The pharmacology of endorphin modulation of chick distress vocalization.
Intraventricular injections of beta-endorphin, gamma-endorphin and alpha-endorphin were demonstrated to reduce isolation-induced distress vocalization on 2-4 day old chicks in a dose response manner at doses as small as 12.5 picomoles (pmol). beta-Endorphin was more potent than the other peptides and morphine, while Met-enkephalin was without effect. However, the D-Ala2 substituted form of Met-enkephalin was as potent as morphine. None of the opioid peptides was effective when injected peripherally in doses of 400 pmol/g body weight. Extension of the interval between injection and behavioral observation from 4 minutes eliminated the ability of alpha- and gamma-endorphin to reduce the peeps. Specificity of the opioid effect was determined by testing intraventricular injections (200 pmol) of 9 other endogenously found peptides. Somatostatin, vasoactive intestinal peptide, and human pancreatic peptide reduced the vocalizations modestly, while alpha-MSH reliably increased them.
D000818:Animals; D001007:Anxiety / Q000503:physiopathology*; D002552:Cerebral Ventricles / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004723:Endorphins / Q000008:administration & dosage / Q000494:pharmacology*; D004744:Enkephalin, Methionine / Q000494:pharmacology; D006801:Humans; D007276:Injections, Intraventricular; D008297:Male; D009020:Morphine / Q000494:pharmacology; D014828:Vocalization, Animal / Q000187:drug effects*; D018822:alpha-Endorphin; D001615:beta-Endorphin; D018823:gamma-Endorphin
D004723:Endorphins; D004744:Enkephalin, Methionine; D001615:beta-Endorphin; D018822:alpha-Endorphin; D018823:gamma-Endorphin; D009020:Morphine