Rat Estrous Cycle Research Articles

Variations in uterine innervation during the estrous cycle in rat

Variations in uterine innervation during the estrous cycle in rat

Variations in uterine innervation during the estrous cycle in rat

Variations in uterine innervation during the estrous cycle in rat

Free postsynaptic densities in the hippocampus of the female rat.

The number of synapses in the adult, female hippocampal CA1 region fluctuates naturally across the estrous cycle in an ovarian steroid-dependent manner. This phasic variation in synapse number occurs without identifiable degenerating synapses. Ultrastructural correlates of the dynamic aspect of this synapse loss and synapse formation thus remain undescribed. During early development, one hallmark of synaptogenesis is the presence of free postsynaptic densities (PSDs). Here we report that the incidence of free PSDs in CA1 fluctuates across the rat estrous cycle. The number of free PSDs is greatest on the afternoon of proestrus and is significantly decreased on the afternoon of estrus, 24 h later. We hypothesize that these free PSDs reflect synapse turnover in the adult CA1 region.

Reduction of mucin-1 expression during the receptive phase in the rat uterus.

Mucin-1 (Muc1), an integral membrane mucin, is expressed on the apical surface of uterine epithelial cells (UE) of various species. Loss of Muc1 is believed to be necessary for embryo attachment. Muc1 expression is markedly reduced in luminal epithelia during the receptive phase in mice, baboons, and pigs. In the present study, we examined Muc1 expression during the rat estrous cycle and at Day 5 of pregnancy, the time of embryo attachment. In contrast to findings in the mouse, indirect immunofluorescence revealed that uterine Muc1 protein expression was unaltered during the estrous cycle. However, similar to what is observed in the mouse and other species, Muc1 protein decreased at Day 5 of pregnancy in luminal UE. The decrease in Muc1 expression was specific to luminal UE and did not occur in glandular UE. A partial cDNA corresponding to the cytoplasmic tail region of rat Muc1 was generated by a reverse transcription-polymerase chain reaction (RT-PCR) strategy. This cDNA sequence is 89% and 91% identical to the corresponding region of mouse Muc1 at the nucleotide and amino acid levels, respectively. The predicted sequence of rat Muc1 protein has 70-90% identity to the Muc1 protein sequence obtained in other species. Semiquantitative RT-PCR experiments indicated that the mRNA encoding rat Muc1 decreased 57% at Day 5 as compared with the levels found at estrus. This value included mRNA from both luminal and glandular UE and so may underestimate the relative decrease in mRNA in the luminal compartment. In conclusion, we have determined that the levels of rat Muc1 protein and mRNA decrease in the luminal UE at the time of implantation, a pattern similar to that seen in the mouse, baboon, and pig. This supports the general theory that reduction of Muc1 expression is necessary for embryo implantation.

Proliferating cell nuclear antigen, estradiol and progesterone receptors as markers for different phases of rat estrous cycle : L. Staneva-Dobrovski,∗ Ch. Hauke, † and H. Korr † ∗Department of Neuroanatomy, H. Heine University of Düsseldorf; and †Department of Anatomy, RWTH Aachen, Germany

Proliferating cell nuclear antigen, estradiol and progesterone receptors as markers for different phases of rat estrous cycle : L. Staneva-Dobrovski,∗ Ch. Hauke, † and H. Korr † ∗Department of Neuroanatomy, H. Heine University of Düsseldorf; and †Department of Anatomy, RWTH Aachen, Germany

Variations in levels of substance P-encoding β-, γ-preprotachykinin and substance P receptor NK-1 transcripts in the rat hypothalamus throughout the estrous cycle: a correlation between amounts of β-preprotachykinin and NK-1 mRNA

