GPA AND CNTF PRODUCE SIMILAR EFFECTS IN SYMPATHETIC NEURONS BUT DIFFER IN RECEPTOR-BINDING

THE effects of growth promoting activity (GPA) on sympathetic neurone development were investigated in vitro and compared with the effects o f ciliary neurotrophic factor (CNTF). GPA interfered with sympathetic neurone proliferation and induced the expression of vasoactive intesti nal peptide (VIP) in neurones from 7-day-old (E7) chick embryos. The b iological effects observed with saturating levels of GPA are indisting uishable from the effects of CNTF. The effects on VIP expression sugge st that GPA may be involved in the specification of sympathetic neuron e phenotypes. Whereas half maximal effects are achieved at lower conce ntrations of GPA than CNTF, GPA competes less efficiently than CNTF fo r the binding of I-125-labelled CNTF. This suggests similar, but not i dentical interactions of CNTF and GPA with receptors on chick sympathe tic neurones.