Female-specific decreases in alcohol binge-like drinking resulting from GABAA receptor delta-subunit knockdown in the VTA.

Binge drinking is short-term drinking that achieves blood alcohol levels of 0.08 g/dl or above. It exhibits well-established sex differences in GABAergic inhibitory neurotransmission, including extrasynaptic δ subunit-containing GABAA receptors (δ-GABAARs) that mediate tonic inhibition, or synaptic γ2-containing GABAARs which underlie fast, synaptic, phasic inhibition have been implicated in sex differences in binge drinking. Ovarian hormones regulate δ-GABAARs, further implicating these receptors in potential sex differences. Here, we explored the contribution of extrasynaptic δ-GABAARs to male and female binge-like drinking in a critical area of mesolimbic circuitry-the ventral tegmental area (VTA). Quantitative PCR revealed higher Gabrd transcript levels and larger tonic currents in the VTA of females compared to males. In contrast, male and female Gabrg2 transcript levels and measures of phasic inhibition were equivalent. Intra-VTA infusion of AAV-Cre-GFP in floxed Gabrd mice downregulated δ-GABAARs and decreased binge-like drinking in females. There was no significant difference in either male or female mice after GABAAR γ2 subunit reduction in the VTA following AAV-Cre-GFP infusion in floxed Gabrg2 mice. Collectively, these findings suggest sex differences and GABAAR subunit specificity in alcohol intake.

Infralimbic and dorsal raphé microinjection of the 5-HT(1B) receptor agonist CP-93,129: attenuation of aggressive behavior in CFW male mice.

RATIONALE: Aggressive behavior and impaired impulse control have been associated with dysregulations in the serotonergic system and with impaired functioning of the prefrontal cortex. 5-HT(1B) receptors have been shown to specifically modulate several types of offensive aggression. OBJECTIVE: This study aims to characterize the relative importance of two populations of 5-HT(1B) receptors in the dorsal raphé nucleus (DRN) and infralimbic cortex (ILC) in the modulation of aggressive behavior. METHODS: Male CFW mice were conditioned on a fixed-ratio 5 schedule of reinforcement to self-administer a 6% (w/v) alcohol solution. Mice repeatedly engaged in 5-min aggressive confrontations until aggressive behavior stabilized. Next, a cannula was implanted into either the DRN or the ILC. After recovery, mice were tested for aggression after self-administration of either 1.0 g/kg alcohol or water prior to a microinjection of the 5-HT(1B) agonist, CP-93,129 (0-1.0 µg/infusion). RESULTS: In both the DRN and ILC, CP-93,129 reduced aggressive behaviors after both water and alcohol self-administration. Intra-raphé CP-93,129 dose-dependently reduced both aggressive and locomotor behaviors. However, the anti-aggressive effects of intra-cortical CP-93,129 were behaviorally specific. CONCLUSIONS: These findings highlight the importance of the serotonergic system in the modulation of aggression and suggest that the behaviorally specific effects of 5-HT(1B) receptor agonists are regionally selective. 5-HT(1B) receptors in a medial subregion of the prefrontal cortex, the ILC, appear to be critically involved in the attenuation of species-typical levels of aggression.

Flunitrazepam in combination with alcohol engenders high levels of aggression in mice and rats.

RATIONALE: Higher doses of benzodiazepines and alcohol induce sedation and sleep; however, in low to moderate doses these drugs can increase aggressive behavior. OBJECTIVES: To assess firstly the effects of ethanol, secondly the effects of flunitrazepam, a so-called club drug, and thirdly the effects of flunitrazepam plus alcohol on aggression in mice and rats. METHODS: Exhaustive behavioral records of confrontations between a male resident and a male intruder were obtained twice a week, using CF-1 mice and Wistar rats. The salient aggressive and non-aggressive elements in the resident's repertoire were analyzed. Initially, the effects of ethanol (1.0g/kg), and secondly flunitrazepam (0; 0.01; 0.1; and 0.3mg/kg) were determined in all mice and rats; subsequently, flunitrazepam or vehicle, given intraperitoneally (0; 0.01; 0.1; and 0.3mg/kg) was administered plus ethanol 1.0g/kg or vehicle via gavage. RESULTS: The most significant finding is the escalation of aggression after a moderate dose of ethanol, and a low dose of flunitrazepam. The largest increase in aggressive behavior occurred after combined flunitrazepam plus ethanol treatment in mice and rats. CONCLUSIONS: Ethanol can heighten aggressive behavior and flunitrazepam further increases this effect in male mice and rats.

