ThisproposalaimstotestthehypothesisthattypeIIafferentsserveascochlearnociceptors.Takingcuesfromthehumancomplaintofhyperacusisafterhearingloss,wewillexaminethestructureandfunctionoftypeIIafferentsinnormalandpost-traumacochleas.Theworkinghypothesisisthatpainfulhyperacusis,noxacusis,includeshyperactivityoftypeIIafferents,byanalogytohyperalgesiaofsomatic nociceptive C-fibers.ThuswewillexaminetypeIIstructureandfunctioninnormalandpost-trauma cochleasofratsandmice.Inparallelwewillinvestigatethepropertiesofsurvivingouterhaircellsinposttraumacochleas.Ourmethodsinclude:exvivoelectrophysiology,lightandelectronmicroscopy,utilizationofoptogeneticandchemogenetictools,andvalidationandquantificationofmousemodelsinwhichtypeIIspecificbio-markersareexpressed.Anecessaryfirststepistoextendourexvivoexperimentalapproachtooldercochleassothatchangeswroughtbyacoustictraumacanbecomparedtothenormalcondition.Wewillcomparedamagingsound,ototoxicantibioticsandgeneticallyencodedbiotoxinstoproduceexperimentallytractableeffectsontissueforexvivoexperiments.ThepropertiesandsynapticconnectionsoftypeII afferentsandouterhaircellswillbeexaminedintheexcisedcochleartissueoftheseanimals.Wewill continuetoexploretypeIIspecificgeneticmousemodels.Genetically-encodedreporterproteins, voltage-andcalcium-sensitiveindicators,biotoxins,andopto-andchemo-geneticmodulatorshave becomehighlyinformativetoolsinneurobiologygenerallyandfortheinnerearspecifically.Ourongoingworkhascharacterizedonemouseline,tyrosinehydroxylasepromoterdrivenCre-recombinaseexpression.ThreeothercandidatetypeIIspecificCrelineswillbevalidatedandquantified.Withsuchtransgenicmodelsitbecomespossibletostudyinnervationpatternsbyexpressionoffluorescentreporterproteins,andtoactivate,eliminate,ormodulatetypeIIactivityforanatomicalandphysiologicalstudies. Cre-dependentexpressionofgenetically-modifiedG-protein coupledreceptors (DREADDS) willprovide mice in which type II activity can be increased or decreased by injection of anovelsyntheticligand,dependingonthespecificconstruct.Varyingcombinationsofsystemicandroundwindowdrugdeliverywillbeemployedtoincreasethespecificityofexperimentalmanipulations.Theover-archinggoalofthisprogramofexperimentsistocompletethedescriptionoftypeII afferents,astill-unresolvedcomponentofcochlearinnervation. Theworkinghypothesisisthatthese serveascochlearnociceptors. Ifcorrectthesearealikelyneurobiologicalsubstratefornoxacusis (painfulhyperacusis). BydefiningthebasiccellularandmolecularmechanismsoftypeIIfunctionand plasticity,futuretherapeutictargetscanbeidentifiedtoameliorateorpreventnoxacusis.
. TypeIIcochlearafferentsareinsensitivetosound,butstronglyactivatedbytissuedamage.Thisisa proposaltoexaminethehypothesisthattypeIIafferentsarecochlearnociceptorsthatbecome hypersensitiveaftercochleartrauma.
| Wu, Jingjing Sherry; Vyas, Pankhuri; Glowatzki, Elisabeth et al. (2018) Opposing expression gradients of calcitonin-related polypeptide alpha (Calca/Cgrp?) and tyrosine hydroxylase (Th) in type II afferent neurons of the mouse cochlea. J Comp Neurol 526:425-438 |
| Vyas, Pankhuri; Wu, Jingjing Sherry; Zimmerman, Amanda et al. (2017) Tyrosine Hydroxylase Expression in Type II Cochlear Afferents in Mice. J Assoc Res Otolaryngol 18:139-151 |
