Lordotic Behavior Research Articles

Potential Estrogenic Properties of 17β-Hydroxy-ethylimine Estradiol Derivative Targeted to Menopause Stage.

Hormone replacement therapy during menopause increases the risk of thromboembolic diseases and cancer, so safety alternative therapeutic strategies are needed. 17β-Aminoestrogens are a synthetic estrogens group that possess mild anticoagulant activity that contrasts with the pro-coagulant effects showed by estradiol's (E2) in rodents. Being considered an alternative to conventional hormone replacement therapy during menopause without thrombogenic risks producing. The present study aimed to determine the estrogenic profile and anxiolytic activity of 17β-[hydroxy-ethylimine]-1,3,5(10)-estratrien-3-ol (IE2), a related compound unknown until now. IE2 was assessed in immature rats by uterotrophic assay administering IE2, E2, or vehicle. In ovariectomized adult Wistar rats (Ovx) to facilitating the lordotic behavior compared with E2, estradiol benzoate, or vehicle. The effect of IE2 on anxiety was estimated in Ovx animals treated with IE2, E2, or vehicle group and evaluated in the elevated plus-maze model. IE2 produced an uterotrophic effect, lordotic behavior, and anxiolytic effect in a dose-dependent manner, similar to E2. IE2 depicted estrogenicity, indicating potential clinical use as hormone replacement therapy during menopause.

Age dynamics of changes in sexual behavior and androgen status of male rats caused by prenatal exposure to low dose dibutylphthalate

The aim of this work was to study the sexual maturation, testicular hormonal activity and sexual behavior of Wistar male rats, which were born to mothers treated intragastrically with di-n-butylphtha- late (DBP) for 15-21 days of their pregnancy, at a daily dose of 100 mg/kg b.w., that do not cause visible developmental morpho- logical abnormalities. Their sexual behaviour was analyzed via the proceptive reactions, the latent and refractory periods of time and number of mounts, intromissions and ejaculations at the presence of a receptive female. Female sexual behaviour was evaluated by lordosis responses of orchidectomized and activated with estradiol and progesterone males in the presence of a normal male. Prenatal administration of DBP induced an accelerated onset of puberty. In young mature males (6-month old), it was, unexpectedly (as for endocrine disruptors), discovered that was featured by hyperactive central (motivational) and peripheral (copulative and ejaculatory) components of male sexual behavior and a two-fold increase in the average levels of plasma testosterone. In 10-month old rats, we found both homosexual and enhanced lordotic behavior. In aging animals (18 months), hyperandrogenism had switched to quite the opposite condition: more than two-fold decrease in the levels of plasma testosterone, close to statistical significance; and a lessen- ing of male sexual behavior compared to controls. These findings show the presence of epigenetic alterations in the programming of the parts of the brain responsible for sexual differentiation (the hypermasculinization combined with feminization) and a regula- tion of testicular hormonopoeisis, as well as premature aging of the reproductive organs resulting from the prenatal influence of low dose DBP. Thereby we proposed the original concept of prenatally determined DBP syndrome. And, finally, the possible mechanism of these changes in the repro- ductive system are discussed. Key words: dibutylphthalate; prenatal effect; sexual behavior; tes- tosterone; male rats. For citation: Reznikov AG, Sachynska OV, Lymareva АA.