Using a sensitive RNase protection assay, the simultaneous quantification of hypothalamic β-, γ-preprotachykinin (PPT) and SP receptor NK-1 transcripts was performed throughout the estrous cycle. The amounts of these 3 transcripts were up-regulated during diestrus II-proestrus night (2-, 1.5- and 1.3-fold, respectively). These levels returned to low values during the proestrous day in the case of γ-PPT mRNA and during the estrus-diestrus I night in the cases of β-PPT and NK-1 mRNAs. These results implicate a differential regulation in amounts of the two alternatively spliced PPT transcripts. The 160 hypothalami of this study had been previously assayed for amounts of substance P (SP) and neurokinin A (NKA) peptides [P. Duval, V. Lenoir, S. Moussaoui, C. Garret and B. Kerdelhué, Substance P and neurokinin A variations throughout the rat estrous cycle; comparison with ovariectomized and male rats: I. Plasma, hypothalamus, anterior and posterior pituitary, J. Neurosci. Res., 45 (1996) 598–609]. Variations in mRNA and peptide levels were compared by statistical analysis. Surprisingly, variations in SP level paralleled those in β-PPT mRNA level and variations in NKA level paralleled those of γ-PPT mRNA level, although β- and γ-PPT transcripts encode both SP and NKA. Furthermore, the level of NK-1 mRNA was positively correlated with the level of β-PPT mRNA ( r=0.90, P<10 −58) and with the level of SP peptide ( r=0.30, P<10 −3) but not with the level of NKA peptide. This analysis suggests that SP receptor NK-1 mRNA could be physiologically regulated by SP peptide in the rat hypothalamus.

Pituitary follistatin regulates activin-mediated production of follicle-stimulating hormone during the rat estrous cycle.

Follistatin, an activin-binding protein, plays a key role in the modulation of activin-dependent functions. In the anterior pituitary, activin stimulates the synthesis and secretion of FSH. In the current study, we assessed the roles of locally produced activin and follistatin in the control of FSH gene expression and secretion. The anterior pituitary gland follistatin content was measured at frequent intervals during the rat estrous cycle. Follistatin protein levels were high before the primary gonadotropin surges, decreased by 50% on proestrous evening, and rebounded to a peak at midnight on proestrus before returning to presurge levels on estrus morning. Changes in pituitary follistatin protein content were preceded by parallel changes in pituitary follistatin messenger RNA (mRNA). The trough in follistatin protein content on proestrus coincided with a peak in circulating levels of free activin A (not bound to follistatin) and a sharp rise in FSHbeta mRNA levels, suggesting that decreased pituitary follistatin leads to increased available activin. To quantitate the contribution of pituitary free activin to pituitary expression of FSHbeta mRNA and the primary and secondary serum FSH surges, rats were infused through carotid catheters with saline or recombinant human follistatin (288-amino acid isoform; rhFS-288) at different times during the estrous cycle. Infusion of rhFS-288 on diestrus did not affect FSH production. In contrast, infusion of rhFS-288 during the secondary FSH surge decreased the peaks in FSHbeta mRNA and serum FSH by 63% and 47%, respectively, relative to those in saline-infused control animals. Infusion of rhFS-288 during the primary FSH surge decreased serum FSH to a lesser degree (24%). These data indicate a physiological role for pituitary follistatin in the control of activin-mediated FSH synthesis and secretion during the rat estrous cycle.

Pituitary Follistatin Regulates Activin-Mediated Production of Follicle-Stimulating Hormone during the Rat Estrous Cycle

Follistatin, an activin-binding protein, plays a key role in the modulation of activin-dependent functions. In the anterior pituitary, activin stimulates the synthesis and secretion of FSH. In the current study, we assessed the roles of locally produced activin and follistatin in the control of FSH gene expression and secretion. The anterior pituitary gland follistatin content was measured at frequent intervals during the rat estrous cycle. Follistatin protein levels were high before the primary gonadotropin surges, decreased by 50% on proestrous evening, and rebounded to a peak at midnight on proestrus before returning to presurge levels on estrus morning. Changes in pituitary follistatin protein content were preceded by parallel changes in pituitary follistatin messenger RNA (mRNA). The trough in follistatin protein content on proestrus coincided with a peak in circulating levels of free activin A (not bound to follistatin) and a sharp rise in FSHβ mRNA levels, suggesting that decreased pituitary follistatin leads to increased available activin. To quantitate the contribution of pituitary free activin to pituitary expression of FSHβ mRNA and the primary and secondary serum FSH surges, rats were infused through carotid catheters with saline or recombinant human follistatin (288-amino acid isoform; rhFS-288) at different times during the estrous cycle. Infusion of rhFS-288 on diestrus did not affect FSH production. In contrast, infusion of rhFS-288 during the secondary FSH surge decreased the peaks in FSHβ mRNA and serum FSH by 63% and 47%, respectively, relative to those in saline-infused control animals. Infusion of rhFS-288 during the primary FSH surge decreased serum FSH to a lesser degree (24%). These data indicate a physiological role for pituitary follistatin in the control of activin-mediated FSH synthesis and secretion during the rat estrous cycle.

