Changes in [3H]muscimol binding in substantia nigra, entopeduncular nucleus, globus pallidus, and thalamus after striatal lesions as demonstrated by quantitative receptor autoradiography.

A quantitative autoradiographic technique for measuring the binding of [3H]muscimol to central nervous system GABA receptors is described using tritium-sensitive film. [3H]Muscimol binding was studied in primary and secondary striatal projection areas of rat brain following kainic acid lesions of the striatum. Seven days after the lesion, binding affinities in the striatum and its projection areas were not altered significantly. There was a loss of [3H]muscimol receptors in the striatum. Receptors increased in numbers in the ipsilateral globus pallidus (19%), entopeduncular nucleus (22%), and substantia nigra pars reticulata (38%). [3H]Muscimol binding was decreased in the ipsilateral anteroventrolateral and ventromedial (8%) thalamic nuclei. [3H]Muscimol binding in other brain areas (layer IV of the cerebral cortex, central gray, superior colliculus, and stratum moleculare of hippocampus) was not affected. The findings suggest that a loss of striatal innervation resulted in increased numbers of GABA receptors in striatal projection sites. It is further suggested that loss of inhibitory striatal inputs to neurons in the entopeduncular nucleus and substantia nigra pars reticulata may activate GABAergic projections to thalamus and thus result in decreased numbers of thalamic GABA receptors.