Journal of Neuroscience, Vol 1, 1103-1112, Copyright © 1981 by Society for Neuroscience
The laminar origin and distribution of the crossed tectoreticular pathways
V Holcombe and WC Hall
The superior colliculus is the source of a prominent descending pathway
which crosses the midline in the mesencephalon and projects to the
paramedian pontine reticular formation. The primary goal of the present
study was to identify the cells in the superior colliculus of the grey
squirrel which give rise to this pathway by using a combination of
anterograde and retrograde tracing techniques. Results from the anterograde
studies demonstrated the course and terminal distribution of this pathway
and suggested that its laminar origin is the intermediate grey layer,
stratum griseum intermediale. The retrograde studies were used to confirm
the results of the anterograde experiments and to provide a more
quantitative estimate of the laminar distribution of the cells which give
rise to this pathway. In most cases, over 90% of the cells retrogradely
labeled following injections of horseradish peroxidase along the course of
this pathway were located in the intermediate grey lamina. This origin is
in contrast to that of the ipsilateral tectoreticular pathway which
originates primarily in stratum griseum profundum (Holcombe, V., and W. C.
Hall (1981) Neuroscience 6: 255-260) and suggests that these two grey
layers of the deep tectum are functionally distinct.