Intracellular recordings from thermosensitive preoptic neurons.

Intracellular recordings were made from locally thermosensitive preoptic neurons in the green sunfish, Lepomis cyanellus. Stable resting potentials, action potentials, and spontaneous synaptic activity were observed over approximately 4 degrees to 5 degrees C changes in local brain temperature. A small percentage of the warm-sensitive neurons showed exponential firing-rate responses to temperature. These cells discharged rhythmically, lacked visible synaptic input, and showed slowly depolarizing potentials leading to action potentials. Other linear and nonlinear warm-sensitive and cold-sensitive neurons showed spontaneous excitatory and inhibitory synaptic potentials giving rise to action potentials. Cells that appear to be endogenously active may be true thermodetectors, and other thermosensitive neuronal activity may be synaptically mediated.