title: Age-related changes in the response properties of cartwheel cells in rat dorsal cochlear nucleus.
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.
authors.affiliation: Department of Pharmacology, Southern Illinois University School of Medicine, P.O. Box 19629, Springfield, IL 62794-9629, USA. dcaspary@siumed.edu
authors.forename: Donald M
authors.initials: DM
authors.lastname: Caspary
authors.forename: Larry F
authors.initials: LF
authors.lastname: Hughes
authors.forename: Tracy A
authors.initials: TA
authors.lastname: Schatteman
authors.forename: Jeremy G
authors.initials: JG
authors.lastname: Turner
mesh_terms: D000367:Age Factors; D000375:Aging / Q000502:physiology*; D000818:Animals; D001309:Auditory Threshold / Q000502:physiology; D017626:Cochlear Nucleus / Q000166:cytology / Q000502:physiology*; D015536:Down-Regulation; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley