Negative affect and voluntary alcohol consumption in Wistar-Kyoto (WKY) and Sprague-Dawley rats

The Wistar Kyoto Rat: A Model of Depression Traits

There is an ongoing debate about the value of animal research in psychiatry with valid lines of reasoning stating the limits of individual animal models compared to human psychiatric illnesses. Human depression is not a homogenous disorder; therefore, one cannot expect a single animal model to reflect depression heterogeneity. This limited review presents arguments that the Wistar Kyoto (WKY) rats show intrinsic depression traits. The phenotypes of WKY do not completely mirror those of human depression but clearly indicate characteristics that are common with it. WKYs present despair- like behavior, passive coping with stress, comorbid anxiety, and enhanced drug use compared to other routinely used inbred or outbred strains of rats. The commonly used tests identifying these phenotypes reflect exploratory, escape-oriented, and withdrawal-like behaviors. The WKYs consistently choose withdrawal or avoidance in novel environments and freezing behaviors in response to a challenge in these tests. The physiological response to a stressful environment is exaggerated in WKYs. Selective breeding generated two WKY substrains that are nearly isogenic but show clear behavioral differences, including that of depression-like behavior. WKY and its substrains may share characteristics of subgroups of depressed individuals with social withdrawal, low energy, weight loss, sleep disturbances, and specific cognitive dysfunction. The genomes of the WKY and WKY substrains contain variations that impact the function of many genes identified in recent human genetic studies of depression. Thus, these strains of rats share characteristics of human depression at both phenotypic and genetic levels, making them a model of depression traits.

Pre-clinical models of reward deficiency syndrome: A behavioral octopus

Individuals with mood disorders or with addiction, impulsivity and some personality disorders can share in common a dysfunction in how the brain perceives reward, where processing of natural endorphins or the response to exogenous dopamine stimulants is impaired. Reward Deficiency Syndrome (RDS) is a polygenic trait with implications that suggest cross-talk between different neurological systems that include the known reward pathway, neuroendocrine systems, and motivational systems. In this review we evaluate well-characterized animal models for their construct validity and as potential models for RDS. Animal models used to study substance use disorder, major depressive disorder (MDD), early life stress, immune dysregulation, attention deficit hyperactivity disorder (ADHD), post traumatic stress disorder (PTSD), compulsive gambling and compulsive eating disorders are discussed. These disorders recruit underlying reward deficiency mechanisms in multiple brain centers. Because of the widespread and remarkable array of associated/overlapping behavioral manifestations with a common root of hypodopaminergia, the basic endophenotype recognized as RDS is indeed likened to a behavioral octopus. We conclude this review with a look ahead on how these models can be used to investigate potential therapeutics that target the underlying common deficiency.

Bupropion, a possible antidepressant without negative effects on alcohol relapse

RATIONALE

the role that antidepressants play on alcohol consumption is not well understood. Previous studies have reported that treatment with a Selective Serotonin Reuptake Inhibitor (SSRIs) increases alcohol consumption in an animal model of relapse, however it is unknown whether this effect holds for other antidepressants such as the atypical dopamine/norepinephrine reuptake inhibitors (SNDRI).

OBJECTIVES

the main goal of the present study was to compare the effects of two classes of antidepressants drugs, bupropion (SNDRI) and fluoxetine (SSRI), on alcohol consumption during relapse. Since glutamatergic and endocannabinoid signaling systems plays an important role in alcohol abuse and relapse, we also evaluated the effects of both antidepressants onthe expression of the main important genes and proteins of both systems in the prefrontal cortex, a critical brain region in alcohol relapse.

METHODS

rats were trained to self-administered alcohol. During abstinence, rats received a 14d-treatment with vehicle, fluoxetine (10 mg/kg) or bupropion (20 mg/kg), and we evaluated alcohol consumption during relapse for 3 weeks. Samples of prefrontal cortex were taken to evaluate the mRNA and protein expression of the different components of glutamatergic and endocannabinoid signaling systems.

RESULTS

fluoxetine treatment induced a long-lasting increase in alcohol consumption during relapse, an effect that was not observed in the case of bupropion treatment. The observed increases in alcohol consumption were accompanied by distinct alterations in the glutamate and endocannabinoid systems.

CONCLUSIONS

our results suggest that SSRIs can negatively impact alcohol consumption in relapse while SNDRIs have no effects. The observed increase in alcohol consumption are accompanied by functional alterations in the glutamatergic and endocannabinoid systems. This finding could open new strategies for the treatment of depression in patients with alcohol use disorders.

Genetic Model to Study the Co-Morbid Phenotypes of Increased Alcohol Intake and Prior Stress-Induced Enhanced Fear Memory

Posttraumatic Stress Disorder (PTSD) is a complex illness, frequently co-morbid with depression, caused by both genetics, and the environment. Alcohol Use Disorder (AUD), which also co-occurs with depression, is often co-morbid with PTSD. To date, very few genes have been identified for PTSD and even less for PTSD comorbidity with AUD, likely because of the phenotypic heterogeneity seen in humans, combined with each gene playing a relatively small role in disease predisposition. In the current study, we investigated whether a genetic model of depression-like behavior, further developed from the depression model Wistar Kyoto (WKY) rat, is a suitable vehicle to uncover the genetics of co-morbidity between PTSD and AUD. The by-now inbred WKY More Immobile (WMI) and the WKY Less Immobile (WLI) rats were generated from the WKY via bidirectional selective breeding using the forced swim test, a measure of despair-like behavior, as the functional selector. The colonies of the WMIs that show despair-like behavior and the control strain showing less or no despair-like behavior, the WLI, are maintained with strict inbreeding over 40 generations to date. WMIs of both sexes intrinsically self-administer more alcohol than WLIs. Alcohol self-administration is increased in the WMIs without sucrose fading, water deprivation or any prior stress, mimicking the increased voluntary alcohol-consumption of subjects with AUD. Prior Stress-Enhanced Fear Learning (SEFL) is a model of PTSD. WMI males, but not females, show increased SEFL after acute restraint stress in the context-dependent fear conditioning paradigm, a sexually dimorphic pattern similar to human data. Plasma corticosterone differences between stressed and not-stressed WLI and WMI male and female animals immediately prior to fear conditioning predict SEFL results. These data demonstrate that the WMI male and its genetically close, but behaviorally divergent control the WLI male, would be suitable for investigating the underlying genetic basis of comorbidity between SEFL and alcohol self-administration.

Role of cortical alpha-2 adrenoceptors in alcohol withdrawal-induced depression and tricyclic antidepressants

INTRODUCTION

Although a role for alpha-2 adrenoceptors (alpha-2 ARs) in alcohol use disorder (AUD) and depression is suggested, very little information on a direct interaction between alcohol and these receptors is available.

METHODS

In this study adult female Wistar and Wistar-Kyoto (WKY) rats, a putative animal model of depression, were exposed to alcohol vapor 3h daily for 10days (blood alcohol concentration ∼150mg%) followed by daily injection of 10mg/kg of imipramine (IMP, a selective norepinephrine NE/serotonin reuptake inhibitor) or nomifensine (NOMI, a selective NE/dopamine reuptake inhibitor). On day 11 animals were tested for open field locomotor activity (OFLA) and forced swim test (FST) and were sacrificed 2h later for measurement of alpha-2 ARs densities in the frontal cortex and hippocampus using [3H]RX 821002 as the specific ligand.

RESULTS

Chronic alcohol treatment increased the immobility in the FST, without affecting OFLA in both Wistar and WKY rats, suggesting induction of depressive-like behavior in Wistar rats and an exacerbation of this behavior in WKY rats. Alcohol treatment also resulted in an increase in cortical but not hippocampal alpha-2 ARs densities in both Wistar and WKY rats. The behavioral effects of alcohol were completely blocked by IMP and NOMI and the neurochemical effects (increases in alpha-2 ARs) were significantly attenuated by both drugs in both strains.

CONCLUSIONS

The results suggest a role for cortical alpha-2 ARs in alcohol withdrawal-induced depression and that selective subtype antagonists of these receptors may be of adjunct therapeutic potential in AUD-depression co-morbidity.

Immediate and delayed anxiety- and depression-like profiles in the adolescent Wistar-Kyoto rat model of endogenous depression following postweaning social isolation

In order to understand links that exist between inherited risk or predisposition, brain and behavioural development, endocrine regulation and social/environmental stimuli, animal models are crucial. The Wistar-Kyoto (WKY) rat has been shown to have validity as a model of adult and adolescent depression. While sex- and age-specific differences in some of the face, predictive and construct validities of the model such as depression-like behaviours have been established, anhedonia and anxiety using other induced anxiety paradigms such as elevated plus maze remain equivocal. First, post-weaning social isolation effects on inherent and induced anxiety behaviours were tested during two critical time periods, early- and mid-adolescence. Isolation induced immediate effects on novel environment-induced hyperactivity and anxiety-related behaviours. Adolescent WKYs demonstrated reduced 50-kHz ultrasonic vocalizations suggesting agoraphobia-like behaviours. Second, isolated rats, despite being subsequently social-/group-housed demonstrated longer lasting effects on social interaction measures and anhedonia. This establishes that the depression-like profile observed during early- and mid-adolescence persists into late adolescence and early adulthood in WKY. Further, that interventions at a later stage during adolescence may not be able to reverse early adolescent effects in the context of pre-disposition, thus highlighting the irreversibility of being double-hit during critical time periods of brain and behavioural development and maturation.

