Does context influence the duration of locomotor sensitization to ethanol in female DBA/2J mice?

Low-level developmental lead exposure does not predispose to adult alcohol self-administration, but does increase the risk of relapsing to alcohol seeking in mice: Contrasting role of GLT1 and xCT brain expression

Lead (Pb) is a neurotoxic heavy metal pollutant. Despite the efforts to reduce Pb environmental exposure and to prevent Pb poisoning, exposure in human populations persists. Studies of adults with history of childhood lead exposure have consistently demonstrated cognitive impairments that have been associated with sustained glutamate signaling. Additionally, some clinical studies have also found correlations between Pb exposure and increased proclivity to drug addiction. Thus, here we sought to investigate if developmental Pb exposure can increase propensity to alcohol consumption and relapse using an alcohol self-administration paradigm. Because Pb exposure is associated with increased glutamatergic tone, we also studied the effects on the expression of synaptic and non-synaptic glutamate transporters in brain regions associated with drug addiction such as the nucleus accumbens (NAc), dorsomedial striatum (DMS), dorsolateral striatum (DLS), and medial prefrontal cortex (mPFC). We found that while developmental Pb exposure did not increase risk for alcohol self-administration, it did play a role in relapsing to alcohol. The effects were associated with differential expression of the glutamate transporter 1 (GLT1) and the glutamate/cystine antiporter (xCT). In the NAc and DLS the expression of GLT1 was found to be significantly reduced, while no changes were found in DMS or mPFC. Contrastingly, xCT was found to be upregulated in NAc but downregulated in DLS, with no changes in DMS or mPFC. Our data suggest that lead exposure is involved in relapse to alcohol seeking, an effect that could be associated with downregulation of GLT1 and xCT in the DLS.

Role of the treatment environment in the effects of aripiprazole on ethanol-induced behavioral sensitization and conditioned place preference in female mice

BACKGROUND

Evidence suggests that aripiprazole, a partial dopamine D2 and serotonin 5-HT1A receptor agonist and 5-HT2A receptor antagonist, show significant efficacy in reducing alcohol use. We have previously demonstrated that treatment with aripiprazole blocked the reinstatement of cocaine-induced behavioral sensitization in a context-dependent manner, suggesting that the treatment environment may modulate the therapeutic effects of aripiprazole. The present study aimed to evaluate the effects of treatment with aripiprazole on ethanol-induced behavioral sensitization and conditioned place preference in female mice, and the role of the treatment environment in those effects.

METHODS

Adult female mice were either sensitized with ethanol injections in the open-field apparatus, or conditioned with ethanol in the conditioned place preference (CPP) apparatus. Animals were then treated with vehicle or 0.1 mg/kg aripiprazole paired to the test environment (open-field or CPP apparatus) or not (home-cage treatments) for 4 alternate days, and the subsequent expression of behavioral sensitization or CPP to ethanol was evaluated during or following an ethanol re-exposure, respectively.

RESULTS

Repeated treatment with aripiprazole attenuated the expression of ethanol-induced behavioral sensitization regardless of the treatment environment. Treatment with aripiprazole was only effective at preventing the reinstatement of ethanol-induced CPP when paired with the ethanol-associated environment, but not when administered in the home-cage.

CONCLUSIONS

The present findings corroborate previous studies suggesting the effectiveness of aripiprazole for the treatment of alcohol use disorder. Our results also point to an important role of the treatment environment in the therapeutic effects of aripiprazole in rodent models of ethanol abuse.

Synthetic cathinones and their phenethylamine analogues produce distinct psychomotor and reward behavior in crayfish

