Journal of Neuroscience, Vol 8, 1384-1399, Copyright © 1988 by Society for Neuroscience
The projection from the superficial to the deep layers of the superior colliculus: an intracellular horseradish peroxidase injection study in the hamster
RD Mooney, MM Nikoletseas, PR Hess, Z Allen, AC Lewin and RW Rhoades
Department of Anatomy, University of Medicine and Dentistry of New Jersey, School of Osteopathic Medicine, Piscataway 08854.
Intracellular recording and horseradish peroxidase (HRP) injection
techniques were employed to examine the projections of superficial layer
[stratum griseum superficiale (SGS) and stratum opticum (SO)] superior
collicular (SC) neurons in the hamster that sent axon collaterals into the
deep laminae (those ventral to the SO) of this structure. Sixty-nine
neurons were studied, selected from a sample of over 185 HRP-filled
superficial layer cells on the basis of having heavily stained axons. Of
the 69 cells included in the study, 43.4% (n = 30) sent at least one axon
collateral to the deep laminae. Not all cell types in the superficial
layers contributed equally to this interlaminar projection: 78.6% (n = 11)
of the recovered wide-field vertical cells, 55.0% (n = 11) of the
narrow-field vertical cells, 16.7% (n = 2) of the stellate cells, 40.0% (n
= 2) of the marginal cells, 18.2% (n = 2) of the horizontal cells, and
28.6% (n = 2) of neurons we could not classify on the basis of their
somadendritic morphology projected to the deep layers. Within a given cell
class, there were no significant morphological or physiological differences
between the neurons that possessed deep axon collaterals and those that did
not. The deep axon collaterals of most of the interlaminar projection
neurons were restricted to the stratum griseum intermediate (SGI). In this
layer, the largest segment of the axon arbor was located lateral to a
projection line that was orthogonal to the SC surface and that passed
through the soma of the cell in question. These results, along with those
of a previous study (Mooney et al., 1984), which demonstrated that the
dendrites of deep layer cells may extend through the SO and into the SGS,
indicate that there is an extensive anatomical substrate by which sensory
information may be communicated from superficial to deep layer SC neurons.
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