Cocaine’s Effects on Neuroendocrine Systems: Clinical and Preclinical Studies

This review examines the effects of cocaine on the neuroendocrine system and summarizes findings from clinical studies of cocaine abusers and preclinical studies in rodents and rhesus monkeys. The effects of acute and chronic cocaine administration on anterior pituitary, gonadal, and adrenal hormones are described, and the functional consequences of chronic cocaine exposure are discussed. Many of cocaine’s acute effects on the endocrine system are consistent with its actions as a monoamine reuptake inhibitor. Acute cocaine administration stimulates release of gonadotropins, ACTH, and cortisol or corticosterone and suppresses prolactin levels. It has been difficult to detect changes in basal levels of most hormones or alterations in hormone responsiveness to a challenge dose of cocaine or other agents after chronic cocaine treatment. Interpretation of clinical data is often complicated by polydrug abuse involving opiates and alcohol as well as cocaine. However, preclinical studies of the effects of chronic cocaine exposure on integrated neuroendocrine function have revealed disruptions of the estrous cycle in rats and the menstrual cycle in rhesus monkeys. Furthermore, the menstrual cycle disorders observed in rhesus monkeys parallel those reported in women who abuse cocaine. Much remains to be learned about cocaine’s interactions with the endocrine system and the consequences of cocaine abuse for reproductive function.

Modulation of mesolimbic dopaminergic activity over the rat estrous cycle

Clinical observations have suggested that ovarian steroid hormones modulate the symptomology of psychiatric disorders and this modulation is thought to be due to a protective effect of estrogen on dopaminergic activity. To test this hypothesis, mesolimbic dopamine (DA) activity was examined in relationship to endogenous hormone levels. Using in vivo electrochemical techniques, K +-stimulated DA release was measured in the nucleus accumbens of control, intact cycling female rats and experimental rats which had received bilateral 6-hydroxydopamine (6-OHDA) lesions to the medial prefrontal cortex (PFC) to produce subcortical hyperactivity. DA release and reuptake fluctuated with changes in circulating steroid levels in both control and lesion groups. In non-lesioned control rats, stimulated DA release peaked during diestrus I (DI) and was attenuated during diestrus II (DII) and estrus. DA transport, as measured by a change in T 1/2 time, was significantly potentiated during proestrus. The expression of subcortical hyperactivity following lesions to the medial PFC appeared to be dependent on the steroid environment; during DII an increased responsiveness was observed while a significant decrease in K +-stimulated release was observed during DI. These cyclic changes in DA release were not associated with dramatic changes in DA transport except during proestrus when transport was significantly prolonged. These data suggest that cyclic fluctuation of ovarian steroids may modulate DA activity presynaptically through an alteration in both release and reuptake and that this modulation effectively dampens the expression of subcortical hyperactivity except under specific hormonal conditions.

Expression of 17β-Hydroxysteroid Dehydrogenase Type 1 and Type 2, P450 Aromatase, and 20α-Hydroxysteroid Dehydrogenase Enzymes in Immature, Mature, and Pregnant Rats.

