Corticotropin-releasing Hormone Gene Expression Research Articles

Increased CRH mRNA levels in the rat amygdala during short-term withdrawal from chronic ‘binge’ cocaine

There is evidence that suggests that increased corticotropin-releasing hormone (CRH) release in the central nucleus of the amygdala underlies the anxiogenic and stress-like consequences of withdrawal that are common in phenomenology to all drugs of abuse. The present studies were undertaken to determine levels of CRH mRNA in the amygdala, and also in the hypothalamus, frontal cortex and brainstem after short-term (2 days) and intermediate-term (10 days) cocaine withdrawal (with continued saline injections) from chronic (14 days) ‘binge’ pattern cocaine administration (3×15 mg/kg per day at hourly intervals). Confirming our recent finding of an activation of stress responsive hypothalamic–pituitary–adrenal activity during early cocaine withdrawal, there was a significant elevation of plasma corticosterone level after 2-day cocaine withdrawal. There was also a significant elevation of CRH mRNA levels in the amygdala, but not in the hypothalamus, frontal cortex or brainstem after 2-day cocaine withdrawal. A negative correlation between amygdalar CRH mRNA and plasma corticosterone levels was found in the 2-day cocaine withdrawn rats but not in control rats, suggesting that CRH neurons in the amygdala may be differentially responsive to glucocorticoids after chronic cocaine exposure and withdrawal. There were no changes in either plasma corticosterone or amygdalar CRH mRNA levels after 10-day cocaine withdrawal. Our findings of an increase in amygdalar CRH gene expression during early cocaine withdrawal support a potentially important role for amygdalar CRH activity in the anxiogenic and aversive consequences of withdrawal from cocaine during a time when humans are most subject to relapse.

Effects of rearing water quality on expression of brain corticotropin-releasing hormone and gonadal development in goldfish (Carassius auratus)

The effects of changes in water quality in a recirculating system on brain corticotropin-releasing hormone (CRH) gene expression in goldfish were examined. In the experimental group, fish were reared without water change, while in the control group, 50% of water was changed everyday. In the experimental group, total ammonia-nitrogen, nitrate and phosphate were increased over the experimental period. Brain CRH mRNA levels in the control group seemed higher than those in the experimental group, but differences were confounded by variation among individuals. There were no differences in gonadal development between both groups.

Repeated citalopram treatment but not stress exposure attenuates hypothalamic-pituitary-adrenocortical axis response to acute citalopram injection

Many experimental, clinical and epidemiological studies have shown a direct connection between exposure to stress or adverse life events and disease, but little is known about the effect of stress on the action of drugs. The aim of this study was to test the hypothesis that previous exposure to stress changes the action of the antidepressant drug citalopram (10 mg/kg, i.p.) on hypothalamic-pituitary-adrenocortical (HPA) axis function, gene expression of selected neuropeptides and serotonin reuptake. Three different stress models were used, which included immobilization, restraint and unpredictable stress stimuli. Samples of plasma for hormone measurement were taken from conscious cannulated animals. Changes in corticotropin-releasing hormone (CRH) and proopiomelanocortin (POMC) gene expression in the paraventricular nucleus of the hypothalamus and the anterior pituitary, respectively, and the ability of citalopram to inhibit serotonin reuptake were investigated. The exposure to three different stress models did not influence citalopram action on individual parameters of HPA axis and on serotonin reuptake. On the other hand, repeated administration of the drug led to significant attenuation of ACTH and CRH mRNA responses. The present results allow to suggest that the stressors used did not influence serotonergic neurotransmission to the extent that would modify HPA axis response to citalopram challenge. Activation of HPA axis by acute citalopram treatment was found to be accompanied by increased CRH gene expression in the hypothalamus. Repeated administration of the drug led to the development of tolerance to activation of central and peripheral components of HPA axis, but not to serotonin reuptake inhibition.

Upregulation of CRH gene expression and downregulation of arginine vasopressin gene expression in the hypothalamus of bilateral nephrectomized rats

The expression of the corticotropin-releasing hormone (CRH) gene and the arginine vasopressin (AVP) gene in the hypothalamus examined in bilateral nephrectomized rats by in situ hybridization histochemistry. The expression of the CRH gene was significantly increased in the parvocellular part of the paraventricular nucleus (PVN) 12 and 20 h after bilateral nephrectomy in comparison with that after sham operation. The plasma concentration of adrenocorticotropic hormone (ACTH) in nephrectomized rats was significantly higher than that in sham operated rats 20 h after surgery. In contrast, the expression of the AVP gene in both the parvocellular and magnocellular parts of the PVN and throughout the supraoptic nucleus (SON) was significantly decreased 20 h after bilateral nephrectomy in comparison with that after sham operation. These results suggest that nephrectomy-induced upregulation of the CRH gene with elevation of plasma ACTH may be due to the activation of the hypothalamo-pituitary adrenal (HPA) axis.

