Controlled and behaviorally relevant levels of oral ethanol intake in rhesus macaques using a flavorant-fade procedure

[Indicators of spontaneous behavior of rhesus monkeys with short-term course alcohol self-administration under free choice]

OBJECTIVE

To analyze spontaneous behavior in 36 male rhesus macaques during formation of alcoholic motivation under free choice.

MATERIAL AND METHODS

The model composed the initiation stage with the provision of an aqueous ethanol solution of increasing concentration from 1 to 4% with a sweetener and restricted access to the tap water supply and the subsequent stage of the formation of alcoholic motivation with a free choice between 4% ethanol solution without sweetener and water. The behavior was recorded by the «One-Zero» method with ethogram compiled in accordance with the behavioral peculiarities of rhesus monkeys when housed individually. Three subgroups of high, medium and low-level ethanol consumption were distinguished.

RESULTS

In the subgroup of high ethanol consumption median consumption was 1.70 g/kg/day at initiation (p<0.05, compared to other subgroups) and 1.79 g/kg/day (p<0.05) at free choice stage. Animals of high consumption subgroup had significantly higher frequency being at the cage bottom and in a sitting posture. We observed significant changes in a number of indicators of spontaneous behavior depending on the level of ethanol consumption, which included displacement behavior, stereotypic behavior and posture of animals. In the high consumption subgroup, there was a significant increase in the frequency of stereotypic behavior, atypical behavior, being on four legs, as well as a decrease in the frequency of being at the back side of the cage and of displacement behavior. At the same time, the inhibitory effect of ethanol on the hypothalamic-pituitary-adrenal system was revealed.

CONCLUSION

In the model of free choice alcohol self-administration rhesus monkeys demonstrate a significant change in a number of indicators of spontaneous behavior depending on the level of ethanol consumption, which includes displacement, stereotypic behaviors and animal posture.

Behavioral effects of ethanol in the Red Swamp Crayfish (Procambarus clarkii)

Alcohol abuse remains one of the primary preventable sources of mortality in the United States. Model species can be used to evaluate behavioral and other biological changes associated with alcohol and to identify novel treatments. This report describes methods for evaluating the behavioral effects of ethanol (EtOH) in crayfish. Crayfish (Procambarus clarkii) were immersed in ethanol concentrations ranging from 0.1 to 1.0 molar, for 10-30 min. Studies evaluated hemolymph alcohol concentration, locomotion in an open field and anxiety-like behavior using a Light/Dark transfer approach. EtOH immersion produced dose-dependent increases in hemolymph EtOH (up to 249 mg/dL) and reductions in open field locomotion that depended on EtOH concentration or exposure duration. Untreated crayfish exhibit avoidance of the open parts of the locomotor arena and a preference for a covered portion. Acute EtOH immersion decreased time spent in the covered portion of the Light/Dark arena, consistent with a decrease in anxiety-like behavior. Daily EtOH immersion for 5 days did not alter locomotor responses, however, activity was increased 3 days after the repeated EtOH regimen. Overall, this study shows that this inexpensive, easily maintained species can be used for behavioral pharmacological experiments designed to assess the acute and repeated effects of EtOH.

GABAB Receptors and Alcohol Use Disorders: Preclinical Studies

Preclinical research over the past several decades has demonstrated a role for the γ-aminobutyric acid_B (GABA_B) receptor in alcohol use disorder (AUD). This chapter offers an examination of preclinical evidence on the role of the GABA_B receptor on alcohol-related behaviors with a particular focus on the GABA_B receptor agonist baclofen, for which effects have been most extensively studied, and positive allosteric modulators (PAMs) of the GABA_B receptor. Studies employing rodent and non-human primate models have shown that activation of the GABA_B receptor can reduce (1) stimulating and rewarding effects of alcohol; (2) signs of alcohol withdrawal in rats made physically dependent on alcohol; (3) acquisition and maintenance of alcohol drinking under a two-bottle alcohol versus water choice procedure; (4) alcohol intake under oral operant self-administration procedures; (5) motivational properties of alcohol measured using extinction and progressive ratio procedures; (6) the increase in alcohol intake after a period of alcohol abstinence (the alcohol deprivation effect or ADE); and (7) the ability of alcohol cues and stress to reinstate alcohol seeking when alcohol is no longer available. Baclofen and GABA_B PAMs reduce the abovementioned behaviors across different preclinical models, which provides strong evidence for a significant role of the GABA_B receptor in alcohol-related behaviors and supports development of medications targeting GABA_B receptors for the treatment of AUD. This chapter highlights the value of examining mechanisms of alcohol-related behaviors across multiple animal models to increase the confidence in identification of new therapeutic targets.

