Vaginal stimulation in rats induces prolonged lordosis responsiveness and sexual receptivity.

Conducted 2 experiments, using a total of 131 female Sprague-Dawley rats. Sexual receptivity to males resulted from stimulation of the vagina with a glass rod in previously unreceptive ovariectomized, estrogen-treated Ss. Several minutes of rejection behavior preceded the receptivity. In Exp II manual palpation was used to determine the duration of the lordosis response facilitation. Initially, all Ss were unresponsive to manual flank-perineum stimulation (palpation). Vaginal stimulation plus palpation, which together elicited lordosis, facilitated subsequent lordosis responses to palpation. This effect persisted for several hours after the vaginal stimulation was applied. Vaginal stimulation alone, which was ineffective in eliciting lordosis, also facilitated lordosis in response to subsequent palpation. Repeated palpation did not facilitate lordosis. These prolonged effects were independent of hormone treatment. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of coital stimulation upon behavior of the female rat.

Tested the importance of vagino-cervical stimulation during coitus in 2 experiments, using 16 intact and 48 ovariectomized Sprague-Dawley female rats, in which intromission was prevented by a vaginal mask. The behavior of Ss was compared to that of unmasked females. Behavioral indices included lordosis quotient, a measure of sexual responsiveness, and rejection quotient, a measure of social response toward the males. The rating of lordosis intensity on a 3-point scale provided a mean lordosis intensity. Exp. I investigated long-term effects of coital stimulation by repeated testing of Ss in natural and hormone-induced heat. Coital stimulation generally decreased the probability of subsequent lordosis and increased display of rejection. Exp. II studied the short-term effects of coital stimulation using single 50-mount tests. Coital stimulation decreased intensity as well as probability of subsequent lordosis. (23 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Medial preoptic area oxytocin and female sexual receptivity.

Intracerebroventricular (icv) administration of the nonapeptide oxytocin (OXT) increases sexual receptivity in female rats. The medial preoptic area (MPOA) appeared to be the most sensitive brain area to the facilitative effects of OXT. Bilateral infusions of 100 ng of OXT into the MPOA significantly elevated lordosis quotients in overiectomized (OVX), estrogen-treated rats. This dose of OXT was ineffective when infused icv or into the ventromedial hypothalamus, mesencephalic central gray, or ventral tegmental area. A 500-ng dose of OXT significantly elevated lordosis responding when infused icv, corresponding with our previous findings. Mounting by males significantly increased immunoreactive levels of OXT and decreased the number of OXT immunostaining cells in the MPOA of sexually receptive rats pretreated with estrogen and progesterone. The MPOA is a primary site of the OXT facilitation of sexual receptivity where OXT may be released during mating. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of repeated testing on sexual behavior of the female rat.

Investigated effects of stimulation during repeated testing, using 24 female Sprague-Dawley rats in which intromission was prevented by a vaginal mask. Ss were ovariectomized and administered 1 mg of estradiol benzoate (EB) daily for 10 days (Exp I) or 5 mg of EB for 2 days (Exp II). Behavioral indices included lordosis quotient (a measure of sexual receptivity) and rejection quotient (a measure of social rejection of the male). Intensity and duration of lordosis gave additional measures. In Exp I hourly testing increased lordosis quotient and duration, especially in Ss receiving EB for 5 days; no effects of daily testing were shown. Exp II compared the behavior of Ss that were either handled hourly and tested hourly with the male rat or only handled hourly to the behavior of Ss that were tested and handled only once. Repeated testing and/or handling facilitated sexual responsiveness, while Ss that received neither treatment were sluggish in their social response to the male rat when they were tested, and were not sexually receptive. (17 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of a muscarinic antagonist on various components of female sexual behavior in the rat.

Effects of the muscarinic antagonist scopolamine on lordosis, solicitation, pacing, approach, attractivity, and activity were evaluated in ovariectomized rats brought into sexual receptivity with estrogen and progesterone. Systemic (1 mg/rat) or intraventricular (10 μg bilaterally) administration of scopolamine significantly reduced the incidence of lordosis and solicitation behaviors and disrupted typical pacing of sexual contacts with a stimulus male. In addition, females avoided contact with a stimulus male, but not a stimulus female, following intraventricular infusion of scopolamine. The levels of general activity and frequencies of sexual contacts were similar in females treated intraventricularly with scopolamine and vehicle solutions. Consequently, scopolamine disrupted various components of sexual behavior, including lordosis, solicitation, pacing, and approach, without altering female attractivity or general activity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cholinergic influences on estrogen-dependent sexual behavior in female rats.

