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  • Title: The development of interneurons in the chick embryo spinal cord following in vivo treatment with retinoic acid.
    Author: Shiga T, Gaur VP, Yamaguchi K, Oppenheim RW.
    Journal: J Comp Neurol; 1995 Sep 25; 360(3):463-74. PubMed ID: 8543652.
    Abstract:
    To investigate the role of retinoic acid (RA) in the development of interneurons in the spinal cord, we examined the expression of cellular retinoic acid binding protein type I (CRABP I). The earliest developing interneurons in the chick spinal cord can be divided into two major groups: circumferential (C) neurons and primitive longitudinal (PL) neurons. In brachial segments, both types of interneurons began to express CRABP I at stage (st.) 13+ of the V. Hamburger and H.L. Hamilton (1951, J. Morphol. 88:49-92) stage series, which is before the onset of axonogenesis. Subsequently, with the onset of axonal outgrowth, C neurons and PL neurons expressed CRABP I in their cell bodies, axons, and growth cones. The expression of CRABP I was developmentally regulated. CRABP I immunoreactivity gradually decreased after st. 36 (embryonic day [E] 10) such that no interneurons expressed this protein by E21. The transient expression of CRABP I during a period of intensive axonal growth suggested that RA may be involved in the development of interneurons. To test this idea, we implanted an all-trans RA-containing ion exchange bead into either rostral segments of the spinal cord at st. 12-13 or into caudal segments at st. 15-16, all stages that are well before the appearance of CRABP-I-positive neurons in these segments. In the RA-treated spinal cord, increased numbers of pyknotic cells were found predominantly in dorsal regions, presumably reflecting the death of neuroepithelial cells, C neurons and premigratory neural crest cells. Surviving C neurons in the RA-treated spinal cord extended their axons ventrally toward the floor plate as in control embryos. PL neurons also projected their axons rostrally or caudally in the RA-treated spinal cord, similarly to control embryos. However, the proportion of caudally projecting PL neurons was significantly increased in segments rostral to the RA-containing bead. These results suggest that RA may regulate the survival and axonal orientation (directionality) of subpopulations of spinal interneurons.
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