Effect of D1- and D2-dopamine agonists on neocortical and hippocampal EEG activity of rat brain: modulation of rimcazole effect.

The effect of selective D1- and D2-dopamine (DA) receptor stimulation on neocortical and hippocampal electroencephalographic (EEG) activity of rat brain was studied. The modulation of the effect of rimcazole, a sigma receptor antagonist, by D1- and D2-DA receptor agonists was also investigated. B-HT 920 (0.5 mg/kg), a D2 DA agonist, produced significant inhibition of EEG activity in neocortex and hippocampus. The lower doses of B-HT 920 (0.1 and 0.25 mg/kg) either enhanced the frequency and amplitude of cortical and hippocampal firing or lacked any significant effect. The inhibitory effect of B-HT 920 was blocked by haloperidol (0.5 mg/kg), a D2-receptor antagonist and enhanced by idazoxan (1.0 mg/kg), an alpha 2-adrenoceptor antagonist. SKF 38393 (5.0 mg/kg), a D1-DA receptor agonist and dopamine (10 mcg/rat) or apomorphine (0.5 mg/kg), a mixed D1-/D2-agonist, also inhibited the frequency and amplitude of cortical and hippocampal EEG. A significantly higher inhibition of electrical activity was observed following concomitant administration of B-HT 920 (0.1 mg/kg) and SKF 38393 (5.0 mg/kg) in comparison with the effect of each drug alone. Rimcazole (6.0 mg/kg) increased the frequency of cortical and hippocampal firing. Amplitude of cortical firing was enhanced but not of hippocampal EEG following administration of rimcazole. Rimcazole blocked the effect of SKF 38393 (5.0 mg/kg) and apomorphine (0.5 mg/kg) but not of B-HT 920 (0.5 mg/kg) on cortical and hippocampal EEG, respectively. The above data suggests a modulatory effect of D1-receptor activation on the inhibitory effect of D2-receptor stimulation in cortex as well as hippocampus and the blockade by rimcazole of the effect of D1-DA receptor agonist in these areas.