Adolescent,but Not Adult,Binge Ethanol Exposure Leads to Persistent Global Reductions of Choline Acetyltransferase Expressing Neurons in Brain

During the adolescent transition from childhood to adulthood, notable maturational changes occur in brain neurotransmitter systems. The cholinergic system is composed of several distinct nuclei that exert neuromodulatory control over cognition, arousal, and reward. Binge drinking and alcohol abuse are common during this stage, which might alter the developmental trajectory of this system leading to long-term changes in adult neurobiology. In Experiment 1, adolescent intermittent ethanol (AIE; 5.0 g/kg, i.g., 2-day on/2-day off from postnatal day [P] 25 to P55) treatment led to persistent, global reductions of choline acetyltransferase (ChAT) expression. Administration of the Toll-like receptor 4 agonist lipopolysaccharide to young adult rats (P70) produced a reduction in ChAT+IR that mimicked AIE. To determine if the binge ethanol-induced ChAT decline was unique to the adolescent, Experiment 2 examined ChAT+IR in the basal forebrain following adolescent (P28–P48) and adult (P70–P90) binge ethanol exposure. Twenty-five days later, ChAT expression was reduced in adolescent, but not adult, binge ethanol-exposed animals. In Experiment 3, expression of ChAT and vesicular acetylcholine transporter expression was found to be significantly reduced in the alcoholic basal forebrain relative to moderate drinking controls. Together, these data suggest that adolescent binge ethanol decreases adult ChAT expression, possibly through neuroimmune mechanisms, which might impact adult cognition, arousal, or reward sensitivity.     

Distinct ethanol drinking microstructures in two replicate lines of mice selected for drinking to intoxication

The High Drinking in the Dark (HDID) mice have been selectively bred for reaching high blood ethanol concentrations (BECs) following the limited access Drinking in the Dark (DID) test. We have shown previously that mice from the first HDID replicate line (HDID‐1) drink in larger, but not longer, ethanol drinking bouts than the low‐drinking HS/Npt control mice when consuming modest amounts in the DID test. Here, we assessed drinking microstructure in HDID‐1 mice during binge‐like levels of ethanol intake using a lickometer system. Mice from both HDID replicates (HDID‐1 and ‐2) and HS mice were also given three DID tests (single‐bottle ethanol, two‐bottle choice and single‐bottle saccharin) using a continuously recording BioDAQ system to determine whether there are selection‐dependent changes in drinking microstructure. Larger ethanol bout size in the HDID‐1 mice than the HS mice was found to be due to a larger lick volume in these mice. HDID‐1 and HDID‐2 mice were also seen to have different drinking microstructures that both resulted in high intake and high BECs. The HDID‐1 mice drank in larger ethanol bouts than HS, whereas HDID‐2 mice drank in more frequent bouts. This pattern was also seen in two‐bottle choice DID. The HDID‐2 mice had a high bout frequency for all fluid types tested, whereas the large bout size phenotype of the HDID‐1 mice was specific to alcohol. These findings suggest that selection for drinking to intoxication has resulted in two distinct drinking microstructures, both of which lead to high BECs and high ethanol intake.     

Adolescent binge drinking leads to changes in alcohol drinking, anxiety, and amygdalar corticotropin releasing factor cells in adulthood in male rats

Heavy episodic drinking early in adolescence is associated with increased risk of addiction and other stress-related disorders later in life. This suggests that adolescent alcohol abuse is an early marker of innate vulnerability and/or binge exposure impacts the developing brain to increase vulnerability to these disorders in adulthood. Animal models are ideal for clarifying the relationship between adolescent and adult alcohol abuse, but we show that methods of involuntary alcohol exposure are not effective. We describe an operant model that uses multiple bouts of intermittent access to sweetened alcohol to elicit voluntary binge alcohol drinking early in adolescence (~postnatal days 28-42) in genetically heterogeneous male Wistar rats. We next examined the effects of adolescent binge drinking on alcohol drinking and anxiety-like behavior in dependent and non-dependent adult rats, and counted corticotropin-releasing factor (CRF) cell in the lateral portion of the central amygdala (CeA), a region that contributes to regulation of anxiety- and alcohol-related behaviors. Adolescent binge drinking did not alter alcohol drinking under baseline drinking conditions in adulthood. However, alcohol-dependent and non-dependent adult rats with a history of adolescent alcohol binge drinking did exhibit increased alcohol drinking when access to alcohol was intermittent. Adult rats that binged alcohol during adolescence exhibited increased exploration on the open arms of the elevated plus maze (possibly indicating either decreased anxiety or increased impulsivity), an effect that was reversed by a history of alcohol dependence during adulthood. Finally, CRF cell counts were reduced in the lateral CeA of rats with adolescent alcohol binge history, suggesting semi-permanent changes in the limbic stress peptide system with this treatment. These data suggest that voluntary binge drinking during early adolescence produces long-lasting neural and behavioral effects with implications for anxiety and alcohol use disorders.     

