Between The Cuticular Plate and the Synaptic Junction

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Between The Cuticular Plate and the Synaptic
Junction

• - Nanootological Re-Examination Of The Auditory
  Mechanisms Missing Link

OLUSESI, A.D. FWACS, FMCORL
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Nanootology - Concept

• Submicron view of otology
• Basically nanotechnology applied to otology
• Fall out of Richard P Feynmans 1959 lecture
• Coined in 2002 October in SA
• Potentials in unsolved otological problems
• Visualization nanoendoscopy
• Monitoring nanoaudiology
• Manipulation nanosurgery, nanootology
• Targeted therapy

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Architecture of Sensory System
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PROBLEM DEFINITION

• Hair cells sensory receptors cells
• Detect sound acceleration stimuli
• Cochlear hair cells function
• Mechano electrical transduction
• Electro-chemical transduction (NT release)
• Electro-mechanical transduction (Electromotility,
  OHCs only)
• Mechano-electrical Electro-chemical
  transduction in response to sound stimulus
• ?HOW ?? MECHANISM

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Research Questions

• What events occur between the moment the inner
  ear fluid displacement secondary to movement of
  stapes to sound stimulus occurs, and the release
  of neurotransmitters from the hair cell primary
  auditory neuron synaptic junction?

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Methodology

• Advances in neurobiology, molecular biology,
  hearing research, and nanotechnology reviewed
  from scientific and medical databases
• Current knowledge of auditory neuroanatomy
  compared and submicroscopic anatomy extrapolated
  in view of new knowledge of inner ear
  ultrastructure

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Cochlear Anatomy The Cochlear Partition
Organ of Corti
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Transduction Evolution of Theories
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Hair Cell Microscopic View
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Actual Micro scale Ciliary Finding
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Hair Cells Versus Normal Cells
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Hair Cells - Microanatomy
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Hair Cell Nanoanatomy Evolution of Tools

• Light Microscopy
• Transmission electron microscopy
• Scanning Electron Microscopy

• Patch Clamp
• Optical Tweezers
• Atomic Force Microscopy
• Soft X-ray Microscopy

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Hair Cell Nanoanatomy Current Tools
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Hair Cells Nanoanatomy Stereocilia
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Hair Cell Membrane Plasma Organelles
Transmembrane Protein
Outer
Inner
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Hair Cell Nanoanatomycontd.

• 1 2 microns thick
• Supports rootlets of stereocilia
• Contains actin myosin
• OHC intracuticular region
• Rich in mitochondria ER

Cuticular Plate
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Hair Cell Nanoanatomycontd.

• Small membrane-enclosed Bodies
• Origin Fusion or Budding
• Exocytosis followed rise Ca2i
• Contain neurotransmitter(s)

Vesicles
What is the link between Ca2i and Exocytosis???
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Mechanism of Exocytosis
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Ca2 Modulation of Exocytosis
Actin Filament
Anchored Vesicle
VAMP
Ca2i
Ca2i
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Vesicle Associated proteins

• Restriction of Mobilization
• Synapsins (1a, 1b, IIa, IIb)
• Vesicle Transporter
• Rab3a Rab3b
• Vesicle Docking Fusion
• NSF
• Soluble NSF-attachment protein (SNAP)
• Synaptobrevin ( SNAP-25 Syntaxin)
  docking/fusion complex at synapses
• Exocytosis
• Synaptotagmin, Synaptophysin

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Cochlear Hair cells Synaptic Proteins
Peculiarity

• Possession of synaptic ribbon -highly specialized
  structure to which the synaptic vesicle must dock
  before exocytosis,
• Ability to maintain high sustain release of
  neurotransmitters, and
• Lack of synaptophysin and synapsin - two
  proteins that feature prominently in exocytosis
  of CNS vesicles.

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Cochlear Hair cells Synaptic Proteins -Fact Sheet

• Syntaxin 1, the predominant syntaxin in CNS
  synapses is also expressed in hair cells
• Vesicle associated membrane protein (VAMP)1, but
  not VAMP3 associated with ribbon synapses of
  retina, is expressed in hair cells, and
• SNAP-25, syntaxin1, and VAMP1 do not appear to be
  concentrated at the base of the hair cells where
  synaptic contacts are made, but rather found
  throughout the cell
• - Saffiedin Wenthold, 2003

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Mechanism of Ca2 Influx in Exocytosis
Ligand-Gated Channel
Voltage-Gated Channel
Stretch/Pressure-Gated Channel
Phospho/dephosphorylation Channel
Calcium Channel Open State
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Unanswered Question
How does ca2 influx translate Into intracellular
Ca2 concentration around the vesicles?
Ca2
Ca2
Ca2
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Synaptic Gap

• IHC to Afferent VIII 140Å
• OHC to Afferent VIII 1µm
• OHC to Efferent VIII 190Å
• Afferent NT Glutamate
• Efferent NT A/chcoline, etc

Synaptic Gap
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Total Picture The Missing Link
Synaptophysin
CAM Kinase II
Rab3c
SYNAPTIC VESICLE
Synapsin
Cytoskeleton
Docking Fusion
Transport
Plasma membrane
Ca2 Channel
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The Ultimate Query

• Is the entire reason for creating a highly
  sophisticated cochlear partition to eventually
  achieve electro-chemical transduction?