Developmental changes in uncoupling protein 1 and F1-ATPase subunit levels in the golden hamster brown adipose tissue mitochondria as determined by electron microscopy in situ immunocytochemistry

The postnatal developmental changes in mitochondrial uncoupling protein 1 (UCP 1) and F1-ATP synthase (ATPase) subunit levels in the interscapular brown adipose tissue (BAT) were studied in golden Syrian hamsters (Mesocricetus auratus) using electron microscopy in situ immunocytochemistry. The relatively low initial density of 5 nm gold conjugated anti-UCP 1 immunocomplexes gradually increased from 7- to 21-day-old animals and numerous immunocomplexes were found on the mitochondrial membranes of adult hamsters. At the age of 7-9 days, a positive reaction was also detected in the cytoplasm of BAT adipocytes. Immunolocalization of F1-ATPase subunit indicated its presence in BAT mitochondria and cytoplasm of 7- to 9-day-old animals. However, contrary to UCP 1, intensity of the immunostaining of F1-ATPase subunit rapidly decreased both in mitochondria and cytoplasm between the 10th and 21st postnatal day and it became stabilized in adult animals at a very low level restricted to mitochondria. These results confirm that profound changes in the enzymatic apparatus of BAT mitochondrial membranes, leading to formation of thermogenic mitochondria, occur not until the early postnatal period of hamster ontogenetic development.