Synthetic cathinones share potent sympathomimetic properties with amphetamines due to their shared phenethylamine backbone. Despite recent work focused on understanding the behavioral effects of synthetic cathinones, a systematic comparison of neuropharmacology, behavior, and physiological effects with other stimulants, has remained elusive. In the present study, we explore the behavioral effects of cathinones in crayfish, a model system which combines a well characterized behavioral paradigm for addiction-like behaviors, a modularly organized nervous system, the lack of a formal blood-brain barrier, and experimental tractability. The objective of this study was to characterize the psychomotor and rewarding effects of methylated cathinones (methylone, mephedrone), and their non β-ketone substituted amphetamine analogs (4-methylmethamphetamine, 4-MMA and 3,4-methylenedioxymethamphetamine MDMA) in crayfish. Our results suggest that these drugs produce psychostimulation, which sensitizes upon repeated drug administration. Furthermore, crayfish demonstrated a conditioned substrate preference for mephedrone and 4-MMA drug-pairings at a 10 μg/g dose, a preference which persisted even through a series of extinction trials. Our study indicates that synthetic cathinones and substituted amphetamine analogues produce distinct behavioral effects in an invertebrate system which consists of a relatively simple neuronal organization. The present findings provide an evolutionary context to our understanding about how drugs of abuse initiate reward at levels far beyond those specific to humans.

Investigating the reciprocal relationships between locomotor sensitization to ethanol and PTSD-like clusters in DBA/2J mice

BACKGROUND

Post-traumatic stress disorder (PTSD) and alcohol use disorder (AUD) are two conditions that co-occur frequently. The mechanistic explanations of this co-morbidity are still unclear. The goal of this study was twofold. First to investigate whether PTSD reduces the threshold for the acquisition of ethanol sensitization in an animal model of PTSD. Then to investigate whether ethanol sensitization modulates the expression of PTSD.

METHODS

152 female inbred DBA/2 J mice were submitted to an inescapable footshock paradigm to induce a PTSD-like condition (PTSDLC) and to a paradigm of locomotor sensitization to ethanol. In a first experiment, mice were submitted to the PTSDLC and then repeatedly injected with either saline, 1 g/kg ethanol or 2 g/kg ethanol. Their sensitization to the locomotor stimulant effects of ethanol was then tested in an open field. In a second experiment, mice were first sensitized to the locomotor stimulant effects of ethanol and then tested for their behavioral response to PTSDLC.

RESULTS

In the first experiment, PTSDLC failed to induce a significant locomotor sensitization at the subthreshold dose of 1 g/kg ethanol. However, with 2 g/kg ethanol, a stronger ethanol sensitization was observed in mice submitted to the footshock relative to the control group. In the second experiment, ethanol sensitization increased only some of the behavioral clusters of PTSDLC, namely the fear generalization in a new context.

CONCLUSION

PTSDLC did not reduce the dose threshold for the acquisition of ethanol sensitization but strengthened the development of ethanol sensitization with effective doses. This suggests that PTSD might interact with one of the mechanisms underlying the development of alcohol sensitization. When the relationship between ethanol sensitization and PTSDLC is tested in the reverse direction, the present study only shows a significant effect of ethanol administration on the "sensitized fear" PTSD cluster.

THC inhibits the expression of ethanol-induced locomotor sensitization in mice

The motivational circuit activated by ethanol leads to behavioral changes that recruit the endocannabinoid system (ECS). Case reports and observational studies suggest that the use of Cannabis sp. mitigates problematic ethanol consumption in humans. Here, we verified the effects of the two main phytocannabinoid compounds of Cannabis sp., cannabidiol (CBD) and delta-9-tetrahydrocannabinol (THC), in the expression of ethanol-induced locomotor sensitization in mice. Male adult DBA/2 mice were exposed to locomotor sensitization by daily intraperitoneal injections of ethanol (2.5 g/kg) for 12 days; control groups received saline. After the acquisition phase, animals were treated with cannabinoids: CBD (2.5 mg/kg); THC (2.5 mg/kg); CBD + THC (1:1 ratio), or vehicle for 4 days with no access to ethanol during this period. One day after the last cannabinoid injection, all animals were challenged with ethanol (2.0 g/kg) to evaluate the expression of the locomotor sensitization. Mice treated with THC alone or THC + CBD showed reduced expression of locomotor sensitization, compared to the vehicle control group. No effects were observed with CBD treatment alone. Our findings showing that phytocannabinoid treatment prevents the expression of behavioral sensitization in mice provide insight into the potential therapeutic use of phytocannabinoids in alcohol-related problems.

