CNS site of clonidine induced hypotension: a microiontophoretic study of bulbar cardiovascular neurons.

To localize the central site and mechanism of clonidine induced hypotension, the drug was applied by the technique of microiontophoresis to neurons of the bulbar cardiovascular center in decerebrate cats. The excitatory and inhibitory cardiovascular neurons (CVN) were identified by their response to an increase in the arterial blood pressure induced by intravenous injections of small doses of norepinephrine (NE). Clonidine had an inhibitory effect on the spontaneous firing rate of excitatory CVN but had no effect on the firing rate of inhibitory CVN. At the same doses, it had no effect on the firing rate of NCVN recorded from the same area. Furthermore, clonidine had a blocking action on the excitatory response of CVN induced by microiontophoretic application of NE. It is concluded that clonidine produces its hypotensive response by acting on alpha-adrenergic receptors of bulbar CVN.