title: Temporomandibular joint-evoked responses by spinomedullary neurons and masseter muscle are enhanced after repeated psychophysical stress.
abstract: Psychological stress is a risk factor for the development of musculoskeletal pain of the head and neck; however, the basis for this relationship remains uncertain. This study tested the hypothesis that psychophysical stress alone was sufficient to alter the encoding properties of spinomedullary dorsal horn neurons and masseter muscle activity in male rats. Repeated forced swim conditioning increased markedly both the background firing rate and temporomandibular joint (TMJ)-evoked activity of neurons in deep dorsal horn, while neurons in superficial laminae were less affected. Stress also increased the responses to stimulation of facial skin overlying the TMJ of neurons in deep and superficial dorsal horn. TMJ-evoked masseter muscle activity was enhanced significantly in stressed rats, an effect that was reduced by prior blockade of the spinomedullary junction region. These data indicated that repeated psychophysical stress induced widespread effects on the properties of medullary dorsal horn neurons and masseter muscle activity. The effects of stress were seen preferentially on neurons in deep dorsal horn and included enhanced responses to chemosensory input from the TMJ and mechanical input from overlying facial skin. The stress-induced elevation in TMJ-evoked masseter muscle activity matched well with the changes seen in dorsal horn neurons. It is concluded that the spinomedullary junction region plays a critical role in the integration of psychophysical stress and sensory information relevant for nociception involving deep craniofacial tissues.
authors.affiliation: Department of Diagnostic and Biological Sciences, University of Minnesota School of Dentistry, 18-186 Moos Tower, 515 Delaware St. SE, Minneapolis, MN 55455, USA. okamo007@umn.edu
authors.forename: Keiichiro
authors.initials: K
authors.lastname: Okamoto
authors.forename: Akimasa
authors.initials: A
authors.lastname: Tashiro
authors.forename: Zheng
authors.initials: Z
authors.lastname: Chang
authors.forename: Randall
authors.initials: R
authors.lastname: Thompson
authors.forename: David A
authors.initials: DA
authors.lastname: Bereiter
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D004576:Electromyography; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology*; D008012:Lidocaine / Q000494:pharmacology; D008297:Male; D008406:Masseter Muscle / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology; D020671:Posterior Horn Cells / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013315:Stress, Psychological / Q000503:physiopathology*; D013550:Swimming; D013704:Temporomandibular Joint / Q000502:physiology*
chemical_list: D000255:Adenosine Triphosphate; D008012:Lidocaine