Fig.1.
Effects of a single dose of morphine on PGi neuronal activities. (A–D) Histograms of excitatory and inhibitory effects of a single dose of morphine on PGi neurons. Morphine was injected i.c.v. at time 0. Naltrexone or saline vehicle was injected 20 min after morphine injection. (E and F) Summary of the reversal effects of naltrexone on acute morphine-induced inhibition and excitation of PGi neurons (E. i.c.v. injection, F. i.v. injection). Bars represent mean firing rate of PGi neurons 10 min before morphine injection (baseline), 10–20 min after morphine injection and 0–10 min after naltraxone injection, respectively. Error bars represent S.E.M. ***P< 0.001, **P<0.005, *P<0.05 (One-way repeated measures analysis of variance and Boferonii test).