Formation of Alcohol Motivation in Monkeys (Macaca mulatta) Kept in Isolation

The effects of environmental factors (flavors, different ethanol concentration, alcoholic deprivation, and food reinforcement) on the formation of alcohol motivation was studied in rhesus macaques (Macaca mulatta, n=6). Motivation for alcohol intake was induced in two stages: initiation (sessions 1-160) and formation of motivation (sessions 161-516). Monkeys preferred multifruit flavor and 4% ethanol solution, while ethanol deprivation did not stimulate alcohol consumption. The pronounced individual differences in the pattern of alcohol motivation were revealed: the intake of 4% ethanol solution ranged from 0.21±0.03 to 0.43±0.06 g/kg without food reinforcement and increased from 0.78±0.03 to 1.22±0.09 g/kg with food reinforcement. The results suggest that the proposed method is valid and can be used as an experimental model of alcohol dependence in non-human primates.

Strategies to Avoid Replication Failure With Evidence-Based Prevention Interventions: Case Examples From the Strengthening Families Program

Research has found disturbing long-term effects of poor parenting on children's behavioral health including addiction, delinquency, depression/anxiety, and poorer health as adults. Poor parenting practices thus contribute substantially to the health crisis in America. However, skilled, nurturing parents, or caretakers can help youth avoid these developmental problems. A number of family and parenting evidence-based interventions (EBIs) that teach parenting skills are now available for dissemination. Unfortunately, replications of EBIs do not always produce the original positive results. Organizations that seek to use family EBIs to improve parenting and family skills need to avoid practices that create replication failure. We examine several possible factors that contribute to replication failure using examples from five replications of the EBI "Iowa Strengthening Families Program for ages 10-14." We then share six strategies conducive to avoid replication failures including (1) choosing the right program and implementation strategy for the population, (2) administering the right "dosage," (3) choosing and properly training implementers, (4) maintaining program integrity and adherence, (5) ensuring cultural sensitivity, and (6) ensuring accurate and complete reporting of evaluation results. These guidelines can advance prevention science to meet the demands of a growing public health agenda.

Chronic alcohol abuse and HIV disease progression: studies with the non-human primate model

The populations at risk for HIV infection, as well as those living with HIV, overlap with populations that engage in heavy alcohol consumption. Alcohol use has been associated with high-risk sexual behavior and an increased likelihood of acquiring HIV, as well as poor outcome measures of disease such as increased viral loads and declines in CD4+ T lymphocytes among those living with HIV-infections. It is difficult to discern the biological mechanisms by which alcohol use affects the virus:host interaction in human populations due to the numerous variables introduced by human behavior. The rhesus macaque infected with simian immunodeficiency virus has served as an invaluable model for understanding HIV disease and transmission, and thus, provides an ideal model to evaluate the effects of chronic alcohol use on viral infection and disease progression in a controlled environment. In this review, we describe the different macaque models of chronic alcohol consumption and summarize the studies conducted with SIV and alcohol. Collectively, they have shown that chronic alcohol consumption results in higher levels of plasma virus and alterations in immune cell populations that potentiate SIV replication. They also demonstrate a significant impact of chronic alcohol use on SIV-disease progression and survival. These studies highlight the utility of the rhesus macaque in deciphering the biological effects of alcohol on HIV disease. Future studies with this well-established model will address the biological influence of alcohol use on susceptibility to HIV, as well as the efficacy of anti-retroviral therapy.

Chronic periadolescent alcohol consumption produces persistent cognitive deficits in rhesus macaques

Although human alcoholics exhibit lasting cognitive deficits, it can be difficult to definitively rule out pre-alcohol performance differences. For example, individuals with a family history of alcoholism are at increased risk for alcoholism and are also behaviorally impaired. Animal models of controlled alcohol exposure permit balanced group assignment, thereby ruling out the effects of pre-existing differences. Periadolescent male rhesus macaques (N = 5) consumed alcohol during 200 drinking sessions (M-F) across a 10-month period (mean daily alcohol consumption: 1.38 g/kg/day). A control group (N = 5) consumed a fruit-flavored vehicle during the same period. Spatial working memory, visual discrimination learning and retention and response time behavioral domains were assessed with subtests of the Monkey CANTAB (CAmbridge Neuropsychological Test Automated Battery). Spatial working memory performance was impaired in the alcohol group after 120 drinking sessions (6 mo) in a manner that depended on retention interval. The chronic alcohol animals were also impaired in retaining a visual discrimination over 24 hrs when assessed 6-8 weeks after cessation of alcohol drinking. Finally, the presentation of distractors in the response time task impaired the response time and accuracy of the chronic alcohol group more than controls after 6 months of alcohol cessation. Chronic alcohol consumption over as little as 6 months produces cognitive deficits, with some domains still affected after acute (6-8 wks) and lasting (6 mo) discontinuation from drinking. Animals were matched on alcohol preference and behavioral performance prior to exposure, thus providing strong evidence for the causal role of chronic alcohol in these deficits.

