The Frorieps' ganglia are dorsal root ganglia (DRG) that form and then degenerate during normal embryonic development of amniotes. Their degeneration or survival has been shown to be modulated by modifying expression of Hox-family and other genes involved in pattern formation, and by the mesodermal microenvironment of the cranial somites in which they develop. In ovo application of the @entity2252 NGF partially rescues @entity69239 from degeneration. To further examine the potential role of neurotrophins in the life cycle of Frorieps' DRG we have now quantified the numbers of neurons expressing @entity2252 receptors @entity2250 and @entity13820 in avian Frorieps' ganglia ( @entity69239 ) and normal cervical DRG (DRG5). We have found that the Frorieps' DRG are different from normal DRG in terms of the numbers of neurons expressing these receptors. @entity13820 -expressing neurons are generally lacking in @entity69239 , this is the earliest (St 18, @entity46883 ) described difference between @entity69239 and normal DRG, preceding morphological differences between these ganglia that appear at St 20. The difference between @entity69239 and DRG5 in terms of numbers of @entity2250 -expressing neurons is evident only at later embryonic stages, where @entity69239 contains a higher proportion of @entity2250 neurons than normal cervical DRG. The few @entity13820 + neurons present late in @entity69239 development are not concentrated in the VL portion of the ganglion, the zone where @entity13820 + neurons are generally found in normal DRG. We also find that @entity69239 neurons are smaller than those of normal DRG, this is true for both @entity2250 + and @entity13820 + populations. These data together therefore suggest that the neurons that survive in the Frorieps' ganglia at later stages belong almost exclusively to the @entity2250 -expressing DM class DRG neurons. We further find that the differences in the populations of @entity2250 / @entity13820 between @entity69239 and DRG5 result from signals from the mesodermal microenvironment, since DRG arising in cranial somites transplanted caudally contain few @entity13820 + neurons and a higher proportion of @entity2250 + cells than contralateral controls.

Differing patterns of XXXX -receptor expressing neurons allow distinction of the transient Frorieps' ganglia from normal DRG before morphological differences appear.

@entity13820 :: ('4916', 'Gene') :: ['trkC'] @entity69239 :: ('1819', 'Gene') :: ['DRG2'] @entity2252 :: ('627', 'Gene') :: ['neurotrophin'] @entity46883 :: ('81618', 'Gene') :: ['E2.5'] @entity2250 :: ('4914', 'Gene') :: ['trkA']
@entity2252 :: (627,Gene) :: ['neurotrophin']
