Neuroscience
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Supraspinal afferents to the pontine micturition center, Barrington's nucleus, were investigated in the rat by visualization of the retrograde tracer, cholera-toxin subunit B, in neurons following iontophoretic injection into Barrington's nucleus. Tissue sections from five rats with injections primarily localized in Barrington's nucleus revealed numerous retrogradely labeled neurons throughout all rostrocaudal levels of the periaqueductal gray (particularly its ventrolateral division), in the lateral hypothalamic area (particularly medial to the fornix), and in the medial preoptic nucleus. Retrogradely labeled neurons were also consistently found in the nucleus of the solitary tract, in the vicinity of the lateral reticular nucleus, nucleus paragigantocellularis, parabrachial nucleus, Kölliker-Fuse nucleus, cuneiform nucleus, raphe nucleus and zona incerta. ⋯ The present results suggest that Barrington's nucleus in the rat receives neuronal inputs from brainstem nuclei as well as from forebrain limbic structures including hypothalamic nuclei, the medial preoptic nucleus, and cortical areas involved in fluid balance or blood pressure regulation. In light of the role of Barrington's nucleus in micturition, the integration of these various inputs may be important for co-ordinating urinary function with fluid and cardiovascular homeostasis. Additionally, as neurons in Barrington's nucleus are immunoreactive for the stress-related neurohormone, corticotropin-releasing hormone, these diverse inputs may regulate stress-related functions of this nucleus.
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Because we believe that macrophage-derived nitric oxide contributes to pathology of demyelinating diseases, we have determined the differential effects of nitric oxide on primary rat glial cells in vitro. Enriched cultures of microglia, astrocytes and oligodendrocytes were treated with S-nitroso,N-acetyl-DL-penicillamine, a nitric oxide-releasing chemical. There was a significantly decreased function of one of the ferrosulfur-containing mitochondrial enzymes after S-nitroso,N-acetyl-DL-penicillamine/nitric oxide treatment in oligodendrocytes and astrocytes compared to microglia, which were much less sensitive to S-nitroso,N-acetyl-DL-penicillamine/nitric oxide at all concentrations. ⋯ These findings suggest that there is differential sensitivity of glial cells to nitric oxide. Although oligodendrocytes and astrocytes are equally susceptible to nitric oxide-induced mitochondrial damage, oligodendrocytes are more sensitive to nitric oxide-induced single stranded DNA breaks, morphological changes and cell death. Compared to both oligodendrocytes and astrocytes, microglia, nitric oxide-producing cells, are resistant to nitric oxide-induced damage.
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The properties of rhythmic low-threshold and multireceptive spinal dorsal horn neurons were determined. Multiple neuron recordings were made via a single electrode in the lumbar spinal cord of pentobarbital-anesthetized or decerebrate, unanesthetized, spinalized rats. The background activity of a total of 223 neurons was analysed: 21.0% of 176 fully characterized neurons were low threshold, 73.3% multireceptive and 5.7% nociceptive-specific neurons. ⋯ Thus, rhythmicity exists in sensory neurons of the spinal dorsal horn probably generated within its local neuronal network and partially modulated by supraspinal descending systems. Rhythmicity is depressed by activity in primary afferent nociceptors. The role of rhythmicity for information transfer and neuronal plasticity is discussed.
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GABAergic neurons in laminae I-III of the spinal dorsal horn may contain one or more of the following compounds: glycine, acetylcholine, neuropeptide Y, enkephalin, nitric oxide synthase or parvalbumin. Although the pattern of co-localization of some of these compounds is understood, it is not known which types of GABAergic neurons contain parvalbumin, or whether nitric oxide synthase coexists with peptides, acetylcholine or parvalbumin in any of these neurons, and in this study we have used immunocytochemistry and enzyme histochemistry to resolve these issues. Parvalbumin-immunoreactivity was restricted to those GABA-immunoreactive neurons that also showed glycine-immunoreactivity and was not co-localized with neuropeptide Y-immunoreactivity or NADPH diaphorase activity. ⋯ By combining immunofluorescent detection of neuropeptide Y or enkephalin with NADPH diaphorase histochemistry, we showed that peptide-immunoreactivity did not coexist with NADPH diaphorase. This suggests that neither of these peptides coexists with nitric oxide synthase or with acetylcholine in neurons in the superficial dorsal horn. Several phenotypically distinct groups of GABA-immunoreactive neuron can therefore be identified in laminae I-III of the dorsal horn, and these may represent different functional types of inhibitory neuron.
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Comparative Study
Anatomical characterization of a novel reticulospinal vasodepressor area in the rat medulla oblongata.
Microinjection of L-glutamate into a subregion of the gigantocellular nucleus of the rat medulla oblongata significantly lowers arterial pressure. This vasodepressor area, the gigantocellular depressor area, is topographically distinct from other vasoactive areas of the medulla. We sought to determine the efferent projections of the gigantocellular depressor area and compare these to the efferent projections of sympathoexcitatory neurons within the rostral ventrolateral medulla. ⋯ Following deposits into the rostral ventrolateral medulla (pressor area), labeled fibers were seen in many of these same autonomic nuclei; however, efferents from the gigantocellular depressor area to the nucleus of the solitary tract, the parabrachial complex and the reticular formation were medial to rostral ventrolateral medulla (pressor area) efferents to these same areas. These data indicate that neurons within the gigantocellular depressor area and the rostral ventrolateral medulla (pressor area) project to autonomic nuclei throughout the central nervous system and further suggest a heterogeneity of function with regard to autonomic control both within the reticular formation and its efferent targets. In addition, these data support the view that the gigantocellular depressor area may be a novel reticulospinal sympathoinhibitory area.