Naloxone disrupts the expression but not the acquisition by male rats of a conditioned place preference response for an oestrous female

Abstract

Two experiments were conducted to investigate the possible role of endogenous opioid peptides in the regulation of masculine sexual reward. In experiment 1 sexually experienced male rats, which had recently been castrated or left gonadally intact, were allowed to mate with an oestrous female in an initially "non-preferred" chamber of a test apparatus. On alternate days these males were placed alone in the initially "preferred" chamber of the same apparatus. After eight such conditioning sessions both intact and castrated males had acquired a conditioned place preference (CPP) for the initially "non-preferred" chamber whereas control males, which were never given access to an oestrous female, showed no evidence of a significant shift in their preference for either chamber. Administration of the opioid receptor antagonist, naloxone (1 or 5 mg/kg, SC) prior to each conditioning session had no significant influence on the acquisition of a CPP for an oestrous female. By contrast, in experiment 2 naloxone treatment significantly attenuated the expression of a previously established CPP for an oestrous female in both gonadally intact and castrated males. The results suggest that opioid components of neural reward circuits are normally activated in the male rat by conditioned incentive stimuli, but not by the primary rewarding stimuli associated with access to and mating with an oestrous female.

Extinction of ethanol-induced conditioned place preference and conditioned place aversion: effects of naloxone

“…Moreover, repeated testing with lithium chloride did not affect rate of extinction or produce an aversion to the CS previously paired with ethanol (experiment 4). The facilitating effect of naloxone on extinction of ethanol-induced conditioned place preference is generally similar to previous reports that naloxone facilitates extinction of learning involving other appetitive events such as food (Benton et al 1984), social reinforcement (Panksepp and DeEskinazi 1980), or access to a sexually receptive female (Mehrara and Baum 1990). Moreover, naloxone's ability to maintain ethanol-induced conditioned place aversion appears consistent with studies suggesting that naloxone may actually retard extinction of aversively motivated responses (Hernandez and Powell 1983;Hernandez et al 1990Hernandez et al , 1991; but see Benton et al 1984;Bormann and Cunningham 1997).…”

“…We described the phenomenon as "facilitation of extinction" and raised the theoretical possibility that naloxone produced its effect by altering the general inhibitory processes thought to underlie extinction of learned responses. In fact, the literature offers mixed evidence on this issue, with some studies showing naloxone-induced facilitation of extinction (e.g., Panksepp and DeEskinazi 1980;Benton et al 1984;Mehrara and Baum 1990), while others show retardation of extinction (e.g., Hernandez and Powell 1983;Hernandez et al 1990Hernandez et al , 1991. Comparisons across such studies are complicated, however, by differences in species, task and reinforcer.…”

Pharmacology for the Treatment of Premature Ejaculation

“…In addition, opioids are involved in the initiation of sexual behavior after ejaculation, because naloxone extends the postejaculatory refractoriness (Szechtman et al, 1981;Van Furth et al, 1994) and inhibits resumption of mating in sexually sated male rats after the reintroduction of a female rat (Miller and Baum, 1987). Finally, opioids play a role in reward-related aspects of ejaculation, because naloxone also blocks the expression of ejaculation-induced place preference (Agmo and Berenfeld, 1990;Mehrara and Baum, 1990).…”

Do rats have orgasms?

“…CPP is said to have developed if the rat spends significantly more time in the reward-paired compartment than the other compartment. Sexual CPP is observed when male rats are placed into a distinctive compartment of the CPP box after ejaculation, in contrast to being placed into the other compartment after mounts or intromissions alone (Ågmo & Berenfeld, 1990; Everitt, 1990; Hughes, Everitt, & Herbert, 1990; Mehara & Baum, 1990). However, intromissions alone can maintain copulatory CPPs in males that have not yet experienced ejaculation (Hughes et al, 1990; Tenk, Wilson, Zhang, Pitchers, & Coolen, 2009).…”