Acute effect of ethanol on anxiety and 5-HT in the prefrontal cortex of rats

The neurobiological markers of acute alcohol's subjective effects in humans

The ingestion of alcohol yields acute biphasic subjective effects: stimulation before sedation. Despite their predictive relevance to the development of alcohol use disorders (AUD), the neurobiological markers accounting for the biphasic effects of alcohol remain poorly understood in humans. Informed by converging lines of evidence, this study tested the hypothesis that alcohol ingestion acutely increases gamma-aminobutyric acid (GABA)-mediated inhibition, which would positively and negatively predict the feeling of stimulation and sedation, respectively. To do so, healthy participants (n = 20) ingested a single dose of 94% ABV alcohol (males: 1.0 ml/kg; females: 0.85 ml/kg) in a randomized placebo-controlled cross-over design. The alcohol's biphasic effects were assessed with the Brief-Biphasic Alcohol Effects Scale, and non-invasive neurobiological markers were measured with transcranial magnetic stimulation, before and every 30 min (up to 120 min) after the complete ingestion of the beverage. Results showed that acute alcohol ingestion selectively increased the duration of the cortical silent period (CSP) as compared to placebo, suggesting that alcohol increases non-specific GABAergic inhibition. Importantly, CSP duration positively and negatively predicted increases in the feeling of stimulation and sedation, respectively, suggesting that stimulation emerges as GABAergic inhibition increases and that sedation emerges as GABAergic inhibition returns to baseline values. Overall, these results suggest that modulations of GABAergic inhibition are central to the acute biphasic subjective effects of alcohol, providing a potential preventive target to curb the progression of at-risk individuals to AUD.

Neurochemical and Behavioral Consequences of Ethanol and/or Caffeine Exposure: Effects in Zebrafish and Rodents

Zebrafish are increasingly being utilized to model the behavioral and neurochemical effects of pharmaceuticals and, more recently, pharmaceutical interactions. Zebrafish models of stress establish that both caffeine and ethanol influence anxiety, though few studies have implemented co-administration to assess the interaction of anxiety and reward-seeking. Caffeine exposure in zebrafish is teratogenic, causing developmental abnormalities in the cardiovascular, neuromuscular, and nervous systems of embryos and larvae. Ethanol is also a teratogen and, as an anxiolytic substance, may be able to offset the anxiogenic effects of caffeine. Co-exposure to caffeine and alcohol impacts neuroanatomy and behavior in adolescent animal models, suggesting stimulant substances may moderate the impact of alcohol on neural circuit development. Here, we review the literature describing neuropharmacological and behavioral consequences of caffeine and/or alcohol exposure in the zebrafish model, focusing on neurochemistry, locomotor effects, and behavioral assessments of stress/anxiety as reported in adolescent/juvenile and adult animals. The purpose of this review is twofold: (1) describe the work in zebrafish documenting the effects of ethanol and/or caffeine exposure and (2) compare these zebrafish studies with comparable experiments in rodents. We focus on specific neurochemical pathways (dopamine, serotonin, adenosine, GABA, adenosine), anxiety-type behaviors (assessed with novel tank, thigmotaxis, shoaling), and locomotor changes resulting from both individual and co-exposure. We compare findings in zebrafish with those in rodent models, revealing similarities across species and identifying conservation of mechanisms that potentially reinforce co-addiction.

Repeated ethanol exposure following avoidance conditioning impairs avoidance extinction and modifies conditioning-associated prefrontal dendritic changes in a mouse model of post-traumatic stress disorder

Treatment of post-traumatic stress disorder is complicated by the presence of alcohol use disorder comorbidity. Little is known about the underlying brain mechanisms. We have recently shown, in mice, that the post-traumatic stress disorder-like phenotype is characterised by the increase and decrease in total dendritic number and length in the prelimbic and infralimbic areas of the medial prefrontal cortex, respectively. Here, we examined whether repeated ethanol exposure would exacerbate these changes and whether this would be associated with difficulty to extinguish passive avoidance behaviour, as an indicator of treatment resistance. We also analysed whether other known trauma-associated changes, like increased or decreased corticosterone and decreased brain-derived neurotrophic factor levels, would also be exacerbated. Male mice underwent trauma exposure (1.5-mA footshock), followed, 8 days later, by a conditioned place preference training with ethanol. Tests for fear sensitization, passive avoidance, anxiety-like behaviour, extinction acquisition and relapse susceptibility were used to assess behaviour changes. Plasma corticosterone and brain-derived neurotrophic factor levels and prefrontal dendritic changes were subsequently measured. Trauma-susceptible mice exposed to ethanol acquired a strong place preference and behaved differently from those not exposed to ethanol, with delayed avoidance extinction and higher avoidance relapse vulnerability. Ethanol potentiated trauma-associated dendritic changes in the prelimbic area and suppressed trauma-associated dendritic changes in the infralimbic area. However, ethanol had no effect on trauma-induced increased corticosterone and decreased brain-derived neurotrophic factor levels. These data suggest that the modification of prefrontal trauma-related changes, due to alcohol use, can characterise, and probably support, treatment-resistant post-traumatic stress disorder.

