Phosphodiesterase-4 (PDE4), an enzyme that catalyzes the hydrolysis of cyclic AMP and plays a critical role in controlling its intracellular concentration, has been implicated in depression-and anxiety-like behaviors. However, the functions of the four PDE4 subfamilies (PDE4A, PDE4B, PDE4C, and PDE4D) remain largely unknown. In animal tests sensitive to anxiolytics, antidepressants, memory enhancers, or analgesics, we examined the behavioral phenotype of mice deficient in PDE4B (PDE4BÀ/À). Immunoblot analysis revealed loss of PDE4B expression in the cerebral cortex and amygdala of PDE4BÀ/À mice. The reduction of PDE4B expression was accompanied by decreases in PDE4 activity in the brain regions of PDE4BÀ/À mice. Compared to PDE4B + / + littermates, PDE4BÀ/À mice displayed anxiogenic-like behavior, as evidenced by decreased head-dips and time spent in head-dipping in the holeboard test, reduced transitions and time on the light side in the light-dark transition test, and decreased initial exploration and rears in the open-field test. Consistent with anxiogenic-like behavior, PDE4BÀ/À mice displayed increased levels of plasma corticosterone. In addition, these mice also showed a modest increase in the proliferation of neuronal cells in the hippocampal dentate gyrus. In the forced-swim test, PDE4BÀ/À mice exhibited decreased immobility; however, this was not supported by the results from the tail-suspension test. PDE4BÀ/À mice did not display changes in memory, locomotor activity, or nociceptive responses. Taken together, these results suggest that the PDE4B subfamily is involved in signaling pathways that contribute to anxiogenic-like effects on behavior.

No abstract

Competitive N-methyl-D-aspartate receptor (NMDAR) antagonists bind to the GluN2 subunit, of which there are four types (GluN2A-D). We report that some N1-substituted derivatives of cis-piperazine-2,3-dicarboxylic acid display improved relative affinity for GluN2C and GluN2D versus GluN2A and GluN2B. These derivatives also display subtype-selectivity among the more distantly related kainate receptor family. Compounds 18i and (−)-4 were the most potent kainate receptor antagonists and 18i was selective for GluK1 versus GluK2, GluK3 and AMPA receptors. Modeling studies revealed structural features required for activity at GluK1 subunits and suggested that S674 was vital for antagonist activity. Consistent with this hypothesis, replacing the equivalent residue in GluK3 (alanine) with a serine imparts 18i antagonist activity. Antagonists with dual GluN2D and GluK1 antagonist activity may have beneficial effects in various neurological disorders. Consistent with this idea, antagonist 18i (30 mg/Kg i.p.) showed antinociceptive effects in an animal model of mild nerve injury.

No abstract

No abstract