Regional differences in substance P-like immunoreactivity in the striatum correlate with levels of pre-protachykinin mRNA.

The distribution of neurons containing the messenger RNA encoding preprotachykinin, the precursor of the neuropeptides substance P and K, was examined in the striatum of the rat. The large majority of cells densely labelled by in situ hybridization histochemistry (using a 35S-radiolabelled RNA probe complementary of the beta-preprotachykinin mRNA) were located within the boundaries of areas of dense [3H]naloxone binding which delineate the striosomes, a striatal compartment distinct from the surrounding matrix with respect to its inputs, outputs and neurochemical content. In view of previous immunohistochemical data, the results suggest that tachykinin-containing neurons of the striosomes have a higher rate of tachykinin synthesis than those neurons located in the surrounding striatal matrix.