Gonadotropin-releasing hormone mRNA and gonadotropin beta-subunit mRNA expression in the adult female rat exposed to ethanol in utero

Periconceptional ethanol exposure alters the stress axis in adult female but not male rat offspring

Ethanol consumption during pregnancy alters offspring hypothalamus-pituitary-adrenal (HPA) axis regulation. However, little is known about the outcomes of alcohol consumption confined to the periconceptional period. This study investigated the effects of periconceptional ethanol (PC:EtOH) exposure on corticosterone concentrations, response to restraint stress and gene expression of adrenal, hypothalamic, and hippocampal glucocorticoid-related pathways in rat offspring. Female Sprague-Dawley rats were treated with PC:EtOH (12.5% v/v EtOH liquid diet) or a control diet from four days before conception, until embryonic day 4. At 6 (adult) and 12-14 (aged) months of age, basal corticosterone concentrations were measured, while in a separate cohort of aged rats, blood pressure, heart rate, and plasma corticosterone concentrations were measured during a 30-minute restraint stress. Adrenal gland, hypothalamic and hippocampal tissue from aged rats were subjected to transcriptomic analysis. PC:EtOH exposure reduced basal plasma corticosterone concentrations in adult and aged female but not male offspring (p < .05). The corticosterone and pressor response were significantly reduced in aged PC:EtOH female offspring following restraint (p < .05). Expression of adrenal steroidogenesis genes (Mc2r, Cyp11a1, Cyp21a1, 11bhsd2, and Nr3c1) and hypothalamic genes (Crh, Crh-r1, Nr3c1, and Hsp90a1) was not affected by PC:EtOH. In aged female offspring exposed to PC:EtOH, adrenal mRNA expression of Hsp90a1 was significantly elevated, and within the hippocampus, mRNAs for glucocorticoid receptor (Nr3c1) and Hsp90a1 were increased (p < .05). This study supports the hypothesis that prenatal alcohol exposure programs sex-specific alterations in the HPA axis and provides the first evidence that the periconceptional period is a critical window for programing of this axis. Lay summary This study investigated the impact of alcohol consumption around the time of conception on offspring stress reactivity in a rat model. Offspring exposed to alcohol displayed altered cardiovascular responses to stress and had reduced circulating concentrations of the stress hormone corticosterone both under basal conditions and following a stressful challenge. This study also identified altered expression of key genes in an important part of the brain known to be involved in stress responsiveness; the hippocampus. If similar outcomes occur in humans, these results would suggest that alcohol consumption, even before a woman knows she is pregnant, may significantly impact stress-related outcomes in children.

Prenatal programming of neuroendocrine reproductive function

It is now well recognized that the gestational environment can have long-lasting effects not only on the life span and health span of an individual but also, through potential epigenetic changes, on future generations. This article reviews the "prenatal programming" of the neuroendocrine systems that regulate reproduction, with a specific focus on the lessons learned using ovine models. The review examines the critical roles played by steroids in normal reproductive development before considering the effects of prenatal exposure to exogenous steroid hormones including androgens and estrogens, the effects of maternal nutrition and stress during gestation, and the effects of exogenous chemicals such as alcohol and environment chemicals. In so doing, it becomes evident that, to maximize fitness, the regulation of reproduction has evolved to be responsive to many different internal and external cues and that the GnRH neurosecretory system expresses a degree of plasticity throughout life. During fetal life, however, the system is particularly sensitive to change and at this time, the GnRH neurosecretory system can be "shaped" both to achieve normal sexually differentiated function but also in ways that may adversely affect or even prevent "normal function". The exact mechanisms through which these programmed changes are brought about remain largely uncharacterized but are likely to differ depending on the factor, the timing of exposure to that factor, and the species. It would appear, however, that some afferent systems to the GnRH neurons such as kisspeptin, may be critical in this regard as it would appear to be sensitive to a wide variety of factors that can program reproductive function. Finally, it has been noted that the prenatal programming of neuroendocrine reproductive function can be associated with epigenetic changes, which would suggest that in addition to direct effects on the exposed offspring, prenatal programming could have transgenerational effects on reproductive potential.

