Role of arginine vasopressin and corticotropin-releasing factor in mediating alcohol-induced adrenocorticotropin and vasopressin secretion in male rats bearing lesions of the paraventricular nuclei

Recognition of Nonneoplastic Hypercortisolism in the Evaluation of Patients With Cushing Syndrome

The evaluation of suspected hypercortisolism is one of the most challenging problems in medicine. The signs and symptoms described by Dr Harvey Cushing are common and often create diagnostic confusion to even experienced endocrinologists. Cushing syndrome is classically defined as neoplastic hypercortisolism resulting from an ACTH-secreting tumor or from autonomous secretion of excess cortisol associated with benign or malignant adrenal neoplasia. The increasing recognition of the negative cardiometabolic effects of mild cortisol excess without overt physical signs of Cushing syndrome has led to more screening for endogenous hypercortisolism in patients with adrenal nodular disease, osteoporosis, and the metabolic syndrome. However, sustained or intermittent activation of the dynamic hypothalamic-pituitary-adrenal axis caused by chemical (alcohol), inflammatory (chronic kidney disease), psychologic (major depression), and physical (starvation/chronic intense exercise) stimuli can result in clinical and/or biochemical features indistinguishable from neoplastic hypercortisolism. Nonneoplastic hypercortisolism (formerly known as pseudo-Cushing syndrome) has been recognized for more than 50 years and often causes diagnostic uncertainty. This expert consultation describes two patients with features of Cushing syndrome who were referred for inferior petrosal sinus sampling for the differential diagnosis of ACTH-dependent hypercortisolism. Both patients were discovered to have nonneoplastic hypercortisolism: one from a covert alcohol use disorder and the other to chronic kidney disease. This consultation emphasizes the value of a good history and physical examination, appropriate laboratory testing, and the desmopressin acetate stimulation test to aid in distinguishing neoplastic from nonneoplastic hypercortisolism.

Alcohol-induced Cushing syndrome: report of eight cases and review of the literature

Introduction

Alcohol-induced hypercortisolism (AIH) is underrecognized and may masquerade as neoplastic hypercortisolism [Cushing syndrome (CS)] obscuring its diagnosis.

Objective and methods

In order to characterize AIH, we performed a chart review of eight patients (4 males and 4 females; 2014-2022) referred for evaluation and treatment of neoplastic hypercortisolism - six for inferior petrosal sinus sampling, one due to persistent CS after unilateral adrenalectomy, and one for pituitary surgery for Cushing disease (CD). Five underwent dDAVP stimulation testing.

Results

All eight patients had clinical features of hypercortisolism and plasma ACTH levels within or above the reference interval confirming hypothalamic-pituitary mediation. All had abnormal low-dose dexamethasone suppression test and increased late-night salivary cortisol. Only one had increased urine cortisol excretion. In contrast to CD, the 5 patients tested had blunted or absent ACTH and cortisol responses to desmopressin. Two had adrenal nodules and one had abnormal pituitary imaging. Most patients underreported their alcohol consumption and one denied alcohol use. Elevated blood phosphatidyl ethanol (PEth) was required in one patient to confirm excessive alcohol use. All patients had elevations of liver function tests (LFTs) with AST>ALT.

Conclusion

AIH is an under-appreciated, reversible cause of non-neoplastic hypercortisolism that is indistinguishable from neoplastic CS. Incidental pituitary and adrenal imaging abnormalities as well as under-reporting of alcohol consumption further confound the diagnosis. Measurement of PEth helps to confirm an alcohol use disorder. Elevations of LFTs (AST>ALT) and subnormal ACTH and cortisol responses to dDAVP help to distinguish AIH from neoplastic hypercortisolism.

The Effects of Alcohol Intoxication and Withdrawal on Hypothalamic Neurohormones and Extrahypothalamic Neurotransmitters

The aim of the present study was to determine the effects of alcohol intoxication and withdrawal on hypothalamic neurohormones such as corticotropin-releasing factor (CRF) and arginine vasopressin (AVP), and extrahypothalamic neurotransmitters such as striatal dopamine (DA), amygdalar gamma aminobutyric acid (GABA), and hippocampal glutamate (GLU). In addition, the participation of the two CRF receptors, CRF1 and CRF2, was investigated. For this purpose, male Wistar rats were exposed to repeated intraperitoneal (ip) administration of alcohol every 12 h, for 4 days and then for 1 day of alcohol abstinence. On the fifth or sixth day, intracerebroventricular (icv) administration of selective CRF1 antagonist antalarmin or selective CRF2 antagonist astressin₂B was performed. After 30 min, the expression and concentration of hypothalamic CRF and AVP, the concentration of plasma adrenocorticotropic hormone (ACTH) and corticosterone (CORT), and the release of striatal DA, amygdalar GABA, and hippocampal GLU were measured. Our results indicate that the neuroendocrine changes induced by alcohol intoxication and withdrawal are mediated by CRF1, not CRF2, except for the changes in hypothalamic AVP, which are not mediated by CRF receptors.

The Mechanisms Underlying Autonomous Adrenocorticotropic Hormone Secretion in Cushing's Disease

Cushing’s disease caused due to adrenocorticotropic hormone (ACTH)-secreting pituitary adenomas (ACTHomas) leads to hypercortisolemia, resulting in increased morbidity and mortality. Autonomous ACTH secretion is attributed to the impaired glucocorticoid negative feedback (glucocorticoid resistance) response. Interestingly, other conditions, such as ectopic ACTH syndrome (EAS) and non-neoplastic hypercortisolemia (NNH, also known as pseudo-Cushing’s syndrome) also exhibit glucocorticoid resistance. Therefore, to differentiate between these conditions, several dynamic tests, including those with desmopressin (DDAVP), corticotrophin-releasing hormone (CRH), and Dex/CRH have been developed. In normal pituitary corticotrophs, ACTH synthesis and secretion are regulated mainly by CRH and glucocorticoids, which are the ACTH secretion-stimulating and -suppressing factors, respectively. These factors regulate ACTH synthesis and secretion through genomic and non-genomic mechanisms. Conversely, glucocorticoid negative feedback is impaired in ACTHomas, which could be due to the overexpression of 11β-HSD2, HSP90, or TR4, or loss of expression of CABLES1 or nuclear BRG1 proteins. Genetic analysis has indicated the involvement of several genes in the etiology of ACTHomas, including USP8, USP48, BRAF, and TP53. However, the association between glucocorticoid resistance and these genes remains unclear. Here, we review the clinical aspects and molecular mechanisms of ACTHomas and compare them to those of other related conditions.

