Fig. 2.

The two nicotinic responses are selectively affected by either TTX or low calcium and high magnesium in the perfusion medium. A, Two voltage tracesfrom the same neuron before and during exposure to TTX show a TTX-dependent blockade of the depolarizing response that reveals a TTX-insensitive hyperpolarizing response to the nicotinic agonist DMPP.B, A histogram of the average of the voltage amplitude of the nicotinic response from the same neurons before (control) and during exposure to TTX demonstrates the reversal of polarity of this response.C, Voltage traces show that the addition of low calcium and high magnesium to the perfusion medium also reverses the polarity of the nicotinic response. D, In the presence of prazosin (1 μm), the nicotinic response is hyperpolarizing, and the hyperpolarization is unaffected by low calcium and high magnesium.