Studies on the neural circuit and neurotransmitters in the mammalian retina.

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The vertebrate retina is a small central nervous system in which the visual information captured by photoreceptors are processed. All visual signals are encoded into the train of action potentials that travel through the optic nerve to higher visual centers. Despite that a vast amount of studies have been made on mammalian retina on the light-evoked responses of the optic nerve, studies on the underlying intraretinal mechanisms are quite limited in the mammalian retina. In stead, lower vertebrates have been used as model preparations, since mammals and the lower vertebrates have similar structures of the retina and the light-evoked responses of the optic nerve show similar characteristics.The aim of the present study was to elucidate ionic currents and transmitter actions on the isolated retinal cells dissociated from mammals. We achieved following studies and made findings listed below. (1)We established tlie method to dissociate mammalian retinal cells in good condition. (2)We established the method to identify solitary ganglion cells by retrograde labeling using Dil. (3)We found that X- and W-cells has a sodium. current with different inactivation kinetics : I_<Na> of X-cells recover rapidly froin inactivation, while recovery was slow in W-cells. (4)We found that cat retinal horizontal cells have qualitatively the same type of ionic currents as horizontal cells of the lower vertebrates. (5)We found two types of bipolar cells in the cat retina. Tlie one type responded to L-glutamate with an outward current response accompanied by a conductance decrease, while tlie other type responded with an inward current accompanied by a conductance increase. The former cells correspond to those showing depolarizing light responses, while the latter correspond to OFF bipolar cells showing hyperpolarizing light responses.