Strain differences in delay discounting using inbred rats

Delay discounting behavior and white matter microstructure abnormalities in youth with a family history of alcoholism

BACKGROUND

Youth with family history of alcohol abuse have a greater risk of developing an alcohol use disorder (AUD). Brain and behavior differences may underlie this increased vulnerability. The current study examined delay discounting behavior and white matter microstructure in youth at high risk for alcohol abuse, as determined by a family history of alcoholism (FH+), and youth without such family history (FH-).

METHODS

Thirty-three healthy youth (FH+ = 15, FH- = 18), ages 11 to 15 years, completed a delay discounting task and underwent diffusion tensor imaging. Tract-based spatial statistics (Smith et al., 2006), as well as follow-up region-of-interest analyses, were performed to compare fractional anisotropy (FA) between FH+ and FH- youth.

RESULTS

FH+ youth showed a trend toward increased discounting behavior and had significantly slower reaction times (RTs) on the delay discounting paradigm compared to FH- youth. Group differences in FA were seen in several white matter tracts. Furthermore, lower FA in the left inferior longitudinal fasciculus and the right optic radiation statistically mediated the relationship between FH status and slower RTs on the delay discounting task.

CONCLUSIONS

Youth with a family history of substance abuse have disrupted white matter microstructure, which likely contributes to less efficient cortical processing and may act as an intrinsic risk factor contributing to an increased susceptibility of developing AUD. In addition, FHP youth showed a trend toward greater impulsive decision making, possibly representing an inherent personal characteristic that may facilitate substance use onset and abuse in high-risk youth.

Strain differences in behavioral inhibition in a Go/No-go task demonstrated using 15 inbred mouse strains

BACKGROUND

High levels of impulsivity have been associated with a number of substance abuse disorders including alcohol abuse. Research has not yet revealed whether these high levels predate the development of alcohol abuse.

METHODS

The current study examined impulsivity in 15 inbred strains of mice (A/HeJ, AKR/J, BALB/cJ, C3H/HeJ, C57BL/6J, C57L/J, C58/J, CBA/J, DBA/1J, DBA/2J, NZB/B1NJ, PL/J, SJL/J, SWR/J, and 129P3/J) using a Go/No-go task, which was designed to measure a subject's ability to inhibit a behavior. Numerous aspects of response to ethanol and other drugs of abuse have been examined in these strains.

RESULTS

There were significant strain differences in the number of responses made during the No-go signal (false alarms) and the extent to which strains responded differentially during the Go and No-go signals (d'). The rate of responding prior to the cue did not differ among strains, although there was a statistically significant correlation between false alarms and precue responding that was not related to basal activity level. Interstrain correlations suggested that false alarms and rate of responding were associated with strain differences in ethanol-related traits from the published literature.

CONCLUSIONS

The results of this study do support a link between innate level of impulsivity and response to ethanol and are consistent with a genetic basis for some measures of behavioral inhibition.

Response bias is unaffected by delay length in a delay discounting paradigm

This study examined the contribution of response bias to measures of delay discounting in Long-Evans rats (n=8) using the adjusting amount procedure. Under this procedure, we assessed preference for 150microl of 10% sucrose solution delivered following a delay over a variable-amount alternative delivered immediately. Bias was calculated based on relative preference when reinforcers were delivered immediately from both alternatives. We extended this assessment procedure to examine preference when rewards from both alternatives were equally delayed (2, 4, 8, or 16s) in addition to assessing a traditional delay discounting function. Relative preference was similar across delays and slightly larger than 150microl. These results indicate that response bias was stable and suggests a relative aversion for the adjusting alternative, which may be due to the variability in reward size associated with that alternative.