Method Standardization for Conducting Innate Color Preference Studies in Different Zebrafish Strains

The zebrafish has a tetrachromatic vision that is able to distinguish ultraviolet (UV) and visible wavelengths. Recently, zebrafish color preferences have gained much attention because of the easy setup of the instrument and its usefulness to screen behavior-linked stimuli. However, several published papers dealing with zebrafish color preferences have contradicting results that underscore the importance of method standardization in this field. Different laboratories may report different results because of variations in light source, color intensity, and other parameters such as age, gender, container size, and strain of fish. In this study, we aim to standardize the color preference test in zebrafish by measuring light source position, light intensity, gender, age, animal size to space ratio, and animal strain. Our results showed that color preferences for zebrafish are affected by light position, age, strain, and social interaction of the fish, but not affected by fish gender. We validated that ethanol can significantly induce color preference alteration in zebrafish which may be related to anxiety and depression. We also explored the potential use of the optimized method to examine color preference ranking and index differences in various zebrafish strains and species, such as the tiger barb and glass catfish. In conclusion, zebrafish color preference screening is a powerful tool for high-throughput neuropharmacological applications and the standardized protocol established in this study provides a useful reference for the zebrafish research community.

Seizure vulnerability and anxiety responses following chronic co-administration and acute withdrawal of caffeine and ethanol in a rat model

BACKGROUND

Caffeine antagonizes the intoxicating effects of alcohol. Consequently, there has been a dramatic global increase in the consumption of caffeinated drinks together with alcohol, especially among young adults. We assessed the seizure vulnerability and anxiety responses following the chronic co-administration of, and withdrawal from, caffeine and ethanol in male rats.

METHODS

The rats were randomly assigned to six groups consisting of 10 animals each: 10 mg/kg of caffeine, 20 mg/kg of caffeine, 4 g/kg of 20% ethanol, combined caffeine (20 mg/kg) and ethanol (4 g/kg of 20%), 4 mL/kg distilled water, and an untreated control group. The test substances were administered intragastrically twice daily for 29 days. On day 29, the rats were tested on the elevated plus maze to assess anxiety-related responses. On day 30, pentylenetetrazol (PTZ), a chemoconvulsant, was administered intraperitoneally at a dose of 40 mg/kg to the animals. Seizure responses and mortality up to 72 h were recorded.

RESULTS

Compared with the control group, the rats that received chronic treatment with low-dose caffeine, ethanol alone, and combined caffeine and ethanol exhibited significant anxiogenic-like effects, unlike with high-dose caffeine. Both low- and high-dose caffeine significantly increased PTZ seizure latency. Ethanol alone and combined caffeine and ethanol both lowered PTZ seizure latency. No significant difference occurred between the controls and the untreated group for either anxiety or seizure expression. Combined caffeine and ethanol increased the seizure-induced mortality from withdrawal effects at 72 h.

CONCLUSIONS

These findings suggest that the chronic co-administration of caffeine and ethanol and the acute withdrawal from these drugs lead to anxiogenic effects and increased seizure vulnerability.

Serotonergic Neuroplasticity in Alcohol Addiction

Alcohol addiction is a debilitating disorder producing maladaptive changes in the brain, leading drinkers to become more sensitive to stress and anxiety. These changes are key factors contributing to alcohol craving and maintaining a persistent vulnerability to relapse.

Serotonin (5-Hydroxytryptamine, 5-HT) is a monoamine neurotransmitter widely expressed in the central nervous system where it plays an important role in the regulation of mood. The serotonin system has been extensively implicated in the regulation of stress and anxiety, as well as the reinforcing properties of all of the major classes of drugs of abuse, including alcohol. Dysregulation within the 5-HT system has been postulated to underlie the negative mood states associated with alcohol use disorders.

This review will describe the serotonergic (5-HTergic) neuroplastic changes observed in animal models throughout the alcohol addiction cycle, from prenatal to adulthood exposure. The first section will focus on alcohol-induced 5-HTergic neuroadaptations in offspring prenatally exposed to alcohol and the consequences on the regulation of stress/anxiety. The second section will compare alterations in 5-HT signalling induced by acute or chronic alcohol exposure during adulthood and following alcohol withdrawal, highlighting the impact on the regulation of stress/anxiety signalling pathways. The third section will outline 5-HTergic neuroadaptations observed in various genetically-selected ethanol preferring rat lines. Finally, we will discuss the pharmacological manipulation of the 5-HTergic system on ethanol- and anxiety/stress-related behaviours demonstrated by clinical trials, with an emphasis on current and potential treatments.

5-HT1A Autoreceptors in the Dorsal Raphe Nucleus Convey Vulnerability to Compulsive Cocaine Seeking

Cocaine addiction and depression are comorbid disorders. Although it is well recognized that 5-hydroxytryptamine (5-HT; serotonin) plays a central role in depression, our understanding of its role in addiction is notably lacking. The 5-HT system in the brain is carefully controlled by a combined process of regulating 5-HT neuron firing through 5-HT autoreceptors, neurotransmitter release, enzymatic degradation, and reuptake by transporters. This study tests the hypothesis that activation of 5-HT1A autoreceptors, which would lessen 5-HT neuron firing, contributes to cocaine-seeking behaviors. Using 5-HT neuron-specific reduction of 5-HT1A autoreceptor gene expression in mice, we demonstrate that 5-HT1A autoreceptors are necessary for cocaine conditioned place preference. In addition, using designer receptors exclusively activated by designer drugs (DREADDs) technology, we found that stimulation of the serotonergic dorsal raphe nucleus (DRN) afferents to the nucleus accumbens (NAc) abolishes cocaine reward and promotes antidepressive-like behaviors. Finally, using a rat model of compulsive-like cocaine self-administration, we found that inhibition of dorsal raphe 5-HT1A autoreceptors attenuates cocaine self-administration in rats with 6 h extended access, but not 1 h access to the drug. Therefore, our findings suggest an important role for 5-HT1A autoreceptors, and thus DRNNAc 5-HT neuronal activity, in the etiology and vulnerability to cocaine reward and addiction. Moreover, our findings support a strategy for antagonizing 5-HT1A autoreceptors for treating cocaine addiction.