Examined the ability of cholinergic agents to influence hormone-dependent sexual behavior in Sherman rats. In Exp I, sexual behavior, indicated by the incidence of lordosis, was significantly increased in estrogen-treated Ss following bilateral infusion of a cholinergic receptor agonist, carbachol (.5 μg/cannula) into the medial preoptic area of the brain. Infusion of an artificial cerebrospinal fluid vehicle failed to facilitate lordosis. The incidence of lordosis was normally highest 15 min after carbachol infusion began to wane by 45 min, and had returned to control levels by 90 min. Centrally administered carbachol activated lordosis at lower levels of estrogen priming than did systemically administered progesterone. In Exp II, Ss brought into sexual receptivity by administration of estrogen and progesterone received preoptic infusions of an acetylcholine synthesis inhibitor, hemicholinium-3 (HC-3). Significant reductions in the incidence of lordosis were observed following bilateral infusion of HC-3 (1.25 μg/cannula). This inhibition of lordosis was prevented when carbachol (.5 μg/cannula) was infused along with HC-3. Results confirm the importance of cholinergic influences on sexual behavior in female rats. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Roles of gonadotropins and releasing hormones in hypothalamic control of lordotic behavior in ovariectomized, estrogen-primed rats.

Intrahypothalamic effects of gonadotropins (luteinizing hormone and follicle-stimulating hormone, LH and FSH, respectively), thyrotropin-releasing hormone (TRH), and luteinizing-hormone-releasing hormone (LRH) on lordotic behavior were evaluated in 63 Wistar ovariectomized (OVX) rats maintained at different receptivity levels. Under low receptivity, in which LRH has been shown to enhance mating behavior, medial preoptic area (MPOA) infusions of LH caused significant depressions in the lordotic response, whereas LH infusions into arcuate ventromedial area (ARC-VM) had no significant effect. FSH infusions into either area did not alter the response. In Exp II, in which OVX Ss were primed with higher doses of estrone to maintain high preinfusion receptivity, MPOA or ARC-VM infusions of either LH or TRH depressed lordotic behavior significantly, whereas neither LRH nor FSH inhibited the response. Exp III evaluated the effects of LH, FSH, and TRH on LRH-facilitated mating behavior with 50 Sprague-Dawley male rats. Infusions of LRH into either MPOA or ARC-VM significantly enhanced mating behavior, whereas addition of TRH or LH to the LRH infusates abolished this response. The antagonistic effects of LH and TRH on LRH-facilitated mating were correlated with previous observations of antagonistic effects on hypothalamic unit activity and monoamine metabolism. The antagonistic interrelation between LRH and LH may represent a mechanism for activation and coordination of sexual receptivity with ovulation. (55 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of pelvic nerves in the postcopulatory abbreviation of behavioral estrus in female rats

The role of the pelvic nerves in the postmating abbreviation of behavioral estrus in domestic female rats was investigated. Mating during a period of 40 min at the beginning of hormonally induced estrus in spayed female rats resulted in a rapid decrease in receptivity as measured hourly by the lordosis response. Moreover, the length of the receptive period was significantly shortened by mating at the start of the period. Bilateral pelvic nerve transection completely abolished these effects of mating. Continuous exposure to sexually active males throughout the period of receptivity resulted in a more pronounced decline in receptivity but again was without effect in pelvectomized females. Apparently genital stimuli mediated by the pelvic nerves are responsible for the postcopulatory decrease in receptive behavior in the female rat.     

Connections between the pontine central gray and the ventromedial hypothalamus are essential for lordosis in female rats.

Lesions and knife cuts were used to study central gray (CG) and ventromedial hypothalamic (VMH) mediation of sexual receptivity in female rats. Lesions of the midbrain–pontine CG eliminated lordosis in female rats. Bilateral sagittal knife cuts that bracketed the rostral pontine CG also eliminated lordosis, and an experiment with the retrograde tracer Fluoro-Gold confirmed the effectiveness of these cuts in severing the lateral connections linking the VMH and the CG. Finally, females with a unilateral hypothalamic cut combined with a contralateral CG transection almost never showed lordosis. Each cut, at a different level for each side of the brain, transected axons linking the VMH and the CG. The demonstration that this combination eliminated lordosis provides new evidence that the lateral connections between the VMH and the CG are essential for the display of sexual receptivity in female rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Facilitation of female rat lordosis behavior by hypothalamic infusion of 5-HT(2A/2C) receptor agonists

