The cardiovascular response to medullary cholinergic and corticoid stimulation is calcium channel dependent in rats

Experiments were performed on anaesthetized Wistar or Sprague-Dawley rats of both sexes. Microinjection of an acetylcholinesterase inhibitor physostigmine (0.4 microgram/0.1 microliter/site) or acetylcholine (ACh, 25 ng/0.1 microliter/site) into the rostral ventrolateral medulla (rVLM) caused an increase in blood pressure (BP), heart rate (HR) and the pressor response produced by stimulation of the dorsal periaqueductal grey (dPAG) in the midbrain. Prior microinjection of the calcium channel blocker verapamil (0.25 microgram/0.1 microliter/site) into the same sites blocked the cardiovascular effect in response to the respective microinjection of the drugs mentioned above. Moreover, verapamil pretreatment blocked the pressor and tachycardiac effect induced by respective microinjection of corticosterone (40 ng/0.1 microliter/site) or aldosterone (40 ng/0.1 microliter/site) into the rVLM, as well as the enhancement of the pressor response to stimulation of the dPAG induced by microinjection of corticoids into the rVLM. These results suggest that the enhancement of cardiovascular activities mediated by cholinergic mechanisms may be due to the activation of postsynaptic calcium channels of neurons in the rVLM. The corticosteroid effect seems to be mediated by similar mechanisms.