Effects of acute ethanol exposure on anxiety measures and epigenetic modifiers in the extended amygdala of adolescent rats

Epigenetic mechanisms appear to play an important role in neurodevelopment. We investigated the effects of acute ethanol exposure on anxiety measures and function of histone deacetylases (HDAC) and DNA methyltransferases (DNMT) in the amygdala and bed nucleus of stria terminalis (BNST) of adolescent rats. One hour after ethanol exposure, rats were subjected to anxiety measures. A subset of adolescent rats was exposed to two doses (24 h apart) of ethanol (2 g/kg) to measure rapid ethanol tolerance to anxiolysis. The HDAC and DNMT activities and mRNA levels of DNMT isoforms were measured in the amygdala and BNST. The lower dose of ethanol (1 g/kg) produced neither anxiolysis, nor inhibited the HDAC and DNMT activities in the amygdala and BNST, except DNMT activity in BNST was attenuated. Anxiolysis by ethanol was observed at 2 and 2.25 g/kg, whereas higher doses (2.5 and 3 g/kg) were found to be sedative. DNMT activity in the amygdala and BNST, and nuclear HDAC activity in the amygdala, but not in the BNST were also inhibited by these doses of ethanol. A lack of tolerance was observed on ethanol-induced inhibition of DNMT activity in the amygdala and BNST, and nuclear HDAC activity in the amygdala, as well to anxiolysis produced by ethanol (2 g/kg). The DNMT1, DNMT3a, and DNMT3b mRNA expression in the amygdala was not affected by either 1or 2 doses of 2 g/kg. However, DNMT1 and DNMT3a expression in the BNST was increased, whereas DNMT3l mRNA was decreased in the amygdala, after 2 doses of 2 g/kg ethanol. These results suggest that reduced sensitivity to anxiolysis and the lack of rapid tolerance to the anxiolytic effects of ethanol and inhibition of HDAC and DNMT functions may play a role in engaging adolescents in binge drinking patterns.

Common effects of fat, ethanol, and nicotine on enkephalin in discrete areas of the brain

Fat, ethanol, and nicotine share a number of properties, including their ability to reinforce behavior and produce overconsumption. To test whether these substances act similarly on the same neuronal populations in specific brain areas mediating these behaviors, we administered the substances short-term, using the same methods and within the same experiment, and measured their effects, in areas of the hypothalamus (HYPO), amygdala (AMYG), and nucleus accumbens (NAc), on mRNA levels of the opioid peptide, enkephalin (ENK), using in situ hybridization and on c-Fos immunoreactivity (ir) to indicate neuronal activity, using immunofluorescence histochemistry. In addition, we examined for comparison another reinforcing substance, sucrose, and also took measurements of stress-related behaviors and circulating corticosterone (CORT) and triglycerides (TG), to determine if they contribute to these substances' behavioral and physiological effects. Adult Sprague-Dawley rats were gavaged three times daily over 5 days with 3.5 mL of water, Intralipid (20% v/v), ethanol (12% v/v), nicotine (0.01% w/v) or sucrose (22% w/v) (approximately 7 kcal/dose), and tail vein blood was collected for measurements of circulating CORT and TG. On day five, animals were sacrificed, brains removed, and the HYPO, AMYG, and NAc processed for single- or double-labeling of ENK mRNA and c-Fos-ir. Fat, ethanol, and nicotine, but not sucrose, increased the single- and double-labeling of ENK and c-Fos-ir in precisely the same brain areas, the middle parvocellular but not lateral area of the paraventricular nucleus, central but not basolateral nucleus of the AMYG, and core but not shell of the NAc. While having little effect on stress-related behaviors or CORT levels, fat, ethanol, and nicotine all increased circulating levels of TG. These findings suggest that the overconsumption of these three substances and their potential for abuse are mediated by the same populations of ENK-expressing neurons in specific nuclei of the hypothalamus and limbic system.

The role of serotonin in drug use and addiction

The use of psychoactive drugs is a wide spread behaviour in human societies. The systematic use of a drug requires the establishment of different drug use-associated behaviours which need to be learned and controlled. However, controlled drug use may develop into compulsive drug use and addiction, a major psychiatric disorder with severe consequences for the individual and society. Here we review the role of the serotonergic (5-HT) system in the establishment of drug use-associated behaviours on the one hand and the transition and maintenance of addiction on the other hand for the drugs: cocaine, amphetamine, methamphetamine, MDMA (ecstasy), morphine/heroin, cannabis, alcohol, and nicotine. Results show a crucial, but distinct involvement of the 5-HT system in both processes with considerable overlap between psychostimulant and opioidergic drugs and alcohol. A new functional model suggests specific adaptations in the 5-HT system, which coincide with the establishment of controlled drug use-associated behaviours. These serotonergic adaptations render the nervous system susceptible to the transition to compulsive drug use behaviours and often overlap with genetic risk factors for addiction. Altogether we suggest a new trajectory by which serotonergic neuroadaptations induced by first drug exposure pave the way for the establishment of addiction.

