Journal of Neuroscience, Vol 15, 190-201, Copyright © 1995 by Society for Neuroscience
Specialized neuronal and glial contributions to development of the hamster lateral geniculate complex and circadian visual system
GI Botchkina and LP Morin
Department of Psychiatry, State University of New York, Stony Brook 11794.
The intergeniculate leaflet (IGL) is an integral part of the adult
circadian visual system. It is characterized by the presence of retinal
afferents and peptidergic cells projecting via a geniculohypothalamic tract
(GHT) to the suprachiasmatic nucleus (SCN), site of the mammalian circadian
clock. The adult IGL also contains abundant reactive astrocytes
immunoreactive to GFAP. Because glia have a large role in brain
development, we examined the ontogeny of the hamster IGL with respect to
both glial and neuronal markers. Neuropeptide Y- immunoreactive (NPY-IR)
cells destined for the IGL appear on embryonic day 11 (E11) in a matrix of
vimentin (VIM)-IR radial glia. Migratory ellipsoid NPY-IR cells with long
leading and trailing processes become oriented between the reticular
thalamic neuroepithelial lobule, and the developing IGL. Most NPY-IR cells
arrive in the IGL by E14 and extend axons ventrally into the GHT. These
penetrate the SCN at P3 and arborize to an adult-like stage by P10. A
specialized GFAP-IR radial glial path coinciding with the migratory route
of NPY-IR cells appears by E14. As early as E15, cells contributing to this
path are found displaced away from the ventricle. As the glial path
disappears from the maturing brain, the entire length of the IGL becomes
filled with GFAP-IR astrocytes. These features are consistent with
translocation and transformation of a specialized set of radial glia into
IGL astrocytes. The results demonstrate that the IGL is a large,
developmentally important, feature of the lateral geniculate complex that
is embryologically distinct from adjacent dorsal and ventrolateral
geniculate nuclei.