Rats In Estrus Research Articles

Role of progesterone receptors during postpartum estrus in rats

We studied the role of progesterone receptor (PR) in the display of female sexual behavior during postpartum estrus in rats. Adult female rats were treated with the PR antagonist, RU486 (1.25 and 5mg), 3h after parturition and sexual behavior was evaluated throughout the first postpartum day. Estradiol and progesterone serum levels changed during the first 24h postpartum. The highest estradiol and progesterone levels were found at 9 and 12h postpartum, respectively. The predominant PR isoform in the hypothalamus and the preoptic area was PR-A during postpartum day. The content of PR-A increased at 6h postpartum in the hypothalamus and the preoptic area, and decreased in both regions at 9h. PR-B content only increased in the preoptic area at 12h postpartum. The highest display of lordotic and proceptive behaviors were found at 12h postpartum. The treatment with 1.25 and 5mg of RU486 respectively reduced lordosis by 61% and 92% at 12h postpartum. These results suggest that PR is essential in the display of postpartum estrus in rats.

Evaluation of Arterial Blood Pressure and Renal Sodium Handling in a Model of Female Rats in Persistent Estrus

The aim of this study was to evaluate the arterial blood pressure and renal function of female rats in persistent estrus. Twenty-five female Wistar-Hannover rats were randomly divided into two groups: Group I (control, n = 15) and experimental (persistent estrus, n = 10). A tail-cuff system was used to measure blood pressure at 12 weeks of life. Parameters to evaluate renal function were taken into consideration. A significant increase in arterial pressure and a significant decrease in fractional sodium excretion were found in the androgenized animals compared to controls. There was no difference between the two groups with respect to glomerular filtration rate or in fractional potassium excretion. An increase in blood pressure and a reduction in fractional sodium excretion occur in female rats in persistent estrus.

Activity of Hypothalamic Dopaminergic Neurones During the Day of Oestrus: Involvement in Prolactin Secretion

A secretory surge of prolactin occurs on the afternoon of oestrus in cycling rats. Pituitary prolactin is inhibited by dopamine. We evaluated the activity of the neuroendocrine dopaminergic neurones during oestrus and dioestrus, as determined by dopaminergic activity in the median eminence and neurointermediate lobe of the pituitary, as well as Fos-related antigen expression in tyrosine hydroxylase (TH)-immunoreactive (ir) neurones of the arcuate nucleus (ARC) and periventricular nucleus (Pe). During oestrus, the 4-dihydroxyphenylacetic acid/dopamine ratio in the median eminence decreased at 16.00 h, coinciding with the increase in plasma prolactin levels. Similarly, the expression of Fos-related antigen in TH-ir neurones of Pe and rostral-, dorsomedial- and caudal-ARC also decreased at 16.00 h. On dioestrus, 4-dihydroxyphenylacetic acid/dopamine ratio in the median eminence and Fos-related antigen expression in TH-ir neurones of Pe and rostral-ARC decreased at 18.00 h, whereas prolactin levels were unaltered. No variation in dopaminergic activity was found in the neurointermediate lobe of the pituitary on either oestrus or dioestrus. The number of TH-ir neurones in the ARC and parameters of dopaminergic activity were found to be generally lower on oestrus compared to dioestrus. The transitory decrease in the activity of neuroendocrine dopaminergic neurones temporally associated with the prolactin surge on the afternoon of oestrus suggests a role for dopamine in the generation of the oestrous prolactin surge.

Effects of 8-OH-DPAT and NAN-190 on anxiety behavior, monoamine metabolism, and the level of sex hormones in female rats during the estrus cycle

In this study, we performed a comparative analysis of the effects of chronic administration of an agonist of 5-HT1A receptors, 8-OH-DPAT, (0.05 mg/kg, subcutaneously) and an antagonist of 5-HT1A receptors, NAN-190, (0.1 mg/kg, intraperitoneally) for 14 days on the anxiety behavior, monoamine metabolism in the hippocampus and amygdala, and the level of sex hormones in the blood of adult female rats during the estrus cycle. Anxiety behavior was tested in an elevated X-maze. The level of monoamines and their metabolites was evaluated using HPLC with an electrochemical detector; the content of sex hormones in the blood was measured using an enzyme immunoassay. We found that chronic administration of 8-OH-DPAT has an anxiolytic effect in rats in estrus and proestrus. After treatment with NAN-190, we found clear modulation of anxiety behavior that depended on the phase of the estrus cycle, an anxiolytic effect at a high level of endogenous estrogens and an anxiogenic effect at a low level of estrogens. The anxiolytic effect of 8-OH-DPAT in female rats was accompanied by its suppressive influence on the pituitary-ovarian and noradrenergic systems and by its activating effect on the dopaminergic system of the brain. In contrast, the behavioral effects of NAN-190 in female rats during key phases of the estrus cycle corresponded to its stimulating effect of the pituitary-ovarian system and the absence of any effect on the monoaminergic systems of the brain. These data suggest that the mechanisms of anxiety include tight interaction between the ovarian hormonal system and the serotonergic brain system.

