Deafferentation increases the intracellular calcium of cochlear nucleus neurons in the embryonic chick.

1. Ratiometric fura-2 imaging was used to measure the intracellular calcium concentration ([Ca2+]i) of neurons in the embryonic avian cochlear nucleus, nucleus magnocellularis (NM), after an in ovo unilateral cochlea removal (deafferentation). 2. The mean [Ca2+]i of NM neurons receiving normal input was 113 nM. 3. Deafferentation increased the mean [Ca2+]i of NM neurons to 247, 311, 339, and 314 nM at 1, 3, 6, and 12 h after cochlear removal, respectively. These values did not differ significantly. 4. The percent frequency distribution of deafferented NM neuron [Ca2+]i shifts away from normative levels toward higher [Ca2+]i at 1 and 3 h after cochlear removal, but shifts back toward normative levels at 6 and 12 h after cochlear removal. 5. This increased [Ca2+]i following cochlear removal temporally coincides with well-characterized changes in NM neurons following activity deprivation. 6. These data suggest that deregulation of [Ca2+]i homeostasis plays a key role in NM neuron degeneration and death following activity deprivation.