SEASONAL ADJUSTMENTS IN CAPTURED WILD NORWAY RATS: I. ORGAN WEIGHTS, EAR VASCULARIZATION, AND HISTOLOGY OF EPIDERMIS

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Abstract
Male wild rats (Rattus Norwegicus) captured during the winter had different organ weights from similar animals captured during the summer. These seasonal changes in organ weights were different from those observed in white rats acclimated to cold in a cold room (indoor) or acclimatized to winter outdoors in groups of 10 to a cage.Unlike both the indoor and outdoor cold-conditioned white rats, the wild rats, in winter, did not have a reduced muscle mass as compared to the summer-captured rats, or a reduced abdominal fat reserve, or an enlargement of the liver and kidney. The abdominal fat reserve actually increased during the winter.Like the outdoor white rats, the wild rats, during the winter, did not show the enlargement of the thyroids, adrenals, pituitary, and digestive tract or the reduction in pelt and the ear cold injury that were invariable outcomes of continuous individual exposure to a constant low-temperature indoors. Like the indoor and unlike the outdoor white rats, however, they showed an hypertrophy of the heart and an increased vascularization of the ear.Because the wild rats trapped during the winter showed very few of the morphological changes usually found in cold-exposed white rats, it is suggested that winter conditions encountered were not stressful to the wild rats.