Tachykinin-Immunoreactive Neurons in Developing Feline Neostriatum: Somatodendritic Morphogenesis Demonstrated by Combined Immunohistochemistry/Golgi Impregnation-Gold Toning

This investigation was designed to survey and characterize the development of a key link between chemically mediated neurotransmission and neuronal cytoarchitecture in mammalian basal ganglia. Peroxidase immunohistochemical and Golgi impregnation/gold toning methods were combined to doubly label the tachykinin neuromodulator signature and somatodendritic structure of neostriatal neurons in late fetal, postnatal and adult cats. The results supported 3 conclusions of considerable significance. (1) Colocalization of immunohistochemical and Golgi impregnation/gold toning labels is a feasible, rational and productive means to identify and determine the somatodendritic morphogenesis of tachykinin neurons. (2) The application of this method to developing feline neostriatum demonstrates directly that the principal tachykinin cells are medium-sized spiny neurons, which undergo progressive growth and elaboration of cell bodies, dendritic arbors and dendritic spines during the late fetal and postnatal periods. (3) There is a strong but incomplete concordance between tachykinin and medium-sized spiny neuronal phenotypes, because a minor variant of medium-sized spiny neurons and rare subgroups of medium- and large-sized sparse spiny neurons also show the tachykinin neuromodulator signature. Taken together, these results suggest that neostriatal neurons show an early commitment to heterogeneous tachykinin phenotypes, although the full and final expression of their somatodendritic characteristics coincides with synaptogenesis.