Identification of barosensitive neurons in the mediobasal forebrain using juxtacellular labeling

Previous investigations suggest a possible role in cardiovascular regulatio n for neurons of the mediobasal forebrain. The present study was designed t o determine the location and morphology of basal forebrain neurons that res pond to acute changes in arterial blood pressure. Extracellular recordings of single units were done in alpha-chloralose- or urethan-anesthetized rats . The effect of cardiovascular presser (phenylephrine, 1-2 mu g/kg iv) and depressor (sodium nitroprusside, 0.5-1 mu g/kg iv) events on the discharge rates of units was determined. Some of the neurons tested were subsequently filled with biocytin using the juxtacellular method. Brain sections were p rocessed using the avidin-biotin complex reaction to reveal a Golgi-like ap pearance of the neuron. Of 32 neurons located in the horizontal limb of the diagonal band of Broca (hDB), 13 (41%) were found to be excited by depress or events. Barosensitive biocytin-labeled cells were located in all regions of the hDB and had small- to medium-sized cell bodies with sparse and simp le dendritic morphology. Only 2 of 47 neurons tested in the region of the o lfactory tubercle, islands of Calleja (IC), and ventral pallidum responded to changes in arterial blood pressure. The results of the present investiga tion suggest a role in the regulation of cardiovascular function for neuron s of the hDB. The findings also suggest that most neurons in the olfactory tubercle, including the IC complex, do not respond to acute changes in arte rial blood pressure.