Distinct populations of hypothalamic dopaminergic neurons exhibit differential responses to brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT3)

We have previously demonstrated that differentiation of hypothalamic dopaminergic (DA) neurons can be induced in culture by their pituitary intermediate lobe target cells, through both membrane and diffusible factors. We also showed that subpopulations of DA neurons from the arcuate nucleus only, not the periventricular area, can respond to the target. Here we investigated the possibility that both neuronal subsets could also respond differentially to brain-derived neurotrophic factor (BDNF) or neurotrophin-3 (NT3). Addition of NT3, but not BDNF, enhanced growth and branching of neurites, tyrosine hydroxylase (TH) as well as increasing levels of cultured arcuate DA neurons. Conversely, BDNF, but not NT3, affected the same parameters in cultured periventricular DA neurons. The neurotrophins thus affect DA neurons in a structure and neuronal type-selective manner, since general neuronal markers were not affected by either neurotrophin. Neurotrophin effects were reversed by addition of specific antibodies directed against them or their respective receptors, TrkB or TrkC. By themselves, the antibodies inhibited development of DA neurons below that of control cultures, suggesting involvement of endogenous neurotrophins. BDNF and NT3 were indeed found in both arcuate and periventricular neurons and in the intermediate lobe. BDNF was always present as the mature peptide. The mature form of NT3 was only detected in the periventricular area; a precursor-like heavier form was present in all tissues studied. The present data suggest that NT3, but not BDNF, could participate in the differentiating action of intermediate lobe cells on arcuate DA neurons.