The Journal of comparative neurology
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The activity of the olivocerebellar complex and the structures related in series with it have been studied using the complementary action of harmaline and 3-acetylpyridine to isolate the two principal inputs to the cerebellar Purkinje cells. The activities of the various nuclei as well as the entire brain have been simultaneously monitored using the [14C]2-deoxy-glucose method under the various combined effects of the pharmacological agents. (1) Tremogenic doses of harmaline increased the frequency of discharge in selected parts of the olivocerebellar system, increasing climbing fiber input and reducing Purkinje cell simple spike discharges in corresponding parts of the cerebellar cortex. The metabolic activity increased in the inferior olive and in the red nucleus. ⋯ In other parts the radioautographic changes caused by the destruction of the inferior olive persisted for about 1 month after the administration of the drug. (3) Tremogenic doses of harmaline were given to rats at different times following treatment with 3-acetylpyridine. It was demonstrated that: (a) intoxication of the inferior olive started within the second hour after 3-acetylpyridine administration, corresponding to the time at which the metabolic response to harmaline was also abolished; and (b) the increased metabolic activity produced by harmaline in the olivocerebellar complex was a consequence of an increased activity of the neurons of the inferior olive rather than a direct pharmacological effect of the drug. (4) Partial lesions of the inferior olive led to increased metabolic activity of those parts of the intracerebellar nuclei topographically related to the destroyed parts of the inferior olive. (5) In 3-acetylpyridine-treated animals, local ablation as well as local inactivation of the cerebellar cortex produced localized suppression of the intense labeling in the intracerebellar nuclei obtained in these animals. Since these regions receive synapses which are normally inhibitory, suppression of labeling clearly supports the hypothesis that regional marking may very well be produced by the activity of the presynaptic terminals themselves...
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Comparative Study
Axonal guidance during development of the great cerebral commissures: descriptive and experimental studies, in vivo, on the role of preformed glial pathways.
Do structures exist within the embryonic central nervous system that guide axons across the midline during development of the great cerebral commissures (corpus callosum, anterior commissure)? With the use of serial section and reconstructive computer graphic techniques we have found that during normal ontogeny of the mouse forebrain and before the arrival of the pioneer fibers of the corpus callosum at the midline, a population of primitive glial cells migrates medially (through the fused walls of the dorsal septum) from the ependymal zones of each hemisphere. At the midline, and well rostral to the lamina terminalis, these cells unite to form a bridgelike structure or "sling" suspended below the longitudinal cerebral fissure. The first callosal axons grow along the surface of this cellular bridge as they travel toward the contralateral side of the brain. ⋯ The callosal pathology in these affected animals mimicked exactly that of the genetically lesioned mutant. Our observations suggest that many different types of oriented glial tissues exist within the embryonic neural anlage. We propose that such tissues have the ability to influence the directionality of axonal movements and, thereby, play a crucial role in establishing orderly fiber projections within the developing central nervous system.
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Repetitive left mystacial vibrissae movements were produced by electrical stimulation of right motor cortex (MI) were a bipolar electrode in the alert, unanesthetized rat. Regional increases of (14C) 2-deoxyglucose (2DG) uptake were mapped autoradiographically during these left vibrissae movements. Uptake of 2DG increased in a 2-4-mm-diameter area about the stimulating electrode in right MI and in a smaller region in left MI cortex. ⋯ Though NCU has been called the "locomotor center" it may play a role in facial movements as well. Polysynaptic activation of GP, EPN, NL, and cerebellar hemisphere occurred since no connections between MI and these regions exist. A pathway from ntV to POm to MI and SI is suggested to provide proprioceptive input to motor-sensory cortex from the moving vibrissae since neither the principal trigeminal sensory nucleus nor the ventrobasal nucleus of the thalamus increased 2DG uptake during MI stimulation.
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Retrograde transport studies revealed that the nuclei pallidus, obscurus, and magnus raphae as well as the adjacent reticular formation innervate the spinal cord in the opposum. HRP-lesion experiments showed that a relatively large number of neurons within the nucleus obscurus raphae and closely adjacent areas of the nucleus reticularis gigantocellularis project through the ventrolateral white matter and that many cells within the nucleus magnus raphae, the nucleus reticularis gigantocellularis pars ventralis, and the nucleus reticularis pontis pars ventralis contribute axons to the dorsal half of the lateral funiculi. Neurons within the rostral pole of the nucleus magnus raphae and the adjacent nucleus reticularis pontis pars ventralis may project exclusively through the latter route. ⋯ The immunohistofluorescence method revealed evidence for indolaminergic axons in each of the spinal areas labeled by injections of 3H-leucine into the raphe and adjacent reticular formation. They were particularly abundant within the intermediolateral cell column and within laminae IX and X. These data indicate that raphe spinal systems are chemically and connectionally heterogeneous.
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Connections of two telencephalic vocal control nuclei, the hyperstriatum ventrale, pars caudale (HVc), and robust nucleus of the archistriatum (RA), were investigated in adult canaries. Methods used were transport of horseradish peroxidase and 3H-adenosine and silver staining of degenerating axons. Three nuclei project to HVc: medial nucleus magnocellularis of the anterior neostriatum (MAN), nucleus interfacialis (NIf) of midneostriatum, and nucleus uvaeformis (Uva) of the diecephalon. ⋯ All these projections are ipsilateral. No gross male/female differences were apparent in the projections to and from HVc. Uptake of HRP by cell somata in HVc following localized injections of this substance into RA or HVc suggests that HVc is composed of rostrocaudally organized clusters of cells, with little lateral communication between them.