Intrastriatal injection of 5,7-dihydroxytryptamine decreased 5-HT levels in the striatum and suppressed locomotor activity in C57BL/6 mice

Effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 5,7-dihy droxytryptamine (5,7-DHT) on striatal levels of dopamine (DA), 5-hydroxytry ptamine (5-HT), and their metabolites, as well as on locomotor activity wer e investigated in C57BL/6 mice. The results showed that MPTP significantly increased locomotor activity and decreased striatal DA levels. However, inj ection of the serotonergic neurotoxin 5,7-DHT in the striatum, either alone or following high doses of MPTP, significantly decreased locomotor activit y, and concomitantly decreased striatal levels of 5-HT and 5-HIAA. This stu dy suggests that the increased locomotor activity may be due to increased s triatal serotonergic activity which overcompensates for the DA deficiency. The locomotor hypoactivity, induced by 5,7-DHT, might be due to the decreas ed striatal levels of 5-HT and 5-HIAA.