Inhibition of copulatory behavior in male rats by D-ALA2-Met-Enkephalinamide

Pharmacological analysis of male rat sexual behavior

“…Similar effects were reported for micromjections of the long lasting synthetic opmte, D-ALA-met-enkephalinamide (DALA) [179], and of morphine [151,159]. The importance of opiate receptors for this effect was confirmed smce it was antagorazed by systemically injected naloxone [179] or naltrexone [160]. Morphine micromjections mto the MPOA decreased the mean number of ejaculattons per ammai, and increased the postejaculatory interval; similar mlcroinjections into the cerebral ventricles slowed the rate of mtromlssions and decreased intromlsslon ratio [24].…”

“…The endogenous opiate,/3-endorphin, micromjected into the LV, produced a dose-dependent decrease in the proportion of males copulating, and increased the mount latency of those that did [151,159,160]. Similar effects were reported for micromjections of the long lasting synthetic opmte, D-ALA-met-enkephalinamide (DALA) [179], and of morphine [151,159]. The importance of opiate receptors for this effect was confirmed smce it was antagorazed by systemically injected naloxone [179] or naltrexone [160].…”

Impaired Copulatory Behaviour of Male Rats with Hyperprolactinaemia Induced by Domperidone or Pituitary Grafts

“…Intraventricular injections of (3-endorphin and a metenkephalin analogue have both been shown to profoundly impair copulation of male rats [31,37] and naloxone, an op iate antagonist, may accelerate copulation [34]. Systemic administration of another peptide, luteinizing hormone-releasing hormone (LHRH), stimulates sexual activity of male and female rats [33], and receptivity of females has also been stimulated by LHRH infusion into the medial ba sal hypothalamus and preoptic area [32] and midbrain cen tral gray [43].…”

Lack of opioid or dopaminergic effects on unconditioned sexual incentive motivation in male rats.

“…Among the others, opioids seem to be of particular interest for motivation (Ågmo & Paredes, 1988; Pfaus & Gorzalka, 1987). Several opioid peptides and opiates have been reported to inhibit male sexual behavior when administered systemically or into the cerebral ventricles (Ågmo & Paredes, 1988; McIntosh, Vallano, & Barfield, 1980; Meyerson & Terenius, 1977; Mumford & Kumar, 1979; Pellegrini-Quarantotti, Corda, Paglietti, Biggio, & Gessa, 1978). When infused directly into the brain they have site-dependent effects: stimulatory in the ventral tegmental area (Mitchell & Stewart, 1990) and inhibitory in the preoptic area (Hughes, Everitt, & Herbert, 1987, Hughes, Everitt, & Herbert, 1990; Matuszewich & Dornan, 1992).…”