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

Strain differences in urocortin expression in the Edinger-Westphal nucleus and its relation to alcohol-induced hypothermia

The Edinger-Westphal nucleus is the primary source of urocortin in rodent brain. Mapping of inducible transcription factors has shown that the Edinger-Westphal nucleus is preferentially sensitive to ethanol self-administration. In the present study we have immunohistochemically compared expression of urocortin and c-Fos in naive and ethanol-treated C57BL/6J and DBA/2J mouse inbred strains. We found that C57BL/6J mice possess significantly higher numbers of urocortin-expressing cells in the Edinger-Westphal compared to DBA/2J mice. Subsequent histological analysis confirmed a lower number of large neurons in the DBA/2J Edinger-Westphal nucleus. Surprisingly, despite the differences in structure, no strain differences were observed in the number of c-Fos-containing cells after acute (0.6-4.8 g/kg, i.p.) and repeated (2.4 g/kg, 14 days, one injection/day) administration of ethanol. Double-label immunohistochemistry showed that ethanol-induced c-Fos expression is present in different sets of Edinger-Westphal cells between the strains. Specifically, expression of c-Fos in C57BL/6J mice is preferentially induced in urocortin cells, while c-Fos in DBA/2J mice occurs in a mixed population of cells. Behavioral analysis of the B6D2 F2 intercross, a heterogeneous mouse strain, showed that the number of urocortin cells is positively correlated with basal temperatures and ethanol-induced hypothermia. Involvement of the Edinger-Westphal in alcohol-induced hypothermia is further confirmed by analysis of urocortin cells in the HOT/COLD selected lines. These results provide evidence that C57BL/6J and DBA/2J mice have structural differences in the Edinger-Westphal that can result in activation of different populations of neurons upon alcohol intoxication contributing to differential thermoregulation between these inbred strains.

A single lipopolysaccharide administration is sufficient to induce a long-term desensitization of the hypothalamic-pituitary-adrenal axis

We have previously shown that a single exposure of adult rats to a severe emotional stressor such as immobilization is able to exert a long-term desensitization of the response of the hypothalamic-pituitary-adrenal (HPA) axis to the same stimulus when applied days to weeks later. Surprisingly, the intensity of the effect increased with time elapsed between the two exposures, suggesting that we are dealing with a new type of stress-associated phenomenon. Taking into account the clinical importance of tolerance to endotoxin, in the present study we assessed whether a single exposure to an immunological stressor such as lipopolysaccharide can induce effects similar to those of immobilization. Rats injected with lipopolysaccharide (1 mg/kg) showed a reduction of the response of the corticotropin-releasing factor mRNA in the paraventricular nucleus of the hypothalamus after a new lipopolysaccharide injection 4, but not 2 weeks later. In an additional experiment using a different blood sampling procedure, adrenocorticotropin hormone, corticosterone and tumor necrosis factor-alpha responses were reduced approximately to the same extent by previous experience with lipopolysaccharide either 1 or 4 weeks before. Our data suggest that a previous single exposure to lipopolysaccharide induces a long-lasting tolerance of the HPA axis that likely involves some kind of learning-like brain plasticity.

Comparison between the influence of the intravenous and intracerebroventricular injection of a nitric oxide donor on adrenocorticotropic hormone release and hypothalamic neuronal activity

We investigated the ability of the nitric oxide (NO) donor 3-morpholino-sydnonimine (SIN-1) to release adrenocorticotropic hormone (ACTH) and up-regulate hypothalamic neurones following its intravenous (i.v.) injection. i.v. SIN-1 (0.2-1.8 mg/kg) produced dose-related increases in plasma ACTH levels which were blocked by prior neutralization of endogenous corticotropin-releasing factor (CRF) but not by vasopressin antibodies. In contrast, the intracerebroventricular (i.c.v.) injection of 50-microg SIN-1 released significantly larger amounts of ACTH, a response blunted by either CRF or vasopressin antibodies. While i.c.v. SIN-1 markedly up-regulated transcripts of the immediate early gene NGFI-B in the paraventricular nucleus (PVN) of the hypothalamus, no such response was observed following the i.v. injection of up to 2.0 mg/kg SIN-1. Finally, we found no evidence that the influence of the peripheral administration of SIN-1 on ACTH secretion is mediated by altered pituitary responsiveness to CRF or vasopressin. The fact that NO has a profound hypotensive influence in the periphery suggests that it may have released ACTH through this mechanism, although the absence of PVN neuronal response in regions that are activated by decreased blood pressure casts some doubt on this hypothesis. As the systemic injection of arginine derivatives that block NOS activity potently augment the ACTH response to circulating pro-inflammatory cytokines or vasopressin, the present findings indicate that the mechanisms responsible for this phenomenon are distinct from those responsible for ACTH released by i.v. SIN-1.

