Blockade of the GABA(B) receptor increases neurogenesis in the ventral but not dorsal adult hippocampus: relevance to antidepressant action.

GABA(B) receptor antagonists have been shown to have antidepressant-like properties in animal models and thus, could represent a novel approach for the treatment of depression. The neurobiological mechanisms underlying these effects are currently unknown. Adult hippocampal neurogenesis (the birth of new neurons) is thought to play a role in antidepressant drug action. However, the ability of GABA(B) receptors to modulate the proliferation and survival of newly-born cells in the adult hippocampus remains unexplored. Therefore, we investigated whether the GABA(B) receptor antagonist, CGP 52432, can induce antidepressant-like behaviour and increase hippocampal neurogenesis in the stress-sensitive mouse strain, BALB/c. Male mice were treated with CGP 52432 either acutely (one injection, 3; 10; 30 mg/kg, i.p.), subchronically (7 days, 3; 10 mg/kg, i.p.) or chronically (21 days, 3; 10 mg/kg, i.p.) and antidepressant-like behaviour was assessed using the forced swim test (FST). The effects of CGP 52432 on the proliferation and survival of newly-born cells in the hippocampus were assessed using BrdU immunohistochemistry. Acute, subchronic and chronic treatment with CGP 52432 induced antidepressant-like behavioural effects in the FST. Moreover, chronic but not acute or subchronic treatment with CGP 52432 increased hippocampal cell proliferation but had no effect on the survival of newly-born cells. This temporal effect is consistent with the time course for the therapeutic action of antidepressants. Interestingly, CGP 52432-induced increases in cell proliferation occurred in the ventral but not in the dorsal hippocampus. This topographical segregation concurs with the hypothesis that the ventral hippocampus is primarily involved in the regulation of stress and emotionality. Taken together, our data suggest that increased hippocampal cell proliferation is a plausible mechanism for the antidepressant-like effects of GABA(B) receptor antagonists following chronic but not acute treatments. Moreover, altered behavioural effects in the FST does not correlate with changes in neurogenesis.