Warm- and cold-sensitive neurons inactive at normal core temperature in rat hypothalamic slices.
Electrical activities of thermosensitive neurons were recorded extracellularly in slices of rat preoptic area and anterior hypothalamus. Of 63 spontaneously firing neurons found at high searching temperature (37-40 degrees C), 33% were warm-sensitive, 8% were cold-sensitive and the remaining 59% were thermally insensitive. In particular, 6 warm-sensitive neurons were active only above 38 degrees C of rat normal core temperature. In contrast, of 38 spontaneously firing neurons found at low searching temperature (32-36 degrees C), 8% were warm-sensitive, 29% were cold-sensitive and the remaining 63% were thermally insensitive. Furthermore, all these cold-sensitive neurons were active only below 38 degrees C. Therefore, the warm- and cold-sensitive neurons active at 38 degrees C would be functioning for narrow band control and the remaining warm- and cold-sensitive neurons inactive at 38 degrees C would be recruited for wide band control when core temperature was changed critically from 38 degrees C. Their firing rate activities often showed obvious threshold responses, large hysteresis of the threshold responses and remarkable transient responses to slice temperature changes. From aspects of automatic control theory, these warm- and cold-sensitive neurons themselves may be thermostats to regulate the brain temperature rather than thermosensors to monitor it.
D000818:Animals; D001831:Body Temperature; D003080:Cold Temperature; D004056:Differential Threshold; D006358:Hot Temperature; D007031:Hypothalamus / Q000166:cytology / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D009474:Neurons / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors