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PubMed2003

Medial preoptic area dopaminergic responses to female pheromones develop during puberty in the male Syrian hamster.

Chemosensory cues from receptive females do not elicit similar reactions before and after puberty in male hamsters. While pheromones facilitate a complex display of reproductive behavior in adults, prepubertal males do not engage in these same behaviors. Dopamine (DA) released from the medial preoptic area (MPOA) in response to a receptive female or her odors is an important component of the neural events underlying adult male rat sexual behavior. The current experiment investigated whether increased dopaminergic activity occurs in the adult male hamster MPOA in response to female pheromones, and if so, whether this response is absent in prepubertal males, which do not mate. Sexually nai;ve prepubertal and adult male hamsters were exposed to cotton swabs with or without pheromone from an estrous female for 0, 5, 15, or 25 min, after which brains were collected and frozen on dry ice. The MPOA was micropunched from frozen coronal sections (500 microm), and concentrations of DA and its primary metabolite DOPAC were determined by high-performance liquid chromatography-electrochemical detection. DOPAC was used as an index of dopaminergic activity. DOPAC levels significantly increased in adults after 15 min exposure to pheromone. In contrast, MPOA DOPAC concentrations did not increase in prepubertal males exposed to pheromone. These data demonstrate that the neural processing of sexually relevant chemosensory stimuli matures during puberty. The absence of a DA response to female pheromones prior to puberty may contribute to the inability of prepubertal males to display reproductive behavior.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1986

Altered endocrine and behavioral responses with reproductive aging in the male Japanese quail.

Experiments were conducted to further characterize the age-related decline in reproductive capability previously described in the male Japanese quail. Behavioral testing of a large number of males in several age groups confirmed earlier results that showed a significant reduction in courtship and mating behavior by 80 weeks of age. Intact males, 78 weeks of age, that showed no reproductive behavior were given Silastic implants containing testosterone. This treatment restored behavior in 80% of the males. Gonadal regression induced by exposure to shortened photoperiod followed by transfer to a stimulatory photoperiod did not successfully restore the endocrine or behavioral components of reproduction. Males of two age groups, 42 and 208 weeks of age, were categorized as behaviorally active or inactive and then castrated. Eight weeks later they were given implants containing testosterone. Older males required longer exposure time to the exogenous steroid and in some cases, an additional implant to restore mating behavior as compared to younger males. The presence or absence of behavioral activity prior to castration did not affect the length of time required for restoration of behavior. Challenge with exogenous luteinizing hormone-releasing hormone revealed that there was reduced release of luteinizing hormone in aged, behaviorally inactive males as compared to young males. Results of these experiments in addition to previous data give evidence that age-related changes occur at the level of the hypothalamus and pituitary as well as at the level of the gonads.

Aging↗
PubMed1998

Evidence for estrogen receptor in cell nuclei and axon terminals within the lateral habenula of the rat: regulation during pregnancy.

The habenular complex is involved in several estrogen-dependent reproductive behaviors in female rats, namely, sexual behavior, maternal behavior, and postpartum sexual behavior. Although it is known that estrogen acts in other brain regions to mediate these behaviors, it is not known whether estrogen may also act directly on the habenular complex. To address this possibility, we examined this region for the presence of estrogen receptor (ER). This analysis was carried out in separate experiments by using in situ hybridization, immunocytochemistry at the light and electron microscopic levels, and steroid autoradiography. Neurons within the lateral habenula (LHb), but not the medial habenula, express ER mRNA, contain ER immunoreactivity (ER-ir) in their nuclei, and concentrate radiolabelled estradiol, providing strong evidence for the presence of functional ER in the lateral habenula. There were also ER-ir containing punctate fibers within the LHb, which, at the electron microscopic level, in part, proved to be axons and presynaptic axonal terminals. Both the level of ER-ir in cell nuclei and the density of ER-ir fibers within the LHb were regulated during the course of pregnancy and the postpartum period, suggesting that the sensitivity of the LHb to estrogen may be altered during this time. Taken together, these results demonstrate that the LHb is likely a more estrogen-sensitive region than was previously considered, and they suggest alternative mechanisms of action for ER. ER within the LHb may play a critical role in the involvement of the LHb in estrogen-dependent female reproductive behaviors.

