Inhibition of nitric oxide synthesis with L-NAME suppresses isolation-induced ultrasounds in rat pups

The present experiments examined the impact of manipulating the NO system o n production of isolation-induced ultrasonic vocalizations (USVs) in 10- an d Ii-day-old rat pups. Pups were tested under both high- and low-baseline U SV emission: the latter was accomplished by pretest administration of cocai ne, a drug known to suppress USVs. Treatment with 10, 50, or 100 mg/kg (but not 1 mg/kg) of the nitric oxide synthase (NOS) inhibitor L-nitro-arginine methyl ester (L-NAME) significantly attenuated USV production, as did inje ction of 10 mg/kg cocaine; combined treatment with both drugs did not resul t in greater suppression, perhaps due to a floor effect. Although cocaine i ncreased locomotor activity, treatment with L- or D-NAME alone did not alte r activity levels. Exposure to L-NAME induced some hypothermia, although th ese alterations in body temperature were not systematically related to the drug-induced suppression of USVs. Alterations in USV production by L-NAME w ere not evident after pretreatment with the less active isomer D-NAME, evid ence supporting the importance of NO synthesis inhibition per se in the mar ked L-NAME-induced suppression of USVs in isolated infant rats. (C) 1999 El sevier Science Inc.