Subchronic treatment with fluoxetine attenuates effects of acute fluoxetine on female rat sexual behavior

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.

The combination of mirtazapine plus venlafaxine reduces immobility in the forced swim test and does not inhibit female sexual behavior

INTRODUCTION

Depression is a psychiatric disorder with higher incidence in women. Among the most common and less investigated adverse effects of antidepressants are the female sexual dysfunctions. Up to one third of the patients fail to respond to antidepressants; therefore, more treatment alternatives are necessary. The combination of mirtazapine plus venlafaxine, known as "California Rocket Fuel" has shown to be an option for treatment-resistant depression. However, there are no reports of the effects of this combination in animal models and its action on female sexual behavior is unknown.

AIM

To analyze the effect of mirtazapine and venlafaxine alone or combined -given at doses with actions on the forced swim test- on female rat sexual behavior.

METHODS

Mirtazapine (10, 20 or 40 mg/kg) and venlafaxine (15, 30 or 60 mg/kg) or their combinations (2.5/3.75, 5/7.5, 10/15 and 20/30 mg/kg mirtazapine and venlafaxine, respectively) were injected to sexually receptive female rats. We evaluated their effect on the forced swim test (FST). The doses that reduced immobility were tested on proceptivity and receptivity.

RESULTS

Mirtazapine (40 mg/kg) and venlafaxine (60 mg/kg), administered alone, or combined (mirtazapine, 5, 10 and 20 mg/kg plus venlafaxine, 7.5, 15 and 30 mg/kg) reduced immobility, but affected motor activity. However, the reduced locomotion after the lowest combination (5/7.5 mg/kg) was smaller. Mirtazapine at 40 mg/kg reduced proceptivity and receptivity, while 60 mg/kg venlafaxine only decreased proceptivity. The combination of 5/7.5 mg/kg mirtazapine and venlafaxine did not affect female sexual behavior.

CONCLUSIONS

Mirtazapine and venlafaxine exerted an effect in the FST, which was also evident when sub-effective doses of both antidepressants were combined. This combination also lacked adverse effects on female sexual behavior. The results suggest that "California Rocket Fuel" could be an effective antidepressant therapy with no adverse sexual effects in women.

Environmentally relevant exposure to an antidepressant alters courtship behaviours in a songbird

Pharmaceuticals in the environment are a recently identified global threat to wildlife, including birds. Like other human pharmaceuticals, the antidepressant fluoxetine (Prozac) enters the environment via sewage and has been detected at wastewater treatment plants. Birds foraging on invertebrates at these sites can be exposed to pharmaceuticals, although the implications of exposure are poorly understood. We conducted experiments to test whether chronic exposure to a maximally environmentally relevant concentration of fluoxetine (2.7 μg day^-1) altered courtship behaviour and female reproductive physiology in wild-caught starlings (Sturnus vulgaris), a species commonly found foraging on invertebrates at wastewater treatment plants. When paired with a female over two days, males sang less and were more aggressive towards fluoxetine-treated females than controls. Fluoxetine-treated females were initially aggressive towards males, becoming significantly less aggressive by the second day. In contrast, control females expressed intermediate levels of aggression throughout. We found no effect of female treatment on female courtship behaviour. Female body condition, circulating testosterone and circulating oestradiol were unaffected by treatment and did not account for male preference. Our findings suggest that exposure to an antidepressant reduced female attractiveness, adding to growing evidence that environmental concentrations of pharmaceuticals can alter important traits related to individual fitness and population dynamics.

Use of an operant paradigm for the study of antidepressant-induced sexual dysfunction

These studies were designed to develop a paradigm for the detection of antidepressant-induced sexual dysfunction in female rats. Ovariectomized, Fischer rats were conditioned to nose poke to open a guillotine door to gain access to a sexually active male. To develop the procedure, we examined the acquisition and stability of the response with a 15-s fixed interval, compared rats treated with 10 μg estradiol benzoate and 500 μg progesterone with those that received only estradiol benzoate, and carried out a preliminary analysis of the effects of 5, 10, and 15 mg/kg fluoxetine. We then more fully evaluated the effects of 5 mg/kg fluoxetine. Fluoxetine reduced sexual motivation, as assessed by the number of nose pokes, the number of nose poke episodes, and the latency to approach the male. In addition, changes in the females' sexual motivation were examined before and after ejaculation during the final conditioning trials. The number of nose pokes was reduced and the latency to initiate a new nose poke episode was increased following ejaculation. The robustness of the antidepressant-induced decline in sexual motivation is in marked contrast to the findings with several other animal models for sexual dysfunction and illustrates the usefulness of the operant procedure.

