Distribution of limbic system-associated membrane protein immunoreactivity in primate basal ganglia

The limbic system-associated membrane protein is a 64,000-68,000 mol.wt molecule known to be preferentially expressed by neurons in limbic structures of rats and cats. The present immunohistochemical study describes the distribution of this protein in the basal ganglia of Macaca fascicularis. The ventral striatum of the cynomolgus monkey displays a very intense immunostaining, whereas the dorsal striatum is much more weakly stained, except for some small zones scattered in the caudate nucleus and, to a lesser extent, in the putamen. These protein-rich zones are in register with striosomes, as visualized on adjacent sections immunostained for calbindin. At pallidal levels, immunostaining for the protein is observed only in the subcommissural regions, at the ventromedial tip of the internal pallidum, and in the caudoventral portion of the external pallidum. At nigral levels, the immunostaining is highly heterogeneous with a marked decreasing rostrocaudal gradient. The staining is most intense in nigral regions that receive striatal inputs and are enriched with calbindin. Nigral sectors populated by dopaminergic neurons, as visualized on adjacent sections immunostained for tyrosine hydroxylase, are largely devoid of immunoreactivity. In contrast, the immunostaining is uniformly intense in the ventral tegmental area. This study provides the first neuroanatomical evidence for teh existence of the limbic system-associated membrane protein in primate brain. It reveals that this glycoprotein is distributed in a highly heterogeneous manner in primate basal ganglia, where it preferentially labels regions that are anatomically and functionally linked to the limbic system.