Basal forebrain GABAergic projections to the amygdala and the BNST in wistar rats

Abstract

Medial septal GABAergic neurons of the basal forebrain selectively innervate GABAergic interneurons in the hippocampus and form a disinhibitory circuit. This long-range GABAergic projection contributes to hippocampal theta oscillations (4- 12 Hz), which correlate with hippocampal forms of learning and memory including spatial navigation. I postulate that basal forebrain-driven disinhibition creates a general neuromodulation for limbic structures. Basal forebrain GABAergic projections to the amygdala and the bed nucleus of the stria terminalis (BNST), structures respectively encoding phasic and sustained fear (anxiety), may be a key regulator of their local network activities. Testing this calls for an anatomical description of the basal forebrain GABAergic projections to the amygdala and the BNST. This thesis provides a detailed description of the projections as well as several projecting subpopulations by utilizing retrograde tract-tracing and fluorescent immunohistochemistry in Wistar rats. Tracing showed that the substantia innominata/sublenticular extended amygdala (SI/EA), the ventral pallidum (VP), and the nucleus of the horizontal limb of the diagonal band/magnocellular preoptic nucleus (hDB/MCPO) project to the amygdala and the BNST. Immunohistochemistry revealed calbindin (CB)- and parvalbumin (PV)- immunopositive putative GABAergic subpopulations among the projecting neurons.