Mutant mice lacking ryanodine receptor type 3 exhibit deficits of contextual fear conditioning and activation of calcium/calmodulin-dependent protein kinase II in the hippocampus

As it is known that ryanodine receptor type 3 is expressed in the hippocampus, we examined the contribution of this receptor to contextual fear conditioning behavior and to the activation of Ca²⁺/calmodulin-dependent protein kinase II using mice lacking the receptor. Ryanodine receptor type 3-deficient mice exhibited impairments of performance in the contextual fear conditioning test, passive avoidance test, and Y-maze learning test. Both the activities of Ca²⁺/calmodulin-dependent protein kinase IIβ and Ca²⁺/calmodulin-dependent protein kinase IIα were significantly increased in the experimental group compared to the control group in the hippocampus, but not in the cingulate cortex on the testing day 24 h after contextual fear training. However, the activities of Ca²⁺/calmodulin-dependent protein kinase IIβ and α were almost the same in the experimental and control groups in the hippocampus on the training day. Ryanodine receptor type 3-deficient mice did not show the increment of Ca²⁺/calmodulin-dependent protein kinase IIβ and α activities in the hippocampus on the testing day. In addition, these mutant mice showed the reduction of fear response in the elevated plus-maze test. The present results suggest that calcium-induced calcium release through the activation of ryanodine receptor type 3 in the hippocampus is important to the expression of the performance of contextual learning through the elevation of Ca²⁺/calmodulin-dependent protein kinase IIβ and α activities. Copyright (C) 2000 Elsevier Science B.V.