In mammals, multiple thermostats in several brain areas, e.g. the preoptic area and anterior hypothalamus (POAH), may regulate core temperature. In these areas, warm-sensitive (WS) and cold-sensitive (CS) neurons have been recorded. In our previous study, we proposed that primary WS and CS neurons act as multiple thermostats having threshold temperatures as target temperatures of regulation. Here we investigated ionic basis of WS neurons in rat POAH slices with patch-clamp technique. In whole-cell current-clamp recordings, warming above threshold temperatures induced depolarization (receptor potential), leading to spike generation. Whole-cell voltage-clamp and cell-attached patch recordings indicated that warming-activated non-selective cation channels underlie the receptor potential and spike generation. We conclude that the warming-activated channel in primary WS neurons is a key factor of thermostats.