The lateral septal area modulates the baroreflex in unanesthetized rats

The septal lateral area (LSA) is a limbic structure that is involved with autonomic and behavioral responses. In the present study we report the effect of acute and reversible LSA synaptic inhibition on the parasympathetic and the sympathetic components of baroreflex in unanesthetized rats. Neurotransmission was temporarily inhibited by bilateral microinjection of the nonselective synapse blocker CoCl2 in the LSA. Bilateral microinjection of 100 nL of 1 mM CoCl2 into the LSA did not affect blood pressure or heart rate baseline, suggesting no tonic LSA influence on resting cardiovascular parameters. However, 10 min after CoCl2 microinjections, maximum tachycardiac responses to blood pressure decreases caused by intravenous infusion of sodium nitroprusside and bradycardiac responses evoked by blood pressure increases caused by intravenous infusion of phenylephrine were enhanced when compared with control values. These enhancement of both the tachycardiac and bradycardiac reflex evoked increase of baroreflex gain. Baroreflex activity returned to control values 60 min after CoCl2 microinjections, confirming the reversible blockade. The present results indicate an involvement of the LSA in baroreflex modulation. Data suggest that synapses in the LSA play a tonic inhibitory influence on both the sympathetic and the parasympathetic components of the baroreflex in unanesthetized rats.