Acute stress- or lipopolysaccharide-induced corticosterone secretion in female rats is independent of the oestrous cycle

Sex-dependent changes in neuroactive steroid concentrations in the rat brain following acute swim stress

Sex differences in hypothalamic-pituitary-adrenal (HPA) axis activity are well established in rodents. In addition to glucocorticoids, stress also stimulates the secretion of progesterone and deoxycorticosterone (DOC) from the adrenal gland. Neuroactive steroid metabolites of these precursors can modulate HPA axis function; however, it is not known whether levels of these steroids differ between male and females following stress. In the present study, we aimed to establish whether neuroactive steroid concentrations in the brain display sex- and/or region-specific differences under basal conditions and following exposure to acute stress. Brains were collected from male and female rats killed under nonstress conditions or following exposure to forced swimming. Liquid chromatography-mass spectrometry was used to quantify eight steroids: corticosterone, DOC, dihydrodeoxycorticosterone (DHDOC), pregnenolone, progesterone, dihydroprogesterone (DHP), allopregnanolone and testosterone in plasma, and in five brain regions (frontal cortex, hypothalamus, hippocampus, amygdala and brainstem). Corticosterone, DOC and progesterone concentrations were significantly greater in the plasma and brain of both sexes following stress; however, the responses in plasma were greater in females compared to males. This sex difference was also observed in the majority of brain regions for DOC and progesterone but not for corticosterone. Despite observing no stress-induced changes in circulating concentrations of pregnenolone, DHDOC or DHP, concentrations were significantly greater in the brain and this effect was more pronounced in females than males. Basal plasma and brain concentrations of allopregnanolone were significantly higher in females; moreover, stress had a greater impact on central allopregnanolone concentrations in females. Stress had no effect on circulating or brain concentrations of testosterone in males. These data indicate the existence of sex and regional differences in the generation of neuroactive steroids in the brain following acute stress, especially for the 5α-reduced steroids, and further suggest a sex-specific expression of steroidogenic enzymes in the brain. Thus, differential neurosteroidogenesis may contribute to sex differences in HPA axis responses to stress.

Palatable Food Affects HPA Axis Responsivity and Forebrain Neurocircuitry in an Estrous Cycle-specific Manner in Female Rats

Eating palatable foods can provide stress relief, but the mechanisms by which this occurs are unclear. We previously characterized a limited sucrose intake (LSI) paradigm in which twice-daily access to a small amount of 30% sucrose (vs. water as a control) reduces hypothalamic-pituitary-adrenocortical (HPA) axis responses to stress and alters neuronal activation in stress-regulatory brain regions in male rats. However, women may be more prone to 'comfort feeding' behaviors than men, and stress-related eating may vary across the menstrual cycle. This suggests that LSI effects may be sex- and estrous cycle-dependent. The present study therefore investigated the effects of LSI on HPA axis stress responsivity, as well as markers of neuronal activation/plasticity in stress- and reward-related neurocircuitry in female rats across the estrous cycle. We found that LSI reduced post-restraint stress plasma ACTH in female rats specifically during proestrus/estrus (P/E). LSI also increased basal (non-stress) FosB/deltaFosB- and pCREB-immunolabeling in the basolateral amygdala (BLA) and central amygdala specifically during P/E. Finally, Bayesian network modeling of the FosB/deltaFosB and pCREB expression data identified a neurocircuit that includes the BLA, nucleus accumbens, prefrontal cortex, and bed nucleus of the stria terminalis as likely being modified by LSI during P/E. When considered in the context of our prior results, the present findings suggest that palatable food reduces stress responses in female rats similar to males, but in an estrous cycle-dependent manner. Further, the BLA may contribute to the LSI effects in both sexes, whereas the involvement of other brain regions appears to be sex-dependent.

