The developmental expression of choline acetyltransferase (ChAT) and the neuropeptide VIP in chick sympathetic neurons: evidence for different regulatory events in cholinergic differentiation

Cholinergic properties in chick sympathetic neurons are detectable early during development of paravertebral ganglia and mature after target contact. The cholinergic marker choline acetyltransferase (ChAT) is first detectable at embryonic day 6 and its expression partly overlaps with that of the noradrenergic marker tyrosine hydroxylase (TH). At late embryonic stages, when sympathetic neurons have established target contact, ganglia consist of two major neuronal populations, TH-positive noradrenergic neurons and cholinergic neurons that at this stage express vasoactive intestinal peptide (VIP) in addition to ChAT. The maturation of sympathetic neurons is paralleled by changes in their response to the neurokine ciliary neurotrophic factor (CNTF). These findings suggest that expression of neurotransmitter properties is controlled differentially before and during target innervation.