A study on synaptic mechanisms in the retinal neural network

点击翻译按钮获取中文摘要

This research has revolved aroud the vertebrate retina that has long been a favorite object of neuroscience research partly because of the same morphogenic origin as the brain. In particular, we have been concerned with the outer-retinal neural circuitry that involves photoreceptors and such second-order neurons as horizontal and bipolar cells. One of the main projects has produced the following findings regarding the synaptic transmission from cone photoreceptors to H1 horizontal cells (H1 HCs) in the cyprinid fish. Thus, the conventional notion of the cone signal being processed by the kanate-type excitatory synapse is correct only for long-wavelength visual signals, and the synapse mediating the short-wavelength transmission operates with a post-synaptic glutamate receptor mechanism which is polarity-reversing, conductance-decreasing and APB-sensitive, thus most likely mGluR6. Moreover, activation of this receptor mechanism requires either light adaptation (high SNR) or nitric oxide (NO). These properties are found to contribute to adaptation-dependent modulation of the spectral sensitivity as well as of the receptive field of H1 HCs. The notion of NO acting as light-adaptation signal for neural plasticity in the retina is found to be also appropriate for EM-level morphological changes in the post-synaptic invagination of horizontal cells dendrites These physiological, . Pharmacological and anatical findings have been combined with computational studies using neural network models, to help developing a new type of image processors which are adaptive to the visual environmental factors such as SNR and color changes. A prototype vision chip was designed and fabricated in this connection.