Neuronal basis of reproductive dysfunctions associated with diet and alcohol: From the womb to adulthood

The theory that individuals are born as tabula rasa and that their knowledge comes from experience and perception is no longer true. Studies suggest that experience is gained as early as in the mother's womb. Moreover, environmental stressors like alcohol or inadequate diet can affect physiological systems such as the hypothalmic-pituitary-gonadal (HPG) axis. The effects of these stressors can manifest as alterations in sexual development and adult reproductive functions. In this review, we consider and compare evidence from animal models and human studies demonstrating the role of environmental stressors (alcohol and under- or overnutrition) on the HPG axis. We review the role of alcohol and inadequate diet in prenatal reproductive system programming and consider specific candidate neurons in the adult hypothalamus through which reproductive function is being regulated. Finally, we review evidence from animal studies on the role that alcohol and diet play in fertility and reproductive disorders. We conclude that in order to better understand reproductive failure in animals and humans we need to consider in utero development and pay more attention to early life experience when searching for the origins of reproductive diseases.

Prenatal alcohol exposure alters response of kisspeptin-ir neurons to estradiol and progesterone in adult female rats

BACKGROUND

Prenatal alcohol exposure (PAE) has adverse effects on reproductive function and hypothalamic-pituitary-gonadal (HPG) activity. Kisspeptin neurons play a role in mediating feedback effects of estradiol (E2 ) and progesterone (P4 ) on the HPG axis. We hypothesized that PAE will have long-term effects on the response of kisspeptin neurons to E2 and P4 .

METHODS

Adult female rats (53 to 58 days) from prenatal ad libitum-fed control (C), pair-fed (PF), and alcohol-exposed (PAE) groups were subjected to Sham ovariectomy (OVX) or OVX without or with replacement with low or high physiological levels of E2 and P4 , and terminated under basal conditions. E2 and P4 levels, and the response of kisspeptin-ir neurons in the arcuate (ARC) and anteroventral periventricular (AVPV) nuclei to these hormones, were measured. As the E2 signal is conveyed to kisspeptin neurons via estrogen receptor-α (ER-α), we investigated PAE effects on the number of kisspeptin-ir/ER-α-ir neurons. To determine whether PAE alters interactions between kisspeptin and gonadotropin-releasing hormone (GnRH) neurons, close contacts between kisspeptin-ir fibers and GnRH-ir cell bodies were examined.

RESULTS

Our data present the novel finding that kisspeptin-ir neurons in the ARC of PAE females show differential responses to E2 and to the combined treatment with E2 and P4 compared with controls: (i) OVX increased the number of kisspeptin-ir neurons in C and PF, but not PAE females compared with their Sham counterparts; (ii) E2 replacement restored kisspeptin-ir cell numbers to Sham levels in C and PF females but caused a robust down-regulation of kisspeptin-ir neurons below Sham levels in PAE females; (iii) OVX and replacement with high physiological concentrations of E2 resulted in fewer kisspeptin-ir cells in PAE than C females; (iv) OVX and replacement with high levels of both E2 and P4 markedly decreased the number of kisspeptin-ir neurons, below levels observed following E2 alone, in PF and C females, but had no significant effect in PAE females.

CONCLUSIONS

These data suggest that a possible mechanism underlying adverse effects of PAE on HPG function involves actions of alcohol on the kisspeptin system.

