Distribution, projection and dopaminergic regulation of the neurokinin B mRNA-containing neurons of the rat caudate-putamen

Neurons containing transcripts encoding neurokinin B, a member of the tachykinin family, were studied in the rat caudate-putamen using hybridization histochemistry. Neurons containing neurokinin B mRNA were distributed throughout the caudate-putamen, with a slightly higher density in the middle portions as compared with the more rostral and caudal portions. These neurons were either isolated, often located close to neurons devoid of neurokinin B mRNA, or in small clusters of three to 10 cells. A larger group of neurons with neurokinin B mRNA was seen in the ventrolateral caudateputamen, near the tip of the external capsule. Neurokinin B mRNA was colocalized in neurons with substance P (59% of neurokinin B neurons had substance P mRNA) and with enkephalin mRNA (25% of neurokinin B neurons had enkephalin mRNA). After injections of the fluorescent dye Fluorogold into the globus pallidus and substantia nigra, retrograde axonal transport studies demonstrated neurokinin B mRNA in striatopallidal but not striatonigral projections. The influence ofdopaminergic input on the level of neurokinin B mRNA in the caudate-putamen was studied after 6-hydroxydopamine lesions of the substantia nigra/ventral tegmental area. Both the number of cells detected containing neurokinin B mRNA as well as the level of transcripts per cell increased on the side ipsilateral to the lesion, whereas the opposite was seen on the contralateral side. These results describe a novel neurochemical system within the rat basal ganglia that is regulated by dopaminergic innervation from the mesencephalon.