In the present study, we evaluated the expression and regulation of 17beta-hydroxysteroid dehydrogenase (17HSD) type 1 and type 2, cytochrome P450 aromatase (P450arom), and 20alpha-hydroxysteroid dehydrogenase (20HSD) in mature and pregnant rats. Immunohistochemical analysis of rat 17HSD type 1 showed that the enzyme is exclusively expressed in the granulosa cells of developing, healthy, primary, secondary, and tertiary follicles at all stages of the estrous cycle and pregnancy, and is not detected in the corpora lutea. The data showed that the amount of the enzyme expressed in the follicle increases as follicular maturation progresses and is highest in tertiary and Graafian follicles. However, Northern blot analysis of total RNA from whole ovaries showed a rather constitutive expression of the 17HSD type 1 enzyme. It is evident that compared with P450arom, 17HSD type 1 is more widely expressed in the follicles during the various maturational stages of folliculogenesis. Hence, the data indicate distinct localization, expression, and regulation patterns for 17HSD type 1 and P450arom during the rat estrous cycle and pregnancy. Furthermore, compared with the two estradiol biosynthetic enzymes, a different expression pattern was detected for 20HSD messenger RNA. During the estrous cycle the enzyme was detected in the ovaries throughout the cycle, and in the ovaries of pregnant animals the enzyme showed an expression pattern the opposite of that observed for P450arom. Rat 17HSD type 2, not detected in the ovaries, was constitutively expressed in both female and male liver and small intestine in 21-day-old fetuses up to 6-week-old mature animals. Similarly, in these tissues the enzyme was constitutively expressed in normal cycling and pregnant animals, but it showed increasing expression in the placenta as pregnancy advanced. The relatively constitutive expression of the enzyme at all physiological stages of the animals suggests a general role for the enzyme in the inactivation of circulating sex steroids.

Regulation of the natriuretic peptide system in rat uterus during the estrous cycle.

Uterine natriuretic peptides may be involved in the alterations that occur in the uterus during the estrous cycle through its role in hydromineral balance. The following studies were performed to determine whether uterine natriuretic peptides and receptors follow a cyclic pattern during the estrous cycle. The results obtained show that atrial natriuretic peptide (ANP) content in rat uterine tissue was low in proestrus (8.5 +/- 2.6 pg/g) and significantly increased (P < 0.001) in estrus (71.5 +/- 16.6 pg/g), metestrus (82.6 +/- 19.7 pg/g) and diestrus (91.0 +/- 19.4 pg/g), whereas plasma ANP was not altered during the cycle. Similarly, measurement of uterine ANP mRNA by reverse transcribed polymerase chain reaction (RT-PCR) indicated lowest levels of ANP mRNA at proestrus. Measurement of C-type natriuretic peptide (CNP) by a specific and sensitive radioimmunoassay revealed that uterine CNP also varies with the estrous cycle. Uterine CNP was low in diestrus (143.2 +/- 22.4 pg/mg protein) as compared with proestrus, estrus and metestrus (305.3 +/- 51.5, 267.5 +/- 44.9, 291 +/- 41.2 pg/mg protein respectively, P < 0.05). Autoradiography performed on uterine tissue slices localized natriuretic peptide receptors to myometrial smooth muscle layers and to endometrial uterine glands. High binding of 125I-ANP was observed in proestrus and estrus with 60-75% decreases during metestrus and diestrus. Binding of 125I-tyr0CNP to uterine slices was also high during proestrus, but declined by 35% at estrus, metestrus and diestrus. The alterations in the receptors were also observed at the level of synthesis. RT-PCR detection of guanylyl cyclase A (GC-A) receptor mRNA and guanylyl cyclase B (GC-B) mRNA showed high signals at proestrus but 4- and 2-fold reductions respectively at metestrus and diestrus. In conclusion, variations in uterine ANP and CNP and their receptors during the rat estrous cycle imply the involvement of the natriuretic peptides in uterine hydromineral balance and myometrial motor activity.

Apoptotic cell death during the estrous cycle in the rat uterus and vagina

Rodent uterus and vagina show marked histological changes during the estrous cycle. Apoptotic cell death has been demonstrated in hamster and rat uterine epithelium during the estrous cycle by electron microscopy: numerous epithelial cells undergo apoptosis at estrus. We examined cell death and cell proliferation in rat uterus and vagina during estrous cycle. To examine the rate of proliferation in uterine and vaginal cells at each estrous stage, the numbers of cells at metaphase were counted separately in epithelial and stromal cells. We identified the apoptotic cells in uterus and vagina at each estrous stage by using DNA fragmentation, in situ DNA 3'-end labeling, and electron microscopy. Mitotic rates in uterine luminal and glandular epithelial cells were low at metestrus and estrus, respectively. Intense fragmentation was found in the uterus at metestrus and in the vagina at proestrus and metestrus. In uterine luminal and glandular epithelial cells, apoptotic index showed peaks at metestrus and estrus, respectively. In vaginal epithelial cells, many apoptotic cells were encountered in the superficial layer at proestrus, which may contribute to keratinization. In the middle and basal layer of vaginal epithelial cells, apoptotic index was high at metestrus, when mitotic rate was low. Electron microscopy confirmed the results of the labeling studies. Apoptotic cell death was encountered in the uterus and vagina during estrous cycle in rats. There is an inverse correlation between cell death and cell proliferation in rat uterine and vaginal epithelial cells during the estrous cycle.