Individual vulnerability to escalated aggressive behavior by a low dose of alcohol: decreased serotonin receptor mRNA in the prefrontal cortex of male mice.

Low to moderate doses of alcohol consumption induce heightened aggressive behavior in some, but not all individuals. Individual vulnerability for this nonadaptive behavior may be determined by an interaction of genetic and environmental factors with the sensitivity of alcohol's effects on brain and behavior. We used a previously established protocol for alcohol oral self-administration and characterized alcohol-heightened aggressive (AHA) mice as compared with alcohol non-heightened (ANA) counterparts. A week later, we quantified mRNA steady state levels of several candidate genes in the serotonin [5-hydroxytryptamine (5-HT)] system in different brain areas. We report a regionally selective and significant reduction of all 5-HT receptor subtype transcripts, except for 5-HT(3), in the prefrontal cortex of AHA mice. Comparable gene expression profile was previously observed in aggressive mice induced by social isolation or by an anabolic androgenic steroid. Additional change in the 5-HT(1B) receptor transcripts was seen in the amygdala and hypothalamus of AHA mice. In both these areas, 5-HT(1B) mRNA was elevated when compared with ANA mice. In the hypothalamus, AHA mice also showed increased transcripts for 5-HT(2A) receptor. In the midbrain, 5-HT synthetic enzyme, 5-HT transporter and 5-HT receptors mRNA levels were similar between groups. Our results emphasize a role for postsynaptic over presynaptic 5-HT receptors in mice which showed escalated aggression after the consumption of a moderate dose of alcohol. This gene expression profile of 5-HT neurotransmission components in the brain of mice may suggest a vulnerability trait for alcohol-heightened aggression.

Increased phasic dopamine signaling in the mesolimbic pathway during social defeat in rats.

While reward-dependent facilitation of phasic dopamine signaling is well documented at both the cell bodies and terminals, little is known regarding fast dopamine transmission under aversive conditions. Exposure to aggressive confrontation is extremely aversive and stressful for many species including rats. The present study used fast-scan cyclic voltammetry and multiunit recording to determine if aggressive encounters and subsequent social defeat affect burst firing of ventral tegmental area (VTA) dopamine neurons and accumbal dopamine transients in defeated rats. Significant increases in the frequency of transient dopamine release were observed during interactions with an aggressive rat but not with a familiar cage mate. In agreement with voltammetric results, significant increases in burst frequency were detected in the VTA dopamine firing patterns during an aggressive confrontation; however, the number of spikes per burst remained unchanged. We found that neurons with lower burst rates under home cage conditions did not switch from nonbursting to bursting types, while neurons with higher burst levels showed amplified increases in bursting. This study demonstrates for the first time that aggressive confrontations in defeated rats are associated with increases in phasic dopamine transmission in the mesolimbic pathway.

Effect of 5-HT1B receptor agonists injected into the prefrontal cortex on maternal aggression in rats.

