Which neurotransmitter is released at preganglionic synapses in BOTH the sympathetic AND parasympathetic divisions of the autonomic nervous system?

Correct answer: B. Acetylcholine

• A. Incorrect. Dopamine is a CNS neurotransmitter not primarily involved at ANS preganglionic synapses.
• B. CORRECT. Acetylcholine (ACh) is the neurotransmitter at ALL preganglionic synapses — both sympathetic and parasympathetic. It binds to nicotinic receptors at the autonomic ganglia. This is a fundamental pharmacology principle (the preganglionic synapse is always cholinergic regardless of division).
• C. Incorrect. Norepinephrine is the postganglionic neurotransmitter of the sympathetic system at effector organs (except sweat glands). It is NOT the preganglionic transmitter.
• D. Incorrect. Serotonin is primarily a CNS and enteric nervous system transmitter, not the main preganglionic ANS neurotransmitter.