Patterns of tachykinin expression and localization in developing feline neostriatum

The development of tachykinins in the neostriatum was determined qualitatively in order to characterize the ontogeny of an early-forming neostriatal peptidergic system. Tachykinins were detected by immunohistochemistry in fetal, postnatal, and adult cats. Neostriatal cells and neurites expressed tachykinins as early as fetal age 30 and increased in frequency progressively with age. Initial tachykinin expression occurred in neostriatal neurons during their postmitotic migration. In the head of the caudate nucleus, clusters of tachykinin-containing cells and fibers formed between fetal days 35 and 45, when the distribution of labeled neurons changed from a dispersed to an aggregated pattern. Between fetal days 45 and 50, tachykinin-rich neuronal clusters increased in frequency and were distributed throughout the rostral caudate nucleus. In contrast to neurons in clusters, neurons in the complementary neuropil expressed tachykinins largely postnatally. Postnatal morphological maturation of tachykinin-containing neurons paralleled the morphogenesis of medium spiny neostriatal cells. In addition, the caudate nucleus and putamen followed different spatiotemporal gradients of tachykinin expression. These results indicate that tachykinins are expressed in neostriatal neurons during the early ontogeny of the neostriatum and may function as trophic factors before synaptogenesis.