Differences in the hypothermic response to ethanol in rats selectively bred for oral ethanol preference and nonpreference

Predictive Value of Grooming Behavior for Development of Dermatitis in Selectively Bred P Rats as a Model of Trichotillomania Hair Pulling Disorder

Trichotillomania (TTM) is a body-focused repetitive disorder affecting as much as 0.5 to 2% of the population, with women four times more likely to be affected than men. This disorder causes impairment in daily function and significant distress. A potential animal model for this disorder is the inbred C57BL/6J mouse which displays clinical signs and behavioral characteristics similar to those described for people affected by this disorder. Because alcohol-preferring P rats also display similar clinical signs and behavioral characteristics, it was hypothesized that this selectively bred stock could be an additional animal model. In this study, 112 female P rats were recorded on digital media for 15 min after being sprayed with a mist of water and assessed for grooming patterns—oral, manual, and scratching. Significant elevations in scratching and oral grooming behavior were predictive of the future development of skin lesions. These findings suggest that P rats may be an additional model to study TTM, with the advantage of increased genetic variation (i.e., non-inbred) which mirrors the human population. The use of this model may help to identify preventative and therapeutic interventions for humans and other animals with similar body-focused repetitive disorders.

A Genetic Animal Model of Alcoholism for Screening Medications to Treat Addiction

The purpose of this review is to present up-to-date pharmacological, genetic, and behavioral findings from the alcohol-preferring P rat and summarize similar past work. Behaviorally, the focus will be on how the P rat meets criteria put forth for a valid animal model of alcoholism with a highlight on its use as an animal model of polysubstance abuse, including alcohol, nicotine, and psychostimulants. Pharmacologically and genetically, the focus will be on the neurotransmitter and neuropeptide systems that have received the most attention: cholinergic, dopaminergic, GABAergic, glutamatergic, serotonergic, noradrenergic, corticotrophin releasing hormone, opioid, and neuropeptide Y. Herein, we sought to place the P rat's behavioral and neurochemical phenotypes, and to some extent its genotype, in the context of the clinical literature. After reviewing the findings thus far, this chapter discusses future directions for expanding the use of this genetic animal model of alcoholism to identify molecular targets for treating drug addiction in general.

Animal models for medications development targeting alcohol abuse using selectively bred rat lines: neurobiological and pharmacological validity

The purpose of this review paper is to present evidence that rat animal models of alcoholism provide an ideal platform for developing and screening medications that target alcohol abuse and dependence. The focus is on the 5 oldest international rat lines that have been selectively bred for a high alcohol-consumption phenotype. The behavioral and neurochemical phenotypes of these rat lines are reviewed and placed in the context of the clinical literature. The paper presents behavioral models for assessing the efficacy of pharmaceuticals for the treatment of alcohol abuse and dependence in rodents, with particular emphasis on rats. Drugs that have been tested for their effectiveness in reducing alcohol/ethanol consumption and/or self-administration by these rat lines and their putative site of action are summarized. The paper also presents some current and future directions for developing pharmacological treatments targeting alcohol abuse and dependence.

What aspects of human alcohol use disorders can be modeled using selectively bred rat lines?

The use of selective breeding to produce animal models for the study of alcohol abuse and alcoholism represents one of the major advances in the field of alcohol research. Rats selectively bred for alcohol preference and alcohol nonpreference have been useful to both preclinical and clinical investigators in the alcohol research community for studying the behavioral, neurobiological, and molecular basis of alcohol drinking, for identifying the genes that may contribute to the development of alcohol abuse and alcoholism, and for evaluating the utility of drugs aimed at reducing alcohol intake and preventing alcohol relapse. Rats selectively bred for alcohol preference (alcohol preferring or "P" line) have enhanced responsiveness to the low dose reinforcing effects of alcohol, less aversion to moderate/high doses of alcohol, and are able to develop tolerance to the aversive effects of alcohol more rapidly and to maintain tolerance longer than rats selectively bred for alcohol nonpreference (alcohol nonpreferring or "NP" line). The increased potency of low-dose alcohol as a reinforcer for P rats might be expected to foster and maintain alcohol drinking. Weaker aversion to the pharmacological effects of moderate/high doses of alcohol in the P line would allow P rats to drink more alcohol than NP rats before the postingestional effects become aversive. Rapid induction of tolerance to the aversive effects of alcohol with repeated bouts of voluntary alcohol drinking, as well as persistence of alcohol tolerance in rats of the P line might serve to maintain alcohol drinking. These are powerful mechanisms that may serve to promote and maintain a high alcohol drinking behavior. Although these rat lines have been used to address several characteristics of excessive alcohol consumption in humans, they have not yet been used to model several aspects of human alcohol use disorders. New applications of these selectively bred rat lines are discussed which may further our understanding of the factors contributing to alcohol abuse and alcoholism.

