Sex and estrous cycle in memory for sequences of events in rats

The ability to remember sequences of events is fundamental to episodic memory. While rodent studies have examined sex and estrous cycle in episodic-like spatial memory tasks, little is known about these biological variables in memory for sequences of events that depend on representations of temporal context. We investigated the role of sex and estrous cycle in rats during training and testing stages of a cross-species validated sequence memory task (Jayachandran et al., 2019). Rats were trained on a two four-odor sequence memory task delivered on opposite ends of a linear track. Training occurred in six successive stages starting with learning to poke in a nose-port for ≥ 1.2 s; eventually demonstrating sequence memory by holding their nose in the port ≥ 1 s for in-sequence odors and < 1 s for out-of-sequence odors. Performance was analyzed across sex and estrous cycle (proestrus, estrus, metestrus, and diestrus), the latter being determined by cellular composition of a daily vaginal lavage. We found no evidence of sex differences in asymptotic sequence memory performance, similar to humans performing an analogous task (Reeders et al., 2021). Likewise, no differences in sequence memory performance were found across the estrous cycle. Some caveats are that males acquired out-of-sequence trials faster during training with a 3-odor sequence, but this apparent advantage did not carry over to the 4-odor sequence. Additionally, males had shorter poke times overall which seem consistent with a decreased overall response inhibition because they occurred regardless of sequence demands. Together, these results suggest sex and estrous cycle are not major factors in sequence memory capacities. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Hippocampal signaling protein levels are different in early and late metestrus in the rat

Early and late metestrus in the rat differ by progesterone levels. As it is known that progesterone shows a potential negative effect on cognitive performances and can counteract the estradiol-induced neural effects, we intended to study signaling proteins in the hippocampus, a structure representing a main brain area of cognitive function. Female OFA Sprague-Dawley rats were used in the studies and estrous phases were determined using vaginal smears. Hippocampal tissue was taken, proteins extracted, run on two-dimensional gel electrophoresis and proteins were identified by mass spectrometry methods (MALDI-TOF-TOF and nano-LC-ESI-MS/MS). Individual signaling protein levels quantified by specific software were shown to vary between the two phases, including NG,NG-dimethylarginine dimethylaminohydrolase 1 for nitric oxide signaling, guanine nucleotide-binding proteins, septin 6, septin 11, G-septin alpha, and 14-3-3 protein gamma. Results from this study indicate that early and late metestrus show differences in signaling pathways, that may help to design further investigations at the protein level and may assist to interpret literature on protein expression and brain protein levels in female rats. Moreover, signaling differences in hippocampus are challenging cognitive studies during these two metestrus phases probably revealing cognitive differences between early and late metestrus.

Effect of the oestral cycle on respiratory mechanics in the rat

AIM

To assess the effect of the oestral cycle on the respiratory mechanics of the rat.

METHODS

We measured the main mechanical respiratory parameters, namely respiratory system and lung resistances and compliances, by the end-inflation occlusion method on two populations of female rats, during proestrous-oestrous and metaoestrous-diestrous phases.

RESULTS

Inflation-deflation loops of the lungs were found to be statistically higher in rats during metaoestrous-diestrous phase. No other statistically significant difference was found in the measured mechanical respiratory parameters.

CONCLUSION

Our results suggest that the naturally occurring fluctuations in serum sexual hormone levels during the sexual cycle influence the lung's hysteresis but do not influence the respiratory system and lung resistances or static compliances. A possible effect of female sexual hormones on surfactant activity is also suggested.

Lactated Ringer’s Solution and Hypertonic Saline Improve Survival in Uncontrolled Hemorrhagic Shock in Female Rats in Metestrus

BACKGROUND

In the present investigation the effect of fluid treatment in uncontrolled hemorrhagic shock after massive splenic injury (MSI) was comparatively studied in male and female rats.

MATERIALS AND METHODS

The anesthetized animals were randomly divided into three groups: in group 1 MSI was induced in males, in group 2 MSI was induced in females in proestrus, in group 3 MSI was induced in females in metestrus. Each group was divided into four subgroups: a) Sham-operated, b) MSI untreated (UT), c) MSI treated with 40 ml/kg lactated Ringer's solution (RL), and d) MSI treated with 5 ml/kg NaCl 7.5% (HTS).

RESULTS

Total blood loss (TBL) in groups 1b, 2b, and 3b was 31.7 +/- 3.6%, 33.1 +/- 2.6%, and 36.7 +/- 2.6%, respectively, and mean survival time (MST) was 143.7 +/- 25.3 min, 174.8 +/- 10.4 min, and 67.8 +/- 11.4 min (P < 0.01 versus group 2b), respectively. TBL in groups 1c, 2c, and 3c increased to 52.4 +/- 5.5% (P < 0.02 versus UT), 48.6 +/- 1.6% (P < 0.02 versus UT), and 48.8 +/- 4.1% (P < 0.02 versus UT), respectively, and MST decreased to 126 +/- 19.4 min, (P < 0.05 versus UT), and 136.8 +/- 13.0 min (P < 0.05 versus UT) in groups 1c and 2c, respectively, and increased in group 3c to 120.4 +/- 23.3 min (P < 0.05 versus UT). TBL in groups 1d, 2d, and 3d was 31.3 +/- 4.8%, 38.0 +/- 4.2%, and 40.6 +/- 3.7%, respectively, and MST increased to 198.5 +/- 13.9 min (P < 0.05 versus UT) in group 1d, decreased to 128.4 +/- 17.2 min (P < 0.01) in group 2d, and increased to 102.6 +/- 19.0 min (P < 0.002 versus group 1d) in group 3d.

CONCLUSIONS

RL infusion significantly increased blood loss in all three groups, reduced survival time in males and female rats in proestrus, but significantly improved survival in females in metestrus. HTS treatment did not alter blood loss in all three groups, but significantly improved survival in females in metestrus and males.

Rat estrous cycle influences the sexual diergism of HPA axis stimulation by nicotine

We previously reported that female rats had significantly greater hypothalamic-pituitary-adrenal (HPA) axis responses to cholinergic stimulation by nicotine (NIC) than did male rats. Females in defined estrous cycle stages, however, were not studied because of sample size limitations. We further explored this finding by determining HPA axis responses to two doses of NIC in female rats (N = 101) during different estrous cycle stages, and in males (N = 69). NIC doses were: 0.3 mg/kg, which provided the greatest female-male difference in the earlier study, and 0.5 mg/kg, which stimulated the HPA axis similarly in the two sexes. Plasma AVP, ACTH, and corticosterone were measured. Proestrous and estrous females had higher ACTH responses to NIC (0.3 mg/kg) compared to metestrous and diestrous females, and compared to males. ACTH responses to NIC (0.5 mg/kg) were similar, regardless of estrous cycle stage or sex. Males had higher AVP responses to both NIC doses compared to females in all estrous cycle stages. Corticosterone responses followed the ACTH responses, except that females in all estrous stages started from a higher corticosterone baseline compared to males. These results are similar to our earlier findings across the estrous cycle with non-specific cholinergic stimulation by physostigmine and suggest that the nicotinic system contributes to the differential HPA axis responses to cholinergic challenge across the estrous cycle.

