Nerve growth factor rapidly induces prolonged acetylcholine release from cultured basal forebrain neurons: Differentiation between neuromodulatory and neurotrophic influences

Long-term exposure to nerve growth factor (NGF) is well established to have neurotrophic effects on basal forebrain cholinergic neurons, but its poten tial actions as a fast-acting neuromodulator are not as well understood. We report that NGF (0.1-100 ng/ml) rapidly (<60 min) and robustly enhanced co nstitutive acetylcholine (ACh) release (148-384% of control) from basal for ebrain cultures without immediate persistent increases in choline acetyltra nsferase activity. More ACh was released in response to NGF when exposure w as coupled with a higher depolarization level, suggesting activity dependen ce. In a long-term potentiation-like manner, brief NGF exposure (10 ng/ml; 60 min) induced robust and prolonged increases in ACh release, a capacity t hat was shared with the other neurotrophins. K252a (10-100 nM), BAPTA-AM (2 5 <mu>M), and Cd2+ (200 muM) prevented NGF enhancement of ACh release, sugg esting the involvement of TrkA receptors, Ca2+, and voltage-gated Ca2+ chan nels, respectively. Forskolin (10 muM), a cAMP generator, enhanced constitu tive ACh release but did not interact synergistically with NGF. Tetrodotoxi n (1 muM) and cycloheximide (2 mu mM) did not prevent NGF-induced ACh relea se, indicative of action at the level of the cholinergic nerve terminal and that new protein synthesis is not required for this neurotransmitter-like effect, respectively. In contrast, after a 24 hr NGF treatment, distinct pr otein synthesis-dependent and independent effects on choline acetyltransfer ase activity and ACh release were observed. These results indicate that neu romodulator/neurotransmitter-like (protein synthesis-independent) and neuro trophic (translation-dependent) actions likely make distinct contributions to the enhancement of cholinergic activity by NGF.