Modulation of α5 subunit-containing GABAA receptors alters alcohol drinking by rhesus monkeys

BACKGROUND

Alcohol's ability to potentiate the activity of γ-aminobutyric acid (GABA) at GABAA receptors has been implicated as a key mechanism underlying the behavioral effects of alcohol. The complex molecular biology of these receptors raises the possibility that particular receptor subtypes may play unique roles in alcohol's abuse-related effects and that subtype-selective ligands with therapeutic specificity against alcohol might be developed. This study evaluated the capacity of α5GABAA receptor ligands to alter selectively the reinforcing effects of alcohol.

METHODS

Two groups of rhesus monkeys were trained to orally self-administer alcohol or sucrose under fixed-ratio schedules and limited daily access conditions. In addition, following daily self-administration sessions, the behavior of each monkey was scored for both species-typical and drug-induced behaviors.

RESULTS

Concentrations of 1 to 6% alcohol maintained self-administration above water levels, engendered pharmacologically relevant blood alcohol levels ranging from 90 to 160 mg/dl, and produced changes in behavior typical of alcohol intoxication. Concentrations of 0.3 to 3% sucrose also reliably maintained self-administration. The α5GABAA receptor agonist QH-ii-066 enhanced and the α5GABAA receptor inverse agonist L-655,708 inhibited alcohol, but not sucrose drinking. The changes in alcohol drinking could be reversed with the α5GABAA receptor antagonist XLi-093. However, L-655,708 increased yawning in both alcohol and sucrose drinkers, possibly indicative of an anxiogenic effect.

CONCLUSIONS

These findings suggest a prominent and specific role for α5GABAA receptor mechanisms in the reinforcing effects of alcohol. Moreover, these results suggest that α5GABAA receptors may represent a novel pharmacological target for the development of medications to reduce drinking. Of ligands modulating this receptor, α5GABAA receptor inverse agonists may hold the most promise as alcohol pharmacotherapies.

The influence of acute and chronic alcohol consumption on response time distribution in adolescent rhesus macaques

BACKGROUND

Analysis of the distribution of reaction times (RTs) in behavioral tasks can illustrate differences attributable to changes in attention, even when no change in mean RT is observed. Detrimental attentional effects of both acute and chronic exposure to alcohol may therefore be revealed by fitting RT data to an ex-Gaussian probability density function which identifies the proportion of long-RT responses.

METHODS

Adolescent male rhesus macaques completed a 5-choice serial reaction time task (5CSRT) after acute alcohol consumption (up to 0.0, 1.0 and 1.5 g/kg). Monkeys were next divided into chronic alcohol (N = 5) and control groups (N = 5); the experimental group consumed 1.5-3.0 g/kg alcohol for 200 drinking sessions. Unintoxicated performance in the 5CSRT task was determined systematically across the study period and the effect of acute alcohol was redetermined after the 180th drinking session. The effect of extended abstinence from chronic alcohol was determined across 90 days.

RESULTS

Acute alcohol exposure dose-dependently reduced the probability of longer RT responses without changing the mean or the standard deviation of the RT distribution. The RT distribution of control monkeys tightened across 10 months whereas that of the chronic alcohol group was unchanged. Discontinuation from chronic alcohol increased the probability of long RT responses with a difference from control animals observed after 30 days of discontinuation.

CONCLUSIONS

Alcohol consumption selectively affected attention as reflected in the probability of long RT responses. Acute alcohol consumption focused attention, chronic alcohol consumption impaired the maturation of attention across the study period and alcohol discontinuation impaired attention.

Acute ethanol reduces reversal cost in discrimination learning by reducing perseverance in adolescent rhesus macaques

BACKGROUND

Acute alcohol exposure produces cognitive deficits in adults but less is known about the acute cognitive effects of alcohol in adolescents. The cognitive impact of acute alcohol exposure includes deficits in discrimination and reversal learning, but traditional experimental approaches make it difficult to distinguish the effect of alcohol on discrimination learning from the effect of alcohol on reversal learning. Young rhesus macaques can be used to model some aspects of human adolescence because of their anatomical, neurophysiological, and cognitive similarities with humans.