Guanylin-immunoreactive cells in the female and male rat adenohypophysis and their changes under various physiological and experimental conditions

The peptide guanylin, first isolated from rat small intestine, is involved in the regulation of water-electrolyte transport between the intracellular and extracellular compartments of the epithelia. The main sites of guanylin expression are the intestinal, airway, or exocrine gland ductal epithelia where guanylin acts in a paracrine/luminocrine fashion. Because guanylin also circulates in the blood, sources of this peptide were sought in endocrine glands. Our group has already demonstrated the presence of guanylin-immunoreactive cells in the pars tuberalis of male rat adenohypophysis. In this study, we investigated whether guanylin-immunoreactive cells exist also in the adenohypophysial pars distalis and whether their appearance or distribution correlates with various physiological conditions in female rats or alters after gonadectomy in both sexes. These studies revealed that the rat pars distalis contains two guanylin-immunoreactive cell types, gonadotrophic cells, whose number varied notably during the estrous cycle, reached a peak in the proestrous phase, and increased consistently during pregnancy, in lactating animals, and after gonadectomy, and folliculo-stellate cells, a discrete number of which were found only in female rats at the estrous phase. These findings suggest that guanylin is involved in regulating gonadotrophic cell function. They also add important information on the controversially discussed functions of folliculo-stellate cells.

Changes in the content of steroid receptor coactivator-1 and silencing mediator for retinoid and thyroid hormone receptors in the rat brain during the estrous cycle

In this work, we determined the variations in the content of the steroid receptor coactivator (SRC-1) and the silencing mediator for retinoic acid and thyroid hormone receptors corepressor (SMRT) in the hypothalamus, the preoptic area, and the hippocampus of adult intact rats during the estrous cycle by Western blot. SRC-1 content changed only in the hypothalamus where its lowest content was found on diestrus day with a significant increase at proestrus. This increase was maintained on estrus day. In contrast, SMRT content changed only in the preoptic area where it diminished at metestrus in comparison with the other days of the cycle. SRC-1 content was higher than that of SMRT in the hypothalamus throughout the estrous cycle, whereas SMRT content was higher in the preoptic area. In the hippocampus, there were no significant differences in the content of any cofactor. These results demonstrate that SRC-1 and SMRT content change in a tissue-specific manner in the rat brain during the estrous cycle, and suggest that the transcriptional activity of steroid hormone receptors in the rat brain in physiological conditions is regulated by changes in SRC-1 and SMRT content.

Magnetic resonance image attributes of the bovine corpus luteum during development and regression

To determine whether magnetic resonance (MR) image attributes of the corpus luteum (CL) reflect its physiologic status at different phases of the bovine ovarian cycle, we analyzed the numerical pixel values (NPVs), relaxation rates, proton densities (PDs), and apparent diffusion coefficients (ADCs) from T(1)-, T(2)-, and diffusion-weighted in vitro images and maps of the CL acquired at defined phases of luteal function. Ovaries were removed and serum samples taken on days 3, 6, and 10, or >/=17 (day 0 = ovulation), representing metestrus (n = 10), early diestrus (n = 7), mid-diestrus (n = 9), and proestrus (n = 7), respectively. Regions of interest (ROIs) in each quadrant of the CL (which occupied at least 20% of the quadrant) were selected for analysis. Three MR image slices were analyzed: the slice with the greatest cross-sectional area of the CL, and the slices acquired immediately before and after that slice. The mean NPVs of the CL in T(1)-weighted images increased at each phase from metestrus (1,104 +/- 40 msec) to early diestrus (1,119 +/- 77 msec), to late diestrus (1,206 +/- 43 msec) and proestrus (1446 +/- 80 msec; P < 0.001). The mean NPVs in T(1)-weighted images were higher in regressing CL (proestrous) than in any other phase (P < 0.002). Grayscale heterogeneity of CL in T(1)-weighted images tended to increase during regression (P < 0.07). Regressing CL (proestrus) exhibited higher T(1)-weighted mean NPVs (P < 0.01) and tended to have greater heterogeneity (P < 0.06) than growing (metestrus) and mature (diestrus) CL, even though similar progesterone concentrations were observed. The increased brightness and heterogeneity of regressing CL in T(1)-weighted images appeared to be correlated with increased connective tissue and triglyceride content and decreased vascularity. It is anticipated that diagnostic markers for luteal viability and atresia in the in vitro bovine model will be applied to in vivo studies in women.

Antiprogestin RU486 blunts the stimulatory effect of galanin on LH secretion from rat pituitaries in vitro in an estrous cycle stage-dependent manner

Galanin (GAL), a neuroactive peptide detected in the hypothalamus and anterior pituitary, stimulated in a dose (0.1 and 1 microM)-dependent manner luteinizing hormone (LH) secretion from metestrous and proestrous rat pituitaries incubated in culture medium devoid of progesterone (P). GAL had no effect on follicle-stimulating hormone (FSH). Antiprogestin RU486 (10 nM) decreased non-stimulated (basal) secretion of LH and FSH only in pituitaries from proestrous rats and blunted the stimulatory effects of GAL on LH secretion in both metestrous and proestrous pituitaries. These findings are consistent with the hypothesis that GAL-mediated signal transduction interacts with estrogen-dependent P receptor at the pituitary level to stimulate LH secretion.

Estrous changes in responses of rat gracile nucleus neurons to stimulation of skin and pelvic viscera

Multi- and single-unit recording was performed in the gracile nucleus in urethane-anesthetized rats to examine estrous variations in responses of its neurons to brushing the hindquarters and mechanical stimulation of the uterus, vaginal canal, cervix, and colon. Six rats each were studied in each of the four estrous stages: proestrus (P), estrus (E), metestrus (M), and diestrus (D). The magnitude of multi-unit responses to gentle brushing of the perineum, hip, and tail, but not the foot and leg, was significantly greater during proestrus than during other stages. Of 70 single units responsive to brush, 56 (80%) responded to stimulation of at least one viscus. Although this percentage did not change with estrous stage, the direction and latency of some responses did. Pressure on the cervix evoked significantly more inhibitory (vs excitatory) responses in P than in E and M, and the response latency was significantly longer in D and P than in E and M. The direction of response to vaginal distention did not change with estrous stage, but response latency was significantly longer in D than in P and E. Uterine distention evoked significantly more inhibitory responses in D than in P, with no estrous changes in latency. Responses to colon distention did not change. These variations in both magnitude of response to tactile stimulation and characteristics of response to stimulation of reproductive organs, but not the colon, correlate with changes in mating behaviors of the female rat, suggesting that the gracile nucleus is a component of neural systems that control reproductive behaviors.

