SELECTIVE MODULATION OF CHOLINERGIC PROPERTIES IN CULTURES OF AVIAN EMBRYONIC SYMPATHETIC-GANGLIA

We have studied the expression of catecholaminergic and cholinergic phenotypes in sympathetic ganglia removed from 7- to 10-day-old quail embryos and grown in vitro under different conditions. Quantitative data were obtained by measuring the conversion of (H-3) tyrosine and (H-3) choline to catecholamines (CA) and acetylcholine (ACh), respectively. In explant cultures, large amounts of both neurotransmitters were synthesized from the onset, but CA generally predominated, the molar ratios of CA:ACh being, on average, of the order of 2:1. If the ganglia were dissociated before plating, there was a selective increase in ACh synthesis (three- to fivefold) such that the CA:ACh ratio fell strikingly. The early expression of the cholinergic phenotype appears to be species-specific in that, under identical conditions, dissociated cell cultures of newborn mouse superior cervical ganglia were overwhelmingly catecholaminergic (CA:ACh ratio of approximately 40:1) and ACh synthesis was only just detectable. Addition of veratridine (1.5 muM) either to explant or to dissociated cell cultures of embryonic quail sympathetic ganglia barely altered CA-synthesizing ability; in contrast, ACh synthesis and accumulation were stimulated about threefold. This effect, which we found to correspond to a quantitatively similar increase in the activity of choline acetyltransferase (ChAT), was completely blocked by tetrodotoxin, indicating that it was due to Na+-dependent depolarization. A preferential stimulation of ACh production was also observed when the concentration of K+ was raised to 20 mM. Veratridine treatment of cultures of presumptive sympathoblasts, in the form of sclerotome-associated neural crest cells, had identical effects. Our results reveal the quantitative importance of ACh-related properties in avian sympathetic ganglia from the earliest stages of their development and suggest that depolarization may be one of the factors selectively enhancing expression of the cholinergic phenotype during ontogeny. In these respects, the neurochemical differentiation of sympathetic neurons unfolds according to dissimilar scenarios in birds and mammals.