[Abstract Title]. - Society for Neuroscience

in polymodal nociceptors. CA and MO induce heat hyperalgesia and mechanical allodynia in
human skin, and sensitize responses of wide dynamic range (WDR)-type dorsal horn neurons to
noxious skin heating in rats. We presently tested if these TRPA1 agonists induce behavioral
evidence of thermal hyperalgesia and mechanical allodynia in rats. After habituation training,
adult male rats underwent baseline testing of hindpaw withdrawal latency to noxious heat
(Hargreaves test), or the threshold for paw withdrawal elicited by a mechanical probe from
below (electronic von Frey). In separate sessions, one hindpaw received intraplantar
microinjection of CA (5-20%= 398 mM-1.56 M, 10 µl) or vehicle. Thermal withdrawal latencies
or mechanical thresholds for both hindpaws were then obtained 3, 15, 30, 45, 60 and 120 min
post-injection. CA induced a significant, concentration-dependent reduction in thermal paw
withdrawal latencies on the injected side. The peak latency change (to 61.7% of pre-injection
baseline) occurred by 30 min with partial recovery at 120 min. Thermal withdrawal latencies of
the uninjected (contralateral) paw did not change significantly. CA also induced a significant,
concentration-dependent reduction in mechanical withdrawal threshold of the injected paw that
peaked sooner (3 min) and was more profound (44.4% for 20% CA). Mechanical withdrawal
thresholds for the uninjected paw were not significantly affected. A similar series is being
conducted with MO. The present results are consistent with reports of allodynia and thermal
hyperalgesia induced by TRPA1 agonists in humans. The thermal hyperalgesia is consistent with
CA and MO enhancement of rat WDR responses to noxious heat. However, the mechanical
allodynia observed presently is inconsistent with the lack of effect of CA or MO on WDR
responses to graded mechanical stimuli, possibly due to different routes of administration of the
TRPA1 agonists (intraplantar vs. topical).
Disclosures: M.G. Tsagareli , None; N. Tsiklauri, None; G. Gurtskai, None; E. Abzianidze,
None; E. Carstens, None; M. Iodi Carstens, None; K. Zanotto, None.
Poster
266. Pain: Psychophysics and Behavior
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 266.10/FF4
Topic: D.08.h. Psychophysics and behavior
Support: NINDS P01 NS047399.
Title: Capsaicin and histamine produce itch when delivered via inactivated-cowhage spicules
Authors: *P. SIKAND 1 , S. G. SHIMADA 1 , B. G. GREEN 2,3 , R. H. LAMOTTE 1 ;
1 2 3
Dept Anesthesiol, Dept Surgery, Yale Univ. Sch. Med., New Haven, CT; Sensory Neurosci.,
The John B. Pierce Lab., New Haven, CT