Behavioral, neurobiological, and neurochemical mechanisms of ethanol self-administration: A translational review

Alcohol use disorder has multiple characteristics including excessive ethanol consumption, impaired control over drinking behaviors, craving and withdrawal symptoms, compulsive seeking behaviors, and is considered a chronic condition. Relapse is common. Determining the neurobiological targets of ethanol and the adaptations induced by chronic ethanol exposure is critical to understanding the clinical manifestation of alcohol use disorders, the mechanisms underlying the various features of the disorder, and for informing medication development. In the present review, we discuss ethanol's interactions with a variety of neurotransmitter systems, summarizing findings from preclinical and translational studies to highlight recent progress in the field. We then describe animal models of ethanol self-administration, emphasizing the value, limitations, and validity of commonly used models. Lastly, we summarize the behavioral changes induced by chronic ethanol self-administration, with an emphasis on cue-elicited behavior, the role of ethanol-related memories, and the emergence of habitual ethanol seeking behavior.

Chronic alcohol disrupts hypothalamic responses to stress by modifying CRF and NMDA receptor function

The chronic inability of alcoholics to effectively cope with relapse-inducing stressors has been linked to dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis and corticotropin-releasing factor (CRF) signaling. However, the cellular mechanisms responsible for this dysregulation are yet to be identified. After exposure of male Sprague Dawley rats to chronic intermittent ethanol (CIE; 5-6 g/kg orally for 35 doses over 50 days) or water, followed by 40-60 days of protracted withdrawal, we investigated CIE effects on glutamatergic synaptic transmission, stress-induced plasticity, CRF- and ethanol-induced NMDAR inhibition using electrophysiological recordings in parvocellular neurosecretory cells (PNCs) of the paraventricular nucleus. We also assessed CIE effects on hypothalamic mRNA expression of CRF-related genes using real-time polymerase chain reaction, and on HPA axis function by measuring stress-induced increases in plasma adrenocorticotropic hormone, corticosterone, and self-grooming. In control rats, ethanol-mediated inhibition of NMDARs was prevented by CRF1 receptor (CRFR1) blockade with antalarmin, while CRF/CRFR1-mediated NMDAR blockade was prevented by intracellularly-applied inhibitor of phosphatases PP1/PP2A, okadaic acid, but not the selective striatal-enriched tyrosine protein phosphatase inhibitor, TC-2153. CIE exposure increased GluN2B subunit-dependent NMDAR function of PNCs. This was associated with the loss of both ethanol- and CRF-mediated NMDAR inhibition, and loss of stress-induced short-term potentiation of glutamatergic synaptic inputs, which could be reversed by intracellular blockade of NMDARs with MK801. CIE exposure also blunted the hormonal and self-grooming behavioral responses to repeated restraint stress. These findings suggest a cellular mechanism whereby chronic alcohol dysregulates the hormonal and behavioral responses to repetitive stressors by increasing NMDAR function and decreasing CRFR1 function.

Vasopressin and alcohol: a multifaceted relationship

BACKGROUND

Arginine vasopressin (VP) has been implicated in a number of neuropsychiatric disorders with an emphasis on situations where stress increased the severity of the disorder. Based on this hypothesized role for VP in neuropsychiatric disorders, much research is currently being undertaken in humans and animals to test VP as a target for treatment of a number of these disorders including alcohol abuse.

OBJECTIVES

To provide a summary of the literature regarding the role of VP in alcohol- and stress-related behaviors including the use of drugs that target VP in clinical trials.

RESULTS

Changes in various components of the VP system occur with alcohol and stress. Manipulating VP or its receptors can alter alcohol- and stress-related behaviors including tolerance to alcohol, alcohol drinking, and anxiety-like behavior. Finally, the hypothalamic-pituitary-adrenal axis response to alcohol is also altered by manipulating the VP system. However, clinical trials of VP antagonists have had mixed results.

CONCLUSIONS

A review of VP's involvement in alcohol's actions demonstrates that there is much to be learned about brain regions involved in VP-mediated effects on behavior. Thus, future work should focus on elucidating relevant brain regions. By using previous knowledge of the actions of VP and determining the brain regions and/or systems involved in its different behavioral effects, it may be possible to identify a specific receptor subtype target, drug treatment combination, or specific clinical contexts that may point toward a more successful treatment.

DIAGNOSIS OF ENDOCRINE DISEASE: Differentiation of pathologic/neoplastic hypercortisolism (Cushing's syndrome) from physiologic/non-neoplastic hypercortisolism (formerly known as pseudo-Cushing's syndrome)

Endogenous hypercortisolism (Cushing's syndrome) usually implies the presence of a pathologic condition caused by either an ACTH-secreting neoplasm or autonomous cortisol secretion from a benign or malignant adrenal neoplasm. However, sustained or intermittent hypercortisolism may also accompany many medical disorders that stimulate physiologic/non-neoplastic activation of the HPA axis (formerly known as pseudo-Cushing's syndrome); these two entities may share indistinguishable clinical and biochemical features. A thorough history and physical examination is often the best (and sometimes only) way to exclude pathologic/neoplastic hypercortisolism. The presence of alcoholism, renal failure, poorly controlled diabetes and severe neuropsychiatric disorders should always raise suspicion that the presence of hypercortisolism may be related to physiologic/non-neoplastic Cushing's syndrome. As late-night salivary cortisol and low-dose dexamethasone suppression have good sensitivity and negative predictive value, normal studies exclude Cushing's syndrome of any form. However, these tests have imperfect specificity and additional testing over time with clinical follow-up is often needed. When there is persistent diagnostic uncertainty, secondary tests such as the DDAVP stimulation test and the dexamethasone-CRH test may provide evidence for the presence or absence of an ACTH-secreting tumor. This review will define and characterize the numerous causes of physiologic/non-neoplastic hypercortisolism and provide a rational clinical and biochemical approach to distinguish it from pathologic/neoplastic hypercortisolism (true Cushing's syndrome).

An Update on CRF Mechanisms Underlying Alcohol Use Disorders and Dependence

Alcohol is the most commonly used and abused substance worldwide. The emergence of alcohol use disorders, and alcohol dependence in particular, is accompanied by functional changes in brain reward and stress systems, which contribute to escalated alcohol drinking and seeking. Corticotropin-releasing factor (CRF) systems have been critically implied in the transition toward problematic alcohol drinking and alcohol dependence. This review will discuss how dysregulation of CRF function contributes to the vulnerability for escalated alcohol drinking and other consequences of alcohol consumption, based on preclinical evidence. CRF signaling, mostly via CRF1 receptors, seems to be particularly important in conditions of excessive alcohol taking and seeking, including during early and protracted withdrawal, relapse, as well as during withdrawal-induced anxiety and escalated aggression promoted by alcohol. Modulation of CRF1 function seems to exert a less prominent role over low to moderate alcohol intake, or to species-typical behaviors. While CRF mechanisms in the hypothalamic-pituitary-adrenal axis have some contribution to the neurobiology of alcohol abuse and dependence, a pivotal role for extra-hypothalamic CRF pathways, particularly in the extended amygdala, is well characterized. More recent studies further suggest a direct modulation of brain reward function by CRF signaling in the ventral tegmental area, nucleus accumbens, and the prefrontal cortex, among other structures. This review will further discuss a putative role for other components of the CRF system that contribute for the overall balance of CRF function in reward and stress pathways, including CRF2 receptors, CRF-binding protein, and urocortins, a family of CRF-related peptides.

