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Effects of morphiceptin in the medial preoptic area on male sexual behavior
L Matuszewich1, J L Ormsby, J Moses
1Psychology Department, State University of New York at Buffalo, NY 14260, USA.
Abstract:
Morphiceptin, a selective mu opioid agonist, injected into the medial preoptic area (MPOA), delayed the onset of copulation in male rats, but did not affect genital reflexes, sexual motivation or general motor activity. In a dose-dependent manner, morphiceptin (100 ng and 1000 ng) injected into the MPOA increased mount and intromission latencies. Similar injections of morphiceptin into the ventromedial hypothalamus had no effect on any parameter of copulation. The increase in copulatory latencies following the injection of the highest dose of morphiceptin was blocked by pretreatment with the opioid antagonist naloxone. In the X-maze task, morphiceptin had no effect on sexual motivation, as measured by the percentage of trials on which the male chose the female's chamber, but it increased the number of trials in which the subject did not select a chamber within 60 s and the latency to the female the first time he chose her chamber. Similar to the copulation task, the mount and intromission latencies were also increased in the X-maze, after the male reached the female. Morphiceptin in the MPOA had no effect on ex copula genital reflexes, tested in restrained supine males, or on motor activity, tested in a grid box. These results suggest that morphiceptin disrupts either the specific copulatory somatomotor pattern or a more general motivational component.
Insights
Morphiceptin, a mu opioid agonist, delays rat mating behavior when administered into the medial preoptic area (MPOA). This effect is dose-dependent and blocked by naloxone, suggesting opioid involvement in sexual performance.
Area of Science:
- Neuroscience
- Behavioral Neuroscience
- Reproductive Biology
Background:
- Opioid systems play a role in regulating complex behaviors, including sexual activity.
- The medial preoptic area (MPOA) is a key brain region involved in male sexual behavior.
- Selective mu opioid agonists like morphiceptin offer a tool to investigate opioid receptor function in specific brain areas.
Purpose of the Study:
- To investigate the role of mu opioid receptors in the MPOA on male rat sexual behavior.
- To determine if morphiceptin affects specific components of copulation, sexual motivation, or general motor activity.
Main Methods:
- Male rats were administered morphiceptin (a selective mu opioid agonist) or saline into the MPOA and ventromedial hypothalamus.
- Copulatory behavior, including mount and intromission latencies, was assessed.
- Sexual motivation was evaluated using an X-maze task.
- Genital reflexes and general motor activity were also measured.
- Naloxone, an opioid antagonist, was used to block morphiceptin's effects.
Main Results:
- Morphiceptin administration into the MPOA dose-dependently increased mount and intromission latencies, delaying copulation onset.
- Morphiceptin did not affect genital reflexes or general motor activity.
- In the X-maze, morphiceptin increased latencies to reach the female chamber and the time taken to select a chamber, but did not alter motivation.
- Injections into the ventromedial hypothalamus had no effect on copulatory parameters.
- Naloxone pretreatment blocked the copulatory delays induced by morphiceptin.
Conclusions:
- Mu opioid receptor activation in the MPOA disrupts the initiation and execution of male rat copulatory behavior.
- The MPOA's mu opioid system appears critical for regulating the timing of sexual performance, rather than general motivation or motor control.
- These findings highlight a specific role for MPOA opioid signaling in the somatomotor aspects of sexual behavior.