Naloxone causes a dose-dependent increase in total power and delta wave activity in the EEG of opioid-naive rats

We studied the effect of opioid blockade with naloxone on the EEG of rats maintained chronically with i.v. catheters and cortical electrodes. EEG was analyzed on line by fast fourier transform, and drug was given as bolus injections during nighttime, active periods. Naloxone caused increases in EEG amplitude, reflected as increased total spectral power, for 60 to 90 min after injections. Power was increased primarily in the delta bandwidth, but spindles of large amplitude theta activity also occurred. An inverted "U" shaped dose-response relationship was obtained, with 1.0 mg/kg being the most effective dose. The appearance of enhanced slow wave activity in the EEG after blockade of opioid receptors suggests that endogenous opioid peptides may play a role in maintaining arousal during active periods in the rat.