Alcohol, stress hormones, and the prefrontal cortex: a proposed pathway to the dark side of addiction

Chronic exposure to alcohol produces changes in the prefrontal cortex that are thought to contribute to the development and maintenance of alcoholism. A large body of literature suggests that stress hormones play a critical role in this process. Here we review the bi-directional relationship between alcohol and stress hormones, and discuss how alcohol acutely stimulates the release of glucocorticoids and induces enduring modifications to neuroendocrine stress circuits during the transition from non-dependent drinking to alcohol dependence. We propose a pathway by which alcohol and stress hormones elicit neuroadaptive changes in prefrontal circuitry that could contribute functionally to a dampened neuroendocrine state and the increased propensity to relapse-a spiraling trajectory that could eventually lead to dependence.

Drinking alcohol has sex-dependent effects on pair bond formation in prairie voles

Alcohol use and abuse profoundly influences a variety of behaviors, including social interactions. In some cases, it erodes social relationships; in others, it facilitates sociality. Here, we show that voluntary alcohol consumption can inhibit male partner preference (PP) formation (a laboratory proxy for pair bonding) in socially monogamous prairie voles (Microtus ochrogaster). Conversely, female PP is not inhibited, and may be facilitated by alcohol. Behavior and neurochemical analysis suggests that the effects of alcohol on social bonding are mediated by neural mechanisms regulating pair bond formation and not alcohol's effects on mating, locomotor, or aggressive behaviors. Several neuropeptide systems involved in the regulation of social behavior (especially neuropeptide Y and corticotropin-releasing factor) are modulated by alcohol drinking during cohabitation. These findings provide the first evidence to our knowledge that alcohol has a direct impact on the neural systems involved in social bonding in a sex-specific manner, providing an opportunity to explore the mechanisms by which alcohol affects social relationships.

Role of hypothalamic corticotropin-releasing factor in mediating alcohol-induced activation of the rat hypothalamic-pituitary-adrenal axis

Alcohol stimulates the hypothalamic-pituitary-adrenal (HPA) axis through brain-based mechanisms in which endogenous corticotropin-releasing factor (CRF) plays a major role. This review first discusses the evidence for this role, as well as the possible importance of intermediates such as vasopressin, nitric oxide and catecholamines. We then illustrate the long-term influence exerted by alcohol on the HPA axis, such as the ability of a first exposure to this drug during adolescence, to permanently blunt neuroendocrine responses to subsequent exposure of the drug. In view of the role played by CRF in addiction, it is likely that a better understanding of the mechanisms through which this drug stimulates the HPA axis may lead to the development of new therapies used in the treatment of alcohol abuse, including clinically relevant CRF antagonists.

Differential roles of cyclooxygenase-2-related signaling in regulating hypothalamic neuronal activity under various acute stresses

We have previously suggested that activation of the hypothalamic-pituitary-adrenal (HPA) axis is dependent on cyclooxygenase (COX)-2-related signaling under infectious and restraint stresses, but less dependent on it under hypoglycemic stress. In the present study, we evaluated the neuronal activity in the brain to elucidate the possible mechanisms underlying a stress-specific relevance between COX-2-related signaling and activation of the HPA axis under infectious (lipopolysaccharide, LPS), hypoglycemic (2-deoxy-D-glucose, 2DG) and restraint (1 hr) stress conditions. The number of c-Fos-immunoreactive (IR) cells in several brain regions including the paraventricular nucleus (PVN) and supraoptic nucleus (SON) was increased at 120 min after application of all stress stimuli. The number of c-Fos-IR cells at 30 min was increased only by 2DG in the SON, but not in the PVN. In the PVN, a selective COX-2 inhibitor (NS-398) did not affect the number of c-Fos-IR cells at any time points. On the other hand, in the SON, NS-398 increased c-Fos-IR cells at 30 min after LPS and restraint stresses, but not after 2DG injection. These results suggest that, among the brain regions responding to acute stresses, the PVN and SON are commonly activated under three acute stresses. In addition, it is also suggested that COX-2-related signaling decreases neuronal activity in the SON under infectious and restraint, but not hypoglycemic, stresses, which may be involved in the suppression of the HPA axis.

Effects of alcohol on the endocrine system

Chronic consumption of a large amount of alcohol disrupts the communication between nervous, endocrine, and immune system and causes hormonal disturbances that lead to profound and serious consequences at physiologic and behavioral levels. These alcohol-induced hormonal dysregulations affect the entire body and can result in various disorders such as stress abnormalities, reproductive deficits, body growth defect, thyroid problems, immune dysfunction, cancers, bone disease, and psychological and behavioral disorders. This review summarizes the findings from human and animal studies that provide consistent evidence on the various effects of alcohol abuse on the endocrine system.

17β-Estradiol is required for the sexually dimorphic effects of repeated binge-pattern alcohol exposure on the HPA axis during adolescence

Alcohol consumption during adolescence has long-term sexually dimorphic effects on anxiety behavior and mood disorders. We have previously shown that repeated binge-pattern alcohol exposure increased the expression of two critical central regulators of stress and anxiety, corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP), in adolescent male rats. By contrast, there was no effect of alcohol on these same genes in adolescent females. Therefore, we tested the hypothesis that 17β-estradiol (E₂), the predominant sex steroid hormone in females, prevents alcohol-induced changes in CRH and AVP gene expression in the paraventricular nucleus (PVN) of the hypothalamus. To test this hypothesis, postnatal day (PND) 26 females were ovariectomized and given E₂ replacement or cholesterol as a control. Next, they were given an alcohol exposure paradigm of 1) saline alone, 2) acute (single dose) or 3) a repeated binge-pattern. Our results showed that acute and repeated binge-pattern alcohol treatment increased plasma ACTH and CORT levels in both E₂- and Ch-treated groups, however habituation to repeated binge-pattern alcohol exposure was evident only in E₂-treated animals. Further, repeated binge-pattern alcohol exposure significantly decreased CRH and AVP mRNA in Ch-, but not E₂-treated animals, which was consistent with our previous observations in gonad intact females. We further tested the effects of E₂ and alcohol treatment on the activity of the wild type CRH promoter in a PVN-derived neuronal cell line. Alcohol increased CRH promoter activity in these cells and concomitant treatment with E₂ completely abolished the effect. Together our data suggest that E₂ regulates the reactivity of the HPA axis to a repeated stressor through modulation of the habituation response and further serves to maintain normal steady state mRNA levels of CRH and AVP in the PVN in response to a repeated alcohol stressor.

