Nitric oxide synthase inhibitors prevent $\text{N-}\text{methyl-}\text{d}\text{-aspartic}$ acid-induced penile erection and yawning in male rats

Abstract

The effect of $\text{N}{}^{\mathrm{<mtext>G</mtext>}}\text{-}\text{nitro-}\text{l}\text{-arginine}$ methylester (NAME) and $\text{N-}\text{mono-methyl-}\text{l}\text{-arginine}$ (NMMA), inhibitors of nitric oxide (NO) synthase on penile erection and yawning induced by $\text{N-}\text{methyl-}\text{d}\text{-aspartic}$ acid (NMDA) injected in the paraventricular nucleus of the hypothalamus (PVN) was studied in male rats. NAME (75–150 μg) and NMMA (250–500 μg), but not $\text{N-}\text{monomethyl-}\text{d}\text{-arginine}$ (d-NMMA)(250–500 μg) prevented both responses in a dose-dependent manner when given intracerebroventricularly (i.c.v.) 15 min before NMDA (50 ng). NMDA-induced penile erection and yawning was also prevented by the guanylate cyclase inhibitor methylene blue (200–400 μg i.c.v.), but not by the NO scavenger methemoglobin (50–100 μg i.c.v.). NAME (10–20 μg), but not Methylene blue or methemoglobin (10–20 μg), prevented NMDA-induced responses also when injected in the PVN 15 min before NMDA. The present results suggest that NMDA-induced penile erection and yawning is mediated by an increased NO synthesis in the PVN.