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1 NPB, UC Davis, Davis, California, United States; Sect. of Neurobiology, Physiology & Behavior, University of California, Davis, Davis, California, United States
2 Anesthesiology, Stanford University, Palo Alto, California, United States
3 NPB, UC Davis, Davis, California, United States
4 Sect. of Neurobiology, Physiology & Behavior, University of California, Davis, Davis, California, United States; NPB, UC Davis, Davis, California, United States
* To whom correspondence should be addressed. E-mail: eecarstens{at}ucdavis.edu.
Mustard oil (allyl isothiocyanate= AITC) and cinnamaldehyde (CA), agonists of the ion channel TRPA1 expressed in sensory neurons, elicit a burning sensation and heat hyperalgesia. We tested if these phenomena are reflected in the responses of lumbar spinal wide-dynamic range (WDR) neurons recorded in pentobarbital-anesthetized rats. Responses to electrical and graded mechanical and noxious thermal stimulation were tested before and after cutaneous application of AITC or CA. Repetitive application of AITC initially increased the firing rate of 52% of units followed by rapid desensitization that persisted when mustard oil was reapplied 30 min later. Responses to noxious thermal, but not mechanical, stimuli were significantly enhanced whether or not the neuron was directly activated by AITC. Windup elicited by percutaneous or sciatic nerve electrical stimulation was significantly reduced post- AITC. These results indicate that AITC produced central inhibition and peripheral sensitization of heat nociceptors. CA did not directly excite WDR neurons, and significantly enhanced responses to noxious heat while not affecting windup or responses to skin cooling or mechanical stimulation, indicating a peripheral sensitization of heat nociceptors.
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