of a cholinergic input to the pulvinar, horseradish peroxidase (HRP) injections and choline acetyltransferase immunohistochemistry were also done. The results of this experiment indicate that the AChE reactivity seen in the midbrain projection zones to the thalamus may be due to the precise overlap of terminal projections from the brainstem cholinergic cell groups, Ch5, Ch6, and Ch8. These results, taken together, imply that there are several anatomically and histochemically distinct zones related to extrageniculate pathways located within classically defined thalamic boundaries.

The organization of connections between the pulvinar and visual area MT in the macaque monkey.

Injections of horseradish peroxidase were placed in visual area MT which is located in the superior temporal sulcus of the macaque monkey occipital cortex. Overlapping retrogradely filled cells and anterogradely transported terminal grains were found to be located only within a crescent shaped region which traverses the brachium of the superior colliculus to include the inferior pulvinar and dorsal overlying lateral pulvinar. The connections between MT and the pulvinar crescent are reciprocal and topographically organized, with the lower visual field represented dorsally and the upper visual field represented ventrally. There is an expanded representation of central vision located caudally within the crescent while peripheral vision is represented rostrally. These findings indicate that any functional properties derived from the visual thalamus must arise from this crescent shaped region of the pulvinar.

Thalamocortical coupling and component properties of visually evoked afterdischarge.

Dorsal lateral geniculate nucleus (dLGN) multiple-unit activity (MUA) and single visual evoked responses (VER) followed by afterdischarge (AD) were examined in lightly restrained albino rats. It was found that VER AD spike components are initially quite prominent, exceeding at times the amplitude of the broad surface negative wave components. As VER AD progresses toward termination spike amplitude systematically declines. Wave amplitude, however, remains relatively stable until spike components disappear. Averaged dLGN MUA and VER AD responses to photic stimuli suggest the existence of a precise time-locked relationship between peak dLGN MUA and VER AD spike components. It is proposed that thalamic and cortical mechanisms sustaining VER AD bursting might be operative during sensory information ;processing, serving to sustain neural activity functionally related to stimulus input.

Visual cortical hypersynchronous bursting as an index of shifts in behavioral state.

Photically evoked after-discharge (PhAD) bursting was examined in lightly restrained albino rats during habituation of a leg flexion response. The initial effect of iterative footshock (200 trials, 0.17 mA, 2.5 msec duration, separated by 1.0 sec) was to block PhAD bursting. As response habituation developed PhAD reappeared at reduced levels, subsequently returning to control levels as habituation progressed and became complete. The number of spindles per PhAD burst was suppressed for a brief period which coincided with response sensitization. These results are interpreted as demonstrating that phasic shifts in behavioral state are reflected by PhAD parameters. In addition, the possible relationship between cortical information processing and PhAD bursting is discussed with reference to putative neural mechanisms involved.