Hormonal variation of rat uterine contractile responsiveness to selective neurokinin receptor agonists

Regulated uterine contractions are important in many reproductive functions such as sperm transport and embryo positioning during implantation. The role of classical neurotransmitters including acetylcholine and norepinephrine in regulating myometrial contractility has been well studied; however, the peripheral role of sensory neurotransmitters such as the neurokinins is less clear. The major neurokinins are substance P, neurokinin A, and neurokinin B, which predominantly activate neurokinin receptors (NK-Rs) 1, 2, and 3, respectively. This study utilized selective receptor agonists to examine the role of NK-Rs in uterine contractility. Uterine tissues, obtained from the major stages of the rat estrous cycle, were stimulated with selective NK-R agonists. Addition of each agonist resulted in a significant contractile response. However, the magnitude and nature of the response were dependent upon the stage of the estrous cycle, with responses to all agonists being significantly decreased in tissue from proestrus and estrus. Furthermore, the nature of NK3-R-mediated contraction was different in tissue from proestrus and estrus compared to metestrus and diestrus. The hormonal dependence of NK-R-mediated contractility was then examined in the ovariectomized estrogen-supplemented rat model. These studies confirmed that the magnitude and nature of uterine contractility in response to NK-R activation depend upon the hormonal environment.

Estrus and estrogen changes in mated and unmated free-living European ground squirrels

The course of behavioral and vaginal estrus and patterns of circulating estrogens were followed in free-living European ground squirrels (Spermophilus citellus) after their emergence from hibernation. Normally mating females were compared to a second group in an area where males had been removed from the population before female emergence. Both groups showed vaginal estrus, but the patterns differed. Mating shortened vaginal estrus to a 3-day period compared to 8 days in unmated females. The extent (cell number) of cell cornification during estrus and the cellular components (percentage distribution) of metestrus did not differ between the two groups. Females in the area without males had significantly higher estrogen levels during estrus and metestrus compared to those in the control area. European ground squirrels were found to be monestrous, as none of the unmated females reentered estrus after metor diestrus was detected. The prolongation of vaginal estrus in unmated females can be viewed as either a physiological inevitability or an adaptation to low mate availability. The extension is still relatively short compared to other sciurid species and perhaps a product of constraints producing a strict time frame for reproduction.

Progesterone receptor A and B messenger ribonucleic acid levels in the anterior pituitary of rats are regulated by estrogen

In target tissues of most mammalian and avian species, progesterone receptors (PR) are expressed as structurally related, but functionally distinct, isoforms A and B, and they are regulated by estrogen (E) as well as by their cognate ligand, progesterone (P(4)). The objectives of the present work were to identify mRNA expression for the A and B isoforms of PR in the anterior pituitary of the rat, to examine its regulation by gonadal steroids, and to compare this regulation with that in the primary target organ, the uterus. Messenger RNAs for the PR isoforms, determined by two separate reverse transcription-polymerase chain reaction protocols, one that detects PR A and PR B equally and the other specific for PR B, were identified in anterior pituitary of female and male rats. In anterior pituitary of cycling female rats, steady-state mRNA levels for both PR A+B and PR B were highest at 0900 h on proestrus, declined rapidly to nadir values at 0900 h on metestrus (PR A+B) or 0900 h on estrus (PR B), and remained below proestrous values through 2100 h on diestrus. Administration of E to intact proestrous female rats caused significant increases in mRNA for both PR A+B and PR B on estrus and metestrus. Blockade of P(4) action by administration of the antiprogestins RU-486 and ZK-98299 on proestrus had no effect on PR mRNA levels on the morning of estrus. Ovariectomy two and ten days after surgery markedly reduced mRNA levels for both PR A+B and PR B. Whereas treatment of 10-day-ovariectomized rats with E led to marked induction of mRNA for PR A+B and PR B two days later, treatment with P(4) one day after treatment had no effect on basal or E-stimulated PR mRNA. Regulation of PR mRNA expression in the pituitary differed from that in the uterus, in which P(4) treatment of ovariectomized rats antagonized the E-induced rise in mRNA for PR B, and antiprogestins increased mRNA for both isoforms. In addition to induction of PR mRNA in the pituitary of female rats by E in vivo, we also demonstrated induction by E in primary culture of anterior pituitary cells in vitro. We conclude that in the anterior pituitary of female rats, both the A and B isoforms of PR are expressed and regulated by E.

[Effect of the long-term exposure of the isolated myometrium from nonpregnant rats to serum from pregnant women on its contractile activity and the beta-adrenergic reactivity]

Pregnant women's blood serum (the whole as well as 50- and 100-diluted) did not alter parameters of spontaneous motility, i.e. it did not affect the uterus myocytes' spontaneous motility, whereas the whole or 50-diluted serum raised considerable the rat myometrium's beta-adrenoreaction. The data obtained suggest that the beta-adrenoreaction of the rat uterus' myocytes increases after a prolonged contact with pregnant women's blood serum which may be due to the beta-adrenoreceptor synthesis activation and to an increase in their concentration because of diffusion from the blood serum. This suggests existence of humoral mechanisms of the myometrium beta-adrenoreaction regulation, the mechanisms creating the optimum uterus' contractile activity.

Estrous variations in behavioral responses to vaginal and uterine distention in the rat

Response properties of peripheral afferent fibers supplying the vagina and uterus of the rat vary with estrous stage (Robbins A, Berkley KJ, Sato Y. Estrous cycle variation of afferent fibers supplying reproductive organs in the female rat. Brain Res 1992,596:353-356), suggesting that behavioral sensitivity to vaginal and uterine stimulation might similarly vary. To test this hypothesis, detection and escape responses of 12 rats to different volumes of distention of the vaginal canal or uterine horn (six rats each) were compared during each of the four estrous stages, proestrus (P), estrus (E), metestrus (M), and diestrus (D), using previously-published behavioral techniques (Berkley KJ, Wood E, Scofield SL, Little M. Behavioral responses to uterine or vaginal distention in the rat. Pain 1995;61:121-131). Estrous variations in vaginal or uterine tone (pressure-volume functions) were also measured in the same rats. Vaginal canal: escape response percentages increased significantly as vaginal distention volume increased, but neither escape nor detection responses varied with estrous stage. Vaginal tone, however, was greater in P and E than in M and D, with the greatest tone in E and the least in D. When escape responses to different pressures were analyzed, it was found that escape response percentages to the same vaginal pressure were lower during P and E than during M and D. One outcome of these estrous influences would be that a vaginal stimulus of a given volume (such as an erect penis) would exert higher pressures during P and E (i.e. the penis would be held within the vaginal canal more firmly) than during M and D, but would be less likely during P and E to provoke escape responses. This modification of nociceptive sensitivity has obvious reproductive advantages, because P and E constitute the rat's fertile period. Uterine horn: escape response percentages increased significantly as uterine distention volume increased only during M and D, with no differences between them. Detection responses also occurred only during M and D. Similarly, uterine tone was significantly greater in M and D than in P and E, with the greatest tone occurring during M and the least during P. Although these changes in uterine tone were opposite to those of the vaginal canal, escape response percentages to the same uterine pressures were, in a manner similar to vaginal pressures, lower during P and E than during M and D. The functional significance of these variations for the uterus is unclear, but does suggest that, under pathophysiological conditions, stimulation of the uterine horn, as well as the vaginal canal, would be more likely to provoke escape behaviors in M and D than in P and E. A similar increased sensitivity in rats during M and D to noxious stimulation of other pelvic organs has been observed by others. This situation resembles that in women, for whom many visceral pain conditions are exacerbated during a comparable part of their ovarian cycle, i.e. perimenstrually.

