Behavioral specificity of beta-endorphin suppression of sexual behavior: differential receptor antagonism

Open field behavior was observed in conjunction with mating behavior to discern whether the effect of intraventricular (ICV) beta-endorphin (beta-END) on sexual behavior may be secondary to akinesia. Three groups of ovariectomized, estrogen-progesterone-primed rats each received counterbalanced treatments of saline ICV, 2 micrograms beta-END ICV, or 2 micrograms beta-END ICV in combination with a selective opioid receptor antagonist. Receptive behavior (lordosis) and proceptive behaviors (presentation and ear wiggling) were consistently suppressed by beta-END, while ambulation was unaffected. Rearing and grooming were generally decreased, although this effect was statistically significant in only one experiment. Pretreatment with the mu-1 antagonist naloxazone (50 mg/kg intravenously) reversed the effects of beta-END on all behaviors tested. The delta receptor antagonist ICI-154,129 (12.5 and 50 micrograms ICV) only partially reversed the sexual effects of beta-END but completely reversed the open field effects. It is concluded that the suppressive effect of beta-END on sexual behavior, while not behaviorally specific, is not secondary to opioid-induced akinesia.