Warm-and cold-sensitive neurons are present in the lateral parabrachial nucleus(LPB),a crucial relay for afferent signals from the skin that drive autonomous and behavioral thermoregulatory responses to environmental thermal challenges.However,the cellular mechanisms by which these thermosensitive neurons sense changes in local temperature have not been determined.To examine the basic mechanisms of neuronal thermosensitivity,rat LPB tissue slices were used to record and compare intracellular activity of temperature-sensitive and-insensitive neurons.The firing rate thermosensitivity of warm-sensitive neurons was not associated with thermally dependent changes in the resting membrane potential,threshold potential,or amplitude of the afterhyperpolarizing potential.The primary mechanism of LPB neuronal warm sensitivity may reside in the depolarizing prepotential that precedes each action potential.In warm-sensitive neurons,warming significantly increased the rate of depolarization of the prepotential,which in turn shortened the interspike interval and increased the firing rate; in contrast,temperature only had a slight or no effect on the depolarizing prepotentials of temperature-insensitive and cold-sensitive neurons.On the contrary,LPB neuronal cold sensitivity was determined not by the depolarizing prepotential but by the temperature dependence of the resting membrane potential since cooling and warming produced membrane depolarization and hyperpolarization,respectively,and there was a strong correlation between the firing rate and membrane potential thermosensitivity of cold-sensitive neurons.These results suggest that warm-and cold-sensitive neurons in the LPB have thermally dependent differences in resting membrane potentials and depolarizing prepotentials.