Ovariectomized rats were hormonally primed with 0.5 microg estradiol benzoate and 500 microg progesterone to produce two groups of rats differing in their lordosis behavior. Females with a lordosis to mount (L/M) ratio < 0.5 were used to test the hypothesis that 5-HT(2A/2C) receptor agonists could facilitate lordosis behavior. Females with L/M ratios > or = 0.5 were used to evaluate the potential suppressive effect of 5-HT(2A/2C) receptor compounds. Lordosis behavior was examined following bilateral infusion of drugs into the ventromedial nucleus of the hypothalamus (VMN). Drugs examined were the 5-HT(2A/2C) receptor agonist, (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl (DOI), the 5-HT(2A/2C) receptor antagonist, 3-[2-[4-(4-fluorobenzoyl)-1-piperdinyl]ethyl]-2,4(1H,3H)-quinazoli nedione tartrate (ketanserin tartrate), and the non-selective 5-HT receptor agents, 2-(1-piperazinyl)quinoline dimaleate (quipazine) and N-(3-trifluoromethylphenyl)piperazine HCl (TFMPP). Drugs with agonist action at 5-HT(2A/2C) receptors increased lordosis behavior in rats with low sexual receptivity. The 5-HT(2A/2C) receptor antagonist, ketanserin, inhibited lordosis behavior in sexually receptive rats. DOI attenuated the lordosis-inhibiting effect of ketanserin, but ketanserin was less effective in preventing DOI from increasing lordosis behavior. These results strengthen prior inferences that activation of 5-HT(2A/2C) receptors can facilitate lordosis behavior and that the VMN is one site at which such facilitation can occur.     

Lordosis in the male golden hamster elicited by manual stimulation: characteristics and hormonal sensitivity

The lordosis response was regularly elicited from 24 of 31 intact, adult male hamsters, using manual somatosensory stimulation of the dorsal rear body. In these males there was no correlation between measures of male-typical behavior and lordosis. Castration had no effect on male lordosis duration scores even when intromissions were eliminated. Combined treatment with estradiol benzoate and progesterone significantly increased male lordosis duration scores. The body surface was mapped with a standardized brush stimulus. For eliciting lordosis, effectiveness of stimulation increased in an almost identical manner for hormone-primed males and females from the anterior to the posterior part of the body, with the stimulation of flanks, rump, and perineum the most effective. Within each skin zone, absolute effectiveness was greater in females than in males. Various types of somato-sensory stimulation were compared for their effectiveness in eliciting lordosis. Females were more responsive to these stimuli than males, even when males were hormonally primed. These behavioral data have implications for concepts of the neural organization of male- and female-typical mating responses existing within the same individual.     

Assuring quality, information, and choice in managed care

The aim of the study was to determine whether there is an increase in responsiveness to estrogen stimulation of maternal behavior and lordosis responsiveness during pregnancy. Using separate groups of pregnancy-terminated females, we measured the initial maternal responsiveness of hysterectomized-ovariectomized (HO) females and their responsiveness to estrogen stimulation. Maternal behavior latencies were studied in females HO on the 8th, 10th, 13th, 16th, or 19th day of pregnancy (8HO-19HO) and in nonpregnant HO (NPHO) females. Groups were injected sc with estradiol benzoate (EB) in doses ranging from 0 to 200 microgram(s)/kg and tested for maternal behavior (retrieving, crouching, and licking pups). In addition, we investigated whether there is an increase during pregnancy (following HO) in lordosis responsiveness to estrogen stimulation. Lordosis behavior was studied in pregnant HO females (days 8, 16, and 22) and NPHO females given 0 to 200 microgram(s)/kg EB. There was an increase in maternal responsiveness in oil-treated HO females starting around midpregnancy. From early pregnancy on there was also an increase in maternal responsiveness to 20 microgram(s)/kg EB. In late pregnant females (16HO) there was a further increase with 50 microgram(s)/kg EB. There was no increase in lordosis responsiveness to EB stimulation during pregnancy; pregnant and nonpregnant HO females had the same EB threshold for stimulating lordosis behavior. The results of both studies were related to increases during the latter half of pregnancy in nuclear estrogen receptor concentrations in the MPOA, an area that mediates estrogen stimulation of maternal behavior, and the absence of such increases during pregnancy in the VMH, an area that mediates estrogen stimulation of lordosis behavior.     

Prelordotic behavior in the hamster: A hormonally modulated transition from aggression to sexual receptivity.