Association between the A107V substitution in the δ-opioid receptors and ethanol drinking in mice selected for high and low analgesia

Experimental evidence suggests that endogenous opioids play an important role in the development of ethanol addiction. In this study, we employed two mouse lines divergently bred for opioid-mediated stress-induced analgesia. In comparison with HA (high analgesia line) mice, LA (low analgesia line) mice, having lower opioid receptor system activity, manifest enhanced basal as well as stress-induced ethanol drinking. Here, we found that recently discovered C320T transition in exon 2 of the δ-opioid receptor gene (EU446125.1), which results in an A107V substitution (ACA23171.1), leads to higher ethanol preference in CT mice compared with CC homozygotes. This genetic association is particularly evident under chronic mild stress (CMS) conditions. The interaction between stress and ethanol intake was significantly stronger in HA than in LA mice. Ethanol almost completely attenuated the pro-depressive effect of CMS (assessed with the tail suspension test) in both the CC and CT genotypes in the HA line. In the LA mice, a lack of response to ethanol was observed in the CC genotype, whereas ethanol consumption strengthened depressive-like behaviours in CT individuals. Our results suggest that constitutively active A107V substitution in δ-opioid receptors may be involved in stress-enhanced vulnerability to ethanol abuse and in the risk of ethanol dependence.

Assessing learned associations between conditioned cocaine reward and environmental stimuli in the Wistar Kyoto rat

Clinical studies demonstrate that anxiety disorders increase the risk of substance use disorder. However, few studies have directly assessed anxiety as a vulnerability factor in processing of rewarding stimuli. The Wistar–Kyoto (WKY) rat has been proposed as a model of anxiety vulnerability because it exhibits extreme behavioral inhibition in novel and social environments; yet, it displays paradoxical rapid active avoidance learning that is resistant to extinction. The present study was designed to characterize the acquisition and persistence of cocaine conditioned place preference (CPP) in WKY rats. In the first of a series of three experiments, adult male WKY and Sprague Dawley (SD) rats were given six pairings of cocaine (3, 5, 10, 15 mg/kg) or saline on alternating days. SD rats developed cocaine-induced CPP to each of the four doses of cocaine tested. In contrast, WKY rats demonstrated CPP when conditioned with 3, 5, and 10 mg/kg, but displayed no preference to the 15 mg/kg dose. Next, separate groups of rats were subject to an extended CPP paradigm, which included acquisition, extinction and reinstatement phases. Rats were conditioned with cocaine and saline on alternating days using either a 6/6 (as above) or 4/4 conditioning regimen. Both SD and WKY rats acquired a lasting CPP with the 6/6 conditioning regimen. Results from the 4/4 conditioning regimen show that SD, but not WKY, rats acquired CPP. Preference scores for SD rats during the cocaine primed reinstatement test were significantly different from pretest scores indicating reinstatement of CPP in this group. Paradoxically, WKY rats demonstrated a latent sensitization to the conditioned rewarding effects of cocaine during the drug-primed reinstatement test. Taken together, WKY rats appear to be more sensitive to high doses of cocaine and need more experience with the drug to acquire a preference than SD rats.

Alcohol induced depressive-like behavior is associated with a reduction in hippocampal BDNF

