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Liju Luan, Chaoran Ren, Jie Gao, Kwok-Fai So, Mingliang Pu; Morphological Properties Of Medial Amygdala Projecting Retinal Ganglion Cells In The Mongolian Gerbil. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4349.
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© ARVO (1962-2015); The Authors (2016-present)
The amygdala is a limbic system structure involved in many brain functions, including emotion, learning and memory. It is demonstrated that melanopsin expressing retinal ganglion cells (ipRGCs) innervate the medial amygdala (MA) (Hattar et al., 2006). However, whether classical RGCs (C-RGCs) innervate MA remains to be investigated. The goal of this study was two-folds: 1) confirm if C-RGCs project to MA; 2) determine morphological properties of MA-projecting RGCs.
Young adult Mongolian gerbils were used in this experiment. Fluorescent microspheres or fluorescein conjugated Cholera toxin B subunit (CTB) were microinjected unilaterally into MA sites of anesthetized gerbil. After survival for three days, animals were deeply anesthetized and enucleated. Retrogradely labeled RGCs in the wholemount retina were intracellularly injected with the fluorescent dye Lucifer Yellow (LY) to reveal their full dendritic morphology. Immunohistochemical staining was performed to label ipRGCs and convert LY into permanent staining.
The present study shows that both ipRGCs and C-RGCs project to MA and approximately 90% of cells send their axons to the contralateral MA. Among them, 95% were C-RGCs and the rest were ipRGCs. On average, we counted close to 320 MA-projecting C-RGCs and up to 15 ipRGCs per retina. MA-projecting RGCs showed an evenly retinal distribution pattern. Dendritic process branching and ramification patterns of MA-projecting RGCs were quantitatively analyzed. Our results shows, in addition to Alpha-like cells, MA-projecting C-RGCs consisted of several morphological types.
Both C-RGCs and ipRGCs project to MA but the majority of them are C-RGCs. The present result suggests that MA-projecting RGCs are structurally heterogeneous. Direct C-RGCs inputs to MA could be important for regulating amygdala functions.
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