Mk. Walton et al., SODIUM-CHANNELS, GABA-A RECEPTORS, AND GLUTAMATE RECEPTORS DEVELOP SEQUENTIALLY ON EMBRYONIC RAT SPINAL-CORD CELLS, The Journal of neuroscience, 13(5), 1993, pp. 2068-2084
It is not well understood when during embryonic development the elemen
ts of a cell's responsiveness first appear, nor the factors controllin
g their appearance. A strategy to approach this issue is to determine
which aspects of neuronal development are highly stereotyped in presen
ce, timing, or pattern across a variety of cell types, and which are m
ore diversified by cell type, region, or other parameters. We have use
d a fluorescent potentiometric oxonol dye in conjunction with a digita
l video imaging system to record the emergence and distribution of spe
cific forms of excitability in dissociated embryonic rat spinal cord c
ells. We studied the expression of responses to veratridine, a sodium
channel activator; muscimol, a GABA(A) receptor agonist; and kainic ac
id, an agonist at a class of glutamate receptors. Responses were consi
stently detectable in a percentage of cells dissociated from the earli
est age examined, embryonic day 13, and increased progressively in lat
er ages. Cells were examined from four regions, with cervical-lumbosac
ral and ventrodorsal distinctions. In the population of cells from eac
h region, functional sodium channels appeared prior to GABA(A) recepto
rs, which in turn emerged prior to kainate-activated glutamate recepto
rs. This pattern was common to all spinal cord regions and revealed ve
ntrodorsal and rostrocaudal gradients reflecting the known pattern of
spinal cord neurogenesis. Analysis of the individual cell responses in
dicated that the stereotypical pattern of sequential channel developme
nt occurs individually on most cells in each region.