MULTIPLE MECHANISMS REGULATE SYMPATHETIC NEURONAL PHENOTYPE

Adult rat sympathetic neurons can possess specific neuropeptides utili zed as cotransmitters along with norepinephrine, but the factors that regulate their expression remain unknown. 60% of adult rat superior ce rvical ganglion (SCG) neurons express neuropeptide Y (NPY) in vivo, To determine whether the restricted expression was an intrinsic property of sympathetic ganglia, we examined if embryonic sympathetic precurso rs gave rise to NPY immunoreactive (-IR) neurons in vitro, After one w eek in culture, 60% of neurons derived from the E14.5 rat SCG were NPY -IR. Thus? ganglia isolated before peripheral target contact or pregan glionic innervation were capable of regulating NPY expression both in the number of neurons with NPY and in the developmental timing of NPY expression, To determine if the restricted expression of NPY was a ref lection of neuroblasts committed to an NPY fate, SCG precursors were l abeled with a replication incompetent retrovirus carrying lacZ, and NP Y expression in lacZ-labeled clones examined after one week, Two third s of neuronal clones obtained were uniformly NPY-IR; that is, ail neur ons in a clone either possessed or lacked NPY. One-third of the neuron al clones were mixed and contained both neurons with and without NPY, We provide a novel demonstration that both lineage and environmental c ues contribute to neuropeptide phenotype.