The Journal of comparative neurology
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Recent studies have demonstrated an important contribution of the A5 noradrenergic cell group of the rostral medulla in the regulation of nociceptive messages at the level of the spinal cord. These noradrenergic controls parallel those arising from the serotonin-containing neurons of the nucleus raphe magnus. In the present study, we used postembedding immunogold staining to identify GABA-immunoreactive terminals that synapse upon identified spinally projecting noradrenergic neurons of the A5 cell group in the rat. ⋯ Labelled terminals contained round or pleiomorphic vesicles, but not flat vesicles; many also contained dense-core vesicles. Our results indicate that noradrenergic neurons of the A5 cell group, which contribute to both antinociceptive and cardiovascular controls through their projection to the spinal cord, are regulated by local GABAergic, presumably inhibitory, mechanisms. Whether the initiation of A5 neuron activity results from a lifting of tonic GABAergic inhibitory control, as has been proposed for the neurons of the nucleus raphe magnus, remains to be determined.
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The ipsilateral cortical connections of primary motor cortex (M1) of owl monkeys were revealed by injecting WGA-HRP and fluorescent tracers into M1 sites identified by intracortical microstimulation. In some of the same animals, the extent and somatotopic organization of M1 was determined by making detailed microstimulation movement maps and relating the results to cortical architectonics. Thus, delineation of M1 was based on a combination of physiological and anatomical characteristics. ⋯ Weaker connections were with area 3b, posterior parietal cortex, the parietal ventral area (PV), and cingulate cortex. M1r and M1c differed connectionally as well as architectonically, M1c being connected primarily with somatosensory areas, while M1r was strongly connected with both non-primary motor cortex and somatosensory cortex. These results indicate that M1 interacts directly with at least three non-primary motor areas and at least six somatosensory areas.