The effect of atrazine administered by gavage or in diet on the LH surge and reproductive performance in intact female Sprague-Dawley and Long Evans rats

Atrazine (ATR) blunts the hormone-induced luteinizing hormone (LH) surge, when administered by gavage (50–100 mg/kg/day for 4 days), in ovariectomized rats. In this study, we determined if comparable doses delivered either by gavage (bolus dose) or distributed in diet would reduce the LH surge and subsequently affect fertility in the intact female rat. ATR was administered daily to intact female Sprague-Dawley (SD) or Long Evans (LE) rats by gavage (0, 0.75 1.5, 3, 6, 10, 12, 50, or 100 mg/kg/day) or diet (0, 30, 100, 160, 500, 660, or 1460 ppm) during one complete 4-day estrous cycle, starting on day of estrus. Estrous status, corpora lutea, ova, and LH plasma concentrations were evaluated. A second cohort of animals was mated on the fourth treatment day. Fertility metrics were assessed on gestational day 20. A higher portion of LE rats had asynchronous estrous cycles when compared to SD rats both during pretreatment and in response to ATR (≥50 mg/kg). In contrast, bolus doses of ATR (≥50 mg/kg) inhibited the peak and area under the curve for the preovulatory LH surge in SD but not LE animals. Likewise, only bolus-treated SD, not LE, rats displayed reduced mean number of corpora lutea and ova. There were no effects of ATR administered by gavage on mating, gravid number, or fetus number. Dietary administration had no effect on any reproductive parameter measured. These findings indicate that short duration, high-bolus doses of ATR can inhibit the LH surge and reduce the number of follicles ovulated; however, dietary administration has no effect on any endocrine or reproductive outcomes

Arginine vasopressin regulation in pre- and postpubertal male rats by the androgen metabolite 3beta-diol

Arginine vasopressin (AVP) is a nonapeptide expressed in several brain regions. In addition to its well-characterized role in osmoregulation, AVP regulates paternal behavior, aggression,circadian rhythms, and the stress response. In the bed nucleus of the stria terminalis (BST), AVP gene expression is tightly regulated by gonadal steroid hormones. However, the degree by which AVP is regulated by gonadal steroid hormones in the suprachiasmatic nucleus (SCN) and medial amygdala (MeA) is unclear. Previous studies have shown that AVP expression in the brain of gonadectomized rats is restored with testosterone, 17beta-estradiol, and 5alpha-dihydrotestosterone(DHT) replacement. In addition, we have demonstrated that 3beta-diol, a metabolite of DHT,increased AVP promoter activity in a neuronal cell line and that the effects of 3beta-diol on AVP promoter activity were mediated by estrogen receptor-beta. To test whether 3beta-diol has a physiological role in the regulation of central AVP expression in vivo, we gonadectomized pre- and postpubertal male rats and followed with once daily injections of estradiol benzoate (EB),DHT-propionate, 3beta-diol-dipropionate, or vehicle. The SCN, BST, and MeA were analyzed for AVP mRNA expression using in situ hybridization. In the BST, intact juveniles had significantly fewer AVP-expressing cells than adults. GDX abolished all AVP mRNA expression in the BST in both age groups, whereas treatment with EB restored >80% and DHTP <10% of the AVP expression. Interestingly, 3beta-diol-proprionate was more effective at inducing AVP expression in juveniles than in adults, suggesting that the regulation of AVP by 3beta-diol might be age dependent [corrected].

Effects of prenatal ethanol exposure on hypothalamic-pituitary-adrenal function across the estrous cycle

BACKGROUND

Rats prenatally exposed to ethanol (E) typically show increased hypothalamic-pituitary-adrenal (HPA) responses to stressors in adulthood. Importantly, prenatal ethanol may differentially alter stress responsiveness in male and female offspring, suggesting a role for the gonadal hormones in mediating the effects of ethanol on HPA activity. We investigated the role of ethanol-induced changes in hypothalamic-pituitary-gonadal (HPG) activity in the differential HPA regulation observed in E compared to control females across the estrous cycle.

METHODS

Peripheral hormones and changes in central neuropeptide mRNA levels were measured across the estrous cycle in adult female offspring from E, pair-fed (PF) and ad libitum-fed control (C) dams.