Strong positive correlation between depression and alcoholism is evident in epidemiological reports. However, a causal relationship for this co-morbidity has not been established. We have observed that chronic daily exposure to a relatively high dose of alcohol can induce depressive-like behavior in rats and that pretreatment with nomifensine or imipramine can block the "depressogenic" effects of alcohol. Since brain derived neurotrophic factor (BDNF) is considered to play an important role in depressive-like behaviors and its elevation, particularly in the hippocampus, appears to be critical for the action of many antidepressants, we hypothesized that: 1. WKY rats, a putative animal model of depression, will show a lower hippocampal BDNF compared to their control Wistar rats, 2. Alcohol-induced depressive like behavior will be associated with a significant decrease in hippocampal BDNF and 3. Treatments with antidepressants will normalize hippocampal BDNF. These postulates were verified by measuring hippocampal BDNF in Wistar and WKY rats at baseline, following chronic (10 day) treatment with alcohol and combination of alcohol with nomifensine or imipramine. Alcohol was administered via inhalation chamber (3 h/day) such that a blood alcohol level of approximately 150 mg% was achieved. Nomifensine (10 mg/kg) or imipramine (10 mg/kg) was administered i.p. daily immediately after alcohol exposure. BDNF was measured by standard ELISA kit. The results support a role for central BDNF in depressogenic effects of alcohol and antidepressant effects of nomifensine and imipramine. Moreover, depression per se as manifested in WKY rats may be associated with a reduction in hippocampal BDNF.

Stress-hyperresponsive WKY rats demonstrate depressed dorsal raphe neuronal excitability and dysregulated CRF-mediated responses

Major depression is a debilitating psychiatric disease that may be precipitated by a dysregulation of stress neurocircuitry caused by chronic or severe stress exposure. Moreover, hyperresponsivity to stressors correlates with depressed mood and may contribute to the etiology of major depression. The serotonergic dorsal raphe nucleus (DRN) is an important site in the neurocircuitry underlying behavioral responses to stressors, and is tightly regulated, in part, by a combination of intrinsic cell properties, autoinhibition, and GABAergic synaptic transmission. The stress-related neurotransmitter corticotropin-releasing factor (CRF) modulates DRN neuronal excitability and subsequent 5-HT release in the forebrain. Wistar Kyoto (WKY) rats exhibit exaggerated behavioral responses to stressors, that is, stress hyperresponsivity, and are considered an animal model of depression. To better understand the neurobiological basis of the stress hyperresponsivity, we used a combination of mRNA analysis and whole-cell electrophysiological techniques to measure differences in intrinsic activity and receptor response, in 5-HT- and non-5-HT-containing neurons of the DRN in WKY rats compared with Sprague-Dawley controls. In the WKY rat, there was a decrease in the neuronal excitability of 5-HT neurons coupled with decreased TPH2 production. Additionally, we found that CRF did not increase GABAergic activity in 5-HT neurons as is normally seen in 5-HT neurons of Sprague-Dawley controls. The CRF modulation of 5-HT DRN neurotransmission at the single-cell level is selectively disrupted in the WKY animal model of depression and may be one of the cellular correlates underlying depression.

Reduced γ range activity at REM sleep onset and termination in fear-conditioned Wistar-Kyoto rats

Recent investigations of rapid eye movement sleep (REMS) continuity have emphasized the importance of transitions both into and out of REMS. We have previously reported that, compared to Wistar rats (WIS), Wistar-Kyoto rats (WKY) responded to fear conditioning (FC) with more fragmented REMS. Gamma oscillations in the electroencephalogram (EEG) are synchronized throughout the brain in periods of focused attention, and such synchronization of cell assemblies in the brain may represent a temporal binding mechanism. Therefore, we examined the effects of FC on EEG gamma range activity (30-50Hz) at REMS transitions in WKY compared to WIS. Relative power in the gamma range (measured as a percent of total power) at Baseline and upon re-exposure to the fear-inducing conditioning stimulus was measured 35s before REMS onset to 105s after REMS onset (ARO) and 85s before REMS termination (BRT) to 35s after REMS termination. After baseline recording, rats received 10 tones, each co-terminating with an electric foot shock. On Days 1 and 14 post-conditioning, rats were re-exposed to three tones. Fast-Fourier transforms created power spectral data in the gamma frequency domain. Relative power was extracted from an average of 4-5 REMS transitions. Relative gamma power was always higher in WIS. On Day 14, at 15s and 25s ARO, WKY had significant increases in relative gamma power from Baseline. WIS had a significant increase on Day 1 at 25s ARO. Despite the increases in relative gamma power, WKY never achieved levels attained by WIS. Moreover, at 5s BRT, only WKY had a significant decrease in relative gamma power from Baseline to Day 14. Gamma range activity may indicate neural activity underlying maintenance of REMS continuity. Low relative gamma power at REMS transitions may be associated with increased REMS fragmentation in WKY after FC.

