Opposite effects of Met-enkephalin and Leu-enkephalin on a discriminated shock-escape task.
Leu-enkephalin was found to impair and Met-enkephalin to enhance acquisition of a discriminated Y-maze shock-escape task in mice at equivalent doses (100 micrograms/kg, ip). Naloxone (1.0 and 10.0 mg/kg) also enhanced acquisition of the escape response and blocked the impairing actions of Leu-enkephalin. Neither naloxone nor the enkephalins influenced shock-induced locomotor activity in an open field. The results suggest that enkephalin actions on escape conditioning are mediated through opioid receptors.
D000818:Animals; D004193:Discrimination Learning / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004743:Enkephalin, Leucine / Q000494:pharmacology*; D004744:Enkephalin, Methionine / Q000494:pharmacology*; D004924:Escape Reaction / Q000187:drug effects*; D008297:Male; D051379:Mice; D009043:Motor Activity / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology
D009270:Naloxone; D004744:Enkephalin, Methionine; D004743:Enkephalin, Leucine