Plasma prolactin concentrations and copulatory behavior after salsolinol injection in male rats

The dopamine-derived endogenous compound, R-salsolinol (SAL), was recently identified as a putative endogenous prolactin (PRL)-releasing factor. However, how SAL influences copulatory behavior is unknown. In this study, we examined the relationship between SAL and copulatory behavior in male rats. Male Sprague-Dawley rats administered SAL were exposed to female rats in estrus, the plasma PRL concentration was measured, and the behavioral frequency and time during copulatory behavior were noted. In the control and SAL groups, plasma PRL concentrations at 15 min before exposure to the female were 7.3 ± 2.0 and 8.0 ± 1.5 ng/ml, respectively. Moreover, plasma PRL concentrations in males immediately after exposure to the female were 7.4 ± 1.2 and 68.0 ± 5.9 ng/ml, respectively (P < 0.05). All (8/8) of the control animals ejaculated in the presence of the female, whereas only 33% (2/6) of the SAL group ejaculated. An increasing tendency for mount latency and intromission latency and a decreasing tendency for intromission frequency were observed in the SAL group. Copulatory behavior was inhibited in male rats after SAL injection, suggesting that SAL is a copulatory behavior inhibiting factor.

Changes in Oestrogen Receptor α Expression in the Nucleus of the Solitary Tract of the Rat Over the Oestrous Cycle and Following Ovariectomy

Oestrogen is capable of modulating autonomic outflow and baroreflex function via actions on groups of neurones in the brainstem. We investigated the presence of oestrogen receptor (ER) alpha in a part of the nucleus of the solitary tract (NTS) associated with central cardiovascular control, aiming to determine whether ERalpha mRNA and protein expression is correlated with levels of circulating oestrogen during the oestrous cycle. Polymerase chain reaction (PCR) detected ERalpha mRNA in the NTS at each stage of the oestrous cycle, from ovariectomised, sham-operated and male rats. Real-time PCR showed variations in ERalpha mRNA expression during the oestrous cycle, with the highest levels seen in oestrus, and lowest levels in metoestrus (P < 0.05 versus oestrus) and proestrus (P < 0.05 versus oestrus). Expression in males was lower than in dioestrus and oestrus females (P < 0.05). After ovariectomy, ERalpha mRNA levels were decreased compared to sham-operated animals (P < 0.01). Confocal fluorescence immunohistochemistry with stereological analysis showed that numbers of ERalpha immunoreactive cell nuclei per mm(3) of tissue in the caudal NTS were significantly greater in proestrus than in other groups of rats (P < 0.05). There were also differences among the groups in the extent of colocalisation of ERalpha in neurones immunoreactive for tyrosine hydroxylase and nitric oxide synthase. These results imply a complex pattern of region-specific oestrogen signalling in the NTS and suggest that ERalpha expression in this important autonomic nucleus may be related to circulating oestrogen levels. This may have consequences for the regulation of autonomic tone and baroreflex sensitivity when oestrogen levels decline, for example following menopause.

