Comparison of brown adipose tissue from arctic and tropic small mammals
Date
1989
Authors
Lisson, Paul Alexander
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The mean weights, histology and ultrastructure of the brown adipose tissue from five species of rodents from Costa Rica (tropical) were compared with the brown adipose tissue from four species of rodents from the Northwest Territories of Canada (arctic). The rate of change (y = 0.612 - 0.269x, r2 = 0.59) of the relative weight of brown adipose tissue (y) with increase in body size (x) in the arctic rodents, compared to that of the tropic rodents (y = 0.965 - 0.468x, r2 = 0.70), was statistically the same (P > 0.50). A comparison of the total amount of brown adipose tissue, as measured by the elevations of the two lines, showed no significant difference (P > 0.50).
In a comparison of members of the family Cricetidae from the arctic, the adult Peromyscus maniculatus and Phenacomys intermedius show remarkable consistency in the microstructure of the brown adipose tissue. The lipids are in a multilocular form with tightly packed, complex mitochondria filling most of the remainder of the cell. Sub-adult and juvenile Peromyscus maniculatus showed nearly identical structure. The neonates of Phenacomys intermedius, however, have almost no lipid in the cells while the mitochondria are more loosely packed and less complex than in the adults.
In contrast to the arctic rodents, the five tropical species show much more variation within each species and between species. Reithrodontomys sp. all have typical brown adipose tissue multilocular lipids in the cells, while Mus musculus has unilocular cells that resemble white adipose tissue. Heteromys desmarestianus, although consistent within individuals, varied among individuals between a multilocular and unilocular form of the lipid. The tissue of Liomys salvini has a dual structure, with a number of multilocular cells on the inside and a layer of large unilocular cells on the outside. Both adults and neonates of Oryzomys fulvescens, have multilocular cells but with only about half of the lipid that the other species have.
In summary, it is possible that in both the arctic and the tropics, small mammals have evolved with the potential for the same amount of brown adipose tissue. In the tropics, where the cold stress on the animals is minimal, the thermogenic function of the tissue is required to a lesser extent and therefore the tissue, in some species, has transformed into what appears to be white adipose tissue by coalescing the numerous smaller lipid droplets into a single larger droplet and thus becoming more of a storage tissue. In the arctic, where the thermogenic function is essential, the cells contain multilocular lipids in a much more uniform pattern between Phenacomys and Peromyscus and between the different age groups of these two species.