Serotonin (5-HT1B) receptors play an essential role in the inhibition of aggressive behavior in rodents. CP-94,253, a 5-HT1B receptor agonist, can reduce aggression in male mice when administered directly into the ventro-orbitofrontal (VO) prefrontal cortex (PFC). The objective of the current study was to assess the effects of two selective 5-HT1B receptor agonists (CP-94,253 and CP-93,129), microinjected into the VO PFC, on maternal aggressive behavior after social instigation in rats. CP-94,253 (0.56 microg/0.2 microL, N = 8, and 1.0 microg/0.2 microL, N = 8) or CP-93,129 (1.0 microg/0.2 microL, N = 9) was microinjected into the VO PFC of Wistar rats on the 9th day postpartum and 15 min thereafter the aggressive behavior by the resident female against a male intruder was recorded for 10 min. The frequency and duration of aggressive and non-aggressive behaviors were analyzed using ANOVA and post hoc tests. CP-93,129 significantly decreased maternal aggression. The frequency of lateral attacks, bites and pinnings was reduced compared to control, while the non-aggressive behaviors and maternal care were largely unaffected by this treatment. CP-94,253 had no significant effects on aggressive or non-aggressive behaviors when microinjected into the same area of female rats. CP-93,129, a specific 5-HT1B receptor agonist, administered into the VO PFC reduced maternal aggressive behavior, while the CP-94,253 agonist did not significantly affect this behavior after social instigation in female rats. We conclude that only the 5-HT1B receptor agonist CP-93,129 administered into the VO PFC decreased aggression in female rats postpartum after social instigation.

Effect of 5-HT1B receptor agonists injected into the prefrontal cortex on maternal aggression in rats

Serotonin (5-HT1B) receptors play an essential role in the inhibition of aggressive behavior in rodents. CP-94,253, a 5-HT1B receptor agonist, can reduce aggression in male mice when administered directly into the ventro-orbitofrontal (VO) prefrontal cortex (PFC). The objective of the current study was to assess the effects of two selective 5-HT1B receptor agonists (CP-94,253 and CP-93,129), microinjected into the VO PFC, on maternal aggressive behavior after social instigation in rats. CP-94,253 (0.56 µg/0.2 µL, N = 8, and 1.0 µg/0.2 µL, N = 8) or CP-93,129 (1.0 µg/0.2 µL, N = 9) was microinjected into the VO PFC of Wistar rats on the 9th day postpartum and 15 min thereafter the aggressive behavior by the resident female against a male intruder was recorded for 10 min. The frequency and duration of aggressive and non-aggressive behaviors were analyzed using ANOVA and post hoc tests. CP-93,129 significantly decreased maternal aggression. The frequency of lateral attacks, bites and pinnings was reduced compared to control, while the non-aggressive behaviors and maternal care were largely unaffected by this treatment. CP-94,253 had no significant effects on aggressive or non-aggressive behaviors when microinjected into the same area of female rats. CP-93,129, a specific 5-HT1B receptor agonist, administered into the VO PFC reduced maternal aggressive behavior, while the CP-94,253 agonist did not significantly affect this behavior after social instigation in female rats. We conclude that only the 5-HT1B receptor agonist CP-93,129 administered into the VO PFC decreased aggression in female rats postpartum after social instigation.

5-HT(1B) receptors, ventral orbitofrontal cortex, and aggressive behavior in mice.

RATIONALE: Systemic injections of 5-HT(1B) receptor agonists have been shown to have specific anti-aggressive effects in aggressive individuals. One site of action for these drugs is the 5-HT(1B) receptors in the ventral orbitofrontal cortex (VO PFC), an area that has been implicated in the inhibitory control of behavior and is a terminal region for 5-HT projections. OBJECTIVE: To assess the anti-aggressive effects of the 5-HT(1B) receptor agonist CP-94,253 when microinjected into the VO PFC (0.1, 0.56, and 1.0 microg/0.2 microl) or into the infralimbic prefrontal cortex (IL PFC; 1.0 microg/0.2 microl) in separate groups of aggressive resident male mice. To confirm the 5-HT(1B) receptor as the critical site of action for the anti-aggressive effects, the 5-HT(1B/D) antagonist GR-127,935 was microinjected at 10.0 microg/0.2 microl into the VO PFC. After recovery from surgery, the anti-aggressive effects of microinjected CP-94,253 were studied during 5-min resident-intruder confrontations that were recorded and analyzed. RESULTS: Microinjections of CP-94,253 (0.56 and 1.0 microg/0.2 microl) dose-dependently reduced the frequency of attack bites and sideways threats. This effect was behaviorally specific because non-aggressive motor activities were not significantly altered by the drug. In the IL vmPFC or in an area lateral to the VO PFC, CP-94,253 (1.0 microg/0.2 microl) did not have significant behavioral effects. CONCLUSIONS: The results highlight the 5-HT(1B) receptors in the VO PFC as a particularly important site for the inhibition of species-typical aggressive behavior in male mice.