Sex differences in the HPA axis

The hypothalamic-pituitary-adrenal (HPA) axis is a major component of the systems that respond to stress, by coordinating the neuroendocrine and autonomic responses. Tightly controlled regulation of HPA responses is critical for maintaining mental and physical health, as hyper- and hypo-activity have been linked to disease states. A long history of research has revealed sex differences in numerous components of the HPA stress system and its responses, which may partially form the basis for sex disparities in disease development. Despite this, many studies use male subjects exclusively, while fewer reports involve females or provide direct sex comparisons. The purpose of this article is to present sex comparisons in the functional and molecular aspects of the HPA axis, through various phases of activity, including basal, acute stress, and chronic stress conditions. The HPA axis in females initiates more rapidly and produces a greater output of stress hormones. This review focuses on the interactions between the gonadal hormone system and the HPA axis as the key mediators of these sex differences, whereby androgens increase and estrogens decrease HPA activity in adulthood. In addition to the effects of gonadal hormones on the adult response, morphological impacts of hormone exposure during development are also involved in mediating sex differences. Additional systems impinging on the HPA axis that contribute to sex differences include the monoamine neurotransmitters norepinephrine and serotonin. Diverse signals originating from the brain and periphery are integrated to determine the level of HPA axis activity, and these signals are, in many cases, sex-specific.

Estradiol replacement enhances fear memory formation, impairs extinction and reduces COMT expression levels in the hippocampus of ovariectomized female mice

Females experience depression, posttraumatic stress disorder (PTSD), and anxiety disorders at approximately twice the rate of males, but the mechanisms underlying this difference remain undefined. The effect of sex hormones on neural substrates presents a possible mechanism. We investigated the effect of ovariectomy at two ages, before puberty and in adulthood, and 17β-estradiol (E2) replacement administered chronically in drinking water on anxiety level, fear memory formation, and extinction. Based on previous studies, we hypothesized that estradiol replacement would impair fear memory formation and enhance extinction rate. Females, age 4 weeks and 10 weeks, were divided randomly into 4 groups; sham surgery, OVX, OVX+low E2 (200nM), and OVX+high E2 (1000nM). Chronic treatment with high levels of E2 significantly increased anxiety levels measured in the elevated plus maze. In both age groups, high levels of E2 significantly increased contextual fear memory but had no effect on cued fear memory. In addition, high E2 decreased the rate of extinction in both ages. Finally, catechol-O-methyltransferase (COMT) is important for regulation of catecholamine levels, which play a role in fear memory formation and extinction. COMT expression in the hippocampus was significantly reduced by high E2 replacement, implying increased catecholamine levels in the hippocampus of high E2 mice. These results suggest that estradiol enhanced fear memory formation, and inhibited fear memory extinction, possibly stabilizing the fear memory in female mice. This study has implications for a neurobiological mechanism for PTSD and anxiety disorders.

Amygdalar neuronal plasticity and the interactions of alcohol, sex, and stress

Alcohol abuse and alcoholism are major medical problems affecting both men and women. Previous animal studies reported a difference in c-Fos neuronal activation after chronic alcohol exposure; however, females remain an understudied population. To model chronic alcohol exposure match-pair fed adult male and female rats were administered 14 days of a liquid ethanol containing diet. Analysis focused on the central nucleus of the amygdala (CeA), a region integral to stress sensitivity and substance abuse. Immunocytochemical approaches identified cells containing ΔFosB, a marker of sustained neuronal activation, and activity patterns within the CeA were mapped by subdivision and rostral-caudal extent. Significant interactions were present between all groups, with gender differences noted among control groups, and ethanol exposed animals having the greatest number of ΔFosB immunoreactive cells indicating baseline dysregulation. Compared with c-Fos, a marker of recent neuronal activation, male ethanol treated animals had similar activity to controls, indicating a neuronal habituation not seen in females. Next, a cohort of animals were exposed to the forced swim test (FST), and c-Fos was examined in addition to FST behavior. Neuronal activity was increased in ethanol exposed animals compared to controls, and control females compared to males, indicating a potentiated stress response. Further, a population of activated neurons were shown to contain either corticotropin releasing factor or enkephalin. The present data suggest that dysregulation in the CeA neuronal activity may underlie some of the negative sequelae of alcohol abuse, and may, in part, underlie the distinctive response seen between genders to alcohol use.

