Fig. 2.
Naloxone (1 μm) depolarized an opioid-sensitive neuron maintained in morphine (5 μm)in vitro from a dependent animal. A, Met-enkephalin (ME, 30 μm, indicated bybar under trace) hyperpolarized the neuron (from −71 mV, −30 pA applied current; resting membrane potential was −66 mV). Then the neuron was hyperpolarized to −85 mV by applying a −100 pA constant current to illustrate the possible amplitude of naloxone-induced depolarizations without the confounding influence of action potential activity. Naloxone superfusion then depolarized the neuron beyond threshold (22 mV; breaks in traces of ∼2 min each for determination of voltage–current relationships) (data not shown).B, Responses of a control neuron to met-enkephalin (ME, 30 μm), morphine (10 μm), and morphine plus naloxone (1 μm) for comparison (from −70 mV, −30 pA applied current; neuron was spontaneously active in the absence of applied current). Voltage–current relationships were determined during breaks intraces (actual breaks were ∼2 min each).