Effect of long-term administration of 1,2,3,4-tetrahydroisoquinoline (TIQ) on striatal dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) content in mice

Effects of long-term administration of 1,2,3,4-tetrahydroisoquinoline (TIQ) on the striatal dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) were investigated in mice and rats. Striatal dopamine content significantly increased and DOPAC decreased after repeated administrations of TIQ at a dose of 50 mg/kg/day s.c. for 70 days in mice. In contrast, dopamine and DOPAC content did not show any significant change in rats. The ratio DOPAC/dopamine decreased significantly in mice treated with TIQ for 70 days. The results presented suggest that TIQ reduces the turnover rate of the nigrostriatal dopamine neurons after repeated administration for a long period in mice.