Fear conditioning fragments REM sleep in stress-sensitive Wistar-Kyoto, but not Wistar, rats

Pavlovian conditioning is commonly used to investigate the mechanisms of fear learning. Because the Wistar-Kyoto (WKY) rat strain is particularly stress-sensitive, we investigated the effects of a psychological stressor on sleep in WKY compared to Wistar (WIS) rats. Male WKY and WIS rats were either fear-conditioned to tone cues or received electric foot shocks alone. In the fear-conditioning procedure, animals were exposed to 10 tones (800 Hz, 90 dB, 5s), each co-terminating with a foot shock (1.0 mA, 0.5s), at 30-s intervals. In the shock stress procedure, animals received 10 foot shocks at 30-s intervals, without tones. All subjects underwent a tone-only test both 24h (Day 1) and again two weeks (Day 14) later. Rapid eye movement sleep (REMS) continuity was investigated by partitioning REMS episodes into single (inter-REMS episode interval >3 min) and sequential (interval ≤ 3 min) episodes. In the fear-conditioned group, freezing increased from baseline in both strains, but the increase was maintained on Day 14 in WKY rats only. In fear-conditioned WKY rats, total REMS amount increased on Day 1, sequential REMS amount increased on Day 1 and Day 14, and single REMS amount decreased on Day 14. Alterations were due to changes in the number of sequential and single REMS episodes. Shock stress had no significant effect on REMS microarchitecture in either strain. The shift toward sequential REMS in fear-conditioned WKY rats may represent REMS fragmentation, and may provide a model for investigating the neurobiological mechanisms of sleep disturbances reported in posttraumatic stress disorder.

Differential patterns of alcohol consumption and dopamine-2 receptor binding in Wistar-Kyoto and Wistar rats

The Wistar-Kyoto (WKY) rat strain has been described as an animal model of depressive behavior that consumes significantly greater amounts of alcohol compared to the Wistar (WIS) rat strain. Since the mesolimbic dopamine (DA) type-2 (D2) receptors mediate reward-related behaviors, the present study measured the binding of [(125)I]-Iodosulpiride to D2 receptors in the brains of WKY versus WIS rats following 24 days of voluntary alcohol or water consumption. Alcohol consuming WKY rats showed a significant increase in D2 receptor binding in several regions of the mesolimbic and nigrostriatal systems. In contrast, alcohol consuming WIS rats showed a reduction in D2 receptor binding in DA cell body areas. The differential regulation of D2 receptors by voluntary alcohol consumption in the two rat strains suggests that D2 receptor mediated neurotransmission may be playing a role in the increased alcohol drinking behavior reported in WKY rats.

Alcohol-induced depressive-like behavior is associated with cortical norepinephrine reduction

Although strong positive association between alcoholism and depression is a common epidemiological observance, the causal relationship and the neurobiological substrates of such observations are far from clear. We have reported that chronic daily exposure to a relatively high dose of alcohol in rats can induce or exacerbate an already existing depressive-like behavior (Pharm Biochem Behav 91:97-103, 2008). Moreover, these effects of alcohol were blocked by pretreatment with desipramine, a tricyclic antidepressant, implicating a role for the biogenic amines in this type of depressive symptoms. In order to further delineate the involvement of specific neurotransmitters in alcohol-induced depressive symptoms, we examined the concentrations of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) in the frontal cortex and hippocampus following alcohol administration as well as pretreatment with two antidepressants, nomifensine and imipramine selective NE/DA and NE/5-HT uptake inhibitors, respectively. Adult female Wistar and Wistar-Kyoto (WKY) rats were exposed to alcohol via inhalation chambers (3h/day for 10 days) to achieve daily blood alcohol concentration of approximately 150 mg%. On day 11, the animals were evaluated for general locomotor activity (LCA) and performance in the forced swim test (FST), followed by neurochemical analyses. As expected WKY rats had lower LCA and higher immobility in the FST compared to Wistar rats. WKY rats also had lower levels of all three biogenic amines compared to Wistar rats in both areas. However, only cortical NE was reduced in both strains following alcohol administration. Treatments with nomifensine and imipramine blocked the behavioral and most of the neurochemical deficits caused by alcohol in both strains. These results implicate cortical NE as a major player in alcohol-induced depression. Moreover, it is suggested that selective NE uptake inhibitors may be of particular therapeutic potential in co-morbid condition of alcoholism and depression.

