Dorsal raphe nucleus projecting retinal ganglion cells: Why Y cells?

Retinal ganglion Y (alpha) cells are found in retinas ranging from frogs to mice to primates. The highly conserved nature of the large, fast conducting retinal Y cell is a testament to its fundamental task, although precisely what this task is remained ill-defined. The recent discovery that Y-alpha retinal ganglion cells send axon collaterals to the serotonergic dorsal raphe nucleus (DRN) in addition to the lateral geniculate nucleus (LGN), medial interlaminar nucleus (MIN), pretectum and the superior colliculus (SC) has offered new insights into the important survival tasks performed by these cells with highly branched axons. We propose that in addition to its role in visual perception, the Y-alpha retinal ganglion cell provides concurrent signals via axon collaterals to the DRN, the major source of serotonergic afferents to the forebrain, to dramatically inhibit 5-HT activity during orientation or alerting/escape responses, which disfacilitates ongoing tonic motor activity while dis-inhibiting sensory information processing throughout the visual system. The new data provide a fresh view of these evolutionarily old retinal ganglion cells. (C) 2015 Elsevier Ltd. All rights reserved.USA National Institutes of Health [EY 017809, NS 077003]; University of Hong Kong; Funds of Leading Talents of Guangdong; Programme of Introducing Talents of Discipline to Universities [B14036]; Project of International; Hong Kong, Macao & Taiwan Science and Technology Cooperation Innovation Platform in Universities in Guangdong Province [2013gjhz0002]; National Basic Research Program of China [2011CB510206]; National Science Foundation of China [30831160516]; Beijing Municipal Science & Technology CommissionSCI(E)PubMedREVIEWhrmaskf@hku.hk; mpu@bjmu.edu.cn118-1315