MK-801-induced disruptions of one-trial inhibitory avoidance are potentiated by stress and reversed by naltrexone.
Five experiments were carried out to investigate opioid and NMDA receptor-mediated responses to one-trial inhibitory avoidance training in CD1 mice. In the first experiment immediate posttraining intraperitoneal administration of the noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist MK-801 impaired the performance of mice. The effects of MK-801 were time-dependent (they were absent in mice injected with the drug starting 120 min after training). No effect was evident in no-foot-shock groups, showing lack of proactive influence of the treatment on performance. In the second experiment preexposure of the mice to the testing apparatus decreased the effects of MK-801. In the the third experiment naltrexone antagonized the effects of MK-801, suggesting an involvement of opioid neurons. In the fourth experiment immediate posttraining immobilization stress exerted a potentiating effect on the performance of MK-801-injected animals. In the fifth experiment the potentiation of the impairing effect of MK-801 induced by immobilization stress was antagonized by naltrexone.
Castellano
C
C
Istituto di Psicobiologia e Psicofarmacologia del CNR, Viale Marx 15, Roma, 00137, Italy. castella@kant.irmkant.rm.cnr.it
Cestari
V
V
Ciamei
A
A
Pavone
F
F
D000818:Animals; D001143:Arousal / Q000187:drug effects*; D001245:Association Learning / Q000187:drug effects; D001362:Avoidance Learning / Q000187:drug effects*; D001921:Brain / Q000187:drug effects; D016291:Dizocilpine Maleate / Q000494:pharmacology*; D005239:Fear / Q000187:drug effects; D008297:Male; D011939:Mental Recall / Q000187:drug effects; D051379:Mice; D008815:Mice, Inbred Strains; D009271:Naltrexone / Q000494:pharmacology*; D009433:Neural Inhibition / Q000187:drug effects*; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects*; D011957:Receptors, Opioid / Q000187:drug effects*
D016194:Receptors, N-Methyl-D-Aspartate; D011957:Receptors, Opioid; D009271:Naltrexone; D016291:Dizocilpine Maleate