An Electron Microscopic Study of Cell Degeneration in Chick Embryo Spinal Ganglia

Abstract

An electron microscopic study of cell degeneration in chick embryo spinal ganglia Cell degeneration which normally occurs during development was studied under the electron microscope in thoracic spinal ganglia of chicken embryos. Cells undergoing degeneration were often identified as primitive neuroblasts or transitional cells between the primitive and intermediate neuroblast, and sometimes as intermediate neuroblasts. Degeneration seems to begin with nuclear alterations (chromatin condensation and segregation of the nucleolar components) and ribosomal changes (polysomal disaggregation, and displacement of many membrane‐associated ribosomes). Soon the Golgi complex is no longer recognizable. Successively, large masses of finely granular material become prominent in the nucleus, the nuclear envelope breaks down, many mitochondria appear altered, many vacuoles with clear contents become evident, and ribosome crystals appear. At the end of the process the degenerated cell appears as a shrunken mass of granular debris and membrane fragments. Some neuroblastic processes contain clumped filaments and microtubules and/or polymorphic dense bodies. These structural changes are not unique to this degenerative process, but closely resemble those following other types of injuries of the nerve cell. A drastic reduction in the nuclear synthesis of RNA, and a profound impairment in protein synthesis are probably the main biochemical events which occur in these degenerating cells. Degeneration, which probably affects the neuroblasts which fail to establish appropriate connections with the periphery, seems to be one of the major factors controlling cell number in the spinal ganglia.

Neuronal death in the spinal ganglia of the chick embryo and its reduction by nerve growth factor

“…The highest counts in the DM population amount lites. We can confirm the observation of Pannese (1976) to only two-thirds of those in the VL population. that occasionally, undifferentiated neuron precursor cells Brachial ganglion 15.…”

“…Macrophages containing debris of several cells were encountered infrequently and were counted as two degenerating cells. Further details of degeneration in sensory ganglia are dealt with extensively by Pannese (1976) who also discussed the pertinent literature. Obviously, we miss the incipient stages of degeneration which are revealed only by the electron microscope, but this is not a problem in the present study since the absolute figures are used only for comparison.…”

“…As shown in Figure 4, degeneration in the VL population of ganglion 18 is well above the base line at stage 25 (4% d) and rises rapidly during the following day. Pannese (1976), in his electron microscopic study of degeneration in chick spinal ganglia, found that the cells which die between 4 and 7 d (and can therefore be identified as VL neurons) are "primitive neuroblasts" which are defined as bipolar neuroblasts, or transitional stages between "primitive" and "intermediate neuroblasts," the latter representing bipolar neurons in which the two processes approach each other but have not yet reached the stage of pseudo-unipolar neurons. Clearly, these sensory neurons become sensitive to trophic deticiencies at a much earlier stage of differentiation than, for instance, the neurons of the lateral motor column or the ciliary ganglion.…”

Postnatal Neuron Death in the Nodose Ganglia of the Rat

“…This was corrected for in this study using Abercrom bie's [12] standard cor rection factor. Even though this would suggest the possi bility of developmental neuron death, light microscopic observations have shown no sign of neuron degenera tion, e.g., shrunken dark nuclei, rounded shrunken cyto plasm [1,6]. This apparent discrepancy may be a t tributed to several possibilities.…”

Developmental neuron death in the rat superior cervical sympathetic ganglion: cell counts and ultrastructure

“…The ultrastructural characteristics of the vast majority of the,neurons that die in the SCG are similar to type I degeneration described in the lateral motor column during normal cell death (Chu-Wang & Oppenheim, 1978). This type of degeneration is also observed during normal ganglion cell death in the retina (Hughes & McLoon, 1979;Cunningham et al, 1981),; and in the spinal ganglia (Pannese, 1976), after target removal in the ciliary ganglion (Pilar & Landmesser, 1976), and after deafferentation of the superior colliculus (Giordano & Cunningham, 1982). Pilar & Landmesser (1976) refer to this type of degeneration as 'nuclear' because of the early appearance of clumped chromatin.…”