Excitotoxic motoneuron disease in chick embryo evolves with autophagic neurodegeneration and deregulation of neuromuscular innervation

Abstract

In the chick embryo, in ovo application of NMDA from embryonic day (E) 5 to E9 results in selective damage to spinal cord motoneurons (MNs) that undergo a long-lasting degenerative process without immediate cell death. This contrasts with a single application of NMDA on E8, or later, which induces massive necrosis of the whole spinal cord. Chronic MN degeneration after NMDA implies transient incompetence to develop programmed cell death, altered protein processing within secretory pathways, and late activation of autophagy. Chronic NMDA treatment also results in an enlargement of thapsigargin-sensitive Ca(2+) stores. In particular MN pools, such as sartorius-innervating MNs, the neuropeptide CGRP is accumulated in somas, peripheral axons and neuromuscular junctions after chronic NMDA treatment, but not in embryos paralyzed by chronic administration of curare. Intramuscular axonal branching is also altered severely after NMDA: it usually increases, but in some cases a marked reduction can also be observed. Moreover, innervated muscle postsynaptic sites increase by NMDA, but to a lesser extent than by curare. Because some of these results show interesting homologies with MN pathology in human sporadic ALS, the model presented here provides a valuable tool for advancing in the understanding of some cellular and molecular processes particularly involved in this disease.

Mechanisms of acute axonal degeneration in the optic nerve in vivo

“…Local application of the calcium ionophore dramatically enhanced axonal degradation processes, whereas application of a calcium channel inhibitor mix nearly prevented degeneration and resulted in an attenuation of autophagosome numbers. Downstream of calcium influx, fragmentation of microtubules due to activation of proteases of the proteasome (35) or calpain (9) were observed after axonal injury and NMDA-induced increase of [Ca 2+ ] i has been associated with the expression of the autophagy marker LC3 (36). Our studies on lesion-dependent LC3 expression now link the initial increase of [Ca 2+ ] i to a secondary increase in autophagy.…”

Development of microglia in the chick embryo spinal cord: Implications in the regulation of motoneuronal survival and death

“…and E16, two ages in which MNs are highly vulnerable to glutamate receptor-mediated toxicity (Calderó et al, 1997). We have previously demonstrated that a single dose of a glutamate receptor agonist, such as KA, administered in ovo after E8 produces extensive neuronal death affecting the entire spinal cord, with a rapid and massive depletion of MNs (Calderó et al, 1997;Lladó et al, 1999;Calderó et al, 2007). KA-induced MN death was accompanied by a significant increase in the number of microglial cells in the lumbar LMC, as shown in Figure 7A.…”

Janus-Faced Autophagy: A Dual Role of Cellular Self-Eating in Neurodegeneration?

“…17 Fourth, N-methyl-D-aspartic acid (NMDA)-induced motoneuron degeneration in chick embryos involves the late activation of autophagy. 18 Fifth, the activity of several proteins mediating autophagosome formation is increased significantly in hippocampal neurons of kainic acid (KA)-treated mice. 19 Together, these results suggest the involvement of autophagy gene-related membrane alterations and a possible role of autophagy itself in excitotoxic necrotic cell death.…”

“…9 Similarly, neurotoxins, such as NMDA, KA and 6-hydroxidopamine, induce the selective, necrotic-like degeneration of specific classes of neurons in divergent animal systems. [18][19][20] Thus, neurons may respond to distinct excitotoxic insults by common processes that can cause degeneration of the affected cell. Indeed, electron microscopy analysis of toxic ion channel-poisoned dying neurons has revealed a reproducible sequence of cellular changes involving aberrant vesicular trafficking.…”