Effects of melatonin on thermally classified anterior hypothalamic neurons in the white-footed mouse (Peromyscus leucopus)

1. The pineal hormone melatonin influences thermoregulation in many species, but the mechanism of action is unknown. 2. We tested whether melatonin could act directly on the primary thermoregulatory control center in the preoptic area and anterior hypothalamus (PO/AH), using a white-footed mouse tissue slice preparation. 3. PO/AH neurons were classified according to their thermosensitivity, then treated with 1 μM melatonin. 4. Thirty percent of warm-sensitive and 41% of temperature-insensitive neurons showed significant changes in firing rate during melatonin treatment. 5. While there was no correlation between responses to melatonin and thermosensitivity, these results constitute the first evidence that melatonin acts directly on PO/AH thermoregulatory neurons.