Compartmental expression of trkB receptor protein in the developing striatum

To investigate the role of neurotrophins in the initial formation of striatal patch versus matrix, the spatial and temporal expression of trkB receptors was examined using immunohistochemistry. Polyclonal antibodies, against the C-terminus or the tyrosine kinase domain, revealed trkB-immunoreactive cells and fibers localized to patches beginning on embryonic day 19 in the rat, which co-localized with patchy dopamine fibers, substance P-immunoreactive neurons and glutamate receptors. Patchy striatal trkB expression was maintained after lesioning the nigrostriatal dopamine system. The patchy trkB distribution persisted through postnatal day 14, then became more homogeneous at the same time that nigrostriatal afferents become homogeneous. Later in development, trkB immunoreactivity was most intense in a subpopulation of large striatal cells that were similar in size and frequency to those immunoreactive for choline acetyltransferase. The spatiotemporal expression of trkB receptor in phenotypically distinct striatal patches, as well as evidence that neurotrophins regulate expression of neuronal phenotypic markers during development, may indicate a convergence of neurotrophins and afferent innervation on to future patch cells that may regulate the establishment of striatal compartmentalization.