WAY100635 blocks the hypophagia induced by 8-OH-DPAT in the hypothalamic nuclei

This study examined the influence of pretreatment with N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane carboxamide maleate (WAY100635, full 5-HT1A receptor antagonist, 37 nmol) on feeding effects evoked by local injections of 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT, 5-HT 1A and 5-HT 7 receptor agonist, 6 nmol) into the LH and into the ARC of female rats adapted to a wet mash diet (enriched with 10% sucrose), during diestrus or estrus. The results showed that the LH-pretreatment with WAY100635 suppressed the hypophagic effects evoked by 8-OH-DPAT during estrus as well as diestrus. The ARC pretreatment with WAY100635 blockaded the hypophagia evoked by 8-OH-DPAT in estrus rats. The previous treatment with WAY100635 in the ARC also suppressed the feeding duration decrease evoked by 8-OH-DPAT in estrus. The latency to start feeding, the drinking behavior and the durations of other non-ingestive behaviors were not affected by the different treatments, hypothalamic regions (LH or ARC), and/or estrous cycle stages (diestrus and estrus), except for the locomotion duration increase after 8-OH-DAPT in LH-pretreated rats in diestrus. The present findings confirm our previous suggestion that ARC- and the LH-5-HT 1A receptors participate in the serotonergic control of feeding and that these feeding-related serotonergic circuits in LH are affected by ovarian hormones, since the treatment with WAY100635 evoked a hypophagia response during the diestrus phases.

The development and stability of estrogen-modulated spatial navigation strategies in female rats

Adult female rats with high levels of circulating estradiol are biased to use a place strategy to solve an ambiguous spatial navigation task and those with low levels are biased to use a response strategy. We examined the development of this hormonal modulation of strategy use by training juvenile female rats on an ambiguous navigation task and probing them for strategy use at postnatal day (PD) 16, 21, or 26, after administration of 17 β-estradiol or oil 48 and 24 h prior to testing. We found that rats could use either strategy successfully by PD21 but that estradiol did not bias rats to use a place strategy until PD26. In order to evaluate the stability of this effect over multiple navigation experiences, we retested oil-treated juveniles three times during adulthood. On the first adult navigation experience, rats were significantly more likely to use the same navigation strategy they used as juveniles, regardless of current estrous cycle phase. On the second and third adult tests, after rats had more experience with the task, previous navigation experience did not predict strategy use. Rats in proestrus were significantly more likely to use a place strategy while rats in estrus and diestrus did not appear to have a group bias to use either strategy. These results suggest that estradiol can modulate spatial navigation strategy use before puberty but that this effect interacts with previous navigation experience. This study sheds light on when and under what circumstances estradiol gains control over spatial navigation behavior in the female rat.

Differential Activation of the Periaqueductal Gray by Mild Anxiogenic Stress at Different Stages of the Estrous Cycle in Female Rats

The effect of acute exposure to mild anxiogenic stress on cutaneous nociceptive threshold was investigated in female Wistar rats at different stages of the estrous cycle. Baseline tail flick latencies did not change significantly during the cycle. However after brief exposure to vibration stress (4 Hz for 5 min), rats in late diestrus, but not at other cycle stages, developed a hyperalgesia (decrease in tail flick latency). Animals in late diestrus revealed a more than fivefold increase in the density of Fos-like immunoreactive nuclei in the dorsolateral, lateral, and ventrolateral columns in the caudal half of the periaqueductal gray matter (PAG). There was no change in the density of Fos-like immunoreactive nuclei in the PAG in rats in estrus and early diestrus, although rats in proestrus showed a smaller (50%) but significant increase. Rats undergoing withdrawal from a progesterone dosing regimen (5 mg/kg i.p. twice daily for 6 days) designed to mimic the fall in progesterone that occurs naturally during late diestrus, exhibited a stress-induced hyperalgesia that was similar to animals in late diestrus and a significant increase in Fos-positive cells in the PAG. We suggest that falling levels of progesterone during late diestrus may be a predisposing factor for the development of stress-induced hyperalgesia, which is linked to differential activation of descending pain control circuits in the PAG. Similar changes in women, when progesterone levels fall during the late luteal phase of the menstrual cycle, may contribute to the development of premenstrual symptoms that include increased anxiety and hyperalgesia.

Adrenergic and cholinergic responses of the tracheal smooth muscle is enhanced during estrus phase in rat

The aim of this study was to evaluate influences of hormonal changes during rat estrous cycle on airway responsiveness to bronchoconstrictor and bronchodilator agents. Materials and methods: The study was performed in 5 groups of rat tracheal smooth muscle obtained during proestrus, estrus, metestrus, and diestrus phases of the estrous cycle, as well as the ovariectomized group (n:8/group). Cumulative acetylcholine contractions ranging from 10^{-8} to 10^{-3} M bath doses and the cumulative isoproterenol relaxations ranging from 10^{-8} to 10^{-3} M precontracted with 10^{-5} M of acetylcholine were recorded on isolated tracheas placed in a computerized tissue bath system. Results: Acetylcholine-induced contractions ranging from 10^{-5} to 10^{-3} M were significantly enhanced dose-dependently in tracheal smooth muscle from estrus rats compared to those from metestrus and ovariectomized rats. The relaxation induced by isoproterenol (10^{-8} -10^{-3} M) also significantly increased in tracheal smooth muscle precontracted with acetylcholine (10^{-5} M) taken from estrus rats. However, acetylcholine-induced contractility increase in tracheal smooth muscle was much more prominent than isoproterenol-induced relaxations in tracheal smooth muscle from estrus rats. Conclusion: These findings indicated that changes in estrogen and/or progesterone levels during rat estrous cycle might affect acetylcholine and isoproterenol sensitivity of the tracheal smooth muscle.