Analyzed the behavioral responses of 60 female golden hamsters to sexually experienced males as a function of the stage of the female's estrous cycle. Exogenous estradiol or estradiol followed by progesterone was given to ovariectomized Ss to determine the role of these hormones in regulation of cyclic changes in the female's response to the male. Ss were paired daily with sexually active males for 10 min, and behavioral interactions were recorded. Significantly more fighting occurred during early diestrus than later in the cycle. By 8 hrs prior to the onset of sexual receptivity, 86% of Ss exhibited a behavior resembling the onset of lordosis without immobilization. Following ovariectomy, fighting was at a high level. Estradiol replacement over 28 days resulted in a significant decrease in aggression and increase in display of the prelordotic response. Initially, treatment with progesterone following 7 days of estradiol caused lordosis display. After 24 hrs a significant increase in aggression, which continued as long as progesterone was present, was observed. Thus, estradiol causes the female to become tolerant of the male's approach, the female exhibiting prelordosis in response to the male's investigation. Estradiol and progesterone are necessary for normal sexual receptivity; however, after 24 hrs, estrogen/progesterone-treated females become agonistic to the male. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of CNS depressants and stimulants on latency for the appearance of copulatory response in the female rat

Diethyl ether anesthesia, sodium hexobarbital (20 mg/kg), diphenylhydantoin (50 mg/kg), strychnine (1 mg/kg) and picrotoxin (1-0.25 mg/kg) effectively induced the copulatory response (lordotic behavior) in estradiol benzoate treated ovariectomized rats although no progesterone was given. As none of the tested compounds were effective in replacing progesterone in adrenalectomized animals, adrenal secretion is likely to be implicated in the lordosis activating effect of these compounds. The lordosis response appeared faster after the CNS stimulants than after treatment with the CNS depressants. The influence of diethylether anesthesia, strychnine (0.5 mg/kg) or picrotoxin (0.25 mg/kg) on the latency for the appearance of the lordosis response after IV injection of isopregnenone was studied in estradiol benzoate treated ovariectomized females. A 10 min ether anesthesia delayed the onset of the lordosis response in adrenal intact as well as adrenalectomized animals. Anesthesia given after receptivity had been fully established suppressed the responses for a short period (10-30 min) after the narcosis. The delay of the appearance of the first lordosis response after IV injection of isopregnone exceeded this period. Strychnine but not picrotoxin significantly shortened the latency to the onset of the female copulatory response. It is concluded that the lordotic activating action of progesterone or steroids with progesteronelike ability released from an endogenous source or given IV is influenced by compounds which exert a depressant or stimulant effect on neuronal activity. The total response obtained is not changed but the appearance of the response is prolonged by CNS depressants and shortened by certain CNS stimulants.     

Evidence for involvement of midbrain central gray in cholinergic mediation of female sexual receptivity in rats.

Conducted 3 experiments with 63 female Sherman rats to determine the role of the midbrain central gray (MCG) in facilitation of lordosis by cholinergic agonists. Selected findings show that Ss with MCG damage displayed significantly less facilitation than sham-lesion Ss. Pretreatment with scopolamine (SCOP) abolished lordosis facilitation in both groups, and after treatment with estradiol and progesterone, sham-lesion Ss showed more receptivity than MCG-lesion Ss. Systemic injection of SCOP produced a significant decline in lordosis for both groups. Results suggest that the MCG plays an important role in the cholinergic mediation of female sexual receptivity. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Progesterone and 3α,5α-THP enhance sexual receptivity in mice.

Progesterone (P) and its metabolites' effects on sexual receptivity (lordosis) of mice was examined. P dosages that produced normal circulating concentrations of P and 5α-pregnan-3α-ol-20-one (3α,5α-THP) enhanced lordosis of ovariectomized, sexually experienced C57BL/6J (C57), +/+ C57BL/6J*129SvEv (C57*129), and -/- C57BL/6JX129SvEv (PRKO) mice. Only C57 and C57*129 mice bad increases in progestin receptor (PR)-immunoreactivity (PR-IR) in the hypothalamus. RU38486, a PR antagonist, attenuated lordosis of C57 and C57*129, but not PRKO, mice; epostane, a progestin biosynthesis inhibitor, reduced plasma progestins; and finasteride, a P metabolism inhibitor, reduced plasma 3α,5α-THP and attenuated lordosis of all mice. For sexually naive mice, greater lordosis on initial sexual experience corresponded to greater concentrations of plasma and central progestins and increased central binding of a GABA≈ agonist, muscimol, compared with that seen in mice with lower lordosis on initial mating. Thus, P-facilitated receptivity in mice involves P and 3α,5α-THP and their actions at PRs and GABAA receptors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Binding of [3H]estradiol by brain cell nuclei and female rat sexual behavior: inhibition by experimental diabetes

