Investigation of molecular mechanisms underlying psychotropic drug action is the main aim of molecular psychopharmacology. Previously, a new synthetic varacin analog, 8-(Trifluoromethyl)-1,2,3,4,5-benzopentathiepin-6-amine (TC-2153) was shown to produce anxiolytic and anticonvulsant effects in mice. This study investigated the effects of chronic TC-2153 administration on the expression of some serotonin-related genes in the mouse brain. The drug was administered (10 mg/kg, per os, 16 days) to adult male mice of the ASC (Antidepressant Sensitive Catalepsy) strain characterized by altered behavior and hereditary impairment of the brain serotonin system. Expression of genes encoding tryptophan hydroxylase 2 (TPH2), the key enzyme of serotonin synthesis, monoamine oxydase A (MAOA), the major serotonin-degrading enzyme, 5-HT transporter (SERT), and 5-HT1A receptor was studied using quantitative RT-PCR. TC-2153 significantly reduced the 5-HT1A receptor and MAOA mRNA levels in the midbrain, but did not have any effect on the expression of these genes in the frontal cortex and the hippocampus. The drug did not affect the expression of TPH2 and SERT in the midbrain. The results indicate that the brain 5-HT system is involved in the molecular basis of TC-2153 action.