Fig. 1.

Acetylcholine activates nicotinic responses in dorsal raphe neurons. A, Three voltagetraces show typical depolarizing and hyperpolarizing membrane potential responses to acetylcholine and a depolarizing response to neostigmine from three different neurons. All responses are associated with a decrease in input resistance, measured with intracellular current injection (600 msec in duration; 50 pA in amplitude; downward deflections in all traces).B, In the presence of the muscarinic antagonist atropine, acetylcholine and nicotine both induce a membrane depolarization, suggesting activation of nicotinic receptors.C, The role of nicotinic receptors in the cholinergic responses is supported further by blockade of both depolarizing and hyperpolarizing responses to the nicotinic agonist DMPP by the nicotinic antagonist mecamylamine in two different neurons in the presence of atropine. The depolarizing response recovers by >50% after a 10 min wash in control medium, and the hyperpolarizing response recovers by >90% after a 6 min wash.