Neurosteroids in depression: a review.

A deregulation in concentrations of the neurosteroids (allo)pregnanolone and 3alpha,5alpha-tetrahydrodeoxycorticosterone (3alpha,5alpha-TH DOC) has been found in depressed patients. These levels normalize following treatment with selective serotonin reuptake inhibitors (SSRIs). Furthermore, administration of the neurosteroid dehydroepiandrosterone (DHEA) to depressed patients is associated with an improvement in the symptoms of depression. The aim of the present review is to clarify the mechanisms whereby neurosteroids, particularly allopregnanolone and DHEA, are involved in depression and to discuss the effect of SSRIs on allopregnanolone concentration. Literature on preclinical and clinical research has been analyzed in relation to the pathophysiology of depression. Decreased plasma and cerebrospinal fluid concentrations of allopregnanolone in depressed patients increase to normal levels following effective psychopharmacological treatment. This might either be a physiological aspect of improvement in the symptoms of depression or a pharmacologically induced alteration. Several findings support the hypothesis of an antidepressant effect of allopregnanolone. These include an antidepressant effect demonstrated in an animal model of depression and a suppressing effect on corticotropin-releasing hormone (CRH) and arginine-vasopressin (AVP) gene expression. SSRIs increase levels of allopregnanolone, but this effect is not confined to this class of drugs alone. The beneficial effect of DHEA administration in depressed patients might result from its sigma 1 receptor-mediated enhancement of noradrenaline and serotonin neurotransmission, antiglucocorticoid effects, and cognition enhancing effects. Indirect genomic (allopregnanolone) and non-genomic (allopregnanolone and DHEA) mechanisms are involved in the neurosteroidogenic pathophysiology of depression. Clinical studies in homogeneous groups of non-pharmacologically treated depressed patients are required to elucidate this relationship further.

Serotonergic stimulation of corticotropin-releasing hormone and pro-opiomelanocortin gene expression.

The neurotransmitter serotonin (5-HT) stimulates adrenocorticotropic hormone (ACTH) secretion from the anterior pituitary gland via activation of central 5-HT1 and 5-HT2 receptors. The effect of 5-HT is predominantly indirect and may be mediated via release of hypothalamic corticotropin-releasing hormone (CRH). We therefore investigated the possible involvement of CRH in the serotonergic stimulation of ACTH secretion in male rats. Increased neuronal 5-HT content induced by systemic administration of the precursor 5-hydroxytryptophan (5-HTP) in combination with the 5-HT reuptake inhibitor fluoxetine raised CRH mRNA expression in the paraventricular nucleus (PVN) by 64%, increased pro-opiomelanocortin (POMC) mRNA in the anterior pituitary lobe by 17% and stimulated ACTH secretion five-fold. Central administration of 5-HT agonists specific to 5-HT1A, 5-HT1B, 5-HT2A or 5-HT2C receptors increased CRH mRNA in the PVN by 15-50%, POMC mRNA in the anterior pituitary by 15-27% and ACTH secretion three- to five-fold, whereas a specific 5-HT3 agonist had no effect. Systemic administration of a specific anti-CRH antiserum inhibited the ACTH response to 5-HTP and fluoxetine and prevented the 5-HTP and fluoxetine-induced POMC mRNA response in the anterior pituitary lobe. Central or systemic infusion of 5-HT increased ACTH secretion seven- and eight-fold, respectively. Systemic pretreatment with the anti-CRH antiserum reduced the ACTH responses to 5-HT by 80% and 64%, respectively. It is concluded that 5-HT via activation of 5-HT1A, 5-HT2A, 5-HT2C and possibly also 5-HT1B receptors increases the synthesis of CRH in the PVN and POMC in the anterior pituitary lobe, which results in increased ACTH secretion. Furthermore, the results indicate that CRH is an important mediator of the ACTH response to 5-HT.