Alcohol dysregulates corticotropin-releasing-hormone (CRH) promoter activity by interfering with the negative glucocorticoid response element (nGRE)

EtOH exposure in male rats increases corticotropin-releasing hormone (CRH) mRNA in the paraventricular nucleus of the hypothalamus (PVN), a brain region responsible for coordinating stress and anxiety responses. In this study we identified the molecular mechanisms involved in mediating these effects by examining the direct effects of EtOH on CRH promoter activity in a neuronal cell line derived from the PVN (IVB). In addition, we investigated the potential interactions of EtOH and glucocorticoids on the CRH promoter by concomitantly treating cells with EtOH and the glucocorticoid receptor (GR) antagonist RU486, and by sequentially deleting GR binding sites within glucocorticoid response element (GRE) on the CRH promoter. Cells were transiently transfected with a firefly luciferase reporter construct containing 2.5 kb of the rat wild type (WT) or mutated CRH promoter. Our results showed that EtOH treatment induced a biphasic response in CRH promoter activity. EtOH exposure for 0.5 h significantly decreased promoter activity compared to vehicle treated controls, whereas promoter activity was significantly increased after 2.0 h of EtOH exposure. Treatment with RU486, or deletion of the GR binding sites 1 and 2 within the GRE, abolished the EtOH-induced increase in the promoter activity, however did not affect EtOH-induced decrease in CRH promoter activity at an earlier time point. Overall, our data suggest that alcohol exposure directly regulates CRH promoter activity by interfering with the normal feedback mechanisms of glucocorticoids mediated by GR signaling at the GRE site of the CRH promoter.

Binge-pattern alcohol exposure during puberty induces long-term changes in HPA axis reactivity

Adolescence is a dynamic and important period of brain development however, little is known about the long-term neurobiological consequences of alcohol consumption during puberty. Our previous studies showed that binge-pattern ethanol (EtOH) treatment during pubertal development negatively dysregulated the responsiveness of the hypothalamo-pituitary-adrenal (HPA) axis, as manifested by alterations in corticotrophin-releasing hormone (CRH), arginine vasopressin (AVP), and corticosterone (CORT) during this time period. Thus, the primary goal of this study was to determine whether these observed changes in important central regulators of the stress response were permanent or transient. In this study, juvenile male Wistar rats were treated with a binge-pattern EtOH treatment paradigm or saline alone for 8 days. The animals were left undisturbed until adulthood when they received a second round of treatments consisting of saline alone, a single dose of EtOH, or a second binge-pattern treatment paradigm. The results showed that pubertal binge-pattern EtOH exposure induced striking long-lasting alterations of many HPA axis parameters. Overall, our data provide strong evidence that binge-pattern EtOH exposure during pubertal maturation has long-term detrimental effects for the healthy development of the HPA axis.

Urocortins are present in the rat testis

The synthesis and release of testosterone (T) depends both on circulating luteinizing hormone (LH) and on an array of testicular factors whose role remains incompletely understood. Corticotropin-releasing factor (CRF) had been reported in the rat testes, where it was thought to inhibit T secretion. However, the discovery that the CRF-related peptides urocortins (Ucns), of which there are currently three subtypes (Ucn 1, 2 and 3), cross-react with many reagents previously used to detect CRF, has cast doubt on this concept. Here we show that while CRF was readily measurable in rat hypothalami (which served as controls), signals for this peptide were barely detectable in total RNA extracted from the testes. On the other hand, microarray, RT-PCR and real-time quantitative RT-PCR (qRT-PCR) analyses all indicated strong signals for Ucn 1 in the male gonads, with weaker levels of Ucn 2 and 3 mRNA gene expression. Results obtained for Ucn 1 gene expression were corroborated by immunohistochemical detection, which appeared restricted to Leydig cells. Finally, to investigate possible changes in testicular Ucn 1 levels induced by homeostatic challenges, we measured them in rats exposed to alcohol. We observed that indeed, the intragastric injection of this drug significantly increased testicular Ucn 1, but not Ucn 2, Ucn 3, CRF, CRFR1 or CRFR2 mRNA levels. Collectively, these results provide novel information regarding the presence of CRF-like peptides in the adult male rat testis.

Activation of the hypothalamic-pituitary-adrenal axis by addictive drugs: different pathways, common outcome

Addictive drugs (opiates, ethanol, cannabinoids (CBs), nicotine, cocaine, amphetamines) induce activation of the hypothalamic-pituitary-adrenal (HPA) axis, with the subsequent release of adrenocorticotropic hormone and glucocorticoids. The sequence of events leading to HPA activation appears to start within the brain, suggesting that activation is not secondary to peripheral homeostatic alterations. The precise neurochemical mechanisms and brain pathways involved are markedly dependent on the particular drug, although it is assumed that information eventually converges into the hypothalamic paraventricular nucleus (PVN). Whereas some drugs may act on the hypothalamus or directly within PVN neurons (i.e. ethanol), others exert their primary action outside the PVN (i.e. CBs, nicotine, cocaine). Corticotropin-releasing hormone (CRH) has a critical role in most cases, but the changes in c-fos and CRH gene expression in the PVN also reveal differences among drugs. More studies are needed to understand how addictive drugs act on this important neuroendocrine system and their functional consequences.

Binge-pattern alcohol exposure during puberty induces sexually dimorphic changes in genes regulating the HPA axis

Maternal alcohol consumption during critical periods of fetal brain development leads to devastating long-term consequences on adult reproductive physiology, cognitive function, and social behaviors. However, very little is known about the long-term consequences of alcohol consumption during puberty, which is perhaps an equally dynamic and critical period of brain development. Alcohol abuse during adulthood has been linked with an increase in clinically diagnosed anxiety disorders, yet the etiology and neurochemical mechanisms of alcohol-induced anxiety behavior is unknown. In this study, we determined the effects of binge ethanol exposure during puberty on two critical central regulators of stress and anxiety behavior: corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP). Our results showed that ethanol increased plasma corticosterone (CORT) levels in both sexes, yet binge-treated animals had significantly lower CORT levels than animals exposed to a single dose, suggesting that the hypothalamo-pituitary-adrenal (HPA) axis habituated to the repeated stressful stimuli of ethanol. Binge ethanol exposure also significantly increased CRH and AVP gene expression in the paraventricular nucleus of males, but not females. Overall, our results demonstrate that binge ethanol exposure during puberty changes the central expression of stress-related genes in a sex-specific manner, potentially leading to permanent dysregulation of the HPA axis and long-term behavioral consequences.

Effects of acute ethanol on opioid peptide release in the central amygdala: an in vivo microdialysis study

RATIONALE

There is experimental evidence that indicates that the endogenous opioid system of the central nucleus of the amygdala (CeA) may mediate some of the reinforcing effects of ethanol. However, the precise interactions of ethanol with the endogenous opioid system at the level of the CeA have not been investigated.

OBJECTIVES

The aim of the current study was to investigate the hypothesis that acute systemic ethanol administration will increase the release of endogenous opioid peptides at the level of the CeA in a time- and dose-dependent manner.

MATERIALS AND METHODS

Rats were implanted with a unilateral guide cannula to aim microdialysis probes at the CeA. Intraperitoneal injections of saline and various doses of ethanol (0.8, 1.6, 2.0, 2.4, and 2.8 g ethanol/kg body weight) were administered to the rats. Dialysate samples were collected at 30-min intervals at distinct time points prior to and following treatment. Radioimmunoassays specific for beta-endorphin, met-enkephalin, and dynorphin A1-8 were used to determine the effect of ethanol on the content of the opioid peptides in the dialysate.

