Regional and subtype-specific loss of GnRH neurons is associated with diminished mating behavior in middle-aged male rats

The current study was to examine the relationship between the number of gonadotropin-releasing hormone (GnRH) neurons and male sexual behavior in middle-aged rats. Based on their sexual performance, middle-aged male rats (18-19 months) were assigned to three groups: (i) Group MIE (showing mounts, intromissions, and ejaculation), (ii) Group MI (displaying mounts and intromissions, but no ejaculation), and (iii) Group NC (showing no copulatory behavior). The brains of these middle-aged animals and of sexually active, young controls were collected and then examined for immunohistochemical localization of GnRH neurons. The numbers of two subtypes of GnRH neurons, smooth (s-GnRH) and irregular (i-GnRH), in the medial septum (MS), organum vasculosum of the lamina terminalis (OVLT), preoptic area (POA), and anterior hypothalamus (AH), were determined under a light microscope. As compared to young controls, an age-related decrease in the number of s-GnRH neurons was found in the MS of MIE rats. Among three groups of middle-aged rats, Groups MIE and MI had more s-GnRH neurons in the POA and i-GnRH neurons in the OVLT and POA than Group NC. In addition, loss of s-GnRH and i-GnRH neurons in the MS was observed in Groups MI and NC and Group NC, respectively. Our results suggest that a decrease in GnRH neuron subtypes occurring in different brain regions might be critical for the loss of specific components of male rat sexual behavior during aging.

Ginkgo biloba extract treatment increases noncontact erections and central dopamine levels in rats: role of the bed nucleus of the stria terminalis and the medial preoptic area

RATIONALE

Penile erection is necessary for successful copulation in males. The extract of Ginkgo biloba leaves (EGb 761) significantly facilitates copulation in male rats, but the effect of EGb 761 on noncontact erection (NCE) remains unknown.

OBJECTIVE

The present study was conducted to evaluate the influence of EGb 761 on NCE in male rats.

MATERIALS AND METHODS

Adult Long-Evans male rats were treated with 50 mg/kg of EGb 761 (experimental group) or distilled water (control group) by gavage for 14 days. The NCE test was carried out after 14 days of EGb 761 treatment, and the latency and the numbers of NCE were recorded. Approximately 14 h following the NCE behavioral tests, animals were sacrificed by means of decapitation, and levels of dopamine in the bed nucleus of the stria terminalis (BNST) and medial preoptic area (MPOA) were measured by means of high-pressure liquid chromatography with electrochemical detection.

RESULTS

Chronic treatment with EGb 761 significantly decreased the NCE latency, but increased the number of NCEs and the dopamine levels in the BNST and MPOA in rats compared to the controls.

CONCLUSION

Treatment with EGb 761 increased both NCEs and the dopamine contents in the BNST and the MPOA. These results suggest that enhanced NCEs in the rats administered with EGb 761 may be related to dopaminergic activity in the BNST and MPOA.

Different subregions of the medial preoptic area are separately involved in the regulation of copulation and sexual incentive motivation in male rats: a behavioral and morphological study

The purpose of this study was to investigate whether sexual incentive motivation and copulatory performance are regulated by different subregions of the medial preoptic area (MPOA). Sexual incentive motivation was measured by means of a partner preference test. Both copulatory behavior and sexual incentive motivation were tested in male rats treated with 50mg/kg of either EGb 761 or a vehicle (distilled water) by gavage for 14 days. Administration of EGb 761 increased the number of intromissions, but had no effect on the number of mounts, mount latency, intromission latency, ejaculation latency, or post-ejaculatory interval. In the partner preference test, the total duration of visits to estrous female rats in both of the groups was significantly different from the total duration of visits to sexually active males. EGb 761 treatment increased the number of ejaculations compared both to vehicle-treated controls on day 14 and the same group on day 0. In comparison with the controls, the EGb 761-treated group showed a significant increase in the number of tyrosine hydroxylase-expressing cells in the dorsal, but not the ventral, subregion of the MPOA, and significantly high dopamine levels in the MPOA. These results indicate that EGb 761 does not affect sexual incentive motivation, but facilitates copulatory performance in male rats, suggesting that the mechanisms responsible for sexual incentive motivation and copulatory performance may be associated with differential functions of MPOA subregions.