The scale bar; A, left = 150 m; A, right = 20 m; C, left = 60 m; C, right = 15 m; D = 2 m. We also examined the distribution of ON bipolar cells 3 months after the injection of the serum (Figure 7C). acutely after the injection, and the shape of the ERGs resembled that of the patient with PR. Immunohistochemical analysis of the eyes injected with the serum showed immunoreactivity against bipolar cells only in wild-type animals and not in TRPM1 knockout mice,consistent with the serum containing anti-TRPM1 antibodies. Histology also showed that some of the bipolar cells were ML367 apoptotic by 5 hours after the injection in wild type mice, but no bipolar cell death was found in TRPM1 knockout mice, . At 3 months, the inner nuclear layer was thinner and the amplitudes of the ERGs were still reduced. These results indicate that the serum of a patient with PR contained an antibody against TRPM1 caused an acute death of retinal ON bipolar cells of mice. == Introduction == Light stimulation of the rod and cone photoreceptors elicits signals that are transmitted to the bipolar cells and then to the retinal ganglion cells (RGCs). At present, there are many retinal diseases that are caused by a degeneration of the photoreceptors or the RGCs. Retinitis pigmentosa is an example of the former type of diseases and is caused by a degeneration of the rods followed by the cones. Glaucoma is an example of the second type of diseases that is caused by the death of RGCs. There is no known retinal disease caused by bipolar cell degeneration. The paraneoplastic retinopathies (PRs) are a group of diseases characterized by a sudden and ML367 progressive decrease in the function of the retina. The retinopathies have been shown to be caused by a circulating anti-retinal autoimmune antibody against a protein of a neoplasm [1-4]. One subtype of the PRs has been reported to be caused by an autoantibody against a protein expressed by ML367 retinal ON bipolar cells [5,6]. The symptoms and signs of these patients were a sudden onset night blindness, photophobia, and a decrease of the visual acuity. The electroretinograms (ERGs) elicited by a standard flash stimuli had a selective reduction of the b-waves with normal a-waves. This resulted in a waveform called a negative type ERG which suggested a dysfunction of the ON GLCE bipolar cells. Additional ocular examinations including fundus examination showed no distinctive features [6]. Originally these diseases were reported in patients with melanomas, and they were named melanoma-associated retinopathies (MARs) [7,8]. However, it has been reported that neoplasms other than melanomas can cause the bipolar cell dysfunction ML367 [5,9]. We and others have recently shown that the transient receptor potential melastatin 1 (TRPM1) was an antigen for the autoantibody against the ON bipolar cells in some patients with PR [10,11]. TRPM1 is a protein associated with the ion-conducting plasma membrane channels that mediates the light responses of ON bipolar cells [12-14]. Several studies have reported the presence of neural degeneration in the paraneoplastic syndrome including other types of paraneoplatic retinopathies [4,15-17], but none have shown that the serum of patients with PR can cause a degeneration of the retinal ON bipolar cells. Thus, the purpose of this study was to determine whether the serum of a PR patient with the TRPM1 antibody will cause a degeneration of ON bipolar cells. To achieve this, we injected serum from a PR patient who had an autoantibody against TRPM1 [11] into the vitreous of mice and evaluated its effects on retinal function and histology. We show serum including autoantibody against TRPM1 caused acute retinal ON bipolar cell degeneration. == Materials and Methods == == Animals == All experimental procedures adhered to the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research and the guidelines for the Use of Animals at the Nagoya University School of Medicine. Nagoya University Animal Experiment Committee approved this project (approval number 24456). Seventy C57BL/6 mice at 7-10 weeks-old-age were used. TRPM1 knock-out mice were kindly given to.