Neuroscience
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Comparative Study
Aspartate-like immunoreactivity in primary afferent neurons.
There is now good evidence that amino acids act as neurotransmitters in primary afferent neurons of dorsal root ganglia. Glutamate is the primary candidate for such a role, and there are reasons to believe that release of glutamate may be accompanied by the release of other neuroactive substances. Using immunocytochemical techniques, we have tested the hypothesis that some dorsal root ganglion neurons contain elevated levels of aspartate as well as glutamate. ⋯ The presence of high levels of aspartate in terminals located in the superficial laminae of the dorsal horn was verified by pre- and post-embedding immunocytochemistry with the electron microscope. Aspartate was demonstrated in scalloped terminals, including dark scalloped terminals believed to be associated with unmyelinated fibers of nociceptors. This evidence supports the hypothesis that aspartate as well as glutamate is present in the cell bodies and terminals of nociceptive primary afferents, and may be released by the terminals of these afferents to activate neurons in the superficial laminae of the dorsal horn.
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The localization and distribution of quinolinic acid phosphoribosyltransferase, the degradative enzyme of the endogenous excitotoxin quinolinic acid, were studied in the post mortem human neostriatum by immunohistochemistry. In eight neurologically normal human brains, quinolinic acid phosphoribosyltransferase immunoreactivity was detected in both glial cells and neurons. Typically, glial cells containing quinolinic acid phosphoribosyltransferase immunoreactivity had numerous processes radiating from the cell bodies. ⋯ The somatic and dendritic morphology of quinolinic acid phosphoribosyltransferase-immunoreactive neurons closely resembles that of aspiny neurons seen in Golgi preparations. The localization of the specific quinolinic acid-catabolizing enzyme in distinct populations of neostriatal cells suggests specific functional correlates. It remains to be examined how the anatomical organization of quinolinic acid phosphoribosyltransferase immunoreactivity relates to the degradation of quinolinic acid in the striatum, and if the morphological characteristics and distribution of quinolinic acid phosphoribosyltransferase-immunoreactive cells are of relevance for the pathogenesis of neurodegenerative basal ganglia disorders.
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The organization of connections between the amygdala, prefrontal cortex and striatum was studied using anterograde and retrograde tract tracing techniques in the rat. The anterograde transport of Phaseolus vulgaris leucoagglutinin and wheat germ agglutinin conjugated to horseradish peroxidase was used to examine the striatal projections of the prefrontal cortex. These studies revealed that the prelimbic area of the medial prefrontal cortex projects mainly to the medial part of the striatum, whereas the dorsal agranular insular area of the lateral prefrontal cortex projects mainly to the ventrolateral part of the striatum. ⋯ The rostral pole and lateral portions of the basolateral nucleus project to both the lateral prefrontal cortex and its associated lateral striatal region. Many neurons in the basolateral amygdaloid nucleus, and to a lesser extent other amygdaloid nuclei, were double-labeled in these experiments, indicating that these cells send collaterals to both the prefrontal cortex and striatum. These findings indicate that discrete areas of the amygdala, and in some cases individual amygdaloid neurons, can modulate information processing in the first two links of distinct cortico-striato-pallidal systems arising in the medial and lateral prefrontal cortex.