Effects of 17β-aminoestrogens on the sexual behavior of female rats

17β-aminoestrogens (AEs) produce anticoagulant effects in rats contrasting with 17β-estradiol (E 2) procoagulant effects, their estrogenic effects are similar to E 2, decreasing serum luteinizing hormone (LH), increasing uterine weight (Uw), activate transcription through the ERα and ERβ receptors and pentolame induces progesterone (P) receptors in the anterior pituitary of ovariectomized (Ovx) rats similarly to E 2, suggesting possible effects on female rats' sexual behavior. This work evaluated the AEs prolame, butolame, pentolame compared to E 2 and estradiol benzoate (EB) as facilitators on the rat lordotic behavior. Dose–response curves were performed in rats by single subcutaneous (s.c.) injection (time zero) of: E 2 (≈ 0.3, 3, 30, 60, 300 µg/kg); EB (≈ 0.4, 4, 40, 80, 400 µg/kg); prolame, butolame, pentolame (≈ 40, 400, 2000 or 4000 mg/kg), vehicle (corn oil; 300 µL/day; ≈ 1.2 mL/kg) as control; 24 h after, P (1 mg/rat in 100 µL of corn oil; ≈ 4 to 5 mg/kg) was administered, and 5 to 7 h later LQ was evaluated (number of lordosis displays / number of mounts × 100). E 2, EB and AEs followed by P administration, induced lordosis in a dose-dependent manner. Prolame induced an LQEmax of 92, butolame 85, EB 81, pentolame 44 and E 2 43. The most potent was EB (LQED50 of 4.1 ± 0.5 µg/kg); then E 2 10 µg ± 2.2/kg; prolame 268 ± 19 µg/kg; butolame 402 ± 21 µg/kg, and pentolame 1037 ± 28 µg/kg. The AEs LQ potency decreases as length substitution on the amine group in C-17 increases. AEs LQDE50 values correlate with previous Uw DE50, LH ID50 and binding studies indicates mediation of the response by estrogen receptors. AEs facilitate sexual behavior of Ovx rats as partial estrogenic agonists.

The effects of partial and complete masculinization on the sexual differentiation of nuclei that control lordotic behavior in the male rat

Male rats, under certain experimental conditions, may show lordosis, the typical expression of female sexual receptivity. This work studies the sexual morphological pattern of facilitatory and inhibitory structures that control lordosis. Three groups of males were neonatally subjected to a gradient of androgen exposure (castrated plus injected oil (GxM + oil); castrated plus androstenedione treated (GxM + AND); and sham operated [CM]); a group of control females (CF) was also added. Lordotic response after these different hormonal and neonatal surgical treatments, as well as the volume or number of neurons in facilitatory (ventromedial nucleus of the hypothalamus [VMN]) and inhibitory (the intermediate region of the lateral septum [LSi] and accessory olfactory bulb [AOB]) nuclei involved in lordosis was studied in adults. The inhibition of lordosis in the males seems to be associated to the neonatal presence of testosterone and the consequent masculinization of the VMN, VMNvl, LSi and AOB. It is suggested that one of the functions of the sex differences consistently seen in these structures might be to inhibit the lordosis response in the male.

Postparturitional Testosterone Surge in Male Offspring of Rats Stressed and/or Fed Ethanol during Late Pregnancy

Male offspring of rats exposed to restraint stress and/or alcohol during late pregnancy show aberrant patterns of sexual behavior masculinization and defeminization that vary as a function of treatment. The impact of these treatments on the postparturitional testosterone (T) surge that contributes to sexual behavior differentiation was investigated. Plasma T was measured using radioimmunoassay in individual males sampled on day 21 of gestation within 10 min of cesarean delivery or 1, 2, or 4 h thereafter. Neonatal T in the group exposed only to stress did not differ from that in the control group. T was lower than control levels at birth in both alcohol groups. The magnitude of the T surge that occurred during the first hour of birth in the control group was diminished by 50% in both alcohol groups, whose T pattern was very similar. There was no common alteration in postparturitional T associated with the increased lordotic behavior potential that males in all three treatment groups typically share, nor were there idiosyncratic endocrine abnormalities linked to the very different male copulatory pattern each exhibits. Exposure to an abnormal T milieu during fetal as well as neonatal ontogeny may underlie the etiology of the different sexual behavior patterns exhibited by males exposed to stress and/or alcohol. Possible unique effects each treatment exerts on perinatal plasma T and it's aromatization to estradiol in hypothalamic targets are discussed.

