The rat parvocellular reticular formation: I. Afferents from the cerebellar nuclei.

The present report elucidates the location of the cells of origin of the cerebellar nuclear-parvocellular reticular projection in the rat. Injection of horseradish peroxidase (HRP) into the parvocellular reticular formation resulted in labeled neurons in the dorsolateral protuberance of the contralateral medial nucleus and bilaterally in the dorsolateral hump region and the large celled subgroup of the lateral nucleus. A small number of labelled cells were found in the middle part of the contralateral medial nucleus. The few HRP-positive cells in the interpositus nuclei were adjacent to the dorsolateral hump. No labeled neurons were observed in the caudomedial portion of the medial nucleus or the small-celled region of the lateral nucleus.

Immunocytochemical localization of glutamic acid decarboxylase (GAD) and glutamine synthetase (GS) in the area postrema of the cat. Light and electron microscopy.

The present study was designed to investigate the existence of two key enzymes involved in the metabolism of gamma-aminobutyric acid, glutamic acid decarboxylase (GAD) and glutamine synthetase (GS), in the area postrema (AP) of the cat. The results showed that punctuate structures of variable size corresponding to axon terminals, exhibited GAD-immunoreactivity and were distributed in varying densities. The greatest accumulation was present in the caudal and middle segment of the AP and particularly in the area subpostrema, where the aggregation of terminals was extremely dense. The population of the GAD-labelled axon profiles gradually decreased toward the solitary complex. No neuronal bodies were labelled in our preparations. The electron microscopic studies revealed a large variety of contacts between labelled terminals and unlabelled dendrites, axons or neurons. The possibility that the GAD-immunoreactive terminals might correspond to vagal afferent projections was discussed on the basis of our observations and of other studies that employed horseradish peroxidase or degeneration methods. GS-immunoreactivity was seen in ependymoglial cells of the AP, particularly toward the caudal region, and in astrocytes and their processes of the AP proper. The latter were frequently observed around capillaries. The presence of both GAD-immunoreactive profiles and GS-immunostained ependymoglial cells and astrocytes in the AP, provided further immunocytochemical evidence of the functional correlation between the two enzymes.

Axoglial contacts in the area postrema of the cat: an ultrastructural study.

Axoglial contacts were observed in an ultrastructural study of the area postrema of the cat. According to the disposition of the electron-dense projections attached to the adjoining membranes these contacts were classified as symmetrical or asymmetrical. The axon profiles contained aggregations of clear vesicles randomly distributed or grouped in cluster adjacent to the electron-dense projections. Dense core vesicles were occasionally seen. The neuroglial profiles were either astrocytic or ependymoglial in nature. The astrocytes showed a clear cytoplasm, polymorphous vesicles, mitochondria, glycogen granules, and bundles of filaments. The ependymal cells, in contrast, had a more electron-dense and granular appearance, tubular structures, irregular vesicular formations, profiles of smooth reticuloendoplasm, and filaments grouped in bundles or isolated in the cytoplasm. The possibility that these contacts might play a role in the chemical transfer from neurons to glial cells is discussed on the basis of existing biochemical data.

Dual efferent projections of the trigeminal principal sensory nucleus to the thalamic ventroposteromedial nucleus in the squirrel monkey.

Anterograde degeneration methods demonstrated two efferent components from the trigeminal principal sensory nucleus (PrV) to the thalamic ventroposteromedial nucleus (VPM) in the squirrel monkey: fibers from the dorsal PrV coursed within the central tegmental tract and terminated in a dorsoventromedial strip of the ipsilateral VPM; fibers from the ventral PrV mainly decussated caudal to the interpeduncular nucleus and terminated in the contralateral VPM exclusive of the sector receiving the dorsal PrV component, contralaterally. Adjacent Nissl sections showed an apparent increase in glial profiles accompanying an intense somal staining among the deafferented neuronal population in the VPM, coextensive with those regions in the VPM exhibiting terminal field degeneration.