Behavioral sensitization of the reinforcing value of food: What food and drugs have in common

Sensitization is a basic property of the nervous system whereby repeated exposure to a stimulus results in an increase in responding to that stimulus. This increase in responding contributes to difficulty with treatment of drug abuse, as stimuli associated with substance use become signals or triggers for drug craving and relapse. Our work over the past decade has applied the theoretical framework of incentive sensitization to overeating. We have shown, in several studies, that lean adults do not commonly demonstrate behavioral sensitization after repeated exposure to snack food, but a subset of obese adults reliably does. This review will discuss this change in behavioral response to repeated consumption of snack food in obese individuals and apply the theoretical framework of incentive sensitization to drugs of abuse to high fat/high sugar snack foods. We will also show data that suggest that behavioral sensitization to repeated administration of snack food is predictive of weight gain, which may enhance its utility as a diagnostic tool for identifying at-risk individuals for obesity. Finally, we will discuss the future directions of this line of research, including studying the phenomenon in children and adolescents and determining if similar principles can be used to increase motivation to eat healthier food. A combination of reductions in unhealthy food intake and increases and healthy food intake is necessary to reduce obesity rates and improve health.

Behavioral sensitization to ethanol: Neural basis and factors that influence its acquisition and expression

Ethanol-induced behavioral sensitization (EBS) was first described in 1980, approximately 10 years after the phenomenon was described for psychostimulants. Ethanol acts on γ-aminobutyric acid (GABA) and glutamate receptors as an allosteric agonist and antagonist, respectively, but it also affects many other molecular targets. The multiplicity of factors involved in the behavioral and neurochemical effects of ethanol and the ensuing complexity may explain much of the apparent disparate results, found across different labs, regarding ethanol-induced behavioral sensitization. Although the mesocorticolimbic dopamine system plays an important role in EBS, we provide evidence of the involvement of other neurotransmitter systems, mainly the glutamatergic, GABAergic, and opioidergic systems. This review also analyses the neural underpinnings (e.g., induction of cellular transcription factors such as cyclic adenosine monophosphate response element binding protein and growth factors, such as the brain-derived neurotrophic factor) and other factors that influence the phenomenon, including age, sex, dose, and protocols of drug administration. One of the reasons that make EBS an attractive phenomenon is the assumption, firmly based on empirical evidence, that EBS and addiction-related processes have common molecular and neural basis. Therefore, EBS has been used as a model of addiction processes. We discuss the association between different measures of ethanol-induced reward and EBS. Parallels between the pharmacological basis of EBS and acute motor effects of ethanol are also discussed.

Determining the heritability of ethanol-induced locomotor sensitization in mice using short-term behavioral selection

RATIONALE

Sensitization to the locomotor stimulant effects of alcohol (ethanol) is thought to be a heritable risk factor for the development of alcoholism that reflects progressive increases in the positive motivational effects of this substance. However, very little is known about the degree to which genes influence this complex behavioral phenomenon.

OBJECTIVES

The primary goal of this work was to determine the heritability of ethanol-induced locomotor sensitization in mice using short-term behavioral selection.

METHODS

Genetically heterogeneous C57BL/6J (B6) × DBA/2J (D2) F2 mice were generated from B6D2F1 progenitors, phenotyped for the expression of locomotor sensitization, and bred for high (HLS) and low (LLS) expression of this behavior. Selective breeding was conducted in two independently generated replicate sets to increase the confidence of our heritability estimates and for future correlated trait analyses.

RESULTS

Large and significant differences in locomotor sensitization between HLS and LLS lines were evident by the fourth generation. Twenty-two percent of the observed line difference(s) were attributable to genes (h² = .22). Interestingly, locomotor activity in the absence of ethanol was genetically correlated with ethanol sensitization; high activity was associated with high sensitization.

CONCLUSIONS

That changes in ethanol sensitivity following repeated exposures are genetically regulated highlights the relevance of studies aimed at determining how genes regulate susceptibility to ethanol-induced behavioral and neural adaptations. As alcohol use and abuse disorders develop following many repeated alcohol exposures, these data emphasize the need for future studies determining the genetic basis by which changes in response to alcohol occur.

Selectively bred crossed high-alcohol-preferring mice drink to intoxication and develop functional tolerance, but not locomotor sensitization during free-choice ethanol access

BACKGROUND

Crossed high-alcohol-preferring (cHAP) mice were selectively bred from a cross of the HAP1 × HAP2 replicate lines and demonstrate blood ethanol concentrations (BECs) during free-choice drinking reminiscent of those observed in alcohol-dependent humans. In this report, we investigated the relationship between free-choice drinking, intoxication, tolerance, and sensitization in cHAP mice. We hypothesized that initially mice would become ataxic after drinking alcohol, but that increased drinking over days would be accompanied by increasing tolerance to the ataxic effects of ethanol (EtOH).