Developmental fluoxetine exposure facilitates sexual behavior in female offspring

RATIONALE

A growing number of infants are being exposed to selective serotonin reuptake inhibitor (SSRI) medications during the perinatal period. SSRIs target the serotoninergic system and are a popular treatment for maternal mood disorders. Serotonin itself plays a key role in the sexual differentiation through its role in the development of the hypothalamic-pituitary-gonadal axis, and previous research has shown that developmental SSRI exposure has an effect on sexual behavior in male offspring.

OBJECTIVES

Our aim was to determine the role of developmental exposure to a popular SSRI medication, fluoxetine, on sexual differentiation of the brain and behavior in female offspring using a rodent model of maternal adversity.

METHODS

Stressed and non-stressed Sprague-Dawley rat dams were chronically treated with either fluoxetine (5 mg/kg/day) or vehicle beginning on postnatal day 1. Four groups of female offspring were used: (1) control + vehicle, (2) control + fluoxetine, (3) prenatal stress + vehicle, and (4) prenatal stress + fluoxetine.

RESULTS

Primary results show that in adult female offspring, developmental fluoxetine exposure facilitates proceptive and receptive behaviors with a significant increase in the number of proceptive behaviors, a significant increase in the lordosis quotient, and a significant decrease in the rejection quotient.

CONCLUSIONS

This research contributes in the understanding of the long-term impact developmental fluoxetine exposure on the hypothalamus-pituitary-gonadal (HPG) system in adult female offspring.

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.

Factors influencing fluoxetine-induced sexual dysfunction in female rats

Treatment with selective serotonin reuptake inhibitors, such as fluoxetine, produces sexual side effects with low sexual desire being the most prevalent effect in females. In few studies have preclinical models for such antidepressant-induced sexual dysfunction been fruitful. In the current manuscript, the effects of fluoxetine on multiple measures of female sexual motivation and sexual receptivity were examined. Ovariectomized, Fischer rats were primed with 10 μg estradiol benzoate and 500 μg progesterone. Partner preference, active investigation of the male, and measures of sexual behavior were examined after injection with 15 mg/kg fluoxetine. Factors (pretesting for sexual behavior, size of the test arena, non-contact time with a male) that differ among experiments designed to study antidepressant-induced female rat sexual dysfunction were studied. The male preference ratio was not affected by fluoxetine treatment but active investigation of the male was reduced; lordosis behavior was inhibited and pretesting for sexual receptivity amplified fluoxetine's inhibition; size of the testing arena or non-contact experience with the male had no effect. Regardless of test condition, when given the opportunity to escape from the male, fluoxetine-treated females displayed escape behavior. Measures of male preference and active investigation, but not lordosis behavior, appeared to be affected by fluoxetine's impact on activity. The collective data provided a behavioral profile of fluoxetine-induced sexual dysfunction. These findings reinforce the value of multiple measures when attempting to model antidepressant-induced female sexual dysfunction.

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 novel synthetic evodiamine analogue on sexual behavior in male rats

Currently phosphodiestrase5 (PDE5) inhibitors are the first-line treatment for erectile dysfunction. Drugs such as sildenafil and tadalafil are available as PDE5 inhibitors which are potent and reversible but lack selectivity with side effects such as headache, facial flushing, dyspepsia, and visual disturbances. We herein report for the first time novel condensed thienopyrimidines as evodiamine analogue and their effect on sexual behavior in male rats hitherto unreported. Novel synthetic evodiamine significantly showed improvement in male rat copulatory behavior. The test compound MKAC9 could be of promising importance in the treatment of sexual disorders like desire disorder or erectile dysfunction.FigureEvodiamine analogue on sexual behavior in male rats.

