The Ontogeny of Thermoregulatory Abilities in Neonatal Cotton Rats and Montane Voles
Date of Graduation
Master of Science in Biology
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.
© Ginny Y Hew
Hew, Ginny Y., "The Ontogeny of Thermoregulatory Abilities in Neonatal Cotton Rats and Montane Voles" (1997). MSU Graduate Theses. 199.