Prolonged alcohol intake leads to reversible depression of corticotropin-releasing hormone and vasopressin immunoreactivity and mRNA levels in the parvocellular neurons of the paraventricular nucleus

The ability of alcohol to activate the hypothalamic–pituitary–adrenal (HPA) axis is well documented in investigations based in acute and short-term experimental paradigms. Herein, we have addressed the possibility that the prolonged exposure to ethanol concentrations that are initially effective in stimulating corticosteroid secretion might induce alterations in the response of the HPA axis that cannot be evinced by shorter exposures. Using conventional histological techniques, immunohistochemistry and in situ hybridization, we have examined the medial parvocellular division of the paraventricular nucleus (PVNmp), and the synthesis and expression of corticotropin-releasing hormone (CRH) and vasopressin (VP) by its constituent neurons, in rats submitted to 6 months of ethanol treatment and to withdrawal (2 months after 6 months of alcohol intake). Ethanol treatment and withdrawal did not produce neuronal loss in the PVNmp. However, the total number of CRH- and VP-immunoreactive neurons and the CRH mRNA levels were significantly decreased by ethanol treatment. In withdrawn rats, the number of CRH- and VP-immunostained neurons and the gene expression of CRH were increased relative to ethanol-treated rats and did not differ from those of controls. No significant variations were detected in VP mRNA levels as a result of ethanol treatment or withdrawal. These results show that prolonged alcohol intake blunts the expression of CRH and VP in the parvocellular neurons of the PVN, and that this effect is, partially at least, reversible by withdrawal. They also suggest that the development of tolerance to the effects of ethanol involve changes that take place at the hypothalamic level.

Interactions between heterotypic stressors and corticosterone reveal integrative mechanisms for controlling corticotropin-releasing hormone gene expression in the rat paraventricular nucleus.

Although the convergence of neural and humoral afferent information onto paraventricular neuroendocrine corticotropin-releasing hormone (CRH) neurons is a major determinant for adaptive stress responses, the underlying integrative mechanisms are poorly understood. To dissect the relative contributions made by neural afferents and corticosterone to these processes, we determined how the concurrent application of two heterotypic physiological stressors, chronic dehydration (produced by drinking hypertonic saline) and sustained hypovolemia (produced by subcutaneous injections of polyethylene glycol), is interpreted by the synthetic and secretory activity of CRH neurons using in situ hybridization and plasma ACTH measurements. These two stressors are encoded by relatively simple, distinct, and well defined sets of neural afferents to CRH neurons. Both increase plasma corticosterone, but they have opposing actions on CRH gene expression when applied separately. In the first experiment, we showed that chronic dehydration suppresses CRH gene transcription after hypovolemia, but not the preproenkephalin and c-fos mRNA responses or ACTH secretion. In the second, we showed that negative feedback actions of corticosterone do not suppress CRH gene activation after hypovolemia, but instead determine the prestress lower limit of a range within which the CRH gene then responds. Collectively, these data show that at least two processes are integrated to control how the CRH gene responds to multiple stimuli. First, the presence of corticosterone, which although permissive for appropriately activating the CRH gene during hypovolemia, does not mediate the suppressed gene response. Second, neural afferent-driven processes that encode dehydration play a central role in suppressing CRH activation.

Interactions between Heterotypic Stressors and Corticosterone Reveal Integrative Mechanisms for Controlling Corticotropin-Releasing Hormone Gene Expression in the Rat Paraventricular Nucleus

Although the convergence of neural and humoral afferent information onto paraventricular neuroendocrine corticotropin-releasing hormone (CRH) neurons is a major determinant for adaptive stress responses, the underlying integrative mechanisms are poorly understood. To dissect the relative contributions made by neural afferents and corticosterone to these processes, we determined how the concurrent application of two heterotypic physiological stressors, chronic dehydration (produced by drinking hypertonic saline) and sustained hypovolemia (produced by subcutaneous injections of polyethylene glycol), is interpreted by the synthetic and secretory activity of CRH neurons usingin situhybridization and plasma ACTH measurements. These two stressors are encoded by relatively simple, distinct, and well defined sets of neural afferents to CRH neurons. Both increase plasma corticosterone, but they have opposing actions onCRHgene expression when applied separately. In the first experiment, we showed that chronic dehydration suppressesCRHgene transcription after hypovolemia, but not the preproenkephalin and c-fosmRNA responses or ACTH secretion. In the second, we showed that negative feedback actions of corticosterone do not suppressCRHgene activation after hypovolemia, but instead determine the prestress lower limit of a range within which the CRH gene then responds. Collectively, these data show that at least two processes are integrated to control how theCRHgene responds to multiple stimuli. First, the presence of corticosterone, which although permissive for appropriately activating the CRH gene during hypovolemia, does not mediate the suppressed gene response. Second, neural afferent-driven processes that encode dehydration play a central role in suppressing CRH activation.