Hypothalamic CRH mRNA levels are differentially modulated by repeated 'binge' cocaine with or without D(1) dopamine receptor blockade

We previously found that there was a rapid stimulatory effect of acute (1 day) 'binge' cocaine on CRH mRNA levels in the rat hypothalamus. In contrast, after 3 days of 'binge' cocaine, there was a modest decrease (12%) in hypothalamic CRH mRNA levels, which after 14 days of 'binge' cocaine was greater (32%) and significantly lower than control values. Also, our previous studies found an elevation of CRH mRNA in the frontal cortex after 3 days of 'binge' cocaine. The present study was designed to investigate the possible role of dopamine receptors in modulating these effects. Administration of 3 days of 'binge' cocaine (3 x 15 mg/kg, i.p.) was preceded by daily injections of either D(1) (SCH23390, 2 mg/kg) or D(2) (sulpiride, 50 mg/kg) dopamine receptor antagonist. Neither SCH23390 nor sulpiride had an effect on basal CRH mRNA levels in the hypothalamus, frontal cortex or amygdala. Small decreases (10-13%) in hypothalamic CRH mRNA levels were found again to be induced by 3 days of repeated 'binge' cocaine. However, this modest decrease was not found in the rats that received D(1) antagonist SCH23390 pretreatment. Pretreatment with D(2) antagonist sulpiride had no effect on this decrease. These findings suggest that the inhibitory effect of repeated 'binge' cocaine on the hypothalamic CRH mRNA expression is absent when there is D(1), but not D(2), dopamine receptor blockade. In the frontal cortex, pretreatment with either SCH23390 or sulpiride did not alter the increases in the CRH mRNA levels induced by repeated 'binge' cocaine. The results suggest that the cocaine-induced modulation of hypothalamic CRH mRNA expression is secondary to changes in the activity of specific components of dopaminergic systems.

A single administration of interleukin-1 or amphetamine induces long-lasting increases in evoked noradrenaline release in the hypothalamus and sensitization of ACTH and corticosterone responses in rats

Single administration of the cytokine interleukin-1beta (IL-1) or the psychostimulant amphetamine causes long-term sensitization of the hypothalamus pituitary adrenal (HPA) axis, i.e. enhanced adrenocorticotropine hormone (ACTH) and corticosterone responses weeks later. HPA responses to these stimuli involve activation of hypothalamic corticotropin-releasing hormone (CRH) neurons by noradrenergic projections to the paraventricular nucleus (PVN). In search of the underlying mechanisms, we studied the temporal pattern of HPA sensitization in relation to (1) the reactivity of noradrenergic projections to the PVN and (2) altered secretagogue production in hypothalamic CRH neurons. Single exposure to IL-1 or amphetamine induced cross-sensitization of ACTH and corticosterone responses 11 and 22 days later, but not after 42 days. Amphetamine-induced HPA sensitization was not accompanied by increased costorage of arginine vasopressin (AVP) in CRH terminals, as found previously after IL-1 pretreatment. The reactivity of noradrenergic terminals was assessed by measuring the electrically evoked release of [3H]-noradrenaline from superfused PVN slices. Single administration of amphetamine and IL-1 induced a long-lasting (up to 22 days) increase (up to 165%) of evoked noradrenaline release. This indicates that single exposure to psychostimulants or to cytokines can induce a long-lasting increase in stimulus-secretion coupling in brainstem noradrenergic neurons that innervate the PVN. This common, long-lasting functional change may underlie, at least in part, IL-1- and amphetamine-induced HPA cross-sensitization. In addition, increased AVP signalling by hypothalamic CRH neurons appears to play a role in IL-1-induced, but not in amphetamine-induced, HPA sensitization.

