title: [Descending modulation of cardiac nociception by the rostral ventromedial medulla in rats].
abstract: OBJECTIVE
  To observe the descending modulation of cardiac nociception by the rostral ventromedial medulla (RVM) in rats.
  
  
  METHODS
  A rat model of cardiosomatic motor reflex (CMR) was established by injecting capsaicin into the pericardial sac to induce cardiac nociception, and the electromyogram (EMG) response of the dorsal spinotrapezius muscle was studied. The RVM was electrically stimulated (25, 75 and 100 µA) or destroyed to examine whether RVM exerted descending modulation on cardiac nociception.
  
  
  RESULTS
  Electrical stimulation of the RVM at 8 sites produced intensity-dependent inhibition of EMG responses to noxious cardiac stimulus (F[2,21]=43.188, P=0.001). Electrical stimulation at 3 sites caused facilitated EMG responses, but the increased magnitude of the EMG was not dependent on stimulation intensity (F[2,6]=0.884, P=0.461). Stimulation at 11 sites produced biphasic effects: at a low intensity (25 µA), the elicited EMG magnitude was significantly larger than baseline (P<0.05), and at greater intensities (75/100 µA), the stimulation caused suppression of the EMG magnitude to a level significantly lower than the baseline (P<0.05). Electrolytic lesion of the RVM resulted in significantly increased EMG responses compared with the baseline and sham lesion group.
  
  
  CONCLUSIONS
  Cardiac nociception evoked by capsaicin stimulation is subjected to descending biphasic modulation by the RVM, which produces predominantly descending inhibition on heart pain.
authors.affiliation: Department of Basic Medical Sciences, Xi'an Medical University, Xi'an 710021, China.E-mail: suna1935@139.com.
authors.forename: Na
authors.initials: N
authors.lastname: Sun
authors.forename: Lingheng
authors.initials: L
authors.lastname: Kong
authors.forename: Ligang
authors.initials: L
authors.lastname: Niu
authors.forename: Juanxia
authors.initials: J
authors.lastname: Zhu
authors.forename: Yan
authors.initials: Y
authors.lastname: Xu
authors.forename: Jianqing
authors.initials: J
authors.lastname: Du
mesh_terms: D000818:Animals; D002211:Capsaicin / Q000494:pharmacology*; D004558:Electric Stimulation; D004576:Electromyography / Q000187:drug effects; D008297:Male; D008526:Medulla Oblongata / Q000502:physiology*; D059225:Nociception; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology; D010146:Pain / Q000503:physiopathology*; D010496:Pericardium / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018689:Sensory System Agents / Q000494:pharmacology
chemical_list: D018689:Sensory System Agents; D002211:Capsaicin