Dendritic morphology of projection neurons in the cat pretectum
M. Schmidt, G. Lehnert, R. G. Baker & K.-P. Hoffmann
Journal of Comperative Neurology, 369:520-532, 1996
- The distribution and dendritic morphology of neurons in the cat pretectal nuclear complex were analyzed with
respect to their projection to the ipsilateral dorsal lateral geniculate nucleus (LGNd) and the ipsilateral inferior
olive (IO). Single and double retrograde tracing techniques were combined with intracellular injections of either
horseradish peroxidase into electrophysiologically identified pretectal neurons or Lucifer Yellow into retrogradely
labeled somata. Pretectal cells afferent to the LGNd were located in the nucleus of the optic tract (NOT), adjacent
dorsal terminal nucleus of the accessory optic system (DTN), and posterior pretectal nucleus (NPP). Cells projecting
to the IO were also distributed throughout the NOT-DTN and dorsal part of the NPP. Separate tracer injections (fluorogold
and horseradish peroxidase [HRP] or granular blue) into the LGNd and the IO showed considerable overlap of labeled
neurons in the NOT and dorsal NPP. Double-labeled neurons, however, were not observed after double tracer injections
into LGNd and IO. Partial topographical segregation of the two populations was observed along the dorsoventral
axis because LGNd-projecting neurons exhibited maximum density ventral to that of IO neurons. Pretectal cells to
the LGNd had cell body diameters
between 16 and 48 microns. Somatic shapes varied between fusiform and multipolar with considerable overlap between
these two morphological appearances. Neurons projecting to the IO exhibited similar cell body sizes and their morphology
also varied from fusiform to multipolar. Quantitative analysis of dendritic field size and orientation, number
and order of dendritic arborizations, and symmetry of the dendritic tree revealed no statistically significant
difference between the two neuronal populations. Hence, neurons of the two populations cannot be unequivocally
identified just from the dendritic morphology. By contrast, dendritic morphology was correlated with the topographical
location of either cell type within the pretectal nuclei rather than projection. Thus, the morphological appearance
of neurons located dorsally predominantly was fusiform while neurons located ventrally mostly were multipolar.
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