Inhibition of Adult Rat Retinal Ganglion Cells by D₁-Type Dopamine Receptor Activation

Abstract

The spike output of neural pathways can be regulated by modulating output neuron excitability and/or their synaptic inputs. Dopaminergic interneurons synapse onto cells that route signals to mammalian retinal ganglion cells, but it is unknown whether dopamine can activate receptors in these ganglion cells and, if it does, how this affects their excitability. Here, we show D1a-receptor-like immunoreactivity in ganglion cells identified in adult rats by retrogradely transported dextran, and that dopamine, D1-type receptor agonists, and cAMP analogs inhibit spiking in ganglion cells dissociated from adult rats. These ligands curtailed repetitive spiking during constant current injections, and reduced the number and rate of rise of spikes elicited by fluctuating current injections without significantly altering the timing of the remaining spikes. Consistent with mediation by D1-type receptors, SCH-23390 reversed the effects of dopamine on spikes. Contrary to a recent report, spike inhibition by dopamine was not precluded by blocking Ih. Consistent with the reduced rate of spike rise, dopamine reduced voltage-gated Na+ current (INa) amplitude and tetrodotoxin, at doses that reduced INa as moderately as dopamine, also inhibited spiking. These results provide the first direct evidence that D1-type dopamine receptor activation can alter mammalian retinal ganglion cell excitability, and demonstrate that dopamine can modulate spikes in these cells by a mechanism different from the pre- and postsynaptic means proposed by previous studies. To our knowledge, our results also provide the first evidence that dopamine receptor activation can reduce excitability without altering the temporal precision of spike firing.

Dopamine and full‐field illumination activate D1 and D2‐D5‐type receptors in adult rat retinal ganglion cells

“…Curiously, both D1 and D2 receptor antibodies, ligands, and mRNA probes bind to the mammalian retinal ganglion cell layer (Brann and Young, 1986; Cohen et al, 1992; Wagner et al, 1993; Bjelke et al, 1996; Veruki and Wassle, 1996; Hayashida et al, 2009; Van Hook et al, 2012). Whereas this could reflect mixtures of cells expressing either D1 or D2 receptors, dopamine responses in other preparations are known to involve more than one receptor subtype and, in some cases, different signaling cascades and heteromeric receptor complexes (Neve et al, 2004; Hasbi et al, 2010).…”

Fixation strategies for retinal immunohistochemistry

“…Likewise, we have found that a mouse monoclonal antibody against D1 dopamine receptors (clone SG2-D1a; cat# NB110-60017; Novus Biologicals) also stains rat retinal ganglion cell somata (Fig. 2M–P; see also Hayashida et al, 2009) and a subsequent study (Van Hook et al, 2012) found similar binding of a polyclonal anti-D1a receptor antibody in rat retina. The monoclonal antibody bound to a protein band of the estimated molecular weight expected of D1a receptors (e.g., Huang et al, 1992) in western blots of whole retinal homogenate.…”

“…Scale bar in (P) is 20 µm and applies to (D,H,L,P). Lack of detectable GCL immunopositivity in A–L contrasts with GCL immunopositivity in M–P and with ganglion cell dopamine-sensitivity (Hayashida et al, 2009; Ogata et al, 2012). …”

“…2A–L). The immunostaining pattern discrepancy between these antibodies is noteworthy because they each stain a protein band of 50–55 kDa in western blots (Hayashida et al, 2009; Free et al, 2007; Luedtke et al, 1999; Partida and Ishida, unpublished observations). It is not known why these antibodies yield such different staining patterns in tissue, but the similarity of their staining patterns on western blots indicates that formaldehdye fixation alters each epitope differentially.…”

“…A third approach would be to test for binding of antibodies directed against different epitopes of a given protein (Rhodes and Trimmer, 2006). A fourth approach is to functionally (e.g., electrophysiologically) test for the presence of proteins of interest (Hattar et al, 2002; Hayashida et al, 2009; Hornstein et al, 2004; Partida et al, 2012; Ryskamp et al, 2011; Stradleigh et al, 2011; Taylor and Morgans, 1998). …”