Progress in a replicated selection for elevated blood ethanol concentrations in HDID mice

Drinking in the dark (DID) is a limited access ethanol‐drinking phenotype in mice. High Drinking in the Dark (HDID‐1) mice have been bred for 27 selected generations (S27) for elevated blood ethanol concentrations (BECs) after a 4‐h period of access to 20% ethanol. A second replicate line (HDID‐2) was started later from the same founder population and is currently in S20. An initial report of response to selection in HDID‐1 was published after S11. This article reports genetic and behavioral characteristics of both lines in comparison with the HS controls. Heritability is low in both replicates (h² = 0.09) but the lines have shown 4–5 fold increases in BEC since S0; 80% of HDID‐1 and 60% of HDID‐2 mice reach BECs greater than 1.0 mg/ml. Several hours after a DID test, HDID mice show mild signs of withdrawal. Although not considered during selection, intake of ethanol (g/kg) during the DID test increased by approximately 80% in HDID‐1 and 60% in HDID‐2. Common genetic influences were more important than environmental influences in determining the similarity between BEC and intake for HDID mice. Analysis of the partitioning of intake showed that 60% of intake is concentrated in the last 2 h of the 4 h session. However, this has not changed during selection. Hourly BECs during the DID test reach peak levels after 3 or 4 h of drinking. HDID mice do not differ from HS mice in their rate of elimination of an acute dose of alcohol .     

Selection for high alcohol preference drinking in mice results in heightened sensitivity and rapid development of acute functional tolerance to alcohol's ataxic effects

Propensity to develop acute functional (or within session) tolerance to alcohol (ethanol) may influence the amount of alcohol consumed, with higher drinking associated with greater acute functional tolerance (AFT). The goal of this study was to assess this potential correlated response between alcohol preference and AFT in second and third replicate lines of mice selectively bred for high (HAP2 and HAP3) and low (LAP2 and LAP3) alcohol preference drinking. Male and female mice were tested for development of AFT on a static dowel task, which requires that animals maintain balance on a wooden dowel in order to prevent falling. On test day, each mouse received one (1.75 g/kg; Experiment 1) or two (1.75 and 2.0 g/kg; Experiment 2) injections of ethanol; an initial administration before being placed on the dowel and in Experiment 2, an additional administration after the first regain of balance on the dowel. Blood samples were taken immediately after loss of balance [when blood ethanol concentrations (BECs) were rising] and at recovery (during falling BECs) in Experiment 1, and after first and second recovery in Experiment 2. It was found that HAP mice fell from the dowel significantly earlier and at lower BECs than LAP mice following the initial injection of ethanol and were therefore more sensitive to its early effects. Furthermore, Experiment 1 detected significantly greater AFT development (BECfalling ? BECrising) in HAP mice when compared with LAP mice, which occurred within ～30 min, supporting our hypothesis. However, AFT was not different between lines in Experiment 2, indicating that ～30–60 min following alcohol administration, AFT development was similar in both lines. These data show that high alcohol drinking genetically associates with both high initial sensitivity and very early tolerance to the ataxic effects of ethanol.     

