Ultrastructure of the adrenal cortex of hibernating, arousing, and euthermic dormouse, Muscardinus avellanarius

Abstract

Background The adrenal gland is a key organ for hibernation (a condition characterized by striking reduction of body functions). Very limited information is available on the fine structure of the gland during hibernation and on the periodical arousal from hibernation. Methods Dormice (Muscardinus avellanarius) were maintained in an external animal house and allowed to hibernate spontaneously (November). Arousal was induced in March by exposure to daylight. Euthermic, active dormice were captured in June. The adrenals were taken from four hibernating, three arousing, and four euthermic dormice and processed for resin embedding. The ultrastructure of the adrenal cortex was investigated by transmission electron microscopy. Results In the zona glomerulosa of hibernating and arousing dormice, the smooth endoplasmic reticulum was prominent in comparison with euthermic animals, and mitochondria showed abundant vesicular cristae. The zona fasciculata and zona reticularis did not show consistent differences, apart from a lower cell lipid content in the outer portion of zona fasciculataof arousing dormice. Conclusions The zona glomerulosa showed signs of increased activity during hibernation. This finding is supported by previous biochemical data demonstrating increased production of renin and aldosterone during such extreme physiological conditions. Activation of the zona glomerulosa in hibernation is probably adaptive to a condition of drastically reduced salt intake. Anat. Rec. 249:359-364, 1997. © 1997 Wiley-Liss, Inc.