Effect of feeding on Fos protein expression in sheep hypothalamus with special reference to the supraoptic and paraventricular nuclei: an immunohistochemical study

The hypothalamus plays an important role in the control of food intake in d ifferent species, but there is little relevant information for ruminants li ke sheep. In order to study the putative role of several hypothalamic nucle i in food intake in sheep, Fos expression, a marker of cellular activity, w as compared by immunohistochemistry between fed and unfed ewes. The express ion of Fos protein was stimulated in the supraoptic nucleus of fed ewes, wh ereas it was increased in the paraventricular nucleus of unfed animals. In the latter nucleus. Fos immunoreactivity was mainly localized close to the third ventricle, an area corresponding to the parvocellular system of the n ucleus, but never in the magnocellular system. In the paraventricular nucle us, the number of corticotrophin releasing factor-immunoreactive neurons an d the number of Fos/corticotrophin releasing factor double-labelled neurons were not affected by feeding or lack of feeding. The number of Fos-immunor eactive neurons was higher in the lateral septum, the infundibular, the ven tromedial and in the dorsomedial nuclei of unfed ewes than in those of fed ewes. Our results show for the first time that the dorsomedial and ventrome dial nuclei are involved in the control of feeding in sheep as in rodents. The supraoptic nucleus of sheep is activated by the same conditions as in r odents but, conversely, the paraventricular nucleus is activated in unfed s heep, whereas in rodents and primates, this nucleus is activated by satiety as well as by fasting. In sheep, unlike in rodents, corticotrophin releasi ng factor did not appear to be involved in short-term regulation of food in take.