The appearance of neural and glial cell markers during early development of the nervous system in the amphibian embryo

Abstract

Cell-type-specific antibodies have been used to follow the appearance of neurones and glia in the developing nervous system of the amphibian embryo. Differentiated neurones were recognized with antibodies against neurofilament protein while glial cells were identified with antibodies against glial fibrillary acidic protein (GFAP). The appearance of neurones containing the neurotransmitters 5-hydroxytryptamine and dopamine has been charted also. In Xenopus, neurofilament protein in developing neurones was observed occasionally at NF stage 21 and was present reliably in the neural tube and in caudal regions of the brain at stage 23. Antibodies to the low molecular weight fragment of the neurofilament triplet recognized early neurones most reliably. Radial glial cells, identified with GFAP antibody, were identified from stage 23 onwards in the neural tube and caudal regions of the brain. In the developing spinal cord, GFAP staining was apparent throughout the cytoplasm of each radial glial cell. In the brain, the peripheral region only of each glial cell contained GFAP. By stage 36, immunohistochemically recognizable neurones and glia were present throughout the nervous system. In the axolotl, by stage 36 the pattern of neural and glial staining was identical to that observed in Xenopus. GFAP staining of glial cells was obvious at stage 23, although neuronal staining was clearly absent. This implies that glial cells differentiate before neurones. 5-HT-containing cell bodies were first observed in caudal regions of the developing brain on either side of the midline at stage 26. An extensive network of 5-HT neurones appeared gradually, with a substantial subset crossing to the opposite side of the brain through the developing optic chiasma. 5,7-dihydroxytryptamine prevented the appearance of 5-HT. Depletion of 5-HT had little effect on development or swimming behaviour. Dopamine-containing neurones in the brain first differentiated at stage 35–36 and gradually increased in number up to stage 45–47, the latest stage examined. The functional role of 5-HT- or dopamine-containing neurones remains to be elucidated. We conclude that cell-type-specific antibodies can be used to identify neurones and glial cells at early times during neural development and may be useful tools in circumstances where functional identification is difficult.