AP-2α modulates human corticotropin-releasing hormone gene expression in the placenta by direct protein–protein interaction

Since AP-2α induces the expression of hPL, hCG and other syncytiotrophoblast-specific marker genes in cytotrophoblast cells during in vitro differentiation, we have examined whether AP-2α also induces hCRH gene expression during differentiation of cytotrophoblast cells. Infection of human cytotrophoblast cells in vitro with an adenovirus expressing AP-2α resulted in a twofold increase in hCRH mRNA levels, while infection with an adenovirus expressing a dominant/negative mutant of AP-2α inhibited basal hCRH mRNA levels by 40% and completely blocked the induction of hCRH mRNA by AP-2α. Transient transfection studies in AtT-20 and HepG2 cells indicated that the induction of hCRH mRNA levels was due, at least in part, to transcriptional activation of the hCRH gene. Gel mobility shift and immunoprecipitation assays strongly suggest that AP-2α induces hCRH gene expression by interacting with CREB and not by binding directly to the hCRH promoter.

Role of corticotropin-releasing hormone in ovarian steroidogenesis.

The physiologic role of corticotropin-releasing hormone (CRH) was examined in the ovary. We investigated the effects of CRH on steroidogenesis in rat and human granulosa cells in vitro as well as the direct effects of CRH on the ovary in vivo. We further examined the gene expression of CRH in human granulosa cells. CRH significantly inhibited the production of estradiol (E2) and progesterone (P4) in rat and human granulosa cells in vitro. These inhibitory effects were completely abolished by alpha-helical CRH, a CRH receptor antagonist. Forskolin-induced increase in E2 and P4 production was attenuated by CRH. On the other hand, CRH significantly increased serum concentrations of E2 and corticosterone in vivo in hypophysectomized rats, but this increase was completely blocked by adrenalectomy. It is probable that these effects did not result from a direct action on the ovary but were an indirect effect via the adrenal gland. Finally, by reverse transcriptase polymerase chain reaction we demonstrated that CRH mRNA was expressed in human granulosa cells. Our findings indicate that CRH exerts inhibitory effects on steroidogenesis in rat and human granulosa cells, acting through the CRH receptor. These effects are attributed to cellular events downstream of cyclic adenosine monophosphate generation. CRH seems to modulate steroidogenesis via autocrine or paracrine actions in the ovary.

Corticotropin-releasing hormone and arginine vasopressin: mRNA and secretion are differentially regulated according to the pattern of exposure to noradrenaline in rat hypothalamic neurones.

Hypothalamic corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) are secreted from the median eminence in a pulsatile manner and regulated by noradrenaline during stress. This study investigated the effect of pulsatile noraderanaline on CRH/AVP mRNAs and secretion. Foetal hypothalamic neurones were cultured on plastic coverslips, inserted into perifusion chambers and noraderanaline pulses given at various doses or pulse intervals for 24 h. CRH and AVP release rose in a dose dependant manner; however, maximal increases in mRNAs were seen with an intermediate noraderanaline pulse dose. The effect of noraderanaline pulse frequency was determined by giving noraderanaline pulses at intervals of 15-120 min vs continuous noraderanaline. Both pulsatile and continuous noraderanaline increased CRH and AVP release, but secretion was reduced after 22 h of treatment in the continuous noraderanaline and rapid pulse groups. CRH mRNA levels were maximally increased by medium interval pulses and AVP mRNA by rapid interval pulses. Neither CRH nor AVP mRNAs were stimulated by continuous noraderanaline. To determine noraderanaline specificity, pulses of veratridine (VER; 15-120 min intervals) vs continuous VER were examined. Only pulsatile VER increased CRH and AVP mRNAs, with maximal effects seen with the 60 min pulse interval for both. Thus, noraderanaline pulse pattern regulates CRH and AVP gene expression in both a coordinate and differential manner. Since noraderanaline plays an important role during stress, the pattern of noraderanaline signals may be critical to the observed changes in CRH and AVP expression.