An integrative analysis of ethanol tolerance and withdrawal in zebrafish (Danio rerio)

The zebrafish is emerging as a popular animal model for alcohol (ethanol or EtOH) addiction due to its simplicity and practical advantages. Two phenomena associated with ethanol addiction are the development of tolerance and withdrawal. Using a multi-level approach in the current study, we characterise ethanol tolerance and withdrawal in zebrafish. We first investigate the temporal trajectory of ethanol concentration in the zebrafish brain in response to an acute exposure and during withdrawal. We report that ethanol concentrations approach a steady state within 60 min of exposure to 0.50% and 1.00% v/v ethanol and rapidly decline and return to zero within 60 min following withdrawal from chronic ethanol exposure (0.50% v/v). We characterise the changes associated with ethanol tolerance and withdrawal in zebrafish by focusing on three domains relevant to ethanol addiction: motor patterns, physiological responses (i.e. cortisol levels), and neurochemical alterations. The use of multiple domains of investigation allowed an in-depth analysis of ethanol induced changes in zebrafish.

β1-adrenoceptor activation is required for ethanol enhancement of lateral paracapsular GABAergic synapses in the rat basolateral amygdala

Ethanol (EtOH) potentiation of GABAergic neurotransmission in the basolateral amygdala (BLA) may contribute to the acute anxiolytic effects of this drug. Previous studies have shown that BLA pyramidal neurons receive GABAergic input from two distinct sources: local interneurons and a cluster of GABAergic cells termed lateral paracapsular (LPCS) interneurons. It is noteworthy that whereas EtOH enhances local GABAergic synapses via a presynaptic increase in GABA release, EtOH potentiation of LPCS inhibition is mediated via a distinct mechanism that requires adrenoceptor (AR) activation. Here, we sought to further characterize the interaction between the AR system and EtOH enhancement of LPCS GABAergic synapses by using in vitro electrophysiology techniques in male Sprague-Dawley rats. Exogenous norepinephrine (NE) enhanced LPCS-evoked inhibitory postsynaptic currents (eIPSCs) via the activation of β-ARs, because this effect was blocked by propranolol. EtOH potentiation of LPCS eIPSCs was also blocked by propranolol and significantly reduced by NE pretreatment, suggesting that NE and EtOH may enhance LPCS inhibition via a common mechanism. EtOH enhancement of LPCS eIPSCs was significantly reduced by a selective β1-, but not β2- or β3-, AR antagonist, and both EtOH and NE potentiation of LPCS IPSCs was blocked by postsynaptic disruption of cAMP signaling. These data suggest that EtOH enhances LPCS synapses via a postsynaptic β1-AR, cAMP-dependent cascade. Because enhancement of LPCS inhibition can reduce anxiety-like behaviors, these findings shed light on a novel mechanism that may play a role in some of the anxiolytic effects of EtOH that are thought to contribute to the development and progression of alcoholism.

Alcohol and the prefrontal cortex

The prefrontal cortex occupies the anterior portion of the frontal lobes and is thought to be one of the most complex anatomical and functional structures of the mammalian brain. Its major role is to integrate and interpret inputs from cortical and sub-cortical structures and use this information to develop purposeful responses that reflect both present and future circumstances. This includes both action-oriented sequences involved in obtaining rewards and inhibition of behaviors that pose undue risk or harm to the individual. Given the central role in initiating and regulating these often complex cognitive and behavioral responses, it is no surprise that alcohol has profound effects on the function of the prefrontal cortex. In this chapter, we review the basic anatomy and physiology of the prefrontal cortex and discuss what is known about the actions of alcohol on the function of this brain region. This includes a review of both the human and animal literature including information on the electrophysiological and behavioral effects that follow acute and chronic exposure to alcohol. The chapter concludes with a discussion of unanswered questions and areas needing further investigation.

Permanent impairment of birth and survival of cortical and hippocampal proliferating cells following excessive drinking during alcohol dependence

Experimenter-delivered alcohol decreases adult hippocampal neurogenesis and hippocampal-dependent learning and memory. The present study used clinically relevant rodent models of nondependent limited access alcohol self-administration and excessive drinking during alcohol dependence (alcohol self-administration followed by intermittent exposure to alcohol vapors over several weeks) to compare alcohol-induced effects on cortical gliogenesis and hippocampal neurogenesis. Alcohol dependence, but not nondependent drinking, reduced proliferation and survival in the medial prefrontal cortex (mPFC). Apoptosis was reduced in both alcohol groups within the mPFC, which may reflect an initiation of a reparative environment following alcohol exposure as decreased proliferation was abolished after prolonged dependence. Reduced proliferation, differentiation, and neurogenesis were observed in the hippocampus of both alcohol groups, and prolonged dependence worsened the effects. Increased hippocampal apoptosis and neuronal degeneration following alcohol exposure suggest a loss in neuronal turnover and indicate that the hippocampal neurogenic niche is highly vulnerable to alcohol.

