Alpha-methyltyptamine blocks facilitation of lordosis by progesterone in spayed, extrogen-primed rats

Sex, estrous cycle, and hormone regulation of CYP2D in the brain alters oxycodone metabolism and analgesia

Opioids, and numerous centrally active drugs, are metabolized by cytochrome P450 2D (CYP2D). There are sex and estrous cycle differences in brain oxycodone analgesia. Here we investigated the mechanism examining the selective role of CYP2D in the brain on sex, estrous cycle, and hormonal regulation. Propranolol, CYP2D-specific mechanism-based inhibitor, or vehicle was delivered into cerebral ventricles 24 hours before administering oxycodone (or oxymorphone, negative control) orally to male and female (in estrus and diestrus) rats. Ovariectomized and sham-operated females received no treatment, estradiol, progesterone or vehicle. Analgesia was measured using tail-flick latency, and brain drug and metabolite concentrations were measured by microdialysis. Data were analyzed by two-way or mixed ANOVA. Following propranolol (versus vehicle) inhibition and oral oxycodone, there were greater increases in brain oxycodone concentrations and analgesia, and greater decreases in brain oxymorphone/oxycodone ratios (an in vivo phenotype of CYP2D in brain) in males and females in estrus, compared to females in diestrus; with no impact on plasma drug concentrations. There was no impact of propranolol pre-treatment, sex, or cycle after oral oxymorphone (non-CYP2D substrate) on brain oxymorphone concentrations or analgesia. There was no impact of propranolol pre-treatment following ovariectomy on brain oxycodone concentrations or analgesia, which was restored in ovariectomized females following estradiol, but not progesterone, treatment. Sex, cycle, and estradiol regulation of CYP2D in brain in turn altered brain oxycodone concentration and response, which may contribute to the large inter-individual variation in response to the numerous centrally acting CYP2D substrate drugs, including opioids.

A review and reevaluation of the role of serotonin in the modulation of lordosis behavior in the female rat

The role of serotonin (5-HT) in the modulation of sexual receptivity (lordosis) in the female rat is reviewed and reevaluated. The effects on lordosis of drug treatments that decrease or increase the activity and availability of central 5-HT are first discussed, and this is followed by an evaluation of the effects of drugs that act directly at 5-HT receptors. In order to shed light on the physiological significance of effects of serotonergic drugs on lordosis, there is also a review of what is known of changes in levels of serotonergic activity and densities of 5-HT receptors in the female rat brain that take place through the estrous cycle and in response to administration of behaviorally effective doses of gonadal steroids. Serotonin has generally been thought to have a tonic, inhibitory effect on lordosis. However, it is concluded that 5-HT can either inhibit or facilitate lordosis depending on which subtypes of central 5-HT receptors become activated. Because of a lack of consistent or compelling evidence of effects of ovarian hormones on serotonergic activity or 5-HT receptors in critical areas of the brain, it is stated that there is at present no basis to conclude that the effects of pharmacological manipulations of serotonergic activity on lordosis reflect an important, physiological role of 5-HT in the modulation of lordosis behavior in the female rat.

Lisuride inhibits temporarily sexual behavior in female rats

The effect of lisuride (0.1 and 0.2 mg/kg IP) on the sexual behavior was studied in the adult, ovariectomized and chronically estradiol-primed female rats. The behavioral tests were done under dyadic interaction with males 60 min before and 30, 120 and 360 min after lisuride or saline injection. Lisuride induced a prompt, short-termed and dose-dependent loss of the precopulatory patterns (darting, hopping, presenting posture) while the effect on the copulatory (lordosis) behavior was weaker. A partial restoration of the precopulatory behavior was observed in the 120th min, the full restoration of the original precopulatory states was found in the 360th min. The inhibitory effect of lisuride on feminine sexual behavior is in contrast with its facilitatory effect on masculine sexual behavior in rats. The results suggest that the serotonergic system participates in the mediation of both copulatory (receptive) behavior and precopulatory (proceptive) behavioral patterns.

Separation of dopaminergic and serotonergic inhibitory mechanisms in the mediation of estrogen-induced lordosis behaviour in the rat