Male and female reproductive toxicity induced by sub-chronic ethanol exposure in CF-1 mice

Since genetic damage induced by ethanol exposure is controversial and incomplete and because germ and somatic cells constitute bioindicators for monitoring reproductive toxicity and genotoxic actions of ethanol consumption, the purpose of the present investigation was to evaluate morphological sperm, oocyte alterations and parental genotoxic effects after sub-chronic ethanol intake in the CF-1 outbred mouse strain. Ethanol 10% was administered to CF-1 adult male (treated males, TM) and female (treated females, TF) mice for 27 days, whereas water was given to controls from both sexes too (CM and CF). Post-treatment micronucleus frequency (MN-PCE/1,000/mouse) and gamete morphology were evaluated. To test whether change of female reproductive status results in maternal genotoxicity, CF-1 females received ethanol 10% (exposed group, periconceptionally treated females (PTF)) or water (control group, pregnant control females (PCF)) in drinking water for 17 days previous and up to 10 days of gestation. TM had a high percentage of abnormal spermatozoa vs CM (p < 0.001) and elevated parthenogenetic activated oocyte frequency appeared in TF vs CF (p < 0.001). Sub-chronic ethanol ingestion induced increased MN frequency in TM and TF (p < 0.01). In PTF, where blood alcohol concentrations were between 19–28 mg/dl, very significantly increased MN frequency was found vs PCF (p < 0.01), whereas MN values were similar to TF. These results show that sub-chronic alcohol ingestion in CF-1 mice produces sperm head dysmorphogenesis and oocyte nuclear anomalies, suggesting that morphological abnormalities in germ cells are probably related to parental genotoxicity after ethanol consumption.     

Pre-pubertal gonadectomy and the social consequences of acute ethanol in adolescent male and female rats

It has previously been shown that pre-pubertal or adult gonadectomy (GX) increases ethanol intake in male rats. This study examined whether this sex-selective increase reflects a GX-induced maintenance in males of more adolescent-typical responsiveness to ethanol characterized by enhanced sensitivity to positive (e.g., socially facilitating) and a decreased sensitivity to adverse (e.g., socially inhibitory) effects of ethanol. Male and female Sprague-Dawley rats were pre-pubertally GX, sham (SH)-operated, or non-manipulated (NM) at postnatal day (P) 25. During the late adolescent transition into adulthood (P48 — baseline day), rats were given a saline injection, placed alone into a familiar test apparatus for 30 min and then exposed for 10 min to an unfamiliar partner of the same age and sex. On the following day (P49), similar testing occurred after administration of 0.5, 0.75, 1.0 or 1.25 g/kg ethanol. At baseline, GX males and females displayed higher levels of social activity (especially adolescent-typical play and contact behavior) than SH and NM animals, with GX females displaying greater social activity than GX males. Neither males nor females demonstrated social facilitation at lower ethanol doses, regardless of hormonal status. Whereas the social inhibitory effects of higher doses of ethanol were similar across groups among females, SH males were less sensitive than both GX and NM males to ethanol-induced social inhibition. These results suggest that enhanced ethanol intake in GX males is not related to alterations in sensitivity to ethanol's social inhibitory effects. GX, however, results in retention of adolescent-typical social behaviors, with older GX adolescent rats resembling early adolescents in exhibiting elevated social activity—particularly play and contact behavior.     

Effects of Methamphetamine Exposure on Fear Learning and Memory in Adult and Adolescent Rats

Methamphetamine (meth) use is often comorbid with anxiety disorders, with both conditions predominant during adolescence. Conditioned fear extinction is the most widely used model to study the fear learning and regulation that are relevant for anxiety disorders. The present study investigates how meth binge injections or meth self-administration affect subsequent fear conditioning, extinction and retrieval in adult and adolescent rats. In experiment 1, postnatal day 35 (P35—adolescent) and P70 (adult) rats were intraperitoneally injected with increasing doses of meth across 9 days. At P50 or P85, they underwent fear conditioning followed by extinction and test. In experiments 2a–c, P35 or P70 rats self-administered meth for 11 days then received fear conditioning at P50 or P85, followed by extinction and test. We observed that meth binge exposure caused a significant disruption of extinction retrieval in adult but not adolescent rats. Interestingly, meth self-administration in adolescence or adulthood disrupted acquisition of conditioned freezing in adulthood. Meth self-administration in adolescence did not affect conditioned freezing in adolescence. These results suggest that intraperitoneal injections of high doses of meth and meth self-administration have dissociated effects on fear conditioning and extinction during adulthood, while adolescent fear conditioning and extinction are unaffected.