N-methyl-d-aspartic acid receptors are altered by stress and alcohol in Wistar-Kyoto rat brain

Previous studies have shown that the Wistar-Kyoto (WKY) rat strain is more sensitive to stressors and consumes significant quantities of alcohol under basal as well as stressful conditions when compared to other strains. Given that the glutamate neurotransmitter system has been implicated in depression and addiction, the goals of the present study were to investigate the effects of stress and stress-alcohol interactions on N-methyl-d-aspartate (NMDA) receptors in the rat brain. Thus this study measured the binding of [(3)H] MK-801 to NMDA receptors in the prefrontal cortex (PFC), caudate putamen (CPu), nucleus accumbens (NAc), hippocampus (HIP) and basolateral amygdala (BLA) in WKY rats in comparison to the Wistar (WIS) rat strain. Our results suggested that while voluntary alcohol consumption did not alter NMDA receptors in the PFC, CPu or NAc in either rat strain, it increased NMDA receptors in the HIP and BLA in both strains. In contrast, chronic stress increased NMDA receptors in the PFC, CPu, NAc in WKY rats but not in WIS rats. Chronic stress also decreased NMDA receptors in the HIP and increased NMDA receptors in the BLA in both strains. Alcohol co-treatment with stress increased NMDA receptors in the PFC, CPu and NAc in WKY rats but not in WIS rats. Interestingly, while alcohol co-treatment did not reverse stress induced decreases in NMDA receptors in the HIP, it reduced the binding of NMDA receptors in the BLA to control levels in both strains. Thus it appears that NMDA receptors in the PFC, CPu and NAc may be more sensitive to the effects of stress and could be implicated in the stress-induced alcohol consumption behavior seen in WKY rats. In contrast, NMDA receptors in the HIP and BLA may reflect an adaptive response and may not be responsible for the stress susceptible phenotype of the WKY rat strain.

Voluntary alcohol consumption alters stress-induced changes in dopamine-2 receptor binding in Wistar-Kyoto rat brain

The Wistar-Kyoto (WKY) rat has been proposed as an animal model of depressive behavior and exhibits hyper-responsiveness to stressful stimulation when compared to other rat strains. We have demonstrated that WKY rats consume 200% more alcohol under naïve conditions as compared to their outbred counterparts, Wistar (WIS) rats. The present study was designed to understand the influence of stress and alcohol consumption on central dopamine type-2 (D2) receptor sites in these two behaviorally distinct rat strains. The first part of this study examined the effects of chronic stress on alcohol consumption, while the second part examined the binding of [(125)I]-Iodosulpiride to D2 receptors in control, stressed or stress and alcohol co-treated WKY compared to WIS rats. Exposure to chronic stress led to an increase in the amount of alcohol consumed by both rat strains, with WKY rats consuming significantly more alcohol than WIS rats with or without stress exposure. Quantitative autoradiography experiments showed that chronic stress increased D2 receptor binding in the caudate putamen (CPu), nucleus accumbens (NAc), substantia nigra (SN) and ventral tegmental area (VTA) of WKY rats, and reduced receptor binding in the CPu and SN of WIS rats. Compared to the stressed animals, WKY rats co-treated with stress and alcohol demonstrated a reduction in D2 receptor sites in the cell body regions (SN and VTA), while WIS rats showed no changes in receptor binding. The observed changes in D2 receptor sites may indicate altered DA neurotransmission following stress and alcohol exposure. Since stressed WKY rats consumed more alcohol, it is possible that consumption of alcohol reverses the stress-induced D2 receptor alterations in the cell body regions, suggestive of a self medicating phenotype.

Test- and behavior-specific genetic factors affect WKY hypoactivity in tests of emotionality

Inbred Wistar-Kyoto rats consistently display hypoactivity in tests of emotional behavior. We used them to test the hypothesis that the genetic factors underlying the behavioral decision-making process will vary in different environmental contexts. The contexts used were the open-field test (OFT), a novel environment with no explicit threats present, and the defensive-burying test (DB), a habituated environment into which a threat has been introduced. Rearing, a voluntary behavior was measured in both tests, and our study was the first to look for genetic loci affecting grooming, a relatively automatic, stress-responsive stereotyped behavior. Quantitative trait locus analysis was performed on a population of 486 F2 animals bred from reciprocal inter-crosses. The genetic architectures of DB and OFT rearing, and of DB and OFT grooming, were compared. There were no common loci affecting grooming behavior in both tests. These different contexts produced the stereotyped behavior via different pathways, and genetic factors seem to influence the decision-making pathways and not the expression of the behavior. Three loci were found that affected rearing behavior in both tests. However, in both contexts, other loci had greater effects on the behavior. Our results imply that environmental context's effects on decision-making vary depending on the category of behavior.

