Effects of globus pallidus lesions and Parkinson's disease on brain glutamic acid decarboxylase

Cats with unilateral lesions in the region of the globus pallidus showed a highly significant loss (to 39%) of glutamic acid decarboxylase (GAD) activity in the substantia nigra on the lesioned side. GAD was unaffected in the caudate nucleus or other structures. Tyrosine hydroxylase was reduced to 49% of the control values in the substantia nigra and to 23.7% in the caudate, while choline acetyltransferase and cholinesterase were not significantly affected in either structure. The data suggest that the lesion interrupted the known dopaminergic pathway between caudate and substantia nigra and interfered with another pathway concerned with GABA metabolism involving the substantia nigra but not the caudate. There appeared to be no major cholinergic pathway coursing through the lesioned area.