The presence and localization of orexin A in the bovine mandibular gland: impact of diets characterized by different chemical composition.

Introduction: The recent literature reports that diets with different amounts and composition of n-3 vs. n-6 fatty acids may affect the expression of neuro-active molecules involved in appetite control. The orexin system, including orexin A (OXA), is expressed in the brain as well as in some peripheral organs. Among such the salivary glands are accounted. Against this background, the presence and distribution of OXA in the bovine mandibular gland (MG) were investigated to test possible effects from different compositions of dietary fatty acids. Materials and Methods: Rumen fistulated cows were fed a total mixed ration based on maize silage and were infused abomasally with coconut oil or a mix composed of linseed-safflower oil combined with the conjugated linoleic acids c9,t11 and t10,c12 (Lutalin™). MG were removed from carcasses and were fixed in buffered formaldehyde prior to embedding in paraffin for routine tissue preparation procedures. The immunohistochemical reaction was visualized on 5 µm serial sections, collected on poly-L-lysine-coated glass slides, using a monoclonal anti OXA antibody and DAB as chromogen, the intensity of the immunoreactions was analyzing using the software ImageJ, IHC Profiler plugin. Results: The immunohistochemical study showed a peculiar immunoreaction for OXA in the MGs of cows. In particular, OXA immunoreaction tested positive in the cytoplasm of ductal epithelial cells and in the serous acinar cells. Conversely, immuno-positivity was not observed in any other glandular structure or in the sections utilized as negative controls. The signal intensity was higher within the coconut oil group. Conclusion: These preliminary results showed that the OXA is present in the bovine MG with a distribution that reflects what has been already described for bovine parotid gland and for major salivary glands of pigs. The expression in this trial seemed to be affected by specific fatty acid amounts and composition in the diet.