Relations between open-field, elevated plus-maze, and emergence tests in C57BL/6J and BALB/c mice injected with GABA- and 5HT-anxiolytic agents

Two 5HT(1A) receptor agonists and chlordiazepoxide were examined in open-field, elevated plus maze, and emergence tests. At doses with no effect in the open-field, chlordiazepoxide increased open and open/total arm visits as well as open arm duration in the elevated plus maze, whereas 5HT(1A) receptor agonists showed an anxiolytic response on a single measure. The anxiolytic action of chlordiazepoxide was limited to the less active BALB/c strain. Unlike the 5HT(1A) receptor agonists, chlordiazepoxide was also anxiolytic in the emergence test, once again only in BALB/c and not C57BL/6J mice. Significant correlations were found between emergence latencies and specific indicators of anxiety in the elevated plus-maze in chlordiazepoxide-treated but not in mice treated with buspirone and 8-OH-DPAT. These results indicate that elevated plus-maze and emergence tests depend on benzodiazepine receptors. In contrast, 5HT(1A) receptor agonists were ineffective in the emergence test and no correlation was found between emergence latencies and specific indicators of anxiety in the elevated plus-maze. Though superficially similar, the emergence test seems to tap into a partially separate facet of anxiety.

Dissociating anxiolytic and sedative effects of GABAAergic drugs using temperature and locomotor responses to acute stress

RATIONALE

The stress-induced hyperthermia (SIH) model is an anxiety model that uses the transient rise in body temperature in response to acute stress. Benzodiazepines produce anxiolytic as well as sedative side effects through nonselective binding to GABA(A) receptor subunits. The GABA(A) receptor alpha(1) subunit is associated with sedation, whereas the GABA(A) receptor alpha(2) and alpha(3) subunits are involved in anxiolytic effects.

OBJECTIVES

We therefore examined the effects of (non)subunit-selective GABA(A) receptor agonists on temperature and locomotor responses to novel cage stress.

RESULTS

Using telemetric monitoring of temperature and locomotor activity, we found that nonsubunit-selective GABA(A) receptor agonist diazepam as well as the alpha(3) subunit-selective receptor agonist TP003 dose-dependently attenuated SIH and locomotor responses. Administration of GABA(A) receptor alpha(1)-selective agonist zolpidem resulted in profound hypothermia and locomotor sedation. The GABA(A) receptor alpha(1)-selective antagonist betaCCt antagonized the hypothermia, but did not reverse the SIH response attenuation caused by diazepam and zolpidem. These results suggest an important regulating role for the alpha(1) subunit in thermoregulation and sedation. Ligands of extrasynaptic GABA(A) receptors such as alcohol and nonbenzodiazepine THIP attenuated the SIH response only at high doses.

CONCLUSIONS

The present study confirms a putative role for the GABA(A) receptor alpha(1) subunit in hypothermia and sedation and supports a role for alpha(2/3) subunit GABA(A) receptor agonists in anxiety processes. In conclusion, we show that home cage temperature and locomotor responses to novel home cage stress provide an excellent tool to assess both anxiolytic and sedative effects of various (subunit-selective) GABA(A)ergic compounds.

Acute and chronic alcohol dose: population differences in behavior and neurochemistry of zebrafish

The zebrafish has been in the forefront of developmental genetics for decades and has also been gaining attention in neurobehavioral genetics. It has been proposed to model alcohol-induced changes in human brain function and behavior. Here, adult zebrafish populations, AB and SF (short-fin wild type), were exposed to chronic treatment (several days in 0.00% or 0.50% alcohol v/v) and a subsequent acute treatment (1 h in 0.00%, 0.25%, 0.50% or 1.00% alcohol). Behavioral responses of zebrafish to computer-animated images, including a zebrafish shoal and a predator, were quantified using videotracking. Neurochemical changes in the dopaminergic and serotoninergic systems in the brain of the fish were measured using high-precision liquid chromatography with electrochemical detection. The results showed genetic differences in numerous aspects of alcohol-induced changes, including, for the first time, the behavioral effects of withdrawal from alcohol and neurochemical responses to alcohol. For example, withdrawal from alcohol abolished shoaling and increased dopamine and 3,4-dihydroxyphenylacetic acid in AB but not in SF fish. The findings show that, first, acute and chronic alcohol induced changes are quantifiable with automated behavioral paradigms; second, robust neurochemical changes are also detectable; and third, genetic factors influence both alcohol-induced behavioral and neurotransmitter level changes. Although the causal relationship underlying the alcohol-induced changes in behavior and neurochemistry is speculative at this point, the results suggest that zebrafish will be a useful tool for the analysis of the biological mechanisms of alcohol-induced functional changes in the adult brain.

Preclinical and clinical pharmacology of alcohol dependence

In recent years, advances in neuroscience led to the development of new medications to treat alcohol dependence and especially to prevent alcohol relapse after detoxification. Whereas the earliest medications against alcohol dependence were fortuitously discovered, recently developed drugs are increasingly based on alcohol's neurobiological mechanisms of action. This review discusses the most recent developments in alcohol pharmacotherapy and emphasizes the neurobiological basis of anti-alcohol medications. There are currently three approved drugs for the treatment of alcohol dependence with quite different mechanisms of action. Disulfiram is an inhibitor of the enzyme aldehyde dehydrogenase and acts as an alcohol-deterrent drug. Naltrexone, an opiate antagonist, reduces alcohol craving and relapse in heavy drinking, probably via a modulation of the mesolimbic dopamine activity. Finally, acamprosate helps maintaining alcohol abstinence, probably through a normalization of the chronic alcohol-induced hyperglutamatergic state. In addition to these approved medications, many other drugs have been suggested for preventing alcohol consumption on the basis of preclinical studies. Some of these drugs remain promising, whereas others have produced disappointing results in preliminary clinical studies. These new drugs in the field of alcohol pharmacotherapy are also discussed, together with their mechanisms of action.

