Hypothalamic orexin A expression and the involvement of AMPK and PPAR-gamma signalling in energy restricted dairy cows
Abstract. A number of circuits controlling feed intake have been identified in rodents in which circulating dietary metabolites are detected by the brainstem and the hypothalamus converting these input signals to anorexic responses. Dietary metabolites used by dairy cows, however, are not identical with those of rodents calling for the elucidation of feedingrelated pathways in ruminants. In the present study we examined potentially relevant plasma metabolites and hypothalamic signalling pathways in ad libitum and restrictively fed early lactating dairy cows. 60 h feed energy restriction led to significantly increased non-esterified fatty acid (NEFA), Gln, Gly, His, and 3-Me-histine but decreased Asp, Asn, beta-Ala, Tyr, and Trp concentrations. In immunohistochemical studies, we found that feed energy restriction is associated with elevated numbers of parvocellular but not magnocellular orexin A neurons in the lateral, dorsomedial and posterior hypothalamic area. In parvocellular orexin A neurons we determined complete colocalisation with cFOS in energy restricted cows. In the majority of orexin A neurons we further found colocalisation with activated adenosine monophosphate activated kinase (AMPK) as well as with peroxisome proliferator-activated receptor-gamma (PPARγ). Feed restriction also induced activation (phosphorylation) of AMPK and increased expression of PPARγ when Western Blots were normalized to β-actin. These results suggest that orexin A associated with AMPK and PPARγ signalling is involved in the control of energy homeostasis of dairy cows.