The Hopkins Pain Workgroup“Seeing Pain More Clearly”

Optogentic and electrophysiological assay of pain fibers in skin (mice): Michael Caterina, Xinzhong Dong ,Yun Guan, Paul Fuchs

Genetically-visualized pain fibers (mice): Xinzhong Dong, Yun Guan, Srinivasa Raja

Functional and molecular characterization of pain fibers in nonhuman primates: Xinzhong Dong, Joseph Mankowski, Matthias Ringkamp

Functional and molecular characterization of pain fibers in patients with painful peripheral neuropathy: Michael Caterina, Michael Polydefkis

Pain…

Pain in the (r)Ear

4

Innervation of the cochlea: analogous to skin?

5

Type I afferents, large myelinated axons,95% of nerve, carry sound.

Type II afferents, small axons, 5% of nerve unmyelinated, carry ???.

Type I neuron:95% of afferentsContacts single IHC

Type II neuron:5% of afferentsContact many OHCs

Berglund and Ryugo ,1987

Cat Weisz6

Progress to date

• Type II afferents poorly driven by OHCs – so would respond only to (very) LOUD sound

• But, type II afferents also excited by ATP (involved in pain sensation in skin). ATP is released during acoustic trauma.

• Do type II afferents carry ‘ear pain’? The jury is still out.

Hyperacusis, tinnitus: altered afferent balance?

Acoustic trauma

Type II afferents remain

Adapt fiber recording methods to excised skinto study transduction of pain

Patapoutian et al. 2003,

The Hopkins Pain Workgroup