METHODS

Male and female cHAP mice had free-choice access to 10% EtOH and water (E), while Water mice (W) had access to water alone. In experiment 1, the first drinking experience was monitored during the dark portion of the cycle. Once E mice reached an average intake rate of ≥1.5 g/kg/h, they, along with W mice, were tested for footslips on a balance beam, and BECs were assessed. In experiments 2, 3, and 4, after varying durations of free-choice 10% EtOH access (0, 3, 14, or 21 days), mice were challenged with 20% EtOH and tested for number of footslips on a balance beam or locomotor stimulant response. Blood was sampled for BEC determination.

RESULTS

We found that cHAP mice rapidly acquire alcohol intakes that lead to ataxia. Over time, cHAP mice developed behavioral tolerance to the ataxic effects of alcohol, paralleled by escalating alcohol consumption. However, locomotor sensitization did not develop following 14 days of free-choice EtOH access.

CONCLUSIONS

Overall, we observed increases in free-choice drinking with extended alcohol access paralleled by increases in functional tolerance, but not locomotor sensitization. These data support our hypothesis that escalating free-choice drinking over days in cHAP mice is driven by tolerance to alcohol's behavioral effects. These data are the first to demonstrate that escalating free-choice consumption is accompanied by increasing alcohol tolerance. In addition to buttressing the hypothesized importance of tolerance in drinking, our findings suggest that cHAP mice may be a unique, translational resource for studying tolerance as a contributor to and consequence of chronic, excessive EtOH consumption.

Blockade of ethanol-induced behavioral sensitization by sodium butyrate: descriptive analysis of gene regulations in the striatum

BACKGROUND

Behavioral sensitization induced by repeated ethanol (EtOH) exposure may play a critical role in the development of alcohol dependence. Because recent data demonstrate that histone deacetylase inhibitor (HDACi) may be of interest in the treatment of addiction, we explored the effect of the HDACi sodium butyrate (NaB) on EtOH-induced behavioral sensitization (EIBS) in DBA/2J mice. We also investigated gene regulations in the striatum of sensitized mice using epigenetic- and signal transduction-related PCR arrays.

METHODS

Mice were injected with saline or EtOH (0.5 to 2.5 g/kg) once a day for 10 days. Mice received NaB (200 to 600 mg/kg) 30 minutes before each injection (prevention protocol) or once daily between days 11 and 16 (reversal protocol). At day 17, brains were removed 30 minutes after a saline or EtOH challenge to assess gene and proteins levels.

RESULTS

Only the intermediate EtOH doses (1.0 and 2.0 g/kg) were effective in inducing EIBS, and both doses were associated with specific gene regulations in the striatum. The induction of sensitization by 1.0 g/kg (but not 2.0 g/kg) EtOH was dose-dependently prevented or reversed by NaB. Among the 168 studied genes, EIBS blockade was associated with specific gene regulations (bcl-2, bdnf, hdac4, pak1, penk, tacr1, vip…) and changes in brain-derived neurotrophic factor in both striatum and prefrontal cortex.

CONCLUSIONS

These results indicate that EIBS is associated with specific gene regulations in the striatum depending on the EtOH dose and that NaB can be useful in blocking some long-lasting neuro-adaptations to repeated EtOH administrations.

Positive allosteric modulation of the GABA(B) receptor by GS39783 attenuates the locomotor stimulant actions of ethanol and potentiates the induction of locomotor sensitization

