Unusual Correlation between Rest–Activityand Body Temperature Rhythms in the Naked Mole Rat (Heterocephalus glaber) as Comparedto Five Other Mammalian Species
2020
Body temperature and locomotor activity were recorded over
a month using intraperitoneal sensors in the following six mammalian
species: naked mole rats (Heterocephalus
glaber, 2♂, 2♀), C57Bl/6j mice (6♂), outbred white rats
(4♂), Mongolian hamsters (Allocricetulus
curtatus, 3♂), sables (Martes
zibellina, 2♂, 2♀), forest ferrets (Mustela
putorius, 2♂, 2♀). During experiments, the naked mole
rats stayed in their colony under special laboratory conditions:
2 weeks in constant darkness (dim red light), 2 weeks under an alternating
light–dark regime (12L/12D). Mice and rats were kept in individual
chambers under standard laboratory conditions and a 12L/12D regime; sables
and ferrets were kept in their outdoor enclosures under natural
light conditions in autumn. All the rodents used in the experiments,
except for mole rats, are nocturnal animals. Accordingly, all of
them showed a clear circadian rest–activity rhythm: a high level
of locomotor activity in the daytime and low at night. The body
temperature rhythm showed a synphase correlation with the rest–activity
rhythm: temperature rose at night and fell in the daytime (0.9 < r < 1). At the same time, in hamsters,
an increase in locomotor activity at night, when the ambient temperature
went down, was accompanied by a corresponding increase in the amplitude
of body temperature elevations. Small predators, sables and ferrets,
demonstrated a more smoothed circadian rhythm. In contrast to all
these species, body temperature of mole rats dropped sharply by
3–5°С (down to 28°С) upon activation of their locomotor activity
(usually in the morning and evening hours) and jumped (up to 36°С)
at rest (in the night hours) both under constant darkness and 12L/12D
regime (–0.7 < r < –0.9).
Overall, these animals showed an original thermoregulatory system
with a possible “set point” at about 33.5°C.
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