Genetic targeting and physiological features of VGLUT3+ amacrine cells

Abstract

Amacrine cells constitute a diverse class of interneurons that contribute to visual signal processing in the inner retina, but surprisingly, little is known about the physiology of most amacrine cell subtypes. Here, we have taken advantage of the sparse expression of vesicular glutamate transporter 3 (VGLUT3) in the mammalian retina to target the expression of yellow fluorescent protein (YFP) to a unique population of amacrine cells using a new transgenic mouse line. Electrophysiological recordings made from YFP-positive (VGLUT3+) amacrine cells provide the first functional data regarding the active membrane properties and synaptic connections of this recently identified cell type. We found that VGLUT3+ amacrine cells receive direct synaptic input from bipolar cells via both N-methyl-d-aspartate receptors (NMDARs) and non-NMDARs. Voltage-gated sodium channels amplified these excitatory inputs but repetitive spiking was never observed. VGLUT3+ amacrine cells responded transiently to both light increments (ON response) and decrements (OFF response); ON responses consisted exclusively of inhibitory inputs, while OFF responses comprised both excitatory and inhibitory components, although the inhibitory conductance was larger in amplitude and longer in time course. The physiological properties and anatomical features of the VGLUT3+ amacrine cells suggest that this bistratified interneuron may play a role in disinhibitory signaling and/or crossover inhibition between parallel pathways in the retina.

Expression of vesicular glutamate transporter 3 mRNA in the brain and retina of the pigeon

“…The present finding of serotonin-immunoreactive cells in pigeon retina is consistent with the findings of those studies. In mammals, amacrine cells express the vGluT3 mRNA and protein (Fremeau et al, 2002;Haverkamp and Wä ssle, 2004;Johnson et al, 2004;Gong et al, 2006;Grimes et al, 2011). The present finding of colocalization of vGluT3 mRNA and serotonin indicates that the vGluT3 mRNA-expressing cells in the pigeon retina are amacrine cells, as that in mammals.…”

“…Amilhon et al (2010) showed that because vGluT3 is colocalized with serotonergic terminals in several brain regions, loss of vGluT3 expression leads to anxiety-associated behavioral patterns. In the retina, Grimes et al (2011) found that light-evoked synaptic inputs to vGluT3-positive amacrine cells are dominated by inhibition, suggesting that they receive inhibitory input primarily from other amacrine cells that are presumably GABAergic or glycinergic, meaning amacrine-to-amacrine cell inhibition. In contrast, the vGluT3 function in birds has not been examined at all.…”

“…The vGluT1 is localized in photoreceptor cells and bipolar cells, whereas vGluT2 is restricted to horizontal cells and ganglion cells (FyK-Kolodziej et al, 2004;Gong et al, 2006;Wä ssle et al, 2006). The vGluT3 is expressed in one subtype of amacrine cells (Fremeau et al, 2002;Haverkamp and Wä ssle, 2004;Johnson et al, 2004;Gong et al, 2006;Grimes et al, 2011).…”

Specific Wiring of Distinct Amacrine Cells in the Directionally Selective Retinal Circuit Permits Independent Coding of Direction and Size

“…SACs express predominantly TTX-insensitive Na + channels (Oesch and Taylor, 2010), excluding them as a target for TTX. On average, we did observe a mild decrease in excitation/inhibition evoked by small spots in the presence of TTX, which could be due to an effect on spiking AII amacrine cells, bipolar cells which express TTX-sensitive Na + channels (Cui and Pan, 2008), and/or noncanonical excitatory amacrine cells recently shown to contact DSGCs and express TTX-sensitive Na + channels (Grimes et al, 2011). However, the most striking effect was that TTX increased the amplitude of both EPSCs and IPSCs evoked by large spots (400-1,000 mm), clearly indicating a presynaptic inhibitory mechanism that relies on spiking.…”

Reward processing by the dorsal raphe nucleus: 5-HT and beyond

“…We now have numerous animal lines that allow us to specifically target 5-HT, glutamate, GABA, and dopamine neurons in the DRN (Scott et al 2005;Zhuang et al 2005;Grimes et al 2011;Taniguchi et al 2011;Vong et al 2011). In light of the overlapping populations of 5-HT and glutamate neurons, additional efforts should be devoted to generating tools that separate neuron subpopulations.…”