5′‐Nucleotidase: A new marker for striosomal organization in the rat caudoputamen

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Abstract
The distribution of the adenosine‐producing ectoenzyme 5′‐nucleotidase was studied by means of a histochemical lead technique in the caudoputamen of normal adult rats and of rats in which injections either of 6‐hydroxydopamine in the medial forebrain bundle or of ibotenic acid in the caudoputamen had been made 1–3 weeks previously. The patterns of striatal 5′‐nucleotidase activity in these animals were compared in serial sections to the patterns of calbindin‐D28k immunoreactivity and of 3H‐naloxone ligand binding, which respectively mark the known matrix and striosome (patch) compartments of the caudoputamen. In the normal rats, 5′‐nucleotidase activity was differentially concentrated in striosomes, where it produced a dense staining of the neuropil. The enzymatic staining followed a striosomal distribution in all but the caudal caudoputamen. Within the striatal matrix, 5′‐nucleotidase staining also observed a lateromedial density gradient. Depletion of the dopamine‐containing nigrostriatal innervation of the caudoputamen with 6‐hydroxydopamine did not alter the striosomal selectivity of 5′‐nucleotidase activity. Destruction of intrastriatal neurons by ibotenic acid led to a strongly 5′‐nucleotidase‐positive gliosis within the resulting necrotic region. Elsewhere in the caudoputamen, the enzyme's striosomal distribution was not detectably altered. We conclude that 5′‐nucleotidase histochemistry provides an advantageous tool for detecting the striosomal architecture of the rat's caudoputamen. Moreover, 5′‐nucleotidase is prominently associated with glial membranes in the central nervous system, so that the concentration of this enzyme in striosomes could mark these as sites of selective glial populations within striatum. These properties and actions of 5′‐nucleotidase in purinergic neurotransmission and in neuroadhesion may contribute to the specialized functions of striosomes and matrix.