Female preproenkephalin-knockout mice display altered emotional responses.

The endogenous opioid system has been implicated in sexual behavior, palatable intake, fear, and anxiety. The present study examined whether ovariectomized female transgenic preproenkephalin-knockout (PPEKO) mice and their wild-type and heterozygous controls displayed alterations in fear and anxiety paradigms, sucrose intake, and lordotic behavior. To examine stability of responding, three squads of the genotypes were tested across seasons over a 20-month period. In a fear-conditioning paradigm, PPEKO mice significantly increased freezing to both fear and fear + shock stimuli relative to controls. In the open field, PPEKO mice spent significantly less time and traversed significantly less distance in the center of an open field than wild-type controls. Further, PPEKO mice spent significantly less time and tended to be less active on the light side of a dark-light chamber than controls, indicating that deletion of the enkephalin gene resulted in exaggerated responses to fear or anxiety-provoking environments. These selective deficits were observed consistently across testing squads spanning 20 months and different seasons. In contrast, PPEKO mice failed to differ from corresponding controls in sucrose, chow, or water intake across a range (0.0001-20%) of sucrose concentrations and failed to differ in either lordotic or female approach to male behaviors when primed with estradiol and progesterone, thereby arguing strongly for the selectivity of a fear and anxiety deficit which was not caused by generalized and nonspecific debilitation. These transgenic data strongly suggest that opioids, and particularly enkephalin gene products, are acting naturally to inhibit fear and anxiety.

Endocrine defects in mice carrying a null mutation for the progesterone receptor gene.

Mice carrying a null mutation of the progesterone receptor gene exhibit several reproductive abnormalities, including anovulation, attenuated lordotic behavior, uterine hyperplasia, and lack of mammary gland development. The hormonal correlates of these abnormalities are unknown, however, and were the focus of these studies. Serum samples from female wild-type (WT) and progesterone receptor knockout (PRKO) mice were obtained and analyzed by RIA for LH, FSH, PRL, estrogen (E2), and progesterone. Hypothalamic tissues were also processed for measurement of LHRH by RIA. Serum LH levels in PRKO mice were found to be elevated by approximately 2-fold over basal (metestrus) values in WT mice. By contrast, basal FSH levels were not different in PRKO and WT mice. Basal levels of E2 and progesterone in serum were likewise similar in the two groups, as were hypothalamic LHRH concentrations. Basal PRL levels were slightly higher in PRKO vs. WT mice. Ovariectomy of both groups of mice was accompanied by significant increases in both LH and FSH. At 5 days following ovariectomy, LH levels were elevated in both groups by 2-fold over PRKO basal and 4-fold over WT basal levels; however, by 10 days postovariectomy LH levels had continued to rise to a greater extent in PRKO mice than in WT animals. The FSH response to ovariectomy was greater for the PRKO mice at 5 days, but was no different from WT at 10 days. Of seven PRKO mice that were exposed to male odor, none exhibited preovulatory surges 3 days later, on the day of presumptive proestrus; this was in marked contrast with WT females, in which 100% exhibited robust LH surges. These results confirm the essential role of progesterone receptors in the regulation of hypothalamic and/or pituitary processes that govern gonadotropin secretion. The finding that basal LH levels are elevated in PRKO mice confirms that circulating progesterone normally conveys a significant portion of the total ovarian negative feedback control of the gonadotropin. That gonadotropin responses to ovariectomy are slightly enhanced in PRKO mice suggests that adrenal progesterone may contribute to the imposition of negative feedback control. The apparent inability of PRKO mice to respond to male odor suggests that anovulation in these mice may not be solely due to reproductive abnormalities within the ovary itself; rather, PRKO mice additionally harbor neuroendocrine defects that render them incapable of mounting normal preovulatory gonadotropin surges. It remains to be determined how the absence of PR in brain and pituitary of PRKO mice may produce this hormonal acyclicity and, conversely, how the presence of PR in brain and pituitary of WT mice may be obligatory in the generation of gonadotropin surges.

