Opioids and sexual behavior of male rats: Involvement of the medial preoptic area.

Abstract

Local infusion of beta-endorphin (beta-END) into the medial preoptic area (MPOA) dose-dependently impaired the gating of the copulatory response and the execution of the sexual performance of sexually experienced, intact male rats. Local naloxone treatment prevented the impairment of the sexual response by beta-END, but failed to facilitate unimpaired copulation. Local infusion into the MPOA of equimolar doses of alpha-endorphin, dynorphin-A-(1-17) or met-enkephalin were less effective than beta-END. It is suggested that endogenous opioid systems in the MPOA are normally quiescent, and increased activity may be related to disrupted or inhibited male sexual behavior.

Effects of Thyroidectomy or Thiouracil Treatment on Copulatory Behavior in Adult Male Rats.

“…GnRH has been known to stimulate copulatory behavior in male rats [1,4,15]. It has been reported that acute microinfusions of CRH into the third cerebral ventricle of male rats produced a dose-dependent suppression of masculine sexual behavior and that a low dose of β-endorphin also inhibited masculine copulatory activity in rats when injected into the lateral ventricle [14] or MPOA [6,30]. We have previously reported that hypothyroidism causes adrenal dysfunction and leads to hypersecretion of ACTH [27].…”

“…The regulation of masculine sexual behavior is a complex process involving several neurochemicals including dopamine [30], opioid peptides [29,30], corticotropin releasing hormone (CRH) [21], and gonadotrophin releasing hormone (GnRH) [1,4,15]. The medial preoptic area (MPOA) is known to be critically important for male sexual behavior in various species [3,20], and there are numerous peptide-containing cell bodies and fibers including CRH, β-endorphin and GnRH within MPOA [3].…”

Reward Processing by the Opioid System in the Brain

“…In contrast, opioid agonists, when injected at low doses into the VTA, facilitated sexual behavior in male rats, whereas naloxone decreased the percentage of sexually active rats (reviewed in Ref. 385) and prevented the anticipatory behavioral activation prior to the introduction of a female rat (386). Injections of the kappa receptor agonist nor-BNI into the VTA increased female directed behavior (214).…”

“…387; see also Refs. 241, 385) and inhibited female sexual behavior under certain conditions (reviewed in Refs. 292, 293).…”

The Endomorphin System and Its Evolving Neurophysiological Role

“…The immunocytochemical data showed that -opioid receptors are widely distributed in some areas involved in female reproductive behavior, such as the ventromedial hypothalamus (VMH), the medial preoptic area (mPOA), and the mesencephalic central gray (MCG) (Pfaff et al, 1994;Martin-Schild et al, 1999). Concurrently, -opioid receptorselective ligands were shown to possess a dual effect on lordosis, a hormone-related behavior displayed by hormonally primed female rodents during mating (Pfaff et al, 1994), depending on the concentration used and the route of administration (Wiesner and Moss, 1984;Sirinathsinghji, 1986;Pfaus and Gorzalka, 1987a,b;Vathy et al, 1991;Pfaff et al, 1994;Van Furth et al, 1995). For example, low doses of ␤-endorphin inhibited lordosis in gonadectomized, steroid-primed female rats when infused into the third ventricle Moss, 1984, 1986), lateral ventricles (Pfaus et al, 1986;Pfaus and Gorzalka, 1987b), the MCG (Sirinathsinghji, 1984(Sirinathsinghji, , 1985, or mPOA (Sirinathsinghji, 1986).…”