Protective effects of luteolin on cognitive impairments induced by psychological stress in mice

In the present study, the protective effects of luteolin were investigated against psychological stress-induced cognitive impairment. To emulate the psychological stress, mice received restraint stress for six hours daily, between 9:00 and 15:00 hours, for 21 consecutive days. The results of step-through test, open-field test and Morris Water Maze test demonstrated that psychological stress treatment could result in cognitive impairments in mice. This cognition dysfunction was improved by treatment with low- and medium-dose luteolin. In addition, psychological stress induced an increased serum corticosterone concentration with a decreased serum norepinephrine and dopamine concentration. These alterations were attenuated by treatment with luteolin. Also, psychological stress significantly decreased the glutathione (GSH) concentrations and superoxide dismutase (SOD) activities in prefrontal cortex and hippocampus, while the malondialdehyde (MDA) concentrations were enhanced. However, these oxidative alterations in prefrontal cortex and hippocampus induced by psychological stress were significantly reversed by treatment of luteolin. Further, the current study indicated a decline of catalase (CAT) activities in the hippocampus of the ST group, which was significantly prevented by low, medium and high dose of luteolin. On the other hand, there was no significance in CAT activities of the prefrontal cortex among the six groups. Collectively, the present results suggest that luteolin treatment serves as a key role in improving the psychological stress-induced cognitive impairments.

Sex differences in activated corticotropin-releasing factor neurons within stress-related neurocircuitry and hypothalamic-pituitary-adrenocortical axis hormones following restraint in rats

Women may be more vulnerable to certain stress-related psychiatric illnesses than men due to differences in hypothalamic-pituitary-adrenocortical (HPA) axis function. To investigate potential sex differences in forebrain regions associated with HPA axis activation in rats, these experiments utilized acute exposure to a psychological stressor. Male and female rats in various stages of the estrous cycle were exposed to 30min of restraint, producing a robust HPA axis hormonal response in all animals, the magnitude of which was significantly higher in female rats. Although both male and female animals displayed equivalent c-fos expression in many brain regions known to be involved in the detection of threatening stimuli, three regions had significantly higher expression in females: the paraventricular nucleus of the hypothalamus (PVN), the anteroventral division of the bed nucleus of the stria terminalis (BSTav), and the medial preoptic area (MPOA). Dual fluorescence in situ hybridization analysis of neurons containing c-fos and corticotropin-releasing factor (CRF) mRNA in these regions revealed significantly more c-fos and CRF single-labeled neurons, as well as significantly more double-labeled neurons in females. Surprisingly, there was no effect of the estrous cycle on any measure analyzed, and an additional experiment revealed no demonstrable effect of estradiol replacement following ovariectomy on HPA axis hormone induction following stress. Taken together, these data suggest sex differences in HPA axis activation in response to perceived threat may be influenced by specific populations of CRF neurons in key stress-related brain regions, the BSTav, MPOA, and PVN, which may be independent of circulating sex steroids.

Differential involvement of the suprachiasmatic nucleus in lipopolysaccharide-induced plasma glucose and corticosterone responses

