Modification by tricyclic antidepressants of cortical EEG changes induced by clonidine in conscious rats

The effects of various tricyclic antidepressants on clonidine-induced electroencephalographic changes were investigated in rats. The EEG pattern of conscious rats was recorded by means of bipolar electrodes, implanted chronically. Clonidine (50, 150 and 300 micrograms/kg) not only synchronized cortical EEG pattern but also evoked signs of behavioural depression within 15 min of its administration. Pretreatment with imipramine, desipramine, trimipramine, amitriptyline, nortriptyline and doxepin reduced clonidine-induced EEG synchrony without showing any effects per se. Acute treatment with tricyclic antidepressants failed to modify but, chronic treatment abolished the clonidine-induced behavioural depressive signs. Chronic administration of tricyclic antidepressants (10 mg/kg/day) evoked more pronounced antagonism of the EEG effects of clonidine. Yohimbine (200 micrograms/kg) pretreatment inhibited both, clonidine-induced EEG synchrony and behavioural effects. Guanfacine as well as B-HT 920, elicited clonidine-like effects on cortical EEG pattern and behaviour. The present data suggests that antagonism of clonidine-induced EEG synchronization in conscious animals could serve as a useful test for screening of antidepressant drugs.