Oestradiol decreases colonic permeability through oestrogen receptor β‐mediated up‐regulation of occludin and junctional adhesion molecule‐A in epithelial cells

Oestradiol modulates paracellular permeability and tight junction (TJ) function in endothelia and reproductive tissues, but whether the ovarian hormones and cycle affect the paracellular pathway in the intestinal epithelium remains unclear. Oestrogen receptors (ERs) are expressed in intestinal epithelial cells, and oestradiol regulates epithelium formation. We examined the effects of oestrous cycle stage, oestradiol benzoate (EB), and progesterone (P) on colonic paracellular permeability (CPP) in the female rat, and whether EB affects expression of the TJ proteins in the rat colon and the human colon cell line Caco-2. In cyclic rats, CPP was determined through lumen-to-blood (51)Cr-labelled EDTA clearance, and in Ussing chambers for dextran permeability. CPP was also examined in ovariectomized (OVX) rats treated with P or EB, with and without the ER antagonist ICI 182,780, or with the selective agonists for ER beta (propyl pyrazole triol; PPT) or ER beta (diarylpropionitrile; DPN). In oestrus rats, CPP was reduced (P < 0.01) relative to dioestrus. In OVX rats, EB dose-dependently decreased CPP, an effect mimicked by DPN and blocked by ICI 182,780, whereas P had no effect. Oestradiol increased occludin mRNA and protein in the colon (P < 0.05), but not zona occludens (ZO)-1. Further, EB and DPN enhanced occludin and junctional adhesion molecule (JAM)-A expression in Caco-2 cells without change in ZO-1, an effect blocked by ICI 182,780. These data show that oestrogen reinforces intestinal epithelial barrier through ER beta-mediated up-regulation of the transmembrane proteins occludin and JAM-A determining paracellular spaces. These findings highlight the importance of the ER beta pathway in the control of colonic paracellular transport and mucosal homeostasis.

Chronic Exposure to Low Levels of Oestradiol‐17β Affects Oestrous Cyclicity, Hypothalamic Norepinephrine and Serum Luteinising Hormone in Young Intact Rats

Chronic exposure to oestrogens is known to inhibit the secretion of luteinising hormone (LH) in rats, leading to anovulation. Hypothalamic catecholamines, norepinephrine and dopamine play an important role in LH regulation. However, the effects of chronic exposure to low levels of oestradiol on hypothalamic catecholamines have not been investigated thoroughly. In the present study, adult female Sprague-Dawley rats were either sham implanted or implanted with 17beta-oestradiol (E(2)) pellets (20 ng/day) for 30 (E-30), 60 (E-60) or 90 (E-90) days. E(2) exposure affected oestrous cyclicity and ovarian morphology in a duration-dependent manner. There was no change in oestrous cyclicity in E-30 rats; however, 75% of E-60 and 95% of E-90 rats were acyclic (P < 0.05). Cycling rats from E-30 or the control group were killed at different time points on the afternoon of pro-oestrous. E-30 rats in oestrous, constant oestrous rats in the E-60 and E-90 groups and a group of old constant oestrous (OCE) rats were killed at 12.00 h. LH was measured in the serum by radioimmunoassay. Individual hypothalamic nuclei that are involved in LH regulation were microdissected and analysed for norepinephrine and dopamine levels using high-performance liquid chromatography/electrochemical detection. Norepinephrine levels in the hypothalamic nuclei increased significantly in control and E-30 groups during the afternoon of pro-oestrous, which was accompanied by a rise in LH levels (P < 0.05). On the day of oestrous, norepinephrine concentrations in hypothalamic nuclei and serum LH were significantly lower in E-60, E-90 and OCE rats compared to E-30 and control rats. On the other hand, dopamine levels declined significantly in one hypothalamic nucleus. These results indicate that chronic E(2) exposure affects hypothalamic catecholamine and serum LH levels in a duration-dependent manner. This coincides well with the loss of cyclicity observed in these animals. These results suggest that repeated exposure to endogenous oestrogens could play a role in reproductive senescence.

