Facilitatory influence of noradrenergic afferents on the excitability of rat paraventricular nucleus neurosecretory cells.

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Abstract
The role of the A1 and A2 noradrenergic cell groups of the caudal medulla in regulating the activity of paraventricular nucleus neurosecretory cells was examined with electrophysiological methods in anesthetized male Sprague-Dawley rats. Antidromically identified neurosecretory cells were classified as vasopressin or oxytocin secreting on the basis of spontaneous firing patterns and responsivity to baroreceptor activation. The effect on cell firing of single pulses (25-200 .mu.A) delivered to either the A1 or A2 cell group areas was then examined using peri-stimulus histograms. Findings suggest that noradrenergic afferents of medullary origin facilitate the activity of paraventricular nucleus neurosecretory cells. The role of the projection from the A1 cell group appears to differ from that of the A2 group, however, in that its effects are specific to putative vasopressin-secreting units.