Erratum to “The regulation of human corticotrophin-releasing hormone gene expression in the placenta” : [Peptides 22 (2001) 795–801

Erratum to “The regulation of human corticotrophin-releasing hormone gene expression in the placenta” : [Peptides 22 (2001) 795–801

Neurobiology of the stress response early in life: evolution of a concept and the role of corticotropin releasing hormone.

Over the last few decades, concepts regarding the presence of hormonal and molecular responses to stress during the first postnatal weeks in the rat and the role of the neuropeptide corticotropin releasing hormone (CRH) in these processes, have been evolving. CRH has been shown to contribute critically to molecular and neuroendocrine responses to stress during development. In turn the expression of this neuropeptide in both hypothalamus and amygdala is differentially modulated by single and recurrent stress, and is determined also by the type of stress (eg, psychological or physiological). A likely transcriptional regulatory factor for modulating CRH gene expression, the cAMP responsive element binding protein CREB, is phosphorylated (activated) in the developing hypothalamus within seconds of stress onset, preceding the transcription of the CRH gene and initiating the activation of stress-induced cellular and neuroendocrine cascades. Finally, early life stress may permanently modify the hypothalamic pituitary adrenal axis and the response to further stressful stimuli, and recent data suggest that CRH may play an integral role in the mechanisms of these long-term changes.

Role of Gonadal Steroids in the Corticotropin-Releasing Hormone and Proopiomelanocortin Gene Expression Response to Δ9-Tetrahydrocannabinol in the Hypothalamus of the Rat

Chronic exposure to Δ⁹-tetrahydrocannabinol (Δ⁹-THC) increases corticotropin-releasing hormone (CRH) and proopiomelanocortin (POMC) gene expression in the rat hypothalamus. The levels of circulating gonadal steroids concurrently modulate both neuropeptides in male and female rats. However, it remains unknown whether gonadal steroids regulate Δ⁹-THC effects on CRH and POMC gene expression in the hypothalamus of male and female rats. To explore this hypothesis, experiments were conducted on intact, 2-week-gonadectomized, 1-week-gonadectomized, 1-week-dihydrotestosterone (DHT)- or estradiol-replaced male and female rats. One week after hormonal replacement, animals were treated with vehicle or Δ⁹-THC (5 mg/kg/day, i.p. for 7 days). Administration of Δ⁹-THC to intact male rats increased CRH gene expression. Castration abolished Δ⁹-THC effects of CRH gene expression in males but not in females. On the other hand, POMC mRNA levels were reduced as a result of castration, and DHT treatment did not prevent this decrease. Δ⁹-THC treatment similarly increases POMC gene expression of intact, orchidectomized and DHT-replaced males. In females, ovariectomy decreased CRH gene expression. Δ⁹-THC administration increased CRH gene expression to the same extent in castrated and estradiol-replaced rats. On the other hand, POMC gene expression was increased by ovariectomy, and Δ⁹-THC administration did only increase POMC transcript levels in the estradiol-replaced group. These data show that gonadal steroids differentially regulate the effects of Δ⁹-THC on both CRH and POMC gene expression in the hypothalamus of male and female rats, suggesting gender differences in the reaction to cannabinoids.

The regulation of human corticotrophin-releasing hormone gene expression in the placenta

Corticotrophin-releasing hormone (CRH) is a 41 amino acid neuropeptide that is expressed in the hypothalamus and the human placenta. Placental CRH production has been linked to the determination of gestational length in the human. Although encoded by a single copy gene, CRH expression in the placenta is regulated differently to the hypothalamus. Glucocorticoids stimulate CRH promoter activity in the placenta but inhibit it’s activity in the hypothalamus, via mechanisms involving different regions of the CRH promoter. We discuss how various stimuli alter CRH promoter activity and why these responses are unique to the placenta.

Appetite-Suppressing Effects of Urotensin I and Corticotropin-Releasing Hormone in Goldfish (Carassius auratus)

