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).

Increased dendritic length in CA1 and CA3 hippocampal neurons during the metestrus phase in Wistar rats.

Studies have shown that changes in ovarian hormone concentrations promote natural fluctuations in the density of dendritic spines of hippocampal neurons in female Sprague-Dawley rats, without changes in dendritic length, throughout the estrous cycle. However, it is still unknown whether these fluctuations are present in other rat strains. Due to our interest in Wistar rats, the objective of the present study was to determine if there is natural dendritic remodeling in the female Wistar rat throughout the estrous cycle. This study analyzed the dendritic arborization of pyramidal neurons CA1 and CA3 of the dorsal hippocampus in each phase of the estrous cycle. We used the Golgi-Cox staining method and Sholl analysis to evaluate the dendritic length and density of dendritic spines. Our results showed that the dendritic length of the basilar and apical trees of CA1 neurons was longer in the metestrus phase. In CA3 neurons, only the apical dendritic trees showed longer dendritic length during metestrus. There was no variation in the density of dendritic spines in relation to any of the phases of the estrous cycle. Taken together, these results indicated that pyramidal neurons of the CA1 and CA3 regions of the dorsal hippocampus in the Wistar rat exhibited changes in dendritic length in the metestrus phase of the estrous cycle. Together, these data are important when considering the use of these organisms in behavioral studies.

Learning and memory are impaired in the object recognition task during metestrus/diestrus and after sleep deprivation.

Females are an under-represented research model and the mechanisms through which sleep loss impairs cognition are not clear. Since levels of reproductive hormones and the estrous cycle are sensitive to sleep loss and necessary for learning and memory, we hypothesized that sleep deprivation impacts learning and memory in female mice by interfering with the estrous cycle. We used the object recognition task to assess learning and memory in female mice during separate phases of the estrous cycle and after sleep loss. Mice in metestrus/diestrus attended to sample objects less than mice in proestrus/estrus during object acquisition, the first phase of the object recognition task. Subsequently, during the recognition phase of the task, only mice in proestrus/estrus displayed a preference for the novel object. Sleep deprivation for 12h immediately before the object recognition task reduced time attending to sample objects and novel object preference for mice in proestrus/estrus, without changing length of the estrous cycle. These results show that sleep deprived mice in proestrus/estrus had learning deficits and memory impairments, like mice in metestrus/diestrus. Since sleep deprivation did not disrupt the estrous cycle, however, results did not support the hypothesis. Cognitive impairments due to acute sleep loss were not due to alterations to the estrous cycle.

High-Yield Superovulation in Adult Mice by Anti-Inhibin Serum Treatment Combined with Estrous Cycle Synchronization.

Producing many mature oocytes is of great importance for assisted reproductive technologies. In mice, superovulation by consecutive injections of equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG) has been the gold standard for oocyte collection. However, the yield of mature oocytes by this regimen can fluctuate according to the stage of the estrous cycle, strain, and age. Therefore, our objective was to develop a high-yield superovulation protocol to collect higher numbers of oocytes from adult female mice of different strains and ages. First, we aimed to synchronize the estrous cycle using C57BL/6 (B6) female mice. Most (93%) were synchronized to metestrus after two daily injections of progesterone. Second, we found that with the injection of anti-inhibin serum (AIS) instead of eCG, the mean number of ovulated oocytes almost doubled (21 vs. 41 per mouse). Third, by combining estrous cycle synchronization with two AIS injections, we obtained 62 oocytes per mouse, about three times that with the eCG-hCG protocol. Importantly, this approach increased the proportion of mice that ovulated >25 oocytes from about 40% (eCG-hCG) to 90%. The same protocol was also effective in other inbred (BALB/cA), outbred (ICR), and hybrid (B6D2F1) strains. In addition, B6 female mice aged over 1 yr ovulated 1.8-fold more oocytes by this protocol. Thus, estrous cycle synchronization followed by AIS-hCG yielded a broadly applicable, highly efficient superovulation. This protocol should promote the effective use of invaluable female mouse strains and decrease the numbers of animals euthanized.

Plasma amino acid profiles at various reproductive stages in female rats.

