ABSTRACT
The majority of neurons in the basal ganglia use the neurotransmitter gamma aminobutyric acid (GABA) and contain glutamic acid decarboxylase (GAD), the enzyme of GABA synthesis. The mRNA encoding GAD67 is much more abundant than GAD65 mRNA in striatal interneurons, whereas GAD65 is slightly more abundant than GAD67 mRNA in striatal efferent neurons. The increase in GAD67 mRNA is accompanied by an increase in immunoreactivity for the protein, GAD67. In rats, the mRNAs encoding both isoforms of GAD were decreased in the contralateral entopeduncular nucleus after unilateral lesions of the nigrostriatal dopaminergic pathway. The reticular thalamic nucleus (RTN) is the only thalamic region that contains GABA-ergic neurons in rats. GABA-ergic neurons of the RTN project to the dorsal thalamus and receive collaterals from thalamocortical and corticothalamic projections. In contrast to the increase in GAD67 mRNA levels seen in the globus pallidus of rats exhibiting catalepsy, levels of GAD67 mRNA decreased in the pallidum of rats exhibiting oral dyskinesia.