5-HT(3) receptors, alcohol and aggressive behavior in mice.

Alcohol is a positive modulator at the 5-HT(3) receptor, which has been implicated in alcohol drinking, anxiety and aggression. The reported experiments explored the role of the 5-HT(3) receptor in aggressive behavior and alcohol-heightened aggression. Male, CFW mice were trained to self-administer 1.0 g/kg of alcohol, after which they confronted an intruder. Half of the CFW mice exhibited consistently increased aggressive behavior after alcohol and were designated as showing alcohol-heightened aggression, the others showed no increase and were designated as showing alcohol non-heightened aggression. The 5-HT(3) antagonist, ondansetron (0.01-1.0 mg/kg), significantly reduced aggression in both groups of CFW mice without affecting non-aggressive behaviors. Zacopride also reduced aggression effectively in both groups of mice, but at high doses began to affect walking. Male B6SJL/F2 transgenic 5-HT(3) over-expressing mice (TG) and wild-type mice (WT) were tested for aggressive behavior in their home cage. In those individuals that fought in tests of resident-intruder aggression, no differences were found in aggression after alcohol intake. In tests of aggression without alcohol intake, zacopride reduced aggression in both TG and WT mice at a dose of 56 mg/kg. Antagonism of 5-HT(3) receptors shows promising anti-aggressive effects, although these effects depend on the genetic background of the mice.

Long-term behavioral and neuronal cross-sensitization to amphetamine induced by repeated brief social defeat stress: Fos in the ventral tegmental area and amygdala.

Repeated exposure to stress induces cross-sensitization to psychostimulants. The present study assessed functional neural activation during social defeat stress-induced sensitization to a subsequent amphetamine challenge. Social defeat stress was induced in intruder rats during short confrontations with an aggressive resident rat once every third day during the course of 10 days. Rats received d-amphetamine injections (1 mg/kg, i.p.) 17 or 70 days after the first social defeat stress exposure. Amphetamine administration induced a significantly higher frequency of locomotor activity in stressed animals than in handled control rats, which was still evident 2 months after the last social stress exposure. Immunohistochemistry for Fos-like proteins was used to detect activated neural profiles in the striatum, nucleus accumbens (NAc), prefrontal cortex, amygdala, and ventral tegmental area (VTA). Repeated social defeat stress significantly increased Fos-like immunoreactive (Fos-LI) labeling 17 days after the start of stress exposure in the prelimbic and infralimbic cortical regions, NAc shell and core, medial, central and basolateral amygdala, and VTA, which probably represented the expression of chronic Fos-related antigens. Amphetamine augmented stress-induced Fos-LI labeling 17 days after the first stress episode in the dorsal striatum, NAc core, and medial amygdala, reflecting a cross-sensitization of Fos response. Amphetamine challenge 70 days after social stress exposures revealed sensitized Fos-LI labeling in the VTA and the amygdala. These data suggest that episodes of repeated social stress induce a long-lasting neural change that leads to an augmented functional activation in the VTA and amygdala, which might represent a neurobiological substrate for long-lasting cross-sensitization of repeated social defeat stress with psychostimulant drugs.

