Excessive alcohol use, a major cause of morbidity and mortality, is less well understood than other addictive disorders. Dopamine release in ventral striatum is a common element of drug reward, but alcohol has an unusually complex pharmacology, and humans vary greatly in their alcohol responses. This variation is related to genetic susceptibility for alcoholism, which contributes more than half of alcoholism risk. Here, we report that a functional OPRM1 A118G polymorphism is a major determinant of striatal dopamine responses to alcohol. Social drinkers recruited based on OPRM1 genotype were challenged in separate sessions with alcohol and placebo under pharmacokinetically controlled conditions, and examined for striatal dopamine release using positron emission tomography and [11C]-raclopride displacement. A striatal dopamine response to alcohol was restricted to carriers of the minor 118G allele. To directly establish the causal role of OPRM1 A118G variation, we generated two humanized mouse lines, carrying the respective human sequence variant. Brain microdialysis showed a four-fold greater peak dopamine response to an alcohol challenge in h/mOPRM1-118GG than in h/mOPRM1-118AA mice. OPRM1 A118G variation is a genetic determinant of dopamine responses to alcohol, a mechanism by which it likely modulates alcohol reward.

The adrenal gland is important for homeostatic responses to metabolic stress: hypoglycemia stimulates the splanchnic nerve, epinephrine is released from adrenomedullary chromaffin cells, and compensatory glucogenesis ensues. Acetylcholine is the primary neurotransmitter mediating catecholamine secretion from the adrenal medulla. Accumulating evidence suggests that a secretin-related neuropeptide also may function as a transmitter at the adrenomedullary synapse. Costaining with highly specific antibodies against the secretin-related neuropeptide pituitary adenylate cyclase-activating peptide (PACAP) and the vesicular acetylcholine transporter (VAChT) revealed that PACAP is found in nerve terminals at all mouse adrenomedullary cholinergic synapses. Mice with a targeted deletion of the PACAP gene had otherwise normal cholinergic innervation and morphology of the adrenal medulla, normal adrenal catecholamine and blood glucose levels, and an intact initial catecholamine secretory response to insulin-induced hypoglycemia. However, insulin-induced hypoglycemia was more profound and longer-lasting in PACAP knock-outs, and was associated with a dose-related lethality absent in wildtype mice. Failure of PACAP-deficient mice to adequately counterregulate plasma glucose levels could be accounted for by impaired long-term secretion of epinephrine, secondary to a lack of induction of tyrosine hydroxylase, normally occurring after insulin hypoglycemia in wild-type mice, and a consequent depletion of adrenomedullary epinephrine stores. Thus, PACAP is needed to couple epinephrine biosynthesis to secretion during metabolic stress. PACAP appears to function as an ''emergency response'' cotransmitter in the sympathoadrenal axis, where the primary secretory response is controlled by a classical neurotransmitter but sustained under paraphysiological conditions by a neuropeptide. T he adrenal medulla has been used extensively as a model for understanding basic features of neurotransmission and transsynaptic regulation, because of the simplicity of its synaptic inputs and the physiological importance and ease of measurement of catecholamine secretion as a final output (1). Recently, the adrenomedullary synapse has been the focus of analysis of the functional meaning of classical neurotransmitter and neuropeptide coexpression and corelease at mammalian synapses (2). Acetylcholine is the primary neurotransmitter mediating catecholamine secretion from the adrenal medulla (3). A second noncholinergic neurotransmitter also is thought to be involved in sympathoadrenal function because acetylcholine, or cholinergic agonists alone, cannot mimic the prolonged secretion and robust stimulation of catecholamine biosynthesis elicited by electrical stimulation of the splanchnic innervation of the adrenal medulla (4-7). It has been proposed that pituitary adenylate cyclaseactivating peptide (PACAP) or a PACAP-related neuropeptide acts as a cotransmitter with acetylcholine at the adrenomedullary synapse, based on neuroanatomical evidence obtained in v...

Alcohol dependence leads to persistent neuroadaptations, potentially related to structural plasticity. Previous work has shown that hippocampal neurogenesis is modulated by alcohol, but effects of chronic alcohol on neurogenesis in the forebrain subventricular zone (SVZ) have not been reported. Effects in this region may be relevant for the impairments in olfactory discrimination present in alcoholism. Here, we examined the effects of prolonged alcohol dependence on neurogenesis. Rats were sacrificed directly after 7 wk of intermittent alcohol vapour exposure, or 3, 7 or 21 d into abstinence. Proliferation was assessed using BrdU and Ki67 immunoreactivity, newly differentiated neurons (neurogenesis) as doublecortin-immunoreactivity (DCX-IR), and neural stem cells using the SOX2 marker. In the dentate gyrus, chronic dependence resulted in a pattern similar to that previously reported for acute alcohol exposure : proliferation and neurogenesis were suppressed by the end of exposure, rebounded on day 3 of abstinence, and returned to control levels by days 7 and 21. In the SVZ, proliferation was also suppressed at the end of alcohol exposure, followed by a proliferation burst 3 d into abstinence. However, in this area, there was a trend for reduced proliferation on days 7 and 21 of abstinence, and this was accompanied by significant suppression of DCX-IR, indicating a long-term suppression of forebrain neurogenesis. Finally, a decrease in the SOX2 stem cell marker was detected at days 7 and 21, suggesting long-term reduction of the SVZ stem cell pool. While suppression of hippocampal neurogenesis by alcohol dependence is transient, the suppression in the forebrain SVZ appears long-lasting.

Background A dysregulation of the corticotropin-releasing hormone (CRH) system has been implicated in the development of excessive alcohol consumption and dependence. The aim of the present study was to evaluate whether the CRH system is also recruited when non-dependent Wistar rats escalate to high alcohol intake in the intermittent (alternate days) model of drinking. Methods We compared intermittent and continuous access to 20% (v/v) alcohol in a two-bottle free choice drinking paradigm. Following a total of twenty 24-hour exposures for every experimental group, we assessed signs of alcohol withdrawal, including anxiety-like behavior and sensitivity to stress. The selective CRH1 receptor (CRH1R) antagonist antalarmin (0, 10, 20 mg/kg, i.p.) was tested on alcohol consumption. Results Intermittent access to 20% alcohol led non-selected Wistar rats to escalate their voluntary intake to a high and stable level, whereas continuously exposed animals maintained a lower consumption. These groups did not differ in physical withdrawal signs. In addition, no differences were found when anxiogenic-like behavior was studied, neither under basal conditions or following restraint stress. Nevertheless, sensitivity to the treatment with the CRH1R antalarmin was observed since a reduction of 20% alcohol intake was found in both groups of animals regardless of the regimen of alcohol exposure. In addition, antalarmin was effective when injected to animals exposed to intermittent 10% (v/v) alcohol whereas it failed to suppress 10% continuous alcohol intake. Conclusions Pharmacological blockade of CRH1R reduced alcohol drinking when sustained high levels of intake were achieved suggesting that the CRH system plays a key role when high doses of ethanol are consumed by non-dependent subjects. This supports the notion that CRH system not only maintains the dependent state but also engages the transition to dependence.