Influence of the stage of the cycle on olfactory sensitivity in laboratory mice

Females in estrus showed maximum olfactory sensitivity as judged by their ability in locating the buried bait. The results suggest that olfactory sensitivity in females varies during the stages of the estrous cycle. The findings further indicate that gonadal steroids play an important role in the expression of olfactory sensitivity in females.

Cytosolic estrogen receptor concentrations in the lumbosacral spinal cord fluctuate during the estrous cycle

Estrogen responsive neurons have been anatomically identified with autoradiographic and immunohistochemical techniques and their distribution mapped in the lumbosacral spinal cord of female rats. Such neurons contain estrogen receptors (ERs). The present study was undertaken to: 1) quantify cytosolic estrogen receptor (ER) concentrations in the lumbosacral spinal cord and 2) determine if there is a relationship between cytosolic ER concentrations and fluctuations in serum estradiol (SE2) levels during the estrous cycle. Lumbosacral spinal segments were removed from intact cycling rats during the morning of proestrus, the afternoon of proestrus, and the morning of estrus, metestrus and diestrus. Trunk blood was collected at euthanasia and SE2 levels were determined using radioimmunoassay. Cytosolic ER concentrations were measured using a dextran-charcoal coated tube method. Concentrations of cytosolic ERs were low during estrus and metestrus, increased during diestrus with maximum concentrations during the afternoon of proestrus. These changes in ER concentrations paralleled SE2 levels measured in intact cycling animals; i.e., during estrus SE2 levels were low, but began to rise during metestrus, diestrus, and during the morning of proestrus with a maximum peak increase during the afternoon of proestrus. These data indicate there are fluctuations of cytosolic ER concentrations during the estrous cycle and that these changes coincide with changing SE2 concentrations suggesting that ER content is influenced by SE2.

Immunocytochemical localization of oestrogen and progesterone receptors in the uterus of the normal bitch during oestrus and metoestrus

Frozen uterine biopsy samples obtained from eight bitches during oestrus and metoestrus were used to develop immunocytochemical methods for identifying steroid receptors. The use of anti-steroid receptor monoclonal antibodies DAKO ID5 and NCL-PGR resulted in reliable detection of oestrogen and progesterone receptors, respectively. The distribution and heterogeneity of both oestrogen receptor and progesterone receptor expression varied during the oestrous cycle. During oestrus, steroid receptor expression was greatest as indicated by a distinct and homogeneous distribution of nuclear staining within cells of the endometrial glandular and luminal epithelium and myometrium. In contrast, during metoestrus there was an overall reduction in both the number and intensity of staining of nuclei. Distribution and intensity of nuclear staining was heterogeneous. This reduction was obvious within the luminal epithelial cells where nuclear staining was negligible compared with that of the glandular epithelial cells. This method could be used for further receptor studies, particularly in those diseases mediated by steroid hormones such as cystic endometrial hyperplasia and mammary neoplasia.

Changes in visceral pain reactivity as a function of estrous cycle in female rats with artificial ureteral calculosis

This study examined estrous differences in the characteristics of behavioral crises of visceral pain in female rats video-taped throughout a 4-day period after implantation of an artificial stone in one ureter. All animals continued to have a regular cycle after ureteral surgery. In the recording period, the percentage of time spent in crises was significantly higher during metestrus/diestrus (M/D) than during proestrus/estrus (P/E) (P < 0.001, chi2-test). Mean duration and complexity of crises were slightly higher in M/D than in P/E, but the difference was not significant. The results in this animal model show an enhancement of ureteral pain sensitivity in M/D, a finding in line with the clinical observation, in fertile women with urinary calculosis, of a greater incidence of colics in the perimenstrual period (equivalent to M/D in rats).

The steroid antagonist RU486 given at pro-oestrus induces hypersecretion of follicle-stimulating hormone from oestrus afternoon to early metoestrus in the rat

Administration of the steroid antagonist RU486 to cyclic rats at pro-oestrus blunts the preovulatory surge of LH and suppresses the first and second surges of FSH. In addition, administration of oestradiol to RU486-treated rats reactivates the LH surge the following day. The present study explored the effects of RU486 (4 mg/0.2 ml oil), administered at 0800 h on the day of pro-oestrus, on serum FSH and LH concentrations through oestrus and early metoestrus. RU486 induced a hypersecretion of FSH, which started at 1400 h on the day of oestrus and was maintained until 0800 h on the day of metoestrus. Because the timing and magnitude of this secretion of FSH were similar to those of the periovulatory secretion of FSH during pro-oestrus and early oestrus in intact cyclic rats, we investigated the effects of: 1) LHRH antagonist (LHRHa) injected at either 0900 h or 2000 h on the day of oestrus, 2) oestradiol benzoate injected at 1600 h on the day of pro-oestrus and at 0900 h on the day of oestrus, 3) bovine follicular fluid (bFF) given either at 1100 h or at 2000 h on the day of oestrus, or 4) adrenalectomy (ADX) at 1100 h on the day of oestrus, on serum FSH and LH concentrations at 1800 h on the day of oestrus and at 0200 h on the day of metoestrus in rats injected with RU486 at pro-oestrus. The results showed that 1) both components (late oestrus and early metoestrus) of FSH hypersecretion in RU486-injected rats in pro-oestrus were inhibited by oestradiol benzoate and bFF, 2) the metoestrous component was not affected by LHRHa, whereas the oestrous component was partially reduced, and 3) ADX partially reduced serum FSH concentrations only on the day of metoestrus, possibly because, as the serum concentrations of corticosterone reflected, the antiglucocorticoid activity of 4 mg RU486 lasted only 24 h. The results support the hypothesis that blockade of progesterone actions at pro-oestrus results in the maintenance of the daily neural signal that activates the release of gonadotrophins. Whereas the expression of LH secretion requires high levels of oestradiol, FSH secretion is expressed against a background of low oestradiol levels. The results of this study also indicate that the release of FSH during oestrus and metoestrus in rats injected with RU486 at pro-oestrus is a consequence of the lack of ovarian negative feedback inhibition on the pituitary.

