Genetics of responses to drugs of abuse

Hippocampal-Dependent Inhibitory Learning and Memory Processes in the Control of Eating and Drug Taking

As manifestations of excessive and uncontrolled intake, obesity and drug addiction have generated much research aimed at identifying common neuroadaptations that could underlie both disorders. Much work has focused on changes in brain reward and motivational circuitry that can overexcite eating and drug-taking behaviors. We suggest that the regulation of both behaviors depends on balancing excitation produced by stimuli associated with food and drug rewards with the behavioral inhibition produced by physiological "satiety" and other stimuli that signal when those rewards are unavailable. Our main hypothesis is that dysregulated eating and drug use are consequences of diet- and drug-induced degradations in this inhibitory power. We first outline a learning and memory mechanism that could underlie the inhibition of both food and drug-intake, and we describe data that identifies the hippocampus as a brain substrate for this mechanism. We then present evidence that obesitypromoting western diets (WD) impair the operation of this process and generate pathophysiologies that disrupt hippocampal functioning. Next, we present parallel evidence that drugs of abuse also impair this same learning and memory process and generate similar hippocampal pathophysiologies. We also describe recent findings that prior WD intake elevates drug self-administration, and the implications of using drugs (i.e., glucagon-like peptide- 1 agonists) that enhance hippocampal functioning to treat both obesity and addiction are also considered. We conclude with a description of how both WD and drugs of abuse could initiate a "vicious-cycle" of hippocampal pathophysiology and impaired hippocampal-dependent behavioral inhibition.

Subjective alcohol effects and drinking behavior: the relative influence of early response and acquired tolerance

OBJECTIVES

(1) To establish the reliability and validity of a modified version of the Self-Rating of Alcohol (SRE) form. (2) To differentiate early subjective alcohol response (SR) from acquired tolerance in the prediction of drinking outcomes.

METHOD

353 undergraduates completed an online survey. SR was assessed using the SRE form and a modified SRE including items assessing global stimulant and sedative effects. The Daily Drinking Questionnaire-Revised (DDQ-R), and the Rutgers Alcohol Problems Index (RAPI) assessed alcohol use and problems, respectively.

RESULTS

The revised version of the SRE showed good internal consistency and incremental validity. Early SR assessed by the modified SRE was consistently associated with use and problems. Acquired tolerance was significantly related to use and problems above and beyond early SR.

CONCLUSIONS

The modified SRE incorporating stimulant and sedative responses demonstrated good psychometric properties and the potential to capture unique variability in drinking outcomes. Differentiating early SR from tolerance showed that each contributes uniquely to drinking behavior and problems. Thus, future studies would benefit from examining the unique contribution of each aspect of SR.

Different effects of stress on alcohol drinking behaviour in male and female mice selectively bred for high alcohol preference

AIMS

The purpose of the present study was to examine the effects of stress on alcohol drinking behaviour in male and female mice with a genetic predisposition toward high alcohol preference (HAP2 line).

METHODS

Alcohol-naïve male (n = 22) and female (n = 23) HAP2 mice were assigned to a restraint stress or no stress control group. Stress was initially applied for 2 h per day on 10 consecutive days. All mice were then given daily 2 h limited-access to a 10% v/v alcohol solution or water, with food freely available, for 21 days. Over the next 20 days, 2 h restraint stress was applied every other day immediately prior to 2 h access to alcohol and water. On intervening days, all mice received 2 h access to alcohol and water in the absence of stress. Following this phase of the study, the effects of restraint stress on acoustic startle reactivity was assessed in all mice. Finally, all mice were given continuous access to alcohol and water for 8 days.

RESULTS

Ten days of prior stress exposure did not significantly alter the acquisition of limited-access alcohol drinking. Subsequent exposures to intermittent restraint stress produced subtle but consistent effects on alcohol intake that differed in males vs females: stress increased alcohol intake in males and decreased alcohol intake in females. Restraint stress did not alter acoustic startle reactivity. Under continuous-access conditions after stress termination, the stress-induced increase in alcohol intake in males became more robust; however, in females, alcohol intake returned to the control group level.

CONCLUSIONS

These findings suggest that the effects of stress on alcohol drinking in mice with a genetic predisposition toward high alcohol preference depend on sex.

