EFFECTS OF COCAINE ON THE EEG POWER SPECTRUM OF RATS ARE SIGNIFICANTLY ALTERED AFTER ITS REPEATED ADMINISTRATION - DO THEY REFLECT SENSITIZATION PHENOMENA

It was previously shown that a moderate dose of cocaine (10 mg/kg i.p. ) produces a pattern in the EEG power spectrum which indicates a prefe rential activation of dopamine D-1-like receptors, namely a decrease o f power in most of the frequency bands. In contrast, a large dose of c ocaine (30 mg/kg i.p.) produces a decrease of power in most of the fre quency bands as well, but a selective increase in the alpha-1 band, ch aracteristic for an additional activation of dopamine D-2-like recepto rs. In the present experiments, it was studied in rats, if in the cour se of sensitization, a shift from D-1-like to additional D-2-like rece ptor activation will occur or not. For this study, the animals were tr eated 10 times with cocaine (either 10 or 20 mg/kg) and, after a drug free interval of 4 days, tested with the same dose administered previo usly. Acute administration of 10 mg/kg of cocaine increased the locomo tor activity slightly and its effect tended to be enhanced after repea ted administration. Twenty mg/kg cocaine increased the locomotor activ ity more than the 10 mg/kg dose and its effect was significantly enhan ced after repeated treatment. In addition, it was shown that the dose of 10 mg/kg of cocaine which activates D-1- but not D-2-like receptors is sufficient to elicit conditioned place preference. Ten mg/kg of co caine produced a decrease of power in most of the frequency bands and this effect was slightly more pronounced after repeated treatment. Twe nty mg/kg of cocaine acutely also produced a decrease in power in most of the frequency bands, but did not decrease the power in the alpha-1 band, being just at the threshold of activating D-2-like receptors as well. Repeated administration led to a significant increase in power in the alpha-1 band and a less pronounced one in the alpha-2 band. Thi s observation demonstrates that sensitization to cocaine can be manife st in the EEG and that after a certain dosage, a shift from an activat ion of D-1-like dopamine receptors to an additional activation of D-2- like receptors becomes obvious.