Cardiovascular effects of carbachol microinjected into the bed nucleus of the stria terminalis of the rat brain

The bed nucleus of stria terminalis (BST) has been reported to be involved in central cardiovascular control in rat. We presently report on the cardiovascular effects of carbachol (CBH) microinjection into the BST as well as on local receptor and peripheral mechanisms involved in their mediation. Microinjection of CBH (0.1 to 3 nmol/100 nL) into the BST of anesthetized rats caused dose-related pressor and bradycardiac responses. The cardiovascular response evoked by 1 nmol of CBH was blocked by local microinjection of the nonselective muscarinic receptor antagonist atropine (3 nmol) or the selective M2-muscarinic receptor antagonist 4-DAMP (2 nmol). Microinjection of the selective M1-muscarinic receptor antagonist pirenzepine (6 nmol) did not affect cardiovascular responses to CBH, suggesting their mediation by local BST M2-muscarinic receptors. Cardiovascular responses to CBH microinjected in the BST were markedly reduced in urethane-anesthetized rats. The pressor response was potentiated by i.v. pretreatment with the ganglion blocker pentolinium (10 mg/kg) and blocked by i.v. pretreatment with the vasopressin antagonist dTyr(CH2)5(Me)AVP (50 μg/kg), suggesting involvement of circulating vasopressin in response mediation. In conclusion, results suggest that microinjection of CBH in the BST activates local M2-muscarinic receptor evoking pressor and bradycardiac responses, which are mediated by acute vasopressin release into circulation.