Acute ethanol-induced locomotor stimulation and ethanol-induced locomotor sensitization are two behavioral assays thought to model the rewarding effects of ethanol. Recent evidence suggests that GS39783, a GABA(B) positive allosteric modulator, may be effective at reducing both the rewarding and reinforcing effects of several drugs of abuse, including ethanol. The goal of this study was to determine if GS39783 was capable of altering acute ethanol-induced stimulation, and the induction and expression of ethanol-induced locomotor sensitization, without effecting basal locomotion levels. Several doses of GS39783 (ranging from 0 to 100 mg/kg, depending on experiment) were tested on adult male DBA/2J mice in four experiments using 3-day basal locomotion and acute ethanol stimulation paradigms, and 14-day induction and expression of ethanol sensitization paradigms. The results of experiment 1 are in agreement with current literature, suggesting that 30 mg/kg doses of GS39783 and lower do not alter basal locomotor activity. In experiment 2, we found that GS39783 significantly decreased acute ethanol stimulation, but only at the 30 mg/kg dose, supporting our hypothesis and other publications suggesting that GABA(B) receptors modulate acute ethanol stimulation. Contrary to our hypothesis, GS39783 did not alter the expression of locomotor sensitization. Additionally, repeated administration of GS39783 in conjunction with ethanol unexpectedly potentiated ethanol-induced locomotor sensitization. Further study of GS39783 is warranted as it may be a more tolerable treatment for alcoholism than full agonists, due to its behavioral efficacy at doses that lack sedative side effects. Our results add to current literature suggesting that the GABA(B) receptor system is indeed involved in the modulation of ethanol-induced locomotor stimulation and sensitization.

Environmental enrichment blocks ethanol-induced locomotor sensitization and decreases BDNF levels in the prefrontal cortex in mice

The use of addictive drugs can lead to long-term neuroplastic changes in the brain, including behavioral sensitization, a phenomenon related to addiction. Environmental enrichment (EE) is a strategy used to study the effect of environment on the response to several manipulations, including treatment with addictive drugs. Brain-derived neurotrophic factor (BDNF) has been associated with behaviors related to ethanol addiction. The aim of the present study was to evaluate the effects of EE on ethanol-induced behavioral sensitization and BDNF expression. Mice were exposed to EE and then repeatedly treated with a low dose (1.8 g/kg) of ethanol. Another group of mice was first subjected to repeated ethanol treatment according to the behavioral sensitization protocol and then exposed to EE. Environmental enrichment prevented the development of ethanol-induced behavioral sensitization and blocked behavioral sensitization in sensitized mice. Both repeated ethanol and EE decreased BDNF levels in the prefrontal cortex but not in the hippocampus. However, BDNF levels were lower in ethanol-treated mice exposed to EE. These findings suggest that EE can act on the mechanisms implicated in behavioral sensitization, a model for drug-induced neuroplasticity and relapse. Additionally, EE alters BDNF levels, which regulate addiction-related behaviors.

Ethanol drinking-in-the-dark facilitates behavioral sensitization to ethanol in C57BL/6J, BALB/cByJ, but not in mu-opioid receptor deficient CXBK mice

BACKGROUND

Neuroplasticity associated with drug-induced behavioral sensitization has been associated with excessive drug pursuit and consumption characteristic of addiction. Repeated intraperitoneal (ip) injections of ethanol (EtOH) can induce psychomotor sensitization in mice. In terms of its clinical relevance, however, it is important to determine whether this phenomenon can also be produced by voluntary EtOH consumption.

METHODS

The present investigation used a drinking-in-the-dark (DID) methodology to induce high levels of EtOH drinking in mice; EtOH replaces water for 2 or 4h, starting 3h after the beginning of the dark cycle. Animals followed a 3-week DID protocol prior to an evaluation of EtOH-induced locomotor activity (acute and repeated EtOH). For the first week, animals had access to 20% EtOH. On weeks 2 and 3, different concentrations of EtOH (10, 20 or 30%) were used. Three different inbred strains of mice were used: C57BL/6J (B6), BALB/cByJ (BALB), and CXBK. The CXBK mouse line was used because of its reduced expression and functioning of brain mu-opioid receptors, which have been suggested to participate in the development of EtOH-induced sensitization. B6 and BALB mice were used as controls.

RESULTS

B6 and CXBK mice presented comparable levels of EtOH drinking (approx. 3g/kg in 2h), that were higher than those showed by BALB. All animals, regardless of genotype, adjusted volume of EtOH intake to obtain stable g/kg of EtOH across concentrations. Previous EtOH DID produced (B6) or potentiated (BALB) sensitization to EtOH; this effect was not seen in CXBK. Western blot analysis showed a reduced number of mu-opioid receptors in several brain regions of CXBK as compared to that of B6 and BALB mice.