Antiovulatory effect of a single injection of pure antiestrogen ZK 191703 at early stage of rat estrus cycle

The effects of ZK 191703 (ZK), a pure antiestrogen, on ovulation, follicle development and peripheral hormone levels were investigated in rats with 4-day estrus cycle and gonadotropin-primed immature rats in comparison to tamoxifen (TAM)-treatment. In adult rats, a single s.c. injection of ZK (5 mg/kg) or TAM (5 mg/kg) at an early stage of the estrus cycle (diestrus 9:00) inhibited ovulation, and was associated with suppression of the surge of preovulatory LH, FSH and progesterone. In rats treated with ZK or TAM at a late stage of the estrus cycle (proestrus 9:00), no inhibitory effects on ovulation, the gonadotropin and progesterone surge were detected. ZK treatment at diestrus 9:00, in contrast to TAM, increased the baseline LH level. When immature rats were treated with antiestrogens in the earlier stage of follicular development, 6 and 30 h but not 48 h or later after injection of gonadotropin (PMSG), ovulation was attenuated, associated with a lowered progesterone level. Unruptured preovulatory follicles were found in most of the ovaries from anovulatory animals treated with ZK or TAM. Antiestrogens, ZK and TAM administered at an early phase of the estrus cycle delay the follicular development functionally and inhibit ovulation in rats and suppression of the preovulatory progesterone surge.

Effects of raloxifene on the mammary epithelium of female rats in persistent estrus

Objective. The aim of this study was to evaluate the morphological and morphometric alterations produced by raloxifene in the mammary epithelium of female rats in persistent estrus.Materials and methods. Twenty-one female Wistar–Hannover rats in persistent estrus induced by 1.25 mg of testosterone propionate were randomly divided into two groups: Group I (n = 10), receiving only water and used as control; Group II (experimental, n = 11), treated with 3 mg of raloxifene daily for 21 days. The first abdominoinguinal pair of mammary glands was extirpated and processed for morphological and morphometric evaluation. The data were statistically analysed using Student's t-test (p < 0.05).Results. Morphology revealed signs of epithelial atrophy, and morphometry showed a significant reduction in the mean number of ducts and alveoli in the experimental group (12.82 ± 0.42 and 2.91 ± 0.53, respectively) when compared with the control group (28.70 ± 1.15 and 7.20 ± 0.57, respectively). This difference was statistically significant, both for the ducts and for the alveoli (p < 0.001).Conclusion. The present results indicate that, at the dose and during the time of treatment used, raloxifene induced atrophy of the mammary epithelium of rats in persistent estrus.

Hippocampal dynorphin immunoreactivity increases in response to gonadal steroids and is positioned for direct modulation by ovarian steroid receptors

The hippocampal formation (HF) is involved in modulating learning related to drug abuse. While HF-dependent learning is regulated by both endogenous opioids and estrogen, the interaction between these two systems is not well understood. The mossy fiber (MF) pathway formed by dentate gyrus (DG) granule cell axons is involved in some aspects of learning and contains abundant amounts of the endogenous opioid peptide dynorphin (DYN). To examine the influence of ovarian steroids on DYN expression, we used quantitative light microscopic immunocytochemistry to measure DYN levels in normal cycling rats as well as in two established models of hormone-treated ovariectomized (OVX) rats. Rats in estrus had increased levels of DYN-immunoreactivity (ir) in the DG and certain CA3 lamina compared with rats in proestrus or diestrus. OVX rats exposed to estradiol for 24 h showed increased DYN-ir in the DG and CA3, while those with 72 h estradiol exposure showed increases only in the DG. Six hours of estradiol exposure produced no change in DYN-ir. OVX rats chronically implanted with medroxyprogesterone also showed increased DYN-ir in the DG and CA3. Next, dual-labeling electron microscopy (EM) was used to evaluate the subcellular relationships of estrogen receptor (ER) α-, ERβ and progestin receptor (PR) with DYN-labeled MFs. ERβ-ir was in some DYN-labeled MF terminals and smaller terminals, and had a subcellular association with the plasmalemma and small synaptic vesicles. In contrast, ERα-ir was not in DYN-labeled terminals, although some DYN-labeled small terminals synapsed on ERα-labeled dendritic spines. PR labeling was mostly in CA3 axons, some of which were continuous with DYN-labeled terminals. These studies indicate that ovarian hormones can modulate DYN in the MF pathway in a time-dependent manner, and suggest that hormonal effects on the DYN-containing MF pathway may be directly mediated by ERβ and/or PR activation.