Further evidence of an inverse genetic relationship between innate differences in alcohol preference and alcohol withdrawal magnitude in multiple selectively bred rat lines

BACKGROUND

We have previously shown that a genetic association exists between low alcohol drinking and high alcohol withdrawal magnitude after acute alcohol exposure in alcohol-naïve rats. However, the behavioral rating scale used in this prior study was not optimal for assessing the magnitude of mild alcohol withdrawal. The present study examined whether a genetic relationship is again found between alcohol preference and alcohol withdrawal magnitude when a sensitive measure is used to index mild alcohol withdrawal in rats.

METHODS

Alcohol-naïve, male rats selectively bred for alcohol preference (P, HAD1, HAD2) or nonpreference (NP, LAD1, LAD2) received a single intragastric infusion of alcohol (4.0 g/20.3 ml/kg body weight; 25% v/v) or water followed by acoustic startle testing.

RESULTS

Startle probability and magnitude was greater in water-treated P than in water-treated NP rats. During alcohol withdrawal, startle probability and magnitude was suppressed in P rats and elevated in NP rats relative to water-treated controls. Startle probability and magnitude was greater in water-treated LAD1 rats than in water-treated HAD1 rats. During alcohol withdrawal, startle probability and magnitude was suppressed in HAD1 and elevated in LAD1 rats relative to water-treated controls at 20 hr after acute alcohol exposure. Startle probability and magnitude did not differ between water-treated HAD2 and water-treated LAD2 rats. During alcohol withdrawal, there was a trend toward decreased startle probability and magnitude in HAD2 rats compared with water-treated controls.

CONCLUSIONS

The acoustic startle response to a tone stimulus is a sensitive measure of mild alcohol withdrawal in rats. Rats selectively bred for low alcohol intake showed greater alcohol withdrawal magnitude than did rats selectively bred for high alcohol intake. These results provide further evidence that an inverse genetic association exists between alcohol withdrawal magnitude and propensity toward alcohol drinking in rats.

Differences between alcohol-preferring (AA) and alcohol-avoiding (ANA) rats in the prodynorphin and proenkephalin systems

The motivation to drink alcohol and the eventual risk of becoming addicted are in part genetically determined. Because opioid peptides are considered central to motivated behaviors, we have analyzed opioid peptides in relevant areas of the brain of two outbred lines of rats: the alcohol-preferring [Alko Alcohol (AA)] line who voluntarily drink alcohol and the alcohol-avoiding [Alko Non-Alcohol (ANA)] line with negligible intake. (Met)enkephalinArg6Phe7 (MEAP) was measured as a marker of proenkephalin, and dynorphin A, dynorphin B, and (Leu)enkephalinArg6 as markers of the prodynorphin system. The major line differences and effects of alcohol intake were observed in mesolimbic brain areas. The mesolimbic dopamine pathway, which projects from the ventral tegmental area (VTA) to the nucleus accumbens, is central in the reward system. Basal levels of MEAP and dynorphin peptides were low in the nucleus accumbens of AA rats, whereas (Leu)enkephalinArg6 levels were lower in the VTA of these rats. Alcohol drinking caused MEAP levels in the accumbens to rise, but had no effect on prodynorphin peptides. Opioids also influence the nigrostriatal dopamine pathway. However, this study showed no significant differences for any peptide between rat lines, or effect of alcohol intake, in either substantia nigra or striatum, except for a decrease of nigral and striatal (Leu)enkephalinArg6 levels in alcohol-drinking AA rats. Large line differences were observed in the pituitary gland. AA rats had high basal levels of MEAP, which became even higher after voluntary alcohol consumption for 4 weeks, and low levels of dynorphin peptides, not affected by alcohol drinking.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol elimination among different racial groups

This study examined the relationship between ethanol elimination and race, specifically exploring differences among Alaskan Natives, American Indians, and whites. Native Americans, believed to be of recent Asian origin, were expected to eliminate alcohol faster than whites. The data suggested that both Native American men and women eliminated alcohol faster than whites. A relationship was also found between age, gender, and rate of alcohol elimination. The implications of these findings were reviewed and specific needs for future research were noted.