Animals↗
PubMedDate not supplied

Preproenkephalin mRNA levels are regulated by acute stress and estrogen stimulation.

Enkephalins facilitate female reproductive behavior. Within the limbic system and hypothalamus, estrogen induced the expression of preproenkephalin (PPE) mRNA. Estrogen injection caused a biphasic increase in the PPE mRNA levels within the ventromedial hypothalamic nucleus and posterodorsal medial amygdala. The first peak of PPE mRNA levels occurred within an hour, and the second 24 to 48 h after subcutaneous injection of estrogen. The present studies indicated that the rapid first peak of PPE mRNA expression was stress induced, whereas the second peak was estrogen induced. In the posterodorsal medial amygdala but not in the ventromedial hypothalamic nucleus, the antiestrogen, tamoxifen, did not inhibit the first peak, but blocked the second peak of PPE mRNA expression. Subcutaneous oil injection induced a 1-h peak of PPE mRNA levels but not a 24-h peak. Peak levels of plasma corticosterone were coincident with peak PPE mRNA levels. Adrenalectomy plus a constant, low level of corticosterone eliminated the injection-induced increase of corticosterone levels and the subsequent increase in PPE mRNA expression in the ventromedial hypothalamic nucleus and posterodorsal medial amygdala. The present results indicate that both stress steroids and estrogen positively regulate PPE mRNA levels in the ventromedial hypothalamic nucleus and posterodorsal medial amygdala. These results are consistent with the hypothesis that acute, mild stress may contribute to the activation of circuits that facilitate reproductive behavior in the female.

Administration, Oral↗
PubMed1988

Estrous cycle variations in levels of cholecystokinin immunoreactivity within cells of three interconnected sexually dimorphic forebrain nuclei. Evidence for a regulatory role for estrogen.

The central part of the medial preoptic nucleus (MPNc), the encapsulated part of the bed nucleus of the stria terminalis (BSTe), and the posterodorsal part of the medial nucleus of the amygdala (MeAp) are all though to be involved in the neural control of female reproductive behavior, as well as other neuroendocrine mechanisms. Although the developmental importance of gonadal steroids during the perinatal period on these sexual dimorphisms is well known, an understanding of possible activational effects on these cell groups of circulating gonadal steroids in the adult is less clear. In the present study we evaluated the number of cholecystokinin (CCK)-immunoreactive cells present within MPNc, BSTe, and MeAp of regularly cycling female rats over the estrous cycle. In addition, the effects of ovariectomy and estrogen replacement on CCK staining were also examined. The number of CCK-immunoreactive cells within each cell group varied over the estrous cycle with the fewest cells present in animals sacrificed while in diestrus. Proestrous female rats showed a greater number of cells within each nucleus, while intermediate numbers were found for animals in estrus. These changes appear to be due, at least in part, to changes in levels of circulating estrogen, since subcutaneous implants of estradiol prevented the decline in the number of CCK-stained cells within MPNC, BSTe, and MeAp that was seen in untreated, ovariectomized female rats. Thus, the present findings support the hypothesis that levels of CCK within cells of these three sexually dimorphic cell groups are regulated by circulating gonadal steroids within a physiologically relevant time frame and may possibly contribute to the activation of female reproductive behavior as well as other neuroendocrine functions.

Amygdala↗
PubMed1998

The foam production system of the male Japanese quail: characterization of structure and function.