RESULTS

We report that the 2.8-g/kg dose of ethanol induced a long-lasting increase in beta-endorphin release from 60 min onwards following administration and, later, an ongoing increase in dynorphin A1-8 release. None of the ethanol doses tested elicited significant changes in dialysate met-enkephalin content compared to the saline treatment.

CONCLUSIONS

Acute systemic ethanol administration induced a dose- and time-dependent increase in beta-endorphin and dynorphin A1-8 release at the level of the CeA, which may be involved in ethanol consumption.

Induction of type 2 iodothyronine deiodinase in the mediobasal hypothalamus by bacterial lipopolysaccharide: role of corticosterone

To determine whether endotoxin-induced activation of type 2 iodothyronine deiodinase (D2) in the mediobasal hypothalamus is dependent on circulating levels of corticosterone, the effect of bacterial lipopolysaccharide (LPS) on D2 gene expression was studied in adrenalectomized, corticosterone-clamped adult, male, Sprague Dawley rats. In sham-adrenalectomized animals, LPS (250 microg/100 g body weight) increased circulating levels of corticosterone and IL-6, as well as tanycyte D2 mRNA in the mediobasal hypothalamus. Adrenalectomized, corticosterone-clamped animals showed no significant rise in corticosterone after LPS, compared with saline-treated controls but increased IL-6 levels and tanycyte D2 mRNA similar to LPS-treated sham controls. To further clarify the potential role of corticosterone in the regulation of D2 gene expression by LPS, animals were administered high doses of corticosterone to attain levels similar to that observed in the LPS-treated group. No significant increase in D2 mRNA was observed in the mediobasal hypothalamus with the exception of a small subpopulation of cells in the lateral walls of the third ventricle. These data indicate that the LPS-induced increase in D2 mRNA in the mediobasal hypothalamus is largely independent of circulating corticosterone and indicate that mechanisms other than adrenal activation are involved in the regulation of most tanycyte D2-expressing cells by endotoxin.

Stress, ethanol, and neuroactive steroids

Neurosteroids play a crucial role in stress, alcohol dependence and withdrawal, and other physiological and pharmacological actions by potentiating or inhibiting neurotransmitter action. This review article focuses on data showing that the interaction among stress, ethanol, and neuroactive steroids may result in plastic molecular and functional changes of GABAergic inhibitory neurotransmission. The molecular mechanisms by which stress-ethanol-neuroactive steroids interactions can produce plastic changes in GABA(A) receptors have been studied using different experimental models in vivo and in vitro in order to provide useful evidence and new insights into the mechanisms through which acute and chronic ethanol and stress exposure modulate the activity of GABAergic synapses. We show detailed data on a) the effect of acute and chronic stress on peripheral and brain neurosteroid levels and GABA(A) receptor gene expression and function; b) ethanol-stimulated brain steroidogenesis; c) plasticity of GABA(A) receptor after acute and chronic ethanol exposure. The implications of these new mechanistic insights to our understanding of the effects of ethanol during stress are also discussed. The understanding of these neurochemical and molecular mechanisms may shed new light on the physiopathology of diseases, such as anxiety, in which GABAergic transmission plays a pivotal role. These data may also lead to the need for new anxiolytic, hypnotic and anticonvulsant selective drugs devoid of side effects.

Attenuated stress response to acute lipopolysaccharide challenge and ethanol administration in vasopressin V1b receptor knockout mice

The arginine vasopressin (Avp) 1b receptor (Avpr1b) present on anterior pituitary corticotrophs is involved in the stimulation of adrenocorticotrophic hormone (ACTH) secretion, especially during times of stress. Corticotrophin-releasing hormone (CRH) is considered the major ACTH secretagogue during acute stress whereas Avp appears to be the more dominant mediator of the hypothalamic-pituitary-adrenal (HPA) axis response during chronic stress situations. To investigate the role of the Avpr1b in the HPA axis response to acute stress, we measured ACTH and corticosterone (CORT) plasma levels in Avpr1b knockout (KO) mice and wild-type controls in response to bacterial lipopolysaccharide (LPS) challenge and ethanol (EtOH) administration. Mice deficient in Avpr1b had markedly compromised plasma ACTH and CORT responses to acute (30 min) LPS, but normal ACTH and CORT response to more extended exposure (4 h) to the immune system activator. The plasma ACTH and CORT levels stimulated by intoxicating, sedative doses of EtOH (3.2 and 4 g/kg) were significantly decreased in the Avpr1b KO mice compared to wild-type littermates. Significantly higher EtOH-induced plasma ACTH and CORT secretion was measured in female than in male Avpr1b wild-type mice. There were no differences in the blood alcohol levels following acute EtOH administration in Avpr1b KO or wild-type mice of either gender. Our results clearly suggest that Avpr1b plays a significant role in the HPA axis response to acute immune stress and EtOH intoxication.

Neurosteroids, GABAA receptors, and ethanol dependence

RATIONALE

Changes in the expression of type A receptors for gamma-aminobutyric acid (GABA) represent one of the mechanisms implicated in the development of tolerance to and dependence on ethanol. The impact of such changes on the function and pharmacological sensitivity of GABAA receptors (GABAARs) has remained unclear, however. Certain behavioral and electrophysiological actions of ethanol are mediated by an increase in the concentration of neuroactive steroids in the brain that results from stimulation of the hypothalamic-pituitary-adrenal (HPA) axis. Such steroids include potent modulators of GABAAR function.

OBJECTIVES

We have investigated the effect of ethanol exposure and withdrawal on subunit expression and receptor function evaluated by subunit selective compounds, as well as the effects of short-term exposure to ethanol on both neurosteroid synthesis and GABAAR function, in isolated neurons and brain tissue.

RESULTS

Chronic treatment with and subsequent withdrawal from ethanol alter the expression of genes for specific GABAAR subunits in cultured rat neurons, and these changes are associated with alterations in receptor function and pharmacological sensitivity to neurosteroids, zaleplon, and flumazenil. Acute ethanol exposure increases the amount of 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) in hippocampal slices by a local action independent of the activity of the HPA axis. This effect of ethanol was associated with an increased amplitude of GABAAR-mediated miniature inhibitory postsynaptic currents recorded from CA1 pyramidal neurons in such slices.

CONCLUSIONS

Chronic ethanol exposure elicits changes in the subunit composition of GABAARs, which, in turn, likely contribute to changes in receptor function associated with the altered pharmacological and behavioral sensitivity characteristic of ethanol tolerance and dependence. Ethanol may also modulate GABAAR function by increasing the de novo synthesis of neurosteroids in the brain in a manner independent of the HPA axis. This latter mechanism may play an important role in the central effects of ethanol.