[Critical comparison of rectal and ultrasonographic results of ovarian conditions in the interestrus of cattle]

41 heifers of 260-440 kg body weight used in an experiment were polyovulated with PGF2 alpha and PMSG (1000 IU). Animals were slaughtered during luteal phase of ovarian cycle (day 12-15). Shortly before slaughter ovarian structures were defined by rectal palpation und ultrasonographical examination. Post mortem ovaries were collected to compare their structures with previously performed in vivo diagnosis. More follicular structures were detected sonographically (109%) than could be found by morphologic examination (100%). Concerning corpora lutea a right diagnosis was made by palpation in 94% of cases, whereas the rate was only 85% for ultrasonographical examination. Main reasons for false diagnoses of ultrasonographical examination are as follows: multiple ovarian structures, corpora lutea with holes inside, atypical shape of ovaries, atypical ultrasonographical pictures and irregular shape of follicles.

Female reproductive cycle influences plasma volume and protein restitution after hemorrhage in the conscious rat

The present study was designed to test the hypothesis that gender and female reproductive cycle phase influence the restitution of blood volume following blood loss. The experiments were performed in conscious 9- to 11-wk-old Sprague-Dawley rats subjected to a slow hemorrhage of 19 ml/kg over 40 min. The effect of hemorrhage was compared in male rats and in female rats in either proestrus (Pro) or metestrus (Met). In comparison with either metestrus females or males, females hemorrhaged on the morning of proestrus showed a significantly larger overall decrease in percent hematocrit (Pro, -17 +/- 1; Met, -10 +/- 1; male, -13 +/- 1; mean +/- SE), increase in plasma volume (Pro, to 151 +/- 15% of initial volume; Met, 104 +/- 8%; male, 120 +/- 4%), and increase in total plasma protein content (Pro, to 164 +/- 14% of initial content; Met, 101 +/- 5%; male, 132 +/- 5%) over the 21-h posthemorrhage recovery period. Proestrus females also showed a larger increase in plasma osmolality during the first 2.5-h posthemorrhage than either metestrus females or males (P < 0.05). In addition, basal hematocrit and total blood volume (51Cr-tagged erythrocyte method) were higher in females studied on the morning of proestrus than in metestrus females. These results indicate that the female reproductive cycle is an important variable in basal blood volume regulation and in plasma protein and plasma volume restitution following blood loss.

Roles of inhibin and estradiol in the regulation of follicle-stimulating hormone and luteinizing hormone secretion during the estrous cycle of the rat

The relative contributions of inhibin and estradiol in the regulation of FSH and LH secretion were examined at various stages of the estrous cycle in the rat. At 1100 h on metestrus, diestrus, or estrus or at 0500 h on proestrus, rats were ovariectomized or given an injection of normal goat serum, antiserum to inhibin (inhibin-AS), antiserum to estradiol (estradiol-AS), or both antisera to examine the role of gonadal hormones in the regulation of tonic gonadotropin secretion. Plasma samples were collected before and at 6, 12, and 24 h after the treatments. Further, to examine the effects of the treatments on preovulatory gonadotropin surges, the five treatments described were carried out at 0500 h on proestrus and blood samples were collected from 1100 h to 2000 h on the same day at 1.5-h intervals. There was a significant rise in the concentration of plasma FSH after injection of inhibin-AS as well as after ovariectomy on each day of the estrous cycle. These treatments, however, had less effect on estrous FSH secretion. The rise in FSH was greater with immunoneutralization against both inhibin and estradiol than with immunoneutralization against inhibin alone on diestrus and proestrus. Basal levels of LH were increased at all stages of the cycle through immunoneutralization against inhibin and were also increased through immunoneutralization against estradiol except at estrus. Especially on diestrus, a remarkable increase in LH secretion was induced at 6 h after immunoneutralization against both inhibin and estradiol (1449.3 +/- 100.3% vs. control). The magnitude of the LH surge increased in inhibin-immunized rats, decreased in estradiol-immunized or ovariectomized rats, and remained at normal levels after injections of both antisera. The magnitude of the primary FSH surge increased very markedly in the inhibin-immunized group and decreased in the estradiol-immunized group. These results suggest that both estradiol and inhibin play a role in the regulation of LH secretion and that inhibin is a major regulator of FSH secretion during the estrous cycle of the rat. Furthermore, it is suggested that one or more extragonadal factors suppress estrous FSH secretion.

Influences of oxytocin on the synthesis of prostaglandins by uterus from rats in different stages of the estrous cycle

We explored the oxytocin-prostaglandin interactions during the rat estrous cycle. The experiments were done with uterine preparations isolated from rats in different stages of the sex cycle incubated 'in vitro' with oxytocin (O) (50 mU/ml). We found that the effect of O on prostaglandin (PG) synthesis was associated to the sex hormones, and varied during the estrous cycle. Indeed, during the estrogenic influence (i.e. at proestrus and estrus) O diminished the synthesis of PGE2 and with the highest estradiol concentration (i.e. during estrus) the hormone also augmented the synthesis of PGF2 alpha. During metestrus, no changes in PG synthesis after treatment were found. Likewise, during diestrus, when progesterone levels fall, O enhanced PGF2 alpha uterine synthesis. In this study an inhibitory action of O on the uterine production of 6-keto-PGF1 alpha at proestrus was also seen. The present results indicate that when estrogen concentration increases (during estrus) 6-keto-PGF1 alpha synthesis also increases. In summary, we have observed that sex hormones exert a modulating action on the influences of O on uterine PGs synthesis.

Variations in uterine kallikrein during cycle and early pregnancy in the rat

We have previously demonstrated the presence of tissue kallikrein and its mRNA in rat uterus, and an increase of the immunoreactive enzyme on Day 7 of gestation, which suggests a hormonal regulation and a role in implantation. This study pursued the sequential variations during the cycle and early pregnancy. During the estrous cycle, immunoreactive uterine kallikrein levels showed a recurrent pattern, with the highest value on proestrus (12.9 +/- 1.5 ng/uterus or 0.49 +/- 0.03 ng/mg protein), and the lowest on metestrus (4.1 ng +/- 0.5 ng or 0.30 +/- 0.03 ng/mg protein); p < 0.05. During gestation, values on Day 1 (6.1 +/- 0.4 ng/uterus or 0.30 +/- 0.01 ng/mg protein) and Day 3 (4.9 +/- 0.3 ng or 0.35 +/- 0.01 ng/mg protein) were similar to levels during estrus and diestrus; a progressive rise, observed from Day 5 (8.2 +/- 1.1 ng or 0.43 +/- 0.02 ng/mg protein), attained the highest value on Day 7 (15.8 +/- 1.7 ng or 0.78 +/- 0.05 ng/mg protein); p < 0.05. The variations observed during the cycle and early gestation coincide with those described for ovarian steroids and uterine vasoactive changes, suggest the hormonal regulation of uterine kallikrein levels, and support its role in implantation.