The research described here characterizes a unique neuromuscular system involved in reproductive behavior--the foam production system of the male Japanese quail (Coturnix japonica). Male quail produce a large amount of foam that is transferred to the female during copulation, enhancing male fertilization success. The source is the foam gland complex, a large sexually dimorphic, androgen sensitive, external protuberance of the dorsal cloaca, consisting of glandular units interdigitated with striated muscle fibers of the sphincter cloacae muscle (mSC). Electromyographic (EMG) analysis of mSC activity in freely moving males interacting with females revealed different characteristics of the EMG signal during copulation, voiding of excreta, and other mSC movement. The amount of mSC activity and also the amount of foam produced were greatly increased by the presence of a female behind a screen. Denervation of mSC eliminated normal mSC movement and also abolished foam production, confirming that mSC activity is the mechanism for foam production. The spinal cord locations of the motoneurons innervating the major cloacal muscles, including mSC, were determined by injecting cholera-toxin conjugated horseradish peroxidase into each muscle. Labelled somata with multiple primary dendrites were located in Area IX of the lateral motor column of synsacral segments 7, 8, or 9 or 8, 9, and 10. The motoneurons serving mSC were intermingled with those projecting to the other cloacal muscles, but there were differences in the rostralcaudal placement of these neural populations. Thus mSC activity is an integral part of the male's reproductive behavior, mSC activity can be socially stimulated, and mSC activity occurring in anticipation of copulation is likely to be functionally significant. Continued investigation of this highly accessible system has the potential to shed light on the mechanisms by which complex motor acts are produced and hormonally regulated.

Animals↗
PubMed2001

Distribution analysis of the two chicken estrogen receptor-alpha isoforms and their transcripts in the hypothalamus and anterior pituitary gland.

Estrogen plays a key role in the control of reproductive behavior and in the regulation of the neuroendocrine system. To elucidate the mechanisms by which it controls these functions it is important to understand how estrogenic effects are mediated. We have investigated the distribution of the two isoforms of the chicken estrogen receptor alpha (cER-alpha) protein; the previously characterized cER-alpha 66 and a new N-terminal truncated isoform, cER-alpha 61. Immunolocalization demonstrated the presence of cER-alpha 66 protein in hypothalamic areas, principally the nucleus septalis lateralis, bed nucleus striae terminalis medialis, nucleus preopticus medialis, and nucleus infundibuli hypothalami, and in the anterior pituitary gland. When the distribution of ER-alpha immunoreactive cells was compared using the antibodies H 222 (directed against the hormone-binding domain) and ER 221 (directed against the 21-amino acid N-terminus), no apparent differences could be detected. Because this immunocytochemical approach was not able to distinguish whether full-length cER-alpha 66 is the only isoform observed in the ER-positive regions or whether both cER-alpha receptor isoforms are present, SI nuclease assays were performed to compare the relative abundance in these regions of the two distinct classes of cER-alpha mRNA variants (A1-D and A2), which encode the cER-alpha 66 and cER-alpha 61 protein isoforms, respectively. In cockerels and hens, both variants of cER-alpha mRNA are expressed in the anterior pituitary gland and basal hypothalamus with a dominance of the mRNA that encodes cER-alpha 66, whereas the mRNA that encodes cER-alpha 61 was not detectable in the anterior hypothalamus. Therefore, because both receptor isoforms differ in their ability to modulate estrogen target gene expression in a promoter and cell type-specific manner, these differences may mediate the pleiotropic actions of estrogen in reproductive behavior and neuroendocrine functions.

Animals↗
PubMed1997

Interactions of estrogen- and thyroid hormone receptors on a progesterone receptor estrogen response element (ERE) sequence: a comparison with the vitellogenin A2 consensus ERE.

