Vagal modulation of bradykinin-induced mechanical hyperalgesia in the female rat.
In male rats, activity in subdiaphragmatic vagal afferents modulates nociception via an adrenal medulla-dependent mechanism. Because both the vagus and adrenal medullae are sexually dimorphic, we evaluated vagotomy-induced changes in mechanical nociceptive threshold and inflammatory hyperalgesia in female rats and compared them to those previously reported in male rats. We have found that (1) mechanical nociceptive threshold is lower in female rats than in male rats, perhaps because of tonic release of adrenal medullary factors in female rats; (2) mechanical nociceptive threshold in female rats is influenced to a lesser degree by activity in the subdiaphragmatic vagus; (3) vagotomy-induced enhancement of bradykinin hyperalgesia is greater in female rats; (4) in female rats, in contrast to male rats, celiac plus celiac accessory branch vagotomy failed to fully account for the enhancement of bradykinin hyperalgesia in complete subdiaphragmatic vagotomy; and (5) in female rats, in contrast to male rats, adrenal medullectomy plus subdiaphragmatic vagotomy only partially (approximately 30%) reversed the effect of vagotomy on bradykinin hyperalgesia. These findings demonstrate sexual dimorphism in the modulation of both mechanical nociceptive threshold and bradykinin-induced hyperalgesia by activity in subdiaphragmatic vagal afferents as well as the adrenal medulla.
Khasar
Sachia G
SG
Department of Oral and Maxillofacial Surgery and UCSF/NIH Pain Center, University of California, San Francisco, California 94143, USA.
Miao
Frederick J-P
FJ
Gear
Robert W
RW
Green
Paul G
PG
Levine
Jon D
JD
D000313:Adrenal Medulla / Q000502:physiology; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D001920:Bradykinin; D004305:Dose-Response Relationship, Drug; D005260:Female; D006930:Hyperalgesia / Q000139:chemically induced* / Q000503:physiopathology*; D009619:Nociceptors / Q000187:drug effects; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology; D010812:Physical Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012018:Reflex / Q000187:drug effects; D014628:Vagotomy; D014630:Vagus Nerve / Q000503:physiopathology*
D001920:Bradykinin