Serotonin 5-HT1A and 5-HT3 Receptors in an Impulsive-Aggressive Phenotype

In adult male hamsters, individual differences in offensive aggression are correlated with differences in impulsive choice and decreased serotonin (5-HT) innervation. As serotonin 1A (5-HT(1A)) receptors participate in the inhibition of aggression, whereas 5-HT(3) receptor activation facilitates aggression, the authors hypothesized that differences in their expression are associated with differences in behavior. The authors confirmed previous behavioral associations, using a delay-discounting paradigm with various delays, as high-aggression (H-Agg) hamsters preferred the immediate-reward lever over the delayed-reward lever under most delays, compared with low-aggression (L-Agg) hamsters. Although the authors observed a greater density of 5-HT(1A) receptor immunoreactivity in H-Agg hamsters within several areas, it appears to be related to a lack of serotonin release, as supported by further observations of decreased immunoreactive perikarya and 5-HT(1A) receptors in fluoxetine-treated hamsters. Also, 5-HT3 receptor density was greater in H-Agg hamsters within select areas. The data indicate a convergence of impulsive and aggressive characteristics to one phenotype that is associated with various aspects of serotonin function, such as serotonin release and differential expression of 5-HT(1A) and 5-HT(3) receptors.