Sleep-wakefulness in alcohol preferring and non-preferring rats following binge alcohol administration

The alcohol-preferring (P) rat is a valid animal model of alcoholism. However, the effect of alcohol on sleep in P or alcohol non-preferring (NP) rats is unknown. Since alcohol consumption has tremendous impact on sleep, the present study compared the effects of binge alcohol administration on sleep-wakefulness in P and NP rats. Using standard surgical procedures, the P and NP rats were bilaterally implanted with sleep recording electrodes. Following post-operative recovery and habituation, pre-ethanol (baseline) sleep-wakefulness was electrographically recorded for 48 h. Subsequently, ethanol was administered beginning with a priming dose of 5 g/Kg followed by two doses of 2 g/Kg every 8 h on the first day and three doses of 3 g/Kg/8 h on the second day. On the following day (post-ethanol), undisturbed sleep-wakefulness was electrographically recorded for 24 h. Our initial results suggest that, during baseline conditions, the time spent in each of the three behavioral states: wakefulness, non-rapid eye movement (NREM) sleep and REM sleep, was comparable between P and NP rats. However, the P rats were more susceptible to changes in sleep-wakefulness following 2 days of binge ethanol treatment. As compared to NP rats, the P rats displayed insomnia like symptoms including a significant reduction in the amount of time spent in NREM sleep coupled with a significant increase in wakefulness on post-ethanol day. Subsequent analysis revealed that binge ethanol induced increased wakefulness and reduced NREM sleep in P rats occurred mainly in the dark period. This is the first study that: (1) demonstrates spontaneous sleep-wake profile in P and NP rats, and (2) compares the effects of binge ethanol treatment on sleep in P and NP rats. Our results suggest that, as compared to NP rats, the P rats were more susceptible to sleep disruptions after binge ethanol treatment. In addition, the P rats exhibited insomnia-like symptoms observed during abstinence from alcohol in human subjects.

Persistent high alcohol consumption in alcohol-preferring (P) rats results from a lack of normal aversion to alcohol

AIMS

In this study, we tested the impact of pretreatment with alcohol on subsequent alcohol drinking in outbred Sprague-Dawley and selectively bred alcohol-preferring (P) rats.

METHODS

As a pretreatment, male Sprague-Dawley and P rats were given a passive oral administration of either alcohol (1.0 g/kg) or tap water. Then, they were given free choice of drinking alcohol (5% v/v) or water in their home cages, which was measured over 4 weeks.

RESULTS

Without alcohol pretreatment, there was no significant strain difference in alcohol preference; both strains preferred 5% (v/v) alcohol solution. The strain difference was only apparent in the groups given alcohol pretreatment. This arose from the fact that alcohol pretreatment significantly reduced alcohol preference in the Sprague-Dawley rats to a level well below 50%, while it did not alter drinking behavior in P rats. The same effects were seen with total alcohol consumption (g/kg/day). These effects persisted throughout the 4 weeks of the study.

CONCLUSIONS

The principal difference between the Sprague-Dawley and P rats was that the P rats did not show the normal aversion to alcohol after forced exposure to alcohol that the Sprague-Dawley rats showed. One of the potential contributors to high alcohol intake and preference in P rats may be lack of sensitivity to aversive effects of alcohol.