Expression of ryanodine receptors in the pituitary gland: evidence for a role in gonadotropin-releasing hormone signaling.

GnRH elicits secretion of LH and FSH from gonadotropes by activating an array of intracellular signals including the generation of inositol triphosphate and the release of intracellular calcium. Given the important role of calcium in the secretory responses to GnRH, we examined the expression and function of the ryanodine receptors, which are known to modulate calcium release from intracellular stores. Using RT-PCR analysis, we found that ryanodine receptor (RyR) types 2 and 3, but not type 1, are expressed in rat pituitaries. Pulses of GnRH were administered to perifused primary rat pituitary cells in the presence or absence of a ryanodine receptor antagonist, ruthenium red, to assess effects on GnRH-mediated LH secretion. Treatment with ruthenium red resulted in a 40% decrease in the spike phase of GnRH-induced LH release and a 35% reduction in the plateau phase. Ruthenium red also inhibited GnRH-mediated transcription of a transfected alpha-LUC reporter plasmid. RyR messenger RNA (mRNA) expression varied during the rat estrous cycle with maximal levels following increases of progesterone. The effects of gonadal steroids on pituitary RyR mRNA levels were examined directly in ovariectomized rats that were treated with estrogen (E), or estrogen and progesterone (P). In this paradigm, E decreased, whereas E + P increased RyR3 mRNA levels. These results indicate that RyR is expressed and hormonally regulated in the rat pituitary and suggest that it might play a role in mediating GnRH-induced gonadotropin synthesis and secretion.

Expression of Ryanodine Receptors in the Pituitary Gland: Evidence for a Role in Gonadotropin-Releasing Hormone Signaling

GnRH elicits secretion of LH and FSH from gonadotropes by activating an array of intracellular signals including the generation of inositol triphosphate and the release of intracellular calcium. Given the important role of calcium in the secretory responses to GnRH, we examined the expression and function of the ryanodine receptors, which are known to modulate calcium release from intracellular stores. Using RT-PCR analysis, we found that ryanodine receptor (RyR) types 2 and 3, but not type 1, are expressed in rat pituitaries. Pulses of GnRH were administered to perifused primary rat pituitary cells in the presence or absence of a ryanodine receptor antagonist, ruthenium red, to assess effects on GnRH-mediated LH secretion. Treatment with ruthenium red resulted in a 40% decrease in the spike phase of GnRH-induced LH release and a 35% reduction in the plateau phase. Ruthenium red also inhibited GnRH-mediated transcription of a transfected α-LUC reporter plasmid. RyR messenger RNA (mRNA) expression varied during the rat estrous cycle with maximal levels following increases of progesterone. The effects of gonadal steroids on pituitary RyR mRNA levels were examined directly in ovariectomized rats that were treated with estrogen (E), or estrogen and progesterone (P). In this paradigm, E decreased, whereas E + P increased RyR3 mRNA levels. These results indicate that RyR is expressed and hormonally regulated in the rat pituitary and suggest that it might play a role in mediating GnRH-induced gonadotropin synthesis and secretion.

