AREGU June 45/6

Kirouac, Gilbert J., and Quentin J. Pittman. Identification of barosensitive neurons in the mediobasal forebrain using juxtacellular labeling. Am. J. Physiol. 276 (Regulatory Integrative Comp. Physiol. 45): R1766–R1771, 1999.— Previous investigations suggest a possible role in cardiovascular regulation for neurons of the mediobasal forebrain. The present study was designed to determine the location and morphology of basal forebrain neurons that respond to acute changes in arterial blood pressure. Extracellular recordings of single units were done in a-chloraloseor urethananesthetized rats. The effect of cardiovascular pressor (phenylephrine, 1–2 μg/kg iv) and depressor (sodium nitroprusside, 0.5–1 μg/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 processed using the avidin-biotin complex reaction to reveal a Golgi-like appearance 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 depressor events. Barosensitive biocytin-labeled cells were located in all regions of the hDB and had smallto medium-sized cell bodies with sparse and simple dendritic morphology. Only 2 of 47 neurons tested in the region of the olfactory tubercle, islands of Calleja (IC), and ventral pallidum responded to changes in arterial blood pressure. The results of the present investigation suggest a role in the regulation of cardiovascular function for neurons 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 arterial blood pressure.