INVOLVEMENT OF GABA(B) RECEPTOR SYSTEMS IN EXPERIMENTAL DEPRESSION - BACLOFEN BUT NOT BICUCULLINE EXACERBATES HELPLESSNESS IN RATS

There are two gamma-aminobutyric acid (GABA) hypotheses of the antidep ressants action: an increase in GABA(A) neurotransmission or a decreas e in GABA(B) neurotransmission may contribute to action of antidepress ants. In this study, involvement of GABA(A) and GABA(B) receptor syste ms was examined in the learned helplessness paradigm in rats. Rats wer e injected with bicuculline or baclofen for 14 days. On day 14, the ra ts were subjected to 15 inescapable shocks. On day 15, they underwent the 40-trial escape test. Baclofen exacerbated the escape failures in the rats subjected to the inescapable shocks, although baclofen had no effects in the animals without shock pre-treatment. Bicuculline faile d to influence the escape failures in the rats with the 15-shock pre-t reatment. These results suggest that the long-term increase in GABA(B) neurotransmission but not the long-term attenuation of GABA(A) neurot ransmission may be related to helplessness in rats.