The hypothalamic suprachiasmatic nucleus (SCN) is an essential component of the circadian timing system, and an important determinant of neuroendocrine and metabolic regulation. Recent data indicate a modulatory role for the immune system on the circadian timing system. The authors investigated how the circadian timing system affects the hypothalamo-pituitary-adrenal (HPA) axis and glucose regulatory responses evoked by an immune challenge induced by lipopolysaccharide (LPS). LPS-induced increases in corticosterone were minimal during the trough of the daily corticosterone rhythm; in contrast, LPS effects on glucose, glucagon, and insulin did not vary across time-of-day. Complete ablation of the SCN resulted in increased corticosterone responses but did not affect LPS-induced hyperglycemia. The paraventricular nucleus (PVN) of the hypothalamus is an important neuroendocrine and autonomic output pathway for hypothalamic information, as well as one of the main target areas of the SCN. Silencing the neuronal activity in the PVN did not affect the LPS-induced corticosterone surge and only slightly delayed the LPS-induced plasma glucose and glucagon responses. Finally, surgical interruption of the neuronal connection between hypothalamus and liver did not affect the corticosterone response but slightly delayed the LPS-induced glucose response. Together, these data support the previously proposed circadian modulation of LPS-induced neuroendocrine responses, but they are at variance with the suggested major role for the hypothalamic pacemaker on the autonomic output of the hypothalamus, as reflected by the effects of LPS on glucose homeostasis. The latter effects are more likely due to direct interactions of LPS with peripheral tissues, such as the liver.

Stress and reproduction: controversies and challenges

Inhibition of reproductive function by the activation of the stress-response has been observed since times of antiquity, however delineating a molecular mechanism by which this occurs in vertebrates continues to present a major challenge. Because recent genome sequencing programs have identified the presence of numerous paralogous peptides and receptors, our understanding of the complexity of the interaction between the reproductive and stress axes has expanded. At the neuroendocrine level, numerous studies have focused on the interaction between the corticotropin-releasing factor (CRF) and gonadotropin-releasing hormone (GnRH) systems in vertebrates. Moreover, most of these studies have been performed using rodent models and may not be completely relevant for non-mammalian vertebrates. A further problem lies in the variation of the functional expression of paralogous genes in the different taxa. In particular, the urocortin 2 and GnRH-II systems have been lost in some lineages, where its function has been taken over by urocortin 3 and GnRH-I, respectively. Establishing an integrated model that incorporates all paralogous systems for both the stress and reproductive system remains to be achieved.

The ultradian and circadian rhythms of free corticosterone in the brain are not affected by gender: an in vivo microdialysis study in Wistar rats

Recently, we described that free corticosterone levels in the brain of male Wistar rats, as assessed by in vivo microdialysis, show an ultradian rhythm with a pulse frequency of 1.2 pulses/h. To establish whether gender influences brain free corticosterone rhythms, we studied free corticosterone levels in the female Wistar rat under baseline and stressful conditions using microdialysis in the hippocampus. Analysis of the data with the PULSAR algorithm revealed that hippocampal free corticosterone levels show a clear ultradian pattern in female rats with a pulse frequency of 1.16+/-0.05 pulses/h between 09.00 h and 21.00 h. Further analysis showed that the pulse amplitude is significantly higher during the late afternoon/early night (15.00-21.00 h) than during the morning/early afternoon (09.00-15.00 h) phase (0.13+/-0.03 versus 0.07+/-0.01 microg/dl, respectively, P < 0.05). Pulse characteristics were extremely reproducible as demonstrated by the almost identical pulse parameters derived from two consecutive 24-h periods [pulse frequency: 1.13+/-0.09 and 1.19+/-0.08 pulses/h; pulse amplitude: 0.11+/-0.05 and 0.10+/-0.02 microg/dl for day 1 and day 2 (09.00-21.00 h) respectively, P > 0.05]. Both exposure to a novel environment and forced swim stress increased hippocampal free corticosterone levels. However, the stress-induced rise reached higher levels and was more prolonged after forced swimming (area under the curve: 46.84+/-9.25 and 12.08+/-1.69 arbitrary units for forced swimming and novelty stress respectively, P = 0.01). Importantly, the ultradian rhythm was rapidly restored after termination of the stress response. This is the first demonstration that the female rat brain is exposed to free corticosterone levels that follow a circadian as well as an ultradian pattern and show almost identical pulse characteristics as recently reported in male animals. These observations are of significance for further investigations into the dynamics of glucocorticoid action in the brain of both genders.

