Relation of neuroendocrine function to reproductive decline during aging in the female rat

Calorie restriction inhibits ovarian follicle development and follicle loss through activating SIRT1 signaling in mice

BACKGROUND

Silent information regulator 2 related enzyme 1 (SIRT1) is one of the key factors in the mechanism of calorie restriction (CR) extending lifespan of animals. The aim of the study is to investigate if CR prolongs ovarian lifespan in mice through activating SIRT1 signaling.

METHODS

In the present study, 21 female C57BL/6 mice were divided into three groups: the control (n = 7), CR (n = 7), and SRT1720 (n = 7) groups. After the 26-week treatment, the number of ovarian follicles at each stage was counted, and Western blot was performed.

RESULTS

The number of surviving follicles in ovaries of the SRT1720 group was less than that of the CR group but more than that of the normal control (NC) group. The number of atretic follicles in the ovaries of the SRT1720 group was similar to that of the CR group but less than that of the NC group. The number of primordial follicles in the ovaries of the SRT1720 group was less than that of the CR group but more than that of the NC group. The numbers of primary follicles, secondary follicles, antral follicles, and corpora lutea in the SRT1720 group were similar to those in the CR group. Western blot analysis showed that the expression of SIRT1, SIRT6, FOXO3a, and NRF1 proteins was upregulated, and p53 was downregulated in both the CR group and the SRT1720 group compared to the control group.

CONCLUSIONS

Our results indicate that CR inhibits the activation of primordial follicles and development of follicles at different stages, thus preserving the reserve of follicle pool (at least partly) through activating SIRT1 signaling.

SIRT1 activator (SRT1720) improves the follicle reserve and prolongs the ovarian lifespan of diet-induced obesity in female mice via activating SIRT1 and suppressing mTOR signaling

BACKGROUND

The prevalence of obesity is increasing worldwide and significantly affects fertility and reproduction in both men and women. Our recent study has shown that excess body fat accelerates ovarian follicle development and follicle loss in rats. The aim of the present study is to explore the effect of SIRT1 activator SRT1720 on the reserve of ovarian follicle pool and ovarian lifespan of obese mice and the underlying mechanism associated with SIRT1 and mTOR signaling.

METHODS

Adult female Kunming mice (n = 36) were randomly divided into three groups: the normal control (NC) group (n = 8), the caloric restriction (CR) group (fed 70% food of the NC group, n = 8) and the high-fat diet (HF) group (fed a rodent chow containing 20% fat, n = 20). After 4 months, the HF mice were further randomly divided into three groups: the control high-fat diet (CHF, n = 8) group (treated every day with an intraperitoneal injection of vehicle), the SRT1720 (SRT, n = 6) group (treated every other day with an intraperitoneal injection of SRT1720 (50 mg/kg)), the SRT1720 and nicotinamide (NAM, n = 6) group (treated every other day with an intraperitoneal injection of SRT1720 (50 mg/kg) and every day with an intraperitoneal injection of nicotinamide (100 mg/kg)). After 6 weeks of treatment, ovaries were harvested for histological and Western blotting analyses.

RESULTS

The body weight, ovary weight and visceral fat in the SRT group were significantly lower than those in the CHF group at the end of treatment. Histological analysis showed that the SRT mice had significantly greater number and percentage of primordial follicles, but lower number and percentage of corpora lutea and atretic follicles than the CHF mice and NAM mice. Western blot analysis demonstrated that the levels of SIRT1, SIRT6, FOXO3a and NRF-1 protein expression significantly increased in the ovaries of SRT mice, whereas those of mTORC1, p-mTOR, p-p70S6K, NFκB and p53 decreased compared to the CHF and NAM mice.

CONCLUSIONS

Our study suggests that SRT1720 may improve the follicle pool reserve in HF diet-induced obese female mice via activating SIRT1 signaling and suppressing mTOR signaling, thus extending the ovarian lifespan.

Effect of age and gender on recovery after stroke in rats treated with bone marrow mononuclear cells

Stroke is a disease of the elderly. However, most of the preclinical studies about the treatment of stroke with bone marrow-derived cells have used young animals. Here, it was assessed whether the sensorimotor recovery promoted by the treatment of the brain ischemia with the bone marrow mononuclear cells (BMMCs) is influenced by age and/or gender. Unilateral cortical ischemia by thermocoagulation was made in the primary motor and sensorimotor cortices in young and middle-aged rats of both genders. Twenty four hours after ischemia, animals received intravenous injection of BMMCs or vehicle. Each combination of age and gender received BMMCs from donor with the same combination. Survival rate and ischemic lesion size were quantified. Sensorimotor recovery was evaluated by the cylinder and adhesive tests. The results showed that the treatment with BMMCs resulted in sensorimotor recovery of both young and middle-aged ischemic rats. No important effect of gender was found, but age was a significant factor. Middle-aged animals had increased mortality and lesion sizes. In the adhesive test, middle-aged animals had lower BMMCs-induced sensorimotor recovery. The results suggest that the treatment of stroke with the BMMCs should be beneficial for males and females in the elderly.