Relationship between ethanol's acute locomotor effects and ethanol self-administration in male Long-Evans rats

BACKGROUND

Human studies have suggested an important relationship between ethanol sensitivity and risk of alcoholism. These studies have led some to hypothesize that a low initial sensitivity to ethanol's depressant effects and/or an elevated response to ethanol's stimulant effects may represent important risk factors associated with the development of abusive drinking behavior. Unfortunately, elucidating neurobiologic mechanisms that may underlie these relationships between ethanol sensitivity and ethanol drinking have been hampered by difficulties in modeling some of these interactions in animals. In this study, we re-examined some of these relationships in an outbred strain of rats using continuous access two-bottle choice drinking and a limited-access operant procedure that engenders pharmacologically relevant levels of ethanol intake and permits the discrete assessment of appetitive and consummatory measures of ethanol drinking behavior.

METHODS

Twenty-three male Long-Evans rats were habituated to a locomotor activity box and then tested for their response to a stimulant (0.5 g/kg) and depressant (1.5 g/kg) ethanol dose. Rats were then trained to complete a lever pressing requirement to gain access to 10% ethanol for 20-minute sessions conducted 5 d/wk for 5 weeks. Appetitive behavior was assessed after 2.5 and 4.5 weeks using 20-minute extinction trials in which ethanol was not presented and lever responses were recorded. Home-cage ethanol preference was also assessed prior to and immediately following the 5-week self-administration regimen using a continuous access, two-bottle choice procedure.

RESULTS

A significant increase in home-cage ethanol preference was observed following the self-administration procedure, however, neither measure of ethanol preference correlated with average daily ethanol intake during the operant self-administration sessions or with initial sensitivity to ethanol's stimulant or depressant effects. Notably, a significant negative correlation was observed between sensitivity to ethanol's locomotor depressant effect and daily intake during the operant self-administration sessions. No significant relationships were noted between sensitivity to ethanol's locomotor effects and extinction responding.

CONCLUSIONS

The results of these studies suggest that the well-established relationship between a low level of response to ethanol and increased ethanol consumption reported in human studies can be observed in an outbred rodent strain using a limited-access operant self-administration procedure, but not with home-cage ethanol drinking.

Chronic ethanol consumption increases dopamine uptake in the nucleus accumbens of high alcohol drinking rats

Past research has indicated that chronic ethanol exposure enhances dopamine (DA) neurotransmission in several brain regions. The present study examined the effects of chronic ethanol drinking on dopamine transporter (DAT) function in the nucleus accumbens (Acb) of High-Alcohol-Drinking replicate line 1 (HAD-1) rats. HAD rats were given concurrent 24-h access to 15% ethanol and water or water alone for 8 weeks. Subsequently, DA uptake and the V(max) of the DAT were compared between the two groups using homogenates of the nucleus accumbens. DA uptake was measured following a 2 min incubation at 37 degrees C in the presence of 8 nM [(3)H]DA. For kinetic analyses, DA uptake was assessed in the presence of 5 concentrations of [(3)H]DA ranging from 8 nM to 500 nM. Analyses of the data revealed a significant increase in DA uptake in the ethanol group compared to water controls. Kinetic analyses revealed the change in DA uptake to be a consequence of an increase in the V(max) of transport. These findings demonstrate that chronic free-choice oral ethanol consumption in HAD-1 female rats increases DA uptake in the Acb by increasing the V(max) of the transporter. However, it is not known whether the ethanol-induced change in V(max) is caused by differences in the actual number of available transporter sites or from a difference in the velocity of operation of a similar number of transporters. Overall, the data indicate that chronic ethanol consumption by HAD-1 rats produces prolonged neuroadaptations within the mesolimbic DA system, which may be important for the understanding of the neurobiological basis of alcoholism.

