Diagonal band of Broca modulates the cardiac component of the baroreflex in unanesthetized rats

The diagonal band of Broca (DBB) is involved in cardiovascular control in rats. In the present study, we report the effect of acute and reversible neurotransmission inhibition in the DBB by bilateral microinjection of the nonselective neurotransmission blocker CoCl2 (1 mM, 100 nL) on the cardiac baroreflex response in unanesthetized rats. Local DBB neurotransmission inhibition did not affect baseline values of either blood pressure or heart rate, suggesting no tonic DBB influence on cardiovascular system activity. However, CoCl2 microinjections enhanced both the reflex bradycardia associated with blood pressure increases caused by i.v. infusion of phenylephrine and tachycardiac response evoked by blood pressure decreases caused by i.v. infusion of sodium nitroprusside. An increase in baroreflex gain was also observed. Baroreflex returned to control values 60 min after CoCl2 microinjections, confirming its reversible effect. In conclusion, our data suggest that synapses within DBB have a tonic inhibitory influence on both the cardiac parasympathetic and sympathetic components of the baroreflex.