Comparison of Responses of Primate Spinothalamic Tract Neurons to Pruritic and Algogenic Stimuli

• Published in: Journal of neurophysiology 2004-01, Vol.91 (1), p.213-222
• Main Authors: Simone, Donald A, Zhang, Xijing, Li, Jun, Zhang, Jun-Ming, Honda, Christopher N, LaMotte, Robert H, Giesler, Glenn J., Jr
• Format: Article
• Language: English
• Subjects: Action Potentials - drug effects; Action Potentials - physiology; Analysis of Variance; Animals; Capsaicin; Electrophysiology; Evoked Potentials; Histamine; Hot Temperature; Hyperalgesia - chemically induced; Hyperalgesia - etiology; Hyperalgesia - physiopathology; Injections, Intradermal - methods; Laminectomy - methods; Macaca fascicularis; Physical Stimulation - methods; Posterior Horn Cells - drug effects; Posterior Horn Cells - physiology; Pruritus - chemically induced; Pruritus - physiopathology; Reaction Time; Skin - drug effects; Skin - innervation; Spinothalamic Tracts - cytology; Spinothalamic Tracts - drug effects; Spinothalamic Tracts - physiology; Stimulation, Chemical; Thalamus - anatomy & histology; Thalamus - physiology; Time Factors
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.00527.2003

1 Department of Oral Sciences, University of Minnesota, Minneapolis, Minnesota 55455 2 Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota 55455 3 Department of Psychiatry, University of Minnesota, Minneapolis, Minnesota 55455 4 Department of Anesthesiology, Yale Medical School, New Haven, Connecticut 06510 Submitted 30 May 2003; accepted in final form 30 September 2003 We investigated the role of mechanosensitive spinothalamic tract (STT) neurons in mediating 1 ) the itch evoked by intradermal injection of histamine, 2 ) the enhanced sense of itch evoked by innocuous stroking (alloknesis), and 3 ) the enhanced pain evoked by punctate stimulation (hyperalgesia) of the skin surrounding the injection site. Responses to intradermal injections of histamine and capsaicin were compared in STT neurons recorded in either the superficial or the deep dorsal horn of the anesthetized monkey. Each neuron was identified by antidromic activation from the ventral posterior lateral nucleus of thalamus and classified by its initial responses to mechanical stimuli as wide dynamic range (WDR) or high-threshold (HT). Approximately half of the WDRs and one of the HTs responded weakly to histamine, some with a duration > 5 min, the maximal time allotted. WDRs but not HTs exhibited a significant increase in response to punctate stimulation after histamine consistent with their possible role in mediating histamine-induced hyperalgesia. Neither type of neuron exhibited significant changes in response to stroking, consistent with their unlikely role in mediating alloknesis. Furthermore, nearly all STT neurons exhibited vigorous and persistent responses to capsaicin, after which they became sensitized to stroking and to punctate stimulation. We conclude that the STT neurons in our sample are more likely to contribute to pain, allodynia, and hyperalgesia than to itch and alloknesis. Address for reprint requests and other correspondence: D. A. Simone, Department of Oral Sciences, University of Minnesota, 515 Delaware St. SE, 17–252 Moos, Minneapolis, MN 55455 (E-mail: simon003{at}umn.edu ).