Reduced locomotor activity of rats made histidinemic by injection of histidine

Acute histidinemia was provoked in 30-d-old male Wistar rats by injecting intraperitoneally either histidine alone (0.5 mg/g body wt) or histidine (0.25 mg/g body wt) plus the histidase inhibitor nitromethane (0.73 mg/g body wt). Histidase activity was approximately 90% inhibited in rats receiving nitromethane. Serum histidine in both groups reached levels similar to those of histidinemic patients. Rats were subjected to the open field behavioral task, and the number of rearings and crossings were counted. A consistently lower locomotor activity was observed in the histidinemic rats. It is proposed that reduced locomotor activity and its relationship to psychomotor development should be investigated in histidinemic children.