     

Comparison of the deleterious effects of binge drinking‐like alcohol exposure in adolescent and adult mice

A major cause of alcohol toxicity is the production of reactive oxygen species generated during ethanol metabolism. The aim of this study was to compare the effect of binge drinking‐like alcohol exposure on a panel of genes implicated in oxidative mechanisms in adolescent and adult mice. In adolescent animals, alcohol decreased the expression of genes involved in the repair and protection of oxidative DNA damage such as atr, gpx7, or nudt15 and increased the expression of proapoptotic genes such as casp3. In contrast, in the adult brain, genes activated by alcohol were mainly associated with protective mechanisms that prevent cells from oxidative damage. Whatever the age, iterative binge‐like episodes provoked the same deleterious effects as those observed after a single binge episode. In adolescent mice, multiple binge ethanol exposure substantially reduced neurogenesis in the dentate gyrus and impaired short‐term memory in the novel object and passive avoidance tests. Taken together, our results indicate that alcohol causes deleterious effects in the adolescent brain which are distinct from those observed in adults. These data contribute to explain the greater sensitivity of the adolescent brain to alcohol toxicity.

     

Genotype modulates age‐related alterations in sensitivity to the aversive effects of ethanol: an eight inbred strain analysis of conditioned taste aversion

Adolescent individuals display altered behavioral sensitivity to ethanol, which may contribute to the increased ethanol consumption seen in this age‐group. However, genetics also exert considerable influence on both ethanol intake and sensitivity. Currently there is little research assessing the combined influence of developmental and genetic alcohol sensitivities. Sensitivity to the aversive effects of ethanol using a conditioned taste aversion (CTA) procedure was measured during both adolescence (P30) and adulthood (P75) in eight inbred mouse strains (C57BL/6J, DBA/2J, 129S1/SvImJ, A/J, BALB/cByJ, BTBR T⁺tf/J, C3H/HeJ and FVB/NJ). Adolescent and adult mice were water deprived, and subsequently provided with access to 0.9% (v/v) NaCl solution for 1 h. Immediately following access mice were administered ethanol (0, 1.5, 2.25 and 3 g/kg, ip). This procedure was repeated in 72 h intervals for a total of five CTA trials. Sensitivity to the aversive effects of ethanol was highly dependent upon both strain and age. Within an inbred strain, adolescent animals were consistently less sensitive to the aversive effects of ethanol than their adult counterparts. However, the dose of ethanol required to produce an aversion response differed as a function of both age and strain.     

Growth and liver morphology after long-term ethanol consumption of rats

Ethanol was administered to female and male Wistar rats by mixing it with their drinking water. Ethanol concentrations were gradually increased up to either 8% or 15%. Female rats receiving 8% ethanol in their drinking water consumed 5-13 g, males 4-10 g daily. The ethanol/total food caloric intake percentages were 13 to 20% and 9 to 15% for female and male rats, respectively. There was no difference in body weight and relative liver weight between treated rats and their controls. Female and male rats receiving 15% of ethanol in their drinking water consumed 8-14 g ethanol per kg body weight per day. The percentages of ethanol/total food caloric intake were stabilized at about 25% for both sexes. Growth of the rats differed only slightly from controls; a tendency for a higher increase of body weight of the control rats was found. No difference in relative liver weight between ethanol-treated and control rats was observed. Microscopic examinations revealed that the ethanol treatment resulted in fat accumulation in the liver cells. A proliferation of the Smooth Endoplasmic Reticulum (SER) was more marked in the 15% dosed rats than in the 8% dosed rats and more distinct in female rats than in male rats in both dosage groups.     

Contribution of P2X4 Receptors to Ethanol Intake in Male C57BL/6 Mice

P2X receptors (P2XRs) are a family of cation-permeable ligand-gated ion channels activated by synaptically released extracellular adenosine 5′-triphosphate. The P2X4 subtype is abundantly expressed in the central nervous system and is sensitive to low intoxicating ethanol concentrations. Genetic meta-analyses identified the p2rx4 gene as a candidate gene for innate alcohol intake and/or preference. The current study used mice lacking the p2rx4 gene (knockout, KO) and wildtype (WT) C57BL/6 controls to test the hypothesis that P2X4Rs contribute to ethanol intake. The early acquisition and early maintenance phases of ethanol intake were measured with three different drinking procedures. Further, we tested the effects of ivermectin (IVM), a drug previously shown to reduce ethanol’s effects on P2X4Rs and to reduce ethanol intake and preference, for its ability to differentially alter stable ethanol intake in KO and WT mice. Depending on the procedure and the concentration of the ethanol solution, ethanol intake was transiently increased in P2X4R KO versus WT mice during the acquisition of 24-h and limited access ethanol intake. IVM significantly reduced ethanol intake in P2X4R KO and WT mice, but the degree of reduction was 50 % less in the P2X4R KO mice. Western blot analysis identified significant changes in γ-aminobutyric acid_A receptor α1 subunit expression in brain regions associated with the regulation of ethanol behaviors in P2X4R KO mice. These findings add to evidence that P2X4Rs contribute to ethanol intake and indicate that there is a complex interaction between P2X4Rs, ethanol, and other neurotransmitter receptor systems.     

