Effects of temperature and volume on intraperitoneal saline-induced changes in blood pressure, nociception, and neural activity in the rostroventral medulla.
ON and OFF cells of the rostral ventromedial medulla are hypothesized to modulate nociception with ON cells facilitating pain and OFF cells inhibiting pain. The current study analyzed the effects of intraperitoneal saline at different volumes and temperatures on nociception (tail flick reflex), blood pressure, and the activity of ON and OFF cells in lightly anesthetized rats. At large volumes (20 cc/kg), room temperature saline excited 7/11 ON cells and inhibited 10/12 OFF cells for 2-5 min. In contrast, large volumes (20 cc/kg) of body temperature saline (37 degrees C) excited only 1/10 ON cells and inhibited only 3/13 OFF cells, and small volumes (1-2 cc/kg) of room temperature saline excited only 3/10 ON cells and inhibited only 4/11 OFF cells. Tail flick latency increased following saline administration at large volumes with a significant effect of time, but not temperature. The excitation of ON cells and inhibition of OFF cells indicate that cold intraperitoneal saline could be painful and the increase in tail flick latency may indicate a diffuse noxious inhibitory control. It is also possible that the changes in ON and OFF cell activity caused a hyperalgesia that was masked by a simultaneous hypoalgesia that was mediated independent of the ON and OFF cells. Because intraperitoneal saline may produce pain or hyperalgesia, care should be used when saline is used experimentally or clinically.
Thurston-Stanfield
Cindy L
CL
Department of Biomedical Sciences, University of South Alabama, UCOM 6000, Mobile, AL 36688, USA. cthursto@usouthal.edu
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000344:Afferent Pathways / Q000187:drug effects* / Q000502:physiology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects* / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D009619:Nociceptors / Q000187:drug effects* / Q000502:physiology; D010146:Pain / Q000139:chemically induced* / Q000503:physiopathology; D010537:Peritoneum / Q000187:drug effects* / Q000294:innervation / Q000502:physiology; D011903:Raphe Nuclei / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D012965:Sodium Chloride / Q000494:pharmacology*; D013696:Temperature
D012965:Sodium Chloride