RESULTS

Ethanol females showed normal estrous cyclicity (vaginal smears) but delayed sexual maturation (vaginal opening). Both HPG and HPA activity were differentially altered in E (and in some cases, PF) compared to control females as a function of estrous cycle stage. In relation to HPG activity, E and PF females had higher basal and stress estradiol (E(2)) levels in proestrus compared to other phases of the cycle, and decreased GnRH mRNA levels compared to C females in diestrus. Further, E females had greater variation in LH than PF and C females across the cycle, and in proestrus, only E females showed a significant LH increase following stress. In relation to HPA activity, both basal and stress CORT levels and overall ACTH levels were greater in E than in C females in proestrus. Furthermore, AVP mRNA levels were increased overall in E compared to PF and C females.

CONCLUSIONS

These data demonstrate ethanol-induced changes in both HPG and HPA activity that are estrous phase-specific, and support the possibility that changes in HPA activity in E females may reflect differential sensitivity to ovarian steroids. E females appear to have an increased HPA sensitivity to E(2), and a possible shift toward AVP regulation of HPA activity. That PF were similar to E females on some measures suggests that nutritional effects of diet or food restriction played a role in mediating at least some of the changes observed.

Prenatal alcohol exposure: foetal programming, the hypothalamic-pituitary-adrenal axis and sex differences in outcome

Prenatal exposure to alcohol has adverse effects on offspring neuroendocrine and behavioural functions. Alcohol readily crosses the placenta, thus directly affecting developing foetal endocrine organs. In addition, alcohol-induced changes in maternal endocrine function can disrupt the normal hormonal interactions between the pregnant female and foetal systems, altering the normal hormone balance and, indirectly, affecting the development of foetal metabolic, physiological and endocrine functions. The present review focuses on the adverse effects of prenatal alcohol exposure on offspring neuroendocrine function, with particular emphasis on the hypothalamic-pituitary-adrenal (HPA) axis, a key player in the stress response. The HPA axis is highly susceptible to programming during foetal and neonatal development. Here, we review data demonstrating that alcohol exposure in utero programmes the foetal HPA axis such that HPA tone is increased throughout life. Importantly, we show that, although alterations in HPA responsiveness and regulation are robust phenomena, occurring in both male and female offspring, sexually dimorphic effects of alcohol are frequently observed. We present updated findings on possible mechanisms underlying differential effects of alcohol on male and female offspring, with special emphasis on effects at different levels of the HPA axis, and on modulatory influences of the hypothalamic-pituitary-gonadal hormones and serotonin. Finally, possible mechanisms underlying foetal programming of the HPA axis, and the long-term implications of increased exposure to endogenous glucocorticoids for offspring vulnerability to illnesses or disorders later in life are discussed.

Effects of Prenatal Ethanol Exposure on Basal Limbic?Hypothalamic?Pituitary?Adrenal Regulation: Role of Corticosterone

BACKGROUND

Rats prenatally exposed to ethanol (E) exhibit hypothalamic-pituitary-adrenal (HPA) hyperresponsiveness and changes in central HPA regulation following exposure to stressors. Whether ethanol-induced alterations in basal HPA regulation play a role in mediating HPA hyperresponsiveness remains unclear. We utilized adrenalectomy (ADX), with or without corticosterone (CORT) replacement, to investigate basal HPA function and the role of CORT in mediating ethanol-induced alterations.

METHODS

Adult males and females from prenatal E, pair-fed (PF), and ad lib-fed control (C) groups were terminated at the circadian peak, 7 days following sham surgery or ADX, with or without CORT replacement. Plasma levels of CORT and adrenocorticotropin (ACTH), and mRNA levels of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) in the paraventricular nucleus, CRH Type 1 receptor (CRH-R1) and pro-opiomelanocortin (POMC) in the anterior pituitary, and mineralocorticoid (MR) and glucocorticoid (GR) receptors in the dorsal hippocampus were determined.

