title: Endogenous opioids: naloxone disrupts learned performance in rats.
abstract: The effect of naloxone on learned performance reinforced by food was examined in 2 experiments. Male rats were trained to run down a short runway for 5 (45 mg) food pellets per trial and were then shifted either to 1 or 0 pellets. Following such an abrupt reinforcement shift, animals typically show an emotional disruption of performance (Crespi, 1942) referred to as "depression". We examined the postshift depression-effect in groups treated either with saline (SAL) or naloxone (NAL). In experiment 1 NAL groups received a single 10 mg/kg (s.c.) injection prior to each postshift session. When compared with SAL controls, NAL animals showed an exaggerated postshift depression-effect. Furthermore, a single (0.3 mg/kg, s.c.) injection of the enkephalin analog FK 33-824 (D-Ala2, MePhe4, Met-(0)5-o1) produced a dramatic recovery of performance. In the second experiment, these effects were replicated at a low NAL dose (1 mg/kg), which had no direct effect on motor performance. These findings suggest that opiate systems may modulate the incentive motivation that maintains learned performance.
mesh_terms: D000818:Animals; D005405:D-Ala(2),MePhe(4),Met(0)-ol-enkephalin; D003863:Depression / Q000503:physiopathology; D004195:Disease Models, Animal; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives / Q000494:pharmacology; D006728:Hormones / Q000494:pharmacology; D006801:Humans; D007858:Learning / Q000187:drug effects*; D008297:Male; D009043:Motor Activity / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012054:Reinforcement, Psychology
chemical_list: D006728:Hormones; D009270:Naloxone; D004744:Enkephalin, Methionine; D005405:D-Ala(2),MePhe(4),Met(0)-ol-enkephalin