INVOLVEMENT OF GABA(B) RECEPTOR SYSTEMS IN ACTION OF ANTIDEPRESSANTS .2. BACLOFEN ATTENUATES THE EFFECT OF DESIPRAMINE WHEREAS MUSCIMOL HASNO EFFECT IN LEARNED HELPLESSNESS PARADIGM IN RATS

Involvement of GABAergic systems in action of antidepressants was exam ined in the learned helplessness paradigm in rats. Rats were treated w ith desipramine, baclofen or muscimol for 14 days. On day 14, the rats were subjected to 90 inescapable shocks. On day 15, the rats received the 40-trial escape test. The inescapable shocks induced the subseque nt increase in escape failures in the escape test. Desipramine dose-de pendently improved the increased escape failures induced by the inesca pable shocks. Baclofen attenuated the escape failures-improving effect of desipramine, although baclofen had no effects on the increased esc ape failures when it was injected alone. Muscimol at any dose failed t o influence the increased escape failures. Therefore, it is suggested that the long-term decrease in GABA(B) neurotransmission may be involv ed in the action of antidepressants. Our present results do not suppor t the hypothesis that activation of GABA(A) receptors may contribute t o the action of antidepressants.