The influence of neuropeptides related to pro-opiomelanocortin on acquisition of heroin self-administration of rats.
The influence of different neuropeptides related to pro-opiomelanocortin were tested on acquisition of heroin self-administration in rats. The animals were allowed to self-administer heroin intravenously on a continuous reinforcement schedule during 6 h daily sessions on 5 consecutive days. Treatment was performed subcutaneously 1 h before each daily session. It was found that the opioid peptides alpha-, gamma- and beta-endorphin hardly influenced acquisition of heroin self-administration, while the non-opioid fragments of alpha- and gamma- endorphin modulated this behavioral response. In fact, beta-endorphin (beta E) 2-9 tended to facilitate the rate of acquisition, while the gamma-type endorphins, des-Tyr1-gamma-endorphin (beta E 2-17) and des-enkephalin-gamma-endorphin (beta E 6-17), decreased heroin intake. Concerning the ACTH/MSH related peptides, a decreasing effect of heroin intake was found following treatment with (D-Phe7)-ACTH 4-10, with a high dose of the ACTH 4-9 analog Org 2766 and with gamma 2-MSH, while ACTH 1-24, ACTH 4-10 and a low dose of Org 2766 did not significantly influence self-injecting behavior. It is concluded that pro-opiomelanocortin serves as a precursor molecule for peptide fragments, which modulate the acquisition of heroin self-administration in rats.
D000324:Adrenocorticotropic Hormone / Q000502:physiology; D000818:Animals; D004723:Endorphins / Q000502:physiology; D006556:Heroin Dependence / Q000503:physiopathology*; D006801:Humans; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000502:physiology*; D010908:Pituitary Hormones, Anterior / Q000502:physiology*; D011333:Pro-Opiomelanocortin; D011498:Protein Precursors / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012646:Self Administration; D001615:beta-Endorphin
D004723:Endorphins; D009419:Nerve Tissue Proteins; D010908:Pituitary Hormones, Anterior; D011498:Protein Precursors; D001615:beta-Endorphin; D011333:Pro-Opiomelanocortin; D000324:Adrenocorticotropic Hormone; D009074:Melanocyte-Stimulating Hormones