Distribution of glutamate decarboxylase, choline acetyl-transferase and aromatic amino acid decarboxylase in the basal ganglia of normal and operated rats. Evidence for striatopallidal, striatoentopeduncular and striatonigral gabaergic fibres

Abstract

The topographical distribution of glutamate decarboxylase (GAD), aromatic amino acid decarboxylase (AAD) and choline acetyltransferase (ChAT) were studied in striatum (i.e. caudate-putamen), globus pallidus, nucleus entopeduncularis and substantia nigra. There were only small differences in the rostrocaudal distribution of enzymes in striatum. The highest concentration of GAD was found in the ventrocaudal part, whereas AAD was highest in the rostral part. ChAT did not show any distinct distribution pattern. Globus pallidus and nucleus entopeduncularis were similar in their content of GAD, AAD and ChAT. They were rich in GAD but poor in AAD and ChAT. The highest concentration of GAD was found in the rostralmost part of globus pallidus. In substantia nigra AAD was concentrated in the rostral part; contents of GAD and ChAT did not differ distinctly in the rostral and caudal nigra. GAD and ChAT were highly localized in a particulate fraction, probably in all 4 regions, whereas AAD was localized in particulate fraction in the striatum and globus pallidus and soluble in the nucleus entopeduncularis and substantia nigra. Transverse and/or oblique hemitransections which passed through the striatum but not through the globus pallidus resulted in substantial loss of GAD in the globus pallidus, nucleus entopeduncularis and substantia nigra. There was a good correlation between the anteroposterior level of hemitransection and the decline in GAD activities, which was generally highest following posterior lesions. The reduction of GAD was largest in the globus pallidus and smallest in the substantia nigra, in which a significant loss of GAD occurred only following transections of the postcommissural part of caudate-putamen. A very high decrease of GAD in the nucleus entopeduncularis and substantia nigra was obtained following posterior oblique hemitransections which passed through posterior part of striatum and rostral globus pallidus. The results indicate that the majority of GABAergic terminals in the globus pallidus belong to striatopallidal fibers. They suggest, furthermore, that a large number of striatoentopeduncular and striatonigral fibers are GABAergic, the latter arising preferentially from the posterior part of caudate-putamen.