Structure and function of photoreceptor and second-order cell mosaics in the retina of Xenopus.

摘要: Abstract The structure, physiology, synaptology, and neurochemistry of photoreceptors second-order (horizontal bipolar) cells Xenopus laevis retina is reviewed. Rods represent 53% the photoreceptors; majority (97%) are green light-sensitive. Cones belong to large long-wavelength-sensitive (86%), short-wavelength-sensitive (10%), miniature ultraviolet wavelength-sensitive (4%) groups. Photoreceptors release glutamate tonically in darkness, hyperpolarize upon light stimulation their transmitter decreases. form ribbon synapses with where postsynaptic elements organized into triads. Their overall adaptational status regulated by ambient conditions set extracellular dopamine concentration. activity photerectors under circadian control independent central body clock. Bipolar cell density about 6000 cells/m m 2 . They receive mixed inputs from rods cones. Some bipolar types violate rule ON-OFF segregation, giving off terminal branches both sublayers inner plexiform layer. them contain glutamate, a small fraction GABA-positive accumulates serotonin. Luminosity-type horizontal more frequent (1000 cells/mm ) than chromaticity (∼450 ). dendritic field size latter type was threefold bigger that former. Luminosity contact all photoreceptor types, whereas chromatic cones rods. involved generating depolarizing responses red which multiple blue-light-sensitive Calculations indicate convergence ratios similar those retinal regions mammals, predicting comparable spatial resolution.