title: Leu-enkephalin actions on avoidance conditioning are mediated by a peripheral opioid mechanism.
abstract: Leu-enkephalin (100 micrograms/kg, i.p.) administered to mice 5 min before training in a one way active avoidance task significantly reduced the number of avoidances observed in the peptide treated animals. This impairing action of Leu-enkephalin was partially attenuated by methylnaloxonium (naloxonium), a quarternary form of naloxone with a limited ability to penetrate the blood brain barrier. Passive immunization (i.v.) of mice with a Leu-enkephalin antiserum 4 hrs before training produced an effect on avoidance conditioning that was the opposite to that observed with Leu-enkephalin alone. That is, passive immunization increased the number of avoidances observed in the treated mice. The results suggest that Leu-enkephalin actions on avoidance conditioning are mediated by a peripheral opioid mechanism, that leu-enkephalin may have a primary site of action outside the blood brain barrier, and that peripheral Leu-enkephalin systems may normally operate to influence conditioned avoidance behavior.
mesh_terms: D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D004743:Enkephalin, Leucine / Q000276:immunology / Q000494:pharmacology*; D007106:Immune Sera / Q000276:immunology; D007116:Immunization, Passive; D008297:Male; D051379:Mice; D009270:Naloxone / Q000031:analogs & derivatives / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology*
chemical_list: D007106:Immune Sera; D000644:Quaternary Ammonium Compounds; D011957:Receptors, Opioid; D009270:Naloxone; D004743:Enkephalin, Leucine; C041269:N-methylnaloxone