The absence of a major Ca(2+) signaling pathway in GABAergic neurons of the hippocampus

The Ca(2+)/calmodulin-dependent protein phosphatase 2B or calcineurin (CN) participates in several Ca(2+)-dependent signal transduction cascades and, thus, contributes to the short and long term regulation of neuronal excitability. By using a specific antibody to CN, we demonstrate its absence from hippocampal interneurons and illustrate a physiological consequence of such CN deficiency. Consistent with the lack of CN in interneurons as detected by immunocytochemistry, the CN inhibitors FK-506 or okadaic acid significantly prolonged N-methyl-d-aspartate channel openings recorded in the cell-attached mode in hippocampal principal cells but not those recorded in interneurons. Interneurons were also devoid of Ca(2+)/calmodulin-dependent protein kinase IIα, yet many of their nuclei contained the cyclic AMP-responsive element binding protein. On the basis of the CN and Ca(2+)/calmodulin-dependent protein kinase IIα deficiency of interneurons, entirely different biochemical mechanisms are expected to govern Ca(2+)-dependent neuronal plasticity in interneurons versus principal cells.