Release of prolactin in response to microinjection of morphine into mesencephalic dorsal raphe nucleus.
Blood samples were collected via jugular catheters from ovariectomized rats at 10-min intervals for 1 h before and 2 h after microinjection of 0.5 microliter of either saline vehicle or morphine sulfate (10 micrograms) into the dorsal raphe nucleus (DRN) or adjacent periaqueductal gray by means of chronically-implanted guide cannulae. Prolactin was measured by radioimmunoassay, and mean preinjection and mean postinjection values were compared for each rat (t test) as well as for each treatment group (paired t test). Neither saline in DRN nor morphine in the surrounding periaqueductal gray significantly altered circulating prolactin. A significant rise in prolactin was observed following injection of morphine into DRN. This effect of morphine was prevented by pretreatment of the animals with the narcotic antagonist naltrexone (10 mg/kg i.v.), indicating the involvement of opiate receptors. These results indicate that DRN is one site at which systemically-administered morphine might act, and suggest the possibility of participation of this mechanism in modulation of prolactin release by endogenous opioids.
D000818:Animals; D001933:Brain Stem / Q000187:drug effects*; D005260:Female; D008636:Mesencephalon / Q000187:drug effects*; D009020:Morphine / Q000494:pharmacology*; D009271:Naltrexone / Q000494:pharmacology; D011388:Prolactin / Q000097:blood*; D011903:Raphe Nuclei / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000187:drug effects
D011957:Receptors, Opioid; D009271:Naltrexone; D009020:Morphine; D011388:Prolactin