Effect of the nitric oxide level in the medial preoptic area on male copulatory behavior in rats

Abstract

We investigated the influence of the extracellular nitric oxide (NO) level on male copulatory behavior. We confirmed the changes of nitrite ([Formula: see text]) and nitrate ([Formula: see text]) in the medial preoptic area (MPOA) by administration of the NO precursorl-arginine (l-Arg, 10 mM) or the NO synthase inhibitor N G-monomethyl-l-arginine (l-NMMA, 10 mM) via a dialysis probe. [Formula: see text] and[Formula: see text] were measured simultaneously by an in vivo microdialysis method coupled with the Griess reaction.l-Arg induced significant elevations of extracellular [Formula: see text]and [Formula: see text].l-NMMA significantly reduced[Formula: see text] and[Formula: see text] levels. We observed male copulatory behavior during infusion ofl-Arg orl-NMMA. The mount rate of male rats significantly increased during infusion ofl-Arg in the MPOA. Administration of l-NMMA reduced the mount rate. These findings suggested that the elevation of extracellular NO in the MPOA facilitates male copulatory behavior of rats, whereas the decrease of NO reduces their copulatory behavior.

A Nitric Oxide Synthesis Inhibitor Administered Into the Medial Preoptic Area Increases Seminal Emissions in an Ex Copula Reflex Test

“…Thus, by inhibiting the inhibitor (NO), L -NMMA in the MPOA enhances seminal emission, which is mediated by the sympathetic nervous system [reviewed in (4)]. In addition, L -NMMA (400 g) injected into the MPOA blocked intromissions in a copulation test, although only among sexually naïve males (Moses, unpublished observations), confirming a recent report (21). Erection, required for successful intromission, is controlled in part by the parasympathetic nervous system [reviewed in (4)].…”

“…One site that may mediate this effect is the medial preoptic area (MPOA), which is critical for male sexual behavior [reviewed in (15)]. Administration of L -NAME into this site reduced mount rate in male rats (21). There are scattered NOS-immunoreactive cells in the MPOA (25), which decrease in number following castration (6).…”

Dopamine, the medial preoptic area, and male sexual behavior

“…Furthermore, reverse dialysis of a different NOS inhibitor, nitro-larginine methyl ester (l-NAME), into the MPOA three hours prior to the introduction of a female prevented the increase of DA normally observed in the presence of a receptive female and during copulation; animals receiving d-NAME, the inactive isomer of l-NAME, showed normal DA responses [100]. The importance of NO in the MPOA for copulation was demonstrated when reverse dialysis of larginine increased the rate of mounting by male rats, and similar administration of l-NMMA decreased mount rate [101].…”

Neurotransmitters: central and peripheral mechanisms

“…16,34 ± 37 NO may act in several discrete brain regions, eg in the medial preoptic area 36,37 as well as in the paraventricular nucleus. 9,16 Injection of NOS inhibitors intracerebroventricularly or in the paraventricular nucleus prevented penile erectile responses induced by dopamine agonists, oxytocin, and NMDA in rats.…”