The relationship between age at first drug use and teenage drug use liability

Notes on Three Decades of Methodology Workshops

Since 1987, a group of behavior geneticists have been teaching an annual methodology workshop on how to use state-of-the-art methods to analyze genetically informative data. In the early years, the focus was on analyzing twin and family data, using information of their known genetic relatedness to infer the role of genetic and environmental factors on phenotypic variation. With the rapid evolution of genotyping and sequencing technology and availability of measured genetic data, new methods to detect genetic variants associated with human traits were developed and became the focus of workshop teaching in alternate years. Over the years, many of the methodological advances in the field of statistical genetics have been direct outgrowths of the workshop, as evidence by the software and methodological publications authored by workshop faculty. We provide data and demographics of workshop attendees and evaluate the impact of the methodology workshops on scientific output in the field by evaluating the number of papers applying specific statistical genetic methodologies authored by individuals who have attended workshops.

Individual differences in cocaine conditioned taste aversion are developmentally stable and independent of locomotor effects of cocaine

Drugs of abuse induce complex motivational states in their users which have been shown to vary developmentally. In addition to developmental variation, interindividual variation in the rewarding and aversive effects of drugs of abuse is an important consideration. A rat model was used to assess whether the conditioned rewarding/aversive effects of cocaine were maintained as individuals matured from adolescence into adulthood. We tested rats in the cocaine conditioned taste aversion task as adolescents and again in adulthood. We observed a wide range of approach/avoidance behaviors in this task, and also observed that the relative interindividual differences in approach/avoidance are remarkably stable across the two developmental stages. Furthermore, we observed that these interindividual differences are not attributable to individual differences in cocaine-induced locomotor effects or individual differences in blood or brain cocaine levels. Taken together, these findings indicate that sensitivity to cocaine’s motivational effects is stable across development and part of a unique neurological process.

Role of individual and developmental differences in voluntary cocaine intake in rats

RATIONALE

Early-onset drug taking is associated with increased likelihood of addiction, but it is unclear whether early onset is causal in development of addiction. Many other factors are associated with increased risk of addiction and also promote early intake. Here, a rodent model is used to explore the causality of early onset in development of self-administration and addiction-like behavior and to examine factors that promote self-administration.

METHODS

We used cocaine self-administration to examine drug taking and addiction-like behavior in adolescent and adult rats a priori characterized for their locomotor responses to novelty and cocaine and behavior in the light-dark task.

RESULTS

Adolescent animals initially sought more cocaine than adults. However, as the adolescents matured, their intake fell and they did not differ from adults in terms of unreinforced lever-pressing, extinction or reinstatement behavior. For both age groups, self-administration was positively correlated with the locomotor response to novelty, the locomotor response to cocaine, and with time in light in the light-dark task. The rats that were insensitive to cocaine's locomotor effects and that spent the least time in light in the light-dark task sought the least cocaine, appearing to be "protected" from the reinforcing effects of cocaine. There was no difference between the two age groups in appearance of this "protected" phenotype.

CONCLUSIONS

These results suggest that early onset of drug taking may promote increased use, but does not promote progression to addiction-like behavior. Furthermore, protective factors, such as innate anxiety and insensitivity to cocaine's pharmacological effects, function across developmental stages.

Are adolescents more vulnerable to drug addiction than adults? Evidence from animal models

BACKGROUND AND RATIONALE

Epidemiological evidence suggests that people who begin experimenting with drugs of abuse during early adolescence are more likely to develop substance use disorders (SUDs), but this correlation does not guarantee causation. Animal models, in which age of onset can be tightly controlled, offer a platform for testing causality. Many animal models address drug effects that might promote or discourage drug intake and drug-induced neuroplasticity.

METHODS

We have reviewed the preclinical literature to investigate whether adolescent rodents are differentially sensitive to rewarding, reinforcing, aversive, locomotor, and withdrawal-induced effects of drugs of abuse.

RESULTS AND CONCLUSIONS

The rodent model literature consistently suggests that the balance of rewarding and aversive effects of drugs of abuse is tipped toward reward in adolescence. However, increased reward does not consistently lead to increased voluntary intake: age effects on voluntary intake are drug and method specific. On the other hand, adolescents are consistently less sensitive to withdrawal effects, which could protect against compulsive drug seeking. Studies examining neuronal function have revealed several age-related effects but have yet to link these effects to vulnerability to SUDs. Taken together, the findings suggest factors which may promote recreational drug use in adolescents, but evidence relating to pathological drug-seeking behavior is lacking. A call is made for future studies to address this gap using behavioral models of pathological drug seeking and for neurobiologic studies to more directly link age effects to SUD vulnerability.