Evaluation of Ki-67 antigen expression in the zona reticularis of the adrenal cortex of female rats in persistent estrus

Hyperandrogenism and chronic anovulation are basic characteristics of polycystic ovary syndrome (PCOS), and androgens from the adrenal glands play an important role in the hyperandrogenism. Our aim was to evaluate the proliferative activity in the zona reticularis cells of the adrenal cortex of female rats in persistent estrus, a model developed to mimic PCOS. Forty-four female Wistar-Hannover rats were randomly divided into two groups: control (n = 17) and animals which received 1.25 mg testosterone propionate s.c. on the second day of life (n = 27). At 90 days of age, after confirmation of persistent estrus, the animals were sacrificed, and the adrenal glands were removed and fixed in 10% buffered formalin to investigate Ki-67 antigen (marker of proliferation) expression by immunohistochemical analysis. Student's t-test and Levene's test were used in the statistical analysis. The mean percentage of Ki-67-stained nuclei per 1000 cells in the zona reticularis of the adrenal cortex was 15.58 +/- 1.14 (SEM) and 51.59 +/- 1.81 in the control and persistent estrus animals, respectively (P < 0.001). Proliferative activity in the zona reticularis cells of the adrenal cortex of the androgenized female rats was significantly greater than that of the control animals.

Antifertility potential of Neem flower extract on adult female Sprague-Dawley rats.

The search for a relatively cheap, widely available, widely accepted and effective contraceptive of plant origin; that is equally non-invasive in administration, non-hormonal in action, non-toxic and that is relatively long-acting, generated our interest in this study (in order to meet the increasing need for population control). The aim of this study was to determine the effects of alcoholic extract of Neem flowers on the estrous cycle, ovulation, fertility and foetal morphology of cyclic adult Sprague-Dawley rats. Adult female Sprague-Dawley rats, weighing between 140-180 g were used. There were 3 main experimental groups. Group 1 rats received 1 g/kg of alcoholic extract of Neem flower by gavage for 3 weeks and the effect on estrous cycle studied. Group 2 rats were administered 1 g/kg of Neem flower alcoholic extract at 9 a.m. and at 6 p.m. on proestrus and the effect on the number of ova shed on the morning of estrus observed. Rats in Group 3 were treated with 1 g/kg of alcoholic extract of Neem flower on days 1 to 5 postcoitum, and observation was made for anti-implantation / abortifacient effects and possible teratogenic effects on the foetuses. All the groups were control-matched. The estrous cycle of 80% of the rats was altered with a marked prolongation of the diestrus phase. Neem flower caused a statistically significant (p < 0.05) reduction in the number of ova shed in the morning of estrus in rats fed with the extract at 9 a.m. on proestrus. Neither anti-implantation / abortifacient nor teratogenic effect was observed in the rats treated with Neem flower. Administration of alcoholic extract of Neem flower disrupted the estrous cycle in Sprague-Dawley rats and caused a partial block in ovulation and thus has the potential of being developed into a female contraceptive.

Ovarian steroids modulate leu-enkephalin levels and target leu-enkephalinergic profiles in the female hippocampal mossy fiber pathway