We measured the plasma levels of amino acids at various reproductive stages in female rats, including the estrous cycle, pregnancy and lactation, and compared the resulting amino acid profiles using two- or three-dimensional figures. These figures revealed that the amino acid profiles of pregnant and lactating dams differed considerably from those during the estrous cycle or in male rats. The plasma levels of individual amino acids were almost the same between proestrus, estrus, metestrus and diestrus, and their profiles did not differ significantly. However, the amino acid profiles changed during pregnancy and lactation in dams. The plasma Ser level decreased significantly in mid and late pregnancy, whereas Tyr, Gly and His decreased significantly in the late and end stages of pregnancy, and Trp and Lys significantly decreased and increased at the end of pregnancy, respectively. Much larger changes in amino acid profiles were observed during lactation, when the levels of many amino acids increased significantly, and none showed a significant decrease. Plasma Pro, Ser and Gly levels increased continuously from day 1 until day 15 of lactation, whereas Asn and Met increased significantly from days 1 and 5 respectively until the end of lactation. These results suggest that the profiles of plasma amino acids show characteristic changes according to reproductive stage and that it may be necessary to consider such differences when performing amino acid-based diagnosis.

Montanoa frutescens and Montanoa grandiflora extracts reduce anxiety-like behavior during the metestrus-diestrus phase of the ovarian cycle in Wistar rats.

In previous studies, the anxiolytic-like effects of Montanoa tomentosa and Montanoa frutescens were reported in male rats, but the potential anxiolytic-like effects of Montanoa plants during the different phases of the ovarian cycle in rats remain to be explored. The anxiolytic-like effects of the aqueous crude extracts of M. frutescens (25 and 50 mg/kg) and M. grandiflora (25 and 50 mg/kg) in the elevated plus maze were investigated in Wistar rats during the estrous cycle and compared with 2 mg/kg diazepam as a reference anxiolytic drug. To investigate any motor effect (i.e., hyperactivity, no changes, or hypoactivity) associated with the treatments, the rats were evaluated in the open field test. The M. frutescens (25 and 50 mg/kg) and M. grandiflora (50 mg/kg) extracts exerted anxiolytic-like effects during the metestrus-diestrus phase, similar to diazepam, without disrupting spontaneous motor activity. No significant effects of the extracts were detected in either behavioral test during the proestrus-estrus phase, whereas diazepam produced motor hypoactivity in the open field test. These results indicate that the M. frutescens and M. grandiflora extracts possess anxiolytic-like effects that depend on the ovarian cycle phase, supporting the Mexican ancient medicinal use of these plants to ameliorate anxiety disorders.

Uterine secretome and its modulation in rat (Rattus norvegicus).

The present study identifies uterine fluid (UF) proteins that display differential abundance during the embryo-permissive phase in nonconception and conception cycles in rats. UF samples were collected from nonpregnant rats in the proestrous (n=17) and metestrous (n=18) phases and also from pregnant (n=17) and pseudopregnant (n=17) rats on day 4 post coitus. UF protein profile in the metestrous phase was compared with that in the proestrous phase. Similarly, UF protein profile of the pregnant rats was compared with that of the pseudopregnant rats. Two-dimensional PAGE, followed by densitometric analysis of the paired protein spots, revealed differential abundance of 44 proteins in the metestrous phase, compared with that in the proestrous phase. Of these, 29 proteins were identified by matrix-assisted laser desorption/ionization time-of-flight or liquid chromatography-tandem mass spectrometry. Functional groups such as proteases, protease inhibitors, and oxidoreductases were enriched in differentially abundant proteins. Total protease activity in UF was found to be significantly (P<0.05; t-test) higher in the proestrous phase, compared with that in the metestrous phase. Furthermore, 41 UF proteins were found to be differentially abundant in pregnant rats, compared with pseudopregnant rats. Of these, 11 proteins could be identified. Immunoblotting analysis confirmed significantly higher (P<0.05; t-test) abundance of ß-actin, Rho-specific guanine nucleotide dissociation inhibitor alpha (Rho-GDIα), and peroxiredoxin-2 and -6 in the metestrous phase, compared with that in the proestrous phase. Compared with pseudopregnant rats, pregnant rats had significantly higher (P<0.05; t-test) levels of UF ß-actin and Rho-GDIα. Furthermore, these proteins could be detected in the culture supernatants of endometrial epithelial cell lines, thereby providing an evidence of their secretion from endometrial epithelial cells. Data obtained from the study expand our knowledge on the uterine milieu that favours embryo implantation.

