EEG POWER SPECTRA AND BEHAVIORAL-CORRELATES IN RATS GIVEN CHRONIC MORPHINE - LACK OF RESIDUAL LONG-TERM EEG AND NEURONAL CHANGES

The short-term (during tolerance to behavioural effects and withdrawal ) and long-term (3, 6, 9 and 12 months after treatment) effects of mor phine on mean total electroencephalographic spectral power (analysed b y means of fast Fourier transform) and band distribution (delta, Theta , alpha, beta) were studied in freely moving young rats implanted with chronic cortical bilateral recording electrodes. Morphine was adminis tered i.p. daily for 1 month at weekly increasing doses of 20, 50, 100 and 200 mg kg(-1), and the electroencephalogram was evaluated for 2 h at every change of dose. Treatment with 20, 50 and 100 mg kg(-1) led to a significant increase in mean total spectral power 30-60 min from treatment. However, the dose of 100 mg kg(-1) led to a smaller increas e than that obtained with 50 mg kg(-1) and no change was shown with th e highest dose, suggesting the progressive development of tolerance. T he modification observed for 100 mg kg(-1) was accompanied by a relati ve increase in the delta and decrease in the Theta and alpha power spe ctra. Between the last day of morphine and the first 3 days of abstine nce, a progressive decrease in mean total spectral power accompanied b y a significant increase in delta and beta and a decrease in Theta and alpha frequency was observed. Long-term EEG activity and the counting of the pyramidal cells of the hippocampus failed to reveal any pathol ogical findings after 3, 6, 9 and 12 months. (C) 1995 The Italian Phar macological Society