Differential responses of rostral subnucleus caudalis and upper cervical dorsal horn neurons to mechanical and chemical stimulation of the parotid gland in rats

Brain Res. 2006 Aug 23;1106(1):123-133. doi: 10.1016/j.brainres.2006.05.074. Epub 2006 Jul 18.

Abstract

Blockage of the salivary duct can produce pain and inflammation from the build up of saliva in the parotid gland. The processing of parotid inflammation-induced pain, however, is poorly understood. The purpose of this study was to clarify the functional involvement of the trigeminal subnucleus interpolaris/caudalis transition region (Vi/Vc) and upper cervical spinal cord (C1/C2) in processing nociceptive input relevant to parotitis. The effect of capsaicin-induced parotitis was examined on a total of 37 nociceptive neurons isolated from the Vi/Vc (n = 23) and C1/C2 (n = 14) regions. Eight of 23 Vi/Vc neurons responded to mechanical distention of the parotid gland, whereas no C1/C2 neurons responded to the parotid distention. Receptive field characteristics in all neurons were examined following capsaicin injections into the parotid gland. Mechanical and cold responses increased significantly in C1/C2 but not Vi/Vc neurons following capsaicin. Receptive field sizes also increased in C1/C2 but not Vi/Vc neurons. At the Vi/Vc transition region, pinch-evoked activity increased in neurons receiving convergent inputs from the parotid gland and facial skin when compared to non-convergent neurons. The present data indicate that the hyperalgesia and referred pain associated with parotitis may result from sensitization of C1/C2, but not Vi/Vc nociceptive neurons.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials / drug effects
  • Action Potentials / physiology
  • Afferent Pathways / drug effects
  • Afferent Pathways / physiology*
  • Animals
  • Capsaicin / pharmacology
  • Cervical Vertebrae
  • Cold Temperature / adverse effects
  • Hyperalgesia / chemically induced
  • Hyperalgesia / physiopathology
  • Inflammation Mediators / pharmacology
  • Male
  • Nociceptors / drug effects
  • Nociceptors / physiology*
  • Pain / chemically induced
  • Pain / physiopathology*
  • Pain Measurement / methods
  • Pain Threshold / drug effects
  • Pain Threshold / physiology
  • Parotid Gland / innervation*
  • Parotid Gland / physiopathology
  • Parotitis / chemically induced
  • Parotitis / physiopathology
  • Physical Stimulation
  • Posterior Horn Cells / drug effects
  • Posterior Horn Cells / physiology*
  • Rats
  • Rats, Sprague-Dawley
  • Skin / innervation
  • Skin / physiopathology
  • Trigeminal Caudal Nucleus / anatomy & histology
  • Trigeminal Caudal Nucleus / drug effects
  • Trigeminal Caudal Nucleus / physiology*

Substances

  • Inflammation Mediators
  • Capsaicin