Alar plate

A fundamental characteristic of the vertebrate central nervous system (CNS) is bilateral symmetry along the midline (Figure 3). This symmetrical structure divides neuronal projections into two types, uncrossed projections to ipsilateral targets and crossed projections to contralateral targets. Over the past decade, the mechanism involved in the formation of crossed projections has been extensively studied in spinal cord commissural projections. Spinal commissural axons, which derive from the dorsal part of the neural tube (alar plate), initially project ventrally along the circumferential axis and then cross the ventral midline [10]. These axons have been shown to be guided by a diffusible molecule released... 

Figure 4. Chemoattraction of spinal cord commissural axons by the floor plate. (A) Axon growth pattern of commissural neurons. (B, C) Collagen gel culture of an alar plate explant with a floor plate explant. Extensive outgrowth of commissural axons occurred toward the floor plate explant (B). Commissural axons were reoriented toward the floor plate explant (C].

Figure 5. Chemoattraction of alar plate commissural axons in the brain by the floor...

Figure 8. Turning of DAPms axons away from floor explants in collagen gel culture. (A) Diagrammatic representation of coronal view of the mesencephalon showing explant origins (hatched areas). RR roof plate AR alar plate VAR ventral alar plate BR basal plate SL, sulcus limitans, the AR/BR boundary. (B, D) Diagrams showing...

Hallonet, M. E. R. and Le Douarin, N. M. (1993) Tracing neuroepithelial cells of the mesencephalic and metencephaUc alar plates during cerebellar ontogeny in quail-chick chimaeras. Eur. J. Neurosci. 5,1145-1155. 

Hgure 3. Basic structure of the vertebrate central nervous system. The CNS is derived from a hollow structure called the neural tube. It has two orthogonal axes, the circumferential axis and the longidudinal axis. Four distinct domains called the roof, alar, basal, floor plates are generated along the circumferential axis (A). The neural tube can also divided along the longitudinal axis into the spinal cord and the brain, which can be further divided into five brain vesicles, the telencephalon, the diencephalon, the mesencephalon, the metencephalon and the myelencephalon (B). 

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