Kainic acid-induced changes of serotonin and dopamine metabolism in the striatum and substantia nigra of the rat.

Levels of the putative neurotransmitters serotonin (5-HT) and dopamine (DA) and their respective metabolites 5-hydroxyindoleacetic acid (5-HIAA) and dihydroxyphenylacetic acid (DOPAC) was determined in the rat striatum after unilateral intrastriatal injection of the convulsive neurotoxin kainic acid. Two days after intrastriatal kainic acid injection, levels of the 5-HT metabolite 5-HIAA were increased by abut 200% in the injected striatum and by about 150% in the contralateral striatum. An elevated striatal 5-HIAA content was still detectable 10 days after the kainate lesion, but approached normal values 10 weeks after the injection of the neurotoxin. Two days after the lesion, but not at the other time intervals, a moderate increase of 5-HIAA also occurred bilaterally in other brain areas such as the substantia nigra, frontal cortex and hypothalamus. Levels of 5-HT were decreased significantly in the injected striatum 2 days after the intrastriatal application of kainic acid and increased by about 40% after 10 weeks. The 5-HT concentration in the contralateral striatum or in the three other brain areas examined was unchanged at all time intervals. Levels of the DA metabolite DOPAC and DA turnover were increased in the lesioned striatum 2 days after kainic acid injection; concomitantly the DOPAC level was increased in the substantia nigra of the contralateral side. DOPAC levels of the contralateral striatum were unchanged or slightly reduced 2 days after the injection. Ten days as well as 10 weeks after the lesion there was a slightly increased DOPAC concentration in both striata. The levels of DA were not altered at any time interval after the injection of kainic acid.