1. 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

2. Pain…

3. Pain in the (r)Ear

4. 4

5. 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 ???.

6. Type I neuron: 95% of afferents Contacts single IHC Type II neuron: 5% of afferents Contact many OHCs Berglund and Ryugo,1987 Cat Weisz 6

7. 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.

8. Hyperacusis, tinnitus: altered afferent balance? Acoustic trauma Type II afferents remain

9. Adapt fiber recording methods to excised skin to study transduction of pain Patapoutian et al. 2003,

10. The Hopkins Pain Workgroup