Aims: We have already shown that the alteration of polyunsaturated fatty acid (PUFA) in the hypothalamus is involved in the regulation of pain. However, how become the changes in composition of hypothalamic PUFA under pain state remain unclear. It is reported that three fatty acid-binding protein (FABP) subtypes, which regulate PUFA intracellular trafficking and signal transduction, are expressed in the mammalian brain. In this study, we confirmed the changes in the expression of FABP3 in the median eminence, which is part of the hypothalamus, of postoperative pain model mice.
Methods: Paw incision-induced postoperative methods were adopted as a pain model in male ddY mice. Mechanical hypersensitivity was examined by the von Frey test. The mRNA analysis of FABP subtypes were measured by real-time PCR, and cellular localization of its protein level were measured by immunofluorescent study.
Results: Postoperative pain mice elicited mechanical allodynia on day 2 after paw incision, and mRNA expression of FABP3 significantly increased in the hypothalamus of the postoperative pain model mice compared to that in control mice. FABP3 positive cells in the median eminence colocalized with Iba-1 positive cells, which is a microglial cell marker, but not neuron and astrocyte marker. Its protein level significantly increased in the median eminence on day 2 after paw incision and returned to the control level on day 4 after paw incision. 
Conclusions: Our results suggest that FABP3 in the median eminence may change in pain stimuli and may be a key molecule to control pain signaling.