Neuroscience
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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 efferent projections of the core and shell areas of the nucleus accumbens were studied with a combination of anterograde and retrograde tract-tracing methods, including Phaseolus vulgaris-leucoagglutinin, horseradish peroxidase and fluorescent tracers. Both the core and shell regions project to pallidal areas, i.e. ventral pallidum and entopeduncular nucleus, with a distinct topography in the sense that the core projection is located in the dorsolateral part of ventral pallidum, whereas the shell projects to the medial part of the subcommissural ventral pallidum. Both regions of the accumbens also project to mesencephalon with a bias for the core projection to innervate the substantia nigra-lateral mesencephalic tegmentum, and for the shell projection to reach primarily the ventral tegmental-paramedian tegmentum area. ⋯ The shell, however, has additional features that are reminiscent of the recently described extended amygdala [Alheid G. F. and Heimer L. (1988) Neuroscience 27, 1-39; de Olmos J. S. et al. (1985) In The Rat Nervous System, pp. 223-334]; in fact, the possibility exists that the shell represents a transitional zone that seems to characterize most of the fringes of the striatal complex, where it adjoins the extended amygdala.
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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.
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Electrical stimuli were applied to tooth-pulp in cats and the thresholds of the jaw-opening reflex and of neurons in the trigeminal sensory nuclei were determined. The effects of the method of preparation of the animal for stereotaxic recording were determined by making observations on animals set up in one of three ways: acutely in the usual manner; chronically, three to five days before recording; and acutely with precautions to minimize nociceptive input to the central nervous system. The threshold of the jaw-opening reflex increased progressively during the setting up of the normal, acute preparations and at the time brainstem recording began was significantly higher in these than in either the chronic or low-trauma acute preparations. ⋯ In the chronic and in low-trauma acute preparations, there was no significant difference between the thresholds of the units in the main sensory trigeminal nucleus and spinal subnucleus oralis compared with those in subnucleus caudalis. Thus the preparation of an animal for stereotaxic recording can cause a severe and long-lasting depression in the excitability of neurons in the trigeminal sensory nuclei and an increase in the threshold of the jaw-opening reflex. This effect will have influenced the results of previous studies on the responses evoked in central neurons by stimulation of tooth-pulp, and may have similarly affected recordings from other regions.
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Comparative Study
Dopamine high-affinity transport site topography in rat brain: major differences between dorsal and ventral striatum.
Investigations were conducted to determine the topography of the high-affinity dopamine uptake process within the rat striatum. [3H]Dopamine uptake into crude synaptosomes prepared from micropunch samples was found to be two- to three-fold higher in dorsal caudate-putamen relative to nucleus accumbens septi. In contrast, the concentrations of dopamine in the two regions were equivalent. The recognition site associated with high-affinity dopamine uptake was labeled using [3H]mazindol, and the binding of this ligand was also found to be two- to three-fold higher in homogenates from dorsal caudate-putamen samples relative to nucleus accumbens septi. ⋯ Further autoradiographic studies revealed less striatal heterogeneity in the pattern of binding of [3H]ketanserin, another radioligand associated with the striatal dopaminergic innervation but not linked to the dopamine uptake process of the plasma membrane. The findings suggest that the dopaminergic fibers of the ventral striatum, especially the medial nucleus accumbens septi, may be relatively lacking in their capacity for dopamine uptake following its release. This organization may result in regional differences in the time-course of of extraneuronal dopamine following transmitter release and may render the dopamine-containing terminals of the ventral striatum less susceptible to the degenerative influences of neurotoxins that are incorporated by the high-affinity dopamine uptake process.