Autism is a congenital neurological disorder characterized by impairment of socialization, abnormalities of communication, and limited activity and curiosity. Whole blood serotonin levels have often been found to be elevated in autistic patients and relatives, although the phenotype of human autism is often referred to hyposerotonin symptoms, rather than hyper. We have recently established an autism model rat by exposing embryonic day (E) 9 rat embryo to either thalidomide or valproic acid(the 32nd SFN). Significant increase of hippocampal serotonin,frontal cortex dopamine, and hyperserotonemia was observed in the E9 teratogen-exposed rat when observed around postnatal day 50 (Narita et al., Ped Res 2002). The model rat exhibited marked behavioral changes, some of which are common with human autism (see also the abstract of Miyahara-T et al.). In the present study, we focused on the function of serotonin transporter (5-HTT) in the autism model rat. 5-HTT controls reuptake of a neurotransmitter serotonin fr...