The administration of the putative 5-hydroxytryptamine1 (5-HT1) agonist 8-hydroxy-2(di-n-propylamino) tetralin (8-OH-DPAT) (0.0625-1.0 mg X kg-1) suppresses lordosis behaviour induced in ovariectomized female rats by daily treatment for 3-5 days with estradiol benzoate (1.25 micrograms/rat). A similar suppressive effect on the lordosis behaviour can be obtained by administration of the dopamine/serotonin agonist, lisuride (0.1-0.4 mg X kg-1), or after the administration of the dopamine (DA) agonists, apomorphine (0.2-0.8 mg X kg-1) or quinpirole (0.75-2.50 mg X kg-1). The suppressive effects on the lordosis behaviour by 8-OH-DPAT cannot be antagonized by the DA receptor antagonist haloperidol (0.2 mg X kg-1) neither with methiotepin (0.5 mg X kg-1), which is assumed to be a non-selective 5-HT receptor blocking agent, nor with pirenperone (0.25 mg X kg-1) which is assumed to be a 5-HT2 receptor blocking agent. However, a partial blockade of the lordosis suppressive effects of 8-OH-DPAT was obtained by treatment with (-)-pindolol, which is thought to be a partial 5-HT1 blocking agent, suggesting that 8-OH-DPAT exerts its suppressive effects on the lordosis behaviour through the 5-HT system. Haloperidol causes a complete blockade of the suppressive effects of apomorphine and quinpirole suggesting that these drugs exert their inhibitory effects on the lordosis behaviour by activating the DA system.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression of lordosis behavior by the putative 5-HT receptor agonist 8-OH-DPAT in the rat

The administration of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), inhibited the lordosis induced by estradiol benzoate or estradiol benzoate plus progesterone in ovariectomized rats. There was no facilitation of lordosis by 8-OH-DPAT in animals pretreated with a threshold dose of estradiol benzoate. The results are consistent with the view that 8-OH-DPAT is an agonist at 5-HT receptors and provide further support for an inhibition role of central 5-HT in the mediation of lordosis behavior.

Intrahypothalamic 5,7-dihydroxytryptamine: temporal analysis of effects on 5-hydroxytryptamine content in brain nuclei and on facilitated lordosis behavior

The long-term relationship between serotonin (5-HT) levels in discrete hypothalamic nuclei and female rat sexual behavior, the lordosis response, was examined following intrahypothalamic injection of 5,7-dihydroxytryptamine (5,7-DHT). One week following 5,7-DHT injection, 5-HT levels in the ventromedial hypothalamic nucleus, dorsomedial nucleus, anterior hypothalamic nucleus and the medial preoptic nucleus were approximately 90% depleted as compared to sham animals. Other hypothalamic and preoptic areas including the arcuate-median eminence, vertical nucleus of diagonal band and lateral septal nucleus showed smaller reductions in 5-HT, from 40 to 70% of sham values. At this time estrogen-dependent lordosis behavior in the lesioned group was facilitated. Behavioral facilitation was greatest at 4 weeks post lesion when depletion of 5-HT in the VMN was maximal. 5-HT levels increased at 57 days after 5,7-DHT treatment in most areas, and by 71 days post lesion, no significant differences in 5-HT levels were found between sham and 5,7-DHT-treated groups. Concomitant with the increases in 5-HT, facilitated lordosis behavior gradually decreased. Loss of behavioral facilitation appeared to be most closely related to increases in content of 5-HT in the ventromedial nucleus. These results further support the hypothesis that 5-HT endings in the hypothalamus exert tonic inhibitory regulation over hormone-dependent lordosis in the female rat. They also indicate that regenerating 5-HT fibers in the hypothalamus can reinstate a normal pattern of hormone-dependent behavioral function.

A facilitatory role for serotonin in the sexual behavior of the female rat

The peripheral administration of the serotonin type 2 receptor (5-HT2) antagonist pirenperone inhibited sexual receptivity in ovariectomized female rats primed either chronically with estradiol benzoate (EB), or acutely with EB plus varying doses of progesterone. An inhibition occurred at 50, 100 and 150 but not 25 micrograms/kg pirenperone. Increasing the dose of progesterone did not attenuate the inhibitory effect of pirenperone. Two other 5-HT2 antagonists, ketanserin (2.5 mg/kg) and spiperone (250 micrograms/kg), also inhibited receptivity in females primed with EB and progesterone. The inhibitory effect of pirenperone on receptivity was attenuated by the 5-HT agonist quipazine (3 mg/kg), though quipazine alone had no effect on receptivity. Whereas the 5-HT antagonist methysergide (3 mg/kg) failed to have an effect on receptivity in EB-primed females, methysergide co-administered with quipazine facilitated receptivity. Pirenperone also inhibited proceptivity in females primed with EB and progesterone. Although quipazine did not attenuate the pirenperone-induced inhibition of proceptivity, quipazine alone increased proceptivity. Moreover, quipazine facilitated proceptivity in EB-primed rats whether progesterone was present or absent. The results suggest that 5-HT may serve both a facilitatory and inhibitory role in female sexual behavior, perhaps reflecting 5-HT2 and 5-HT1 receptor activity, respectively.