The alcohol-preferring P rat and animal models of excessive alcohol drinking

The alcohol-preferring, P, rat was developed by selective breeding to study ethanol drinking behavior and its consequences. Characterization of this line indicates the P rat meets all of the criteria put forth for a valid animal model of alcoholism, and displays, relative to their alcohol-non-preferring, NP, counterparts, a number of phenotypic traits associated with alcohol abuse and alcoholism. Behaviorally, compared with NP rats, P rats are less sensitive to the sedative and aversive effects of ethanol and more sensitive to the stimulatory effects of ethanol. Neurochemically, research with the P line indicates the endogenous dopaminergic, serotonergic, GABAergic, opiodergic, and peptidergic systems may be involved in a predisposition for alcohol abuse and alcoholism. Paralleling the clinical literature, genetically selected P rats display levels of ethanol intake during adolescence comparable to that seen during adulthood. Binge drinking has been associated with an increased risk for health and other problems associated with ethanol abuse. A model of binge-like drinking during the dark cycle indicates that P rats will consume 6 g/kg/day of ethanol in as little as three 1-hour access periods/day, which approximates the 24-hour intake of P rats with free-choice access to a single concentration of ethanol. The alcohol deprivation effect (ADE) is a transient increase in ethanol intake above baseline values upon re-exposure to ethanol access after an extended period of deprivation. The ADE has been proposed to be an animal model of relapse behavior, with the adult P rat displaying a robust ADE after prolonged abstinence. Overall, these findings indicate that the P rat can be effectively used in models assessing alcohol-preference, a genetic predisposition for alcohol abuse and/or alcoholism, and excessive drinking using protocols of binge-like or relapse-like drinking.

Current state of knowledge about the mechanisms of alcohol tolerance

Far from being a simple homeostatic response to the presence of ethanol in the brain, tolerance is now recognized as a complex process which can develop within various time frames (acute, rapid, chronic) and in which the drug interacts with various environmental and cognitive factors, including associative and operant learning. A major question is whether the acute form is an innate adaptive response, which is converted into the rapid and chronic forms by the action of these external influences. So far, all behavioral and neuropharmacological manipulations that alter chronic tolerance also modify rapid and acute tolerance in similar ways. These include lesions of serotonergic forebrain projections, blockade of NMDA-type glutamate receptors and calcium "L" channels, central or peripheral injection of vasopressin and blockade of vasopressin V1 receptors. Cytochemical and immunofluorescence studies, combined with use of retrograde tracers, indicate the existence of a septohippocampal circuit which may mediate the interactions of these diverse elements in the production and maintenance of tolerance. There is limited evidence that development of tolerance leads to increased consumption of ethanol in experimental animals, but the clinical significance of these findings remains to be proven.

Effect of a dose of ethanol on acute tolerance and ethanol consumption in alcohol drinker(UChB) and non-drinker (UChA) rats

Acute tolerance that develops within minutes of ethanol exposure appears to influence the apparent acute behavioral sensitivity of laboratory animals to ethanol actions. The existence of a correlation between voluntary ethanol consumption and the speed of acquiring acute tolerance has been proposed. In the present paper we investigated the effect of an acute dose of ethanol on tolerance development and on ethanol voluntary consumption in our two selected bred strains, UChA (low ethanol drinker) and UChB (high ethanol drinker) rats. Acute tolerance developed to motor impairment induced by a dose of ethanol of 2.3 g/kg. administered intraperitoneally was evaluated by the tilting plane test. Voluntary ethanol consumption was compared in rats receiving the ethanol dose, to rats receiving a saline intraperitoneal (i.p.) injection. The results show that UChB rats receiving an intoxicating dose of ethanol develop more tolerance and they significantly increased their ethanol consumption compared to the same line that received a saline injection, while no change in acute tolerance and voluntary ethanol consumption were obtained in UChA rats. In conclusion, a possible mechanism by which UChB rats drink high amounts of ethanol appears to be the development of tolerance to the pharmacological effects of ethanol.

Tolerance and sensitization to the hypnotic effects of alcohol induced by chronic voluntary alcohol intake in rats

The effect of a chronic alcohol exposure on the development of tolerance to the depressive effects of alcohol were examined in male Wistar rats that voluntary self-administered alcohol. A free-choice drinking procedure based on the limited access paradigm and the addition of glucose that implies an early availability of the alcoholic solution was used (Alcoholism Primary Praecox procedure). Alcohol induced sleep time (3.5 g alcohol per kg i.p.) was measured at 90 days (after 2 months of alcohol consumption) or at 60 + 90 days old (1 or 2 months of alcohol consumption). The psychomotor performance was also evaluated by means of an 80 degrees inclined screen test. Subjects that had been tested for the hypnotic effects at both 60 and 90 days showed a higher intake of alcoholic solution than the animals only tested at 90 days. The same consumption increase was observed in the glucose group. No significant differences between groups were observed in the inclined screen test. Tolerance to the hypnotic effects of alcohol was observed at 90 days. On the other hand, no significant differences between alcohol and control groups (glucose or water) were observed in the sleep time at 60 days. In the alcohol-drinking rats tested for two trials (60 and 90 days), sensitization instead of tolerance to the second hypnotic alcohol injection was seen. Tolerance to the hypnotic effects of alcohol observed after chronic voluntary alcohol consumption may provide animal models of alcoholism based on limited access to sweetened alcoholic solutions with construct validity.