Differences in sexual behaviour in male and female rodents: role of serotonin

Serotonin plays an important role in both male and female sexual behaviour. In general, reduction of 5-HT function facilitates, whereas enhancement inhibits sexual behaviour. Most fundamental research on the involvement of 5-HT in sex has been performed in rats. Selective serotonin reuptake inhibitors (SSRIs) have comparable effects on male and female sexual behaviour in rats; they inhibit it but only after chronic administration. Activation of the 5-HT(1A) receptor facilitates sexual behaviour in male rats but inhibits sexual behaviour in female rats, suggesting a differential role for 5-HT(1A) receptors in male and female rats. Research on sexual behaviour in rats with null mutations in the serotonin transporter (SERT) indicated also a differential role for 5-HT(1A) receptors in male and female sexual behaviour. Evidence exists that different pools of 5-HT(1A) receptors have differential roles in various parts of the cascade of sexual events occurring during sexual interactions. Roles for other 5-HT receptors are less well defined although 5-HT(1B), 5-HT(2A/B) and 5-HT(7) receptors seem to be involved. Identification of putative differential or comparable roles in female and male sexual activities requires more research.

Griffonia simplicifolia negatively affects sexual behavior in female rats

At present Griffonia simplicifolia is used in food supplement aimed to treat mood disorders as well as to reduce food intake and body weight. The plant has gained increasing interest for its high content in 5-hydroxy-L-tryptophan (5-HTP) particularly in the seed. The present study was designed to evaluate the influence of a seed extract of the plant, dosed at 25, 50 and 100 mg/kg, on the sexual behavior of ovariectomized hormone-primed rats after acute and subchronic treatment. The single administration of G. simplicifolia significantly reduced lordosis response and increased rejection behavior in female rats treated with the highest dose while it did not influence proceptive behaviors. On the other hand the subchronic administration of the extract significantly reduced proceptivity but not receptivity, and increased rejection behavior. All the tested dosages were able to markedly decrease food intake and body weight after a 9-day treatment. Taken together the present results, possibly ascribed to increased levels of 5-hydroxytryptamine (5-HT) in the brain, suggest a cautious administration of the plant extract owing to its negative influence on female sexual behavior.

A new female rat animal model for hypoactive sexual desire disorder; behavioral and pharmacological evidence

INTRODUCTION

Female sexual dysfunction (FSD) affects 33-48% of women. Female rats with low sexual activity might model FSD.

AIM

In this study, we have investigated whether in a population of normal female rats, subpopulations of rats exist with different levels of sexual behavior.

METHODS

Sexually experienced, intact, estradiol-primed female rats were placed in an empty compartment adjacent to a compartment with a male. The females were allowed, during 30 minutes, to switch between the compartments via a hole through which only the females could pass (paced mating). Next, we investigated the acute effects on female sexual behavior of apomorphine, a D(1) - and D(2) -type dopamine receptor agonist, (+/-)-8-hydroxy-2-(dipropylamino)tetralin hydrobromide (± 8-OH-DPAT), a 5-HT1A receptor agonist, and paroxetine, a selective serotonin reuptake inhibitor.

MAIN OUTCOME MEASURES

Time spent in compartments, proceptive behaviors, contact-return latencies, and percentages of exits were quantified.

RESULTS

Based on their behavior in the paced mating sex test, estradiol-primed, intact female rats can be divided into three groups: those that mostly avoid the male, a large middle group, and those that mostly approach the male. The avoiders also showed significantly less proceptive behavior than the male approachers. The sexual behavior of the females was relatively stable over time, suggesting the existence of different endophenotypes in female rats. Apomorphine and ± 8-OH-DPAT had an inhibiting effect on sexual behavior, but only females dosed with apomorphine showed a different response in avoiders and approachers, more inhibiting effect in avoiders than approachers. Paroxetine had no effect on proceptive behavior.

DISCUSSION

The stable, male-avoiding behavior of some females might correspond to the characteristics of women with FSD. Therefore, these avoiders are a promising new model for FSD, specifically for sexual desire and/or arousal disorders. Furthermore, the apomorphine data suggest that differences in the dopamine system may (partly) underlie the differences in sexual behaviors between avoiders and approachers.