The identification of hormone response elements in the promoter regions of hormonally regulated genes has revealed a striking similarity between the half-site of the estrogen-response element (ERE) and a consensus sequence constituting the thyroid hormone-response element. Because of the potential for thyroid hormone (T3) to affect estrogen (E)- and progesterone-dependent female reproductive behavior via EREs, we have begun to investigate the activity of an ERE identified in the progesterone receptor (PR) proximal promoter and its interactions with the estrogen receptor (ER) and thyroid hormone receptors (TR). In addition, we have compared ER and TR interactions on the PR ERE construct with that of the vitellogenin A2 (vit A2) consensus ERE. Electrophoretic mobility shift assays demonstrated that TR binds to the PR ERE as well as to the consensus ERE sequence in vitro. Further, these two EREs were differentially regulated by T3 in the presence of TR. T3 in the presence of TR alpha increased transcription from a PR ERE construct approximately 5-fold and had no inhibitory effect on E induction. Similarly, T3 also activated a beta-galactosidase reporter construct containing PR promoter sequences spanning -1400 to +700. In addition, the TR isoforms beta1 and beta2 also stimulated transcription from the PR ERE construct by 5- to 6-fold. A TR alpha mutant lacking the ability to bind AGGTCA sequences in vitro failed to activate transcription from the PR ERE construct, demonstrating dependence on DNA binding. In contrast to its actions on the PR ERE construct, TR alpha did not activate transcription from the vit A2 consensus ERE but rather attenuated E-mediated transcriptional activation. Attenuation from the vit A2 consensus ERE is not necessarily dependent on DNA binding as the TR alpha DNA binding mutant was still able to inhibit E-dependent transactivation. In contrast to TR alpha, the isoforms TRbeta1 and TRbeta2 failed to inhibit E-induced activation from the vit A2 consensus ERE. These results demonstrate that the PR ERE construct differs from the vit A2 consensus ERE in its ability to respond to TRs and that divergent pathways exist for activation and inhibition by TR. Since ERs, PRs, and TRs are all present in hypothalamic neurons, these findings may be significant for endocrine integration, which is important for reproductive behavior.

Animals↗
PubMed1998

The acute toxicity of lindane to hyalella azteca and the development of a sublethal bioassay based on precopulatory guarding behavior

Acute and sublethal toxicity of the organochlorine insecticide lindane to the amphipod crustacean Hyalella azteca was investigated. Acute experiments were conducted for a maximum test exposure period of 240 h with adult and neonate H. azteca. Median lethal concentrations (LC50s) determined for adult Hyalella included a 48-h LC50 of 47.6 &mgr;g/L and 240-h LC50 of 26.9 &mgr;g/L. For neonate H. azteca 24-, 48-, and 240-h LC50s were 29.5, 14.8, and 9.8 &mgr;g lindane/L, respectively. Neonate H. azteca were approximately three times more sensitive than adults. Two sublethal toxicity bioassays were developed based on the direct and indirect disruption of the precopulatory or mate guarding behavior of Hyalella. This reproductive behavior is readily quantifiable and of ecological significance as it is a vital component of the mating success of the species. The direct disruption bioassay examined the separation of precopulatory pairs maintained in control water and a range of lindane concentrations during a 24-h exposure period. Median separation times (ST50s) were determined and the LOEC was 24.4 &mgr;g lindane/L. The indirect disruption bioassay consisted of a test exposure period of just 4 h after which an invertebrate anesthetic solution was administered to induce separation of precopulatory pairs. The LOEC was 17.3 &mgr;g lindane/L, suggesting that the indirect precopulatory separation bioassay was comparable to the 24-h direct separation study. Both bioassays are rapid, relatively simple to perform, and have yielded effect concentrations that correspond with LC50 values determined using adult and neonate H. azteca life stages over more prolonged lindane exposures. Following some modification, these behavioral bioassays may be suitable for use in the hazard evaluation of sediments and for deployment as in situ toxicity tests.

Journal Article↗
PubMed2001

Measures of menopausal status in relation to demographic, reproductive, and behavioral characteristics in a population-based study of women aged 35-49 years.

The purpose of this cross-sectional analysis of women aged 35-49 years from the Third National Health and Nutrition Examination Survey, conducted between 1988 and 1994, was to assess associations with menopausal status based either on menstrual cycle patterns or on elevated (>20 IU/liter) follicle-stimulating hormone. Menstrual cycle-based menopausal status was defined for women who had not had surgical menopause by months since the last period (<2, 2-12, and >12 months for pre-, peri-, and postmenopause, respectively). Logistic regression was adjusted for age, smoking, and unilateral oophorectomy. Higher body mass index (> or =30 kg/m(2) compared with < 25.0 kg/m(2)) was associated with a lower likelihood of elevated follicle-stimulating hormone (odds ratio (OR)=0.6, 95% confidence interval (CI): 0.4, 0.9) but this association was not seen with the menstrual measure of menopause. Exercise (three or more times per week) was associated with a lower likelihood of being postmenopausal on the basis of menstrual (OR = 0.3, 95% CI: 0.2, 0.7) and hormonal (OR = 0.6, 95% CI: 0.4, 1.0) measures. Alcohol use also tended to be associated with postmenopausal status by either measure, but not significantly so. There was little evidence of associations with ethnicity, education, age at menarche, number of livebirths, and oral contraceptive use. Menstrual-based definitions of menopause can be misclassified for women with menstrual irregularity. This might explain why obese women were classified menstrually as menopausal while remaining hormonally premenopausal.

