Effects of stimulation of putative dopamine autoreceptors on electroencephalographic power spectrum in comparison with effects produced by blockade of postsynaptic dopamine receptors in rats.

Alterations in cortical EEG activity in male rats produced by putative agonists at dopamine (DA) autoreceptors and by antagonists at postsynaptic DA receptors were compared in order to study, whether an impairment in dopaminergic neurotransmission via two different mechanisms might result in similar or different effects. Simultaneously to the EEG recordings, gross behaviour was observed. Putative agonists at DA autoreceptors (apomorphine 0.05 mg/kg, quinpirole 0.05 mg/kg, or talipexole 0.02 mg/kg s.c.) produced increases in the power in all of the frequency bands, except beta-2, with the most pronounced increase in the delta band. These EEG alterations were accompanied by hypokinesia, ptosis and yawning. In contrast, antagonists at DA receptors (haloperidol 0.1 mg/kg i.p., D2 blocker) or SCH 23390 (0.2 mg/kg i.p., D1 blocker) led to little increases in the delta band, but more pronounced increases in the alpha-2 band. Behavioural signs were hypokinesia, but little ptosis and yawning. The combination of both blockers produced, in addition, strong increases in the delta band and behavioural signs of ptosis and yawning. These results suggest that activation of putative dopamine autoreceptors produces EEG patterns and behavioural patterns different from those produced by blockade of either D1 or D2 postsynaptic dopamine receptors. In contrast, the effects following a stimulation of putative DA autoreceptors, which are expected to decrease the release of the agonist and its action at postsynaptic D1 and D2 receptors, were very similar to those found after a combined blockade of both types of postsynaptic dopamine receptors.