The Ontogeny of Thermoregulatory Abilities in Neonatal Cotton Rats and Montane Voles


Ginny Y. Hew

Date of Graduation

Summer 1997


Master of Science in Biology



Committee Chair

Thomas Tomasi


Physiological maturity play a vital role in determining thermoregulatory ability in newborn (neonatal) eutherians. Oxygen consumption (stp mlO₂/h*g⁰·⁶⁷) was measured in open chambers at temperatures 20, 25, 30 and 35°C for cotton rat (Sigmodon hispidus) neonates and at temperatures 25, 30 and 35°C for montane vole (Microtus montanus) neonates to determine the response to cold, and to estimate the thermal neutral zone (TNZ) of each species. TNZ for cotton rats was 33-35°C and for montane voles around 30°C. Since norepinephrine (NE) stimulated BAT metabolism, the effect of NE was measured at thermoneutrality in 2, 4, 6-8 and 12 day old cotton rat neonates, and in 4, 8, 12 and 16 day old montane vole neonates. Two day old cotton rats, and 4 and 8 day old montane voles were unable to raise their metabolism at the lowest temperature. At all ages, NE elevated metabolic rate above control and saline-injected values for both species (repeated measured two-way ANOVA: P<0.001). The response to NE increased with age for both cotton rats and montane voles (repeated measures two-way ANOVA: P<0.001). The number of NE treatments that an animal received did not effect its NE-induced metabolism at day 12 for cotton rats (repeated measures two-way ANOVA: p=0.860), but number of treatments did effect NE-induced metabolism for 16 day old montane voles (repeated measures two-way ANOVA: P<0.001). First NE treatment was lower than third NE treatment (Tukey's test: P<0.022). Adjusted time for peak response to NE treatment showed strong positive correlation with NE-induced metabolic rate. Cotton rats, a precocial species were compared to montane voles, an altricial species. The data show that M. montanus have a slower thermogenic development than S. hispidus.

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