Expression of Neuronal Connexin36 in AII Amacrine Cells of the Mammalian Retina

Abstract

We have studied the expression pattern of neuronal connexin36 (Cx36) in the mouse and rat retina. In vertical sections of both retinas, a polyclonal antibody directed against Cx36 produced punctate labeling in the inner plexiform layer (IPL). Intense immunoreactivity was localized to the entire OFF sublamina of the IPL, and much weaker staining could be observed in the ON sublamina. Double-labeling experiments in the rat retina with antibodies directed against parvalbumin indicate that Cx36 is expressed on dendrites of AII amacrine cells. Cx36-like immunoreactivity in sublamina a of the IPL did not overlap with lobular appendages or cell bodies of AII amacrine cells. In a mouse retinal slice preparation, AII amacrine and ON cone bipolar cells were intracellularly injected with Neurobiotin and counterstained with antibody against Cx36. Punctate labeling appeared to be in register with dendritic arborization of AII amacrines and cone bipolar cells in the ON sublamina of the IPL. Whereas AII amacrine cells isolated from the rat retina clearly displayed Cx36-like immunoreactivity, isolated ON cone bipolar cells were negative for Cx36. Axon terminals of rod bipolar cells were decorated with Cx36-positive contacts but did not express Cx36 themselves.These results indicate that Cx36 is expressed by AII amacrine cells in homologous and heterologous gap junctions made with AII amacrines and cone bipolar cells, respectively. The heterologous gap junctions appear to be heterotypic, because ON cone bipolar cells do not express Cx36.

Screening of gap junction antagonists on dye coupling in the rabbit retina

“…AII amacrine cells express Cx36 (Feigenspan et al, 2001;Mills et al, 2001), Atype HCs express Cx50 (O'Brien et al, 2006) and the mouse homolog of the rabbit B-type HC may use Cx57 (Hombach et al, 2004). MFA, 18-β-GA, mefloquine and 2-APB blocked coupling in all these networks, and so we conclude they have little selectivity between different connexins, at least within the group of neuronal connexins such as Cx36, Cx50 and Cx57 in the retina.…”

“…Atype HCs are coupled via Cx50 gap junctions while B-type HCs may be coupled by Cx57 (Hombach et al, 2004). In the inner retina, AII amacrine cells are coupled by Cx36 gap junctions (Feigenspan et al, 2001;Mills et al, 2001). To test if the potential gap junction antagonists are effective on different connexins, we tested their effects on coupling in different neural networks.…”

“…AII/AII coupling is mediated by Cx36 gap junctions (Feigenspan et al, 2001;Mills et al, 2001) while the coupling between AII amacrine cells and ON cone bipolar cells may rely on heterotypic Cx36/Cx45 gap junctions (Dedek et al, 2006). After dye injecting an AII amacrine cell, a large coupled patch of AII amacrine cells was recovered with an overlying set of cone bipolar cells (Fig.…”

“…In the inner retina, AII amacrine cells of the rod pathway are coupled to other AII amacrine cells via Cx36 gap junctions (Feigenspan et al, 2001;Mills et al, 2001) but they also make heterotypic Cx36/Cx45 gap junctions with ON cone bipolar cells (Han & Massey, 2005;Lin et al, 2005;Maxeiner et al, 2005;Dedek et al, 2006). This pathway has been shown to be essential for the transmission of dark-adapted rod signals through the retinal network (Deans et al, 2002).…”

Electrical synapses between AII amacrine cells in the retina: Function and modulation

“…It is well established that the homologous gap junctions between the arboreal dendrites of AII amacrine cells contain the neuronal gap junction protein connexin 36 (Cx36) (Deans et al, 2002;Feigenspan et al, 2001;Mills et al, 2001) and tracer coupling between AII amacrine cells is virtually abolished between AII amacrine cells in Cx36-deficient ("knock-out"; KO) mice (Deans et al, 2002). Cx36 gap junction channels display very low voltage-sensitivity and a low single-channel conductance (~15 pS; Srinivas et al, 1999;Teubner et al, 2000).…”