PENILE ERECTION AND YAWNING INDUCED BY PARAVENTRICULAR NMDA INJECTIONIN MALE-RATS ARE MEDIATED BY OXYTOCIN

The effect of N-methyl-D-aspartic acid (NMDA), pha-amino-3-hydroxy-5-m ethyl-isoxazole-4-propionic acid (AMPA), or (+/-)-trans-1-amino-1,3-cy clo-pentanedicarboxylic acid (ACPD) (5-60 ng in 0.3 mu l of saline) mi croinjected in the paraventricular nucleus of the hypothalamus on peni le erection and yawning was studied in male rats. NMDA induced both pe nile erection and yawning in a dose-dependent manner. AMPA and ACPD al so induced penile erection but less potently than NMDA, but were ineff ective in causing yawning. NMDA effect on penile erection and yawning was prevented by (+)-MK-801 (0.05-0.1 mg/kg IP, 10 min before NMDA), b y the oxytocin antagonist d(CH2)(5)Tyr(Me)-Orn(8)-vasotocin (50-100 ng ICV 10 min before NMDA), but not by haloperidol (0.1-0.5 mg/kg IP 10 min before NMDA). The results suggest that NMDA induces penile erectio n and yawning by increasing oxytocinergic transmission by acting in th e paraventricular nucleus of the hypothalamus.