Influence of the estrous cycle on tolerance development to LPS-induced sickness behaviors in rats

The relations between the estrous cycle, inflammatory responses and the development of tolerance to endotoxin were examined. Female Long-Evans rats were injected intraperitoneally with lipopolysaccharide (LPS; 200 microg/kg) or saline vehicle at 08:00h on either diestrus (D) or proestrus (P). Ninety-five minutes after injection locomotor activity was assessed in an automated non-novel open-field for 20 min. To assess tolerance development to LPS, rats were re-injected at the next identical stage (i.e. 4 days later; groups: DD, PP) or at the alternate stage (i.e. 6 days later; groups: DP, PD) of the estrous cycle and locomotor activity was again assessed. On Test Day 1 all groups injected with LPS exhibited similar significant activity decrements, regardless of the stage of the estrous cycle. However, on Test Day 2 rats which received both injections of LPS during proestrus (PP) showed no signs of tolerance development, whereas rats in all other groups were tolerant to LPS. In a follow up study, the time between injections was extended to 8 days. Still the animals injected both times at proestrus showed no signs of tolerance to LPS after the second injection. Thus, the stages of the estrous cycle both at the time of initial exposure and of re-exposure appear critical in the formation of behavioral tolerance to LPS in rats.

Analgesia and hyperalgesia from CRF receptor modulation in the central nervous system of Fischer and Lewis rats

This study examines the contribution of central corticotropin-releasing factor (CRF) to pain behavior. CRF is the principal modulator of the hypothalamo-pituitary-adrenal (HPA) axis, in addition to acting on many other areas of the central nervous system. We compared nociceptive thresholds (heat and mechanical) and pain behavior in response to a sustained stimulus (formalin test) between Fischer and Lewis rats that have different HPA axis activity. Intracerebroventricular (i.c.v.) administration of CRF produced dose-dependent antinociception at a lower dose in Lewis (40 ng, paw pinch 71+/-0 g) compared to Fischer rats (200 ng, 112+/-3 g). The antinociceptive effect of CRF was mostly preserved in adrenalectomized Fischer rats. The i.c.v. administration of the CRF receptor antagonist, astressin, had a hyperalgesic effect, suggesting that CRF is tonically active. Lewis rats required higher doses of astressin (5 ng, paw pinch 51+/-1 g) to show nociceptive effects compared to Fischer rats (1 ng, 79+/-1 g). Only Lewis rats vocalized during mechanical stimulus, and this behavior was prevented by diazepam or morphine but was worsened by CRF, despite its antinociceptive property. In the formalin test, CRF and astressin had the largest effect on the interphase suggesting that they act on the endogenous pain inhibitory system. CRF also increased anxiety/fear-like behaviors in the forced swim and predator odor tests. Our results establish that central CRF is a key modulator of pain behavior and indicates that CRF effects on nociception are largely independent of its mood modulating effect as well as its control of the HPA axis.

Long-term behavioural alterations in female rats after a single intense footshock followed by situational reminders

Post-traumatic stress disorder (PTSD) affects a vulnerable sub-population of individuals exposed to a traumatic event. This psychopathology induces long-lasting hypothalamo-pituitary-adrenal (HPA) axis hypoactivity, hyperarousal and avoidance of trauma-like situation. PTSD also manifests a high co-morbidity with anxiety disorders. The aim of the present study was to characterise long-term biobehavioural alterations in female rats in an animal model of PTSD consisting in an intense footshock (2 mA, 10s) followed by three weekly situational reminders. This procedure induced several long-term alterations: increased anxiety behaviour, reduced time spent in an 'aversive-like' context, altered social behaviour and blunted corticosterone response to stress. These results demonstrate that exposure to an intense footshock associated with repeated situational reminders elicited long-term disturbances which lasted more than 1 month after the footshock administration. Our findings suggest that this paradigm could provide a useful animal model of PTSD.

