The effects of salmon calcitonin on the concentrations of periaqueductal gray monoamines in the formalin test

Abstract

Background: The receptors of salmon calcitonin, located in such areas of brain as periaqueductal gray matter (PAG), are responsible for pain modulation. Aims: In the current study, the effects of intracerebroventricular (ICV) injection of sCT on the behavioral response to pain and on the levels of monoamines in PAG are explored in a biphasic animal model of pain. Study Design: Animal experimentation study. Methods: 45 male rats in four groups were considered (n=6). sCT was infused into the lateral ventricle of the brain (1.5 nmol, with a volume of 5 μl). After twenty minutes, formalin 2.5% was injected (SC) into the right leg claw and pain behavior was recorded on a numerical basis. At the time of the formalin test, the PAG area was microdialized. High-performance liquid chromatography (HPLC) method was used to gauge the levels of monoamines and their metabolites. Results: ICV injections of sCT led to the reduction of pain in the formalin test (p<0.05). Dialysate concentrations of serotonin, dopamine, norepinephrine, HIAA, DOPAC, and HMPG increased in the PGA area in different phases of the formalin pain test (p<0.05). Conclusions: sCT reduced pain by increasing the concentrations of monoamines and the metabolites derived from them in the PAG area.