VENTILATION AND RESPIRATORY SENSITIVITY OF EUTHERMIC COLUMBIAN AND GOLDEN-MANTLED GROUND-SQUIRRELS (SPERMOPHILUS-COLUMBIANUS AND SPERMOPHILUS-LATERALIS) DURING THE SUMMER AND WINTER

The first objective of this study was to determine whether species exhibiting different breathing patterns during hibernation have different relative sensitivities to changing blood gases while euthermic. The second was to determine whether the species-specific changes that appear in the relative sensitivities to O2 and CO2 as respiratory stimuli in ground squirrels during hibernation are the consequence of changes in ambient temperature and/or seasonal changes as animals prepare for hibernation or whether they are the consequence of entrance into hibernation per se. Toward this end, we examined the changes in ventilatory sensitivity and response thresholds to hypoxia, hypercarbia, and hypoxia plus hypercarbia in summer animals at ambient temperature (T(A)) = 22-degrees-C and 5-degrees-C (acute exposure) as well as in winter animals at T(A) = 5-degrees-C (chronic exposure) during periodic arousal from hibernation in golden-mantled and Columbian ground squirrels. At T(A) = 22-degrees-C, awake, unrestrained golden-mantled and Columbian ground squirrels breathe continuously and show similar, strong ventilatory responses to hypoxia, but comparatively blunted responses to hypercapnia, typical of fossorial mammals. Neither acute nor chronic exposure to reduced ambient temperature significantly altered the hypoxic or hypercapnic ventilatory responses of the Columbian ground squirrel. Thus, neither species differences, changes in ambient temperature, nor seasonal changes associated with preparation for hibernation affected the thresholds or sensitivities of the ventilatory responses to changing blood gases in these animals. This suggests that the species-specific changes seen in respiratory control during hibernation in these two species must arise during the transition into hibernation per se.