CONCLUSIONS

In summary, here we show that the DID methodology can be used to trigger EtOH-induced neuroplasticity supporting psychomotor sensitization, a process that might require participation of mu-opioid receptors.

Selective breeding for magnitude of methamphetamine-induced sensitization alters methamphetamine consumption

RATIONALE

Genetically determined differences in susceptibility to drug-induced sensitization could be related to risk for drug consumption.

OBJECTIVES

Studies were performed to determine whether selective breeding could be used to create lines of mice with different magnitudes of locomotor sensitization to methamphetamine (MA). MA sensitization (MASENS) lines were also examined for genetically correlated responses to MA.

METHODS

Beginning with the F2 cross of C57BL/6J and DBA/2J strains, mice were tested for locomotor sensitization to repeated injections of 1 mg/kg MA and bred based on magnitude of sensitization. Five selected offspring generations were tested. All generations were also tested for MA consumption, and some were tested for dose-dependent locomotor-stimulant responses to MA, consumption of saccharin, quinine, and potassium chloride as a measure of taste sensitivity, and MA clearance after acute and repeated MA.

RESULTS

Selective breeding resulted in creation of two lines [MA high sensitization (MAHSENS) and MA low sensitization (MALSENS)] that differed in magnitude of MA-induced sensitization. Initially, greater MA consumption in MAHSENS mice reversed over the course of selection so that MALSENS mice consumed more MA. MAHSENS mice exhibited greater sensitivity to the acute stimulant effects of MA, but there were no significant differences between the lines in MA clearance from blood.

CONCLUSIONS

Genetic factors influence magnitude of MA-induced locomotor sensitization and some of the genes involved in magnitude of this response also influence MA sensitivity and consumption. Genetic factors leading to greater MA-induced sensitization may serve a protective role against high levels of MA consumption.

Role of genotype in the development of locomotor sensitization to alcohol in adult and adolescent mice: comparison of the DBA/2J and C57BL/6J inbred mouse strains

BACKGROUND

Animal models that explore differential sensitivity to the effects of acute and repeated exposure of alcohol (ethanol) may be influenced by both the developmental and genetic profile of the population. Therefore, we sought to compare the influence of ontogeny on sensitivity to ethanol-induced locomotor stimulation and on the induction of locomotor sensitization to this effect across 2 inbred strains of mice; the ethanol consuming C57BL/6J and the ethanol avoiding DBA/2J strains.

METHODS

C57BL/6J and DBA/2J adults (postnatal day [PD] 60 to 80) and adolescents (PD 30±2) were assessed for basal activity, acute response to 2.0 g/kg ethanol, and the expression of locomotor sensitization following repeated administration of 2.5, 3.0, or 3.5 g/kg ethanol.

RESULTS

Basal activity was different across development for the C57BL/6J, but not DBA/2J, with adult B6 mice showing persistently greater baseline activity. Adolescents of both strains were more sensitive than adults to acute ethanol-induced locomotor stimulation; adults exhibited a decrease in their acute response across the testing session. Adolescent DBA/2J mice developed less ethanol sensitization compared to adults, with significant sensitization observed only following repeated administration of the lowest ethanol dose (2.5 g/kg), whereas DBA/2J adults sensitized to all doses. Age did not influence the development of ethanol sensitization for the C57BL/6J strain, as both adults and adolescents displayed a sensitized response following all ethanol doses.

CONCLUSIONS

These results suggest that the developmental pattern of locomotor sensitivity to ethanol is unique to the genotypic profile of the animal model.

Ethanol-induced locomotor sensitization in DBA/2J mice is associated with alterations in GABA(A) subunit gene expression and behavioral sensitivity to GABA(A) acting drugs