The menopause and aging, a comparative perspective

The neuroendocrinology of menopause is reviewed from a comparative perspective, with emphasis on laboratory rodent models. These changes are compared by the 2011 STRAW criteria (Stages of Reproductive Aging Workshop). Ovarian cell loss begins prenatally in all mammals studied, with exponential depletion of primary follicles and oocytes in association with loss of fecundity by midlife. Rodents and humans also share progressively increasing irregularity in ovulatory cycles and increasing fetal aneuploidy as oocyte depletion become imminent. Hypothalamic impairments of the estrogen-induced surge of pituitary gonadotrophins (luteinizing hormone, LH; follicle stimulating hormone, FSH) are prominent in middle-aged rodents, but sporadic in peri-menopausal women. In aging rodents, hypothalamic impairments of the LH surge have been experimentally associated with prolonged phases of sustained estradiol (E2) and very low progesterone (P4) ('unopposed estradiol'). Although peri-menopausal women also show hyper-estrogenic cycles, there is no indication for irreversible hypothalamic desensitization by E2. Ongoing cognitive assessments in clinical trials of estrogen therapy with and without P4 or other progestins may further inform about possible persisting effects of unopposed estrogens.This article is part of a Special Issue entitled 'Menopause'.

Obesity accelerates ovarian follicle development and follicle loss in rats

OBJECTIVE

Studies have shown that excess body fat negatively affects reproductive functions in females. However, whether obesity affects the ovarian follicle development and ovarian lifespan and the underlying mechanism has not been well elucidated. The aim of the present study was to investigate the association between obesity and ovarian follicle development.

METHODS

Adult female Sprague-Dawley rats (n = 36) were randomly divided into three groups: the normal control (NC) group, the caloric restriction (CR) group (fed 70% food of the NC group) and the high-fat diet (HF) group. They were maintained on these regimens for 18 weeks.

RESULTS

The body weight, ovary weight and visceral fat in the HF group were significantly higher than those in the NC group and the CR group at the end of treatment. Histological analysis showed that the HF rats had significantly less number and percentage of primordial follicles, but greater number and percentage of developing and atretic follicles than the NC rats and CR rats. Western blot analysis demonstrated that the level of mTORC1 and p-S6K1 proteins significantly increased in the ovaries of HF rats, whereas that of SIRT1, SIRT6, FOXO3a and NRF-1 decreased compared to the NC rats. In contrast, the expression of mTORC1 and p-S6K1 dramatically declined, while that of SIRT1, SIRT6, FOXO3a and NRF1 increased in the ovaries of CR rats.

CONCLUSIONS

Our study suggests that the HF diet induced obesity may accelerate the ovarian follicle development and rate of follicle loss through activating mTOR and suppressing SIRT1 signaling, thus leading to POF, and that CR may inhibit the activation of primordial follicles, follicular development and loss, thus extending the ovarian lifespan through suppressing mTOR and activating SIRT1 signaling.

Aging-related changes in RP3V kisspeptin neurons predate the reduced activation of GnRH neurons during the early reproductive decline in female mice

Kisspeptin neurons in the rostral periventricular area of the third ventricle (RP3V) play a key role in relaying the positive feedback effects of estradiol that activate gonadotropin-releasing hormone (GnRH) neurons and drive a surge in the GnRH/luteinizing hormone (LH) level. However, the precise role of kisspeptin neurons during female reproductive senescence remains unclear. Focusing on middle-aged intact female mice with irregular estrous cycles, we found a parallel decline in c-Fos-positive kisspeptin neurons and c-Fos-positive GnRH neurons at the time of the GnRH/LH surge. Furthermore, in kisspeptin neurons, the expression of estrogen receptor α (ERα), but not progesterone receptor (PR), decreased with age. Interestingly, some kisspeptin neurons in the RP3V, but none of the GnRH neurons in the rostral preoptic area (rPOA), had a characteristic cellular senescence in middle-aged mice and old mice. These data suggest that, among the groups of neurons involved in reproductive control, the kisspeptin neurons in the RP3V are likely among the earliest to undergo aging processes and thus participate in initiating the early reproductive decline.