Circadian and acamprosate modulation of elevated ethanol drinking in mPer2 clock gene mutant mice

The PER2 clock gene modulates ethanol consumption, such that mutant mice not expressing functional mPer2 have altered circadian behavior that promotes higher ethanol intake and preference. Experiments were undertaken to characterize circadian-related behavioral effects of mPer2 deletion on ethanol intake and to explore how acamprosate (used to reduce alcohol dependence) alters diurnal patterns of ethanol intake. Male mPer2 mutant and WT (wild-type) mice were entrained to a 12:12?h light-dark (12L:12D) photocycle, and their locomotor and drinking activities were recorded. Circadian locomotor measurements confirmed that mPer2 mutants had an advanced onset of nocturnal activity of about 2?h relative to WTs, and an increased duration of nocturnal activity (p < .01). Also, mPer2 mutants preferred and consumed more ethanol and had more daily ethanol drinking episodes vs. WTs. Measurements of systemic ethanol using subcutaneous microdialysis confirmed the advanced rise in ethanol intake in the mPer2 mutants, with 24-h averages being ～60 vs. ～25?mM for WTs (p < .01). A 6-day regimen of single intraperitoneal (i.p.) acamprosate injections (300?mg/kg) at zeitgeber time (ZT) 10 did not alter the earlier onset of nocturnal ethanol drinking in the mPer2 mutants, but reduced the overall amplitude of drinking and preference (both p < .01). Acamprosate also reduced these parameters in WTs. These results suggest that elevated ethanol intake in mPer2 mutants may be a partial consequence of an earlier nighttime activity onset and increase in nocturnal drinking activity. The suppressive action of acamprosate on ethanol intake is not due to an altered diurnal pattern of drinking, but rather a decrease in the number of daily drinking bouts and amount of drinking per bout.     

Depression‐like symptoms of withdrawal in a genetic mouse model of binge methamphetamine intake

Binge methamphetamine (MA) users have higher MA consumption, relapse rates and depression‐like symptoms during early periods of withdrawal, compared with non‐binge users. The impact of varying durations of MA abstinence on depression‐like symptoms and on subsequent MA intake was examined in mice genetically prone to binge‐level MA consumption. Binge‐level MA intake was induced using a multiple‐bottle choice procedure in which mice were offered one water drinking tube and three tubes containing increasing concentrations of MA in water, or four water tubes (control group). In two studies, depression‐like symptoms were measured using a tail‐suspension test and a subsequent forced‐swim test, after forced abstinence of 6 and 30 hours from a 28‐day course of chronic MA intake. An additional study measured the same depression‐like symptoms, as well as MA intake, after prolonged abstinence of 1 and 2 weeks. MA high drinking mice and one of their progenitor strains DBA/2J escalated their MA intake with increasing MA concentration; however, MA high drinking mice consumed almost twice as much MA as DBA/2J mice. Depression‐like symptoms were significantly higher early after MA access was withdrawn, compared to levels in drug‐naïve controls, with more robust effects of MA withdrawal observed in MA high drinking than DBA/2J mice. When depression‐like symptoms were examined after 1 or 2 weeks of forced abstinence in MA high drinking mice, depression‐like symptoms dissipated, and subsequent MA intake was high. The MA high drinking genetic mouse model has strong face validity for human binge MA use and behavioral sequelae associated with abstinence.     

