Molecular characterization of T-type Ca²⁺ channels responsible for low threshold spikes in hypothalamic paraventricular nucleus neurons

The hypothalamic paraventricular nucleus (PVN) is composed of functionally heterogeneous cell groups, possessing distinct electrophysiological properties depending on their functional roles. Previously, T-type Ca²⁺ dependent low-threshold spikes (LTS) have been demonstrated in various PVN neuronal types, including preautonomic cells. However, the molecular composition and functional properties of the underlying T-type Ca²⁺ channels have not been characterized. In the present study, we combined single cell reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemistry and patch-clamp recordings to identify subtypes of T-type Ca²⁺ channels expressed in PVN cells displaying LTS (PVN-LTS), including identified preautonomic neurons. LTS appeared at the end of hyperpolarizing pulses either as long-lasting plateaus or as short-lasting depolarizing humps. LTS were mediated by rapidly activating and inactivating T-type Ca²⁺ currents and were blocked by Ni²⁺. Single cell RT-PCR and immunohistochemical studies revealed Cav3.1 (voltage-gated Ca²⁺ channel) as the main channel subunit detected in PVN-LTS neurons. In conclusion, these data indicate that Cav3.1 is the major subtype of T-type Ca²⁺ channel subunit that mediates T-type Ca²⁺ dependent LTS in PVN neurons.