Adult↗
PubMed1975

Birth trajectory under changing fertility conditions.

An initially stable population of women is assumed to shift its reproductive behavior to a different level either abruptly or in a prescribed gradual fashion. A closed-form solution which is exact up to about 30 years after the reproductive adjustment is found for the resulting birth trajectory. Exact expressions are also found for the long-time asymptotic behavior of both the birth trajectory and the total population size when the shift in reproductive behavior is to bare replacement level. Accurate approximations to these asymptotic results are then derived and used to illustrate why a growing population continues to grow even after shifting to bare replacement reproductive behavior.

Age Factors↗
PubMed1999

Genomic and membrane actions of progesterone: implications for reproductive physiology and behavior.

Progesterone, produced by the ovaries and adrenal glands, regulates reproductive behavior and the surge of luteinizing hormone which precedes ovulation by acting on neurons located in different parts of the hypothalamus. The study of the activation of these reproductive functions in female rats has allowed to explore the different mechanisms of progesterone action in the brain. It has allowed to demonstrate that new actions of the hormone, which have been observed in particular in vitro systems, are also operational in vivo, and may thus be biologically relevant. This mainly concerns the direct actions of progesterone on receptors of neurotransmitters such as oxytocin and GABA. Activation of the progesterone receptor in the absence of ligand by phosphorylation may also play a role.

Animals↗
PubMed1999

THE EVOLUTION OF ASEXUAL FUNGI: Reproduction, Speciation and Classification.

Phylogenetic and population genetic methods that compare nucleic acid variation are being used to identify species and populations of pathogenic fungi and determine how they reproduce in nature. These studies show that asexual or sexual reproductive morphology does not necessarily correlate with clonal or recombining reproductive behavior, and that fungi with all types of reproductive morphologies and behaviors can be accommodated by a phylogenetic species concept. Although approximately one fifth of described fungi have been thought to be asexual and clonal, recent studies have shown that they are also recombining. Whether a particular pathogen reproduces clonally or by recombination depends on factors relating to its biology and its distribution in space and time. Knowing the identity of species and populations and their reproductive modes, while taking a broad view of pathogen behavior in space and time, should enhance the ability of pathologists to control pathogens and even predict their behavior.

Journal Article↗
PubMed1986

Seasonality of adult male Japanese macaques (Macaca fuscata): androgens and behavior in a confined troop.

Seasonal variations in levels of serum testosterone, dihydrotestosterone (DHT), reproductive behavior, and social behavior were investigated in 12 adult males (5 to 20+ years of age) of the Oregon troop of Japanese macaques (Macaca fuscata). Blood samples were collected at 2- to 4-month intervals, and behaviors were monitored twice weekly over a 15-month period. Significant seasonal variations in levels of testosterone and DHT, and in frequencies of mount series, ejaculations, number of female partners, displays, courtship, and aggression were observed. Seasonal variations in reproductive and social behaviors did not correlate with seasonal variations in androgen levels because seasonal increases in these behaviors followed seasonal increases in the androgens with a 1- to 2-month delay. However, significant correlations between increased androgen levels and the onset of mating activity occur when mean monthly frequencies of mount series are shifted 1 to 2 months earlier to coincide with the rise in serum androgen levels. The frequency of adult male play and male-male mounting increased significantly when androgen levels were low. We suggest that photoperiod changes may function as a proximate cue in male Japanese macaques which induces a state of biological readiness for mating, and the behavioral consequences (i.e., mating) are then dependent upon the presence of receptive females.

Agonistic Behavior↗