Enkephalin and fear-motivated behavior.
Leu[Enkephalin (400.0 micrograms/kg) and the enkephalin analog [DAla,DLeu]enkephalin (0.4, 4.0, and 40.0 micrograms/kg) were intraperitoneally administered to rats 5 min before they were trained on aversively motivated tasks. The peptides impaired acquisition of a one-way active avoidance response, facilitated acquisition of an inhibitory avoidance response, and had no effect on acquisition of a swim-escape response. The data indicate that the enkephalin effects are not mediated through actions on locomotor activity, pain perception or reactivity, or light sensitivity. Rather, we suggest that [Leu]enkephalin and its analog strengthen the tendency of rats to suppress behavior in the presence of cues previously associated with aversive stimulation. This effect may be due to an enkephalin-induced increase in fear or arousal. The enkephalin effect on behavior was obtained at low doses and was observed within a few minutes after administration. These findings are consistent with the interpretation that enkephalin effects may be initiated at a peripheral site.
D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects; D001522:Behavior, Animal / Q000187:drug effects*; D004597:Electroshock; D004723:Endorphins / Q000494:pharmacology*; D004743:Enkephalin, Leucine; D016308:Enkephalin, Leucine-2-Alanine; D004745:Enkephalins / Q000494:pharmacology*; D004924:Escape Reaction / Q000187:drug effects; D005239:Fear / Q000187:drug effects*; D008027:Light; D008297:Male; D010146:Pain / Q000523:psychology; D010465:Perception / Q000187:drug effects; D051381:Rats; D012684:Sensory Thresholds / Q000187:drug effects; D014796:Visual Perception / Q000187:drug effects; D014867:Water
D004723:Endorphins; D004745:Enkephalins; D014867:Water; D004743:Enkephalin, Leucine; D016308:Enkephalin, Leucine-2-Alanine