Amplitude and spectral quantification of the effects of morphine on the cortical EEG of the rat.

The effect of systemically administered morphine sulfate on the cortical EEG of the rat was studied using direct visual scoring procedures and spectral and amplitude distribution analysis techniques. The EEG effect was found to be dose-dependent, i.e., as higher doses of morphine were administered morphine-induced spindles or spike-like activity progressively increased and were eventually replaced by a highly synchronized EEG. In quantifying these EEG patterns, using spectral analysis, distinct frequency spectra were found for morphine-induced spindles and epochs of high voltage low frequency (HVLF) activity. The power in the 5-7 Hz frequency band was found to be a good indicator of the duration of the morphine effect since the value of this index was elevated during the time course of the drug effect. In addition, amplitude distribution methods revealed the sensitivity of two specific measures to the EEG changes induced by morphine. Values of standard amplitude followed closely the degree of EEG synchronization while kurtosis proved sensitive enough to follow the effect of specific doses of morphine sulfate.