Alcohol consumption alters dopamine transporter sites in Wistar–Kyoto rat brain

Even though animal and human studies show alterations in dopamine transporter (DAT) sites after alcohol withdrawal, the role of DAT in influencing either alcoholic or depressive behavior has not been examined extensively. Given that the Wistar-Kyoto (WKY) rat is a putative animal model of depressive behavior, the present study examined the effects of chronic alcohol consumption on DAT sites in WKY versus Wistar (WIS) rats. Brains from both strains were sectioned for autoradiographic analysis of [3H]-GBR12935 binding to DAT sites after 24 days of alcohol exposure. The results indicated that WKY rats consumed a greater amount of alcohol (P < 0.001) than WIS rats did throughout the experiment. Autoradiographic analyses of discrete brain regions indicated that alcohol consumption increased DAT sites in a greater number of brain areas in WKY compared to WIS rats. In WKY rats, the binding of [3H]-GBR12935 to DAT sites was increased in the basolateral, central and lateral nuclei of the amygdala, lateral nucleus of the hypothalamus, olfactory tubercle, caudate-putamen, nucleus accumbens and substantia nigra (P < 0.05) and decreased in the ventromedial nucleus of the hypothalamus and the CA1 region of the hippocampus. In WIS rats, alcohol consumption increased DAT sites in the CA1 region of the hippocampus, basolateral nucleus of the amygdala, ventral tegmental area and substantia nigra, and decreased DAT sites in the lateral and ventromedial hypothalamus and dentate gyrus. These results indicate a strain dependent alteration in DAT sites which may be related to altered dopamine neurotransmission in select brain regions following alcohol consumption.

Helplessness in the tail suspension test is associated with an increase in ethanol intake and its rewarding effect in female mice

BACKGROUND

Depression is frequently observed in drug abusers. However, depression may be a primary factor of predisposition to drug abuse or a consequence of drug abuse. The aim of this study was to analyze the influence of a preexisting depressive-like state/helplessness on subsequent alcohol responsiveness in mice.

METHODS

Male and female CD1 mice were selected according to their immobility time in the tail suspension test, and only mice with "high immobility" and "low immobility" time were retained. Using a two-bottle free-choice paradigm, these mice were given continuous access to tap water or solutions of ethanol (3-20% v/v), quinine (12.5-50 mg/liter), or sucrose (1-4% w/v). In female mice, rewarding and aversive effects of ethanol (1.5 and 3 g/kg, intraperitoneally) were also investigated using the conditioned place preference and the conditioned taste aversion paradigms.

RESULTS

Female mice were more immobile and drank more ethanol than male mice. No striking sex difference was observed in quinine consumption. Sucrose intake was higher in female than in male mice, whatever the solution concentration. At the 4% concentrated solution, a sucrose-induced increase in daily fluid intake was observed only in female mice. Female mice with high immobility time (HI) consumed more ethanol at the highest concentration than female mice with low immobility time (LI), whereas no difference was observed between HI and LI male mice. Moreover, whereas LI female mice failed to express place conditioning induced by the 3-g/kg dose of ethanol, HI female mice were strongly responsive to the rewarding effect of this high ethanol dose. Ethanol dose-dependently induced a conditioned taste aversion with a similar magnitude in both LI and HI female mice.

CONCLUSIONS

The findings indicate that female CD1 mice tend to drink greater amounts of ethanol or sucrose solutions than male CD1 mice, suggesting that female mice may be a better model of excessive alcohol intake. Furthermore, no relationship was found between immobility scores and ethanol consumption in male mice. On the contrary, within female mice, HI mice consumed higher amounts of ethanol than LI mice probably because they experienced greater rewarding effects of ethanol. The present results support the hypothesis that depressive-like responses may predispose to ethanol abuse in female mice.

Voluntary alcohol intake in two rat lines selectively bred for learned helpless and non-helpless behavior

RATIONALE

A high comorbidity between depression and alcoholism has been reported in several studies, but the mechanisms underlying this relationship remain unknown.

OBJECTIVES

We tested whether learned helplessness in rats as a model for depression is associated with enhanced alcohol intake and relapse behavior.

METHODS

Congenital learned helplessness (cLH) and congenital non-learned helplessness (cNLH) rats were selectively bred for differences in an escape paradigm. Sucrose preference was tested at the first hour of the dark phase. In order to study an association with alcohol drinking behavior, rats underwent a free-choice procedure with access to water, and 5% and 20% alcohol solutions for 6 weeks. After acquisition of alcohol drinking behavior, the alcohol deprivation effect (ADE) was assessed. Sensitivity to the sedative-hypnotic effect of alcohol was measured by loss of the righting reflex.