METHODS

Adolescent male rhesus monkeys (n = 10) were trained to respond to visual stimuli on touch-sensitive LCD panels controlled by the nonhuman primate version of CANTAB software. Discrimination and reversal learning tasks were subsequently assessed after monkeys were allowed to consume varying amounts of ethanol (EtOH) in a flavored vehicle (vehicle only, up to 0.5 g/kg EtOH, up to 1.0 g/kg EtOH, and up to 1.5 g/kg EtOH).

RESULTS

Acute exposure to EtOH reduced perseverance, increased response accuracy, and reduced errors during reversal learning when the task was completed within 90 minutes of EtOH consumption. No reduction in reversal errors was observed when EtOH was consumed 3 or 24 hours prior to reversal learning. EtOH only impaired discrimination learning when monkeys had very little previous EtOH exposure.

CONCLUSIONS

The temporal relationship between EtOH consumption and reversal learning was consistent with selective EtOH-induced impairment of retrieval, but not storage, processes. This was evidenced by diminished perseverance on the previously correct stimulus leading to decreased errors to criterion.

Mephedrone (4-methylmethcathinone) and d-methamphetamine improve visuospatial associative memory, but not spatial working memory, in rhesus macaques

BACKGROUND AND PURPOSE

The novel cathinone derivative 4-methylmethcathinone (4-MMC; mephedrone) is increasingly popular with recreational users. Little scientific information is available but users report both entactogen-like and classic stimulant-like subjective properties. A recent study in humans reported psychomotor speed improvement after intranasal 4-MMC suggesting classic stimulant properties. Limitations of the user group (which was impaired on some tasks) prompt controlled laboratory investigation.

EXPERIMENTAL APPROACH

Adult male rhesus monkeys were trained to perform tasks from the non-human primate Cambridge Neuropsychological Test Automated Battery, which assess spatial working memory, visuospatial associative memory, learning and motivation for food reward. Test of bimanual motor coordination and manual tracking were also included. The subjects were challenged with 0.178-0.56 mg·kg(-1) 4-MMC and 0.056-0.56 mg·kg(-1) d-methamphetamine (MA), i.m., in randomized order for behavioural evaluation.

KEY RESULTS

A pronounced improvement in visuospatial memory and learning was observed after the 0.32 mg·kg(-1) dose of each compound, this effect was confirmed with subsequent repetition of these conditions. Spatial working memory was not improved by either drug, and the progressive ratio, bimanual motor and rotating turntable tasks were all disrupted in a dose-dependent manner.

CONCLUSIONS AND IMPLICATIONS

These studies show that 4-MMC produces behavioural effects, including improvements in complex spatial memory and learning that are in large part similar to those of MA in non-human primates. Thus, the data suggest that the effects of 4-MMC in monkeys can be classified with classical psychomotor stimulants.

Upregulation of cathepsin D in the caudate nucleus of primates with experimental parkinsonism

BACKGROUND

In Parkinson's disease there is progressive loss of dopamine containing neurons in the substantia nigra pars compacta. The neuronal damage is not limited to the substantia nigra but progresses to other regions of brain, leading to loss of motor control as well as cognitive abnormalities. The purpose of this study was to examine causes of progressive damage in the caudate nucleus, which plays a major role in motor coordination and cognition, in experimental Parkinson's disease.

RESULTS

Using chronic 1-methyl-4phenyl-1,2,3,6-tetrahydropyridine treatment of rhesus monkeys to model Parkinson's disease, we found a upregulation of Cathepsin D, a lysosomal aspartic protease, in the caudate nucleus of treated monkeys. Immunofluorescence analysis of caudate nucleus brain tissue showed that the number of lysosomes increased concurrently with the increase in Cathepsin D in neurons. In vitro overexpression of Cathepsin D in a human neuroblastoma cell line led to a significant increase in the number of the lysosomes. Such expression also resulted in extralysosomal Cathepsin D and was accompanied by significant neuronal death associated with caspase activation. We examined apoptotic markers and found a strong correlation of Cathepsin D overexpression to apoptosis.

CONCLUSIONS

Following damage to the substantia nigra resulting in experimental Parkinson's disease, we have identified pathological changes in the caudate nucleus, a likely site of changes leading to the progression of disease. Cathepsin D, implicated in pathogenic mechanisms in other disorders, was increased, and our in vitro studies revealed its overexpression leads to cellular damage and death. This work provides important clues to the progression of Parkinson's, and provides a new target for strategies to ameliorate the progression of this disease.