Brain steroidogenesis mediates ethanol modulation of GABAA receptor activity in rat hippocampus

An interaction with the GABA type A (GABA(A)) receptor has long been recognized as one of the main neurochemical mechanisms underlying many of the pharmacological actions of ethanol. However, more recent data have suggested that certain behavioral and electrophysiological actions of ethanol are mediated by an increase in brain concentration of neuroactive steroids that results from stimulation of the hypothalamic-pituitary-adrenal (HPA) axis. Neuroactive steroids such as 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP) are, in fact, potent and efficacious endogenous positive modulators of GABA(A) receptor function. Because neurosteroids can be synthesized de novo in the brain, we have investigated whether ethanol might affect both neurosteroid synthesis and GABA(A) receptor function in isolated rat hippocampal tissue. Here, we show that ethanol increases the concentration of 3alpha,5alpha-THP as well as the amplitude of GABA(A) receptor-mediated IPSCs recorded from CA1 pyramidal neurons in isolated hippocampal slices. These effects are shared by the neurosteroid precursor progesterone, the peripheral benzodiazepine receptor-selective agonist CB34, and gamma-hydroxybutyrate, all of which are known to increase the formation of neuroactive steroids in plasma and in the brain. The action of ethanol on GABA(A) receptor-mediated IPSC amplitude is biphasic, consisting of a rapid, direct effect on GABA(A) receptor activity and an indirect effect that appears to be mediated by neurosteroid synthesis. Furthermore, ethanol affects GABA(A) receptor activity through a presynaptic action, an effect that is not dependent on neurosteroid formation. These observations suggest that ethanol may modulate GABA(A) receptor function through an increase in de novo neurosteroid synthesis in the brain that is independent of the HPA axis. This novel mechanism may have a crucial role in mediating specific central effects of ethanol.

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.

Site of action of acute alcohol administration in stimulating the rat hypothalamic-pituitary-adrenal axis: comparison between the effect of systemic and intracerebroventricular injection of this drug on pituitary and hypothalamic responses

The peripheral injection of alcohol stimulates the activity of the hypothalamic-pituitary-adrenal (HPA) axis, but the ready penetration of this drug in most bodily compartments has made it difficult to identify its specific sites of action. Here we determined whether alcohol can directly influence the corticotropes. We first determined whether alcohol acted within the brain to stimulate neurons in the paraventricular nucleus (PVN) of the hypothalamus, which synthesizes corticotropin-releasing factor (CRF) and vasopressin (VP). To test this hypothesis, we injected alcohol intracerebroventricularly (icv; 5 microl of 200-proof; 86 micromol) and compared these results with those obtained after its ip administration (3.0 g/kg). Although not causing neuronal damage and not leading to detectable levels of the drug in the general circulation, icv alcohol significantly up-regulated PVN CRF heteronuclear RNA levels and increased plasma ACTH levels, a change comparable to the one observed in the ip model. To determine whether alcohol stimulated the corticotropes independently of CRF and/or VP, we injected the drug ip or icv and measured changes in anterior pituitary proopiomelanocortin (POMC) transcripts and ACTH release in the presence or absence of endogenous CRF and/or VP. Intracerebroventricular and ip alcohol significantly increased POMC primary transcript levels, measured by ribonuclease protection assay, over a time-course that corresponded to ACTH release. Both the POMC and the ACTH responses were completely abolished by removal of CRF and VP. Collectively, these results indicate that alcohol-induced activation of the corticotropes does not represent a direct influence of the drug on the pituitary but requires CRF and VP.

Neuropeptides: implications for alcoholism

The role of neuromodulatory peptides in the aetiology of alcoholism has been relatively under-explored; however, the development of selective ligands for neuropeptide receptors, the characterization and cloning of receptors, and the development of transgenic mouse models have greatly facilitated this analysis. The present review considers the most recent preclinical evidence obtained from animal models for the role of two of the opioid peptides, namely b-endorphin and enkephalin; corticotropin-releasing factor (CRF), urocortin I and neuropeptide Y (NPY) in deleterious and excessive alcohol consumption, focussing on specific brain regions, in particular the central nucleus of the amygdala, that appear to be implicated in the pathophysiology of alcoholism. The review also outlines potential directions for further research to clarify neuropeptide involvement in neuromodulation within discrete brain nuclei pertinent to behavioural patterns.

A hypothalamic-testicular neural pathway is influenced by brain catecholamines, but not testicular blood flow

We previously reported the existence of a descending multisynaptic, pituitary-independent, neural pathway between the hypothalamus and the testes in the male rat. Stimulation of this pathway by the intracerebroventricular (icv) injection of IL-1beta or corticotropin-releasing factor blunts the testosterone (T) response to human chorionic gonadotropin (hCG). This response is mediated at least in part by catecholamine beta-adrenergic receptor activation. The present work was performed to further investigate the role of brain catecholamines and testicular blood flow in this pathway. The icv injection of 5 microl of 200 proof ethanol (EtOH; 86 micromol) did not result in detectable levels of the drug in the general circulation and did not induce neuronal damage, but rapidly blunted hCG-induced T release while not decreasing LH levels or altering testicular blood flow. EtOH significantly up-regulated transcripts of the immediate-early gene c-fos in the paraventricular nucleus (PVN) of the hypothalamus. Lesions of the PVN blocked the inhibitory effect of IL-1beta on T, but only partially interfered with the influence of EtOH. PVN catecholamine turnover significantly increased after icv injection of IL-1beta, but not EtOH. Brain catecholamine depletion due to the neurotoxin 6-hydroxydopamine did not alter the ability of hCG to induce T release, but significantly reversed the inhibitory effect of icv EtOH or IL-1beta on this response. Collectively, these results indicate that icv-injected IL-1beta or EtOH blunts hCG-induced T secretion through a catecholamine-mediated mechanism that does not depend on either peripherally mediated effects or pituitary LH, and that the PVN plays a role in these effects.

Social isolation-induced increase in the sensitivity of rats to the steroidogenic effect of ethanol

Social isolation of rats for 30 days immediately after weaning results in marked decreases in the cerebrocortical and plasma concentrations of pregnenolone, progesterone, 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-TH PROG), and 3alpha,5alpha-tetrahydrodeoxycorticosterone (3alpha,5alpha-TH DOC), as well as a moderate increase in the plasma concentration of corticosterone. This mildly stressful condition has now been shown to increase the sensitivity of rats to the effect of acute ethanol administration on the cerebrocortical and plasma concentrations of neuroactive steroids. The percentage increases in the brain and plasma concentrations of pregnenolone, progesterone, 3alpha,5alpha-TH PROG, and 3alpha,5alpha-TH DOC, apparent 20 min after a single intraperitoneal injection of ethanol (1 g/kg), were thus markedly greater in isolated rats than in group-housed animals. A subcutaneous injection of isoniazid (300 mg/kg) also induced greater percentage increases in the concentrations of these steroids in isolated rats than in group-housed animals. These results suggest that mild chronic stress, such as that induced by social isolation, enhances the steroidogenic effect of ethanol, a drug abused by humans under stress or affected by neuropsychiatric disorders. Social isolation also induced hyper-responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis, as was apparent after reduction of GABA-mediated inhibitory tone by isoniazid administration.