Fish urotensin I (UI), a member of the corticotropin-releasing hormone (CRH) family of peptides, is a potent inhibitor of food intake in mammals, yet the role of UI in the control of food intake in fish is not known. Therefore, to determine the acute effects of UI on appetite relative to those of CRH, goldfish were given intracerebroventricular (i.c.v.) injections of carp/goldfish UI and rat/human CRH (0.2–200 ng/g) and food intake was assessed for a 2-hour period after the injection. UI and CRH both suppressed food intake in a dose-related manner and UI (ED₅₀ = 3.8 ng/g) was significantly more potent than CRH (ED₅₀ = 43.1 ng/g). Pretreatment with the CRH receptor antagonist, α-helical CRH_(9–41), reversed the reduction in food intake induced by i.c.v. UI and CRH. To assess whether endogenous UI and CRH modulate fish appetite, goldfish were given intraperitoneal implants of the glucocorticoid receptor antagonist, RU-486 (50 and 100 µg/g), or the cortisol synthesis inhibitor, metyrapone (100 and 200 µg/g), and food intake was monitored over the following 72 h. Fish treated with either RU-486 or metyrapone were characterized by a sustained and dose-dependent reduction in food intake. Pretreatment with i.c.v. implants of α-helical CRH_(9–41) partially reversed the appetite-suppressing effects of RU-486 and metyrapone. In a parallel experiment, the effects of RU-486 (100 µg/g) and metyrapone (200 µg/g) intraperitoneal implants on brain UI and CRH gene expression were assessed. Relative to sham-implanted controls, fish treated with RU-486 or metyrapone had elevated UI mRNA levels in the hypothalamus and CRH mRNA levels in the telencephalon-preoptic brain region. Together, these results suggest that UI is a potent anorectic peptide in the brain of goldfish and that endogenous CRH-related peptides can play a physiological role in the control of fish appetite.

Mechanism of Anticonvulsant Action of ACTH

The hypothesis that systemic or intraventricular administration of corticotropin (ACTH) acts directly on limbic neurons to modulate corticotropin-releasing hormone (CRH) gene expression, independently of adrenal stimulation, was tested and confirmed in experiments on developing rats (9-11 days postnatal) at the University of California, Irvine.

Corticotropin (ACTH) acts directly on amygdala neurons to down‐regulate corticotropin‐releasing hormone gene expression

The hormone corticotropin (ACTH) is employed as therapy for diverse neurological disorders, but the mechanisms for its efficacy remain unknown. ACTH promotes the release of adrenal steroids (glucocorticoids), and most ACTH effects on the central nervous system (CNS) have been attributed to activation of glucocorticoid receptors. However, in several human disorders, ACTH has therapeutic actions that differ qualitatively or quantitatively from those of steroids. This study tested the hypothesis that ACTH directly influences limbic neurons via the recently characterized melanocortin receptors and focused on the effects of ACTH on the expression of corticotropin-releasing hormone (CRH), a neuropeptide involved in neuroimmune functions and in certain developmental seizures. The results demonstrated that ACTH potently reduced CRH expression in amygdala neurons. This down-regulation was not abolished by experimental elimination of steroids or by blocking their receptors and was reproduced by a centrally administered ACTH fragment that does not promote steroid release. Importantly, selective blocking of melanocortin receptors prevented ACTH-induced down-regulation of CRH expression. Taken together, these data indicate that ACTH activates central melanocortin receptors to modulate CRH gene expression in amygdala, supporting the notion that direct, steroid-independent actions of ACTH may account for some of its established clinical effects on the CNS.

Corticotropin-releasing hormone mRNA levels in response to chronic mild stress rise in male but not in female rats while tyrosine hydroxylase mRNA levels decrease in both sexes.

Corticotropin-releasing hormone (CRH) and catecholamines are suggested to play a significant role in the pathophysiology of depression. In the present study we investigated gene expression of CRH in the hypothalamic paraventricular nucleus (PVN) and tyrosine hydroxylase (TH) in the locus coeruleus (LC) in an experimental model of depression. A chronic mild stress model was applied in rats of both genders for a three-week period. Anhedonic behaviour, a typical sign of depression-like state, was measured by a sucrose preference test. The chronic mild stress induced a decrease in sucrose preference in both genders. The body weight gain was reduced in males only. The total activity in the open field test was unchanged, however, male rats exposed to chronic mild stress showed enhanced locomotor activity during the first minute of the session, suggesting increased anxiety. Basal plasma corticosterone levels, thymus and adrenal weights measured on the third day after cessation of the stress regimen, were not affected by the stress procedure. Evaluation of CRH mRNA levels in the PVN by in situ hybridisation revealed a significant rise in response to chronic mild stress in males. In females, the basal CRH mRNA levels were higher compared to those in males, but the stress-induced rise was absent. Chronic mild stress resulted in a decrease in TH mRNA levels in the LC. These data demonstrate that chronic mild stress model of depression induces a specific stress response with a reduction of TH gene expression in the LC and clear gender differences in gain of body weight, anxiety-like behaviour, and CRH mRNA levels in the PVN.