Effects of metestrous administration of a norgestomet implant and injection of norgestomet and estradiol valerate on luteinizing hormone release and development and function of corpora lutea in suckled beef cows

Sixteen suckled beef cows were used to determine effects of Syncro-Mate-B (SMB) on the development and function of corpora lutea (CL) and LH release. Twelve cows were treated 2 d after estrus with the standard SMB treatment regimen, a 6-mg Norgestomet ear implant (in situ 9 d) and a 2-mL i.m. injection of 3 mg of Norgestomet and 5 mg of estradiol valerate at time of implant insertion. Four cows served as untreated controls. In cows treated with SMB with subsequently nonfunctional CL (n = 5), mean concentrations of progesterone (P4) were lower on d 9, 12 (implant removal), and 14 of the treated cycle than in control cows or in those cows treated with SMB that developed functional CL (P < .01). In cows treated with SMB that developed functional CL (n = 7), mean concentrations of P4 were lower only on d 12 of the treated cycle than those in control cows (P < .01). In cows treated with SMB with subsequently nonfunctional CL, CL were smaller from d 9 through 14 of the treated cycle than in control cows or in those cows treated with SMB that developed functional CL (P < .01). In cows treated with SMB that developed functional CL, CL were smaller on d 9 and 11 of the treated cycle than in control cows (P < .01). Regardless of subsequent CL function, mean concentrations of LH and numbers of LH pulses were lower in cows treated with SMB than in control cows on d 3 and 4 of the treated cycle (P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Differential gonadotropin responses to N-methyl-D,L-aspartate in metestrous, proestrous, and ovariectomized rats

Peripheral administration of N-methyl-D,L-aspartate (NMA), an analogue of the excitatory amino acid aspartate, elicits LH and prolactin (PRL) release in rats, most likely by increasing endogenous releasing-hormone secretion. These experiments were carried out to assess the degree to which NMA stimulates FSH and to analyze the relationship between endocrine status and responsiveness to NMA in female rats, in contrast to male rats, as described in the companion paper [Biol Reprod 48:000-000]. In experiment 1, estrous rats (n = 10) and diestrous rats (n = 10) and in experiment 2, estrous rats (n = 11) and rats ovariectomized (OVX) 8 days previously (n = 10) were fitted with atrial catheters and injected s.c. with 100 micrograms of an LHRH antagonist or vehicle at 2100 h. Starting at 0900 h the next day (metestrus, proestrus, or Day 9 post-OVX), blood was withdrawn every 10 min for 3 h. Each animal received i.v. 5 mg NMA after the first hour and i.v. 500 ng LHRH after the second hour. NMA significantly increased LH in metestrous and proestrous females, and LHRH antagonist blunted the increases. In OVX females, LH decreased after NMA. FSH was not affected by NMA in any group. PRL increased after NMA in proestrous and metestrous animals. LHRH caused surge-like LH and small FSH increases in vehicle groups; these increases did not differ in amplitude between intact and OVX animals and were blunted by pretreatment with LHRH antagonist. In experiment 3, 10 diestrous rats were fitted with atrial catheters and were serially bled at 2-h intervals from 1200 h on the following day (proestrus) until 0600 h on estrus morning. After the first sample the animals were injected s.c. with 0.2 mg/kg MK801, a noncompetitive NMA receptor antagonist, or with saline. Four of the 5 saline-treated animals exhibited surges of LH and FSH as well as elevated progesterone levels, with LH and progesterone peaking at 2000 h. Five of 5 MK801-treated animals failed to have elevated LH, FSH, or progesterone levels at any time point. These data demonstrate that LHRH mediates the LH response to NMA in rats and that endogenous NMA receptor binding may be necessary for the preovulatory gonadotropin surges. The lack of FSH responses to NMA during periods of low-level gonadotropin secretion suggests that physiological increments in endogenous LHRH secretion sufficient to induce a pulse of LH are insufficient to stimulate pulse-like FSH release.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuropeptide Y gene expression in the arcuate nucleus is increased during preovulatory luteinizing hormone surges

Recent studies have suggested that neuropeptide Y (NPY) plays an important role in the induction of the preovulatory LH surge. The present study was performed in order to determine if a change in NPY gene expression within arcuate nucleus NPY neurons is associated with the generation of the preovulatory LH surge. In Exp 1, in situ hybridization was used to measure NPY messenger RNA (mRNA) levels in the arcuate nucleus of female rats at 0900 h and every 2 h from 1400-2200 h on the day of proestrus (PRO). Comparisons between groups showed a clear, stepwise increase in NPY gene expression throughout the day of PRO. At 1600 h, when LH values were significantly greater than 0900 h values, NPY mRNA labeling intensities in the arcuate nucleus were significantly greater than 0900 h levels (P < 0.01). By 1800 h, the time at which the LH surge peaked, NPY mRNA levels also peaked and were nearly 3-fold greater than levels observed at 0900 h (P < 0.01). NPY mRNA levels at 2000 h and 2200 h remained elevated above 0900 h levels (P < 0.01) but by 2000 h had decreased significantly from 1800 h levels (P < 0.05). In Exp 2, NPY mRNA levels were measured once again at 0900 h and 1800 h on PRO, and then at 0900 h and 1800 h on metestrus (MET), in order to determine if the change in gene expression seen in Exp 1 was unique to the day of PRO, or if it simply reflected a daily rhythm of gene expression in the nucleus. Analysis of mRNA levels showed no difference in NPY mRNA levels between 0900-1800 h on MET. Also, NPY mRNA levels at 0900 h and 1800 h on MET were significantly less than levels at 1800 h on PRO (P < 0.01). These results are consistent with the hypothesis that NPY neurons participate in the generation of LH surges through increased production of NPY and subsequent potentiation of the release and/or actions of LHRH.

Decreased luteinizing hormone-stimulated progesterone secretion by preovulatory follicles isolated from cyclic rats treated with the progesterone antagonist RU486

Since administration of the antiprogesterone RU486 to cyclic female rats at metestrus and diestrus results in increased serum levels of LH, estradiol, and testosterone at proestrus, we investigated whether RU486 affects follicular steroidogenesis. Female rats with a 4-day estrous cycle, induced experimentally by a single injection of bromocriptine on the morning of estrus, were given RU486 (2 mg) twice daily (0900 and 1700 h) on metestrus and diestrus. At proestrus the preovulatory follicles were isolated and incubated for 4 h in the absence and presence of LH. In the absence of LH, accumulation of estradiol, testosterone, and progesterone in the medium was not different for RU486-treated rats and oil-treated controls. In contrast, LH-stimulated estradiol, testosterone, and progesterone secretions were significantly lower in RU486-treated rats compared with controls. Addition of pregnenolone to the incubation medium resulted in a significantly lower increase of progesterone in follicles from RU486-treated rats compared with those from oil-treated controls. This suggests that 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity is decreased by administration of RU486 in vivo. Aromatase and 17 alpha-hydroxylase/C17-20 lyase activities were not affected: addition of substrate (androstenedione and progesterone respectively) did not affect differently the amount of product formed (estradiol and testosterone) in RU486- and oil-treated rats. However, LH-stimulated pregnenolone secretion was lower in follicles from RU486-treated rats compared with follicles from oil-treated controls, suggesting that either cholesterol side-chain cleavage activity or LH responsiveness is decreased. At proestrus the preovulatory follicles from RU486- and oil-treated rats were not morphologically different.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in feeding and sexual behaviour during reproductive cycle in female rats

Alterations in feeding and sexual behaviour were studied in adult female rats. During estrous phase there was decrease in food intake and increased sexual behaviour, as manifested by increased lordosis quotient. During met-and diestrous phases, increase in food intake and depressed sexual behaviour were observed, indicating inverse relationship between these two behaviours. Multisensory hypothalamic neurons may explain interactions among regulatory systems.

