This research is designed to study sympatho-adrenal responses during seasonal acclimatization to cold. The overall objectives will be to characterize specific seasonal adjustments in sympatho-adrenal activity, to assess the importance of these adjustments for the maintenance of homeothermy, and to elucidate possible functional capacities and changes which may be unique adaptations in small subarctic mammals. Wild mice will be collected from their natural habitat during all seasons of the year and transfered to the lab for 24-48 hours before being studied in the following ways. Seasonal metabolic acclimatization to cold will be determined by the assessment of resting metabolic rate. The seasonal changes in norephinephrine (NE) stimulated thermogenesis will be estimated by measuring the metabolic response to NE injection. To show changes in the level of sympathetic nervous activity in different tissues, the rates of cathecholamine (CA) turnover will be studied. To provide additional details of the general cathecholamine synthesis and metabolism in different seasonal groups, urinary excretion of CA and certain metabolites will be measured. Seasonal induction of the activity CA synthesizing enzymes in certain tissues will be examined by assays of tyrosine hydroxylase and phenylethanolamine amine-N-methyltransferase. Results of these studies on seasonally acclimatized wild mice will be compared with those from similar studies of lab-kept cold-acclimated mice of the same species. Additional studies may be done to elucidate adequate stimuli in addition to cold which may effect seasonal adjustments in sympatho-adrenal activity. BIBLIOGRAPHIC REFERENCES: Feist, D. D. and Rosenmann, M. 1976. Norepinephrine thermogenesis in seasonally acclimated and cold acclimated red-backed voles in Alaska. MS submitted to Can. J. Physiol. Pharmacol. Feist, D. D. 1976. Norepinephrine turnover in tissues of laboratory acclimated and wild acclimatized subarctic voles. Abstract submitted for presentation of paper at Federal Meetings (FASEB) in April, 1976.