Ethanol-stimulated serotonin release in the ventral hippocampus: an absence of rapid tolerance for the alcohol-preferring P rat and insensitivity in the alcohol-nonpreferring NP rat

This study examined the acute effects of intraperitoneal administration of ethanol on the extracellular levels of serotonin (5-HT) in the ventral hippocampus (vHIP) of adult, male alcohol-preferring P and -nonpreferring NP rats. Using in vivo microdialysis coupled with HPLC and electrochemical detection, the effects of acute administration of saline or 1.0, 1.75, or 2.5 g/kg ethanol on the extracellular levels of 5-HT in the vHIP were examined. Saline and 1.0 g/kg ethanol did not alter the extracellular levels of 5-HT. However, the 1.75-g/kg dose resulted in a transient increase in 5-HT levels in the vHIP of P rats only. Administration of 2.5 g/kg ethanol increased 5-HT levels to 180% of baseline in P rats (P<.05), but was without effect on NP rats. The 2.5-g/kg dose also significantly increased the extracellular levels of 5-HT in the vHIP of P rats, which had been pretreated with the same dose of ethanol 18-24 h earlier (P<.05). Comparison of the response of ethanol pretreated P rats with animals that had been pretreated with saline 24 h earlier did not reveal any significant differences in ethanol-stimulated increases in 5-HT levels between the groups. These data suggest that ethanol may activate terminals of the median raphe 5-HT system in P rats because the vHIP receives its 5-HT inputs primarily from the median raphe nucleus (MRN). Rapid tolerance does not develop to this activation of the system in the vHIP of P rats. In addition, the data suggest that the 5-HT system in the vHIP of NP rats may be relatively insensitive to the stimulating effect of acute ethanol of 5-HT release.

Genetic selection of alcohol preference can be countered by conditioning processes

Twenty-four P rats and 24 NP rats were conditioned to consume 10% w/v alcohol in daily 0.5-h limited access periods using a modified version of Samson's sucrose fading procedure. Both P and NP rats demonstrated a strikingly similar day-to-day pattern of alcohol intakes. For the most part, P rats drank more than NP rats, but by the middle of the fourth month of drinking, P and NP rats were drinking equivalent amounts of alcohol. Both P and NP rats consumed alcohol in amounts similar to two outbred strains of rats (Wistar and Sprague-Dawley) previously conditioned to drink alcohol in this laboratory.

Adenylyl cyclase signal transduction and alcohol-induced sedation

This study examined adenylyl cyclase (AC) signal transduction in alcohol-sensitive brain regions of rats selectively bred for high (HAD) and low (LAD) alcohol drinking and correlated these findings with differences in sensitivity and tolerance to alcohol-induced sedation found within these lines. LAD rats were more sensitive to the sedative effects of alcohol than were HAD rats as evidenced by a shorter latency to lose the righting response (RR) after a single alcohol challenge. When time to recover the RR was compared after each of two alcohol challenges, HAD rats recovered the RR more rapidly following the second challenge compared to the first, indicating that the HAD rats rapidly developed tolerance to the sedative effects of alcohol. Tolerance did not develop in rats of the LAD line. Two months after completion of behavioral testing, adenylyl cyclase (AC) signal transduction was examined in alcohol-sensitive brain regions of rats from both lines. Immunoblot analyses indicated that LAD rats had greater Gs alpha expression in the frontal cortex (FC) and hippocampus (HIP) compared to HAD rats. Rats with the highest HIP and FC Gs alpha levels were more rapidly affected by the sedative properties of alcohol than were rats with lower Gs alpha levels. G protein expression and AC activity in the FC, HIP, cerebellum (CERE), and nucleus accumbens (ACB) were also correlated with sensitivity to the sedative properties of alcohol and with the rapid development of tolerance to this alcohol effect. The results suggest that sensitivity and tolerance to alcohol-induced sedation may be mediated in part through AC signal transduction.

