NOCICEPTIN ORPHANIN FQ MICROINJECTED INTO HIPPOCAMPUS IMPAIRS SPATIAL-LEARNING IN RATS/

The newly discovered peptide nociceptin/orphanin FQ has been found to increase reactivity to pain and to influence locomotor activity after intracerebroventricular administration. This study investigated the po ssible role of hippocampal nociceptin/orphanin FQ in spatial learning and in spontaneous locomotion. Male rats were trained in the Morris wa ter task after microinjection of 10 nmol nociceptin/orphanin FQ or art ificial cerebrospinal fluid (as control) into the CA3 region of the do rsal hippocampus. Nociceptin/orphanin FQ was found to severely impair spatial learning without interfering with swimming performance. Intrah ippocampal injection of nociceptin/orphanin FQ markedly decreased expl oratory locomotor activity including vertical movements (rearing). The data suggest that nociceptin/orphanin FQ is a potent modulator of syn aptic plasticity within the hippocampus.