Naloxone Blocks the Deterioration of Male Sexual Behavior Induced by Alarm Pheromone in Rats

Abstract

ABSTRACT. Previously, we have demonstrated that the alarm pheromone deteriorates sexual behavior in male rats, which was blocked by pretreatment with a corticotrophin-releasing hormone (CRH) antagonist. Studies have shown that an opioid antagonist blocked the deterioration of male sexual behavior following intracerebroventricular administration of CRH. Therefore, possibly, the pheromone effects could also be mediated by the opioid system. In this study, we pretreated rats with naloxone, an opioid receptor antagonist, and examined the following sexual behavior modulations in male rats that were exposed to the alarm pheromone. Naloxone blocked the deterioration of sexual behavior in a dose-dependent manner. On the basis of these data and the results of the previous study, we conclude that the alarm pheromone activates the CRH system, which then activates the opioid system, to deteriorate male sexual behavior. KEY WORDS: alarm pheromone, naloxone, opioid, rat, sexual behavior.doi: 10.1292/jvms.12-0454; J. Vet. Med. Sci. 75(6): 761-765, 2013 Sexual behavior is one of the most important activities for organisms and has been studied for many years. In addition to sexual behavior itself, it also has been demonstrated that various types of stressors can deteriorate male sexual behavior. For example, 2 hr of immobilization elongated intromission latency, increased number of mounts needed for an ejaculation and decreased hit rate (number of intromissions/sum of mounts and intromissions) in male rat [27]. Similarly, water immersion elongated mount, intromission and ejaculation latency, and post ejaculation interval (PEI), and it increased the number of mounts and intromissions, and decreased the hit rate [27]. In addition, we have shown that sexual behavior was also deteriorated by the alarm pheromone [16].We previously showed that foot-shocked male Wistar rats release an alarm pheromone, which aggravates stressinduced hyperthermia (SIH) in pheromone-exposed rats [10] via the vomeronasal system [14]. We can induce the release of this pheromone by electrical stimulation to the perianal region of the anesthetized donor rat [14]. In addition, this alarm pheromone was shown to be water-soluble, because exposure to water droplets collected from the ceiling of the box in which the alarm pheromone was released produced all responses that are observed in recipients directly exposed to the pheromone [12]. This pheromone solution allows us to observe pheromone effects in different experimental paradigms; it can evoke several responses, such as aggravated SIH in the home cage [12,14], increased defensive and risk assessment behaviors in a modified open-field test [15] and enhanced acoustic startle reflex (ASR) [7,8]. In addition to its effects on individual animals, the effects of the alarm pheromone on social behavior have been analyzed [16]. When we presented the alarm pheromone during sexual behavior, male sexual behavior was deteriorated as indicated by the increasing number of mounts and decreasing hit rate, whereas female se...

Neural correlates underlying naloxone-induced amelioration of sexual behavior deterioration due to an alarm pheromone

“…In addition, pretreatment with naloxone blocked these effects in the mPVN, vlPAG, and nPGi. Based on these results, we have revised our hypothesis regarding the neural mechanisms underlying the alarm pheromone-induced deterioration in sexual behavior (Kobayashi et al, 2013a , b ) as follows: when a male rat detects the alarm pheromone, the vomeronasal system, including the BNSTp, and the main olfactory system (Inagaki et al, 2014 ) receive information about the pheromone. Information from these 2 olfactory systems activates the pPVN, which subsequently activates opioidergic neurons in the Arc.…”

“…Before the sexual behavior test, water samples that contained either the alarm pheromone or a control odor were prepared according to a previously described method (Kiyokawa et al, 2005a ; Kobayashi et al, 2013b ). Adult male Wistar Imamichi rats (aged 12–16 weeks) were anesthetized and 2 intradermal needles (27G) were attached at either the neck or perianal region.…”

“…Sexual behavior tests were conducted as described in previous studies (Kobayashi et al, 2011 , 2013a , b ). Briefly, 1 day before the test, male rats were housed individually and acclimatized for 30 min to the experimental room and devices.…”

“…Male sexual behavior was analyzed as described in previous studies by a researcher who was blind to the experimental conditions (Kobayashi et al, 2011 , 2013a , b ). The following measures of sexual behavior were recorded: mount latency (pelvic thrusting from the rear of the female rat without penile insertion), intromission latency (deeper pelvic thrusting from the rear of the female rat with penile insertion), latency for tenth intromission (time from the first intromission to tenth intromission), and number of mounts (number of mounts needed for 10 intromissions).…”

“…We found that systemic pretreatment with the opioid receptor antagonist naloxone attenuated sexual deterioration in male rats. This suggests that opioids are involved in the neural mechanism (Kobayashi et al, 2013b ). However, regions in which we found increased Fos expression during deterioration (Kobayashi et al, 2013a ), such as the nPGi and several other nuclei, to our knowledge, do not express opioid receptors.…”