Gonadal steroid replacement reverses gonadectomy-induced changes in the corticosterone pulse profile and stress-induced hypothalamic-pituitary-adrenal axis activity of male and female rats

We investigated the effects of gonadal hormone replacement on the pulsatile parameters underlying basal circadian corticosterone secretion in castrated male and ovariectomized female rats using an automated sampling system. Blood was collected from freely moving, unanaesthetized rats every 10 min over a 24-h period and sampling was continued during a noise stress and after lipopolysaccharide (LPS) administration. Castrated male rats had markedly higher corticosterone levels than intact controls. This was reflected by increased number and frequency of pulses in addition to an increase in the pulse height and amplitude under both basal circadian and stress conditions. Hormone replacement with either testosterone or dihydrotestosterone returned these corticosterone levels and circadian profile to those found in intact males, confirming an androgen-mediated effect. Ovariectomized females had significantly lower basal and stress-induced corticosterone levels with lower frequency and amplitude of corticosterone pulses than intact females. 17beta-oestradiol replacement returned basal levels, pulsatile measurements and stress-induced corticosterone levels to those found in intact females. Three hours post-LPS administration, castrated males demonstrated significantly higher values of parvocellular paraventricular nucleus (PVN) arginine vasopressin and corticotrophin-releasing factor and anterior pituitary pro-opiomelanocortin mRNA while ovariectomized females showed significantly lower levels of all three transcripts compared to intact controls. PVN glucocorticoid receptor mRNA levels 3 h post-LPS administration were significantly decreased in castrated males and significantly increased in ovariectomized female rats. Replacement of gonadal steroids resulted in a return to the levels found in intact controls after LPS. Gonadal steroid replacement is sufficient to reverse changes in the pulsatile characteristics of corticosterone release after gonadectomy. In addition, gonadal steroid replacement reverses stress-induced alterations in hypothalamic-pituitary-adrenal (HPA) activity. These data demonstrate a major contribution of gonadal steroids to the regulation of HPA axis activity and to the pulsatile characteristics of corticosterone release.

Gender, sex steroids, corticotropin-releasing factor, nitric oxide, and the HPA response to stress

We used two stresses--exposure to mild electrofoot shocks (a neurogenic stress) and acute alcohol injection (a systemic stress)--to investigate the influence of gender and circulating sex steroids on ACTH and corticosterone released by adult rats. Both types of stresses significantly increased plasma levels of these hormones. Following exposure to shocks, intact females secreted significantly more ACTH than intact males, a difference that was abolished by ovariectomy. Gender differences in corticosterone responses were sometimes, but not always, present. In contrast, in this series of experiments males released more ACTH when acutely injected with alcohol, while there was no obvious effect of sex on corticosterone secretion. Corticotropin-releasing factor (CRF) antagonists were more effective at reducing ACTH compared to corticosterone levels. Finally, pituitary response to CRF, but much less so to vasopressin (VP), was larger in intact females compared to intact males. Blockade of endogenous nitric oxide formation slightly enhanced the effect of CRF in males, but not in females, and while it produced the expected enhancement of VP-induced ACTH release, this effect was more pronounced in females. Collectively, these results provide evidence for an influence of circulating sex steroids on pituitary and adrenal activity under some, but not all circumstances.

