Retrieval of Context-Associated Memory is Dependent on the Ca(v)3.2 T-Type Calcium Channel

Among all voltage-gated calcium channels, the T-type Ca(2+) channels encoded by the Ca(v)3.2 genes are highly expressed in the hippocampus, which is associated with contextual, temporal and spatial learning and memory. However, the specific involvement of the Ca(v)3.2 T-type Ca(2+) channel in these hippocampus-dependent types of learning and memory remains unclear. To investigate the functional role of this channel in learning and memory, we subjected Ca(v)3.2 homozygous and heterozygous knockout mice and their wild-type littermates to hippocampus-dependent behavioral tasks, including trace fear conditioning, the Morris water-maze and passive avoidance. The Ca(v)3.2 (−/−) mice performed normally in the Morris water-maze and auditory trace fear conditioning tasks but were impaired in the context-cued trace fear conditioning, step-down and step-through passive avoidance tasks. Furthermore, long-term potentiation (LTP) could be induced for 180 minutes in hippocampal slices of WTs and Ca(v)3.2 (+/−) mice, whereas LTP persisted for only 120 minutes in Ca(v)3.2 (−/−) mice. To determine whether the hippocampal formation is responsible for the impaired behavioral phenotypes, we next performed experiments to knock down local function of the Ca(v)3.2 T-type Ca(2+) channel in the hippocampus. Wild-type mice infused with mibefradil, a T-type channel blocker, exhibited similar behaviors as homozygous knockouts. Taken together, our results demonstrate that retrieval of context-associated memory is dependent on the Ca(v)3.2 T-type Ca(2+) channel.