The regulation of intracellular free-calcium is altered as a function of age. This dysregulation can reduce neuronal excitability within the hippocampus, and is linked to profound but specific deficits in learning and memory. Via the binding protein calmodulin, two calcium sensitive enzymes play roles as major effector mechanisms, through changes in the phosphorylation/dephosphorylation of proteins. Prior work (Vaccha et. al., SFN Abstracts, 1999) indicated significant alterations in the expression of these enzymes in aged rats. Age-dependent decreases in CaMKII expression and increases in calcineurin expression, detected via immunocytochemistry, was observed in hippocampal, entorhinal cortex and parahippocampal regions, which are all strongly involved in multiple forms of learning and memory. The present study observed age-dependent changes in the expression of mRNA of CamKII and calcineurin. Standard in situ hybridization techniques were applied, yielding fluorescent labeled sections that were quantified...