The orientation of horizontal cell dendrites in the superior colliculus of the hamster: an analysis based on three-dimensional reconstruction of intracellularly injected neurons.

We have employed intracellular injection of horseradish peroxidase (HRP) and 3-dimensional, computer-assisted reconstruction to delineate the organization of the dendrites of horizontal cells in the superficial laminae (the stratum griseum superficiale-SGS, and stratum opticum-SO) of the hamster's superior colliculus. Fifteen well-filled cells were analyzed. The dendrites of these cells were generally parallel to the frontal plane. An average of 74.8 +/- 13.0% of the total dendritic arbor of the recovered horizontal cells was located within 30 degrees of this plane. The long axis of horizontal cell dendritic trees deviated an average (mean +/- s.d.) of 21.7 +/- 13.2 degrees from the frontal plane and the average extent of the dendritic tree in this plane was 637 +/- 216 microns. This differed significantly from the average dendritic extent in the rostrocaudal axis (358 +/- 146 microns, p less than 0.001). In some cases, portions of the dendritic arbors of horizontal cells appeared to be oriented along lines of isoelevation or isoazimuth of the visual field representation in the superficial laminae. For other cells, there was no clear relationship between dendritic orientation and the visual field map.