Prolonged alcohol intake leads to irreversible loss of vasopressin and oxytocin neurons in the paraventricular nucleus of the hypothalamus

Previous data revealed that numerous neurons in the supraoptic nucleus degenerate after prolonged ethanol exposure, and that the surviving neurons increase their activity in order to prevent dramatic changes in water metabolism. Conversely, excess alcohol does not induce cell death in the suprachiasmatic nucleus, but leads to depression of neuropeptide synthesis that is further aggravated by withdrawal. The aim of the present study is to characterize the effects of prolonged ethanol exposure on the magnocellular neurons of the paraventricular nucleus (PVN) in order to establish whether or not magnocellular neurons display a common pattern of reaction to excess alcohol, irrespective of the hypothalamic cell group they belong. Using conventional histological techniques, immunohistochemistry and in situ hybridization, the structural organization and the synthesis and expression of vasopressin (VP) and oxytocin (OXT) in the magnocellular component of the PVN were studied under normal conditions and following chronic ethanol treatment (6 or 10 months) and withdrawal (4 months after 6 months of alcohol intake). After ethanol treatment, there was a marked decrease in the number of VP- and OXT-immunoreactive magnocellular neurons that was attributable to cell death. The surviving neurons were hypertrophied and the VP and OXT mRNA levels in the PVN unchanged. Withdrawal did not alter the number of VP- and OXT-producing neurons or the gene expression of these peptides. These results substantiate the view that after prolonged ethanol exposure numerous neurons of the hypothalamic magnocellular system degenerate, but the mRNA levels of VP and OXT are not decreased due to compensatory changes undergone by the surviving neurons.

Acute ethanol induction of c-Fos immunoreactivity in pre-pro-enkephalin expressing neurons of the central nucleus of the amygdala

Previous studies have shown that acute ethanol administration induces expression of c-Fos immunoreactivity in the central nucleus of the amygdala (CNA) [S.L. Chang, N.A. Patel, A.A. Romero, Activation and desensitization of Fos immunoreactivity in the rat brain following ethanol administration, Brain Res., 679 (1995) 89-98; M. Morales, J.R. Criado, P.P. Sanna, S.J. Henriksen, F.E. Bloom, Acute ethanol induces c-fos immunoreactivity in GABAergic neurons of the central nucleus of the amygdala, Brain Res., 798 (1998) 333-336; A.E. Ryabinin, J.R. Criado, S.J. Henriksen, F.E. Bloom, M.C. Wilson, Differential sensitivity of c-Fos expression in hippocampus and other brain regions to moderate and low doses of alcohol, Mol. Psychiatry, 2 (1997) 32-43]. We recently showed that over 70% of these c-Fos immunoreactive neurons are GABAergic [M. Morales, J.R. Criado, P.P. Sanna, S.J. Henriksen, F.E. Bloom, Acute ethanol induces c-fos immunoreactivity in GABAergic neurons of the central nucleus of the amygdala, Brain Res, 798 (1998) 333-336]. In the present study, we report that ethanol-induced c-Fos immunoreactivity was mainly confined to neurons that express pro-enkephalin (ENK). In contrast, a small number of c-Fos immunoreactive neurons express corticotrophin releasing factor (CRF). Our results thus provide anatomical evidence indicating that within the amygdala, GABAergic neurons that contain ENK are responsive to acute ethanol exposure.

Effect of alcohol on the proestrous surge of luteinizing hormone (LH) and the activation of LH-releasing hormone (LHRH) neurons in the female rat

Reproduction is adversely affected by alcohol abuse in humans and laboratory animals. In rats, alcohol exposure suppresses both luteinizing hormone (LH) and sex steroid secretion, although consensus is lacking as to which level of the hypothalamic-pituitary-gonadal (HPG) axis is primarily affected. We tested the hypothesis that acute alcohol treatment inhibits the HPG axis by blunting release of LH-releasing hormone (LHRH) in female rats, by examining the effect of this drug on the central reproductive endocrine event; i.e., the proestrous surge of gonadotropins, which triggers ovulation. In a first series of experiments, we injected alcohol at 8 A.M. and 12 P.M. on proestrus and measured plasma levels of LH, estradiol (E2), and progesterone during the afternoons of proestrus and estrus. Alcohol administration blocked the proestrous surge of LH and ovulation. In subsequent experiments, alcohol inhibited the surge of LHRH (measured by push-pull cannulation) and LHRH neuronal activation (measured by Fos labeling in LHRH neurons). Because alcohol also decreased E2 levels, we reasoned that it might have prevented positive feedback; however, alcohol retained its ability to inhibit the LH surge evoked by E2 implantation in ovariectomized females, disproving this hypothesis. Additionally, alcohol does not act via increased corticosteroid secretion, because alcohol also blocked the proestrous surge in adrenalectomized females. Last, exogenous administration of LHRH to alcohol-blocked animals evoked LH secretion and ovulation, indicating that pituitary and/or ovarian function could be restored by mimicking the hypothalamic signal. Collectively, these data indicate that in female rats, alcohol inhibits the gonadotropin surge primarily by decreasing LHRH secretion.

Effects of alcohol on the synthesis and expression of hypothalamic peptides

Studies aimed at analyzing the deleterious effects of excess alcohol in the brain have revealed structural alterations that are often associated with functional and behavioral disturbances. Among the neuronal damage related to prolonged alcohol exposure, alterations in the synthesizing capabilities and levels of expression of neuroactive peptides have been increasingly reported. Actually, such changes frequently represent the sole repercussion of acute and short-term exposure to ethanol. This review gathers the existing data on the effects of ethanol exposure on the synthesis and expression of hypothalamic peptides. Amid those that can act both as neurotransmitters and neurohormones, we allude to vasopressin, corticotropin-releasing hormone, thyrotropin-releasing hormone and pro-opiomelanocortin and related peptides produced by paraventricular, supraoptic and arcuate neurons. With respect to peptides that act exclusively as neurotransmitters, we address the effects of alcohol on vasoactive intestinal polypeptide, gastrin-releasing peptide, somatostatin and vasopressin synthesized by suprachiasmatic neurons. Hypothalamic neurons that produce peptides that act as neurotransmitters are supposed to be modulated primarily by influences exerted by neuronal afferents, whereas those producing peptides that additionally act as neurohormones are also regulated by peripheral stimuli (e.g., plasma levels of circulating hormones, osmotic challenges). These peculiar features endue the hypothalamus with characteristics that are particularly propitious to enlighten the still cryptic mechanisms underlying the ethanol effects on protein synthesis.