In streptozotocin-diabetic female rats acute (24 h) withdrawal of insulin significantly impairs both estradiol + progesterone-induced sexual receptivity and cell nuclear concentration of [3H]estradiol in hypothalamus, preoptic area, and pituitary gland. Omission of insulin treatment for the first 24 h of a 30-h or 54-h estradiol benzoate-conditioning period significantly reduced mean lordosis ratings of ovariectomized-diabetic rats. Insulin withdrawal at the time of progesterone treatment and behavioral testing did not diminish sexual receptivity. One-half or 2 h after an intravenous injection of [3H]estradiol-17beta diabetic rats without insulin exhibited reduced cell nuclear [3H]estradiol concentrations (2 h) and/or diminished cell nuclear/whole homogenate concentration ratios (0.5 and 2 h). Twenty-four hour insulin withdrawal affected neither whole tissue [3H]estradiol uptake nor hypothalamus-preoptic area cytoplasmic estrogen-receptor content. These results: (1) suggest that diminished estradiol binding by target tissue cell nuclei may contribute to the well-known reproductive failures of female diabetics, and (2) support the concept that estradiol acts at the level of brain cell nuclei to induce female sexual behavior.     

Mating-induced inhibition of receptivity in the female golden hamster (Mesocricetus auratus): II. Stimuli mediating short-term effects.

In the female golden hamster, mating with an intact male results in reduced receptivity toward a second male. In Experiment 1, females received various types of mating stimuli (e.g., mounts from an aproned male, intromissions from a vasectomized male, a simulated copulatory plug, a male in a hardware cloth cylinder, or several of these stimuli in combination). Although stimuli associated with male intromissions appeared to be most effective in altering the female's responsiveness to a subsequent male, treatments that included intromissive stimuli also resulted in the longest periods of lordosis. In Experiment 2 we found a highly significant inverse relation between the duration of lordosis in the presence of a male enclosed in a hardware cloth cylinder and lordosis duration with a second male that was free to copulate. In Experiment 3 we further showed that it was not the presence of a male in the cylinder that was the essential stimulus for producing this effect but rather the act of lordosis itself. By varying lordosis time and the number of intromissions independently (Experiment 4), we convincingly showed that short-term inhibition of receptivity in the hamster is attributable to lordosis duration per se rather than to male intromissions, as had been previously reported. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Estradiol benzoate facilitates lordosis and ear wiggling of 4- to 6-day-old rats.

The effects of exogenous and endogenous steroids on components of female sexual behavior of neonatal male and female rats were investigated. In Experiment 1, 4-day-old rats were treated with 0, 0.1, 1.0, 10, or 100 μg/10 g body weight estradiol benzoate (EB) and were tested 44 hr later. In Experiment 2, male rats castrated within 24 to 48 hr of birth were compared with sham operated controls and castrates given steroid replacement. The results indicated that most 6-day-old pups will display lordosis and ear wiggling, therefore, the display of these responses is not dependent upon exogenous steroids. However, a fine-grain behavioral analysis revealed that EB treatment increased the frequency, duration, and intensity of lordosis and the frequency of ear wiggling in infant females, and it increased lordosis duration in males. Castration of infant males decreased the likelihood that male infants would display lordosis, whereas testosterone replacement restored behavior to control levels. These data question the concept that organizational and activational actions of estrogens occur during completely separable times in development and should provide new insights into the development of estrogen receptor function and the process of sexual differentiation of brain and behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of monoamines in the control of hormones of sexual receptivity in the female rat.

Investigated the involvement of indole- and catecholamines in the hormonal regulation of sexual receptivity in ovariectomized Sprague-Dawley rats. Drugs that reduce 5-hydroxytryptamine, dopamine, and adrenaline or increase noradrenaline neurotransmission tended to facilitate the occurrence of estrous behavior in estrogen-treated Ss, and drugs having opposite effects tended to inhibit receptivity induced by estrogen and progesterone. Estrogen decreased noradrenaline turnover in cortex and brain stem; progesterone enhanced this effect in brain stem but prevented it in cortex. Both hormones tended to block noradrenaline uptake in hypothalamus in vitro. In a schedule used to induce receptivity, estrogen accelerated serotonin turnover, an effect prevented by progesterone. Results suggest that a number of monoamines may be involved in the control by hormones of estrous behavior and that hormones affect both amine turnover and uptake mechanisms. (85 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)