Repeated exposure to ethanol may produce increased sensitivity to its acute locomotor stimulant actions, a process referred to as locomotor sensitization. Neuroadaptation within certain brain circuits, including those possessing GABA(A) receptors, may underlie locomotor sensitization to ethanol. Indeed, GABA(A) receptors are documented mediators of ethanol's cellular and behavioral actions. Moreover, because subunit composition of this receptor is predictive of its pharmacology, it is possible that alterations in subunit composition contribute to the expression of locomotor sensitization to ethanol. The goal of the present study was to determine if alterations in GABA(A) subunit composition are associated with the expression of locomotor sensitization in DBA/2J mice, a strain known to be particularly susceptible to the development of this behavioral phenomenon. Following a modified 14day sensitization procedure (Phillips et al., 1994) relative changes in GABA(A) subunit gene expression were assessed in discrete mesolimbic brain regions. To determine if the observed changes in gene expression produced functional changes in the locomotor responses to drugs known to either preferentially or generally activate GABA(A) receptors normally possessing the significantly altered subunits, separate cohorts of animals were challenged with one of several low doses of zolpidem (alpha1-selective), etomidate (beta2/3-selective), or flurazepam (gamma2-directed) and assessed for locomotor alterations. Sensitized animals displayed increased expression of the alpha1, beta2, and gamma2 (v1) subunits in the Nucleus Accumbens (NAc) but not Ventral Tegmental Area (VTA). Additionally, sensitized animals displayed altered sensitivity to the locomotor actions of etomidate and flurazepam. These results support the hypothesis that neuroadaptive changes in GABA(A) subunit composition participate in the expression of locomotor sensitization.

Agonism of the endocannabinoid system modulates binge-like alcohol intake in male C57BL/6J mice: involvement of the posterior ventral tegmental area

Recent studies have indicated a role for the endocannabinoid system in the behavioral and physiological effects of alcohol (ethanol), particularly ethanol seeking behaviors. However, its role in modulating binge-like intake and/or the mechanism by which it may exert these effects remain poorly understood. The current study used a newly developed strain-specific animal model of binge drinking, dubbed 'Drinking In the Dark' (DID), to determine if facilitation of the endocannabinoid system with the synthetic cannabinoid agonist WIN 55-212,2 (WIN) modulates binge-like ethanol intake in male C57BL/6J (B6) mice. Based on the results of these systemic (i.p.) manipulations, and evidence in support of the involvement of subregions of the Ventral Tegmental Area (VTA) in governing self-administration of ethanol (Rodd-Henricks et al., (2000) Psychopharmacology (Berl) 149(3):217-224) as well as binge-like intake using the DID model (Moore & Boehm, (2009 Behav Neurosci 123(3):555-563), we extended these findings to evaluate the role of the endocannabinoid system within the anterior and posterior sub regions of the VTA using site-specific microinjections. Consistent with previous research, the lowest systemic dose of WIN (0.5 mg/kg) significantly increased ethanol intake in the first 30 minutes of access whereas the two highest doses (1 and 2 mg/kg) decreased ethanol intake within this time interval. Intra-posterior ventral tegmental area (pVTA) (but not aVTA (anterior ventral tegmental area) microinjections elicited time-dependent and dose-dependent increases (0.25 and 0.5 mug/side) and decreases (2.5 mug/side) in ethanol intake. Importantly, follow-up studies revealed that in some cases alterations in fluid consumption may have been influenced by competing locomotor activity (or inactivity). The present data are consistent with previous research in that agonism of the endocannabinoid system increases ethanol intake in rodents and implicate the pVTA in the modulation of drinking to intoxication. Moreover, the dose-dependent alterations in locomotor activity emphasize the importance of directly assessing multiple (possibly competing) behaviors when evaluating drug effects on voluntary consumption.

Ethanol induces locomotor activating effects in preweanling Sprague-Dawley rats

Abuse of drugs exerts biphasic motor activity effects, which seem to be associated with their motivational effects. In the case of ethanol, heterogenous rat strains appear to be particularly sensitive to the sedative effects of the drug. In contrast, ethanol's activating effects have been consistently reported in rats genetically selected for ethanol affinity. Heightened ethanol affinity and sensitivity to ethanol's reinforcement are also observed in nonselected rats during early ontogeny. In the present study, we examined psychomotor effects of ethanol (1.25 and 2.5 g/kg) in 8-, 12-, and 15-day-old pups. Motor activity in a novel environment was assessed 5-10 or 15-20 min following drug treatment. Rectal temperatures and latency to exhibit the righting reflex were recorded immediately after locomotor activity assessment. Ethanol exerted clear activating effects at 8 and 12 days of age (Experiments 1a and 1b) and to a lesser extent at 15 days. At this age, ethanol enhanced locomotor activity in the first testing interval (Experiment 1b) and suppressed locomotion at 15-20 min (Experiment 1a). Ethanol-mediated motor impairment was more pronounced in the youngest group (postnatal day 8) than in the older ones. Blood ethanol concentrations were equivalent in all age groups. The present study indicates that preweanling rats are sensitive to ethanol's stimulating effects during the second postnatal week, and suggest that specific periods during early ontogeny of the rat can provide a valuable framework for the study of mechanisms underlying ethanol's stimulation and reinforcement effects.

