Alpha 1-adrenergic receptor-mediated excitation from the locus coeruleus of the sacral parasympathetic preganglionic neuron.

Electrophysiological studies using alpha-chloralose anesthetized cats were performed to elucidate whether or not noradrenaline derived from the locus coeruleus (LC) activates sacral intermediolateral (IML) cell column neurons, from which the sacral parasympathetic neurons originate. LC stimulation induced a spike in the sacral IML cell column neurons (parasympathetic interneurons), which were not antidromically activated by stimulation of the pelvic nerve, with a mean latency of 65.4 +/- 4.64 msec (mean +/- S.E., n = 12). In the sacral IML cell column neurons (parasympathetic preganglionic neurons), which were antidromically activated by pelvic nerve stimulation with a mean latency of 5.32 +/- 1.23 msec, LC stimulation also elicited a spike with the mean latency of 67.9 +/- 4.53 msec (n = 7). Iontophoretic application of prazosin, an alpha 1-adrenergic blocking agent, inhibited spikes elicited by LC stimulation in 8 of 12 sacral parasympathetic interneurons tested, but no alterations of LC stimulation-induced spikes were seen during iontophoretic application of sotalol, a beta-blocking agent. In contrast, spikes elicited by LC stimulation in the sacral parasympathetic preganglionic neurons tested were not affected by iontophoretic application of either prazosin or sotalol. These results suggests that noradrenaline derived from the LC activities the parasympathetic interneurons in the sacral IML cell column through alpha 1-adrenergic receptors, thereby inducing excitation of the sacral parasympathetic neurons receiving impulses from the interneuron.