Increased vesicular γ-GABA transporter and decreased phosphorylation of synapsin I in the rostral preoptic area is associated with decreased gonadotrophin-releasing hormone and c-Fos coexpression in middle-aged female mice

Hypothalamic glutamate (Glu) and γ-GABA neurotransmission are involved in the ovarian hormone-induced gonadotrophin-releasing hormone (GnRH)/luteinising hormone (LH) surge in rodents. Studies have shown that reduced Glu and increased γ-GABA in the rostral preoptic area (rPOA) of the hypothalamus, where most activated GnRH neurones are located, play a key role in decreasing the reproductive function of female rats. However, the mechanism underlying the altered balance of these neurotransmitters is poorly understood. In the present study, we observed a decline in the function of GnRH neurones in the rPOA at the time of the GnRH/LH surge in middle-aged intact female mice with regular oestrous cycles. In young mice, there is an increase of vesicular Glu transporter 2 on the pro-oestrus afternoon, which is not observed in middle-aged mice. By contrast, vesicular γ-GABA transporter levels in young mice decrease at the time of the LH surge, whereas they increase in middle-aged mice. Of note, we found that, in middle-aged mice at the time of the GnRH/LH surge, the phosphorylation of synapsin I at Ser603 and Ca(2+) /calmodulin-dependent kinase IIα was significantly lower than in young mice. These data suggest that, in middle-aged mice, higher levels of presynaptic stores of GABA, a lack of increase of Glu and a decreased ability of synaptic vesicle mobilisation could account for the imbalance of Glu and GABA in the rPOA, which decreases the activation of GnRH neurones.

The Neurosteroid Progesterone Underlies Estrogen Positive Feedback of the LH Surge

Our understanding the steroid regulation of neural function has rapidly evolved in the past decades. Not long ago the prevailing thoughts were that peripheral steroid hormones carried information to the brain which passively responded to these steroids. These steroid actions were slow, taking hours to days to be realized because they regulated gene expression. Over the past three decades, discoveries of new steroid receptors, rapid membrane-initiated signaling mechanisms, and de novo neurosteroidogenesis have shed new light on the complexity of steroids actions within the nervous system. Sexual differentiation of the brain during development occurs predominately through timed steroid-mediated expression of proteins and long term epigenetic modifications. In contrast across the estrous cycle, estradiol release from developing ovarian follicles initially increases slowly and then at proestrus increases rapidly. This pattern of estradiol release acts through both classical genomic mechanisms and rapid membrane-initiated signaling in the brain to coordinate reproductive behavior and physiology. This review focuses on recently discovered estrogen receptor-α membrane signaling mechanisms that estradiol utilizes during estrogen positive feedback to stimulate de novo progesterone synthesis within the hypothalamus to trigger the luteinizing hormone (LH) surge important for ovulation and estrous cyclicity. The activation of these signaling pathways appears to be coordinated by the rising and waning of estradiol throughout the estrous cycle and integral to the negative and positive feedback mechanisms of estradiol. This differential responsiveness is part of the timing mechanism triggering the LH surge.

Formalin-induced nociceptive behavior and c-Fos expression in middle-aged female rats

The impact of the estrous cycle on the nociceptive response in middle-aged female rats was assessed using the formalin test and c-Fos immunoreactivity as a marker of neural activation. Young (2-month-old) and middle-aged (11-month-old) rats were examined, dividing the middle-aged rats into two groups based on their estrous cycle: regular 4-day estrous cycle and irregular estrous cycle. The right hind paw was subcutaneously injected with 50microl of 2% formalin or saline as a control. Behavioral changes were observed for 1h. Cycling rats were used during proestrus. Middle-aged female rats had a significantly higher score for nociceptive behavior compared to young rats, irrespective of estrous cyclicity, which suggests that aging, not the ability to maintain estrous cyclicity, causes hypersensitivity to the formalin injection. Immunohistochemical analysis found that the brain response to formalin injection was also more sensitive in middle-aged rats than young rats; a significant increase in the number of c-Fos immunoreactive cells was found in the ventral portion of the lateral septum of middle-aged rats injected with formalin compared to young and middle-aged rats injected with saline, irrespective of estrous cyclicity. Based on these results, we conclude that the sensitivity to painful stimuli in middle-aged female rats, which are in a neuroendocrine state similar to pre- and peri-menopausal women, is associated with age and not affected by reproductive ability.

Proximate mechanisms driving circadian control of neuroendocrine function: Lessons from the young and old

Circadian rhythms impact a variety of behavioral and physiological functions contributing to longevity and successful reproduction. In their natural environments, individuals of a species are faced with a multitude of challenges and the coordination of internal processes and behavior with external pressures has been hypothesized to be an important target of natural selection. Several lines of evidence from cyanobacteria, Drosophila, and plants provide strong support for an important role of the circadian clock in survival and reproductive success. Similarly in mammals, disruptions in circadian function markedly impact reproduction and lifespan. The present review discusses research outlining the proximate and ultimate mechanisms responsible for the central and peripheral control of the reproductive axis. Because precise temporal coordination of the endocrine system is particularly crucial for reproduction by females, the present overview focuses on the role of circadian timing in this sex.

