Afferent regulation of cytochrome-c and active caspase-9 in the avian cochlear nucleus

• Published in: Neuroscience Vol. 120; no. 4; pp. 1071 - 1079
• Main Authors: Wilkinson, B.L, Elam, J.S, Fadool, D.A, Hyson, R.L
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.01.2003; Elsevier
• Subjects: ACSF; analysis of variance; Animals; ANOVA; Apaf-1; apoptosis; apoptosis activating factor-1; artificial cerebrospinal fluid; auditory nerve, eighth nerve; auditory system; Aves; Biological and medical sciences; Blotting, Western; Brain Stem - metabolism; Caspase 9; Caspases - metabolism; Cell Death; Cell Survival; Chickens; Cochlea - metabolism; Cochlea - surgery; Cochlear Nucleus - enzymology; Cytochrome c Group - metabolism; Cytoplasm - metabolism; deafferentation; Denervation; Densitometry; Ear and associated structures. Auditory pathways and centers. Hearing. Vocal organ. Phonation. Sound production. Echolocation; EDTA; ethylenediaminetetraacidic acid; Fundamental and applied biological sciences. Psychology; IAP; ICC; immunocytochemical; Immunohistochemistry; In Vitro Techniques; inhibitor of apoptosis; Mitochondria - metabolism; n. magnocellularis; Neurons - metabolism; nucleus magnocellularis; nVIII; PAGE; PCD; phosphatase inhibitor; polyacrylamide gel electrophoresis; PPI; Precipitin Tests; programmed cell death; SDS; second mitochondrial-derived activator of caspase/direct inhibitor of apoptosis-binding protein with low pI; Smac/DIABLO; sodium dodecyl sulfate; Time Factors; Vertebrates: nervous system and sense organs; n. magnocellularis; SDS; Smac/DIABLO; auditory system; ICC; PPI; apoptosis; PAGE; ACSF; EDTA; deafferentation; PCD; ANOVA; nVIII; IAP; Apaf-1; NM; Enzyme; Central nervous system; Cochlear nucleus; Caspase; Cytochrome c; Peptidases; Vertebrata; Hydrolases; Auditory pathway; Chicken; Aves; Deafferentation; Brain (vertebrata); Apoptosis
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/S0306-4522(03)00387-7

During development, a subpopulation (approximately 30%) of neurons in the avian cochlear nucleus, nucleus magnocellularis (NM), dies following removal of the cochlea. It is clear that neuronal activity coming from the auditory nerve provides trophic support critical for cell survival in the NM. Several aspects of the intracellular signaling cascades that regulate apoptosis have been defined for naturally occurring, or programmed cell death, in neurons. These intracellular cascades involve the extrusion of cytochrome-c from the mitochondria into the cytosol and the subsequent activation of proteolytic caspase cascades, which ultimately act on substrates that lead to the death of the cell. In contrast, the intracellular signaling cascades responsible for deafferentation-induced cell death are not fully understood. In the present series of experiments, the potential extrusion of cytochrome-c from the mitochondria into the cytosol, and the activation of caspases were examined in the NM following deafferentation. Cytochrome-c immunoreactivity increased within 6 h following deafferentation and persisted for at least 3–5 days following surgery. However, cytochrome-c was not detectable within immunoprecipitates obtained from cytosolic fractions of deafferented NM neurons. This suggests that the increased immunoreactivity of cytochrome-c is related to mitochondrial proliferation. As a positive control, cytochrome-c was detected in cytosolic fractions of deafferented NM neurons treated with kainic acid, a substance known to cause cytochrome-c release into the cytosol. In addition, immunoreactivity for downstream active caspase-9 did increase following cochlea ablation. This increase was observed within 3 h following cochlea removal, but was not observed 4 days following surgery, a time point after the dying population of NM neurons have already degenerated. Together, these findings suggest that deafferentation of NM neurons results in caspase activation, but this activation may be cytochrome-c independent.