The thyroid gland brown adipose tissue of forest mice and bank voles over the annual cycle

Abstract

Examinations were carried out in the Białowieża National Park during 4 consecutive years on 295 bank voles and 265 forest mice caught in February, April, June, July, October and December. The examination material was fixed in the fluids of Bouin, Carnoy, Hell and Lison-Vokaer; 6 μm paraffin sections were stained with hematoxylin-eosin, gallacyanin and by the Azan methods according to Heidenhain. Brown adipose tissue (BAT) together with thyroid was fixed in l0% formalin and sliced frozen for control staining; 10 μm sections were stained with Sudan black B. BAT hyperplasia was observed in rodents caught in winter months -- it was most strongly expressed in December and it was the weakest in October In December the BAT cells appeared in the thyroid of majority of the animals but in different amounts, The BAT cells penetrated deep into the thyroid in about half of the animals but only in some of them the hyperplasia was significant and disappearing thyroid follicles could be observed between the BAT cells. But in may be supposed that BAT may grow in rodents living in unfavorable for survival winter conditions even at the cost of thyroid as a tissue more important for processes of effective thermogenesis.