Vasopressin mediates the cardiovascular effects of GABAergic system in the bed nucleus of the stria terminalis

The nucleus bed of the stria terminalis [BST] is a part of the limbic system. Previous studies have shown that inhibition of GABA A receptor increases blood pressure and heart rate. This study was performed to find the possible mechanisms and circuits that mediate these responses. In 39 urethane-anesthetized male rats the femoral artery and vein were cannulated for recording the blood pressure and heart rate and drug injection respectively. Trachea was cannulated to ease ventilation, and bicuculline was unilaterally microinjected into the BST using micropipette. The maximum changes of mean arterial pressure [MAP] heart rate [HR] were compared with the preinjection values using the paired t-test. Injection of bicuculline methiodide [BMI, 100 pmol/100 nl], a GABAA antagonist, caused a significant increase in the MAP [41.3 +/- 5.1 mmHg] as well as in the HR [33.2 +/- 5.6 beats/min]. Administration [i.v.] of the muscarinic receptor blocker, homatropine methyl bromide had no effect on the magnitude of mean arterial pressure or heart rate responses to BMI, suggesting that the parasympathetic system is not involved in these responses. However administration [i.v.] of the nicotinic receptor blocker, hexamethonium bromide, althought it had no effect on the magnitude of mean arterial pressure response, did abolish heart rate response to BMI, indicating that the sympathetic system is involved in the bradycardic effect of GABA. On the other hand, administration [i.v.] of a selective vasopressin V1 receptor antagonist abolished the pressor effect of BMI, which suggests that the GABAergic system of the BST decreases the arterial pressure via tonic inhibition of vasopressin release. We demonstrated, for the first time, that inhibition of GABAA, receptors increase blood pressure and heart rate via tonically inhibiting vasopressin release and sympathetic outflow to the heart

electrical stimulation effect of the horizontal limb of diagonal band of Broca on blood pressure and heart rate of rats

It has already been shown that diagonal band of broca has a regulatory effect on cardiovascular system. In this study we electrically stimulated the horizontal limb of the diagonal band of broca [hDB] to find its effect on blood pressure and heart rate. In this experimental study 34 rats were anesthetized with urethane and hDB was stimulated [80-150 microamperes for 15 sec] by a silver electrode coated with glass except for its tip. Blood pressure and heart rate were continuously recorded by a computer. Paired t-test was used for comparison of the prestimulation data and the maximum changes after the stimulation. The results showed that electrical stimulation caused a significant decrease in blood pressure and heart rate. The maximum changes for long-term responses were 9.39 +/- 1.13 mmHg for mean blood pressure and 15.4 +/- 3.19 for heart rate. For short-term responses the maximum changes were 9.08 +/- 1.4 mmHg for mean blood pressure and 7.5 +/- 2.36 for heart rate. It is possible that glutaminergic system of the hDB suppresses the vasopressin release from hypothalamus, thereby decreasing the blood pressure, and suppresses the sympathetic flow to the heart, thereby decreasing the heart rate