Early postnatal development of laminar characteristics in the dorsal lateral geniculate nucleus of the tree shrew

Abstract

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.

Glial cells develop a laminar pattern before neuronal cells in the lateral geniculate nucleus.

“…4. Although there are differences in the details 1 Am. B shows a higher power stereo pair of the same cell in an adjacent section.…”

“…For some time now, we have been interested in the mechanisms that result in the presence of distinctive cell layers in the lateral geniculate nucleus (LGN), the major thalamic target of retinal fibers in mammals (1)(2)(3)(4). One aspect of these studies has been to examine correlations between the various events involved in lamination in the LGN of the tree shrew (Tupaia belangeri), one of the few species in which LGN cell layers develop postnatally (1)(2)(3)(4).…”

“…One aspect of these studies has been to examine correlations between the various events involved in lamination in the LGN of the tree shrew (Tupaia belangeri), one of the few species in which LGN cell layers develop postnatally (1)(2)(3)(4).…”

“…However, this describes only one of at least three types of lamination in the LGN. Each type has a distinct time course and may involve a distinct mechanism (1)(2)(3)(4). Retinal terminals innervating the LGN are found in layers at birth in tree shrews (1)(2)(3)(4) and probably begin and end their segregation process during the last 2 weeks of embryonic development (V.A.C.…”

“…This afferent lamination is contrasted with cytoarchitectonic lamination, the differential packing density of cells (i.e., into cellular and cell-free zones). The latter process occurs during postnatal week 1 in tree shrews (1)(2)(3)(4). Finally, the LGN exhibits cytological lamination-differences in the size and shape of cell bodies.…”