Factor structure of the Comprehensive Adolescent Severity Inventory (CASI): results of reliability, validity, and generalizability analyses

This article describes the results of psychometric work conducted on the Comprehensive Adolescent Severity Inventory (CASI) among 205 in-treatment substance-abusing adolescents. Four dimensions, each composed of component subscales, resulted from standard psychometric analyses: Chemical Dependency, Psychosocial Functioning, Delinquency, and Risk Behavior. Each dimension had high internal consistency (alpha coefficients for the component subscales comprising each clinical dimension range from .78 to .96) and test-retest reliability (intraclass correlation coefficients range from .88 to .96 and all are significant at p < .0001.). Concurrent validity and specificity of the CASI dimensions also were found: significant and substantial variance in NIMH Diagnostic Interview Schedule for Children-Revised (DISC-IV) and Brief Symptom Inventory (BSI) scores was associated with relevant CASI dimensions; CASI dimensions that theoretically should show no significant relationship with divergent pathology were not associated. The dimensions forecasted substantial variance in adolescent functioning posttreatment discharge, supporting predictive validity. Finally, the dimensional clinical structure was found to be generalizable over male and female adolescents, younger and older adolescents, and adolescents from different ethnic groups. These results provide further evidence for the CASI's promise in research and practice as an adolescent-specific assessment instrument that comprehensively assesses multidimensional areas of functioning within a developmental context of measurement. Limitations of the study along with future work currently being conducted on the CASI are discussed.

Effects of periadolescent versus adult cocaine exposure on cocaine conditioned place preference and motor sensitization in mice

RATIONALE

Age of initial exposure to addictive substances is inversely proportional to risk of developing drug dependence. There is debate, however, as to whether intake at a young age causes dependency or whether young people who experiment with addictive substances are predisposed to dependency by other factors. OBJECTIVES. We tested the relationship between cocaine exposure at two different ages in mice and the development of subsequent drug-seeking behavior to test for age-specific exposure effects.

METHODS

We performed dose-response analysis of cocaine conditioned place preference (CPP) and locomotor activity in periadolescent and adult C57Bl/6J mice. In addition, we pretreated periadolescent and adult C57Bl/6J mice with cocaine or saline in the home cage or a drug-associated context, and then examined their behavior in a biased CPP procedure in adulthood.

RESULTS

Dose-response relationships were similar between the two age groups. In the pretreatment experiments, we observed locomotor sensitization during the pretreatment in periadolescent but not adult mice. We also observed an enhanced aversion to the non-preferred side of the chamber in periadolescent mice compared to adult mice, which was alleviated by cocaine association with that side. Third, we observed that after further conditioning in adulthood, there were no pretreatment-specific effects.

CONCLUSIONS

Our results are consistent with a "vulnerable brain" hypothesis for responses to cocaine based on our findings that periadolescent mice exhibit greater locomotor sensitization to cocaine, and greater baseline anxiety responses that are alleviated by cocaine exposure compared to adult mice.

Validity of the substance abuse subtle screening inventory-adolescent version (SASSI-A)

The construct and convergent validity of the Substance Abuse Subtle Screening Instrument-Adolescent (SASSI-A) were examined in a population of suburban youth offenders. The analysis was conducted on archived data of 490 adolescent offenders from a suburban Circuit Court-Juvenile Division. Exploratory factor analysis results best supported a 5-factor solution that accounted for a modest 32.5% of the total variance. This 5-factor solution had a poor goodness of fit with the purported factor structure upon which the formal SASSI-A scoring is based. The relationship between the SASSI-A and variables with known relationships to adolescent substance abuse (i.e., lack of religious involvement, single parent household, learning disability, early onset of use, conduct problems) was examined. Results revealed moderately strong relationships between the SASSI-A and these variables, indicating reasonable convergent validity. It is concluded that the SASSI-A face valid scales have moderate utility for identifying substance dependence within this sample, while the subtle scales do not.

Structure and predictive power of intraindividual variability in health and activity measures

Intraindividual variability has been shown in many studies to be well structured over time and capable of predicting a wide range of behaviors. This study provides analyses of weekly variations of health and activity measurements in a sample (N = 52) of elderly persons (mean age = 77.5, SD = 7.2). The three main goals and results entailed: 1. Assessing the reliable nature of a health and an activity factor through a metric invariant confirmatory factor model; 2. Assessing the independence of intraindividual variability from level information and showing that the amount of intra-person variability during the first and second half of data collection correlate very highly; 3. Showing that intraindividual variability information of health and activity scores is superior to level information in predicting mortality.

Individual, family, and peer affiliation factors predisposing to early-age onset of alcohol and drug use

In this study, a multifactorial model of liability to early-age alcohol and drug use was elucidated on a sample of sons of substance-abusing fathers (n = 59) and sons of normal fathers (n = 71) at time 1 when the boys were 10-12 years of age. Three hierarchical regression analyses were computed to test models to identify salient risk characteristics associated with sons' perception of family dysfunction unconventional activities among peers, and affiliation with peers engaged in delinquent behaviors. The respective models explained 28% of the variance on sons' Dysfunctional Family Index scores, 21% of the variance on sons' Conventional Activities of Friends Scale scores, and 53% of the variance was accounted for on sons' Peer Delinquency Scale scores. In subsequent logistic regression analyses, a multifactorial model comprised of individual, family, and peer risk characteristics obtained at time 1 correctly predicted 83.7% of sons who had used alcohol and/or drugs by time 2 when they were 12-14 years old. The findings also suggest that temperament phenotype influences family interaction patterns that in turn influence the psychosocial development of the child.