L-type calcium channels refine the neural population code of sound level.
The coding of sound level by ensembles of neurons improves the accuracy with which listeners identify how loud a sound is. In the auditory system, the rate at which neurons fire in response to changes in sound level is shaped by local networks. Voltage-gated conductances alter local output by regulating neuronal firing, but their role in modulating responses to sound level is unclear. We tested the effects of L-type calcium channels (CaL: CaV1.1-1.4) on sound-level coding in the central nucleus of the inferior colliculus (ICC) in the auditory midbrain. We characterized the contribution of CaLto the total calcium current in brain slices and then examined its effects on rate-level functions (RLFs) in vivo using single-unit recordings in awake mice. CaLis a high-threshold current and comprises ∼50% of the total calcium current in ICC neurons. In vivo, CaLactivates at sound levels that evoke high firing rates. In RLFs that increase monotonically with sound level, CaLboosts spike rates at high sound levels and increases the maximum firing rate achieved. In different populations of RLFs that change nonmonotonically with sound level, CaLeither suppresses or enhances firing at sound levels that evoke maximum firing. CaLmultiplies the gain of monotonic RLFs with dynamic range and divides the gain of nonmonotonic RLFs with the width of the RLF. These results suggest that a single broad class of calcium channels activates enhancing and suppressing local circuits to regulate the sensitivity of neuronal populations to sound level.
Department of Anatomy and Neurobiology, Northeast Ohio Medical University, Rootstown, Ohio.
Calum Alex
CA
Grimsley
Department of Anatomy and Neurobiology, Northeast Ohio Medical University, Rootstown, Ohio.
David Brian
DB
Green
Department of Anatomy and Neurobiology, Northeast Ohio Medical University, Rootstown, Ohio ssivaram@neomed.edu.
Shobhana
S
Sivaramakrishnan
D015761:4-Aminopyridine / Q000031:analogs & derivatives / Q000494:pharmacology; D000161:Acoustic Stimulation; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000077770:Amifampridine; D000818:Animals; D055592:Biophysical Phenomena / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D066298:In Vitro Techniques; D007245:Inferior Colliculi / Q000166:cytology*; D051379:Mice; D008808:Mice, Inbred CBA; D009474:Neurons / Q000502:physiology*; D009553:Nimodipine / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D013016:Sound; D014851:Wakefulness; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D018691:Excitatory Amino Acid Antagonists; D026902:Potassium Channel Blockers; D011810:Quinoxalines; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; D009553:Nimodipine; D020866:omega-Conotoxin GVIA; D015761:4-Aminopyridine; D000077770:Amifampridine; D002118:Calcium
auditory midbrain; dynamic range; inferior colliculus; level tuning; local circuits; rate-level functions