ELECTROENCEPHALOGRAPHIC CORRELATES OF THE SEDATIVE EFFECTS OF DOPAMINE AGONISTS PRESUMABLY ACTING ON AUTORECEPTORS

Alterations both in the activity of the cortical EEG and behaviour were studied after administration of dopamine receptor agonists. In addition to apomorphine, which provided contrasting effects, both on the EEG and behaviour, when small and large doses were compared, alterations elicited by the D2 agonist, quinpirole and another agonist, with preference for dopamine D2 autoreceptors, talipexole (B-HT 920), were evaluated by using telemetric EEG recordings in rats. Similarly to apomorphine, quinpirole produced opposite effects after small and large doses: a small dose (0.05 mg/kg) led to sedation and an increase of EEG power spectra in all of the bands, except beta2, whereas a larger dose (0.5 mg/kg) elicited stereotypy and desynchronization of the EEG, with a characteristic increase of power in the alpha1 band. The effects on the EEG and on behaviour, obtained with the small dose of quinpirole were very similar to those of a small dose of apomorphine (0.05 mg/kg) and a small dose of talipexole (0.02 mg/kg) but even the large dose of talipexole (0.5 mg/kg) produced similar effects: all of these treatments produced behavioural sedation and an increase of power in the EEG in all of the bands, except beta2; such increases appeared most pronounced in the delta band. The present study provides further evidence that drugs, which are assumed to activate dopamine autoreceptors, are effective in inducing sedation. This sedation was accompanied by a characteristic pattern, observed in EEG power spectra analysis.