Fluoxetine-induced decrements in sexual responses of female rats and hamsters are reversed by 3α,5α-THP

II. Antidepressants and sexual behavior: Acute fluoxetine, but not ketamine, disrupts paced mating behavior in sexually experienced female rats

Female sexual dysfunction is both a symptom of depression and exacerbated by treatments for depression. Ketamine, a novel treatment for depression, has been shown to enhance, whereas fluoxetine has been shown to impair sexual motivation. Sexual experience leads to more robust partner preference and paced mating behavior in female rats. Whether acute ketamine and fluoxetine similarly affect sexual motivation and mating behavior in sexually experienced female rats is unknown. Sexually experienced female rats received 10 mg/kg i.p. of ketamine or saline vehicle (Experiment 1) or 10 mg/kg i.p. of fluoxetine or water vehicle (Experiment 2) 30 min before a 10-min no-contact partner preference test followed immediately by a 15-intromission paced mating test. Partner preference and paced mating behavior did not differ between ketamine- and saline-treated rats. In contrast, rats treated with fluoxetine spent significantly less time with either stimulus animal and were less active during the partner preference test than water-treated rats. Additionally, contact-return latency to ejaculation was significantly longer in fluoxetine-treated rats and they spent less time with the male during paced mating in comparison to water-treated rats. Thus, even with sexual experience, fluoxetine disrupts sexual function whereas ketamine has no detrimental effects on sexual behavior in female rats. A growing body of evidence suggests that ketamine is an encouraging new approach to treat depression particularly because it is not associated with sexual dysfunction.

Correlation between allopregnanolone levels and depressive symptoms during late menopausal transition and early postmenopause

OBJECTIVES

This observational, cross-sectional study included 140 women with climacteric symptoms. The aim of the study was to evaluate the correlation between the presence and severity of depressive symptoms and allopregnanolone levels in women during late menopausal transition and early postmenopause.

METHODS

The study group was divided into two groups: 45 women in late menopausal transition and 95 early postmenopausal women. We evaluated Kupperman index, Hamilton scale and serum follicle-stimulating hormone, luteinizing hormone, 17β-estradiol, prolactin, total testosterone, dehydroepiandrosterone sulfate and allopregnanolone levels.

RESULTS

We found that serum allopregnanolone concentration was lower in early postmenopausal women compared to women in late menopausal transition; that there was a correlation between serum allopregnanolone levels in early postmenopausal women and time since last menstruation, intensity of climacteric symptoms, and intensity of depression symptoms and that there was a correlation between serum allopregnanolone levels and several depression symptoms presence (shallow sleep and symptoms of the digestive tract in women during late menopause transition; feelings of guilt, sleep disorders and general somatic symptoms in early postmenopausal women).

CONCLUSION

We concluded that reproductive aging is characterized by a reduction of allopregnanolone circulating levels that correlate to Hamilton depression index in early postmenopause and presence of specific depressive symptoms during late menopausal transition and early postmenopause.

Effect of newly synthesized 1,2,4-triazino[5,6-b]indole-3-thione derivatives on olfactory bulbectomy induced depression in rats

OBJECTIVE

To study the derivatives of 1,2,4-triazino[5,6-b]indole-3-thione for antidepressant activity in olfactory bulbectomized (OBX) rats. Out of various derivatives tested for acute tail suspension test, the two derivatives showing prominent action were selected for bilateral olfactory bulbectomy model of chronic depression in rats.

METHODS

The sub acute effects of 14-day oral pretreatment of two derivatives labeled as 3a (70 mg/kg) and 3r (70 mg/kg), imipramine (20 mg/kg), fluoxetine (30 mg/kg) and moclobemide (15 mg/kg) were evaluated on bilateral bulbectomy induced rise in body weight, hyperphagia, hyperactivity, and on sexual dysfunction. The serum sodium concentration, body temperature, and heart rate were also recorded.

RESULTS

The derivatives 3a and 3r showed reversal of drop in body weight, reversed OBX induced hyperactivity, normalized body temperature, heart rate, and serum sodium concentration. In elevated maze test, moclobemide, 3a, 3r treatment significantly reduced time spent in open arm as compared to OBX rats. 3a and 3r also improved sexual behavior parameters.

CONCLUSIONS

The present study shows promising antidepressant action and provides a proof of concept for the chronic treatment of 3a, 3r to treat depression.

Pharmacology of serotonin and female sexual behavior

In this review, first a historical perspective of serotonin's (5-HT) involvement in female sexual behavior is presented. Then an overview of studies implicating 5-HT is presented. The effect of drugs that increase or decrease CNS levels of 5-HT is reviewed. Evidence is presented that drugs which increase 5-HT have negative effects on female sexual behavior while a decrease in 5-HT is associated with facilitation of sexual behavior. Studies with compounds that act on 5-HT₁, 5-HT₂ or 5-HT₃ receptors are discussed. Most evidence indicates that 5-HT₁A receptor agonists inhibit sexual behavior while 5-HT₂ or 5-HT₃ receptors may exert a positive influence. There is substantial evidence to support a role for 5-HT in the modulation of female consummatory sexual behavior, but studies on the role of 5-HT in other elements of female sexual behavior (e.g. desire, motivation, sexual appetite) are few. Future studies should be directed at determining if these additional components of female sexual behavior are also modulated by 5-HT.

Sprague-Dawley and Fischer female rats differ in acute effects of fluoxetine on sexual behavior

INTRODUCTION

The selective serotonin reuptake inhibitor (SSRI), fluoxetine, leads to sexual dysfunction in a substantial proportion of women. In studies with the Fischer inbred rat, the 5-HT(1A) receptor has been implicated in this sexual dysfunction. Whether this association with 5-HT(1A) receptors holds for other rat strains is not known.