Accumbal dopamine and serotonin in anticipation of the next aggressive episode in rats.

Autonomic and limbic neural activities are linked to aggressive behavior, and it is hypothesized that activities in the cardiovascular and monoaminergic systems play a role in preparing for an aggressive challenge. The objective was to learn about the emergence of monoamine activity in nucleus accumbens before an aggressive confrontation that was omitted at the regular time of occurrence, dissociating the motoric from the aminergic activity. Dopamine, serotonin, heart rate and behavioral activity were monitored before, during and after a single 10-min confrontation in resident male Long-Evans rats fitted with a microdialysis probe in the n. accumbens and with a telemetry sender (experiment 1). DA, but not 5-HT efflux, was confirmed to increase in n. accumbens during and after a single aggressive episode. In aggressive males that confronted an opponent daily for 10 days (experiment 2) heart rate rose 1 h before the regularly scheduled encounter relative to control rats, as measured on day 11 in the absence of any aggression. Concurrently, DA levels increased by 60-70% over baseline levels and 5-HT levels decreased by 30-35% compared to baseline levels. These changes were sustained over 1 h, and contrasted with no significant changes in DA, 5-HT, heart rate or behavioral activity in control rats. The rise in mesolimbic DA appears to be significant in anticipating the physiological and behavioral demands of an aggressive episode, and the fall in 5-HT in its termination, dissociated from the actual execution of the behavior.

Short or continuous social stress: suppression of continuously available ethanol intake in subordinate rats.

We explored the effects of short, intermediate, and continuous social stress on daily ethanol and water intake in rats. The study was designed to: (1) detect increases in intake during hours when animals were not stressed; and (2) detect shifts in preference from solutions with high to low alcohol content. Male Long-Evans rats acquired ethanol self-administration using a sucrose-fading procedure, which was followed by continuous access to 10% and 3% ethanol solutions and water. After intake stabilized, rats were exposed to three periods of five consecutive days of social stress, with 8-10 days without stress in between. Short social stress consisted of being attacked and defeated by an aggressive opponent, followed by 30 min exposure to threats by the aggressive male while in a protective cage. Intermediate and continuous social stress consisted of a 6 h or 24 h 'threat of attack' exposure, respectively. All stress exposures reduced daily intake of 10% ethanol, did not cause changes in intake of 3% ethanol, and caused increases in water intake. No compensatory ethanol consumption was observed on stress days or after stress exposure was discontinued. These results are at variance with the hypothesis for increased alcohol consumption during or following social stress episodes.

Oral drug self-administration in the home cage of mice: alcohol-heightened aggression and inhibition by the 5-HT1B agonist anpirtoline.

RATIONALE: In order to model heightened aggression after alcohol consumption and to study the inhibitory influence of 5-HT1B receptors on drinking and fighting, an experimental procedure should enable self-administration of precise amounts of alcohol in a limited period of time before an aggressive confrontation. OBJECTIVES: To design a new device that can reinforce operant responding by the delivery of sweet alcohol in the resident mouse home cage, where aggressive behavior toward an intruder can subsequently be examined, and to demonstrate inhibition of alcohol-heightened aggression by 5-HT1B receptor agonist treatment. METHODS: Within one experimental session, all singly housed CFW male mice (n=26) performed a nose-poke response that was reinforced by 0.05 ml sucrose. Using the sucrose fading technique, eventually the mice consumed a 6% ethanol/4% sucrose solution after each fifth nose poke during daily 15-min experimental sessions. The number of ethanol reinforcements was adjusted so that 0.6, 1.0, 1.7, and 3.0-g/kg doses were consumed in 15 min or less. Assays confirmed blood alcohol levels at 68.1 mg/dl for intake of 1.0 g/kg. After consuming a specific dose of ethanol in the form of a fixed number of response-dependent deliveries, the response panel was removed from the home cage and, 15 min later, the resident confronted a male intruder. Anpirtoline was administered either before alcohol self-administration or before the aggressive confrontation. RESULTS: After being reinforced with 1.0 g/kg or 1.7 g/kg sweet ethanol, the mice significantly increased attack and threat behavior relative to their aggressive behavior following sucrose or water consumption only. Treatment with the 5-HT1B receptor agonist anpirtoline (0.125, 0.25, 0.5 mg/kg, i.p.) before the confrontation decreased alcohol-heightened aggression and species-typical aggression in the absence of changes in other elements of the behavioral repertoire. Anpirtoline affected ethanol-reinforced behavior only at doses that were 5-10 times higher than those producing anti-aggressive effects. CONCLUSIONS: Self-administration of alcohol in the home cage of mice is readily accomplished with the aid of a simple, removable panel. The effective inhibition of high levels of aggressive behavior due to alcohol consumption after anpirtoline treatment confirm the 5-HT1B receptor as a critical site in the termination of aggression.