The Effects of 17α-Methyltestosterone, Methandrostenolone, and Nandrolone Decanoate on the Rat Estrous Cycle

Blasberg, M. E., C. J. Langan and A. S. Clark. The effects of 17α-methyltestosterone, methandrostenolone, and nandrolone decanoate on the rat estrous cycle. Physiol Behav 61(2) 265–272, 1997.—In a series of four separate experiments, the effects of anabolic-androgenic steroid (AAS) compounds on the estrous cycle of adult Long-Evans rats were examined. Sexual receptivity, vaginal cytology, and body weight were monitored throughout a 2-week baseline, AAS treatment, and recovery periods. In Experiments 1–3, subjects were administered 17α-methyltestosterone, methandrostenolone, or nandrolone decanoate at doses selected to mimic the human abuse levels of each compound. In these studies, the highest doses of 17α-methyltestosterone (7.5 mg/kg) and nandrolone decanoate (5.6 mg/kg) disrupted behavioral and vaginal cyclicity, whereas the highest dose of methandrostenolone (3.75 mg/kg) appeared to have slightly less robust effects. To compare effects on estrous cyclicity across AAS compounds, subjects in Experiment 4 received a single high dose (7.5 mg/kg) of each compound for 2 weeks. At this dose, all AAS compounds interfered with vaginal cyclicity, although effects on behavioral cyclicity and uterine weight were not uniform. Across all 4 experiments, AAS effects on body weight were minimal. The short-term administration of AAS compounds at levels commonly used by humans disrupts female neuroendocrine function in a dose-dependent manner.

Spatial and nonspatial learning across the rat estrous cycle.

Spatial and nonspatial learning across the rat estrous cycle.

Inhibin A and inhibin B are inversely correlated to follicle- stimulating hormone, yet are discordant during the follicular phase of the rat estrous cycle, and inhibin A is expressed in a sexually dimorphic manner

Inhibin A and inhibin B are inversely correlated to follicle- stimulating hormone, yet are discordant during the follicular phase of the rat estrous cycle, and inhibin A is expressed in a sexually dimorphic manner

Inhibin A and inhibin B are inversely correlated to follicle-stimulating hormone, yet are discordant during the follicular phase of the rat estrous cycle, and inhibin A is expressed in a sexually dimorphic manner.

Inhibin A and inhibin B are related dimeric protein hormones and endocrine regulators of the reproductive axis. Specifically, inhibin inhibits FSH secretion from the anterior pituitary. The inhibins are synthesized by the gonads and are themselves modulated by FSH. Although the activity of these ligands has been well characterized, the circulating concentrations of dimeric inhibin A and dimeric inhibin B have not previously been reported for the rat. Our group examined the serum concentration of inhibin A and inhibin B in normally cycling female rats, male rats, and in gonadectomized animals. Both inhibin isoforms are detected in intact female rat serum. Interestingly, inhibin B, but not inhibin A, is detected in intact male rat serum. Neither inhibin isoform is detected in long-term castrate female or male rats. In normally cycling female rats, inhibin A was low on the morning of metestrus and rose steadily to a peak on proestrus. In contrast, inhibin B was elevated on the mornings of metestrus, diestrus, and proestrus. Both ligands persisted in the serum until proestrus evening. Serum inhibins then declined beginning at 2100 h (inhibin A) or 1800 h (inhibin B) on proestrus, and the concentrations reached a nadir on the morning of estrus (0600 h). The nadir coincided with the peak of the secondary FSH surge. Both inhibins rebounded later on the morning of estrus. The results of this study demonstrate that dimeric, ovarian-derived inhibin A and inhibin B circulate in the female rat. The inverse relationship of the inhibins during the secondary FSH surge is consistent with the hypothesis that they participate in the regulation of reproductive cyclicity. The differing patterns of inhibin A and inhibin B during the period of follicular development on metestrus and diestrus suggest different follicle sources or regulation of these molecules during this period. We further demonstrate that inhibin B is the dominant form of FSH regulating protein in the male rat.

Age and reproductive status affect basal venous tone in the rat

Objective: Changes in venous tone alter vessel diameter and capacitance of veins. These alterations may be induced by the steroid hormonal milieu. Therefore, our question was whether venous tone differs between estrous cycle, pregnancy and old rats. Study design: Mesenteric veins from young, pregnant and old Sprague-Dawley rats were dissected and cannulated in a venograph system with a continous readout of pressure-dependent lumen diameter. Results: During estrous cycle venous tone was increased in metestrous ( P < 0.05), whereas it was decreased in all old rats ( P < 0.05). There was higher venous tone in pregnant animals compared to controls ( P < 0.05). Conclusions: Venous tone exhibits marked differences during rat estrous cycle. It is increased during pregnancy and decreased in old rats.