Approximately 20-30% of neurons in the avian cochlear nucleus (nucleus magnocellularis) die following deafferentation (i.e. deafness produced by cochlea removal) and the remaining neurons show a decrease in soma size. Cell death is generally accepted to be a highly regulated process involving various pro-survival and pro-death molecules. One treatment that has been shown to modify the expression of these molecules is chronic administration of lithium. The present experiments examined whether lithium treatment can protect neurons from deafferentation-induced cell death. Post-hatch chicks were treated with LiCl or saline for 17 consecutive days, beginning on the day of hatching. On the 17th day, a unilateral cochlea ablation was performed. Five days following surgery, the nucleus magnocellularis neurons were counted stereologically on opposite sides of the same brains. Lithium reduced deafferentation-induced cell death by more than 50% (9.8% cell death as compared with 22.4% in saline-treated subjects). Lithium did not affect cell number on the intact side of the brain. Lithium also did not prevent the deafferentation-induced decrease in soma size, suggesting a dissociation between the mechanisms involved in the afferent control of soma size and those involved in the afferent control of cell viability. A possible mechanism for lithium's neuroprotective influence was examined in a second set of subjects. Previous studies suggest that the pro-survival molecule, bcl-2, may play a role in regulating cell death following deafferentation. Tissues from lithium-and saline-treated subjects were examined using immunocytochemistry. Chronic administration of lithium dramatically increased the expression of bcl-2 protein in nucleus magnocellularis neurons. These data suggest that lithium may impart its neuroprotective effect by altering the expression of molecules that regulate cell death. Keywords apoptosis; neuroprotection; auditory brainstemCell death is a regulated process that is common during normal development of the nervous system, but can be initiated by a variety of events including deafferentation, disease, or injury. Neuronal cell death can also be induced during development in many sensory systems following the loss of sensory input. For example, mitral and tufted cells of the olfactory system die following unilateral naris occlusion (Frazier and Brunjes, 1988;Meisami and Safari, 1981), and in the visual system, the survival of tectal neurons depends on activity-dependent release of trophic factors from retinotectal axon terminals (Catsicas et al., 1992). In the auditory system, cell death can occur in the cochlear nucleus following deafness (Born and Rubel, 1985;Hashisaki and Rubel, 1989;Tierney et al., 1997). Although cell death following sensory deprivation has been widely studied in a variety of systems, little work has gone into efforts *Corresponding author. Tel: +1-850-644-1200; fax: +1-850-644-7739. E-mail address: hyson@psy.fsu.edu (R. L. Hyson).. The present experiments examine the control of cel...

The avian brainstem serves as a useful model to answer the question of how afferent activity influences the viability of target neurons. Approximately 20-30% of neurons in the avian cochlear nucleus, nucleus magnocellularis (NM) die following deafferentation (i.e., deafness produced by cochlea removal). Interestingly, Bcl-2 mRNA (but not protein) is upregulated in 20-30% of NM neurons following deafferentation. We have recently shown that chronic treatments of lithium upregulates the neuroprotective protein Bcl-2 and increases neuronal survival following deafferentation. The pathways leading to the upregulation of Bcl-2 expression following these two manipulations are unknown. The present experiments examine changes in glycogen synthase kinase-3 beta (Gsk-3beta), and transcription factors nuclear factor kappaB (NFkappaB), beta-catenin, and pCreb following lithium administration and following deafferentation. These molecules are known to be influenced by lithium and to regulate Bcl-2 expression in other model systems. Lithium decreased immunolabeling for Gsk-3beta and increased expression for all three transcription factors. Deafferentation, however, did not alter Gsk-3beta or NFkappaB, resulted in lower beta-catenin expression, but did increase pCreb immunoreactivity. While it is possible that pCreb is a common link in the regulation of Bcl-2 following these two manipulations, the timing and distribution of pCreb labeling suggests that it is not the sole determinant of Bcl-2 upregulation following deafferentation. It is likely that the regulation of Bcl-2 gene expression by lithium and by deafferentation involves different molecular pathways.

The avian brainstem serves as a useful model system to address the question of how afferent activity influences viability of target neurons. Approximately 20-30% of neurons in the avian cochlear nucleus, nucleus magnocellularis (NM) die following deafferentation (i.e., deafness produced by cochlea removal). Previous studies have identified cellular events that occur within hours following cochlea removal, which are thought to lead to the ultimate death of NM neurons. We have recently shown that chronic lithium treatment increases neuronal survival following deafferentation. To assess where in the cell death cascade lithium is having its effect, we evaluated some of the early deafferentation-induced cellular changes in NM neurons. Lithium did not affect deafferentationinduced changes that occur across the entire population of NM neurons. There were still deafferentation-induced increases in intracellular calcium concentrations and early changes in the ribosomes, as indicated by Y10b immunolabeling. Lithium did, however, affect changes that are believed to be indicative of the subpopulation of NM neurons that will eventually die. Ribosomes recovered in all of the deafferented NM neurons (as assessed by Y10b labeling) by 10 hours following cochlea removal in subjects pretreated with lithium, while a subpopulation of the NM neurons in saline-treated subjects showed dramatic reduction in Y10b labeling at that time. Lithium treatment also prevented the robust upregulation of Bcl-2 mRNA that is observed in a subpopulation of deafferented NM neurons 6 hours following cochlea removal. KeywordsAuditory system; Cell death; Bcl-2; Fura-2; Neuroprotection; Nucleus magnocellularis It is generally accepted that sensory experience plays an important role in the development of the brain. This idea is supported by studies showing changes in innervation patterns, or even cell death, following the loss of sensory experience in young animals (e.g. Catsicas et al., 1992;Pope and Wilson, 2007;Meisami and Safari, 1981). The effects of sensory deprivation have been extensively studied in the brainstem auditory system of the chick (Rubel et al., 1990). Loss of sensory input, produced by cochlea removal, results in the death of Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. approximately 20-30% of the neurons in the ipsilateral cochlear nucleus, nucleus magnocellularis (NM) (Born and Rubel, 1985). NIH Public AccessThe brainstem auditory system of the chick has proven to be a fruitful model system for examining the effects of sensory deprivation, in part, because of its relatively simple or...