the role of muscarnic cholinergic receptor of the bed nucleus of stria terminalis on cardiovascular response and baroreflex modulation in rat.

introduction: the bed nucleus of the stria terminalis (bst) is a limbic structure which is involved in cardiovascular regulation and baroreflex modulation. the presence of cholinergic synaptic terminalis with high level of muscarinic receptors in the bst has been demonstrated. this study was performed to find the role of the cholinergic muscarinic receptor in cardiovascular response and baroreflex activity in urethane anesthetized rat. methods: acetylcholine (ach, 3, 6 nmol in 50 nl) was microinjected unilaterally into the bst of 53 urethane anesthetized male rats. femoral artery and vein were cannulated to record the blood pressure (ap) and heart rate (hr), respectively. the maximum average changes in the mean arterial pressure (map) and (hr), were compared with control group and before injection using t-test and paired t-test, respectively. to evaluate baroreflex activity, bradycardia values corresponding to progressive 20 mmhg increases in map were determined. the slope of the linear regression curves was calculated and compared to before injection using anova repeated measure. results: microinjection of ach into the dorsal, lateral and ventral portion of the bst resulted in an increase of ap (20.69 ± 1.8 mmhg, p<0.01) with no significant changes of the hr. the pressor response evoked by ach was blocked by microinjection of atropine into the bst. however, atropine did not affect the bradycardia reflex evoked by increased blood pressure caused by intravenous phenylephrine injection. microinjection of cobalt chloride into the bst did not affect the baseline ap and hr but significantly increased bradycardic response to lower pressure changes (less than 40 mm hg) and decreased bradycardic response to higher pressure changes (more than 40 mm hg) (p>0.05) indicating that neuronal circuitry of bst is an essential part of the baroreflex.. conclusion: the present study indicated that the bst muscarinic receptors are involved in the cardiovascular regulation but are not involved in the modulation of baroreflex activity, although synapses within the bst have influence on the bradycardia baroreflex component.