Estradiol and progesterone influence L-5-hydroxytryptophan-induced myoclonus in male guinea pigs: sex differences in serotonin-steroid interactions

The effects of castration in males and sex differences in the effects of estradiol and progesterone on L-5-hydroxytryptophan (L-5-HTP)-induced myoclonus in guinea pigs were examined. Castration had no effect on L-5-HTP-induced myoclonus in males. There were sex differences in sensitivity to L-5-HTP. In the absence of steroids, L-5-HTP-induced myoclonus was higher in gonadectomized males than females. A low dose of estradiol benzoate (EB; 3.5 micrograms) given 46 h before L-5-HTP (100 mg/kg) enhanced myoclonus in gonadectomized females but not males. However, at a higher dose of EB (10 micrograms) and a lower dose of L-5-HTP (80 mg/kg), myoclonic responding was enhanced in males. These findings indicate that estradiol has a similar effect on L-5-HTP-induced myoclonus in males and females, but do not rule out the possibility of sex differences in sensitivity to L-5-HTP when both sexes are given estradiol priming. When L-5-HTP was given 6 h after 0.5 mg progesterone in estradiol-primed males, myoclonus was enhanced. Progesterone treatment reverses the facilitative effect of EB on L-5-HTP-induced myoclonus in females. Therefore, progesterone has opposite effects on L-5-HTP-induced myoclonus in males and females. These findings were discussed with respect to the interaction of steroids and 5-HT transmission in the regulation of steroid-dependent reproductive behavior.

Estradiol and progesterone influence a serotonin mediated behavioral syndrome (myoclonus) in female guinea pigs: comparison with steroid effects on reproductive behavior

L-5-hydroxytryptophan (L-5-HTP)-induced myoclonus was used as a behavioral index of central serotonergic activity. Estradiol benzoate (EB) and progesterone (P) influenced the induction of myoclonus by L-5-HTP. When L-5-HTP was injected 46 h after EB, myoclonus was enhanced. P blocked this effect on EB when 100 or 125 mg/kg L-5-HTP (but not 80 mg/kg) was given 6 h after P in EB-primed animals. When L-5-HTP was given 3 or 11-15 h after P in EB-primed animals, there was no inhibitory effect of P on myoclonus. In fact, at the lowest dose (80 mg/kg), L-5-HTP increased myoclonus when given 3 h after P in EB-primed animals. The inhibitory effects of P in EB-primed females on myoclonus were temporally correlated with the display of lordosis, suggesting that the neural progestin receptor mechanisms that have been proposed to mediate P effects on lordosis are also involved in the inhibitory effects of P on myoclonus.

Effects of serotonin agonists on lordosis, myoclonus, and cytoplasmic progestin receptors in guinea pigs

Peripheral treatment with the serotonin releaser fenfluramine or the serotonin agonist quipazine abolished lordosis behavior in ovariectomized estradiol and progesterone-primed female guinea pigs. Quipazine was also effective when administered into a lateral cerebral ventricle. The lowest dose of fenfluramine that induced myoclonus (10 mg/kg) was higher than the dose needed to inhibit lordosis (5 mg/kg). Therefore, it appears that myoclonus and lordosis are differentially sensitive to serotonin agonists. The effects of quipazine on lordosis were time dependent. Quipazine had no effect on lordosis when given prior to the onset of sexual receptivity. These data suggest that serotonin agonists might be effective only when progesterone has had sufficient time to induce sexual receptivity. Quipazine did not affect cytoplasmic progestin receptors in brain areas involved in steroid hormone effects on lordosis. This finding, and the finding that quipazine had no effect on lordosis when given prior to the onset of sexual receptivity, suggest increased serotonin transmission does not interfere with estrogen priming or sensitivity of hypothalamic cells to progesterone.

Effects of paced coital stimulation on termination of estrus and brain indoleamine levels in female rats

Serotonin (5-HT) and 5-hydroxy-indoleacetic acid (5-HIAA) levels were measured in brain regions of ovariectomized, steroid-primed rats at the end of behavioral estrus. At the onset of behavioral estrus three groups of rats received coital stimulation which included (1) mounts without penile intromission only, (2) temporally-controlled (paced) mounts with intromission, and (3) non-paced mounts with intromission. Within 12 hr after the initial treatment, sexual receptivity was significantly lower in females given paced intromissions than in the other two groups. Brain stem 5-HT and 5-HIAA concentrations were significantly higher in females which received intromissions, regardless of whether or not they were paced than in females given mounts only. Hypothalamic and cortical concentrations of 5-HT and 5-HIAA were equivalent in the two groups. These results suggest that the termination of behavioral estrus is not associated with increased metabolic activity in central serotonergic neurons.