Sex steroid hormones regulate the expression of growth-associated protein 43, microtubule-associated protein 2, synapsin 1 and actin in the ventromedial nucleus of the hypothalamus.

The ventromedial nucleus of the hypothalamus is well known for its involvement in the regulation of the female reproductive behavior. The dendritic trees of neurons in its ventrolateral division (VMNvl), the dendritic spines, and the dendritic and spine synapses undergo alterations along the estrous cycle. Because these changes are conspicuous, we thought of interest to examine the influence of sex steroids in the levels of the structural proteins of axons and dendrites. The VMNvl of female rats at all phases of the estrous cycle was labeled for growth-associated protein-43, microtubule-associated protein 2, synapsin 1 and actin. The intensity of the labeling was measured using a modified Brightness-Area-Product method that is sensitive to variations the size of the VMN. The brightness per unit area of these proteins did not undergo significant variations over the estrous cycle, except synapsin 1 that was significantly reduced in diestrus relative to the remaining phases of the ovarian cycle. Conversely, the Brightness-Area-Product of all labeled proteins changed along the estrous cycle and was greater at proestrus than at all other phases. Our results show the presence of estrous cycle-related oscillations in the levels of the structural proteins that are involved in dendritic and synaptic plasticity.

Estrous cycle phase and gonadal hormones influence conditioned fear extinction.

Gonadal hormones modulate fear acquisition, but less is known about the influence of gonadal hormones on fear extinction. We assessed sex differences and the influence of gonadal hormone fluctuations and exogenous manipulations of estrogen and progesterone on acquisition, extinction learning and extinction recall in a 3 day auditory fear conditioning and extinction protocol. Experiments were conducted on males and naturally cycling female rats. Regarding female rats, significant differences in fear extinction were observed between subgroups of females, depending on their phase of the estrous cycle. Extinction that took place during the proestrus (high estrogen/progesterone) phase was more fully consolidated, as evidenced by low freezing during a recall test. This suggests that estrogen and/or progesterone facilitate extinction. In support of this, injection of both estrogen and progesterone prior to extinction learning in female rats during the metestrus phase of the cycle (low estrogen/progesterone) facilitated extinction consolidation, and blockade of estrogen and progesterone receptors during the proestrus phase impaired extinction consolidation. When comparing male to female rats without consideration of the estrous cycle phase, no significant sex differences were observed. When accounting for cycle phase in females, sex differences were observed only during extinction recall. Female rats that underwent extinction during the metestrus phase showed significantly higher freezing during the recall test relative to males. Collectively, these data suggest that gonadal hormones influence extinction behavior possibly by influencing the function of brain regions involved in the consolidation of fear extinction. Moreover, the elevated fear observed in female relative to male rats during extinction recall suggests that gonadal hormones may in part play a role in the higher prevalence of anxiety disorders in women.

Ciliary transport, gamete interaction, and effects of the early embryo in the oviduct: ex vivo analyses using a new digital videomicroscopic system in the cow.

Using a digital videomicroscopic analysis system in the bovine, we showed that the mechanisms of transport caused by ciliary beating are distinctly different in ampulla and isthmus of the oviduct. The average particle transport speed (PTS) in the oviduct (mean, 133 microm/sec) does not differ in the cycle (metestrus) and during pregnancy after implantation, but it is locally modulated at the site of the embryo. Using videomicroscopy, we were able to document that after entering the ampulla, the cumulus-oocyte complex (COC) is not transported by ciliary beating down the oviduct, but firmly attaches to the ampullar epithelium. This attachment is mediated by the cumulus cells. However, when a COC is degenerated, it is floating in the oviductal lumen. As soon as a vital COC is in the ampulla, the sperm bound in the sperm reservoir of the ampullar isthmic junction leave the reservoir and hurry to the oocyte. When a sperm has penetrated the zona pellucida, the COC detaches and continues its migration. Quantitative measurements showed that the early embryo is able to locally downregulate PTS during its migration down the oviduct. It locally changes the pattern of vascularization and induces the formation of secretory cells. Our studies imply that the oviductal epithelium is able to select vital oocytes. The early embryo is able to induce the formation of secretory cells, modify vascularization, and downregulate speed of transport, thus creating the prerequisite for the first embryo-maternal communication in the oviduct.

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.

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.

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.

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.

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.

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.