Neuroscience
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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.
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Electrical stimulus intensity, capsaicin, excitatory amino acid antagonists and the substance P antagonist, spantide, have been used to investigate the roles of primary afferent C fibres and excitatory amino acid receptors in the generation of long duration (half time 9.1 s +/- 1.1 S. E. M., N = 24) contralateral reflexes recorded in ventral roots of immature rat spinal cords in vitro. ⋯ The depressant effect of spantide, unlike that of (+/-)-2-amino-5-phosphonopentanoic acid, was associated with a long lasting excitatory action. In the presence of tetrodotoxin (0.1 microM), spantide (33 microM) failed to antagonize substance P-induced depolarizations. It is suggested that long duration of the dorsal root-evoked contralateral ventral root potential is a consequence of the activation of the N-methyl-D-aspartate receptor operated ion channels by excitatory amino acid transmitters.
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We have examined the distribution of microglia in the normal adult mouse brain using immunocytochemical detection of the macrophage specific plasma membrane glycoprotein F4/80. We were interested to learn whether the distribution of microglia in the adult brain is related to regional variation in the magnitude of cell death during development and resulting monocyte recruitment, or whether the adult distribution is influenced by other local microenvironmental cues. We further investigated the possibility that microglia are sensitive to their microenvironment by studying their morphology in different brain regions. ⋯ They can be extremely elaborate and there is wide variation in the length and complexity of branching of the processes. There was no evidence of monocyte-like cells in the adult CNS. The systematic variation in microglial morphology provides further evidence that these cells are sensitive to their microenvironment.
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[3H]GABA quantitative autoradiography was used to examine the binding kinetics and regional distribution of GABAB receptors in rat brain. The regional distribution was compared to that of GABAA receptors. At 4 degrees C, [3H]GABA binding to GABAB receptors reached equilibrium within 45 min. ⋯ Areas high in GABAB binding included the medial and lateral geniculates, the superior colliculus and certain amygdaloid nuclei. Binding to white matter tracts and ventricles was negligible. The distribution of GABAB receptors was in agreement with previously postulated sites of action of baclofen.
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A major ascending nociceptive pathway from spinal lamina I to the mesencephalon has previously been reported in the cat, rat and monkey. In the present paper, we have used single and double retrograde labeling techniques to describe this projection system and its collateralization to the thalamus in the rat. Injections of wheat germ agglutinin-horseradish peroxidase into the pontomesencephalic parabrachial area labeled cell bodies bilaterally in lamina I and deeper laminae of the spinal cord. ⋯ The significance of these findings rest on previous work in this and other laboratories and concerns the understanding of spinal nociceptive mechanisms. Lamina I projection neurons are primarily nociceptive-specific in their response properties and have been shown to project to both the midbrain and thalamus via the dorsolateral funiculus in a number of species. The role of this projection system in nociceptive transmission may lie in its ability to distribute precise information to multiple brain stem sites which in turn activate autonomic or affective responses or descending pain modulatory mechanisms.