Aggressive behavioral phenotypes in mice.

Aggressive behavior in male and female mice occurs in conflicts with intruding rivals, most often for the purpose of suppressing the reproductive success of the opponent. The behavioral repertoire of fighting is composed of intricately sequenced bursts of species-typical elements, with the resident displaying offensive and the intruder defensive acts and postures. The probability of occurrence as well as the frequency, duration, temporal and sequential patterns of aggressive behavior can be quantified with ethological methods. Classic selection and strain comparisons show the heritability of aggressive behavior, and point to the influence of several genes, including some of them on the Y chromosome. However, genetic effects on aggressive behavior critically depend upon the background strain, maternal environment and the intruder. These factors are equally important in determining changes in aggressive behavior in mice with a specific gene deletion. While changes in aggression characterize mutant mice involving a variety of genes, no pattern has emerged that links particular gene products (i.e. enzyme, peptide, receptor) to either an increase or a decrease in aggressive behavior, but rather emphasizes polygenic influences. A potentially common mechanism may be some components of the serotonin system, since alterations in 5-HT neurotransmission have been found in several of the KO mice that display unusual aggressive behavior.

Alprazolam withdrawal and tolerance measured in the social conflict test in mice.

RATIONALE: It is difficult to assess withdrawal from benzodiazepines, and preclinical assessment of behaviour during social conflict offers the opportunity to quantify tolerance and withdrawal by measuring aggressive, defensive and social behaviour. The relationship between benzodiazepine withdrawal symptoms and the development of tolerance is not well understood. Are withdrawal symptoms dependent on the development of tolerance? OBJECTIVE: The aim of the present study was to compare the development of tolerance to alprazolam effects on the behavioural repertoire during the social conflict test in mice, and to determine whether or not behavioural changes during alprazolam withdrawal are correlated with the development of tolerance. METHODS: An experimental model consisting of interactions of pairs of singly housed male mice with non-aggressive group-housed male mice was used. Alprazolam (1 mg/kg) was given orally once or repeatedly (twice daily) for 8 or 21 days. Behaviour was measured, based on videoanalysis, in aggressive mice before treatment, 30 min or 3 days after the last dose, respectively. RESULTS: A single administration of alprazolam significantly reduced aggressive activities and increased social investigation without changing locomotion or other behaviour. Tolerance developed to the inhibitory effects of alprazolam on aggressive behaviour but not to the effects of alprazolam to increase social investigation. When withdrawn from alprazolam, mice exhibited less social investigation and locomotion while aggression tended to be increased. CONCLUSIONS: Tolerance to the alprazolam effects on aggressive and social behaviour developed at different rates suggesting that they are differentially regulated. Furthermore, the evidence of withdrawal responses appearing in a behaviour to which tolerance had not developed does suggest that tolerance and withdrawal phenomena are dissociated in benzodiazepines.

Zolmitriptan--a 5-HT1B/D agonist, alcohol, and aggression in mice.