The role of the brain in female reproductive aging

In middle-aged women, follicular depletion is a critical factor mediating the menopausal transition; however, all levels of the hypothalamic-pituitary-gonadal (HPG) axis contribute to the age-related decline in reproductive function. To help elucidate the complex interactions between the ovary and brain during middle-age that lead to the onset of the menopause, we utilize animal models which share striking similarities in reproductive physiology. Our results show that during middle-age, prior to any overt irregularities in estrous cyclicity, the ability of 17beta-estradiol (E(2)) to modulate the cascade of neurochemical events required for preovulatory gonadotropin-releasing hormone (GnRH) release and a luteinizing hormone (LH) surge is diminished. Middle-aged female rats experience a delay in and an attenuation of LH release in response to E(2). Additionally, although we do not observe a decrease in GnRH neuron number until a very advanced age, E(2)-mediated GnRH neuronal activation declines during the earliest stages of age-related reproductive decline. Numerous hypothalamic neuropeptides and neurochemical stimulatory inputs (i.e., glutamate, norepinephrine (NE), and vasoactive intestinal peptide (VIP)) that drive the E(2)-mediated GnRH/LH surge appear to dampen with age or lack the precise temporal coordination required for a specific pattern of GnRH secretion, while inhibitory signals such as gamma-aminobutyric acid (GABA) and opioid peptides remain unchanged or elevated during the afternoon of proestrus. These changes, occurring at the level of the hypothalamus, lead to irregular estrous cycles and, ultimately, the cessation of reproductive function. Taken together, our studies indicate that the hypothalamus is an important contributor to age-related female reproductive decline.

Increasing blunting of inhibin responses to dynamic ovarian challenge is associated with reproductive aging in the rat

Reproductive aging results in declines in female fertility and in slight declines in baseline serum inhibins in humans. The authors tested the hypothesis that exogenous ovarian stimulation as a noninvasive dynamic test, by amplifying inhibin levels, can define more accurately than baseline serum inhibin levels the ovarian age of female rats. Female rats--young (immature, 26 days old), adult (65-75 days old), and reproductively aged (8- to 9-month-old retired breeders)--were administered pregnant mare's serum gonadotropin to stimulate the ovaries and the serum inhibin A and inhibin B, and ovarian inhibins were measured. The young and adult females had at least a 4- to 10-fold increase in serum inhibin A and inhibin B after ovarian stimulation, but the reproductively aged females did not. Adult female serum inhibin measurements after stimulation at every stage of the estrous cycle revealed a consistent 4- to 5-fold increase in all stages, whereas the reproductively aged females did not. Western blot analyses of ovarian lysates were consistent with the serum inhibin level results and revealed that ovarian inhibin alpha, inhibin beta A, and inhibin beta B subunit levels in adult ovaries were elevated after ovarian stimulation but not in the reproductively aged ovaries. The data presented here demonstrate that young, adult, and reproductively aged female inhibin responses after exogenous ovarian stimulation were different. Inhibin measurement in serum after ovarian challenge in rats, therefore, is a noninvasive method that could be used to dissect ovarian function in aging in more detail.

Molecular endocrinology and physiology of the aging central nervous system

Aging is associated with a progressive decline in physical and cognitive functions. The impact of age-dependent endocrine changes regulated by the central nervous system on the dynamics of neuronal behavior, neurodegeneration, cognition, biological rhythms, sexual behavior, and metabolism are reviewed. We also briefly review how functional deficits associated with increases in glucocorticoids and cytokines and declining production of sex steroids, GH, and IGF are likely exacerbated by age-dependent molecular misreading and alterations in components of signal transduction pathways and transcription factors.

Effects of combined estrogen and progesterone on brain infarction in reproductively senescent female rats