Genetic differences in tolerance and sensitization to the sedative/hypnotic effects of alcohol

Initial sensitivity to alcohol and the development of alcohol tolerance were examined in rats of the selectively bred alcohol-preferring (P) and -nonpreferring (NP) lines. All rats received two alcohol injections (3.0 g/kg b.wt., IP) separated by either 1 or 2 days. P rats were less sensitive to the behaviorally impairing effects of alcohol than were NP rats, as evidenced by a longer latency to lose righting reflex (RR) and a shorter time to recover RR following an initial alcohol injection. When 1 day separated the two alcohol injections, P rats recovered the RR more rapidly following a second injection compared to the first, indicating that the P rats developed tolerance to the sedative/hypnotic effects of alcohol. In contrast, the NP rats recovered the RR more slowly following the second injection compared to the first, indicating that the NP rats developed sensitization to alcohol. Tolerance in the P line and sensitization in the NP line disappeared when 2 days separated the two alcohol injections. Line differences in initial sensitivity and tolerance/sensitization to the behaviorally impairing effects of alcohol may contribute to the differences in alcohol consumption observed in the P and NP lines.

Comparison of innate EEG parameters in rat lines selected for ethanol preference

Through bidirectional selective breeding, lines of rats that differ greatly in their voluntary alcohol drinking behavior have been developed--namely, the alcohol-preferring (P) and high-alcohol-drinking (HAD) lines and the alcohol-nonpreferring (NP) and low-alcohol-drinking (LAD) lines. The present experiments were designed to determine if an association exists between ethanol preference and features of the electroencephalogram (EEG) during various sleep-wake behaviors. Of the EEG parameters measured, only theta activity in the hippocampus revealed differences in the lines. However, these differences were not generally associated with ethanol preference. The peak frequency and distribution mean of hippocampal theta activity during REM sleep were significantly higher in NP rats than in P, HAD, and LAD rats. In addition, theta frequency during alert immobility tended to be higher in NP rats than in P, HAD, and LAD rats. A qualitative comparison of these data with published data from unselected rats further suggested that the NP rats are uniquely different with respect to theta frequency.

Consumption of sweet, salty, sour, and bitter solutions by selectively bred alcohol-preferring and alcohol-nonpreferring lines of rats

To determine whether selective breeding for high or low oral ethanol consumption is associated with different preferences for nonpharmacological solutions with various flavors, the oral intake of a range of concentrations of sucrose (0.5-64.0 g/100 ml), NaCl (0.025-3.2 g/100 ml), citric acid (0.008-2.048 g/liter), and sucrose octaacetate (0.002-0.512 g/liter) was studied in alcohol-preferring (P) and alcohol-nonpreferring (NP) rats. Separate groups of 7-8 rats from each line were tested for consumption of each of the four flavors. The flavored solutions were presented continuously with water and food always available, and the concentrations were doubled every 48 hr. Although rats from both lines showed a strong preference for the sucrose solutions, P rats consumed greater amounts than NP rats [F(7,98) = 5.57, p < 0.001]. Rats of the P line drank less of the NaCl solutions than NP rats [F(7,98) = 3.88, p < 0.001], but the effect was not as robust as the line differences seen with sucrose. The P and NP rats did not differ in citric acid or sucrose octaacetate intake at any of the concentrations tested. Selective breeding for high oral ethanol preference appears to be positively associated with consumption of sweet solutions and negatively associated with intake of salty solutions.

Septal TRH in alcohol-naive P and NP rats and following alcohol challenge

Regional brain content of TRH was evaluated in selectively bred alcohol-preferring (P) and -nonpreferring (NP) rats before, during, and upon awakening from ethanol sedation. TRH content was significantly lower in both the medial and lateral septum of alcohol-naive P rats compared with alcohol-naive NP rats. Following a sedating dose of ethanol, P rats righted themselves sooner than NP rats. TRH content in the medial septum of P and NP rats was significantly higher when the rats regained their righting reflex. While sedated, TRH in the medial septum of P rats was insignificantly increased. These data are the first to show that endogenous TRH in the medial septum may be involved in arousal from drug-induced sedation and that the events preceding arousal may occur sooner in P than in NP rats. In addition, innate differences in septal TRH may be associated with preference for ethanol.