Chronic alcohol consumption impairs visuo-spatial associative memory in periadolescent rhesus monkeys

Alcohol abuse in the adult is often preceded by high alcohol consumption during adolescence. Profound changes in brain structure and function occur during this developmental period, therefore alcohol may impact essential cognitive skill development during the formal educational years. The objective of this study was to determine if chronic oral alcohol intake slows acquisition and performance of cognitive tasks in male adolescent rhesus monkeys. Treatment groups (Alcohol, N=4; Control, N=3) were evaluated on bimanual dexterity and tests of visuo-spatial memory and learning adapted from the Cambridge Neuropsychological Test Automated Battery. Animals were trained daily in 30 min sessions and had subsequent access to alcohol/Tang® solutions (Alcohol group) or Tang® only (Control group) Monday through Friday for 11 months. Recordings of brainstem auditory evoked potentials (BSAEP) were conducted periodically before and during the chronic drinking.

RESULTS

Chronic alcohol drinking (ave of 1.78 g/kg alcohol per session) impaired behavioral performance assessed ∼22 h after the prior drinking session. The Alcohol group required more trials than the Control group to reach criterion on the visuo-spatial memory task and showed increased sensitivity to trial difficulty and retention interval. Alcohol animals also had slowed initial acquisition of the bimanual task. The latency of P4 and P5 BSAEP peaks were also delayed in the Alcohol group. Chronic alcohol consumption impaired the acquisition and performance of a spatial memory task and disrupted brainstem auditory processing, thus these results show that repeated alcohol exposure in adolescence interferes with a range of brain functions including complex visuo-spatial mnemonic processing.

The acute impact of ethanol on cognitive performance in rhesus macaques

Decreased cognitive control over prepotent responses has been hypothesized to contribute to ethanol-induced behavioral disinhibition. However, the effects of ethanol on specific cognitive domains associated with decision making have not been extensively studied. We examined the impact of acute ethanol administration on cognitive performance of nonhuman primates. Studies were conducted using 0.2, 0.5, and 1 g/kg intravenous ethanol in rhesus macaques performing touch screen-based tasks examining stimulus discrimination, stimulus reversal, and stimulus response performance. The impact on attentional processing was also evaluated. Ethanol reduced the accuracy of reversal performance marginally at 0.2 g/kg and significantly at 0.5 g/kg. This effect was selective given an absence of impairment on the stimulus discrimination and stimulus response tasks at these doses. Performance on stimulus discrimination was impaired at 1.0 g/kg, which prevented determination of reversal performance. Analysis of post-error response times demonstrated that error processing was impaired at both 0.2 and 0.5 g/kg. Ethanol also increased the number of omissions and delayed responses on an attentional task, suggesting more frequent attentional lapses. These data demonstrate that cognitive function mediated by specific prefrontal cortical brain regions is particularly sensitive to ethanol and suggest specific cognitive mechanisms that may underlie harmful decisions made at low doses of ethanol.

Long-lasting reduction in hippocampal neurogenesis by alcohol consumption in adolescent nonhuman primates

Binge alcohol consumption in adolescents is increasing, and studies in animal models show that adolescence is a period of high vulnerability to brain insults. The purpose of the present study was to determine the deleterious effects of binge alcohol on hippocampal neurogenesis in adolescent nonhuman primates. Heavy binge alcohol consumption over 11 mo dramatically and persistently decreased hippocampal proliferation and neurogenesis. Combinatorial analysis revealed distinct, actively dividing hippocampal neural progenitor cell types in the subgranular zone of the dentate gyrus that were in transition from stem-like radial glia-like cells (type 1) to immature transiently amplifying neuroblasts (type 2a, type 2b, and type 3), suggesting the evolutionary conservation of milestones of neuronal development in macaque monkeys. Alcohol significantly decreased the number of actively dividing type 1, 2a, and 2b cell types without significantly altering the early neuronal type 3 cells, suggesting that alcohol interferes with the division and migration of hippocampal preneuronal progenitors. Furthermore, the lasting alcohol-induced reduction in hippocampal neurogenesis paralleled an increase in neural degeneration mediated by nonapoptotic pathways. Altogether, these results demonstrate that the hippocampal neurogenic niche during adolescence is highly vulnerable to alcohol and that alcohol decreases neuronal turnover in adolescent nonhuman primate hippocampus by altering the ongoing process of neuronal development. This lasting effect, observed 2 mo after alcohol discontinuation, may underlie the deficits in hippocampus-associated cognitive tasks that are observed in alcoholics.