Role of 5-HT(1A) receptors in fluoxetine-induced lordosis inhibition

The selective serotonin reuptake inhibitor (SSRI), fluoxetine (Prozac(R)), is an effective antidepressant that is also prescribed for other disorders (e.g. anorexia, bulimia, and premenstrual dysphoria) that are prevalent in females. However, fluoxetine also produces sexual side effects that may lead patients to discontinue treatment. The current studies were designed to evaluate several predictions arising from the hypothesis that serotonin 1A (5-HT(1A)) receptors contribute to fluoxetine-induced sexual dysfunction. In rodent models, 5-HT(1A) receptors are potent negative modulators of female rat sexual behavior. Three distinct experiments were designed to evaluate the contribution of 5-HT(1A) receptors to the effects of fluoxetine. In the first experiment, the ability of the 5-HT(1A) receptor antagonist, N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide (WAY100635), to prevent fluoxetine-induced lordosis inhibition was examined. In the second experiment, the effects of prior treatment with fluoxetine on the lordosis inhibitory effect of the 5-HT(1A) receptor agonist, (+/-)-8-hydroxy-2-(dipropylamino)tetralin (8-OH-DPAT), were studied. In the third experiment, the ability of progesterone to reduce the acute response to fluoxetine was evaluated. WAY100635 attenuated the effect of fluoxetine; prior treatment with fluoxetine decreased 8-OH-DPAT's potency in reducing lordosis behavior; and progesterone shifted fluoxetine's dose-response curve to the right. These findings are consistent with the hypothesis that 5-HT(1A) receptors contribute to fluoxetine-induced sexual side effects.

Serotonin transporter null mutation and sexual behavior in female rats: 5-HT1A receptor desensitization

INTRODUCTION

Serotonin plays a key role in sexual behavior. In serotonin transporter (SERT) knockout rats (-/-), basal extracellular 5-HT levels are considerably increased, indicating a serotonergic disturbance. Heterozygous SERT(+/-) rats express 50% of SERT in comparison to wild-type rats and may therefore model the s/s phenotype of the human SERT promoter (5-HTTLPR) polymorphism.

AIM

In the present study, we used both homozygote and heterozygote SERT knockout and wild-type rats (+/+) to study the putative role of the SERT in female sexual behavior.

METHODS

Female rats were brought into estrous by hormonal injections before a paced mating sex test. The effects of the 5-HT(1A)/5-HT(7) receptor agonist (+/-)-8-hydroxy-2-(dipropylamino)tetralin hydrobromide (+/-8-OH-DPAT) (0.03-1 mg/kg s.c.) and the 5-HT(1A) receptor antagonist WAY-100635 (0.1-1-mg/kg i.p.) on sexual behaviors of the females were tested separately and in a selected combination of both in all three genotypes.

MAIN OUTCOME MEASURES

Proceptive (darting and hopping) and receptive (lordosis) behaviors were quantified.

RESULTS

Basal proceptive and receptive sexual activities were not different between SERT+/+, +/- and -/- female rats. The dose-effect curve after +/-8-OH-DPAT for these activities was clearly shifted to the right in SERT-/- animals compared to other genotypes. WAY-100635 alone had no effect on sexual behavior in any genotype, but was able to antagonize the +/-8-OH-DPAT-induced decrease in sexual activities indicating the involvement of the 5-HT(1A) receptor.

CONCLUSIONS

The absence (-/-) or reduced (+/-) expression of SERT does not affect basal sexual activity in female rats in a paced mating situation. The data indicate a desensitized 5-HT1A receptor in the SERT-/-, but not in the SERT+/- females. Under normal basal conditions, desensitized 5-HT1A receptors apparently do not play a role in female sexual behavior of the SERT-/-. However, upon activation of the 5-HT1A receptor in "normal" females (SERT+/+ and SERT+/-), a hyposexual behavior is induced.

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

INTRODUCTION

Sexual dysfunction, as a result of selective-serotonin reuptake inhibitor (SSRI) treatment among women, is relatively common and is a factor in medication compliance. The mechanisms that underlie these side-effects of SSRIs are not well-understood. SSRIs can alter activity of catabolic enzymes that are involved in progesterone's conversion to 5 α-pregnan-3 α-ol-20-one (3 α,5 α-THP). 3 α,5 α-THP plays a key role in female reproductive physiology and behavior.

AIMS

This study aimed to determine whether 3 α,5 α-THP, in the midbrain ventral tegmental area (VTA) may be a potential mechanism for fluoxetine's reduction in sexual responding of female rodents. We hypothesized that if fluoxetine induces decrements in sexual responding in part through actions of 3 α,5 α-THP, then fluoxetine will inhibit sexual receptivity concomitant with reducing 3 α,5 α-THP levels, effects which can be reversed by 3 α,5 α-THP administration.

