Afferent regulation of chicken auditory brainstem neurons: Rapid changes in phosphorylation of elongation factor 2

Abstract

The relationships between protein synthesis and neuronal survival are poorly understood. In chicken nucleus magnocellularis (NM), significant alterations in overall protein synthesis precede neuronal death induced by deprivation of excitatory afferent activity. Previously we demonstrated an initial reduction in the overall rate of protein synthesis in all deprived NM neurons, followed by quick recovery (starting at 6h) in some, but not all, neurons. Neurons with recovered protein synthesis ultimately survive while others become “ghost” cells (no detectable Nissl substance) at 12–24h and die within 48h. To explore the mechanisms underlying this differential influence of afferent input on protein synthesis and cell survival, the current study investigates the involvement of eukaryotic translation elongation factor 2 (eEF2), the phosphorylation of which reduces overall protein synthesis. Using immunocytochemistry for either total or phosphorylated eEF2 (p-eEF2), we find significant reductions in the level of phosphorylated, but not total, eEF2 in NM neurons as early as 0.5h to 1h following cochlea removal. Unexpectedly, neurons with low levels of p-eEF2 show reduced protein synthesis at 6h indicated by a marker for active ribosomes. At 12h, all “ghost” cells exhibited little or no p-eEF2 staining although not every neuron with a comparable low level of p-eEF2 was a “ghost” cell. These observations demonstrate that a reduced level of p-eEF2 is not responsible for immediate responses (including reduced overall protein synthesis) of a neuron to compromised afferent input, but may impair the neuron’s ability to initiate recovery signaling for survival and make the neuron more vulnerable to death.

Intense and specialized dendritic localization of the fragile X mental retardation protein in binaural brainstem neurons: A comparative study in the alligator, chicken, gerbil, and human

“…According to the manufacturer's data sheet, anti‐MAP2 recognizes rat, mouse, and chicken MAP2 as 200–300 kDa bands on western blots. This antibody has been used as a somatodendritic marker in the chicken brain (Wang et al, ; McBride et al, ). The staining pattern in the current study is comparable to that reported in these studies.…”

Neurocognitive factors in sensory restoration of early deafness: a connectome model

“…Even before the onset of auditory function, loss of cochlear cells might result in death of subsequent auditory neurons in the brainstem. 33,34 Therefore, the age at onset of cochlear deficits in utero might affect profoundly the functional integrity of auditory pathways and, as a result, higher order brain systems and functions that rely on this sensory input.…”

The observed alteration in BCL2 expression following lithium treatment is influenced by the choice of normalization method

“…Rather, a more likely interpretation (in light of the increased BCL2 transcript in these cells prior treatment) is cellular recovery from cessation of protein synthesis as a result of lithium treatment. Indeed, it has been demonstrated that inhibition of protein synthesis in the deafferentiated cochlear nucleus results from phosphorylation of elongation factor 2 (eEF2) 38 , 39 that can be reversed by lithium treatment 40 . It is thus conceivable that the observed lithium-induced upregulation of BCL2 in Bush and Hyson’s study 35 does not reflect a specific upregulation of the BCL2 protein, but, rather, a general increase in protein synthesis.…”