EFFECT OF EXCITATORY AMINO-ACID RECEPTOR ANTAGONISTS ON APOMORPHINE-INDUCED, OXYTOCIN-INDUCED AND ACTH-INDUCED PENILE ERECTION AND YAWNING IN MALE-RATS

The effect of excitatory amino acid receptor antagonists. (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclo-hepten-5,10-imine hydrogen maleate ((+)-MK-801), (+/-)-3-(2-carboxy-piperazin-4-yl)-propyl-1-phosphonic acid (CPP), 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX) and (+/-)-2-amino-4-phosphonobutanoic acid (AP-4), on penile erection and yawning induced by subcutaneous apomorphine (80-mu-g/kg), intracerebroventricular (i.c.v.) oxytocin (30 ng) and adrenocorticotropin (ACTH)-(1-24) (10-mu-g) was studied in male rats. Intraperitoneal (0.1-0.4 mg/kg) and i.c.v. (10-50-mu-g) (+)-MK-801 prevented dose dependently the penile erection and yawning induced by the three drugs. The (+)-MK-801 effect coincided with the appearance of head weaving, body rolling, hyperlocomotion and ataxia. Haloperidol (0.5 mg/kg i.p.) antagonized the prevention by (+)-MK-801 of oxytocin responses. Penile erection but not yawning was also prevented by high, but not low doses of CPP and CNQX, which impaired motor performance, AP-4 was ineffective at all doses tested. The above compounds were ineffective when injected into the paraventricular nucleus of the hypothalamus, the brain area where apomorphine and oxytocin act to induce penile erection and yawning. The results suggest that excitatory amino acid transmission is not involved in the expression of penile erection and yawning induced by the above compounds.