Activation of extrasynaptic δ-GABAA receptors globally or within the posterior-VTA has estrous-dependent effects on consumption of alcohol and estrous-independent effects on locomotion

Recent reports support higher than expected rates of binge alcohol consumption among women and girls. Unfortunately, few studies have assessed the mechanisms underlying this pattern of intake in females. Studies in males suggest that alcohol concentrations relevant to the beginning stages of binge intoxication may selectively target tonic GABAergic inhibition mediated by GABA_A receptor subtypes expressing the δ-subunit protein (δ-GABA_ARs). Indeed, administration of agonists that interact with these δ-GABA_ARs prior to alcohol access can abolish binge drinking behavior in male mice. These δ-GABA_ARs have also been shown to exhibit estrous-dependent plasticity in regions relevant to drug taking behavior, like the hippocampus and periaqueductal gray. The present experiments were designed to determine whether the estrous cycle would alter binge drinking, or our ability to modulate this pattern of alcohol use with THIP, an agonist with high selectivity and efficacy at δ-GABA_ARs. Using the Drinking-in-the-Dark (DID) binge-drinking model, regularly cycling female mice were given 2 h of daily access to alcohol (20%v/v). Vaginal cytology or vaginal impedance was assessed after drinking sessions to track estrous status. There was no fluctuation in binge drinking associated with the estrous cycle. Both Intra-posterior-VTA administration of THIP and systemic administration of the drug was also associated with an estrous cycle dependent reduction in drinking behavior. Pre-treatment with finasteride to inhibit synthesis of 5α-reduced neurosteroids did not disrupt THIP's effects. Analysis of δ-subunit mRNA from posterior-VTA enriched tissue samples revealed that expression of this GABA_A receptor subunit is elevated during diestrus in this region. Taken together, these studies demonstrate that δGABA_ARs in the VTA are an important target for binge drinking in females and confirm that the estrous cycle is an important moderator of the pharmacology of this GABA_A receptor subtype.     

Mouse inbred strain differences in ethanol drinking to intoxication

Recently, we described a simple procedure, Drinking in the Dark (DID), in which C57BL/6J mice self-administer ethanol to a blood ethanol concentration (BEC) above 1 mg/ml. The test consists of replacing the water with 20% ethanol in the home cage for 4 h early during the dark phase of the light/dark cycle. Three experiments were conducted to explore this high ethanol drinking model further. In experiment 1, a microanalysis of C57BL/6J behavior showed that the pattern of ethanol drinking was different from routine water intake. In experiment 2, drinking impaired performance of C57BL/6J on the accelerating rotarod and balance beam. In experiment 3, 12 inbred strains were screened to estimate genetic influences on DID and correlations with other traits. Large, reliable differences in intake and BEC were detected among the strains, with C57BL/6J showing the highest values. Strain means were positively correlated with intake and BEC in the standard (24 h) and a limited (4 h) two-bottle ethanol vs. water test, but BECs reached higher levels for DID. Strain mean correlations with other traits in the Mouse Phenome Project database supported previously reported genetic relationships of high ethanol drinking with low chronic ethanol withdrawal severity and low ethanol-conditioned taste aversion. We extend these findings by showing that the correlation estimates remain relatively unchanged even after correcting for phylogenetic relatedness among the strains, thus relaxing the assumption that the strain means are statistically independent. We discuss applications of the model for finding genes that predispose pharmacologically significant drinking in mice.     

Circadian and Acamprosate Modulation of Elevated Ethanol Drinking in mPer2 Clock Gene Mutant Mice

The PER2 clock gene modulates ethanol consumption, such that mutant mice not expressing functional mPer2 have altered circadian behavior that promotes higher ethanol intake and preference. Experiments were undertaken to characterize circadian-related behavioral effects of mPer2 deletion on ethanol intake and to explore how acamprosate (used to reduce alcohol dependence) alters diurnal patterns of ethanol intake. Male mPer2 mutant and WT (wild-type) mice were entrained to a 12:12?h light-dark (12L:12D) photocycle, and their locomotor and drinking activities were recorded. Circadian locomotor measurements confirmed that mPer2 mutants had an advanced onset of nocturnal activity of about 2?h relative to WTs, and an increased duration of nocturnal activity (p < .01). Also, mPer2 mutants preferred and consumed more ethanol and had more daily ethanol drinking episodes vs. WTs. Measurements of systemic ethanol using subcutaneous microdialysis confirmed the advanced rise in ethanol intake in the mPer2 mutants, with 24-h averages being ～60 vs. ～25?mM for WTs (p < .01). A 6-day regimen of single intraperitoneal (i.p.) acamprosate injections (300?mg/kg) at zeitgeber time (ZT) 10 did not alter the earlier onset of nocturnal ethanol drinking in the mPer2 mutants, but reduced the overall amplitude of drinking and preference (both p < .01). Acamprosate also reduced these parameters in WTs. These results suggest that elevated ethanol intake in mPer2 mutants may be a partial consequence of an earlier nighttime activity onset and increase in nocturnal drinking activity. The suppressive action of acamprosate on ethanol intake is not due to an altered diurnal pattern of drinking, but rather a decrease in the number of daily drinking bouts and amount of drinking per bout. (Author correspondence: jglass@kent.edu)     

