title: Hypothermia and deranged circadian rhythm of core body temperature in nickel chloride-treated rats.
abstract: To quantify the immediate hypothermic response to an injection of NiCl2, and to delineate the ensuing derangements of circadian rhythms, the core body temperature and physical activity of rats were monitored by radiotelemetry from a thermistor probe implanted in the peritoneal cavity. The rats were housed in individual cages in a quiet room at 20 +/- 1 degrees C with 12 h light/dark cycles. After an injection of NiCl2 (e.g., 250 mumol/kg), the core body temperature diminished to a nadir at 1.5 h and returned to the baseline at 4 h; core body temperature at 1.5 h post-dose averaged 3.0 +/- 0.5 degrees C below the simultaneous value in control rats. During the period from 8 to 80 h post-dose, the mean body temperature of NiCl2-treated rats did not differ from controls, but the amplitude of the diurnal cycle of body temperature was dampened and the acrophase of the temperature cycle was delayed from 10:32 pm to 3:00 am. These parameters returned towards the control values during the period from 80 to 152 h post-dose. Physical activity of rats was reduced during the period from 8 to 80 h post-dose and the amplitude of the diurnal cycle of physical activity was dampened, but the acrophase of the activity cycle was not retarded in synchrony with the temperature cycle. This study shows that, in addition to causing prompt hypothermia that lasts 4 h, injection of NiCl2 deranges the circadian rhythm of thermoregulation during 3 days after recovery from hypothermia, causing 4.5 h delay of the temperature acrophase. Thus, the transient bout of hypothermia evidently sets back the biological clock of thermoregulation.
authors.affiliation: Department of Laboratory Medicine, University of Connecticut School of Medicine, Farmington 06032.
authors.forename: S M
authors.initials: SM
authors.lastname: Hopfer
authors.forename: F W
authors.initials: FW
authors.lastname: Sunderman
mesh_terms: D000818:Animals; D001833:Body Temperature Regulation / Q000187:drug effects*; D002940:Circadian Rhythm / Q000187:drug effects*; D007035:Hypothermia / Q000139:chemically induced*; D008297:Male; D009532:Nickel / Q000633:toxicity*; D051381:Rats; D011916:Rats, Inbred F344; D013997:Time Factors
chemical_list: C022838:nickel chloride; D009532:Nickel