RATIONALE: Zolmitriptan is an anti-migraine agent with action at 5-HT1B/D receptors. It penetrates into the central nervous system and, like other 5-HT1B/D agonists, its pharmacotherapeutic profile may include significant anti-aggressive effects. OBJECTIVES: To examine whether zolmitriptan has potential anti-aggressive effects by studying two kinds of aggressive behavior in mice--species-typical and aggression under the influence of alcohol. A second objective was to study whether pre- or post-synaptic receptors mediate these anti-aggressive effects. METHODS: Initially, the anti-aggressive effects of zolmitriptan were studied in male CFW mice during 5-min resident-intruder confrontations. To confirm the 5-HT1B receptor as a critical site of action for the anti-aggressive effects, the zolmitriptan dose-effect determinations were repeated after pretreatment with GR 127935 (10 mg/kg, i.p.). In further experiments, mice were treated concurrently with alcohol (1.0 g/kg, p.o.) and zolmitriptan (1-30 mg/kg, i.p.) in order to compare the effects of this agonist on species-typical and alcohol-heightened aggression. Finally, mice were infused with the neurotoxin 5,7-DHT (10 microg) into the raphé area to eliminate somatodendritic and presynaptic autoreceptors. The anti-aggressive effects of zolmitriptan (17 mg/kg, i.p.) or CP-94,253 (10 mg/kg, i.p.) were assessed 10 days after the lesion, and levels of 5-HT and 5-HIAA were measured in the hippocampus and prefrontal cortex. RESULTS: Zolmitriptan exerted behaviorally specific anti-aggressive effects. The reduction in aggression was antagonized by GR 127935, indicated by a rightward shift in the dose-effect curves of zolmitriptan, showing the specificity for the 5-HT1B receptors. Zolmitriptan also decreased alcohol-heightened aggression with equal efficacy. The anti-aggressive effects of CP-94,253 and zolmitriptan remained unaltered by 5,7-DHT lesions that depleted cortical and hippocampal 5-HT by 60-80%. CONCLUSIONS: Zolmitriptan proved to be an effective and behaviorally specific anti-aggressive agent in situations that engender moderate and alcohol-heightened levels of aggression. These effects are potentially due to activation of post-synaptic 5-HT1BD receptors.

Persistent suppression of ethanol self-administration by brief social stress in rats and increased startle response as index of withdrawal.

Excessive alcohol drinking is often linked to the experience of stress, but experimental approaches using animal models of alcohol self-administration have had widely varying outcomes. The objective was to determine how daily exposure to brief, predictable social stress would change alcohol self-administration in rats in a daily limited access protocol. Male Long-Evans rats had either access to a 10% ethanol solution for 15 min in the home cage setting (n=20) or were reinforced with 15% ethanol deliveries for every fifth lever press (n=10). Subsequently, all rats were subjected to brief social stress for five consecutive days. Social stress consisted of attacks by an opponent for 5 min followed by exposure to threats while in a protective cage for 30 min. In both the home cage drinking and operant conditioning groups, social stress exposure significantly decreased alcohol intake or rate of alcohol reinforcements, respectively. When alcohol intake was scheduled immediately before social stress (i.e., 24 h after the previous social stress episode), a decrease was observed with a delay of 1 or 2 days. When alcohol intake was scheduled 4 h after stress, no changes in intake or alcohol reinforcements were observed. Animals that consumed a low dose of ethanol displayed less defensive behavior during social stress compared to water-drinking animals, and showed an increased startle reflex at 8 and 56 h after discontinuation of daily ethanol access. The current experimental protocols of social defeat stress reveal a transient suppression rather than a facilitation of alcohol consumption.

Repeated self-administered cocaine "binges" in rats: effects on cocaine intake and withdrawal.

RATIONALE: Repeated access to cocaine may engender behavioral sensitization, which emerges as an enhanced response to the effects of cocaine. Repeated exposure to prolonged self-administration sessions has been shown to produce an escalation in cocaine intake. OBJECTIVE: The objective of the present study was to identify the consequence of repeated exposure to prolonged access to self-administered cocaine. METHODS: Pairs of rats that were matched for training, housing, and surgery were treated as a single experimental unit, and these pairs were separated into groups for two separate experiments. In the first experiment, one animal of the pair acquired and maintained a stable rate for i.v. cocaine self-administration (0.5 mg/infusion), while the second rat was yoked such that it passively received saline infusions in the same pattern. After acquisition, the active self-administration rats were given free access to cocaine for 16 h (binge), while the yoked animal continued to receive infusions of saline. Twenty-four hours after the binge, both animals were exposed to tactile startle stimuli, and ultrasonic vocalizations (USVs) and startle reflexes were measured. The animals were exposed to three cocaine binges and 24 h post-binge startle tests with an interval of 10 days between binges, and then a fourth binge, with an interval of 24 h separating binges three and four. In the second experiment, pairs of rats were separated into three groups (A, B, and C). The active cocaine rats acquired self-administration and were allowed access to a 16-h cocaine binge while their yoked controls received saline. Twenty-four hours after the binge, all animals were tested for emission of USVs and startle reflexes with an identical protocol as that in experiment 1. Immediately after exposure to the startle stimuli, the self-administering animals were again allowed to self-administer cocaine for either 16 (group A), 12 (group B), or 8 h (group C). RESULTS: In experiment 1, the total amount of cocaine self-administered was significantly decreased when the cocaine binges were separated by 10 days, but total cocaine intake during the binge significantly increased when the drug-free interval was 24 h. The pattern of self-administration and the withdrawal response remained unchanged over consecutive binges. In experiment 2, rats that self-administered cocaine for either 16 or 12 h emitted significantly less USVs immediately after renewed access than they emitted 24 h after the first access period. CONCLUSION: It appeared that consecutive prolonged self-administration was insufficient to produce sensitization, as measured by cocaine intake and renewed access to self-administered cocaine was sufficient to reduce the large number of USVs that characterize withdrawal from a cocaine binge.

Zolpidem, triazolam, and diazepam decrease distress vocalizations in mouse pups: differential antagonism by flumazenil and beta-Carboline-3-carboxylate-t-butyl ester (beta-CCt).

In response to stressful events, neonatal mice emit ultrasonic vocalizations (USVs), which are suppressed by BZ agonists. The present study examined the role of the benzodiazepine/alpha1 (BZ/alpha1) receptor subtype in the suppression engendered by the BZ/alpha1-preferring agonist zolpidem and the nonselective BZ agonists triazolam and diazepam. The role of BZ receptor subtypes was explored further by conducting antagonism studies using the BZ/alpha1-preferring antagonist beta-carboline-3-carboxylate-t-butyl ester (beta-CCt), in comparison with the nonselective BZ antagonist flumazenil. Mouse pups (CFW strain) were separated from their dam and littermates at day 7, and placed for 4 min in a test chamber with reduced ambient temperature (19 +/- 1 degrees C) for recording USVs, motor incoordination (measured as a pup rolling on its back per grid cross), and body temperature. Zolpidem, triazolam, and diazepam suppressed USVs in a dose-dependent manner, concomitant with increases in incoordination and augmentation of hypothermia. These effects of the three BZ agonists were blocked by flumazenil in a manner consistent with surmountable antagonism. The ability of zolpidem, but not triazolam or diazepam, to suppress USVs and augment hypothermia was antagonized by beta-CCt, whereas the increase in motor incoordination engendered by zolpidem, triazolam, and diazepam was not sensitive to beta-CCt administration. Collectively, these results suggest that zolpidem suppresses distress USVs in mouse pups by a mechanism distinct from that of typical BZs. Furthermore, suppression of distress USVs by zolpidem may involve BZ/alpha1 receptors and a nonanxiolytic mechanism, such as hypothermia.