ITF expression in mouse brain during acquisition of alcohol self-administration

Expression of inducible transcription factors (ITFs) c-Fos and FosB was investigated during acquisition of alcohol drinking in C57BL/6J mice. A slight but statistically significant increase in c-Fos expression was found in the Edinger-Westphal nucleus (EW) of animals consuming 2% ethanol/10% sucrose for the first time. Stronger expression of c-Fos in EW was found in animals repeatedly consuming ethanol-containing solutions. These findings underscore the potential importance of EW in alcohol-related behaviors.

Cocaine- and alcohol-mediated expression of inducible transcription factors is blocked by pentobarbital anesthesia

Identifying the neurocircuitry involved in behavioral responses to drugs of abuse is an important step towards understanding the mechanisms of drug addiction. The present study sought to distinguish brain regions involved in pharmacological effects of cocaine and ethanol from secondary effects by administering these drugs in the presence or absence of pentobarbital anesthesia. Changes in neuronal activity were assessed by immunohistochemical analysis of expression of an inducible transcription factor (ITF), c-Fos, in the brain of rats habituated to repeated pentobarbital anesthesia or saline administration. Cocaine administration (15 mg/kg, i.v.) in non-anesthetized animals produced a strong induction of c-Fos in the striatum and large number of other brain areas. Ethanol administration (2 g/kg, i.p.) induced c-Fos in a smaller number of characteristic brain areas, including the central nucleus of amygdala and paraventricular nucleus of hypothalamus. However, neither of these drugs was able to induce c-Fos in pentobarbital-anesthetized rats (50 mg/kg, i.v.). The suppressive effects of pentobarbital were not specific to c-Fos, such that pentobarbital also suppressed expression of ITFs FosB and Egr1 in the striatum of cocaine-treated rats. On the other hand, pentobarbital by itself strongly induced c-Fos expression in the lateral habenula of saline-, cocaine-, and ethanol-injected rats. It is not clear whether the suppressive effects of anesthesia on ITF expression in other areas are mediated by activation of lateral habenula, or are independent of this event. Our data suggest that in the absence of conscious awareness of drug-associated cues, cocaine and alcohol activate only a fraction of the neural elements engaged in the unanesthetized state.

Nitric oxide stimulates ACTH secretion and the transcription of the genes encoding for NGFI-B, corticotropin-releasing factor, corticotropin-releasing factor receptor type 1, and vasopressin in the hypothalamus of the intact rat

We investigated the effect of the intracerebroventricular injection of the nitric oxide (NO) donor 3-morpholino-sydnonimine (SIN-1) on the release of adrenocorticotropin hormone (ACTH) and the neuronal response of hypothalamic neurons responsible for this release. Rats that were administered SIN-1 showed significant elevations in plasma ACTH levels, a response that was virtually abolished by antibodies against corticotropin-releasing factor (CRF) and significantly blunted by vasopressin (VP) antiserum. SIN-1 also upregulated heteronuclear (hn) transcripts for CRF and VP and messenger RNA (mRNA) levels for the immediate early gene NGFI-B and for CRF receptor type 1 (CRF-R(1)) in the parvocellular portion of the paraventricular nucleus (PVN) of the hypothalamus. Blockade of prostaglandin synthesis with ibuprofen did not alter the ACTH or the PVN response to SIN-1. The central nucleus of the amygdala and the supraoptic nucleus, regions that are involved in autonomic adjustments to altered cardiovascular activity, also responded to SIN-1 with elevated NGFI-B mRNA levels. However, the only change in mean arterial blood pressure caused by this NO donor was a transient and modest increase. To our knowledge, this is the first demonstration that in the intact rat NO stimulates the activity of PVN neurons that control the hypothalamic-pituitary-adrenal axis. It must be noted, however, that our results do not allow us to determine whether this effect was direct or mediated through PVN afferents. This study should help resolve the controversy generated by the use of isolated brain tissues to investigate the net effect of NO on hypothalamic peptide production.

Drugs of abuse and brain gene expression

Addictive drugs like cocaine, ethanol, and morphine activate signal transduction pathways that regulate brain gene expression. Such regulation is modulated by the presence of certain transcription factor proteins present in a given neuron. This article summarizes the effects of several addictive drugs on transcriptional processes contributing to the development of a drug-dependent state. The characterization of drug-induced changes in gene expression shows promise for improving our understanding of drug-addiction phenomena and cellular modes of cocaine, ethanol, and morphine action.

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.