Journal of Neurophysiology, Vol 43, Issue 3 595-611, Copyright © 1980 by APS
Effects of neonatal enucleation on receptive-field properties of visual neurons in superior colliculus of the golden hamster
R. W. Rhoades and L. M. Chalupa
1. Monocular enucleation in infant hamsters results in a marked expansion
of the normally very limited ipsilateral retinotectal projection (13). In
34 hamsters subjected to removal of one eye within 12 h of birth, the
receptive-field characteristics of superior collicular neurons ipsilateral
and contralateral to the remaining eye were investigated quantitatively and
compared to those of normal animals. In six additional neonatal enucleates,
the density of the expanded retinotectal projection was studied with the
autoradiographic method and an attempt was made to relate the anatomical
reorganization with the electrophysiological findings, 2. The response
characteristics of visual cells in the colliculus contralateral to the
remaining eye were not significantly different from those observed in
normal animals. In the ipsilateral tectum, however, numerous changes were
observed. Visual receptive fields were abnormally large. The incidence of
directional selectivity was markedly reduced, as were the magnitudes of the
discharges elicited by either flashed or moving stimuli. Fewer cells were
activated by small flashed spots and most of the units that were responsive
to such stimulation failed to exhibit the surround suppression typical for
the majority of tectal neurons in normal hamsters. Most cells in the
ipsilateral colliculus responded only to relatively low (less than 50
degrees/s) stimulus velocities and response decrements resulting from
repeated stimulation also occurred much more readily for the neurons tested
on this side. 3. The results of additional experiments in neonatal
enucleates (n = 8), which were also subjected to acute bilateral removal of
the visual cortex, demonstrated that such damage resulted in a marked
reduction in the incidence of directional selectivity in the colliculus
contralateral to the remaining eye but had no effect on the responses of
cells innervated by the aberrant ipsilateral pathway. 4. A correlation
between the relative density of the ipsilateral retinal projection at
different points in the colliculus, as demonstrated by the autroradiography
and the nature of the visual responses obtained in different portions of
the structure, indicated that receptive-field size was negatively
correlated with the density of the aberrant retinotectal projection and
that absolute responsivity (number of impulses elicited by an optimal
stimulus) was positively correlated with autoradiographic grain density. 5.
These findings demonstrate that while the aberrant retinocollicular
projection can, along with the other visual inputs to the tectum, result in
the organization of normal response properties for a small number of tectal
neurons, the majority of the visual cells innervated by this pathway have
responses that are appreciably different from normal.