Parametric analysis of the development and expression of ethanol-induced behavioral sensitization in female Swiss mice: effects of dose, injection schedule, and test context

RATIONALE

Repeated administrations of ethanol induce a progressive and enduring increase in its locomotor stimulant effects, a phenomenon termed behavioral sensitization that has not been systematically characterized.

OBJECTIVE

The aim of the present studies was to characterize the development and expression of ethanol sensitization in female Swiss mice by examining (1) the doses of ethanol that induce behavioral sensitization, (2) the doses of acute ethanol challenges that are necessary to express behavioral sensitization, (3) the effects of the intervals between administrations, and (4) the context dependency of ethanol sensitization.

MATERIALS AND METHODS

Mice were i.p. injected for 8 days with various ethanol doses, and locomotion was recorded for 5 min. Two days after the last sensitization session, ethanol sensitization was tested in 30-min test sessions.

RESULTS

Mice repeatedly injected with 2.5 g/kg ethanol showed a progressive (200-300%) increase in locomotor activity. In response to a 2.5 g/kg ethanol challenge, the mice repeatedly treated with doses above 1.5 g/kg showed a significant sensitization. Following the induction of sensitization with the maximally effective sensitizing dose (2.5 g/kg), mice showed greater activation after challenges with 1.5, 2.0, 2.5, and 3.0 g/kg ethanol. The intervals (24, 48, or 96 h) between ethanol injections did not affect the induction or expression of sensitization. Finally, sensitization to 2.5 g/kg ethanol was expressed regardless of the context in which it was induced.

CONCLUSIONS

Female Swiss mice develop a robust context-independent sensitization after repeated ethanol injections at all doses above 1.5 g/kg, including highly sedative doses such as 4 g/kg.

Ethanol-induced behavioral sensitization in adolescent and adult mice: role of the nNOS gene

BACKGROUND

In the brain, nitric oxide (NO) produced by neuronal nitric oxide synthase (nNOS) has a role in synaptic plasticity. Recent evidence suggests the role of NO in a variety of effects produced by alcohol in the central nervous system. The current study investigated the role of the nNOS gene in the development of behavioral sensitization to ethanol in adolescent and adult mice.

METHODS

Adolescent and adult wild type (WT; B6;129SF2) and nNOS knockout (KO; B6;129S4-Nos1) mice of both sexes received saline or ethanol (1.5 g/kg; intraperitoneally) for 5 consecutive days, and locomotor activity was recorded daily. The locomotor response to challenge ethanol and saline injections was investigated at various time points following withdrawal from ethanol.

RESULTS

Adolescent WT but not nNOS KO mice developed a long-lasting sensitized response to ethanol as well as context-dependent hyperlocomotion (in response to saline) from adolescence through adulthood; sex-dependent differences were not observed. Compared to adolescent WT mice, adult WT males developed a short-term sensitized response to ethanol and context-dependent hyperlocomotion; adult WT females showed only short-term context-dependent hyperlocomotion. Adult nNOS KO males (like their adolescent counterparts) did not develop behavioral sensitization; no significant differences between adult nNOS KO and WT females were observed. Blood ethanol concentrations did not show genotype- or sex-dependent differences.

CONCLUSIONS

(1) The nNOS gene is required for the development of behavioral sensitization to ethanol in adolescent male and female mice. (2) Adolescent exposure to ethanol results in long-lasting behavioral sensitization through adulthood, while adult exposure to ethanol results in a shorter behavioral sensitization. (3) Sex-dependent differences are observed when ethanol exposure begins in adulthood but not in adolescence. (4) Ethanol-induced behavioral sensitization in adulthood is nNOS-dependent in males but not in females. Taken together, results suggest genotype-, ontogeny-, and sex-dependent differences in the development of behavioral sensitization to ethanol.