Neurotrophins differentially enhance acetylcholine release, acetylcholine content and choline acetyltransferase activity in basal forebrain neurons

Several lines of evidence indicate that nerve growth factor is important fo r the development and maintenance of the basal forebrain cholinergic phenot ype, in the present study, using rat primary embryonic basal forebrain cult ures, we demonstrate the differential regulation of functional cholinergic markers by nerve growth factor treatment (24-96 h). Following a 96-h treatm ent, nerve growth factor (1-100 ng/mL) increased choline acetyltransferase activity (168-339% of control), acetylcholine content (141-185%), as well a s constitutive (148-283%) and K+-stimulated (162-399%) acetylcholine releas e, but increased release was not accompanied by increased high-affinity cho line uptake. Enhancement of ACh release was attenuated by vesamicol (1 muM) , suggesting a vesicular source, and was abolished under choline-free condi tions, emphasizing the importance of extracellular choline as the primary s ource for acetylcholine synthesized for release. A greater proportion of ac etylcholine released from nerve growth factor-treated cultures than from ne rve growth factor-naive cultures was blocked by voltage-gated Ca2+ channel antagonists, suggesting that nerve growth factor modified this parameter of neurotransmitter release. Cotreatment of NGF (20 ng/mL) with K252a (200 nM ) abolished increases in ChAT activity and prevented enhancement of K+-stim ulated ACh release beyond the level associated with K252a, suggesting the i nvolvement of TrkA receptor signaling. Also, neurotrophin-3, neurotrophin-4 and brain-derived neurotrophic factor (all at 5-200:ng/mL) increased acety lcholine release, although they were not as potent as nerve growth factor a nd higher concentrations were required. High brain-derived neurotrophic fac tor concentrations (100 and 200 ng/mL) did, however, increase release to a level similar to nerve growth factor, in summary, long-term exposure (days) of basal forebrain cholinergic neurons to nerve growth factor, and in a le ss-potent fashion the other neurotrophins, enhanced the release of acetylch oline, which was dependent upon a vesicular pool and the availability of ex tracellular choline.