ELB139 an agonist at the benzodiazepine binding site increases 5-HT in the striatum and prefrontal cortex of rats: a microdialysis study

Benzodiazepines induce an immediate anxiolytic activity at the expense of side effects such as sedation, tolerance and withdrawal. In contrast, selective serotonin receptor uptake inhibitors (SSRIs) are known to offer long-term symptom improvement without inducing tolerance and withdrawal, but with a delayed onset of the anxiolytic effect. ELB139 is a novel agonist at the benzodiazepine binding site with pronounced anxiolytic and anticonvulsant activity without inducing tolerance to both effects after chronic administration. ELB139 shows a selectivity for alpha-3-subunit containing GABA(A) receptors. In the present study the effect of the compound on monoaminergic neurotransmitter levels were investigated by microdialysis. ELB139 induced a significant increase of extracellular 5-HT in the striatum and the medial prefrontal cortex of rats without affecting dopamine levels in these areas. The increase of 5-HT in the striatum was reversed by systemic and by local administration of the benzodiazepine antagonist flumazenil in the dorsal raphe nucleus by a microdialysis probe, suggesting that the increase in 5-HT was mediated by the activity of ELB139 at the benzodiazepine binding site. As the dorsal raphe nucleus is rich in alpha-3 subunits, this effect of ELB139 may be mediated by its subtype selectivity. Thus, ELB139 seems to combine effects seen with benzodiazepine agonists and SSRIs in one compound.

Alteration of 5-HIAA levels in frontal cortex and dorsal raphe nucleus in rats treated with combined administration of tryptophan and ethanol

The present studies sought to investigate the effect of tryptophan alone or coadministration of tryptophan and ethanol on the interaction of central frontal cortex and dorsal raphe nucleus serotonergic functional activities by utilizing in vivo microdialysis. Tryptophan (50 mg/kg, i.p.) led to a significant increase in the levels of 5-HIAA, a metabolite of serotonin (5-HT), in the dorsal raphe nucleus, but not in the frontal cortex. Coadministration of tryptophan and ethanol caused very marked increases in 5-hydroxyindoleacetic acid (5-HIAA) levels in both the frontal cortex and the dorsal raphe nucleus, although ethanol (1.25 g/kg) did not change 5-HIAA levels in both areas. Moreover, the application of WAY100635 (10 muM), 5-HT(1A) antagonist, into the frontal cortex after coadministration caused a marked increase in 5-HIAA levels in the frontal cortex and a decrease in the levels in the dorsal raphe nucleus, although WAY100635 alone had no effect on these levels. This may suggest that WAY100635-induced increase of 5-HIAA levels in the frontal cortex resulted from negative feedback following the blockade of serotonergic 5-HT(1A) autoreceptors, and that this increase in 5-HIAA levels decreased 5-HIAA levels in the dorsal raphe nucleus by preventing the activation of dorsal raphe 5-HT(1A) autoreceptors. WAY100635 into the dorsal raphe nucleus did not significantly change 5-HIAA levels in both areas. This may indicate that the blockade of dorsal raphe 5-HT(1A) autoreceptors by WAY100635 resulted in unchanged 5-HIAA levels in the frontal cortex. Behavioral sign of teeth-chattering was markedly observed following the coadministration and in combination with WAY100635. These results may suggest that the increased 5-HIAA levels in both areas after coadministration are indicative of the interrelation via activation of serotonergic neurons, and that the increased levels are partly responsible for behavioral activation of rats.

Effects of acute ethanol or amphetamine administration on the acoustic startle response and prepulse inhibition in adolescent and adult rats

RATIONALE

Adolescents differ from adults in their sensitivity to a variety of psychoactive drugs. For example, adolescent rats are less sensitive to locomotor stimulant and stereotypic effects of amphetamine as well as to motor-impairing and hypnotic effects of ethanol while more sensitive to ethanol-induced disruption of brain plasticity.

OBJECTIVE

The current study further explored age differences in psychopharmacological sensitivity by examining the effects of d-amphetamine (1.0 and 4.0 mg/kg) or ethanol (0.5, 1.0 and 1.5 g/kg) given interperitoneally on the acoustic startle response (ASR) and prepulse inhibition (PPI) in male adolescent and adult Sprague-Dawley rats.

MATERIALS AND METHODS

The animals were given five startle trials (120 dB for 40 ms) before semi-randomized presentation of 12 startle trials interspersed with ten trials at each prepulse intensity (40 ms pulse of 5, 10, or 20 dB above background; 100 ms before the startle stimulus).

RESULTS

Adolescent controls showed significantly less PPI than adults, replicating previous ontogenetic findings. The higher dose of amphetamine disrupted PPI in adult but not in adolescent animals, extending previous reports of an adolescent insensitivity to amphetamine to include this measure of sensorimotor gating. Ethanol exposure failed to alter PPI at either age, although both the 1.0 and 1.5 g/kg doses of ethanol significantly suppressed the magnitude of the ASR at both ages, potentially reflecting sedative or anxiolytic effects.

CONCLUSION

These data provide further evidence of the relative insensitivity of adolescent animals to amphetamine, although no age effects were found in terms of ethanol sensitivity using these measures of startle and sensorimotor gating.

