Postnatal changes in the distribution and morphology of rat substantia nigra dopaminergic neurons

Significant changes in the neurophysiology and neuropharmacology of nigral dopaminergic neurons take place in the first postnatal month. In order to correlate these changes with the postnatal development of dopaminergic neuron morphology and substantia nigra cytoarchitecture, brains from Sprague-Dawley rat pups of age postnatal days 1, 7, 14, 21 and 28 and adult rats were sectioned and processed for tyrosine hydroxylase immunocytochemistry. At postnatal day 1, pars compacta and pars reticulata were not clearly delineated; tyrosine hydroxylase positive neurons and a dense plexus of fibers were scattered throughout the substantia nigra. By day 7 the density of tyrosine hydroxylase positive neurons decreased markedly in ventral substantia nigra, and a dopaminergic pars compacta and a non-dopaminergic pars reticulata could be more clearly distinguished. By day 14 the substantia nigra appeared essentially as it does in the adult. Cell counts during development revealed that the number of tyrosine hydroxylase positive neurons/section in both pars compacta and pars reticulata decreased significantly from postnatal day 1 to postnatal day 14, while those in pars lateralis did not change. Tyrosine hydroxylase-positive somatic size increased modestly but significantly from postnatal day 1 to day 14 as did the diameter of the proximal and distal dendrites. However, even at day 1, the morphology of tyrosine hydroxylase positive neurons appeared essentially the same as in adults. Dendritic arborizations were well developed. The dendrites were non-varicose and modestly branched, with some of the longer ventrally directed dendrites passing through pars reticulata into the crus cerebri.(ABSTRACT TRUNCATED AT 250 WORDS)