Postnatal Testicular Secretions Partially Restore the Disturbances in Reproductive Activity Caused by Prenatal Hormonal Manipulation

Vega Matuszczyk, J., R. S. Appa and K. Larsson. Postnatal testicular secretions partially restore the disturbances in reproductive activity caused by prenatal hormonal manipulation. Physiol Behav 62(1) 137–143, 1997.—Male rats that prenatally had been exposed to an antiestrogen, nitromifene citrate (CI 628), showed evidence of impaired defeminization and masculinization in adulthood, suggesting a role of endogenous estrogen for the sexual differentiation of the male. The present study was undertaken to investigate a possible role of postnatal testicular secretions for the above behavioral effects. Male rats were exposed prenatally to CI 628 (l mg/rat) or saline, and castrated on Day 0, Day 10, or Day 90 after birth. After treatment with gonadal hormones in adulthood, the males were tested for feminine and masculine sexual behavior and for sexual orientation, both when sexually naive and after they had acquired sexual experience. The following conclusions were drawn: 1. Permanent deficits of lordotic behavior were observed in all experimental groups, suggesting the importance of prenatal estrogen for the defeminization process. 2. Hop/darting and ear wiggling behaviors were enhanced in Day-0 and Day-10 castrates, and blocked in the Day-90 castrates. The restitution of these behaviors to normal levels in Day-90 castrates suggests that, in addition to prenatal estrogen, postnatal testicular secretions also are involved in the behavioral defeminization process. 3. Prenatal estrogen contributes to masculinization as evidenced by the impaired ejaculatory behavior observed in all experimental groups. 4. Male-typical sexual orientation toward the female seems to be facilitated by prenatal estrogen. Both the masculinization and the defeminization of male-typical sexual orientation toward a female were impaired by castration at birth and at Day 10 in the experimental animals, but a full restoration of the sexual orientation toward females was seen in Day-90 castrates, suggesting the restorative role of postnatal testicular secretions for these processes.

Effects of prenatal testosterone on sexual behavior, reproductive morphology and LH secretion in the female rat.

Sexual differentiation of many brain structures and functions is dependent on levels of testosterone (T) or its metabolites during certain 'sensitive' developmental periods. If T is present during these perinatal periods, masculinization and defeminization of sexual behavior occur; also, reproductive physiology, and central nervous system morphology and function are altered. The purpose of the present study was to characterize the influence of T at specific prenatal developmental intervals on offspring reproductive morphology, physiology, locomotor activity and sexual behavior during postnatal development. To avoid complications induced by endogenous testicular activity, only females were examined. Free T was used because of its relative short half-life, so that the effects induced by its administration on a specific gestational day (GD) could be evaluated. Pregnant rats received a single subcutaneous injection of either sesame oil (controls) or 5 mg of T on GD 16, 17, 18, 19, 20, 21, or 22. Female offspring of pregnant rats exposed to T displayed significant alterations in morphology and behavior. The anogenital distance, measured at 25 days postbirth, was significantly increased if T was administered on GD 16, 17 or 18. T treatment on GD 16 or each day thereafter through GD 20 significantly delayed the normal occurrence of vaginal opening (controls at 37.5 days vs. T treatment which ranged from 38.5 to 41.4 days). Abnormal vaginal morphology (enlarged clitoris) was also observed when T was injected during a similar prenatal interval (i.e. GD 16 to GD 22). Furthermore, prenatal T treatment on GD 18 (and each day thereafter), until GD 22 significantly decreased lordotic behavior compared to control values. However, exposure to T, on any prenatal GD did not alter the animals' ability to exhibit an induced luteinizing hormone (LH) surge. These results suggest that the onset for altered reproductive morphology occurs at least as early as GD 16, whereas the onset of sexual behavior sensitivity occurs precisely at GD 18, and that the normal pattern of adult LH release in females is not altered by prenatal androgen treatment using this specific paradigm.

