Structure-function correlation in transient amacrine cells of goldfish retina: basic and multifractal analyses of dendritic trees in distinct synaptic layers.

Abstract

Amacrine cells generating light-evoked transient ON-OFF responses were stained by intracellular injection of horseradish peroxidase after determining their input-output (voltage response vs. light intensity) profiles. Ten cells specifically having bistratified dendritic trees were analyzed. The cross-sectional area of the dendrites in each sublamina (a and b) of the inner plexiform layer was initially measured. Although some variability was observed, there was no statistically significant overall difference in the cross-sectional areas of the dendritic trees in sublaminae a and b. Also, the amplitudes of the ON and OFF responses, generated by a midrange criterion stimulus, could not be correlated with the cross-sectional areas or the number of branches of the dendrites in sublaminae b and a, respectively. On the other hand, determination of the generalized fractal spectra revealed that the negative (up to -3) and zero-order fractal dimensions of the dendritic trees in sublamina a were consistently higher than those for sublamina b. Furthermore, there was a positive correlation between response amplitude and some part of the generalized fractal dimension in the respective parts of the dendritic trees. It is concluded that dendritic tree characteristics differ in the two halves of the inner plexiform layer and that these can be related to the cells' light-evoked response amplitudes. Furthermore, generalized fractal analysis appears to be a useful method for correlating structure and function in retinal amacrine cells with complex dendritic trees.