Nerve growth factor (NGF) is a member of a family of molecules (the neurotrophins) that can regulate the survival and/or outgrowth of many vertebrate cells. NGF also induces outgrowth from Lymnaea neurons under experimental conditions. Recent studies have shown that the neurotrophins can also acutely modulate some physiological properties of adult neurons. Here we examined the actions of NGF on high-voltage-activated (HVA) Ca2+ currents in Lymnaea motoneurons. 2. NGF induced a dose-dependent and reversible increase in HVA Ca2+ currents within 2 min. 3. The threshold dose of the NGF-induced enhancement of HVA Ca2+ currents ranged between 1 and 1,000 pg/ml. In the most sensitive cells, the response saturated at doses higher than 1 ng/ml. 4. The results indicate that neurotrophins acutely modulate voltage-gated Ca2+ currents in molluscan neurons through a high affinity signal transduction pathway. The data support the existence of neurotrophins in invertebrates. Moreover, this property of NGF may explain the neuromodulatory actions of neurotrophins observed in various preparations.
