Interactions between N-methyl- d-aspartate and nitric oxide in the modulation of ultrasonic vocalizations of infant rats

Abstract

The effects of interactions between N-methyl- d-aspartate (NMDA) and nitric oxide on ultrasonic vocalizations, motor activity and body temperature was investigated in 9–10-day-old rat pups. The competitive NMDA receptor antagonist, 3-((±)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP), and the nitric oxide synthase inhibitor, nitro- l-arginine-methyl ester ( l-NAME), decreased the emission of ultrasonic vocalizations while NMDA and the nitric oxide precursor, l-arginine, produced a trend toward increased emission of ultrasonic vocalizations. CCP also attenuated the geotaxic response. Co-administration of CPP with l-NAME virtually abolished the emission of ultrasonic vocalizations and the ability to show the geotaxic response while co-administration of NMDA with l-arginine increased the emission of ultrasonic vocalizations and decreased body temperature with no effect on the geotaxic response. NMDA and l-arginine reversed the effects of l-NAME, but not of CPP, on ultrasonic vocalizations. l-arginine but not NMDA antagonized the effect of CPP on the geotaxic response. Our results confirmed the functional coupling between NMDA receptor activation and nitric oxide in modulating anxiety-like behavior and motor coordination in infant rats.