IMMUNOHISTOCYTOCHEMICAL AND ELECTROPHYSIOLOGICAL STUDIES ON THE NEURONAL REORGANIZATION IN THE CEREBELLUM OF JAUNDICED GUNN RAT

To evaluate the compensatory mechanism after reduced Purkinje cell function in jaundiced Gunn rats, we investigated the changes in intracerebellar immunoreactive distribution of tyrosine hydroxylase (TH) and gamma-aminobutyric acid (GABA) using antisera to them. In homozygous Gunn rats (jj), TH-positive cells were observed in the granular layer and cerebellar nuclei where they were undetectable in the heterozygous Gunn rat (j+). Moreover, remarkable immunoreactivity was observed in the jj cerebellum and may be due to the increase in the density of TH-positive varicose fibers in both the granular layer and the cerebellar nuclei, whereas the reactivity in those varicose fibers was negligible in the j+ cerebellum. In contrast, in the jj cerebellar nuclei GABA-positive interneurons were significantly increased in their number compared with those in the j+ cerebellar nuclei. Either noradrenaline or GABA, when injected into the cerebellar nuclei of the norma rat, decreased in the frequency of spontaneous discharge of the nuclear neurons. Contrary, their antagonists, injected into the nuclei in the same way, caused increased in the firing rate. These findings suggest that noradrenaline-and GABA-related neural circuit is modified in the jj cerebellum, leading to the increase in inhibitory input to the cerebellar nuclear neurons.