The Sin Nombre virus (SNV) is the etiologic agent of hantavirus pulmonary syndrome in humans but does not cause disease in chronically infected deer mice (Peromyscus maniculatus), the natural host. In this study, murine antiserum raised against recombinant SNV nucleocapsid protein was utilized to localize viral antigen immunohistochemically in tissues from both humans (n = 20; 11 positive, 9 negative) and deer mice (n = 6; 4 positive, 2 negative). Viral infection status was confirmed by Western blot or reverse transcriptase-polymerase chain reaction. SNV antigen was detected in pulmonary and cardiac endothelium in both species, but positive cells in deer mice were rare. Other deer mouse tissues, including kidney, were negative; in contrast, vascular elements of several tissues from infected humans were positive, with strong staining of renal endothelium. The paucity of positive cells in chronically infected mice suggests a low virus burden compared with that of acutely infected humans.

In the present paper we examine the ability of rodents to maintain body temperature (TB) following the marked reductions in metabolic heat production associated with torpor. Previously published values for metabolic rate (M), TB and ambient temperature (TA) were used to calculate thermal conductances (C') during normothermy and torpor in rodents capable of daily torpor (11 species) and hibernation (18 species). Values of C' for torpid animals are uniformly lower than C' in normothermic animals. In addition, C' of normothermic and torpid rodents decreases with increasing body mass (BM). However, the slope of the relationship between C' and BM is almost 4-fold greater for normothermic than for torpid animals. Thus, the ability of torpid rodents to conserve body heat by reducing C' decreases with increasing mass. Rodents that use daily torpor tend to be small and they tend to maintain TB well above TA during torpor. Hibernators tend to be larger and regulate TB relatively close to TA. Thus, the reductions in C' appear to be closely correlated with the level of TB regulation during torpor. We suggest that the changes in C' represent a suite of physiological adaptations that have played a central role in the evolution of torpor, enabling rodents to regulate TB above TA during periods of very low heat production. Based on the approach used here we address the controversy of whether reductions in M during torpor are due entirely to temperature effects or whether metabolic inhibition in addition to temperature effects may be important. We suggest that the controversy has been confused by using Q10 to evaluate the relationship of M and TB in endotherms.(ABSTRACT TRUNCATED AT 250 WORDS)

Retention ofCO2 and respiratory acidosis have previously been reported to accompany entrance to hibernation, with acid-base and CO, balance returning to normal upon arousalfrom hibernation. The present study indicates that these alterations are not limited to species which have the ability to undergo deep hibernation, but are also involved in another mammalian dormancy state, daily torpor. Deer mice (Peromyscus maniculatus) were used to examine the time course of changes in respiratory quotient (RQ), metabolic rate (MR), and body temperature (Tb) during daily torpor at an ambient temperature of 10" C For several hoursprior to daily torpor, RQ steadily declinedfrom 0.92 to 0. 74, indicating a shift in primary metabolic substratefrom carbohydrate tofat, while MR andTb remained constant at 4.23 + 0 44 mL 02/g . h and 36 6' + 0. 9" C, respectively. Entrance to daily torpor involved a transitory decrease in RQ (0. 74-0 63-0 73) that lasted less than 12 min and reflected C02 retention and accompanying respiratory acidosis. This was subsequentlyfollowed by a rapid drop in MR andTb. Respiratory quotient remained stable during steady-state torpor (0. 74 0. 02). Metabolic rate and Tb in daily torpor were 1.12 + 0. 35 mL O/g . h and 21. 6' 1. 6 C, respectively. A transitory increase in RQ (0. 76-0.96-0. 76) was associated with arousal, signifying release of the excess C2O,, with MR and then Tb increasing after the RQ change. The order of change in the measuredparameters suggests that adjustments in the CO, content of the body contribute to the induction and termination ofdaily torpor in deer mice.

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