Transient receptor potential vanilloid 1 (TRPV1) is a critical ion channel that responds to various physical and chemical stimuli including heat, pain, and capsaicin. Although TRPV1 expression was originally thought to be restricted to peripheral neural tissues such as primary afferent nociceptors, there has been an argument for a much wider distribution of TRPV1 in the brain. In the scenario of gout, while this disease condition increased peripheral TRPV1 immunoreactivity, it remains unknown whether central TRPV1 expression is affected correspondingly. The present study took advantage of cerebral blood volume (CBV) weighted functional magnetic resonance imaging (fMRI) method and applied it to rats with gouty arthritis. The evoked activity changes were compared between normal and gouty conditions with respect to central TRPV1 changes caused by gout.The gouty arthritis rat model was induced by injection of MSU into the wrist. Briefly, 0.42 g of uric acid (U2625; Sigma-Aldrich, MO, USA) was dissolved in 100 mL of distilled water alkalized by 0.1 g of sodium hydroxide (Sigma-Aldrich). Direct injection of 50 μL of 24 mg/mL MSU crystals was performed on the left wrist joint cavity while injection of 50 μL of saline was done on the right wrist as control [1-3]. The observation was focused on the gait and wrist swelling, two key overt signs in rats with gouty arthritis [4]. fMRI was conducted using a 4.7-T spectrometer (Biospec 47/40, Bruker, Germany). For each sensory stimulation evoked fMRI data set, a time series of 60 images were acquired in the axial plane. The first 12, second 12, third 12, fourth 12, and last 12 time frames correspond to the off, on, off, on, and off phases of nociceptive electrical stimulation, respectively, which was delivered to a left or right forepaw via a pair of needle electrodes. Gradient-echo images were acquired in the time series with a repetition time of 150 ms, an echo time of 15 ms, a flip angle of 22.5°, a field of view of 2.56 cm by 2.56 cm, a slice thickness of 1.5 mm, an acquisition matrix of 128×64 (zero-filled to 128×128), and a temporal resolution of 9.6 s. The stimulation intensity was 3 mA or 1 mA, administered by a constant-current stimulator (model 2100, A-M Systems, Carlsborg, WA, USA). The contrast agent was from MegaPro Biomedical Co. Ltd. fMRI correlation maps were generated by the Pearson correlation coefficient (CC) between the image signals and the off–on–off–on–off electrical stimulation paradigm on a voxel-by-voxel basis using the cross-correlation method 12. The cutoff point for the CC was r=±0.2513, 14. Intrathecal administration of AMG9810 (2316; Tocris Bioscience, Bristol, UK), a selective TRPV1 receptor antagonist [8], was through the cisterna magna in rats [9, 10]. The injection of AMG9801 was performed after the 1st electrical stimulation paradigm, and its effects were assessed in the 2nd stimulation paradigm.The MSU-treated wrist exhibited an obvious gait abnormality and swelling as compared to the contralateral wrist. This gait change and swelling were resolved with time. Pain evoked fMRI showed that, in the gouty animals, the cortical CBV increase in response to the electrical stimulation were most pronounced at the 3hr time point. The magnitude of the cortical response decreased with time. Electrical stimulation to the MSU treated forepaw also triggered more widespread CBV increases in the thalamus. Immunohistology shows that distinct increases in TRPV1 expression was observed in the 24hr MSU treated wrist tissues, whereas very little TRPV1 signals were found in the saline treated wrist tissues. In the brain, the TRPV1 expression of both the inner and outer layers of the cortex contralateral to the MSU treated side was significantly enhanced as compared to the other cortex. Importantly, the cortical, striatal, and thalamical CBV responses and gait abnormality were reduced significantly after a TRPV1 antagonist, AMG9810.The fMRI findings established that increased TRPV1 levels in the brain is a key mediator in augmented pain responses induced by gout. This new information may promote the development of TRPV1 antagonists acting in the brain as new drug leads for treating gout, while fMRI can be a useful application for evaluating drug effects.