Partial Demasculinization and Feminization of Sex Behavior in Male Rats by in Utero and Lactational Exposure to 2,3,7,8-Tetrachlorodibenzo-p-dioxin Is Not Associated with Alterations in Estrogen Receptor Binding or Volumes of Sexually Differentiated Brain

In utero and lactational 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure partially demasculinizes and feminizes sexual behavior in adult male rats, presumably by causing incomplete sexual differentiation of the central nervous system (CNS). Our objective was to determine if TCDD exposure affects other aspects of sexual differentiation of the CNS. Because sex differences in the estrogen receptor system are thought to play a role in sexually dimorphic estrogen-mediated responses, and because estrogen is an important activator of both male and female sex behavior, the possible effect of TCDD exposure on estrogen binding in specific brain nuclei was examined. In addition, we investigated effects of in utero and lactational TCDD exposure on sex differences in the volumes of brain nuclei which are dependent on steroid hormone stimulation during the period of CNS sexual differentiation. Pregnant Holtzman rats were given TCDD (0.7 μg/kg, po) or vehicle (control) on gestation Day 15. Offspring were exposed to TCDD in utero and via lactation and then assessed in adulthood. Demasculinized sexual behavior was evidenced in the TCDD-exposed males by increased intromission latencies and a greater number of intromissions prior to ejaculation. These males were then castrated, primed with ovarian steroids, and tested for feminine sexual behavior. In utero and lactational TCDD exposure increased both the frequency and intensity of lordotic behavior, indicating that the males were partially feminized. To determine if TCDD exposure had a generalized effect on estrogen receptor concentrations the arcuate nucleus, cortical and medial amygdala and the bed nucleus of the stria terminalis, previously found to have equivalent numbers of estrogen receptors in males and females, were evaluated in littermates of the rats whose sexual behavior had been assessed. TCDD had no effect in either sex. To determine if TCDD exposure had an effect specific to sexual differentiation of the brain, estrogen receptor concentrations in the medial preoptic nucleus (MPO), ventrolateral aspect of the ventromedial nucleus, and periventricular preoptic area were assessed. As expected, females had higher estrogen receptor concentrations in these nuclei than did males, but TCDD exposure did not affect estrogen receptor concentrations in any of these sexually dimorphic brain nuclei. The volumes of sexually dimorphic brain nuclei were examined in additional littermates. In control rats, the volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) is larger in males than in females whereas the MPO is larger in females than in males. TCDD exposure had no effect on the volume of either the SDN-POA or MPO in either males or females. Our results indicate that in utero and lactational TCDD exposure causes a partial demasculinization and feminization of sex behavior that is not associated with an apparent effect on the sexual differentiation of the estrogen receptor system or the volume of sexually dimorphic brain nuclei.

Ca2+/calmodulin system: participation on rat sexual hypothalamic differentiation.

Modifications of male rat hypothalamic sexual differentiation after neonatal administration of drugs that participate on the Ca2+/calmodulin system (haloperidol, trifluoperazine, penfluridol, pimozide, and verapamil) were studied. Pups treated 72 h after birth were behaviorally tested on day 120 of extrauterine life. Five tests for homotypical behavior were conducted. Afterwards animals were castrated and tested twice for heterotypical (female) behavior under replacement hormonal therapy. Fifty percent (80% in the case of pimozide) of all treated males showed lordotic behavior compared with none of the controls. Haloperidol (39%, lordosis quotient) and pimozide (40%, lordosis quotient) were more active than the others. Results obtained with verapamil were not statistically different from the controls. Pimozide was the most active agent influencing the appetitive masculine behavior (mount latency, intromission latency, and postejaculatory interval). Verapamil was more efficient than the rest of the drugs on the consummatory behavior (mount latency, intromission frequency, interintromission interval, and ejaculatory latency). Our results support the participation of the Ca2+/calmodulin system in hypothalamic sexual differentiation and in the differential modulation of the masculine and feminine behavioral patterns.

