Elizabeth Wood; Nathaniel Landis; Stephen Day; S.U. Suomi, Brigham Young University
Between 13-46% of adolescent populations report engaging in self-injurious behavior (SIB), with the majority of those who attempt suicide engaging in some form of SIB. Studies of the association between the serotonin transporter genotype (5-HTT) and SIB suggest that the long allele (L) may be associated with lower likelihood of SIB and the short allele (s) associated with increased likelihood of SIB. However, the etiology of SIB remains unclear, a problem stemming from difficulty in tracking and studying SIB among human populations. Thus, animal models may be of use, as their environment can be experimentally manipulated, their genetic history known, and their behavior readily observed. As SIB affects between 14-25% of laboratory-living rhesus macaques, they may provide a unique contribution to understanding the etiology of SIB. To investigate the origins of SIB, we assessed the physiological and behavioral response of 161 laboratory-living rhesus monkeys in a stressful social challenge, 18 of which had a history of self-biting. Blood samples were obtained to determine 5-HTT genotype and concentrations of adrenocorticotropic hormone (ACTH). Univariate ANOVAs were used to assess associations between self-biting status and 5-HTT genotype on hormones and behavior. There were main effects of self-biting status on frequency of approaching the intruder and vocalizations, with self-biting subjects exhibiting increased approaches and vocalizing more. There were interactions between 5-HTT genotype and self-biting status on concentrations of ACTH and on duration of stereotypic behaviors, with self-biting subjects that were homozygous for the L allele exhibiting higher ACTH concentrations and increased durations of stereotypic behavior. There were interactions between 5-HTT genotype and self-biting status on frequency of approaching the intruder, on time spent moving, and on rates of vocalizations, heterozygous self-biting subjects exhibiting increased approaches, more locomotion, and more vocalizations. It appears that SIB is associated with impulsive behavior in the face of a social stressor, as well as a heightened stress response. Central serotonin availability plays a role in subjective response to a social stressor, with self-injurious subjects with high serotonin availability exhibiting increased ACTH and stereotypic behaviors and those subjects with low serotonin availability exhibiting increased impulsivity. These findings suggest that 5-HTT genotype may be an important factor in understanding SIB.