Age-related changes in the response properties of cartwheel cells in rat dorsal cochlear nucleus

Hear Res. Jun-Jul 2006;216-217:207-15. doi: 10.1016/j.heares.2006.03.005. Epub 2006 Apr 27.

Abstract

The fusiform cell and deep layers of the dorsal cochlear nucleus (DCN) show neurotransmitter and functional age-related changes suggestive of a downregulation of inhibitory efficacy onto DCN output neurons. Inhibitory circuits implicated in these changes include vertical and D-multipolar cells. Cartwheel cells comprise a large additional population of DCN inhibitory neurons. Cartwheel cells receive excitatory inputs from granule cell parallel fibers and provide a source of glycinergic inhibitory input onto apical dendrites of DCN fusiform cells. The present study compared the response properties from young and aged units meeting cartwheel-cell criteria in anesthetized rats. Single unit recordings from aged cartwheel cells revealed significantly higher thresholds, increased spontaneous activity and significantly altered rate-level functions characterized by hyperexcitability at higher intensities. Aged cartwheel cells showed a significant reduction in off-set suppression. Collectively, these findings suggest a loss of tonic and perhaps response inhibition onto aged DCN cartwheel neurons. These changes likely reflect a compensatory downregulation of synaptic inhibition in response to a loss of excitatory drive from auditory and non-auditory excitatory inputs via granule cells. The impact of increased excitability of cartwheel cells on DCN output neurons is likely to be complex, influenced by loss of glycinergic release and/or subunit receptor changes which would only partially off-set age-related loss of inhibition onto the somata and basal dendrites of fusiform cells.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural

MeSH terms

  • Age Factors
  • Aging / physiology*
  • Animals
  • Auditory Threshold / physiology
  • Cochlear Nucleus / cytology
  • Cochlear Nucleus / physiology*
  • Down-Regulation
  • Evoked Potentials, Auditory, Brain Stem / physiology
  • Neural Inhibition / physiology*
  • Neurons / physiology*
  • Rats
  • Rats, Sprague-Dawley