input: The following are multiple choice questions (with answers) about medical knowledge.   **Question:** An investigator is studying the pattern of glutamate release from presynaptic nerve terminals in human volunteers with Alzheimer disease. The concentration of glutamate in the CA1 region of the hippocampus is measured using magnetic resonance spectroscopy after Schaffer collateral fibers are electrically stimulated. Which of the following events most likely occurs immediately prior to the release of neurotransmitters?   (A) Activation of G protein-coupled receptors   (B) Accumulation of cAMP   (C) Opening of ligand-gated ion channels   (D) Influx of calcium
output: ['(D) Influx of calcium <> answer', 'The following are multiple choice questions (with answers) about medical knowledge. <> instruction', '(A) Activation of G protein-coupled receptors  (B) Accumulation of cAMP  (C) Opening of ligand-gated ion channels  (D) Influx of calcium <> possible answers', '  An investigator is studying the pattern of glutamate release from presynaptic nerve terminals in human volunteers with Alzheimer disease. The concentration of glutamate in the CA1 region of the hippocampus is measured using magnetic resonance spectroscopy after Schaffer collateral fibers are electrically stimulated. Which of the following events most likely occurs immediately prior to the release of neurotransmitters? <> context']