Genetic differences in progestin sensitivity in CD-1 and SW female mice

The lordotic behavior of ovariectomized CD1 and SW female mice was tested in response to estradiol benzoate(EB) + progesterone (P) or EB + 5 α-dihydroprogesterone (DHP) to determine (i) the role of progestin metabolism in the regulation of sexually receptive behavior, and (ii) strain differences in sensitivity to these progestins. A greater proportion of SW females resisted mounting attempts than CD-1 females, regardless of the progestin administered. However, the differences in mounting were not correlated with the expression of lordotic behavior. A greater proportion of SW females exhibited sexually receptive behavior when given EB + P in comparison to the CD-1 females. There were no genotypic differences in lordotic behavior in response to EB + DHP. The potential mechanisms mediating genotype-based differences in responsiveness are discussed, and the relationship of this report to previously described strain differences in progestin sensitivity are considered.

An assessment of agonist/antagonist effects of tamoxifen in the female mouse brain

Ovariectomized CFW mice were treated with tamoxifen (TAM) alone or in combination with estradiol benzoate (EB) to determine its ability to promote/block lordotic behavior and the induction of hypothalamic progestin receptors (PR). Across a range of doses, TAM plus progesterone treatment did not activate female sexual behavior. When given with EB, TAM suppressed lordotic behavior in a dose-dependent fashion. TAM did not induce PR when given alone and it completely blocked the ability of EB to induce PR. It therefore appears that for these responses TAM functioned as a pure antagonist in the female mouse brain, although the degree of its antiestrogenicity varied with the response under consideration. A potential mechanism mediating this differential effectiveness is discussed.

Pelvic and pudendal nerves influence the display of paced mating behavior in response to estrogen and progesterone in the female rat.

Two experiments examined whether the pudendal and pelvic autonomic nerves are important for pacing behavior shown by the female rat during mating. Ovariectomized female rats received bilateral transection of the pudendal (Pux), pelvic (Pex), or pudendal and pelvic (Pu + Pex) nerves or were sham-operated (Shx). Lordotic behavior, precopulatory solicitations, postural adjustments, and pacing behavior were measured 14 days after nerve transection in Experiment 1 after sequential treatment with estradiol benzoate (EB) and progesterone (P) and in Experiment 2 on the day after 7 daily injections of EB. After combined EB and P treatment, disruption of pacing behavior occurred in Pex and Pu + Pex animals. After EB-only treatment, Pux animals as well as Pex and Pu + Pex animals showed decreased pacing behavior. Thus, afferent input via the pelvic nerve is important for the display of pacing behavior, and P may counteract the effects of autonomic nerve transection.

Chemical structure of corticosteroids and its relationship with their acute induction of lordosis in the female rat

The intravenous injection of several corticosteroids in the spayed estrogenprimed rat resulted, 5 min later, in a remarkable induction of lordosis response for deoxycorticosterone and 11-deoxycortisol. A lower but important effect was induced with corticosterone and 17α-hydroxyprogesterone. A chemical structure-biological effect analysis showed that C-21 hydroxylation (e.g., deoxycorticosterone, 11-deoxycortisol, and corticosterone) induces the behavioral effect. However, C-11 or C-17 hydroxylation alone promotes the lordosis response to a lesser degree (corticosterone and 17α-hydroxyprogesterone, respectively). However, the effect of these latter compounds is significant. From the results, it is concluded that deoxycorticosterone and 11-deoxycortisol along with other steroids such as 20α-hydroxyprogesterone are suitable candidates for synergizing the well-known estrogen-progesterone induction of lordotic behavior.