Chronic alcohol consumption generates a vulnerable immune environment during early SIV infection in rhesus macaques

BACKGROUND

Alcohol consumption is a common problem in HIV-infected individuals, and the effects of alcohol may alter the efficiency of the immune response, potentially aggravating the disease as well as affecting end organs, such as the brain. However, the elements of the virus-host interaction that are modulated by ethanol are poorly dissected.

METHODS

Ethanol intake was conditioned in rhesus macaques prior to SIV infection, in order to mimic this common human behavior, and allow the evaluation of aspects of the virus-immune system interactions during acute time-points, when important facets of the infection are set up and when virus reproducibly enters the brain.

RESULTS

Although ethanol had a limited effect on the acute plasma viral load, it resulted in reduced circulating memory CD4(+) T cells and increased levels of monocytes expressing the viral coreceptor CCR5. In organs, ethanol consumption impacted immune cells in the liver as well as lymphoid and other nonlymphoid tissues, where CD4(+) T cells were predominantly affected.

CONCLUSION

Overall, the consumption of alcohol causes immune cell alterations that can contribute to the generation of a disease susceptible environment upon SIV infection.

Consistent, high-level ethanol consumption in pig-tailed macaques via a multiple-session, limited-intake, oral self-dosing procedure

BACKGROUND

Alcohol abuse is a major public health burden that can lead to many adverse health effects such as impaired hepatic, gastrointestinal, central nervous system and immune system function. Preclinical animal models of alcohol abuse allow for experimental control over variables often difficult to control in human clinical studies (e.g., ethanol exposure before or during the study, history of other drug use, access to medical care, nutritional status, etc). Nonhuman primate models in particular provide increased genetic, anatomic and physiologic similarity to humans, relative to rodent models. A small percentage of macaques will spontaneously consume large quantities of ethanol; however, most nonhuman primate models of "voluntary" ethanol intake produce relatively low daily ethanol intake in the majority of monkeys.

METHODS

To facilitate study of chronic exposure to high levels of ethanol intake, a macaque model has been developed that induces consistent, daily high-level ethanol consumption. This multiple-session procedure employed 4 drinking sessions per day, with sessions occurring once every 6 hours.

RESULTS

The group average alcohol consumption was 4.6 g/kg/d (SEM 0.4), roughly twice the group average consumption of previous reports. Ethanol drinking sessions produced group mean blood ethanol levels of 95 mg/dl after 60 minutes, and fine motor control was impaired up to 90 minutes after a drinking session.

CONCLUSION

This model of multiple-session, limited access, oral ethanol self-dosing produced consistent, high-level ethanol consumption with each session qualifying as a "binge" drinking session using the definition of "binge" provided by the NIAAA (>80 mg/dl/session). This model of ethanol drinking in macaques will be of great utility in the study of immunological, physiological and behavioral effects of ethanol in nonhuman primates.

Dissociation of alcohol-seeking and consumption under a chained schedule of oral alcohol reinforcement in baboons

BACKGROUND

Initiation and maintenance of compulsive alcohol drinking involves a sequence of behaviors which occur in the presence of environmental cues. Animal models using chained schedules of alcohol reinforcement may be useful for examining the complex interactions between cues and alcohol-seeking and -consumption.

METHODS

Four baboons self-administered alcohol under a 3-component chained schedule of reinforcement; distinct cues were presented in the context of different behavioral contingencies associated with gaining access to 4% w/v alcohol (alcohol-seeking) and concluding with alcohol self-administration. First, the response strength of alcohol-related seeking responses was evaluated using a between-sessions progressive ratio (PR) procedure in which the response requirement to initiate the final contingency and gain access to the daily supply of alcohol was increased each session. The highest response requirement completed that resulted in alcohol access was defined as the breaking point (BP). Second, water was substituted for alcohol and PR procedures were repeated. The effects of increasing the "seeking" response requirement on subsequent alcohol or water consumption were also determined.

RESULTS

When alcohol was available, operant responses to gain access to and self-administer alcohol were maintained. When water was substituted for alcohol, alcohol-related cues continued to maintain alcohol-seeking responses. However, higher BPs, higher rates of self-administration and higher volumes of intake occurred when alcohol was available compared with water. Increasing the response requirement to gain access to alcohol did not reduce alcohol consumption (total alcohol intake).

CONCLUSIONS

These results show that alcohol-related cues maintained alcohol-seeking even after a prolonged period of only water availability. Cue-maintained alcohol-seeking behavior can be dissociated from subsequent alcohol consumption.

