Autoshaping in adolescence enhances sign-tracking behavior in adulthood: impact on ethanol consumption

Abstract

Autoshaping refers to a procedure during which a cue repeatedly paired with a reward elicits a conditioned response directed at either the reward delivery location ("goal-tracking") or the cue itself ("sign- tracking"). Individual differences in expression of sign-tracking behavior may be predictive of voluntary ethanol intake. The present study was designed to explore the development of differences in sign-tracking behavior in adolescent and adult male and female rats in an 8-day autoshaping procedure. Consistency of sign-tracking and goal-tracking across age was examined by retesting adolescents again in adulthood and comparing their adult data with animals tested only as adults to explore pre-exposure effects on adult responding. In order to assess the relationship between sign-tracking and ethanol intake, voluntary ethanol consumption was measured in an 8-day, 2-hr limited access drinking paradigm following the 8-day autoshaping procedure in adulthood. Animals tested as adolescents showed notably less sign-tracking behavior than animals tested as adults, and sign-tracking behavior was not correlated across age. Animals exposed to the autoshaping procedure as adolescents demonstrated greater sign-tracking behavior as adults when compared to control animals tested only in adulthood. When examining the relationship in adulthood between sign-tracking and ethanol intake, an increase in ethanol intake among sign-trackers was found only in animals pre-exposed to autoshaping as adolescents. Whether or not these results reflect an adolescent-specific experience effect is unclear without further work to determine whether comparable pre-exposure effects are seen if the initial autoshaping sessions are delayed into adulthood.

Fig. 1

Group assignment data. Z-scores based on number of ST and GT trials for individual animals are plotted for each age/sex condition. Black symbols indicate the animals classified as sign-trackers (z-scores above 0.5) whereas white symbols indicate animals identified as goal-trackers (z-scores below −0.5). Gray symbols are the z-scores of an intermediate group of animals that were eliminated from all analyses. Group sizes are listed below each column of symbols.

Fig. 2

Number of trials with a sign-tracking response. Regardless of age/pre-exposure, sex and day, sign-trackers had more ST trials than goal-trackers. * indicates a decrease relative to adult control sign-trackers, collapsed across sex. + indicates an increase relative to adult control sign-trackers, collapsed across sex. Sex effects are described in the text.

Fig. 3

Number of trials with a goal-tracking response. Goal-trackers had more GT trials than sign-trackers on days indicated in the text on each graph. + indicates an increase relative to adult control goal-trackers of the same sex. Sex effects are described in the text.

Fig. 4

Latency data. Differences between sign-trackers and goal-trackers are described in the text on each graph. + indicates a shorter latency relative to adult controls assigned to the same group. Data are collapsed across sex.

Fig. 5

Conditioned reinforcement test data. Collapsed across sex, increases among signtrackers relative to goal-trackers are indicated in the text on the graphs. Sex differences are described in the text.

Fig. 6

Ethanol intake in adulthood. Collapsed across day and sex, retested adult signtrackers consumed more ethanol than retested adult goal-trackers, an effect not seen in the adult controls. Sex differences are described in the text.