The role of T-type calcium channels in the subiculum: to burst or not to burst?

Key points: Pharmacological, molecular and genetic data indicate a prominent role of low-voltage-activated T-type calcium channels (T-channels) in the firing activity of both pyramidal and inhibitory interneurons in the subiculum. Pharmacological inhibition of T-channels switched burst firing with lower depolarizing stimuli to regular spiking, and fully abolished hyperpolarization-induced burst firing. Our molecular studies showed that Ca_V3.1 is the most abundantly expressed isoform of T-channels in the rat subiculum. Consistent with this finding, both regular-spiking and burst firing patterns were profoundly depressed in the mouse with global deletion of Ca_V3.1 isoform of T-channels. Selective inhibition of T-channels and global deletion of Ca_V3.1 channels completely suppressed development of long-term potentiation (LTP) in the CA1–subiculum, but not in the CA3–CA1 pathway. Abstract: Several studies suggest that voltage-gated calcium currents are involved in generating high frequency burst firing in the subiculum, but the exact nature of these currents remains unknown. Here, we used selective pharmacology, molecular and genetic approaches to implicate Cav3.1-containing T-channels in subicular burst firing, in contrast to several previous reports discounting T-channels as major contributors to subicular neuron physiology. Furthermore, pharmacological antagonism of T-channels, as well as global deletion of CaV3.1 isoform, completely suppressed development of long-term potentiation (LTP) in the CA1–subiculum, but not in the CA3–CA1 pathway. Our results indicate that excitability and synaptic plasticity of subicular neurons relies heavily on T-channels. Hence, T-channels may be a promising new drug target for different cognitive deficits.