Apomorphine-induced alterations in cortical EEG activity of rats. Involvement of D-1 and D-2 dopamine receptors.

EEG activity after activation of dopamine receptors of D-1 and/or D-2 type was studied by using telemetric recordings in rats. Apomorphine, a preferential D-2 agonist, produced a characteristic increase in the power of alpha-1 band (7.00-9.50 Hz) when given in doses mediating stereotypies (0.2 or 0.5 mg/kg s.c.). Low doses produced a general increase in the power of all of the bands except beta-2. In particular, delta activity was enhanced which seems to be in correspondence with the sedation observed after these doses (0.02 and 0.05 mg/kg). Haloperidol in a dose which is assumed to block both D-1 and D-2 receptors (0.1 mg/kg i.p.) completely antagonized the alpha-1 activation produced by apomorphine (0.5 mg/kg). A similar, although not complete inhibition of alpha-1 activation was found after administration of a large dose of the selective D-1 antagonist SCH 23390 (0.2 mg/kg i.p.). The selective agonist at D-2 receptors quinpirole (1.0 mg/kg s.c.) produced a less pronounced activation of the power in the alpha-1 band than apomorphine. In general, there was found to be a good correlation between the activation of the alpha-1 activity and stereotyped behaviour. The results suggest that for the full expression of alpha-1 activation, a pronounced activation of D-2 receptors and at least a minimal activation of D-1 receptors, for instance by the endogenous dopamine, is necessary.