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Regina Nobles, Stephen Massey; Two Types of M1 Melanopsin Ganglion Cell in the Rabbit Retina. Invest. Ophthalmol. Vis. Sci. 2013;54(15):304.
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© ARVO (1962-2015); The Authors (2016-present)
Intrinsically sensitive ganglion cells (ipRGCs) express the photopigment melanopsin and are differentiated mainly by their stratification patterns within the inner plexiform layer (IPL) (Sand et al, 2012). M1 ipRGCs stratify in the outermost layer of the IPL and have somas located in either the ganglion cell layer (GCL) or displaced to the inner nuclear layer (INL). In mouse, M1 ipRGCs are classified as morphologically similar (Berson et al, 2010) but have different molecular identities to the transcription factor, Brn3b (Chen et al, 2011). Like mouse, there are multiple types of ipRGC in the rabbit retina. In this study, we found evidence for two types of M1 ipRGC in the rabbit retina based on their morphology and dendritic stratification patterns.
Rabbit retina was immunolabeled with antibodies against melanopsin, Brn3b and choline acetyltransferase (ChAT). The melanopsin signal was enhanced using a tyramide signal amplification protocol. Confocal microscopy was used to image and characterize M1ipRGCs. Statistical analysis was performed using SPSS software.
A cluster analysis performed on 410 identified M1 ipRGCs separated them into two groups. One group, M1Type I, was smaller with fewer primary dendrites and stratified more distal to ChAT band a. The second group, M1 Type II, was larger with multiple branch points and stratified slightly more proximal to M1 Type I ipRGCs. Interestingly, regardless of type, M1 ipRGCs showed differences in the expression of Brn3b depending on where their somas originate. Displaced M1 ipRGCs were negative for Brn3b expression whereas M1 ipRGCs in the GCL were positive for Brn3b expression.
In rabbit retina, we provide evidence for two types of M1 ipRGCs based on their morphological properties. The distribution of Brn3b differs between M1 ipRGCs in the GCL versus those displaced to the INL but does not predict the M1 subtype. Further research is needed to determine any functional differences among M1 subtype.
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