Differential Effects of an Luteinizing-Hormone-Releasing Hormone (LHRH) Antagonist Analogue on Lordosis Behavior Induced by LHRH and the LHRH Fragment Ac-LHRH<sup>5–1</sup>⁰

Both the luteinizing-hormone-releasing hormone (LHRH) decapeptide and an LHRH fragment consisting of the last 6 amino acids of the decapeptide, Ac-LHRH, have been shown to enhance lordosis behavior in ovariectomized, estradiol-benzoate treated female rats. Although the behavioral efficacy of the 2 peptides is similar, several lines of research suggest that the fragment and the decapeptide may act via different mechanisms. The present study attempted to differentiate the behavioral action of the 2 peptides by administering a long-acting LHRH antagonist analogue prior to infusion of either Ac-LHRH or LHRH. Without antagonist administration, the decapeptide and the fragment were equally effective in elevating lordotic posturing 90 min after bilateral infusion through cannulae positioned in the ventromedial nucleus of the hypothalamus (VMH). Infusion of a potent LHRH antagonist analogue [Ac-dehydro, Pro, pCl, D-Phe, DTrp]-LHRH, into the VMH significantly reduced the lordosis-to-mount ratio in animals subsequently treated with the LHRH decapeptide, but had no significant effect on lordotic behavior when the animals were subsequently infused with the Ac-LHRH fragment. The results indicate that LHRH enhancement of mating behavior is a receptor-mediated event and suggest that the Ac-LHRH fragment enhances lordotic behavior via a mechanism that is distinct from that of the LHRH decapeptide.

Differential effects of estradiol and 16 alpha-hydroxyestrone on pituitary and preoptic estrogen receptor regulation.

16 alpha-Hydroxyestrone (16OHE1), an endogenous metabolite of estradiol (E2), binds to the estrogen receptor (ER) with low affinity, but is estrogenic in various bioassay systems. 16OHE1 binds covalently to the ER in vitro, exhibits prolonged estrogenic bioactivity in vivo, and has been implicated in several estrogen-dependent diseases. This study examined the effects of 13 days of continuous infusion of E2 or 16OHE1 on lordotic behavior, pituitary growth, and ER regulation in the cytosolic and nuclear fractions of the pituitary and preoptic area of both sexes. Finally, simultaneous pituitary nuclear exchange assays and enzyme immunoassays were performed to search for covalent 16OHE1-ER complexes in vivo. E2 induced lordosis and pituitary growth in both sexes, while 16OHE1 was only slightly less effective. While E2 treatment increased nuclear ER concentrations 2-fold vs. control values, it decreased both cytosolic and total (cytosolic plus nuclear) ER concentrations in pituitary and preoptic area by approximately 3-fold vs. control values in both sexes by exchange assay. In contrast, 16OHE1 did not decrease total pituitary ER concentrations and only minimally decreased total preoptic ER concentrations. Simultaneous exchange assay and immunoassay of pituitary nuclear extracts demonstrated proportionate increases in ER levels in female vs. male and in E2-treated vs. 16OHE1-treated rats. The ratios of (ER enzyme immunoassay divided by ER-exchange) for each rat were similar regardless of metabolite administration. The correlation of individual measurements implied that ER localized to the nuclear fraction by either E2 or 16OHE1 retained both exchangeability and immunoassayability to similar extents, but did not support the presence of 16OHE1-ER covalent complexes. The results of this study suggest that 16OHE1 has significant estrogenic bioactivity, as manifest by its effects on lordosis and pituitary growth, but, in contrast to E2, does not decrease pituitary ER concentrations and only minimally decreases preoptic ER concentrations. This property may be important in the proposed pathogenetic action of 16OHE1 in estrogen-dependent disease.

