Ultrastructural observations on the hypothalamic arcuate nuclei of aged rats in the fasting/refeeding model.

The arcuate nucleus of the hypothalamus (ARH) is involved in the control of energy homeostasis. This is the first study on the ultrastructural response of ARH neurons in aged rats after short-term fasting and subsequent refeeding. Male Wistar rats (24 weeks old) were fasted for 48 or 96 hours and were then refed for 24 hours. The controls were normally fed. The rats received water ad libitum. In both groups of fasting animals, we observed a rearrangement of the arcuate rough endoplasmic reticulum (RER) and Golgi complexes to form membranous whorls. Moreover, refeeding for 24 hours did not reverse this process. The RER was frequently found to be well organized into lamellar bodies composed of several cisternae. The membranous whorls were composed of concentric layers of endoplasmic reticulum and Golgi complexes. In addition, multiform lipofuscin granules were observed in close relationship with Golgi complexes and membranous whorls. Lipofuscin granules within the neurons of the arcuate nucleus are assumed to be a morphological manifestation of oxidative stress phenomena, which are presumably implicated in the formation of membranous whorls in both fasting and fasting/refed animals. This observation correlates with a significant increase in 8-isoprostane serum levels in the fasting and fasting/refed animals as compared to the fed control rats.