Recent data from the Women's Health Initiative have highlighted many fundamental issues about the utility and safety of long-term estrogen use in women. Current hormone replacement therapy for postmenopausal women incorporates progestin with estrogen, but it is uncertain if combined therapy provides major cerebrovascular risks or benefits to these women. No experimental animal stroke studies have examined combined hormone administration. The authors tested the hypothesis that combined hormone treatment reduces ischemic injury in middle-aged female rat brain. Reproductively senescent female rats underwent 2-hour middle cerebral artery occlusion (MCAO) followed by 22 hours reperfusion. Estrogen implants were placed subcutaneously at least 7 days before MCAO, and progesterone intraperitoneal injections were given 30 minutes before MCAO, at initiation, and at 6 hours of reperfusion. Rats received no hormone, a 25-microg estrogen implant, a 25-microg estrogen implant plus 5 mg/kg intraperitoneal progesterone, or 5 mg/kg intraperitoneal progesterone. Cortical, caudoputamen, and total infarct volumes were assessed by 2,3,5-triphenyltetrazolium chloride staining and digital image analysis at 22 hours reperfusion. Cortical and total infarct volumes, except in the acute progesterone-treated group, were significantly attenuated in all estrogen-alone and combined hormone-treated groups. There were no significant differences in caudoputamen infarct volumes in all hormone-treated groups as compared with untreated rats. These data have potential clinical implications relative to stroke for postmenopausal women taking combined hormone replacement therapy.

Estrogen modulates synapticN-methyl-D-aspartate receptor subunit distribution in the aged hippocampus

Estrogen interacts with N-methyl-D-aspartate (NMDA) receptors to regulate multiple aspects of morphological and functional plasticity. In hippocampus, estrogen increases both dendritic spine density and synapse number, and NMDA antagonists block these effects. Thus, estrogen-mediated hippocampal plasticity may be of particular importance in the context of age-related changes in endocrine status and cognitive performance. NR1 levels per synapse are increased in CA1 by estrogen in aged rats but not young rats, although no information is available on estrogen-induced synaptic alterations in other NMDA receptor subunits that might impact function. Therefore, the present study was designed to investigate the effect of estrogen on the synaptic and subsynaptic distributions of the NMDA receptor subunits, NR2A and NR2B in CA1 pyramidal cells, within the context of aging. Our results demonstrated that the overall synaptic levels of NR2A and NR2B are similar in young and aged female rats, regardless of estrogen treatment. However, in the aged CA1, estrogen restores NR2B levels back to young levels in the lateral portions of the active synaptic zone. Thus, estrogen may impact the mobility of NMDA receptors across the synapse and, in the process, restore a more youthful synaptic profile. These findings have important implications for the mechanism of estrogen-induced alterations in NMDA receptor-mediated processes, particularly in the context of aging.

Aging and increased hypothalamic glial fibrillary acid protein (GFAP) mRNA in F344 female rats. Dissociation of GFAP inducibility from the luteinizing hormone surge

During reproductive aging, female rodents show impaired inducibility of the estradiol (E2)-induced (preovulatory) surge of luteinizing hormone (LH), which is associated with hypothalamic neuronal impairments of aging. To evaluate if astrocytes show comparable age changes, we analyzed the regulation of glial fibrillary acidic protein (GFAP) mRNA which is transiently increased in the arcuate nucleus in association with the proestrus LH surge in young rats. In aging (18-month-old) F344 rats in persistent estrus, the loss of the E2-induced LH surge was paralleled by the lack of increased GFAP mRNA in the arcuate nucleus (in situ hybridization with X-ray film). We then tested the hypothesis that restoration of the LH surge by chronic ovariectomy (OVX) in aging rats would restore or block GFAP mRNA induction, respectively. Despite restoration of the inducible LH surge in aging rats by chronic OVX, there was no induction of GFAP mRNA in the arcuate nucleus. Moreover, young rats given chronic E2 implants for 6 weeks as a model for persistent estrus, retained induction of arcuate nucleus GFAP mRNA, despite loss of the induced LH surge. The aging rats were highly sensitive to gross pituitary enlargement from chronic E2 with 50% mortality; thus, the F344 genotype is not optimum for studies of aging-E2 interactions that require prolonged E2 treatments. More detailed cellular level analysis of GFAP mRNA is needed to define the relationship of GFAP expression to synaptic reorganization during the LH surge. The aging rats also showed higher levels of GFAP mRNA in the arcuate nucleus and ventromedial nucleus, consistent with the general trend for elevated GFAP mRNA during aging in other brain regions and in both sexes.

Different modes of hippocampal plasticity in response to estrogen in young and aged female rats

Estrogen regulates hippocampal dendritic spine density and synapse number in an N-methyl-D-aspartate (NMDA) receptor-dependent manner, and these effects may be of particular importance in the context of age-related changes in endocrine status. We investigated estrogen's effects on axospinous synapse density and the synaptic distribution of the NMDA receptor subunit, NR1, within the context of aging. Although estrogen induced an increase in axospinous synapse density in young animals, it did not alter the synaptic representation of NR1, in that the amount of NR1 per synapse was equivalent across groups. Estrogen replacement in aged female rats failed to increase axospinous synapse density; however, estrogen up-regulated synaptic NR1 compared with aged animals with no estrogen. Therefore, the young and aged hippocampi react differently to estrogen replacement, with the aged animals unable to mount a plasticity response generating additional synapses, yet responsive to estrogen with respect to additional NMDA receptor content per synapse. These findings have important implications for estrogen replacement therapy in the context of aging.