Who is at risk? Population characterization of alcohol self-administration in nonhuman primates helps identify pathways to dependence

Alcohol abuse and dependence are human conditions for which no full equivalent exists in animals. Nevertheless, animal models frequently are used to study various aspects of alcohol dependence that cannot be easily or ethically assessed in humans, including neurobiological mechanisms underlying alcohol dependence. Many of these animal models involve rodents; however, the characteristics (i.e., phenotypes) of chronic heavy drinking may be limited in these species. Nonhuman primates add an important translational aspect to the study of alcohol abuse and alcoholism. Their genetic, anatomical, physiological, and behavioral similarity to humans offers unique opportunities for identifying risk factors that may predispose a person to or accelerate the course of alcohol addiction. Studying alcohol consumption in nonhuman primates, including the distribution of drinking levels in a population, also can be uniquely informative to alcohol research. For example, research on the self-administration procedures in primates can help scientists identify risk factors for excessive alcohol consumption in humans. The phenotype of excessive drinking then can serve as the starting point to test and verify the underlying genetic and environmental influences. The resulting findings, in turn, can help guide prevention and treatment strategies.

Neuroimmunity, drugs of abuse, and neuroAIDS

It has long been postulated that drugs of abuse may represent significant cofactors in the progression of human immunodeficiency virus (HIV)-induced disease. Both HIV infection and drugs of abuse have significant effect on the immune system as well as on the nervous system. In HIV infection, abnormalities in these systems intersect to lead to a constellation of symptoms known as neuroAIDS. Drugs of abuse may synergize with such damage, acting on immune and/or neural cells. However, definitive epidemiological evidence for such an interaction is lacking. Here we review such studies as well as the use of the nonhuman primate/simian immunodeficiency virus system to investigate the interaction of neuroAIDS with drugs of abuse. Furthermore, recent findings on mechanisms of actions of selected drugs reveal the possibility of protective as well as detrimental effects on the central nervous system damage induced by HIV.

Robust and stable drinking behavior following long-term oral alcohol intake in rhesus macaques

Face validity in animal models of alcohol abuse and dependence is often at odds with robust demonstrations of ethanol-seeking. This study determined the relative influence of ethanol and a flavorant in maintaining ethanol intake in a nonhuman primate model of "cocktail" drinking. Four-year-old male monkeys were maintained on a 6% ethanol/6% Tang solution made available in daily (M-F) 1-h sessions. Experiments determined the effect of (1) a second daily access session, (2) concurrent presentation of the Tang vehicle, (3) sequential presentation of the vehicle in the first daily session and the ethanol solution in the second session, (4) altering the Tang concentration, (5) altering the ethanol concentration, and (6) removal of the flavorant. Mean daily intake (2.7+/-0.2 g/kg/day) was stable over 7 months. Simultaneous availability of a large, but not a low-moderate, volume of the vehicle reduced ethanol intake by about 50%. Decreasing the concentration of Tang in the first daily session reduced ethanol intake, whereas intake of the standard solution was increased in the second session. Ethanol consumption was decreased by only 27% when the flavorant was removed. In summary, alterations that reduced intake in the first daily session resulted in compensatory increases in ethanol intake in the second session, suggesting that animals sought a specific level of ethanol intake per day. It is concluded that models with excellent face validity (flavored beverages) can produce reliable ethanol intake in patterns that are highly consistent with ethanol-seeking behavior.

Oral administration of (+/-)3,4-methylenedioxymethamphetamine and (+)methamphetamine alters temperature and activity in rhesus macaques

RATIONALE

Emergency Department visits and fatalities in which (+/-)3,4-methylenedioxymethamphetamine (MDMA) or (+)methamphetamine (METH) are involved frequently feature unregulated hyperthermia. MDMA and METH significantly elevate body temperature in multiple laboratory species and, most importantly, can also produce unregulated and threatening hyperthermia in nonhuman primates. A majority of prior animal studies have administered drugs by injection whereas human consumption of "Ecstasy" is typically oral, an important difference in route of administration which may complicate the translation of animal data to the human condition.

OBJECTIVE

To determine if MDMA and METH produce hyperthermia in monkeys following oral administration as they do when administered intramuscularly.

METHODS

Adult male rhesus monkeys were challenged intramuscularly (i.m.) and per os (p.o.) with 1.78 or 5 mg/kg (+/-)MDMA and with 0.1 or 0.32 mg/kg (+)METH. Temperature and activity were monitored with a radiotelemetry system.

RESULTS

Oral administration of either MDMA or METH produced significant increases in body temperature. Locomotor activity was suppressed by MDMA and increased by METH following either route of administration.

