Development of a micromethod to study the Na +-independent l-[ 3H]glutamic acid binding to rat striatal membranes. II. Effects of selective striatal lesions and deafferentations

Abstract

An apparent single class of Na +-independent l-[ 3H]glutamate ( l-[ 3H]Glu) binding sites was biochemically and pharmacologically identified on rat striatal tissue. The K d value was 1.75 μM and the B max3.89 nmol/g protein. In order to further elucidate the putative physiological role of these binding sites and to valid our binding assay, experiments were conducted to determine the anatomical location of the l-[ 3H]Glu binding sites in the striatum. Local injection of the neurotoxin, kainic acid into the striatum caused degeneration of target cells in the structure followed by an important decrease (-37%) in the number of these binding sites, with no significant change in the affinity constant. Lesions of the cortical frontal and parietal areas projecting to the striatum via putative glutamatergic fibers led, on the other hand, after 3 weeks to one month, to a significant increase (+23%) in the number of l-[ 3H]Glu binding sites. The K d value does not significantly change after decortication. Finally, suppression either of the nigrostriatal dopaminergic input or of the partially cholinergic thalamostriatal tract do not affect [ 3H]Glu binding to striatal tissue. These results suggest that about 40% of our [ 3H]Glu binding sites are located on striatal target cell sensitive to the neurotoxic effect of kainic acid. Therefore, they seem to be partly postsynaptic. The existence of a relation between these binding sites and the corticostriatal glutamatergic input was shown by the development of a supersensitivity response after suppression of this cortical input. These sites might therefore constitute one of the receptor subclass for Glu linked to the excitatory action of the corticostriatal afferent. Since degeneration of either the nigrostriatal dopaminergic or the thalamostriatal fibres did not affect the binding of l-[ 3H]Glu characterized in our study, the binding sites will probably not occur at the presynaptic level on these nerve terminals in the striatum.