Effects of Voluntary Alcohol Intake on Risk Preference and Behavioral Flexibility during Rat Adolescence

Alcohol use is common in adolescence, with a large portion of intake occurring during episodes of binging. This pattern of alcohol consumption coincides with a critical period for neurocognitive development and may impact decision-making and reward processing. Prior studies have demonstrated alterations in adult decision-making following adolescent usage, but it remains to be seen if these alterations exist in adolescence, or are latent until adulthood. Here, using a translational model of voluntary binge alcohol consumption in adolescents, we assess the impact of alcohol intake on risk preference and behavioral flexibility during adolescence. During adolescence (postnatal day 30–50), rats were given 1-hour access to either a 10% alcohol gelatin mixture (EtOH) or a calorie equivalent gelatin (Control) at the onset of the dark cycle. EtOH consuming rats were classified as either High or Low consumers based on intake levels. Adolescent rats underwent behavioral testing once a day, with one group performing a risk preference task, and a second group performing a reversal-learning task during the 20-day period of gelatin access. EtOH-High rats showed increases in risk preference compared to Control rats, but not EtOH-Low animals. However, adolescent rats did a poor job of matching their behavior to optimize outcomes, suggesting that adolescents may adopt a response bias. In addition, adolescent ethanol exposure did not affect the animals'' ability to flexibly adapt behavior to changing reward contingencies during reversal learning. These data support the view that adolescent alcohol consumption can have short-term detrimental effects on risk-taking when examined during adolescence, which does not seem to be attributable to an inability to flexibly encode reward contingencies on behavioral responses.     

Changes in avoidance behaviour following ethanol treatment in rats of different ages

Avoidance learning and pain sensitivity were studied in rats after chronic ethanol administration (1.1 to 1.7 g per kg b.w. in drinking water) at prenatal, adolescent and adult ages. The behavioural reactions were tested in adulthood by studying passive and active avoidance learning and the threshold of pain sensitivity to electric tail shock. Chronic ethanol consumption led to an impairment of avoidance learning and to hyperalgesia in each experimental series, although the alterations were greater in the prenatally treated groups. The experimental observations are discussed in the light of fetal alcohol syndrome.     

Chronic voluntary ethanol intake hypersensitizes 5‐HT1A autoreceptors in C57BL/6J mice

Alcoholism is a complex disorder involving, among others, the serotoninergic (5‐HT) system, mainly regulated by 5‐HT_1A autoreceptors in the dorsal raphe nucleus. 5‐HT_1A autoreceptor desensitization induced by chronic 5‐HT reuptake inactivation has been associated with a decrease in ethanol intake in mice. We investigated here whether, conversely, chronic ethanol intake could induce 5‐HT_1A autoreceptor supersensitivity, thereby contributing to the maintenance of high ethanol consumption. C57BL/6J mice were subjected to a progressive ethanol intake procedure in a free‐choice paradigm (3–10% ethanol versus tap water; 21 days) and 5‐HT_1A autoreceptor functional state was assessed using different approaches. Acute administration of the 5‐HT_1A receptor agonist ipsapirone decreased the rate of tryptophan hydroxylation in striatum, and this effect was significantly larger (+75%) in mice that drank ethanol than in those drinking water. Furthermore, ethanol intake produced both an increased potency (+45%) of ipsapirone to inhibit the firing of 5‐HT neurons, and a raise (+35%) in 5‐HT_1A autoreceptor‐mediated stimulation of [³⁵S]GTP‐γ‐S binding in the dorsal raphe nucleus. These data showed that chronic voluntary ethanol intake in C57BL/6J mice induced 5‐HT_1A autoreceptor supersensitivity, at the origin of a 5‐HT neurotransmission deficit, which might be causally related to the addictive effects of ethanol intake.