Contribution of caudal ventrolateral medulla to the cardiovascular responses elicited by activation of bed nucleus of the stria terminalis.

The contribution of caudal ventrolateral medulla (cVLM) to the mean arterial pressure (MAP) and heart rate (HR) responses elicited by microinjections of L-glutamate (GLU) into the cardiovascular responsive region of bed nucleus of the stria terminalis (BST) was investigated in the chloralose-anesthetized, paralysed and artificially ventilated rat. Unilateral injections of GLU into BST elicited decreases in MAP of -25 +/- 3 mmHg (n = 10) and HR of -13 +/- 3 bpm (n = 10). These cardiovascular responses were not altered after a 100 nl microinjection of 0.9% NaCl into cVLM. However, the magnitudes of the decreases in MAP and HR were attenuated (-11 +/- 3 mmHg and HR, -4 +/- 1 bpm, respectively) 5 min after a 100 nl microinjection of the reversible synaptic blocker cobalt chloride (CoCl2) into cVLM. Restimulation of BST 40 min after the 100 nl microinjection of CoCl2 in cVLM elicited cardiovascular responses that were not significantly different in magnitude from those evoked before the microinjection of CoCl2 (MAP, -23 +/- 4 mmHg; HR, -12 +/- 5 bpm). In an additional series of experiments (n = 3), restimulation of BST 1 h after an ipsilateral electrolytic lesion in cVLM elicited decreases in MAP (-11 +/- 2 mmHg) and HR (-8 +/- 4 bpm) that were significantly smaller than those elicited prior to cVLM lesion. These data suggest that a component of the pathways originating in BST involved in mediating depressor responses and cardiac slowing relays in cVLM.