Sexual orientation, proceptivity, and receptivity in the male rat as a function of neonatal hormonal manipulation

The influence of neonatal androgen on the potential to exhibit feminine sexual behavior was investigated. Male rats castrated on Day 0 but not those castrated on Day 4 or later showed hop/darting, ear wiggling, and lordotic behavior in response to treatment with estrogen and progesterone in adulthood at a frequency equal to that of females. Neonatal treatment with testosterone propionate (1 mg/rat for 4 days) abolished the capacity to show these behaviors. In subsequent experiments, involving castration of male rats at 0 or 4 hr after cesarean delivery, the effect of the postnatal surge of testicular secretions on the expression of female sexual behavior was investigated. No differences were seen in the frequency of hop/darting, ear wiggling, and receptivity between males castrated immedately or 4 hr after delivery. In a preference test where the experimental male could choose between an estrous female and a sexually active male, the neonatally castrated males preferred the company of a male when treated with estrogen and progesterone. The implantation of testosterone resulted in a preference for an estrous female. It was concluded that testicular secretions in the newborn male influence adult sexual orientation and suppress the ability to show proceptive and receptive behaviors.

Muscarinic receptors in preoptic area and hypothalamus: effects of cyclicity, sex and estrogen treatment

Cholinergic muscarinic receptor binding was measured in the preoptic area (POA) and whole hypothalamus (HTH) of adult Sprague-Dawley rats using the tritiated antagonist quinuclidinyl benzilate ([ 3H]QNB) as the ligand. Binding of [ 3H]QNB expressed as fmol/mg protein was 30% higher in POA than in HTH from gonadectomized rats. Cyclic changes were observed in the POA with the highest binding at proestrus and the lowest binding at diestrus. In HTH, no significant changes occurred over the estrous cycle. Estrogen treatment (10 μg of estradiol benzoate (EB)/120 g b. wt./48 and 24 h before sacrifice) increased [ 3H]QNB binding by 42% in the POA and 17% in HTH, relative to the ovariectomized controls. The enhancement of [ 3H]QNB binding in POA as compared with controls was evident with both the filtration and the centrifugation methods, although binding levels were higher when centrifugation assay was used. A lower estrogen dose (2 μg EB/rat/48 and 24 h before sacrifice) which is routinely used to activate lordotic behavior in female rats increased muscarinic binding by 26% in the POA but had no appreciable effect in HTH. A significant sex difference was found in the ability of estrogen to induce [ 3H]QNB binding in the central nervous system (CNS). Estrogen was ineffective in altering [ 3H]QNB binding in either brain region of castrated males, although the level and pattern of cholinergic binding between untreated gonadectomized males and females were similar. These data suggest that physiological changes in estrogen secretion over the estrous cycle are capable of modulating cholinergic muscarinic binding in the POA and these changes may be physiological relevance. The failure of estrogen to enhance binding in either the POA or HTH of male rats is consistent with the hypothesis that cholinergic mechanisms are involved in mediating sensitivity to estrogenic hormones and implicates the sexual differentiation process in its regulation.

Facilitation of lordosis in female rats by CNS-site specific infusions of an LH-RH fragment, Ac-LH-RH-(5–10)

Structural alterations of the luteinizing hormone-releasing hormone (LH-RH) molecule have been performed to yield analogs which are more potent than, or which complete with, the parent hormone to increase or decrease the release of LH from the pituitary gland. The effects of these analogs on mating behavior, however, do not always parallel their effects on LH release. The present study tested the effectiveness of a pituitary-inactive fragment of LH-RH, namely Ac-LH-RH-(5–10), in potentiating mating behavior in the ovariectomized, estrogen-primed female rat. This fragment, when infused bilaterally into the medial preoptic area (POA), the ventromedial hypothalamus (VMH), or the midbrain central gray (MCG), significantly enhanced lordosis. Infusion of the fragment into the cerebral cortex was ineffective. Elevated lordotic responding was first apparent in the POA at 15 min postinfusion and was maintained for the duration of the testing session (180 min). Ac-LH-RH-(5–10) infused into the VMH or MCG enhanced lordotic behavior at 90 and 180 min postinfusion. The results indicate that only a portion of the LH-RH molecule may be required for behavioral activity and suggest that degradation of the LH-RH molecule is physiologically relevant.