AIM

The effects of acute fluoxetine on sexual behavior in two strains of rats that differ in their response to a 5-HT(1A) receptor agonist were examined. Whether the strain difference is comparable in naturally cycling and hormonally primed, ovariectomized rats was determined.

METHODS

Proestrous rats and ovariectomized rats, hormonally primed with estradiol benzoate and progesterone, were treated with varying doses of fluoxetine. Sexual behavior was examined before and after treatment with the SSRI.

MAIN OUTCOME MEASURES

Lordosis to mount ratios, lordosis quality, and proceptive behaviors were quantified. Sprague-Dawley and Fischer females were compared on each of these measures. The IC(50) for inhibition of lordosis behavior was determined.

RESULTS

In both the intact and the hormonally primed, ovariectomized model, Sprague-Dawley females were less sensitive to the effects of fluoxetine on sexual behavior. In both groups, fluoxetine showed dose dependency in behavioral inhibition, but a higher dose was required for Sprague-Dawley than for Fischer females. Naturally cycling, proestrous rats required a higher dose of fluoxetine than hormonally primed ovariectomized rats to produce significant inhibition of sexual behavior. Thus, the strain difference in the response to fluoxetine does not parallel strain differences in the response to a 5-HT(1A) receptor agonist.

CONCLUSIONS

Acute treatment with fluoxetine inhibits lordosis behavior in both Fischer and Sprague-Dawley females and the strain difference cannot be explained by reported strain differences in the response to a 5-HT(1A) receptor agonist. Fluoxetine's inhibition of female rat sexual behavior may involve effects of the SSRI in addition to activation of the 5-HT(1A) receptor.

Paroxetine-induced reduction of sexual incentive motivation in female rats is not modified by 5-HT1B or 5-HT2C antagonists

RATIONALE

Clinical data show that paroxetine causes sexual dysfunction in a substantial proportion of women taking this compound.

OBJECTIVES

This work was conducted to determine whether chronic paroxetine reduces sexual incentive motivation in female rats and whether this compound can modify any aspect of paced mating. The role of the 5-HT(1B) and 5-HT(2C) receptors in any potential effects was also evaluated.

METHODS

Ovariectomized female rats were implanted with osmotic minipumps releasing 10 mg/kg per day of paroxetine or vehicle for 28 days. Tests for sexual incentive motivation and paced mating were performed just before implantation and at regular intervals thereafter. The females were primed with estradiol benzoate (25 μg/rat) and progesterone (1 mg/rat) before each of these tests. On days 25-27 of treatment, the females were injected with the 5-HT(1B) antagonist GR125,743 (5 mg/kg), the 5-HT(2C) antagonist SB206,553 (5 mg/kg) and vehicle in counterbalanced order. Preinjection time was 30 min.

RESULTS

Paroxetine reduced sexual incentive motivation on day 20 of treatment without affecting any aspect of paced mating. None of the antagonists modified the inhibitory effect of paroxetine on sexual incentive motivation. In the group chronically treated with vehicle, SB206,553 reduced proceptive behaviors in the paced mating test. No other effect was obtained.

CONCLUSION

The effects of paroxetine seen in female rats are similar to those observed in women, suggesting that disturbances of sexual incentive motivation in rats are predictive of sexual dysfunction in women. The 5-HT(1B) and 5-HT(2C) receptors do not seem to be of any importance for paroxetine's inhibitory effect.

Effect of corticosterone and paroxetine on masculine mating behavior: possible involvement of neurogenesis

INTRODUCTION

Corticosterone inhibits male rodent sexual behavior while the mechanism remains obscured. Recent studies have disclosed that neurogenesis in the subventricular zone (SVZ) can be increased by pheromone exposure from the opposite sex, and neurogenesis is essential for normal mating behavior of female mice. Together with the neurogenesis-inhibiting effect of corticosterone, we hypothesize that cell proliferation in the olfactory system is essential for male rodent sexual functioning.

AIM

The current study explored the relationship between cell proliferation in the olfactory system and male sexual behavior.

MAIN OUTCOME MEASURES

Sexual behavior performance, proliferative cell counts, and c-fos-expressing cell counts.

METHODS

Adult male rats were treated with corticosterone and/or paroxetine, an antidepressant, for 2 weeks. These two drugs were shown to suppress and enhance hippocampus and SVZ cell proliferation, respectively. Mating behavior was assessed after the treatment, and proliferation of new cells and c-fos-expressing cells, activated neurons in the mating-related regions in the brain, were analyzed. To further confirm the necessity of cell proliferation in mating, inhibition of cell proliferation was performed by intracerebroventricular infusion of cytostatic cytosine arabinose (Ara-c).

RESULTS

Corticosterone treatment, which inhibited cell proliferation in both the SVZ and olfactory epithelium, led to inhibited male sexual performance. In contrast, paroxetine increased cell proliferation and improved the performance in corticosterone-treated animals. When cell proliferation in the brain was inhibited by Ara-c, a suppressed sexual performance was found. However, cell proliferation in olfactory epithelium was not inhibited by Ara-c and thus the sexual inhibition is unlikely to be linked to this region. Furthermore, a decrease in c-fos expression in the mating-related regions upon female pheromone stimulation was found.

CONCLUSIONS

These results suggest that cell proliferation in the SVZ and hippocampus may be involved in the reproduction of the male rodents, and pharmacological treatments may affect sexual functioning through alteration of neurogenesis.