Estrogen receptor messenger ribonucleic acid in female rat brain during the estrous cycle: a comparison with ovariectomized females and intact males

Variations in levels of estrogen receptor mRNA were investigated in the medial preoptic nucleus, arcuate nucleus, and ventromedial nucleus of the hypothalamus throughout the phases of the female estrous cycle and compared with those in ovariectomized female and intact male rats. Female Wistar rats were killed during estrus, metestrus, diestrus, or proestrus or 72 h after ovariectomy as were a group of intact male rats. Brains were removed and frozen, and 20-microns cryostat sections were thaw-mounted onto slides and hybridized with a 35S-labeled antisense estrogen receptor probe. Section-mounted slides were processed, apposed to x-ray film, then dipped in liquid emulsion, and quantified. After exposure, estrogen receptor mRNA was detected in several brain regions, including the medial preoptic nucleus, arcuate nucleus, and ventromedial nucleus of the hypothalamus. Estrogen receptor mRNA levels in the medial preoptic nucleus were highest during estrus and metestrus, attenuated at diestrus, and low during proestrus. In contrast, the hybridization signal in the arcuate and ventromedial nuclei was low during estrus and then gradually increased throughout the cycle until it peaked during proestrus. Ovariectomized females exhibited an elevated level of estrogen receptor mRNA in all brain regions investigated. Hybridization signal in male medial preoptic nucleus and ventromedial nucleus was reduced compared with those in both intact and ovariectomized females. Estrogen receptor mRNA levels in the arcuate nucleus were similar to those in intact females, but less than those in ovariectomized animals. The results of these studies demonstrate that estrogen receptor mRNA levels are sexually dimorphic, vary during the estrous cycle, and increase after ovariectomy. Furthermore, these results indicate that the magnitude and direction of change observed during the estrous cycle are region specific and suggest that factors other than endogenous estrogen levels differentially modulate estrogen receptor mRNA expression in the hypothalamus.

Ovarian and circulating levels of oxytocin and arginine vasopressin during the estrous cycle in the rat

Ovarian extracts of Long-Evans rats separated using high performance liquid chromatography (HPLC) were measured by radioimmunoassays (RIAs) for the presence of oxytocin and arginine vasopressin (AVP). The results showed that the ovary contains both, and that they are indistinguishable from the respective standard synthetic peptides. During the estrous cycle, the ovarian content of oxytocin was 10-fold higher (p less than 0.01) in estrus than in the other phases, while AVP was 16- and 25-fold higher (p less than 0.01) in metestrus than in the other phases. In contrast, the plasma levels of oxytocin showed no significant difference among the various phases of the estrous cycle. However, the plasma level of AVP level was significantly higher (p less than 0.01) in diestrus than in other phases. The present study thus strongly supports the hypothesis that both oxytocin and AVP can be produced by the ovary itself in the rat. The possible roles of oxytocin and AVP in the reproductive cycle are discussed.

Acute inhibitory effects of 17 beta-estradiol are observed on gonadotropin secretion from perifused pituitary fragments of metestrous, but not proestrous, rats

The in vivo suppression of LH by 17 beta-estradiol (E2) has been documented frequently. However, the demonstration of a direct inhibitory action of E2, in contrast to a stimulatory action, on the secretion of LH from the anterior pituitary has been inconsistent. The aim of this study was to determine if E2 can suppress either basal (unstimulated) or GnRH-stimulated gonadotropin secretion directly at the level of the anterior pituitary gland. Anterior pituitaries were obtained from metestrous and proestrous females rats at 0900 h, and trunk blood was collected for serum measurements of LH, FSH, E2, and progesterone (P). Each anterior pituitary was cut into eighths and placed into a microchamber for perifusion. Pituitary fragments were perifused at a rate of 10 ml/h using medium 199 (without phenol red) that contained E2 (1 nM) or ethanol as a control. Six pulses of GnRH (peak amplitude, 50 ng/ml; duration, 2 min) were administered one per h starting at 60 min. Fractions of perfusate were collected every 5 min for measurement of LH and FSH. The total amounts of LH and FSH secreted during the 1-h interval after each GnRH pulse or corresponding basal hour were calculated. Both basal and LH and FSH responses to GnRH were significantly greater from pituitaries of proestrous compared to metestrous rats. The selective suppression of LH secretion by in vitro treatment with E2 was demonstrated using pituitaries from metestrous rats receiving GnRH pulses, but not using pituitaries from proestrous rats. Thus, a negative feedback effect of E2 on LH secretion was observed only in pituitaries from donors with low serum levels of E2 and high P, but not from donors with high serum levels of E2 and low P. We believe that the in vivo steroid environment determined the subsequent responses to in vitro treatment with E2 on GnRH-stimulated gonadotropin secretion from the isolated pituitary gland.

In vivo and in vitro modulation of gonadotropin-releasing hormone metabolism by estradiol and progesterone

The metabolism of GnRH by membrane-bound and serum-degrading enzymes may play an important role in the regulation of pituitary gonadotropin secretion. We examined GnRH metabolism by pituitary cells in vitro and the metabolism of exogenously administered GnRH in vivo in the presence and absence of estradiol (E2) and progesterone (P4). Ovariectomized cynomolgus monkeys were implanted with E2- and/or P4-filled Silastic capsules to simulate the estrogen and progesterone patterns of the normal menstrual cycle. Peripheral levels of GnRH after a 1-microgram iv injection were highest in the E2-replaced monkeys. Peripheral GnRH levels reached a higher peak and remained in circulation longer in monkeys treated with E2-filled Silastic implants than in those treated with E2 plus P4 or nonsteroid-replaced ovariectomized monkeys. In agreement with the in vivo data, GnRH was rapidly metabolized by acutely dispersed cells isolated from pituitaries removed from nonsteroid-replaced ovariectomized monkeys. Priming with E2 followed by P4 in vivo attenuated the clearance of GnRH in vitro, and E2 treatment alone almost completely blocked the ability of pituitary cells to bind and/or degrade GnRH in vitro. In a parallel study, cells prepared from rat pituitaries removed on the morning of proestrus (when serum E2 is highest) metabolized GnRH in vitro more slowly than pituitary cells removed at estrus, diestrus, or metestrus. In summary, our data suggest that E2 inhibits GnRH metabolism by monkey and rat pituitary cells in vitro and exogenously administered GnRH in vivo. Although the precise mechanism of action of E2 is unknown, inhibition of membrane-bound and serum proteases seems likely. The action of E2 may be to increase GnRH presentation to the pituitary and enhance LH and FSH secretion under conditions where circulating levels of the hormone are elevated, such as at midcycle.

