MESENCEPHALIC THMRNA-REDUCED EXPRESSION BY BLOCKING AXONAL-TRANSPORT WITH COLCHICINE

COLCHICINE, an axonal transport blocking agent, was unilaterally injec ted in the medial forebrain bundle of rats. As early as 18 h after the injection a rapid decrease in TH-mRNA level was observed in the subst antia nigra and the ventral tegmental area (SN/VTA) on the injected si de. In contrast, TH protein levels remained stable for 48 h, and decre ased later in both cells bodies and terminals (caudate/putamen). The n umber of TH-immunopositive cells in SN/VTA increased after colchicine equally in both sides, excluding a neurotoxic effect. These results su ggest that TH gene expression is controlled by a retrogradely transpor ted activating factor rather than by feedback inhibition by the end pr oduct, i.e. TH protein. (C) 1998 Rapid Science Ltd.