In the hippocampal formation (HF), the enkephalin opioids and estrogen are each known to modulate learning and cognitive performance relevant to drug abuse. Within the HF, leu-enkephalin (LENK) is most prominent in the mossy fiber (MF) pathway formed by the axons of dentate gyrus (DG) granule cells. To examine the influence of ovarian steroids on MF pathway LENK levels, we used quantitative light microscopic immunocytochemistry to evaluate LENK levels in normal cycling rats and in estrogen-treated ovariectomized rats. Rats in estrus had increased levels of LENK-immunoreactivity (ir) in the DG hilus compared to rats in diestrus or proestrus. Rats in estrus and proestrus had higher levels of LENK-ir in CA3a-c compared to rats in diestrus. Ovariectomized (OVX) rats 24 h (but not 6 or 72 h) after estradiol benzoate (EB; 10 μg) administration had increased LENK-ir in the DG hilus and CA3c. Electron microscopy showed a larger proportion of LENK-labeled small terminals and axons in the DG hilus compared to CA3 which may have contributed to region-specific changes in LENK-ir densities. Next we evaluated the subcellular relationships of estrogen receptor (ER) α, ERβ and progestin receptor (PR) with LENK-labeled MF pathway profiles using dual-labeling electron microscopy. ERβ-ir colocalized in some LENK-labeled MF terminals and smaller terminals while PR-ir was mostly in CA3 axons, some of which also showed colocalization with LENK. ERα-ir was in dendritic spines, but no colocalization with LENK-labeled profiles was observed. The present studies indicate that estrogen can modulate LENK in subregions of the MF pathway in a dose-and time-dependent manner. These effects might be triggered by direct activation of ERβ or PR in LENK-containing terminals.

The effects of metergoline and 8-OH-DPAT injections into arcuate nucleus and lateral hypothalamic area on feeding in female rats during the estrous cycle

The present study examined the effects of local injections of metergoline (MET, an antagonist of 5-HT1/2 receptors, 2 and 20 nmol) and 8-hydroxy-2-(di- n-propylamino)-tetralin (8-OH-DPAT, selective 5-HT1A receptor agonist, 0.6 and 6 nmol) into the arcuate nucleus (ARC) and the lateral hypothalamus (LH), on ingestive and non-ingestive behaviors of female rats. These effects were examined during the diurnal periods of diestrus and estrus in rats adapted to eat a wet mash diet (enriched with 10% sucrose) during 1h for 3 consecutive days at the recording chamber. The results showed that 8-OH-DPAT injected into the LH significantly reduced food intake at all doses and both cycle stages, while in the ARC these treatments evoked hypophagia only at the highest 8-OH-DPAT dose and only at the estrous phase. MET administered into the ARC (at all doses) failed to affect food intake during both estrous stages. On the other hand, food intake decreased after injection of both doses of MET into the LH of rats during estrous and diestrus phases. In estrus stage, injections of the higher dose of 8-OH-DPAT into the ARC and into the LH decreased the duration of feeding. Latency to start feeding, drinking, and non-ingestive behaviors were not affected by 8-OH-DPAT or MET treatments in the ARC or the LH in both cycle phases. These results indicated that 5-HT1A receptors participate in the serotonergic control of feeding-related mechanisms located at the ARC and the LH. These feeding-related serotonergic circuits in both areas are possibly affected by ovarian hormones that could increase sensitivity of ARC neurons to the hypophagic effects of 8-OH-DPAT or increase the efficacy of satiety signals that terminate feeding. In addition, the present data indicated that serotonergic inputs do not exert a tonic inhibitory activity on the ARC and the LH feeding-related circuits.

Exploratory, anti-anxiety, social, and sexual behaviors of rats in behavioral estrus is attenuated with inhibition of 3α,5α-THP formation in the midbrain ventral tegmental area

The progesterone (P 4) metabolite and neurosteroid, 5α-pregnan-3α-ol-20-one (3α,5α-THP) acts in the midbrain ventral tegmental area (VTA) to modulate lordosis of female rats. 3α,5α-THP also mediates exploratory, affective, and social behaviors; whether actions of 3α,5α-THP in the VTA mediate these behaviors is of interest. To elucidate the role of the VTA in mediating exploratory, affective, and social behaviors, the present study examined effects of inhibiting 3α,5α-THP formation in the VTA. Rats received intra-VTA infusions of either PK11195 (400 ng/μl, which inhibits de novo 3α,5α-THP production), indomethacin (10 μg/μl, which blocks metabolism of P 4 to 3α,5α-THP), PK11195 and indomethacin together, or β-cyclodextrin vehicle and tested on a battery of anxiety (open field and elevated plus maze), social (partner preference and social interaction), and sexual (paced mating) tasks. Compared to rats infused with vehicle to the VTA, rats infused with inhibitor(s) demonstrated significant reductions in central entries in the open field, time on open arms of an elevated plus maze, time spent interacting with a conspecific, initiation and intensity of lordosis, sexual solicitations, and midbrain 3α,5α-THP levels. These findings suggest that actions of 3α,5α-THP in the VTA are important for mediating aspects of exploration, anxiety, and social behavior related to mating.