The type I BMP receptor BmprIB is essential for female reproductive function

Maintenance of female reproductive competence depends on the actions of several hormones and signaling factors. Recent reports suggest roles for bone morphogenetic proteins (BMPs) in early stages of folliculogenesis. A role for the type I BMP receptor BmprIB as a regulator of ovulation rates in sheep has been described recently, but little is known about the roles of BMP signaling pathways in other aspects of reproductive function. We report here that BMPRIB is essential for multiple aspects of female fertility. Mice deficient in BmprIB exhibit irregular estrous cycles and an impaired pseudopregnancy response. BmprIB mutants produce oocytes that can be fertilized in vitro, but defects in cumulus expansion prevent fertilization in vivo. This defect is associated with decreased levels of aromatase production in granulosa cells. Unexpectedly, levels of mRNA for cyclooxygenase 2, an enzyme required for cumulus expansion, are increased. BmprIB mutants also exhibit a failure in endometrial gland formation. The expression of BmprIB in uterine linings suggests that these defects are a direct consequence of loss of BMP signaling in this tissue. In summary, these studies demonstrate the importance of BMP signaling pathways for estrus cyclicity, estradiol biosynthesis, and cumulus cell expansion in vivo and reveal sites of action for BMP signaling pathways in reproductive tissues.

Influences of age and ovarian follicular reserve on estrous cycle patterns, ovulation, and hormone secretion in the Long-Evans rat

This study examined the influences of aging and reduced ovarian follicular reserve on estrous cyclicity, estradiol (E(2)) production, and gonadotropin secretion. Young virgin and middle-aged (MA) retired breeder female rats were unilaterally ovariectomized (ULO) or sham operated (control). Unilateral ovariectomy of young rats reduced the ovarian follicular reserve by one-half, to a level similar to that found in MA controls. Unilateral ovariectomy of MA females reduced the follicular pool further, to one half of MA controls. The incidence of regular cyclicity was significantly lower in MA ULO females than in young controls, with intermediate cycle frequency in young ULO and MA controls. Among cyclic rats, the magnitude of the proestrous LH surge was highest in young controls, intermediate in young ULO rats and MA controls, and lowest in MA ULO females. Similarly, ovulation rates were highest in young controls, intermediate in young ULO rats and MA controls, and lowest in MA ULO females. While young ULO rats exhibited augmented secondary FSH surges on estrous morning, middle-aged ULO females displayed secondary FSH levels comparable to young controls. The effects of age and reduced follicle number on estrous cyclicity and gonadotropin secretion were not due to altered E(2) secretion, as preovulatory E(2) levels were similar among all groups. Thus, experimental reduction in the follicular reserve exerts acute effects on the preovulatory LH surge, ovulation rate, and estrous cyclicity in both young and MA rats. However, decreased follicle number increases FSH levels only in young rats, indicating aging-related alterations in the feedback regulation of FSH.

Hypothalamic alterations and reproductive aging in female rats: evidence of altered luteinizing hormone-releasing hormone neuronal function

Prior to the age-related loss of regular estrous cycles, female rats exhibit an attenuated preovulatory LH surge, a sign that reproductive decline is imminent. Numerous studies have revealed an important role for the hypothalamus in aging of the reproductive axis in this species. Because LHRH represents the primary hypothalamic signal that regulates gonadotropin release, assessments of LHRH neuronal activity can provide a window into hypothalamic function during reproductive aging. Studies of the dynamic activity of LHRH neurons during times of enhanced secretion have revealed deficits in middle-aged females. Available data are consistent with a decline in LHRH synthesis, transport, and secretion in middle-aged females during times of increased demand for LHRH output. Moreover, the alterations noted in LHRH neuronal function could account, in part, for the attenuation and eventual loss of the preovulatory LH surge with age. Elements extrinsic to LHRH neurons undoubtedly contribute to the decline in the parameters of LHRH neuronal function observed in middle-aged females. Whether alterations intrinsic to LHRH neurons also play a role in the age-associated reduction in LHRH synthesis and secretion remains to be determined. Recent examinations of hormone profiles during the perimenopausal period suggest that a potential hypothalamic contribution to aging of the reproductive axis in women warrants further examination.

Neuroprotective effects of female gonadal steroids in reproductively senescent female rats

BACKGROUND AND PURPOSE

Young adult female rats sustain smaller infarcts after experimental stroke than age-matched males. This sex difference in ischemic brain injury in young animals disappears after surgical ovariectomy and can be restored by estrogen replacement. We sought to determine whether ischemic brain injury continues to be smaller in middle-aged, reproductively senescent female rats compared with age-matched males and to test the effect of ovarian steroids on brain injury after experimental stroke in females.

