Abstract
Purpose: :
We identified the synaptic transmitters used by, and received by, ON, OFF and ON-OFF amacrine cell types. We measured the spatial extent of amacrine cell processes and the extent of the inhibitory input to these amacrine cell types.
Methods: :
We patch clamped about 100 amacrine cells with somas in the inner nuclear layer in the retinal flat mount. We measured excitation, inhibition, and voltage responses to 600µm light or dark flashes. Using different sized spots, we determined the spatial extent of the inhibitory input. We used the inhibitory receptor blockers strychnine and SR95531 to determine the neurotransmitters that mediate the inhibition to the recorded cells. APB was used to block the ON pathway. Amacrine cells were fluorescently labeled following recording to reveal morphology by confocal microscopy. We also used glycine and GABA antibodies to determine the neurotransmitter present in the recorded amacrine cell.
Results: :
1. ON cells received narrow glycinergic OFF inhibition, OFF cells received narrow glycinergic ON inhibition2. A variety of amacrine cell types received narrow ON-OFF glycinergic inhibition. None of this ON-OFF inhibition was wide or GABAergic3. ON-OFF amacrine cells appeared to receive no inhibition. Using immunocytochemistry, we distinguished between the neurotransmitters contained in the wide, monostratified and the narrow, diffusely stratified ON-OFF cells.
Conclusions: :
Narrow amacrine cells that carry inhibition from the ON to OFF and OFF to ON sublamina are glycinergic. Widely ramifying ON-OFF amacrine cells receive no inhibition. They likely only feed forward to ganglion cells using GABA (Roska and Werblin 2003) because no bipolar (Molnar and Werblin 2007) or amacrine cells receive ON-OFF GABAergic inhibition. These results suggest that the inhibitory neurotransmitters in the IPL are segregated both "functionally" and spatially: local cross-lamina ON to OFF and OFF to ON inhibitory circuits use glycine, while wide inhibitory circuits use GABA. These two rules dictate how the retina encodes different aspects of the visual world.Molnar, A. and F. S. Werblin (2007). "Inhibitory Feedback Shapes Bipolar Cell Responses in the Rabbit Retina." J Neurophysiol.Roska, B. and F. Werblin (2003). "Rapid global shifts in natural scenes block spiking in specific ganglion cell types." Nat Neurosci 6(6): 600-8.
Keywords: retina: proximal (bipolar, amacrine, and ganglion cells) • amacrine cells • neurotransmitters/neurotransmitter systems