Autopsy analysis of the safety, efficacy and cartography of electrical stimulation of the central gray in humans.

Electrical brain stimulation is effective in controlling certain intractable chronic pain syndromes in humans, but the specific target site(s) for stimulation producing a maximal analgesic effect is (are) not well defined. This prospective study correlates the clinical results of chronic stimulation of the periaqueductal gray (PAG) and periventricular gray (PVG) matter in humans with the anatomic site of electrode placement as determined at autopsy, and documents the histologic reactions to electrode implantation and electrical stimulation of the area. Seven patients underwent electrode implantation to control their chronic pain; two had electrodes implanted bilaterally. All patients obtained complete analgesia with stimulation, although 3 subsequently found the stimulation to have diminished efficacy. The opiate antagonist naloxone reversed the analgesia in the 4 patients so tested. All 7 patients later died of causes unrelated to electrode implantation or stimulation. Postmortem analysis showed that, for 6 of the 9 electrodes implanted, the electrode tip was located in the ventrolateral PAG at the level of the posterior commissure; the other 3 electrodes were found in the white matter adjacent to the PAG. No evidence of gliosis or parenchymal reaction was observed along the tracts and tips of the electrodes. The results indicate that the ventrolateral PAG and PVG matter at the level of the posterior commissure is the optimal site for therapeutic electrical brain stimulation for opiate-responsive pain in humans.

Immunocytochemical localization of glial fibrillary acidic protein (GFAP) in the area postrema of the cat. Light and electron microscopic study.

Glial fibrillary acidic protein (GFAP) was demonstrated in the cytoplasm and processes of ependymal cells and astroglial components of the area postrema of the cat. These observations differ from the findings in the ependyma of the ventricular cavities which are consistently negative for the protein. Since some studies have suggested sensory functions of the glial cells in this emetic chemoreceptor trigger zone, a careful consideration of morphological and biochemical attributes of these cells seems appropriate.

The intrinsic organization of the vestibular complex: evidence for internuclear connectivity.

The HRP anterograde and retrograde labeling techniques provide evidence for extensive internuclear connectivity within the vestibular complex. Specifically: (1) the superior vestibular nucleus is topographically and reciprocally related to the spinal (spr) and medial vestibular nuclei (mv); (2) the lateral vestibular nucleus (lv) is reciprocally related to the mv, and (3) the lv receives afferent fibers from the spv but does not reciprocate this input.

Observations on the connectivity of the parvicellular reticular formation with respect to a vomiting center.

The intrinsic and extrinsic connections of the parvicellular reticular formation (PCRF) that have been demonstrated by fiber degeneration studies and studied by more recently introduced horseradish peroxidase retrograde cell labeling are reviewed in an attempt to delimit the connectivity of the region in the PCRF where electrical stimulation produced emesis. Evidence is presented that certain specific functional subdivisions in PCRF such as the salivatory nuclei and the cells which give rise to the vestibular efferent projections can be delimited. An attempt is made to differentiate the sources of brain stem afferent connections with the nucleus of the tractus solitarius, the vagal nucleus and the nucleus ambiguus complex. The literature bearing on the histochemistry of the brain stem is reviewed in a search for clues to possible unique histo- or immunochemical cytological subdivisions in the parvicellular reticular formation.

The basal ganglia-circa 1982. A review and commentary.

Our review has shown that recent studies with the new anterograde and retrograde axon transport methods have confirmed and extended our knowledge of the projection of the basal ganglia and clarified their sites of origin. They have thrown new light on certain topographic connectional relationships and revealed several new reciprocal connections between constituent nuclei of the basal ganglia. Similarly, attention has been drawn to the fact that there have also been many new histochemical techniques introduced in recent years that are now providing regional biochemical overlays for connectional maps of the central nervous system, especially regions in, or interconnecting with, the basal ganglia. However, although these new morphological biochemical maps are very complex and technically highly advanced, our understanding of the function controlled by the basal ganglia still remains primitive. The reader who is interested in some new ideas of the functional aspects of the basal ganglia is directed to Nauta's [88] proposed conceptual reorganization of the basal ganglia telencephalon and to Marsden's [72] more clinically orientated appraisal of the unsolved mysteries of the basal ganglia participation in the control of movement.