METHODS

Four groups of 16-month old Wistar rats (males [n=9], untreated females [n=9], and females pretreated with 17beta-estradiol [25-microgram pellets administered subcutaneously for 7 days; n=9] or progesterone [10-mg pellets administered subcutaneously for 7 days; n=9] were subjected to 2 hours of middle cerebral artery occlusion with the intraluminal filament technique, followed by 22 hours of reperfusion. Physiological variables and laser-Doppler cerebral cortical perfusion were monitored throughout ischemia and early reperfusion. In a separate cohort of males (n=3), untreated females (n=3), females pretreated with 17beta-estradiol (n=3), and females pretreated with progesterone (n=3), end-ischemic regional cerebral blood flow was measured by [(14)C]iodoantipyrine autoradiography.

RESULTS

As predicted, infarct size was not different between middle-aged male and female rats. Cortical infarcts were 21+/-5% and 31+/-6% of ipsilateral cerebral cortex, and striatal infarcts were 44+/-7% and 43+/-5% of ipsilateral striatum in males and females, respectively. Both estrogen and progesterone reduced cortical infarct in reproductively senescent females (5+/-2% and 16+/-4% in estrogen- and progesterone-treated groups, respectively, compared with 31+/-6% in untreated group). Striatal infarct was smaller in the estrogen- but not in the progesterone-treated group. Relative change in laser-Doppler cerebral cortical perfusion from preischemic baseline and absolute end-ischemic regional cerebral blood flow were not affected by hormonal treatments.

CONCLUSIONS

We conclude that the protection against ischemic brain injury found in young adult female rats disappears after reproductive senescence in middle-aged females and that ovarian hormones alleviate stroke injury in reproductively senescent female rats by a blood flow-independent mechanism. These findings support a role for hormone replacement therapy in stroke injury prevention in postmenopausal women.

Effects of estradiol and calcium on gonadotrophic cells in middle-aged female rats

The effects of multiple treatment with estradiol dipropionate (EDP) or calcium glucoheptonate (Ca) or a combination of the two on gonadotrophic cells in the pituitary pars distalis of middle-aged female rats were examined. The animals were treated daily for two weeks with EDP (0.625 mg i.p./kg body weight) or Ca (11.4 mg/kg body weight) or EDP + Ca. Luteinising (LH) and follicle stimulating hormone (FSH)-producing cells were examined by immunohistochemistry using antisera to the specific (beta) beta-subunits of LH and FSH and a peroxidase-anti-peroxidase immunohistochemical procedure. Plasma levels of FSH and LH were measured by radio-immune assay. A stereological method for determining morphometric parameters in immunopositive FSH and LH cells was used. The number of gonadotrophs per unit area (mm2), their cellular volume and relative volume densities, as well as plasma levels of FSH and LH, were decreased in all treated females in comparison with the controls. The most significant decrease of these parameters was observed in EDP-treated animals. Such changes were also expressed in Ca-treated animals, but the alterations were less distinct. These results demonstrate that multiple EDP or Ca application to middle-aged female rats is able to inhibit, directly or indirectly, the morphofunctional state of gonadotrophic cells in the pituitary pars distalis.

Effects of aging and gonadal failure on the hypothalamic-pituitary axis in women

OBJECTIVE

Our aim was to determine the effect of aging on the hypothalamic-pituitary-gonadal axis function.

STUDY DESIGN

We studied 9 women aged 25 to 40 years with well-defined idiopathic premature ovarian failure and compared them with 8 women aged 51 to 70 years who had age-appropriate menopause. All women underwent 24 hours of frequent blood sampling every 10 minutes before and after replacement with transdermal estradiol targeted to achieve serum concentrations of approximately 100 pg/ml.