Influence of fluoxetine and paroxetine in behavioral sensitization induced by ethanol in mice

The serotonergic system is involved in depression, anxiety and alcoholism. The rewarding properties of ethanol, mainly its anxiolytic and stimulant effects, as well as the development of dependence on ethanol have been related to the serotonergic system. Consequently, the use of selective serotonergic reuptake inhibitors (SSRI) has been proposed in the treatment of alcoholism. In this study we investigated whether acute administration of the SSRIs fluoxetine or paroxetine is able to (i) reverse the behavioral effects induced by chronic ethanol consumption, and conversely, (ii) to determine whether acute ethanol is able to substitute for the chronically induced behavioral effects of fluoxetine or paroxetine. Four groups of male Swiss mice (n=60/group) received daily i.p. saline, ethanol (2 g/kg), fluoxetine (10 mg/kg) or paroxetine (5 mg/kg) for 27 days. On the 28th day, each group was challenged with saline, ethanol, fluoxetine or paroxetine. The 14 groups (SS, SE, SP, SF, EE, ES, EP, EF, PP, PE, PS, FF, FE, and FS) were then tested in open field, activity cage and plus-maze. EP and EF groups were able to reverse the behavioral sensitization to the psychomotor stimulant effects of chronic ethanol administration. In contrast, a sensitized stimulatory effect was observed in chronically fluoxetine- or paroxetine treated mice challenged with ethanol (PE and FE). An anxiolytic effect was observed whether ethanol was substituted for SSRI or, conversely, SSRI was substituted for ethanol. SSRIs facilitated ethanol-induced locomotor sensitization, although SSRIs by themselves are unable to produce the locomotor stimulation similar to that induced by ethanol. Finally, SSRIs are unable to interfere in the ethanol anxiolytic effect.

Ethanol, 3,4-methylenedioxymethamphetamine (ecstasy) and their combination: long-term behavioral, neurochemical and neuropharmacological effects in the rat

This study investigated long-term behavioral, neurochemical, and neuropharmacological effects of ethanol-(+/-)-3,4-methylenedioxymethamphetamine (MDMA, ecstasy) combinations. Over 4 consecutive days, male Long-Evans rats received 1.5 g/kg ethanol and/or 10 mg/kg MDMA, or saline. Rectal temperatures were taken in some rats. Starting 4 days after the last injection, we tested working memory, sensory-motor coordination, and anxiety. Subsequently, we measured cortical, striatal, septal, and hippocampal monoamines (last MDMA injection-euthanasia delay: 20 days), or electrically evoked release of serotonin (5-HT) in cortical and hippocampal slices, and its modulation in the presence of CP 93,129 (3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrollo[3,2-b]pyrid-5-one) or methiotepin (last MDMA injection-euthanasia delays: 3-6 weeks). Ethanol attenuated the MDMA-induced hyperthermia, but only on the first day. In the long-term, MDMA reduced 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) content in most brain regions. The behavioral and neurochemical effects of the ethanol-MDMA combination were comparable to those of MDMA alone; sensory-motor coordination was altered after ethanol and/or MDMA. In hippocampal slices from rats given ethanol and MDMA, the CP 93,129-induced inhibition and methiotepin-induced facilitation of 5-HT release were stronger and weaker, respectively, than in the other groups. This is the first study addressing long-term effects of repeated MDMA and EtOH combined treatments in experimental animals. Whereas the drug combination produced the same behavioral and neurochemical effects as MDMA alone, our neuropharmacological results suggest that MDMA-EtOH interactions may have specific long-term consequences on presynaptic modulation of hippocampal 5-HT release, but not necessarily related to MDMA-induced depletion of 5-HT. Thus, it is likely that the psycho(patho)logical problems reported by ecstasy users drinking alcohol are not solely due to the consumption of MDMA.

The role of acetaldehyde in the neurobehavioral effects of ethanol: A comprehensive review of animal studies

Acetaldehyde has long been suggested to be involved in a number of ethanol's pharmacological and behavioral effects, such as its reinforcing, aversive, sedative, amnesic and stimulant properties. However, the role of acetaldehyde in ethanol's effects has been an extremely controversial topic during the past two decades. Opinions ranged from those virtually denying any role for acetaldehyde in ethanol's effects to those who claimed that alcoholism is in fact "acetaldehydism". Considering the possible key role of acetaldehyde in alcohol addiction, it is critical to clarify the respective functions of acetaldehyde and ethanol molecules in the pharmacological and behavioral effects of alcohol consumption. In the present paper, we review the animal studies reporting evidence that acetaldehyde is involved in the pharmacological and behavioral effects of ethanol. A number of studies demonstrated that acetaldehyde administration induces a range of behavioral effects. Other pharmacological studies indicated that acetaldehyde might be critically involved in several effects of ethanol consumption, including its reinforcing consequences. However, conflicting evidence has also been published. Furthermore, it remains to be shown whether pharmacologically relevant concentrations of acetaldehyde are achieved in the brain after alcohol consumption in order to induce significant effects. Finally, we review current evidence about the central mechanisms of action of acetaldehyde.

