Effect of Lithium on the Expression of Phosphodiesterase type 4B mRNA in the Rat Frontal Cortex and Hippocampus

Background : It has been suggested that lithium, which is widely used in the treatment of mood disorders, affects the cyclic adenosine monophosphate (cAMP) signaling system. Previous studies have indicated that the mRNA expression level of phosphodiesterase (PDE) 4B, which metabolizes cAMP, is a useful index of the net change in cAMP signaling. In the present study, the effect of lithium on the expression of PDE4B mRNA was examined to further characterize its effect on cAMP signaling.Methods and Results : Rats were treated with lithium for 2 weeks (subchronic treatment) or 4 weeks (chronic treatment), and the expression of PDE4B mRNA in the frontal cortex and hippocampus was quantified by northern blot analysis. Chronic lithium treatment significantly (p < 0.05) decreased the expression of PDE4B mRNA in the hippocampus but produced no such change in the frontal cortex.Conclusion : This result suggests that cAMP signaling in the hippocampus is attenuated by chronic lithium treatment. Furthermore, this change may be associated with the antimanic and prophylactic effects of lithium