Stress and self-injurious behavior; Hormonal and serotonergic parameters in mentally retarded subjects

Self-injurious behavior (SIB) and stereotyped behavior (SB) are major chall enges for professionals in the field of mental retardation. From animal exp eriments it has become obvious that these behavioral disturbances are not p urposeless but may emerge secondary to restrictive environment and may serv e de-arousing objectives. In mentally retarded subjects, several hypotheses have been formulated concerning the pathogenesis of SIB, particularly abou t the involvement of serotonin and beta-endorphin, which are supported by b eneficial treatment effects of the opiate antagonist naltrexone and seroton in modulating compounds, respectively. The present study was designed to in vestigate basal levels of stress-hormonal and serotonergic parameters as we ll as plasma levels of amino-acids and the beta-carboline norharman in a gr oup of 64 mentally retarded subjects with SB and/or SIB. Allocation to thre e different groups comprising 17 retarded controls, 26 subjects with mainly SIB and 21 subjects with mainly SB, was originally performed using the sco res on the factors Irritability, Stereotypic Behaviour and Hyperactivity of the Aberrant Behavioral Checklist. Because of the overlapping nature of th e behavioral parameters, subjects were subsequently divided into three maxi mally contrasting groups, viz. predominantly SIB, predominantly SE and reta rded controls, each comprising 11 subjects. With respect to beta-endorphin, no differences were found either between both the original and maximally c ontrasting groups or in comparison to nonretarded controls. As compared to retarded controls, a tendency to lower values for total cortisol and cortis ol binding globulin appeared to be present in the SIB group, whereas in the SB group a tendency toward higher levels of the major serotonin metabolite 5-HIAA was found. In the contrasting SB group, a trend toward decreased to tal cortisol level was observed as compared to the retarded control group. In addition, significantly lower values for norharman and tryptophan were d emonstrated in the total group of mentally retarded subjects as compared to non-retarded controls. The results of the present study, yielding co-exist ent disturbances in stresshormonal and monoaminergic mechanisms as well as in the metabolism of norharman, are in line with the hypothesis that mental ly retarded subjects are at risk for the development of stress-related beha vioral disorders such as SIB and SB.