RESULTS

In the absence of estrogen exposure, women with premature ovarian failure demonstrated a greater 24-hour mean luteinizing hormone concentration compared with that in the older women with age-appropriate menopause (32.3+/-4.3 mlU/ml vs 19.2+/-2.4 mlU/ml, p=0.0001). Despite the lesser luteinizing hormone serum levels in the older group, the luteinizing hormone pulse frequency per 24 hours was similar (22.1+/-3.0 pulses per 24 hours in prematurely menopausal women vs 21.9+/-2.5 pulses per 24 hours in the older postmenopausal women, p=0.94). When exposed to estrogen, mean luteinizing hormone concentrations decreased to 11.6+/-2.7 mlU/ml in prematurely menopausal women versus 4.4+/-1.0 mlU/ml in older postmenopausal women, p=0.017. Both groups had suppressed mean luteinizing hormone secretion compared with their paired, non-estradiol-exposed studies, p=0.0001. Frequency of luteinizing hormone pulsations was reduced to 16.5+/-3.5 pulses per 24 hours in prematurely menopausal women exposed to estradiol (p < 0.0058, compared with non-estradiol-exposed women). Further reduction was observed in older postmenopausal women (11.5+/-1.1 pulses per 24 hours, p=0.0001, compared with nonestradiol exposure, and p=0.0125, vs prematurely menopausal, estradiol-exposed women). Pulse amplitude was suppressed in both prematurely menopausal women (5.6+/-0.5 mlU/ml to 2.3+/-0.5 mlU/ml, p=0.0001) and older postmenopausal women (3.6+/-0.4 mlU/ml to 2.3+/-0.6 mlU/ml p=0.04) in the presence of estradiol. Although luteinizing hormone pulse amplitudes were greater in the women with premature menopause in the absence of estradiol (p=0.0028) compared with those in older postmenopausal women, pulse amplitudes became similar in the presence of estradiol. Parallel changes in mean follicle-stimulating hormone were observed. Women with premature ovarian failure had a mean follicle-stimulating hormone level of 71.1+/-9.4 mlU/ml that was suppressed to 18.0+/-4.1 mlU/ml after estradiol exposure (p=0.0001); values in older postmenopausal women were 45.9+/-6.0 and 10.3+/-2.0, respectively (p=0.0001). Although the women with premature ovarian failure secreted more follicle-stimulating hormone in the absence and presence of estradiol, only the former situation was statistically significant (p=0.0008 and p=0.23, respectively).

CONCLUSIONS

These data suggest that there is an age-related decrease in gonadotropin secretion that may be hypothalamic or pituitary in origin. There is less luteinizing hormone secreted in women older than age 50. There is greater suppression of luteinizing hormone and follicle-stimulating hormone secretion by estradiol in aged women. Thus these data indicate that postmenopausal hormone changes involve central hypothalamic-pituitary alterations, as well as ovarian changes.

Luteinizing hormone-releasing hormone gene expression differs in young and middle-aged females on the day of a steroid-induced LH surge

LHRH mRNA levels were examined in young and middle-aged female rats at 4 times (10:00 h, 14:00 h, 18:00 h and 20:00 h) on the day of a steroid-induced LH surge by in situ hybridization with a digoxigenin-labeled riboprobe. Young, but not middle-aged females, exhibited dynamic temporal changes in the number of LHRH mRNA positive neurons detected in the organum vasculosum of the lamina terminalis-preoptic area (OVLT-POA) continuum. Specifically, fewer LHRH mRNA positive neurons were detected at 18:00 h compared with the number detected at 14:00 h and 20:00 h (P < 0.01) in the OVLT-POA of young females. All LHRH mRNA positive neurons present in 4 anatomically matched sections through the rostral POA of young and middle-aged animals were digitized for detailed computer-assisted analysis of the hybridization reaction product. The mean hybridization area (P < 0.00025) and integrated optical density per cell (P < 0.006) were reduced in middle-aged compared to young females consistent with a relative age-related decline in LHRH mRNA levels. Moreover, an age-related reduction in cellular and/or regional hybridization area was noted at each of the time points examined (P < 0.05-P < 0.001). These data confirm earlier reports of dynamic changes in LHRH mRNA levels on the day of an LH surge. Furthermore, they support a role for age-related alterations in LHRH gene expression in the disruption of regular estrous cyclicity in middle-aged females.

Delay in manifestations of aging by grafting NGF cultured chromaffin cells in adulthood

Dopamine agonists or grafts compensate impaired motor functions in aged rats. However, there is no evidence showing whether grafting in adulthood retard aging manifestations. Motor performance of 13-month-old rats was tested on 2 meter-long wooden beams which had a 15 degree inclination and whose thickness varied from 3, 6, 12, 18, to 24 mm. Rats at 14 months were randomly assigned to 3 groups: sham graft (Group 1); intrastriatal graft of chromaffin cells cultured with NGF (Group 2); intrastriatal graft of chromaffin cells (Group 3). Motor performance was tested at monthly intervals up until rats were 26 months old. Two more groups were included: 26-month-old naive rats (Group 4); and 3- to 5-month-old naive rats (Group 5) both evaluated only once. At 26 months, the basal activity of ventral mesencephalic dopaminergic neurons was recorded. Results showed in Group 2 delay of motor detriments seen in aged rats, maintenance of basal firing rates of nigral cells compared to those of younger rats, and greater survival of substantia nigra cells. It is suggested that NGF cultured chromaffin cells produce a delay of motor detriments in aged rats, as a result of inducing survival and firing rates of nigral cells comparable to those seen in young rats.