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Studies on the collateralization of some basal forebrain and mesopontine tegmental projection systems in the rat

University of British Columbia

Many basal forebrain and mesopontine tegmental cholinergic projection systems tend to overlap in their origins. This raises the possibility that these projection systems are collateralized to innervate divergent areas. In experiment one, the degree to which basal forebrain and mesopontine tegmental neurons that innervate the reticular thalamic nucleus have axons that collateralize to innervate the cortex as well was examined with a retrograde fluorescence labeling method combined with immunohistochemistry. A significant portion of the labeled neurons in the region of the nucleus basalis magnocellularis and pedunculopontine tegmental nucleus projecting to the reticular thalamic nucleus were observed to be also labeled (double-labeled) following intracortical tracer injections. Many of these double-labeled neurons displayed choline acetyltransferase choline acetyltransferase immunoreactivity. It was also shown that numerous basal forebrain neurons that innervated the reticular thalamic nucleus contained the calcium-binding protein, parvalbumin. These neurons tended to be located more rostrally than the ChAT immunoreactive neurons; primarily in the region of the ventral pallidum. There was some indication that parvalbumin-containing neurons in the basal forebrain that innervate the reticular thalamic nucleus also have axons that branch to innervate the cortex. Finally, none of the basal forebrain neurons innervating the reticular thalamic nucleus was found to contain somatostatin. In experiment two, the degree to which basal forebrain neurons have axons that collateralize to innervate the interpeduncular nucleus and hippocampus was examined with retrograde fluorescence labeling methods. Labeled neurons projecting to both of these limbic structures were observed only occasionally. Comparison of the distribution of single labeled neurons innervating each of these structures revealed that within the region of origin, in the horizontal limb of the diagonal band, neurons innervating the interpeduncular nucleus tended to be located dorsally to those innervating the hippocampus. The results of these experiments are discussed in relation to their anatomical and functional implications toward a greater understanding of the basal forebrain and mesopontine cholinergic and non-cholinergic projection systems.

Text

2010-08-30

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http://hdl.handle.net/2429/27969

Neuroscience

University of British Columbia

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