Involvement of nitric oxide-dependent pathways of dorsolateral periaqueductal gray in the effects of ethanol in rats submitted to the elevated plus-maze test

Our previous study showed the microinjection of drugs that influence the nitric oxide (NO)-mediated neurotransmission in the hippocampus impacts upon the anxiolytic-like effect of ethanol. In this study, we examined whether NO-dependent pathways of the dorsolateral periaqueductal gray (dlPAG) participate in the anxiolytic effect of ethanol in rats submitted to the elevated plus-maze test. We evaluated the impact on ethanol effects of the nitric oxide synthase (NOS) inhibitor 7-nitroindazole, the soluble guanylate cyclase inhibitor 1H-(1,2,4)-oxodiazolo (4,3-a) quinoxalin-1-one (ODQ), the cyclic guanylate monophosphate (cGMP) analogue 8-bromo-cGMP and the NO donor sodium nitroprusside. The results showed that ODQ and 7-nitroindazole increased the percentage of open arm entries and of time spent on open arms in the elevated plus maze in rats injected with ethanol at 1.0g/kg, a dose that did not produce anxiolysis per se. Conversely, 8-bromo-cGMP and sodium nitroprusside blocked the increased exploration of open arms exhibited by rats treated with a higher dose of ethanol (1.2g/kg). Taken together, the results suggest that the inhibition of NO-dependent pathways of the dlPAG enhances the anxiolytic effect of ethanol, whereas the activation of these pathways results in an opposite effect.

Anxiety as a predictor of alcohol preference in rats?

Many clinical studies based on retrospective self-reports indicate a relationship between anxiety and increased alcohol consumption or relapse in individuals with alcohol abuse or dependence. However, by these retrospective studies it cannot be definitely concluded whether the alcohol abuse or the anxiety was first. In the present study, alcohol-consuming behaviour was determined in three rat strains showing different anxiety-related behaviour but being not genetically selected for high or low alcohol consumption. The innate anxiety of the three rat strains (Harlan-Fischer, Wistar-BgVV and Wistar-Harlan) was measured by the elevated plus maze test. Thereafter voluntary ethanol intake was measured for 3 months followed by a progressive ratio paradigm, in which the number of responses required to obtain alcohol was successively increased during session. The point at which rats ceased to respond (breaking point) was taken as a measure of their motivation to obtain ethanol. The study revealed that Harlan-Fischer rats showing most anxiety-related behaviour in the elevated plus maze test displayed the lowest ethanol intake [g/kg/d b.w.] and the lowest breaking points in the progressive ratio paradigm. The Wistar-Harlan rats with least anxiety-related behaviour and the Wistar-BgVV rats with medium anxiety-related behaviour drank more alcohol and showed higher breaking points than the Harlan-Fischer rats. Thus, in the present study, a distinct relationship between innate anxiety and alcohol-consuming behaviour in rat strains not genetically selected for high and low ethanol intake could not be shown.

Differential effect of anterior cingulate cortex lesion on mechanical hypersensitivity and escape/avoidance behavior in an animal model of neuropathic pain

Various limbic system structures have been implicated in processing noxious information. One such structure is the anterior cingulate cortex (ACC), a region that is thought to modulate higher order processing of noxious input related to the affective/motivational component of pain. The present experiment examined the involvement of the ACC in higher order pain processing by measuring paw withdrawal threshold and escape/avoidance responses in the L5 spinal nerve ligation model of neuropathic pain before and following electrolytic lesion of the ACC. In the place/escape avoidance paradigm, the afflicted paw is mechanically stimulated when the animal is in the preferred dark area of the chamber and the contralateral paw is stimulated when the animal is in the light area. Escape/avoidance was defined as a shift from the preferred dark area to an increase of time spent in the light area of the chamber. Animals with L5 ligation had significantly lower mechanical paw withdrawal threshold (hypersensitivity) and enhanced escape/avoidance behavior. ACC lesion in animals with L5 ligation did not alter mechanical hypersensitivity, but did significantly decrease escape/avoidance behavior. Anxiety, as measured using the light-enhanced startle paradigm, was not altered by ACC lesion. These results highlight the utility of novel behavioral test paradigms and provide additional support for the role of the ACC in higher order processing of noxious information, suggesting that ACC lesions selectively decrease negative affect associated with neuropathy-induced hypersensitivity.

Acute alcohol administration improves skilled reaching success in intact but not 6-OHDA dopamine depleted rats: a subsystems analysis of the motoric and anxiolytic effects of alcohol

Low doses of alcohol impair movement and reduce anxiety. Most assessments of movement under ethyl alcohol (alcohol) in the rat have been tests of whole body movements, however. There has been no examination of the effects of alcohol on skilled limb movements, such as reaching for food with a forelimb. This was the purpose of the present study. Rats were trained to reach through a slot of a box with a forelimb in order to obtain a food pellet located on an external shelf. Once asymptotic performance was achieved, rats were given alcohol (20 ml of 8, 12 or 20% (v/v) solution) in separate tests to establish a relationship between alcohol ingestion and skilled reaching performance. Acute treatment with all doses of alcohol impaired postural support, but doses of 8 and 12% alcohol improved skilled reaching success. Qualitative analysis of the movements used for reaching at doses of 8 and 12% indicated that some limb components of the reaching movement were also impaired, perhaps secondarily due to impaired posture. In contrast, the reaching success of rats with unilateral dopamine depletion, induced with the neurotoxin 6-hydroxydopamine (6-OHDA) in the nigrostriatal bundle, was impaired by the same dose of alcohol that improved reaching success in control rats. The finding of improved success in reaching associated with reduced postural support in normal rats suggests a differential action of alcohol on movement subsystems underlying posture relative to skilled movement that depends upon an intact dopaminergic system. The results are also discussed with respect to the relationship of subsystems of movement and anxiety.