Divergence in the expression of molecular markers of neuronal activation in the parvocellular paraventricular nucleus of the hypothalamus evoked by alcohol administration via different routes

Immediate early gene (IEG) expression has been routinely used by neuroscientists as an index of neuronal activation. In the case of the hypothalamic-pituitary-adrenal axis, induction of c-fos and/or NGFI-B mRNAs in the parvocellular paraventricular nucleus (pPVN) has been documented after a variety of stimuli that increase adrenocorticotropin (ACTH) in the systemic circulation. However, the functional relationship between expression of IEGs and transcription of the genes for the ACTH secretagogues corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) is not clear. While investigating the neuroendocrine correlates of alcohol administration via different routes (intraperitoneal vs intragastric), we noted a difference in the time course of NGFI-B mRNA expression in the pPVN, despite comparable dynamics in ACTH secretion. By comparing the temporal cascade of transcriptional events in vivo after alcohol injection via either route, we sought to determine functional relationships between IEGs and the induction of CRF and AVP heteronuclear RNAs (hnRNAs). One advantage of our paradigm is the use of the same stimulus (systemic alcohol injection) in which access to the CNS does not differ between the groups to be compared. Intraperitoneal administration of the drug resulted in significant increases in c-fos mRNA, Fos protein, CRF hnRNA, and AVP hnRNA. In contrast, intragastric treatment evoked a brief, modest elevation in c-fos mRNA and Fos protein, increased AVP hnRNA, and caused no detectable change in CRF hnRNA. These data indicate that robust increases in CRF hnRNA are closely linked to full expression of c-fos mRNA and Fos protein. In addition, the expression of NGFI-B after both routes of administration is indicative of cellular activation within the pPVN in parallel with secretion of ACTH.

An initial, three-day-long treatment with alcohol induces a long-lasting phenomenon of selective tolerance in the activity of the rat hypothalamic-pituitary-adrenal axis

We determined whether an initial alcohol challenge induced long-lasting changes in the activity of the hypothalamic-pituitary-adrenal (HPA) axis. Adult male rats received intragastric injections of the vehicle or a moderately intoxicating dose of alcohol (3.0 gm/kg) daily for 3 d. When animals were acutely challenged with alcohol 3-12 d later, their ACTH and corticosterone responses were significantly blunted, compared with that of vehicle-pretreated rats. In contrast, exposure to mild electric foot shocks induced a pattern of ACTH secretion that was comparable in animals administered alcohol or the vehicle previously, indicating a lack of cross-tolerance. No significant differences were observed in pituitary responsiveness to corticotropin-releasing factor or vasopressin in rats pretreated with the vehicle or alcohol. The influence of the initial drug treatment was not mimicked by exposure to foot shocks, nor was it prevented by administering a potent corticotropin-releasing factor antagonist to block the elevations in plasma ACTH and corticosterone induced by this initial treatment. Finally, we found that rats injected initially with the vehicle and challenged subsequently with alcohol exhibited the expected increased neuronal activation (measured by the upregulation of steady-state mRNA and protein levels of immediate early genes) in the paraventricular nucleus of their hypothalamus. In contrast, this response was markedly decreased in animals exposed previously to the drug. To our knowledge, this is the first report that exposure to a stress (i.e., alcohol), although not immediately altering the response of the HPA axis to this particular signal, induces a selective tolerance that is both slow to develop and long-lasting. The primary mechanism mediating the ability of an initial drug treatment to decrease subsequent responses of the HPA axis to a second drug challenge seems to be the inability of hypothalamic neurons to respond adequately to this second challenge.

Gender difference in hypothalamic-pituitary-adrenal axis response to alcohol in the rat: activational role of gonadal steroids

Alcohol administration activates the hypothalamic-pituitary-adrenal (HPA) axis of both male and female rats, with females secreting more adrenocorticotropin (ACTH) and corticosterone than males in response to the same dose of alcohol. Our earlier work suggested that this gender difference arises due to the activational effects of gonadal steroids. In particular, we hypothesized that both androgens and estrogens play a role, with androgens exerting an inhibitory influence while estrogens elevate activity of the HPA. In the present studies, we tested this hypothesis by manipulating steroidal milieu in male rats using surgical castration and chronic implantation of testosterone (T), dihydrotestosterone (DHT), or estradiol (E2). Intact male and female rats were included as controls. Injection of alcohol (3 g/kg b.wt., i.p.) resulted in elevation of blood alcohol levels, ACTH and corticosterone in all groups. However, the amount of ACTH secreted was greater in females and castrated males implanted with E2 than in intact males. In castrated males, regardless of androgen implantation, the ACTH response was intermediate, with mean levels between those of females and males, but not differing significantly from either. In contrast to the ACTH results, significantly higher corticosterone secretion was measured in females and castrated males which did not receive a steroid implant. Since there were no significant differences between groups in blood alcohol levels (BALs), these results are not due to steroid-dependent alterations in alcohol metabolism. Because the ACTH data confirmed an activational effect of E2, we sought to determine whether this steroid regulated levels of corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) mRNAs in the paraventricular nucleus of the hypothalamus (PVN). Four pretreatment groups were studied: intact males, intact females, castrated males, and castrated males implanted with E2. Two weeks after surgery, alcohol or vehicle was administered 3 h before brains were collected. In intact males, alcohol treatment elevated levels of both CRF and AVP mRNAs in the PVN, as previously reported. In contrast, this treatment decreased CRF mRNA in castrated males implanted with E2. In addition, steroid pretreatment alone elevated CRF mRNA levels in castrated males. Although we did not observe E2-dependent increases in CRF or AVP mRNAs, our data do support a complex effect of gonadal steroids on expression of these mRNAs in the PVN.

Effect of three different modes of alcohol administration on the activity of the rat hypothalamic-pituitary-adrenal axis

The present study compared the effect of different modes of alcohol administration on the activity of the hypothalamic-pituitary-adrenal (HPA) axis. In a first series of studies, we investigated the influence of the intraperitoneal (ip) and intragastric (ig) effect of acutely administered alcohol. Over a 3-hr period, alcohol induced dose-related increases in adrenocorticotropic hormone (ACTH) and alcohol levels in the circulation. There was a good correlation between blood ACTH and alcohol levels (ip treatment, R = 0.84; ig treatment, R = 0.79). Measurement of steady-state mRNA of the immediate early gene NGFI-B, taken as an index of neuronal activation in the paraventricular nucleus (PVN) of the hypothalamus of rats administered 3 g of alcohol/kg, indicated significant (p < 0.01) increases between 60 and 180 min after both ip and ig alcohol injection, with peak stimulation at 1 and 2 hr, respectively. Although NGFI-B mRNA levels had returned to control level in the parvicellular portion of the PVN of animals administered the drug ip 4 hr earlier, they were still significantly (p < 0.01) elevated 4 hr after ig treatment. A second series of studies used rats fed an alcohol diet containing 6.4% alcohol (w/v), or pair-fed. The rats were tested during the 4th or 6th night of treatment. Despite blood alcohol levels ranging between 0.060 and 0.140% w/v, there was no significant rise in plasma ACTH/corticosterone levels in animals fed the drug, and no detectable NGFI-B mRNA in their PVN. Collectively, these results indicate that both the ip and the ig acute injection of alcohol induced dose-related increases in plasma ACTH levels. PVN neuronal activation was also observed. In contrast, the alcohol diet had no effect on HPA hormone levels or PVN expression of NGFI-B.