A comparative study of the neurons of origin of the spinocerebellar afferents in the rat, cat and squirrel monkey based on the retrograde transport of horseradish peroxidase.

The cell bodies of the neurons of the spinocerebellar pathways were examined using large injections of horseradish peroxidose into the cerebellum. Sections of each spinal segment were examined with both the DAB and the de Olmos O-dianisidine techniques. Results common to all three species were found. In Clarke's nucleus, the central cervical nucleus, and the spinal border cells there were many heavily labeled cells. Clarke's nucleus was found to project primarily ipsilaterally; the spinal border cells primarily contralaterally; and the central cervical nucleus bilaterally. In addition to these aggregates of spinocerebellar neurons there were numerous labeled neurons scattered throughout the spinal grey. Labeled neurons were found in all portions of the spinal grey except the substantia gelatinosa and lateral cervical nucleus and occurred in all spinal segments. They varied in morphology from large multipolar neurons, found predominantly in the ventral horn to small globular and fusiform neurons that were most abundant in the dorsal horn. These cells were found to project both ipsilaterally and contralaterally. Results common to only two of the species examined were also found. In the dquirrel monkey and the cat, but not the rat, the marginal layer of the dorsal horn in all segments of the spinal contained numerous labeled neurons. These marginal neurons were especially numerous in the squirrel monkey, where as many as 13 to 16 labeled neurons per section of the dorsal horn were found. In the rat and the squirrel monkey but not the cat, some intensely labeled large multipolar neurons were found in the sacral and caudal segments. These are the cells of Stilling's nucleus, a column of cells similar in position and orientation to that of Clarke's column but different in its projections and details of cytoarchitecture. Thus we have not only confirmed that Clarke's nucleus, the central cervical nucleus, and the spinal border cells project to the cerebellum but we have also found several new sources of spinocerebellar afferents.

The effects of centrifugation on the morphology of the lateral vestibular nucleus in the rat: a light and electron microscopic study.

Very little is known about structural changes in the central nervous system following exposure to increased g forces. Sprague-Dawley rats were centrifuged at Ames Research Center at 2.76-4.15 x g for periods ranging from 4 days to 21 months. The lateral vestibular nuclei were processed for electron microscopy and examined for evidence of structural alteration as a result of centrifugation. The number of filamentous nuclear inclusions, varicosities, and relative number of axosomatic synaptic terminals containing flattened vesicles (presumed inhibitory in function) increased in centrifuged rats. Altered mitochondria also were noted in that cell bodies of Deiters' neurons. Neuroaxonal dystrophy (NAD) was found in long-term centrifuged rats and was characterized by axons filled with reticulated mitochondria. The NAD found in the lateral vestibular nuclei of centrifuged rats is different from that seen in the dorsal column nuclei of aged mice.

A fine structural study of degenerative changes in the dorsal column nuclei of aging mice. Lack of protection by vitamin E.

The dorsal column nuclei of young, old, and vitamin E-supplemented old mice were examined by light and electron microscopy. Evidence of neuroaxonal dystrophy (NAD) was found in young (3-mo.-old) mice and increased with age. Vitamin E, added to the diet in the amount of 0.3%, did not protect the nuclei from age-associated degeneration. The NAD was characterized by enlarged profiles containing patches of smooth reticular networks and groups of vesicles. Various stages of mitochondrial alteration, producing multivesicular bodies as intermediate stages, were found, and other unusual forms of dense bodies were also observed. Axons, synaptic terminals, and possibly glial cells were affected, and, by 23 mo. of age, a large number of nerve fibers in nucleus gracilis were dystrophic, while nucleus cuneatus was affected to a lesser extent.