Consideration of the relevance of ethological animal models for human repetitive behavioral spectrum disorders

Treatment successes of various stereotyped behaviors in animals and humans has renewed interest in ethologic animal models for the study of psychiatric disorders. This report presents another such behavior occurring in horses to weaving. This anomalous, repetitive, and purposeless behavior draws analogies to human compulsive spectrum behaviors. A “weaver” provided an opportunity to evaluate serotonin, dopamine, and opioid neurotransmitter system contributions by probing each with a selective agent in A-B-A-C-A-D design. The horse was treated in sequential 1-month periods separated by 1-month washouts with a serotonin transport inhibitor (SRI), opiate antagonist (OA), and neuroleptic (DA). Videotape was taken weekly and analyzed by two blind raters. Frequency of head swings, latency to onset, and severity were recorded. The SRI showed > 95% symptom reduction, the DA 40%, and OA 30%. The findings suggest that neurochemical explanations of disturbance based on single drug vs. placebo trials may be oversimplified. Multiple-system probes are needed to dissect complex interactive biological systems. Animal model research can have an important role in such investigations.