RESULTS

Adrenalectomy resulted in significantly greater plasma ACTH elevations in E and PF males, and parallel CRH mRNA elevations in both E and PF males and females compared with their C counterparts. In contrast, pituitary CRH-R1 mRNA levels were lower in E compared with C males, with no differences in POMC. In addition, in response to ADX, E females showed a greater MR mRNA response, and E males showed a greater GR mRNA response compared with their C counterparts, and CORT replacement was ineffective in normalizing ADX-induced alterations in ACTH levels in E and PF females, hippocampal MR mRNA levels in E males, and AVP mRNA levels in PF males and females.

CONCLUSIONS

Together, these data indicate that the prenatal ethanol exposure induces HPA dysregulation under basal conditions at multiple levels of the axis, resulting in alterations in both HPA drive and feedback regulation and/or in the balance between drive and feedback. While some effects may be nutritionally mediated, it appears that the mechanisms underlying basal HPA dysregulation may differ between E and PF animals rather than occurring along a continuum of effects on the same pathway. Altered basal HPA tone may play a role in mediating the HPA hyperresponsiveness to stressors observed in E offspring.

Alcohol and gene expression in the central nervous system

AIMS

To describe recent research focusing on the analysis of gene and protein expression relevant to understanding ethanol consumption, dependence and effects, in order to identify common themes.

METHODS

A selective literature search was used to collate the relevant data.

RESULTS

Over 160 genes have been individually assessed before or after ethanol administration, as well as in genetically selected lines. Techniques for studying gene expression include northern blots, differential display, real time reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridization. More recently, high throughput functional genomic technology, such as DNA microarrays, has been used to examine gene expression. Recent gene expression analyses have dramatically increased the number of candidate genes (nine array papers have illuminated 600 novel gene transcripts that may contribute to alcohol abuse and alcoholism).

CONCLUSIONS

Although functional genomic experiments (transcriptome analysis) have failed to identify a single alcoholism gene, they have illuminated important pathways and gene products that may contribute to the risk of alcohol abuse and alcoholism.

Activin subunit, follistatin, and activin receptor gene expression in the prepubertal female rat pituitary

In the prepubertal female rat, a transient and selective increase in FSH secretion and mRNA expression by the pituitary gland occurs toward the end of the second postnatal week of life. To begin to investigate the possibility that activin may play a role in up-regulating FSH during this time, we have studied the ontogeny of the expression of the activin ss subunits, follistatin, and activin receptor subtypes in the prepubertal female rat pituitary. The levels of expression of ssA, ssB, and follistatin mRNAs were determined in the pituitary gland on postnatal days (PND) 8, 10, 12, 15, and 21 by semiquantitative reverse transcription-polymerase chain reaction. All values were compared to those of adult females killed on diestrus. mRNA levels of subunit ssA were significantly (p < 0.05) elevated on all postnatal days examined; ssB mRNA levels were elevated above adult levels only on PND 10 (p < 0.05). Follistatin mRNA was high on PND 8 (p < 0.05) and then decreased to adult levels. The level and distribution of activin receptor type II subtype mRNAs were determined by in situ hybridization. Activin receptor type II (Act RII) mRNA expression was diffusely expressed throughout all areas of the pituitary. Activin receptor type IIB (Act RIIB), on the other hand, was highly expressed by a subset of anterior pituitary cells. In situ hybridization for activin receptor subtype mRNAs was combined with immunocytochemistry to detect FSH-containing cells. We determined that in the infantile female pituitary, Act RII mRNA was generally not expressed in FSH-immunoreactive cells, while Act RIIB mRNA was expressed in FSH-immunoreactive cells. Act RII mRNA was lower on PND 10 and 15 when compared to PND 21 (p < 0.05), whereas Act RIIB mRNA expression did not change with age. These data suggest that the essential components of the activin regulatory system are present in the infantile female pituitary gland and thus may be involved in the differential regulation of FSH at this time.

