The role of the cholinergic system of the bed nucleus of the stria terminalis on the cardiovascular responses and the baroreflex modulation in rats

Abstract

The bed nucleus of the stria terminalis (BST) is a limbic structure involved in cardiovascular regulation and modulation of responses to stress. The BST contains high levels of muscarinic receptors. This study was performed to find the effects of cholinergic system of the BST on the cardiovascular regulation and the baroreflex modulation in rats. Drugs (50–100 nl) were microinjected into the BST of 53 urethane anesthetized male rats. The mean arterial pressure and heart rate changes were measured. The baroreflex gain was evaluated by finding the slope of the reflex bradycardia in response to increases in mean arterial pressure due to phenylephrine injection (i.v.). We found that microinjection of acetylcholine (3 and 6 nmol/50 nl) into the BST increased mean arterial pressure and had no effect on heart rate. Local microinjection of homatropine abolished the effect of Ach on the cardiovascular responses indicating involvement of muscarinic receptors. Local injection of homatropine did not affect the reflexive bradycardia. Local injection of acetylcholine decreased the slope of the reflexive bradycardia indicating that Ach system of the BST inhibits the baroreflex. Acute ablation of the BST by cobalt chloride also significantly decreased the slope, indicating the excitatory action of the BST on the baroreflex parasympathetic component. In conclusion, we showed for the first time that microinjection of acetylcholine into the BST evokes a pressor response by activating the local muscarinic receptors. Release of Ach into the BST, probably during stress, inhibits the baroreflex, but with no stress, the BST facilitates the baroreflex.