GJD2 and glaucoma: In addition, in contrast to these beneficial effects of astrocyte gap junction in glaucoma, neuronal gap junctions are detrimental to RGCs in glaucoma, as pharmacological blockade of gap junctions or knock out connexin 36 (Cx36) subunits, which are highly expressed in retinal neurons, protected RGCs and optic nerve axons in a mouse model of glaucoma (Akopian et al., 2017).