Effects of an Agonist and an Antagonist of α2-Adrenoreceptors on Selection of Reinforcement Value in Rats with Different Levels of Impulsivity

Abstract

The effects of an agonist and an antagonist of α2-adrenoreceptors – clonidine and yohimbine, respectively – were studied in rats with different levels of impulsivity identified using the “right to choose” the value of a food reinforcement (delay discounting paradigm). Selection of either an immediate but low-value or a delayed but high-value reinforcement was used to divide rats into three groups. Rats selecting the high-value, delayed reinforcement in more than 60% of trials were placed in the low-impulsivity (self-controlled) group, in contrast to animals mainly choosing the low-value immediate reinforcement, which formed the high-impulsivity group. Rats not defined by their choices were placed in the ambivalent group. Systemic administration of the α2-adrenoreceptor agonist clonidine led to a statistically significant increase in the choice of responses with the low-value immediate reinforcement in low-impulsivity rats and an increase in the number of missed reactions in high-impulsivity animals. Shortening of the latent period of moving the feeder curtain was seen in all groups of animals. Administration of the α2-adrenoreceptor blocker yohimbine produced no changes in the previously selected behavioral strategy in any of the groups of animals, but did lead to a decrease in the number of missed reactions in highly impulsive rats. The results suggest that the influences on α2-adrenoreceptors of the pharmacological agents used here depend on the individual-typological characteristics of the rats, particularly high and low levels of impulsivity.