CONCLUSIONS

The data show that the oral route of administration is not likely to qualitatively reduce the temperature increase associated with MDMA or METH although oral administration did slow the rate of temperature increase. It is further established that MDMA reduces activity in monkeys even after relatively high doses and oral administration.

Battle of animal models

This is a brief summary of the animal models session held during the 12th Annual Meeting of the Society on NeuroImmune Pharmacology, Santa Fe, NM, USA. This session provided important information for participants on availability and utility of animal models for the studies of HIV-1 central nervous system infection and drug abuse. It highlighted animal model relevance to human disease/condition, its utility for the studies of pathogenesis, potential importance for the development of therapeutics, and demonstrated limitations/pitfalls.

Differential contributions of dopaminergic D1- and D2-like receptors to cognitive function in rhesus monkeys

RATIONALE

Dopaminergic neurotransmission is critically involved in many aspects of complex behavior and cognition beyond reward/reinforcement and motor function. Mental and behavioral disorders associated with major disruptions of dopamine neurotransmission, including schizophrenia, attention deficit/hyperactivity disorder, Parkinson's disease, Huntington's disease, and substance abuse produce constellations of neuropsychological deficits in learning, memory, and attention in addition to other defining symptoms.

OBJECTIVE

To delineate the role dopaminergic D1- and D2-like receptor subtypes play in complex brain functions.

MATERIALS AND METHODS

Monkeys (N = 6) were trained on cognitive tests adapted from a human neuropsychological assessment battery (CAmbridge Neuropsychological Test Automated Battery). The battery included tests of spatial working memory (self-ordered spatial search task), visuo-spatial associative memory and learning (visuo-spatial paired associates learning task, vsPAL) and motivation (progressive ratio task, PR). Tests of motor function (bimanual motor skill task, BMS; rotating turntable task, RTT) were also included. The effects of the dopamine D2-like antagonist raclopride (10-56 microg/kg, i.m.) and the D1-like antagonist SCH23390 (SCH, 3.2-56 microg/kg, i.m.) on cognitive performance were then determined.

RESULTS

Deficits on PR, RTT, and BMS performance were observed after both raclopride and SCH23390. Spatial working memory accuracy was reduced to a greater extent by raclopride than by SCH, which was unexpected, given prior reports on the involvement of D1 signaling for spatial working memory in monkeys. Deficits were observed on vsPAL performance after raclopride, but not after SCH23390.

CONCLUSIONS

The intriguing results suggest a greater contribution of D2- over D1-like receptors to both spatial working memory and object-location associative memory.

Effects of (+/-)3,4-methylenedioxymethamphetamine, (+/-)3,4-methylenedioxyamphetamine and methamphetamine on temperature and activity in rhesus macaques

Severe and malignant hyperthermia is a frequently reported factor in emergency department (ED) visits and fatalities in which use of amphetamine drugs, such as (+/-)3,4-methylenedioxymethamphetamine (MDMA), (+/-)3,4-methylenedioxyamphetamine (MDA) and (+)methamphetamine (METH), is confirmed. Individuals who use "ecstasy" are also often exposed, intentionally or otherwise, to several of these structurally-related compounds alone or in combination. In animal studies the degree of (subcritical) hyperthermia is often related to the severity of amphetamine-induced neurotoxicity, suggesting health risks to the human user even when emergency medical services are not invoked. A clear distinction of thermoregulatory risks posed by different amphetamines is therefore critical to understand factors that may produce medical emergency related to hyperthermia. The objective of this study was therefore to determine the relative thermoregulatory disruption produced by recreational doses of MDMA, MDA and METH in nonhuman primates. Body temperature and spontaneous home cage activity were monitored continuously in six male rhesus monkeys via radiotelemetric devices. The subjects were challenged intramuscularly with 0.56-2.4 mg/kg MDMA, 0.56-2.4 mg/kg MDA and 0.1-1.0 mg/kg METH. All three amphetamines significantly elevated temperature; however the time course of effects differed. The acute effect of METH lasted hours longer than MDA or MDMA and a disruption of nighttime circadian cooling was observed as long as 18 h after 1.0 mg/kg METH and 1.78-2.4 mg/kg MDA, but not after MDMA. Activity levels were only reliably increased by 0.32 mg/kg METH. It is concluded that while all three substituted amphetamines produce hyperthermia in rhesus monkeys, the effects do not depend on elevated locomotor activity and exhibit differences between compounds. The results highlight physiological risks posed both by recreational use of the amphetamines and by current trials for clinical MDMA use.