Effects of beta-endorphin and its fragments on inhibitory avoidance behavior in rats.
The effects on retrieval of a one-trial learning inhibitory avoidance response of beta-endorphin, alpha-endorphin, and gamma-endorphin, given prior to test have been studied in rats. beta-Endorphin (beta-LPH 61-91) in a relatively low dose (1.56 micrograms sc. or 50 ng icv.) facilitated inhibitory avoidance behavior, while a higher dose (10 micrograms sc. or 100 ng icv.) caused bimodal changes (facilitation in 50% of the animals and attenuation in another 40%. Peripheral injection of gamma-endorphin attenuated inhibitory avoidance behaviour in a dose-dependent manner. The C-terminus of beta-endorphin (beta-LPH 78-91) was ineffective. alpha-Endorphin facilitated inhibitory avoidance behavior in a dose dependent manner. Naltrexone pretreatment antagonized the bimodal effect of beta-endorphin: following pretreatment with the opiate antagonist the low latency component disappeared, but the facilitatory effect of the neuropeptide remained the same. It is suggested that beta-endorphin carries more than one bit of behavioral information. Inherent activities either related or unrelated to naltrexone-sensitive opiate as well as biotransformation into alpha- and gamma-endorphin may contribute to the multiple behavioral effects of this neuropeptide.
D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004723:Endorphins / Q000494:pharmacology*; D007276:Injections, Intraventricular; D007279:Injections, Subcutaneous; D008297:Male; D011939:Mental Recall / Q000187:drug effects; D009020:Morphine / Q000494:pharmacology; D009271:Naltrexone / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects; D010446:Peptide Fragments / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000187:drug effects; D012153:Retention, Psychology / Q000187:drug effects; D018822:alpha-Endorphin; D001615:beta-Endorphin; D008083:beta-Lipotropin / Q000494:pharmacology* / Q000031:analogs & derivatives; D018823:gamma-Endorphin
D004723:Endorphins; D010446:Peptide Fragments; C041209:beta-lipotropin (78-91); D009271:Naltrexone; D001615:beta-Endorphin; D018822:alpha-Endorphin; D018823:gamma-Endorphin; D009020:Morphine; D008083:beta-Lipotropin