Journal of Neuroscience, Vol 2, 589-597, Copyright © 1982 by Society for Neuroscience
Early postnatal development of laminar characteristics in the dorsal lateral geniculate nucleus of the tree shrew
JK Brunso-Bechtold and VA Casagrande
Three characteristics distinguish the six layers of the adult tree shrew
dorsal lateral geniculate nucleus (LGN). First, interlaminar spaces divide
the nucleus into cell layers. Second, input from the two eyes projects to
the nucleus such that two layers (1 and 5) receive input from the
ipsilateral retinal and four layers (2, 3, 4, and 6) receive input from the
contralateral retina. Finally, distinct cytological features characterize
individual layers. In this report, we describe the postnatal development of
LGN layers in the tree shrew in terms of the development of these three
characteristics. At birth, the nucleus appears homogenous in Nissl-stained
sections. Thus, no interlaminar spaces are present and all cells look
similar in shape, size, and staining intensity. However, autoradiographic
data show that, at birth, retinal afferents are segregated in an adult-like
pattern. Interlaminar spaces begin to be evident between layers innervated
by opposite eyes on postnatal day 2. Several days later, interlaminar
spaces between layers innervated by the same eye (i.e., the borders of
layer 3) appear, while the others continue to widen. Although some
cytological maturation begins before interlaminar space formation, it is
not until interlaminar spaces are apparent that features such as
differential staining intensity and cell size can be used to distinguish
individual layers. The results suggest that the three characteristics that
define LGN layers in the tree shrew may be temporally separate events in
the developing nucleus. Thus, retinal afferents are segregated prior to
interlaminar space formation which, in turn, is initiated prior to final
maturation of the cytological features that characterize the cell layers.
This may indicate a degree of developmental independence among these
maturational events.