Defeat is a major stressor in males while social instability is stressful mainly in females: towards the development of a social stress model in female rats

Social stress models appear useful in elucidating the interrelationship between stress, mood disorders, and drug efficacy. However, reliable social stress models for females are virtually lacking. The aim of this study was to determine stress-related consequences of (a) defeat in aggressive encounters and (b) social instability, in male and female rats. Defeat in male and female subjects was induced by aggressive male residents and female residents made aggressive by surgery (mediobasal hypothalamic lesion [MBHL]), respectively. Aggressiveness of resident males and resident MBHL females was remarkably similar. Alternating isolation and mixed-sex crowding phases with membership rotation were used to induce social instability. Aggression was kept low in the latter paradigm by manipulating crowding group composition. Defeat stress reduced weight gain, and increased both adrenals and plasma corticosterone in males. Only adrenal weight was affected in females. Social instability reduced weight gain, and induced thymus involution, adrenal hypertrophy and elevated plasma corticosterone levels in females. Only weight gain and thymus weights were affected in males. It is concluded that defeat stresses males more than females, while social instability is more stressful for females than for males, if aggressive contacts are low. It is suggested that the social instability model is a good model of social stress in females.

Effect of acute corticotropin releasing factor on pituitary-adrenocortical responsiveness in elderly women and men

Aging is related to critical changes of the hypothalamo-pituitary-adrenal function. A decline in serum DHEA levels has been demonstrated in healthy elderly subjects, while ACTH and cortisol concentrations remain at normal values. The purpose of the present study was to investigate the effect of aging on pituitary-adrenal responsiveness to hCRF in subjects of both sexes. A group of 12 physically and mentally healthy elderly subjects and a group of 12 young controls of both sexes have been selected. Blood samples were collected before and after i.v. bolus injection of hCRF; ACTH, cortisol and DHEA levels were then determined by RIA. Basal ACTH and cortisol levels did not result statistically different between controls and elderly subjects, while DHEA showed a clear and significant age-related decrease (p < 0.01). Following the hCRF injection, the responses of ACTH, cortisol and DHEA in aged subjects were higher than in young controls; ACTH (p < 0.03) and cortisol (p < 0.01) were higher in aged women than in men. The present study demonstrated that aging is associated with an increased responsiveness of ACTH, cortisol and DHEA to exogenous hCRF supply. A hyperactivation of the pituitary-adrenal secretory activity may explain the age-related of the same axis. Gender probably has a significant influence on basal and stimulated hormonal secretion. In conclusion, hCRF test may become a useful clinical tool in establishing a neuroendocrine correlation with central disturbances associated to aging.

Ectopic expression of the CRF-binding protein: minor impact on HPA axis regulation but induction of sexually dimorphic weight gain

Corticotrophin-releasing factor (CRF) and urocortin possess a high-affinity binding protein. Although the CRF binding protein (BP) can sequester these ligands and inhibit their activity, the endogenous activity of this protein is not understood. Therefore, transgenic mouse lines that over-express the CRF-BP were created. The transgene was constructed by ligating rat CRF-BP cDNA (1.1 kb) between a mouse metallothionein-I promoter (1.8 kb) and a nonfunctional human growth hormone gene sequence (2.1 kb) in a modified pBR322 plasmid and microinjecting the transgene into C57BL/6 x SJL hybrid ova. The transgene was expressed in 50% in both male and female progeny. All transgenic lines were maintained by crossing transgenic animals with wild-type C57BL/6 mates. Reverse-transcriptase (RT) PCR of the CRF-BP transgene showed that it is widely expressed not only in the brain and pituitary, but also peripheral tissues including the liver, kidney and spleen. Transgenic animals of both sexes showed significant increases in weight gain as established by analysis of variance; however, the weight gain profiles for each sex were distinct. High levels of circulating CRF-BP were detected in the transgenic animals, but the basal ACTH and corticosterone levels were not significantly decreased compared to wild-type littermates. The hypothalamopituitary-adrenal (HPA) axis was stimulated by systemic inflammation induced with lipopolysaccharide (LPS). An expected increase in transgene expression was observed and was accompanied by a significant attenuation of ACTH secretion at 3 h after LPS injection in the transgenic males but not the females. These data suggest that HPA axis regulation is significantly affected only with very high circulating levels of CRF-BP. Moreover, this work supports previous studies that implicate CRF and urocortin in the regulation of appetite and the binding protein expression may play a sexually dimorphic role in regulating this and other responses.