Morphologies of rabbit retinal ganglion cells with concentric receptive fields

Abstract

Rabbit retinal ganglion cells with concentric receptive fields were intracellularly recorded and stained in the isolated superfused eyecup preparation to relate specific physiological response properties to dendritic morphology. Concentric ganglion cells, as traditionally defined, were those that had On or Off centers with antagonistic surrounds but lacked complex response properties such as direction or orientation selectivity. Concentric cells were classified into different groups by extracellular recordings of their On- or Off-center response sign, excitatory receptive field center size, linearity of spatial summation, and brisk vs. sluggish and transient vs. sustained responses to step changes in light intensity. The cells were then impaled, confirmed in identity during intracellular recording, and iontophoretically injected with horseradish peroxidase for histological analysis. Twenty-three concentric ganglion cells were recovered and morphometrically analyzed. Their physiological response properties were found to be related to a number of underlying two- and three-dimensional attributes of the cell's dendritic branching patterns. The dendrites of all 20 brisk concentric cells and two of the three sluggish cells were found to ramify narrowly in either the proximal or distal half of the inner plexiform layer, corresponding to whether they are On center or Off center, respectively. One of the sluggish concentric cells was found to have a more complex, partially bistratified ramification. Physiologically identified brisk-sustained-linear, brisk-transient-nonlinear, brisk-transient-linear, and at least two classes of sluggish concentric ganglion cells were stained. Each of these physiological classes appears to exhibit a distinct and identifiable dendritic branching pattern.