COMPARISON OF THE EFFECTS OF THE NEUROTROPHINS ON THE MORPHOLOGICAL STRUCTURE OF DOPAMINERGIC-NEURONS IN CULTURES OF RAT SUBSTANTIA-NIGRA

The effect of the various neurotrophin family members on the morpholog ical structure of dopaminergic neurons was compared in dissociated cul tures of embryonic rat ventral mesencephalon. Cultures were maintained in vitro in the presence of brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin-4/5 (NT-4/5), nerve growth factor (NGF) or no added growth factors. Three-dimensional reconstructions o f 48 neurons were made in each of the experimental groups following im munocytochemical staining for tyrosine hydroxylase to detect dopaminer gic neurons, In addition [H-3]mazindol binding analyses were carried o ut in replicate cultures in order to quantify the effects of the neuro trophins on the number of dopamine uptake sites. Among the neurotrophi ns tested, NT-4/5 influenced the proximal morphological parameters mos t, as determined by a 36% increase in the soma profile area and 35% in the number of stem neurites. Analysis of neuritic size and complexity in these cultures revealed that combined neuritic length and number o f segments/cell were increased by 45 and 40% respectively, A change in neurite complexity in the NT-4/5 treated cultures was further confirm ed using Scholl's concentric sphere analysis, In addition, relative to the control, NT-4/5 increased the neuronal differentiation as evidenc ed by increases in varicosity density and [H-3]mazindol binding by 114 and 101% respectively, BDNF and, to a lesser extent, NT-3 also increa sed both proximal parameters and parameters of differentiation, but we re without effect on parameters of neuritic size and complexity, No ef fects on neuronal structure were observed in NGF treated cultures, The se findings demonstrate that BDNF, NT-3 and NT-4/5 influence the morph ological differentiation of dopaminergic neurons in vitro, suggesting they may play a role in the structural development and plasticity of t hese neurons in the mesencephalon.