Direct actions of gonadal steroid hormones on FSH secretion and expression in the infantile female rat

FSH-beta mRNA is dramatically regulated in the infantile female rat anterior pituitary. Elevated plasma levels of FSH correspond with increased FSH-beta mRNA levels which peak on PND 12. The source of this regulation does not appear to be GnRH, since the administration of a potent GnRH antagonist does not suppress FSH-beta mRNA levels. Consequently, we have examined the effects of the gonadal steroid hormones, estrogen and androgen, on the maintenance of gonadotropin secretion and gene expression both in vivo and in vitro. Androgen and estrogen action was blocked in vivo with the specific receptor antagonists, flutamide (150 microg) and tamoxifen (200 microg). Administration of antagonists during two different three day time-periods of infantile life [postnatal day (PND) 8-11 and PND 11-14] resulted in differing effects on both FSH and LH secretion as well as on FSH-beta and LH-beta mRNA levels. Flutamide and tamoxifen treatment both suppressed FSH secretion at either age examined (p < 0.01). LH secretion was suppressed by both treatments but only at the younger of the two ages (p < 0.01). In contrast to its effects on FSH secretion, tamoxifen suppressed FSH-beta mRNA levels in the later group only. LH-beta mRNA levels were suppressed by tamoxifen, but only in the younger age group (p < 0.05). The direct effects of steroid hormones on infantile pituitary gonadotrophs were examined in vitro by incubating cells with dihydrotestosterone propionate (DHTP; 10(-8) M) or 17beta-estradiol (E; 10(-8) M). Both DHT and E treatment stimulated FSH secretion when measured 48 h later (p < 0.01). There were no effects on LH secretion. FSH-beta mRNA levels were also stimulated by DHT at 48 h (p < 0.01). Estradiol treatment transiently increased FSH-beta mRNA levels at 2 and 6 h following treatment (p < 0.01) but not at 48 h. LH-beta levels were suppressed by DHT treatment (p < 0.05), and E transiently elevated LH-beta mRNA levels at 2 h (p < 0.05). Taken together these studies indicate that gonadotrophs from infantile female rats are capable of responding directly to steroid hormones, and may play a role in the selective stimulation of FSH secretion and expression in vivo.

Effects of prenatal alcohol and pair feeding on lipopolysaccharide-induced secretion of TNF-alpha and corticosterone

Fetal alcohol exposure (FAE) produces profound alterations in immunological and neuroendocrine functions. The present study examined the effects of FAE on the secretion of tumor necrosis factor (TNF-alpha) and corticosterone following administration of lipopolysaccharide (LPS) in normal (N) adult rats, in adult offspring of dams fed a liquid diet supplemented with ethanol (E), and in pair-fed control offspring (P). LPS-induced TNF-alpha secretion was not affected by either gender or prenatal treatment. In contrast, LPS-induced corticosterone secretion was significantly greater in female than in male rats, and at 60-min post-LPS was significantly higher in E and P, compared to N females. Ovariectomy significantly inhibited LPS-induced TNF-alpha secretion in E, but not in P and N, rats and chronic replacement with 17-beta-estradiol markedly inhibited TNF-alpha secretion in ovariectomized E and N, but not in P, rats. In contrast, ovariectomy reduced the effects of LPS on corticosterone secretion in all groups, and chronic replacement with 17-beta-estradiol reversed this effect. These findings indicate that LPS-induced secretion of corticosterone, but not TNF-alpha, is affected by prenatal manipulations and by gender. In addition, alterations in the hormonal environment in females modulate LPS-induced corticosterone secretion in all prenatal treatment groups, but differentially influence TNF-alpha secretion in rats exposed to alcohol, restricted feeding, or normal diets in utero.