Estrous cycle-related changes of high affinity luteinizing hormone/human chorionic gonadotropin binding sites in the rat uterus

LH/human CG (LH/hCG) high affinity binding sites were detected in crude membrane preparations of rat uteri. There was little competition for receptor occupancy between hCG and ovine FSH (oFSH) (0.05%) and no competition between hCG and ovine PRL (less than 0.01%). No similar binding sites were detected in crude membrane preparation of heart, kidney, skeletal muscle, liver, and lung tissues. Concentrations of uterine unoccupied binding sites (RLH) were determined for each stage of the 4-day estrous cycle. The RLH were found in all preparations of metestrus uteri (n = 10) but only in some preparations from the other stages of the estrous cycle (1 of 7 on proestrus, 3 of 4 on estrus, 5 of 7 on diestrus). The concentration of uterine RLH varied throughout the estrous cycle with highest values during the metestrus (1.50 +/- 0.15 fmol/mg protein) and lowest values during the proestrus (less than 0.2 fmol/mg protein). The affinity constant for hCG of uterine RLH remained constant during the estrous cycle (about 0.8 x 10(11) M-1) and was nearly identical to that of rat ovarian receptors. On metestrus, RLH concentration appeared to be approximately 35-fold lower in the uterus than in the ovaries when expressed per mg protein (1.50 +/- 0.15 vs. 52.83 +/- 3.61 fmol/mg protein) but only 20 times lower when expressed per organ (2.2 vs. 48.3 fmol/organ). The estrous cycle-related changes of uterine RLH concentration, together with our data establishing an in vitro influence of hCG on progesterone metabolism in rat uterus, suggest that some uterine functions could be directly regulated either by LH from the pituitary or during early pregnancy by an LH-like substance originating from the embryo.

[The neuronal reaction of the amygdaloid complex in the dynamics of the estrous cycle]

For investigation of the structural and functional organization of the amygdaloid complex (the cerebral neuroendocrine center) a response of its neurons to the fluctuations of circulating hormones was studied in the time course of the estrous cycle. Karyometry of 22 zones of the corticomedial group and 25 zones of the basolateral groups of the structure of the amygdaloid complex was performed in adult Wistar rats. A response of neurons of several zones of the corticomedial group of nuclei was revealed. A response of neurons of the basolateral nucleus at the caudal level of the central region was revealed in the basolateral group of structures of the amygdaloid complex.

[Structural-functional organization of the brain amygdaloid complex in the dynamics of the estrous cycle]

As a result of amygdaloid complex detailed histology-physiological investigation statistically proved increase in estrus has been discovered in comparison with metestrus of medium size cell nucleus of some cortico-medial group structures and basolateral nucleus. The presence of differences in the level of estrogen binding of rostral and caudal parts of this brain structure, taking place both in male and female rats has been shown for the first time. It was also discovered the dependence of the level of estrogen binding on estrus stage.

Distinct pulsatile prolactin secretory patterns during the estrous cycle: possible encoding for diverse physiological responses

PRL levels during the estrous cycle have been reported to be low, with the notable exception of the afternoon proestrous surge. The present study was designed to evaluate the pulsatile pattern of PRL secretion during the low secretory phases of the cycle. Animals were bled at 3-min intervals for 150 min during proestrus morning (AM), estrus AM and evening (PM), metestrus AM, and diestrus AM and PM. Using the algorithm Detect, pulse frequency, duration, interval, peak and trough values, area under the pulses, and mean PRL levels were calculated. PRL secretion was pulsatile during all stages of the estrous cycle, although the pattern varied considerably among the different cycle stages. Pulse frequency was highest during estrus and lowest during diestrus. All quantitative pulse parameters (peak, trough, amplitude, and area under pulse) were also higher during estrus and lowest in diestrus. Analysis of area under the pulse using frequency distribution indicated that at least two subpopulations of pulses, i.e. small mass and large mass pulses, were observed in certain stages of the cycle. Small mass pulses were present at all stages of the cycle; while their frequency remained unchanged, changes in other parameters were observed at different stages which did not always correlate with changes in mean PRL levels. Big mass pulses, on the other hand, presented a clear change in pulse frequency with values rising progressively from diestrus PM through proestrus to peak at estrus. Between estrus PM and metestrus AM these big mass PRL pulses essentially disappeared. In contrast to the marked changes in frequency, big mass PRL pulses were remarkably homogeneous in other quantitative characteristics. The results indicate that distinct changes in PRL pulsatility patterns occur during the estrous cycle; these changes are related to both the pattern and the quality of PRL pulses. Based on the observations of a companion study (28) and other data, we suggest that the genesis of the big mass and small mass PRL pulses involves dopaminergic and nondopaminergic mechanisms, respectively. The timing and selectivity of the changes in PRL pulsatile patterns suggest that those patterns may encode different signals for expression of the diverse actions of PRL on reproductive tissues.

Nuclear pores in rat hypothalamic arcuate neurons: sex differences and changes during the oestrous cycle

The numerical density of nuclear pores was assessed on freeze-fracture replicas of hypothalamic arcuate neurons from adult male and female rats. In females the nuclear pore density fluctuated during the oestrous cycle and was higher in oestrus than in pro-oestrus, metoestrus and dioestrus. Nuclear pore density in males and in metoestrus and dioestrus females was similar. The nuclear pore density in male rats was significantly less than that in oestrus and pro-oestrus females. The variation of the number of pores per unit nuclear volume and the total number of pores per nucleus was similar to the variation of the numerical density of nuclear pores. These results provide morphological evidence of cyclic changes in neuronal nucleocytoplasmic traffic during the ovarian cycle.

The influence of the estrous cycle, persistent estrus, ovariectomy and estrogen replacement, on the numbers and frequency of spontaneously active neurons in slices of the rat preoptic region in vitro

Spontaneous single-unit activity was studied in the preoptic region of rat brain slices. Similar unit frequencies were recorded during the estrous cycle and for all ovariectomized (OVX) rats (median frequencies between 0.8 and 2.0 Hz). Higher frequencies were recorded in persistent estrus (PE) (median 3.5 Hz) and in males (median 3.4 Hz), P vs estrus less than 0.001. The mean percentage of tracks with units was low at estrus (15%), at diestrus (18%), in OVX rats (16%) and male rats (22%), and was significantly increased in metestrus (36%) and proestrus (33%) (P vs estrus less than 0.01) and in OVX rats after estrogen treatment (P less than 0.05 to P less than 0.01). It is suggested that the increased number of units found in OVX rats after estrogen treatment and in PE rats are both effects of prolonged elevated levels of estrogen in the brain.