The alpha 7 nicotinic acetylcholine receptor subtype mediates nicotine protection against NMDA excitotoxicity in primary hippocampal cultures througha Ca2+ dependent mechanism

Neuronal nicotinic acetylcholine receptors (nAChR) have been suggested to p lay a role in a variety of modulatory and regulatory processes, including n europrotection. Here we have characterized the neuroprotective effects of n icotine against an excitotoxic insult in primary hippocampal cultures. Expo sure of hippocampal neurons to 200 muM NMDA for 1 h decreased eel viability by 25+/-5%, an effect blocked by NMDA receptor antagonists. Nicotine (10 m uM) counteracted the NMDA-induced cell death when co-incubated with NMDA or when present subsequent to the NMDA treatment. Nicotine protection was pre vented by 1 muM MLA, confirming that it was mediated by nAChR, and by 1 muM alpha -bungarotoxin, demonstrating that the alpha7 nAChR subtype was respo nsible. Both the NMDA evoked neurotoxicity and nicotine neuroprotection wer e Ca2+-dependent. In Fura-2-loaded hippocampal neurons, nicotine (10 muM) a nd NMDA (200 muM) acutely increased intracellular resting Ca2+ from 70 nM t o 200 and 500 nM, respectively. Responses to NMDA were unaffected by the pr esence of nicotine. Ca-45(2+) uptake after a 1 h exposure to nicotine or NM DA also demonstrated quantitative differences between the two drugs. This s tudy demonstrates that the alpha7 subtype of nAChR can support neuronal sur vival after an excitotoxic stimulus, through a Ca2+ dependent mechanism tha t operates downstream of NMDA receptor activation. (C) 2000 Elsevier Scienc e Ltd. All rights reserved.