Interconnection of GABA-ergic neurons in rat extrapyramidal tract: Analysis using intracerebral microinjection of kainic acid

Abstract The interconnection of γ-aminobutyric acid (GABA)-ergic neurons in the rat extrapyramidal tract was analyzed neurochemically using the technique of intracerebral microinjection of kainic acid. Two days after the stereotaxic microinjection of kainic acid (2 μg/μl) into the left striatum and thereafter, the rats exhibited an ipsilateral rotational movement which persisted until they were killed, and the striatal, pallidal, and nigral GABA concentrations and 1-glutamate decarboxylase (GAD) activities of the ipsilateral side in these animals were significantly reduced. On the other hand, a significant reduction of GABA-transaminase·succinic semialdehyde dehydrogenase activity was found only in the left striatum. The intrapallidal injection of kainic acid induced a significant decrease in the ipsilateral pallidal and nigral GABA concentrations without affecting that in the striatum. In contrast, the unilateral nigral injection of kainic acid induced no significant alteration of GABA concentrations in any central nervous system regions examined. The striatal kainic acid treatment not only selectively abolished the high-affinity uptake system for [ 3 H]GABA, but also exhibited a selective suppression of the high K + -evoked release of [ 3 H]GABA from striatal slices. Histological examination of kainic acid-treated striatal, pallidal, and nigral tissues revealed that the degeneration of neurons and subsequent gliosis occurred only at each injection site. Our results indicate that in the extrapyramidal system the striatopallidal, striatonigral, and pallidonigral GABA-ergic neurons are present, and may be involved in the occurrence of behavioral abnormalities observed in kainic acid treated animals. We also suggest that the high-affinity uptake and evoked release systems for GABA indeed reside within neurons which are susceptible to kainic acid.