Persistence of dihydrotestosterone inhibition of lordosis in estrogen-primed rats fed a tryptophan-deficient diet

Administering increasing dosages of 5alpha-dihydrotestosterone propionate (DHTP) (0, 40, or 80 microgram/100 g in oil daily) to ovariectomized female rats treated concurrently with estradiol benzoate (EB) (1 microgram/100 g in oil daily) caused significant, equivalent reduction in lordotic responsiveness in rats maintained either on a tryptophan-deficient corn diet or on a corn diet to which L-tryptophan was added. Whole brain concentrations of 5-hydroxytryptamine (5-HT) and of 5-hydroxyindoleacetic acid were approximately two times higher in rats fed corn+tryptophan versus corn alone. These findings suggest that the ability of DHTP to inhibit lordosis probably depends upon some mechanism other than a facilitation of 5HT release from serotonergic neurons.

Enhancement by progesterone of lysergic acid diethylamide inhibition of the copulatory response in the female rat

Copulatory behavior in the ovariectomized rat, the lordosis response (L.R.) was induced by either estrogen alone or estrogen followed by progesterone. L.R. has been shown to be inhibited dose-dependently by lysergic acid diethylamide (LSD). The effects of various hormone treatments on the LSD-induced inhibition were tested in the present study. Progesterone but not estrogen was found to significantly enhance the LSD effect in a dose-dependent manner. In contrast, the effect of LSD on spontaneous behaviors in an exploratory situation was not influenced by progesterone treatment. This phenomenon of increased L.R. inhibitor effect by LSD was probably not due to a steroid-induced change in LSD metabolism. The data show instead that progesterone specifically influences monoaminergic mechanisms, which are related to the action of LSD. This has important implications for the possibility that progesterone induces the L.R. by acting on monoaminergic mechanisms.

Monoamines, estrogen and female sexual behavior in the golden hamster

In the golden hamster drugs which inhibit monoaminergic function (including p-chlorophenylalanine (PCPA), methysergide and a-methyl-p-tyrosine (a-MPT) facilitated lordosis in ovariectomized female hamsters as a function of the duration of estradiol benzoate (EB) priming. a-MPT (200 mg/kg), methysergide (6 mg/animal) or PCPA (150 or 360 mg/kg) potentiated lordosis if 6 days of EB priming preceded drug treatment. However, if female hamsters were primed with EB for only 2 days, a-MPT and methysergide were ineffective. PCPA (360 mg/kg) was less effective after 2 days of EB than after 6 days of EB priming. alpha-MPT produced a three-fold elevation in progesterone levels in ovariectomized females but methysergide and PCPA did not influence serum progesterone. PCPA (360 mg/kg) facilitated lordosis in adrenalectomized, ovariectomized females, eliminating the possibility that adrenal progesterone is essential for the behavioral effects of the drug. Luteinizing hormone-releasing hormone levels in the preoptic/anterior hypothalamic area and the medial basal hypothalamus were also not significantly altered at 1 h after PCPA injection. Pimozide (1.5 mg/kg) and pimozide (1.5 mg/kg) and amphetamine (2.5 mg/kg) did not potentiate lordosis in ovariectomized hamsters after either 2 or 6 days of EB priming. Pargyline, a monoamine oxidase inhibitor, inhibited female sexual behavior in females in estrogen alone-induced estrus. Lordosis in the female rat is more readily elicited both by drugs and estrogen. It is proposed with regard to female sexual behavior that species differences in estrogen sensitivity may underlie apparent differences in drug sensitivity.

Estrogen-induced sexual receptivity and localization of 3H-estradiol in brains of female mice: effects of 5 alpha-reduced androgens, progestins and cyproterone acetate

Sexual receptivity induced in ovariectomized CD-1 mice with chronic daily administration of estradiol benzoate (E2 B) was blocked by concurrent administration of the 5 alpha-reduced androgen, dihydrotestosterone (DHT). Receptivity was restored in these females with progesterone-, but not with dihydroprogesterone-priming 6 hr prior to testing. Delaying the DHT injections until 12 hr after the E2 B injections greatly reduced its inhibitory properties. Receptivity in E2 B-primed females was also blocked by concurrent treatment with cyproterone acetate and 3 alpha-, but not 3 beta-adrostanediol. Pretreatment with DHT, or 3 alpha- or 3 beta-androstanediol failed to consistently affects 3H-estradiol accumulation in crude nuclear and supernatant fractions from brain and pituitary.

The influence of alpha-receptors on lordosis in the female rat

The alpha-adrenergic agonist clonidine suppressed lordotic responding in spayed female rats brought into heat by estrogen and progesterone. The suppression was blocked by the alpha-antagonist yohimbine, but not by phenoxybenzamine or pimozide. The suppression was blocked by the alpha-antagonist yohimbine, but not by phenoxybenzamine or pimozide. Phenoxybenzamine itself had no suppressive effect on lordosis, though yohimbine did under some conditions. These results argue against an important facilitatory influence of norepinephrine on lordosis in the rat. Further, in comparison with the quite different findings recently reported from the guinea pig, they offer support for the presence of two different kinds of alpha-adrenergic receptors in the brain with different physiological functions.