Differential gene expression and immune localization of the orexin system in the major salivary glands of pigs

The aim of the present work was to characterize the expression and cell type distribution of the orexinic system in the major swine salivary glands by RT-PCR and immunohistochemistry techniques. Tissue samples of the mandibular (MSG), sub-lingual, and parotid glands were obtained from six pigs. Marked differences in the expression of the orexinergic system were observed among the salivary glands. Prepro-orexin (PPOX) mRNA abundance was approximately 15-fold higher (P < 0.05) in MSG than in the others salivary glands. The expression level of OX1R mRNA did not differ among the salivary glands, while that for OX2R transcript was undetectable. The hypothalamus, used as positive control tissues, showed the highest expression level for each component of the orexinic system. Immunoreactivity (IR) for both orexins A and B (OXA and OXB), and cognate receptors (OX1R and OX2R) were identified only in the excretory striated ducts of the MSG while acinar cells were not immunoreactive. Both sub-lingual and parotid glands completely lacked IR for any component of the orexinergic system. In the MSG, parasympathetic neurons and axons of local salivary gland ganglia were IR to both OXA and OXB and also to their receptors.