Gonadotropin secretion in infantile rats exposed to ethanol in utero

Previous studies have shown that fetal alcohol exposure (FAE) alters reproductive function in both male and female rats. In females, FAE delays the onset of puberty, reduces a preovulatory-like LH surge, and results in an early onset of acyclicity. In males exposed to ethanol in utero, the perinatal surge of testosterone is reduced. During the infantile period of the female rat, there is a dramatic increase in plasma follicle-stimulating hormone (FSH), which is thought to play a role in initiating ovarian activity and perhaps the onset of puberty. In this study, we determined the effects of FAE on the patterns of gonadotropin secretion during the infantile period [postnatal days (PND) 8-21] in both male and female rats. Timed pregnant dams were fed a liquid diet containing 35% ethanol-derived calories during the final week of gestation. Control dams were fed either an isocaloric diet with sucrose substituted for ethanol (pair fed, PF) or laboratory chow (chow fed, CF). Male and female pups were sacrificed on PND 8, 10, 12, 15, 18, and 21, and trunk blood was collected. In males, LH levels decreased to a nadir on PND 18, and this decrease was blunted by FAE (p < 0.05). In contrast, FSH secretion was not altered by FAE. In females, plasma FSH levels were greater than males, and increased to peak on PND 12. This FSH peak was significantly delayed in FAE females (p < 0.02). There was no age-related change in LH levels in FAE females, and LH levels were not altered by FAE. The delayed peak of FSH secretion by FAE correlates with the delay in puberty previously seen in females. To investigate this further, we examined the possibility that the delay in the peak of serum FSH in FAE females is due to a reduced number of FSH-producing gonadotrophs. FSH-containing gonadotrophs were identified by immunocytochemistry. Cell counts of FSH-immunoreactive cells in pituitaries from PND 8, 15, and 21 control-fed and FAE female rats showed developmental increases in the number of FSH gonadotrophs per unit area (p < 0.001), but no treatment differences were observed. Overall, these data show that fetal alcohol exposure can alter gonadotropin secretion in infantile life in male and female rats. Importantly, the delay in FSH secretion in females may ultimately play a role in the delay in puberty observed in the FAE female rat.

Alterations in the estrogen sensitivity of hypothalamic proenkephalin mRNA expression with age and prenatal exposure to alcohol

Studies suggest that exposure to alcohol in utero causes reproductive and neuroendocrine deficits in adult female rats. The ventromedial nucleus of the hypothalamus (VMN) is an estrogen-sensitive brain region which is regarded as a primary locus for modulating female reproduction. Proenkephalin (PE) mRNA expression in the VMN is dramatically increased by estrogen and this elevation is thought to be involved in modulating female reproductive behavior and neuroendocrine function. To examine whether prenatal alcohol exposure has long-term effects on the ability of estrogen to influence hypothalamic PE mRNA levels, female rats at 2-3, 6-7 or 15-18 months of age, derived from alcohol- or control-fed dams, were studied. 7 days following ovariectomy, animals received either estrogen or sham treatment for 2 days prior to sacrifice. PE mRNA levels in the VMN and striatum were determined by in situ hybridization histochemistry. Film autoradiogram density, numbers of PE mRNA-expressing cells and exposed silver grains/cell were analyzed. Estrogen treatment increased hybridization density, the number of PE mRNA-expressing cells and PE mRNA (grains) level/cell in the VMN of normal adult female rats. In old rats, estrogen increased the number of PE mRNA-expressing cells without up-regulating PE mRNA grain density/cell. In fetal alcohol-exposed (FAE) female rats, the number of cells that expressed PE mRNA did not increase following estrogen treatment at any age. Elevation of grain density/cell following estrogen was observed in FAE animals but only at 7-8 months of age. Overall, these data indicate that the estrogen responsiveness of PE mRNA expression in the VMN declines with age and, furthermore, prenatal exposure to alcohol blunts estrogen's effects on PE mRNA expression in the adult VMN. These finding may help to explain the mechanisms underlying the loss of reproductive function observed in FAE females.