RESULTS

cLH rats showed significantly lower preference for sucrose solutions during the second half hour of the dark phase than cNLH rats. Alcohol intake of male cLH rats was not significantly different from that of male cNLH rats. In contrast, cLH female rats consumed higher amounts of alcohol than female cNLH rats. The ADE was more pronounced in female animals, although the magnitude of the ADE was similar in both cNLH and cLH female rats. The time to regain the righting reflex was significantly higher in both male and female cLH rats than in cNLH rats.

CONCLUSIONS

In summary, these data suggest that an inborn depressive-like behavior in female rats is associated with enhanced alcohol intake.

Strain differences in the distribution of dopamine transporter sites in rat brain

The Wistar Kyoto (WKY) rat has long been proposed as an animal model of depressive behavior. Exposure to stress produces symptoms such as anhedonia, psychomotor retardation, ambivalence, and negative memory bias. Autoradiographic studies have revealed significant differences in the density of norepinephrine transporter (NET) and serotonin transporter (5-HTT) sites in several brain regions in WKY rats compared to Sprague-Dawley (S-D) rats. Since the mesolimbic dopamine (DA) system is involved in cognitive, emotional, and motivational behaviors, this study examined the distribution of dopamine transporter (DAT) sites in the brains of WKY compared to Wistar (WIS) and S-D rats. DAT sites were labeled with [3H]-GBR12935 (1 nM), and mazindol (50 microM) was used to define nonspecific binding. Quantitative analysis of the specific binding indicated that WKY rats exhibited significant differences in DAT binding sites in the cell body as well as mesolimbic areas in comparison to WIS and S-D rats. While the binding of [3H]-GBR to DAT sites was significantly decreased in the nucleus accumbens (NAc), the amygdala, the ventral tegmental area (VTA), and the reticular part of the substantia nigra (P<.05), the binding was significantly increased in the hippocampal subregions and the hypothalamus (P<.05) in WKY rats compared to the other two strains. In contrast, no strain differences were found in the caudate-putamen. The observed differences in the density and distribution of DAT sites in WKY rats may lead to altered modulation of synaptic DA levels in the cell body and mesolimbic regions, thereby contributing to the noted depression-like behaviors reported in this rat strain.

The open field as a paradigm to measure the effects of drugs on anxiety-like behaviors: a review

The open field is a very popular animal model of anxiety-like behavior. An overview of the literature on the action elicited by effective or putative anxiolytics in animal subjected to this procedure indicates that classical treatments such as benzodiazepine receptor full agonists or 5-HT(1A) receptor full or partial agonists elicit an anxiolytic-like effect in this procedure in most cases (approximately 2/3). However, compounds (triazolobenzodiazepines such as adinazolam and alprazolam, selective serotonin reuptake inhibitors) that have a different spectrum of therapeutic efficacy in anxiety disorders such as panic attacks, generalized anxiety disorder or obsessive-compulsive disorder were poorly effective as anxiolytics in the open field test, suggesting that this paradigm may not model features of anxiety disorders. The procedure is also relevant for the study of compounds endowed with anxiogenic effects, as such effects were detected after treatments with benzodiazepine receptor inverse agonists or with corticotropin releasing factor (CRF) receptor agonists.

Effects of nicotine on alcohol intake in a rat model of depression

Clinical studies suggest that depression facilitates alcohol abuse. Depressed individuals also have increased rates of smoking, and it has been suggested that nicotine may improve depression. It is therefore possible that nicotine may reduce alcohol use in depression. To investigate this potential relationship, we evaluated alcohol intake in an animal model of depression, which consists of administering clomipramine (CLI), a preferential serotonin reuptake inhibitor, to neonatal rats. This pharmacological manipulation produces adult depression-like behaviors, such as reduced aggressiveness, decreased pleasure seeking, diminished sexual activity, increased locomotor activity and increased REM sleep. In this study, we found that CLI rats exhibited significantly higher locomotor activity, lower aggressiveness and higher alcohol intake than control rats. Chronic administration of a low dose of nicotine (0.25 mg/kg/day) or a sham operation did not modify these behaviors. However, chronic administration of nicotine at a higher dose (1.5 mg/kg/day) significantly increased aggressive behavior and reduced alcohol intake in CLI rats. The effect of nicotine on alcohol intake lasted at least 1 month after cessation of nicotine administration. These results indicate that nicotine reverted some depression signs and reduced alcohol self-administration in the CLI model of depression.