GPR103 is known as an orphan G protein-coupled receptor with reported expression in brain, heart, kidney, adrenal gland, retina, and testis. GPR103 mRNA has been reported to be highly expressed in the superficial layers of the entire spinal cord and a high density of 26RFa binding sites was observed in the superficial layers of the dorsal horn. QRFP binds and activates the human GPR103, as well as mouse GPR103A and GPR103B, with nanomolar affinities in transfected cells. Therefore, the current experiments investigated the effects of QRFP administration in rats and the effects of a high fat diet on prepro-QRFP mRNA and GPR103 receptor mRNA levels. 26RFa and QRFP are endogenous ligands of GPR103. An immunohistochemical study revealed that GPR103-like immunoreactivity (LI) was observed in the superficial layers of spinal dorsal horn, that QRFP-LI was observed in the dorsal root ganglion and that intrathecal 26RFa suppressed the expression of Fos-LI induced by paw formalin injection in the superficial layers of the spinal dorsal horn.