METHODS

  Experiment 1 investigated effects of acute systemic fluoxetine [20 mg/kg intraperitoneal (IP)] and/or 3 α,5 α-THP [500 µg, subcutaneous (SC)] administration on sexual responding of ovariectomized, hormone-primed rats. Experiment 2 examined effects of 3 α,5 α-THP administration to the midbrain VTA (100 ng) on fluoxetine-induced decrements in lordosis of ovariectomized, hormone-primed rats and hamsters.

MAIN OUTCOME MEASURES

Sexual responding was determined in rats and hamsters. For rats, the percentage of times that the lordosis response occurred following mounting by a sexually-vigorous male (lordosis quotients) was utilized. For hamsters, lateral displacement, the pelvic movement that females will make to facilitate intromissions by a male hamster, was utilized.

RESULTS

Fluoxetine significantly reduced lordosis, and this was reversed SC 3 α,5 α-THP. Intra-VTA 3 α,5 α-THP attenuated fluoxetine's detrimental effects on lordosis quotients and lateral displacement of rats and hamsters, respectively.

CONCLUSIONS

Thus, fluoxetine's effects to disrupt female sexual responses may involve its effects on progestogens in the midbrain VTA.

Fluoxetine does not prevent interspecific mating between two hamster species

In a recent study we showed that female Syrian hamsters (Mesocricetus auratus) from a laboratory stock readily mated with male Turkish hamsters (M. brandti). We hypothesized that captivity and/or unconscious selection of the most receptive females by researchers or animal caretakers results in heightened female sexual receptivity and reduces the tendency to reject heterospecific males. To test this hypothesis, we decided to decrease female receptivity by injection of fluoxetine, which increases the levels of serotonin in a number of brain loci, including areas involved in mediating sexual behavior, and determine whether such a decrease in receptivity would result in better discrimination of heterospecific males and rejection of such males as mates. We treated estrous female Syrian hamsters with 20mg/kg fluoxetine or vehicle and paired them with both a conspecific and a heterospecific male (Turkish hamster) in two sequential tests. All females showed similar behavior - they exhibited lordosis toward both conspecific and heterospecific males. We did not observe any sign of aggression. Latency to display lordosis and the duration of lordosis were not affected by fluoxetine. Fluoxetine thus did not have an effect on the behavior of females toward conspecific or heterospecific males. Independent of treatment (fluoxetine or vehicle injection), females did display lordosis significantly faster and for a longer duration in the presence of a conspecific male, even though these differences were small.

Modest effects of repeated fluoxetine on estrous cyclicity and sexual behavior in Sprague Dawley female rats

In an earlier study, we reported that daily fluoxetine treatment (10 mg/kg/day) rapidly disrupted estrous cyclicity and sexual receptivity in adult, regularly cycling Fischer rats. The current study was designed to investigate if comparable fluoxetine treatment would similarly affect intact, regularly cycling Sprague Dawley rats. In the first experiment, fluoxetine was injected for 24 days. After 11-14 days of daily fluoxetine treatment, 40% of the rats showed a transient disturbance of the estrous cycle with elimination of sexual receptivity. In these affected rats, reduced sexual receptivity generally preceded disruption of vaginal cyclicity. In a second experiment, a shorter exposure was used to attempt to dissociate effects of fluoxetine on behavior and estrous cyclicity. Nine days of fluoxetine treatment eliminated sexual receptivity and proceptivity (hops/darts) in 40% and 46%, respectively, of rats without altering the estrous cycle. Female rats then received a 10th fluoxetine injection 30 min prior to assessment of sexual motivation (measured with the male preference paradigm). There was no effect of fluoxetine on male preference, but fluoxetine significantly reduced the number of crossings and seconds of grooming during preference testing. Therefore, effects of fluoxetine on estrous cyclicity and behavior of Sprague Dawley female rats were smaller and required longer to develop than previously reported in Fischer female rats. These findings reinforce a probable relationship between fluoxetine's effect on sexual activity and neuroendocrine disturbances and illustrate the importance of strain selection in attempting to model human disease.