Ophthalmic Research Symposium with Dr....

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Ophthalmic Research Symposium with Dr. Jeff Diamond, NIH, Bethesda, USA

The Institute for Ophthalmic Research Tübingen invited Dr. Jeffery Diamond from the NIH to give a talk in the Ophthalmic Research Symposium on Monday, July 15th. His talk was hosted by François Paquet-Durand and entitled „Diverse Synaptic Signaling in mammalian retina during night vision”.

Ophthalmic Research Symposium with Dr. Jeff Diamond, NIH, Bethesda, USA - hosted by Prof. Francois Paquet-Durand of the Institute for Ophthalmic Research Tübingen, Germany

Ophthalmic Research Symposium with Dr. Jeff Diamond, NIH, Bethesda, USA - Introduction by Francois Paquet-Durand from the Institute for Ophthalmic Research Tübingen

Ophthalmic Research Symposium in the Institute for Ophthalmic Research Tübingen with Dr. Jeff Diamond, NIH, Bethesda, USA

Ophthalmic Research Symposium in the Institute for Ophthalmic Research Tübingen with Dr. Jeff Diamond, NIH, Bethesda, USA

Dr. Jeffery Diamond began his talk by focusing on the differences between studying the brain and the retina. The circuitry in the hippocampus, for example, is not well understood due to difficulties in studying the complex circuitry under microscopy. The retina on the other hand can be cultured in a dish and imaged under different stimuli. The neurons in the retina are interesting due to their large diversity. For instance, there are over 45 different types of amacrine cells, the morphology of which is unique. As opposed to other neurons, amacrine cells do not have an axon. Instead, the signal input and output is located in the soma and dendrites, respectively. Among the amacrine cells, the AII is of most interest, because it connects the rod to the cone signaling pathway. Classically, AII is thought to have output in the OFF layer of the inner plexiform layer (IPL) and input in the ON layer, but recent findings suggest that there are also some local inputs and outputs in the ON layer. During the night, rods transmit signal through rod bipolar cells (RBCs) to amacrine cells, and then the AII, which plays the intermediate role, to transfer the signal from rods to cone bipolar cells.

In his talk Dr. Diamond further explored the signaling at the synapses of RBCs and AII amacrine cells. Immediate signal can travel from RBCs to AII amacrine cells through the release of vesicles from the readily-releasable pool (RRP). The size of the RRP varies with presynaptic membrane potential and is directly reflected by the transient response at light onset. In dim light conditions, the difference between an object and its background is the same as under strong light according to Weber’s law. Under night condition, contrast must therefore be strengthened. The transient potential is responsible for this contrast enhancement.

Next, Dr. Diamond talked about AII signaling to cone bipolar cells. 60 % of AII signal is to the cone bipolar cell type-2 in the OFF layer of IPL. AII pass transient signal to OFF cone bipolar cells 2 (CBC2s).

Remarkably, his group also observed AII synaptic contact with some OFF ganglion cell soma in the ON layer of the IPL. OFF δ ganglion cells express glycine receptors and AII synapses appear to reach into the ON layer. Electron microscopy images indicate contacts between AII and OFF δ ganglion cells. This means that RBCs may relay their signal to AII cells for direct synaptic output to OFF ganglion cells, increasing signal strength and fidelity. OFF ganglion cells have narrow receptive fields, which is dominated by the signal from the AII.

In summary, Prof. Jeff Diamond demonstrated that depending on the status of the retinal network visual signals in AII amacrine cells can encode both luminance and Weber contrast, and then transmit both transient and sustained signals to CBC2s. The synapses of AII contact with OFF ganglion cells, creating a more direct pathway for rod signals to the circuit output. Some inputs of RBCs to AII are close to AII outputs to OFF ganglion cells, enabling powerful signal transfer that may enhance signaling fidelity at the visual threshold.

Summary by Gustav Christensen, Yiyi Chen, and Peter Jenisch of the Paquet-Durand Lab - the Ophthalmic Research Symposium May Edition was hosted by Prof François Paquet-Durand.