Volume 17, Number 6,
Issue of March 15, 1997
pp. 2040-2055
Copyright ©1997 Society for Neuroscience
Experimentally Induced Retinal Projections to the Ferret Auditory
Thalamus: Development of Clustered Eye-Specific Patterns in a Novel
Target
Received Oct. 3, 1996; revised Dec. 23, 1996; accepted Jan. 3, 1997.
Alessandra Angelucci,
Francisco Clascá,
Emanuela Bricolo,
Karina S. Cramer, and
Mriganka Sur
Department of Brain and Cognitive Sciences, Massachusetts Institute
of Technology, Cambridge, Massachusetts 02139
We have examined the relative role of afferents and targets in
pattern formation using a novel preparation, in which retinal projections in ferrets are induced to innervate the medial geniculate nucleus (MGN). We find that retinal projections to the MGN are arranged
in scattered clusters. Clusters arising from the ipsilateral eye are
frequently adjacent to, but spatially segregated from, clusters arising
from the contralateral eye. Both clustering and eye-specific
segregation in the MGN arise as a refinement of initially diffuse and
overlapped projections. The shape, size, and orientation of retinal
terminal clusters in the MGN closely match those of relay cell
dendrites arrayed within fibrodendritic laminae in the MGN. We conclude
that specific aspects of a projection system are regulated by afferents
and others by targets. Clustering of retinal projections within the MGN
and eye-specific segregation involve progressive remodeling of retinal
axon arbors, over a time period that closely parallels pattern
formation by retinal afferents within their normal target, the lateral
geniculate nucleus (LGN). Thus, afferent-driven mechanisms are
implicated in these events. However, the termination zones are aligned
within the normal cellular organization of the MGN, which does not
differentiate into eye-specific cell layers similar to the LGN. Thus,
target-driven mechanisms are implicated in lamina formation and
cellular differentiation.
Key words:
retinogeniculate;
eye-specific segregation;
cholera toxin
subunit B;
medial geniculate nucleus;
afferents;
cross-modal
plasticity