title: Chemical stimulation of the lateral hypothalamus by carbachol attenuated the formalin-induced pain behaviors in rats.
abstract: Electrical and chemical stimulation of the lateral hypothalamus (LH) produces analgesia. Previous studies emphasized the importance of LH in the modulation of nociceptive behaviors in the acute pain models. In the current study, for the first time, we examined the effect of direct chemical stimulation of the LH with cholinergic receptor agonist, carbachol, on pain-related behaviors in the formalin test as a model of persistent inflammatory pain. Forty-eight adult male Wistar rats were implanted unilaterally with cannula into the LH. Four doses of carbachol (62.5, 125, 250 and 500 nM/0.5 μl saline) were microinjected into the LH just 5 min before the formalin test. Vehicle group received 0.5 μl saline into the LH. Pain-related behaviors were quantified and monitored in 5-min blocks for 60 min test period. Average nociceptive scores and area under the curve (AUC) as raw pain scores × time by the linear trapezoidal method were used for the statistical analyses. One important finding of our study was that carbachol blocks the nociceptive responses in both phases of formalin-induced nociception in a dose-dependent manner. Altogether, the percentage decrease of AUC values calculated for treatment groups, compared to the control group, was more significant in the late phase than the early phase. These findings suggest that LH modulates formalin-induced nociception through spinal and/or supraspinal sites.
authors.affiliation: Department of Basic Sciences, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran.
authors.forename: Somayeh
authors.initials: S
authors.lastname: Ezzatpanah
authors.affiliation: Department of Basic Sciences, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran.
authors.forename: Vahab
authors.initials: V
authors.lastname: Babapour
authors.affiliation: Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Bahman
authors.initials: B
authors.lastname: Sadeghi
authors.affiliation: Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Electronic address: Haghparast@yahoo.com.
authors.forename: Abbas
authors.initials: A
authors.lastname: Haghparast
mesh_terms: D000818:Animals; D019540:Area Under Curve; D002217:Carbachol / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D007031:Hypothalamus / Q000187:drug effects*; D008297:Male; D051381:Rats; D017208:Rats, Wistar
chemical_list: D002217:Carbachol
keywords: Carbachol; Formalin test; Lateral hypothalamus; Pain; Rat