[Leu]enkephalin and its metabolite, Tyr-Gly-Gly, impair active avoidance retention.
The current study examined the effects of [leu]enkephalin and its metabolite, Tyr-Gly-Gly, given immediately posttraining on active avoidance performance measured 24 h later. Initial experiments revealed that, in comparison to zero or one training trials, providing mice with two training trials significantly increased active avoidance performance measured 24 h later; this enabled us to examine the effects on retention of peptides administered immediately after the two training trials. It was found that Tyr-Gly-Gly (16 and 53 micrograms/kg) and [leu]enkephalin (30 and 100 micrograms/kg) administered in this fashion both significantly impaired retention; the dose-response functions for both peptides were U-shaped. Since the effects of enkephalins are most likely mediated by opioid delta-receptors, and Tyr-Gly-Gly has little or no activity at opioid receptors, the effects of the parent peptide(s) and metabolite are presumably pharmacologically distinct.
Schulteis
G
G
Department of Psychology, University of California, Berkeley 94720.
Martinez
J L
JL
D000595:Amino Acid Sequence; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D003864:Depression, Chemical; D004305:Dose-Response Relationship, Drug; D004743:Enkephalin, Leucine / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000494:pharmacology*
D009842:Oligopeptides; C044757:tyrosyl-glycyl-glycine; D004743:Enkephalin, Leucine