ULTRASTRUCTURAL, MORPHOMETRICAL AND IMMUNOCYTOCHEMICAL ANALYSES OF THE EXOCRINE PANCREAS IN A HIBERNATING DORMOUSE

Pancreatic acinar cells of euthermic, hibernating and arousing individ uals of the hazel dormouse Muscardinus avellanarius (Gliridae) have be en observed at the electron-microscopic level and analysed by means of ultrastructural morphometry and immunocytochemistry in order to inves tigate possible fine-structural changes of cellular components during periods of strikingly different degrees of metabolic activity. During hibernation, the cisternae of the rough endoplasmic reticulum (RER) fl atten assuming a parallel pattern, the Golgi apparatus is extremely re duced and the mitochondria contain many electron-dense particles. The cell nuclei appear irregularly shaped, with deep indentations containi ng small zymogen granules. They also contain abundant coiled bodies an d unusual constituents, such as amorphous bodies and dense granular bo dies. Large numbers of zymogen granules occur in all animals. However, the acinar lumina are open and filled with zymogen only in euthermic animals, whereas, in hibernating and arousing individuals, they appear to be closed. Morphometrical analyses indicate that, in pancreatic ac inar cells, nuclei and zymogen granules significantly decrease in size from euthermia to hibernation, probably reflecting a drastic decrease of metabolic activities, mainly protein synthesis and processing. In all the studied animals, immunocytochemistry with specific antibodies has revealed an increasing gradient in a-amylase content along the RER -Golgi-zymogen granule pathway, reflecting the protein concentration a long the secretory pathway. Moreover, during deep hibernation, signifi cantly larger amounts of a-amylase accumulate in RER and zymogen granu les in comparison to the other seasonal phases analysed. Upon arousal, all cytoplasmic and nuclear constituents restore their euthermic aspe ct and all morphometrical and immunocytochemical parameters exhibit th e euthermic values, thereby indicating a rapid resumption of metabolic activities.