CCK-8 EXCITES OXYTOCIN-SECRETING NEURONS IN THE PARAVENTRICULAR NUCLEUS IN RATS - POSSIBLE INVOLVEMENT OF NORADRENERGIC PATHWAY

Systemic administration of CCK-8 increased plasma oxytocin (OXT) level in rats anesthetized with a mixture of urethane and alpha-chloralose. Extracellular recordings were made from magnocellular neurosecretory neurons in the paraventricular nucleus (PVN) of the hypothalamus in an esthetized rats to examine the effects of CCK-8 on the firing of PVN n eurons. Thirteen out of 16 nonphasic neurons (putative OXT-secreting n eurons) were excited by intravenous and/or intraperitoneal administrat ion of CCK-8. By contrast, 8 out of 10 phasic cells, vasopressin(AVP)- secreting cells, were inhibited by systemic administration of CCK-8. F our out of five nonneurosecretory neurons in the PVN were excited by t he administration of CCK-8. Moreover, microion-tophoretically applied phentolamine blocked the excitatory responses induced by CCK-8 in nonp hasic neurons. We measured extracellular noradrenaline (NA) level in t he PVN, using in vivo microdialysis. Intravenous administration of CCK -8 induced NA release in the PVN. These results suggest that CCK-8 act ivates the excitatory afferent pathway to putative OXT-secreting neuro ns in the PVN which may, at least in part, be involved in the central noradrenergic projection.