Age, strain and anesthetic dependent differences in the nociceptive responses produced by i.v. 5-HT in the rat.
The intravenous (i.v.) administration of serotonin (5-HT) to rats is a noxious visceral stimulus which produces distinct vagal afferent-mediated pseudaffective responses, a passive avoidance behavior, a vagal afferent-mediated inhibition of the tail-flick (TF) reflex and a complex cardiovascular response. In the present study, we examined the effects of age (10 or 16 weeks), strain (Sprague-Dawley, SD; Wistar-Kyoto, WKY; spontaneously hypertensive rats, SHR) and anesthetic (conscious or lightly pentobarbital-anesthetized) on nociceptive (TF reflex and pseudaffective responses) and cardiovascular responses produced by 5-HT (3-288 micrograms/kg, i.v.). There were no age-related differences in baseline TF latencies in the 3 strains. Further, latencies were generally not significantly different whether rats were tested conscious or lightly anesthetized. There were, however, strain differences. Both conscious or lightly pentobarbital-anesthetized SHR and WKY rats at 10 weeks of age had significantly faster response latencies than 10 week old SD rats. At 16 weeks of age, only the lightly pentobarbital-anesthetized WKY and SHR showed faster response latencies than SD rats. The WKY and SHR, but not the SD rats, were more sensitive to the nociceptive effect of i.v. 5-HT at 16 weeks of age compared to 10 weeks of age. At both ages, WKY and SHR, but not SD rats, showed an anesthetic-dependent increase in nociceptive sensitivity to i.v. 5-HT. In addition, at both ages, regardless of the presence of anesthetic, the order of sensitivity to the nociceptive effects of i.v. 5-HT was SD greater than WKY much much greater than SHR.(ABSTRACT TRUNCATED AT 250 WORDS)
Meller
S T
ST
Department of Pharmacology, College of Medicine, University of Iowa, Iowa City 52242.
Lewis
S J
SJ
Brody
M J
MJ
Gebhart
G F
GF
D000375:Aging / Q000502:physiology*; D000758:Anesthesia; D000818:Animals; D005260:Female; D006439:Hemodynamics / Q000187:drug effects; D007275:Injections, Intravenous; D008297:Male; D009619:Nociceptors / Q000187:drug effects*; D010147:Pain Measurement / Q000187:drug effects; D051381:Rats; D011918:Rats, Inbred SHR; D011919:Rats, Inbred Strains; D011921:Rats, Inbred WKY; D012701:Serotonin / Q000494:pharmacology*; D013045:Species Specificity
D012701:Serotonin