Baroreceptor sensitivity of rat supraoptic vasopressin neurons involves noncholinergic neurons in the DBB

Previous studies suggest that cholinergic neurons in the diagonal band of B roca (DBB) participate in the baroreceptor-mediated inhibition of phasic va sopressin neurons in the supraoptic nucleus (SON). To test this hypothesis, extracellular recordings were obtained from putative vasopressin SON neuro ns of anesthetized rats injected with the cholinergic immunotoxin 192 IgG-s aporin (0.8 mug/mul) in the DBB. Baroreceptor sensitivity of neurons was te sted with brief phenylephrine-induced (10 mug/10 mul iv) increases in blood pressure of at least 40 mmHg. In rats injected with vehicle or unconjugate d saporin, 19 of 21 and 18 of 20 phasic neurons, respectively, were inhibit ed by increased blood pressure. In rats injected with 192 IgG-saporin, whic h significantly reduced the number of choline acetyltransferase (ChAT)-posi tive DBB neurons, 33 of 36 phasic neurons were inhibited. Normal rats and r ats with DBB saporin injections received rhodamine bead injections into the perinuclear zone (PNZ) to retrogradely label DBB neurons, and their brains were stained for ChAT. ChAT-positive DBB neurons were not retrogradely lab eled from the PNZ. Together, these results indicate that the pathway relayi ng baroreceptor information to the SON involves noncholinergic DBB neurons.