The role and mechanism of Apelin in modulation of pain in rat caudate

Abstract

Objective To study the effect and possible mechanism of Apelin in candate on the pain behavior of rat. Methods Tail flick latency(TFL)of rat was taken as pain threshold and radiant heat as nociceptive stimulus. Microinjected Apelin into rat's caudate to observe the effect of Apelin on modulating of pain in CNS and then to study the interaction between Apelin and morphine in modulation of pain.And the contents of cAMP and cGMP in candate tissue and blood plasma were detected.Results Compared with control groups,the pain threshold of rat decreased when Apelin Was injected into caudate alone.Injected 0.5μl Apelin of 10~(-4) moL/L into rat caudate 10 min later,the pain threshold of rat Was reduced(-9.22±1.26)%and 40 min later(-16.95±1.46)%compared with normal saline group(-0.32±1.2)%,(0.17±0.80)%),and it had statistical significance(P<0.01).The contents of cAMP in caudate Was(14.08±2.25)nmol/g and blood plasma(19.94± 4.43)nmol/L compared with normal saline(133.05±20.41)nmol/g,(38.66±6.73)nmol/L,and they had statistical significance(P<0.01).Conclusions Apelin can facilitate the pain behavior of rat induced by radiant heat stimulus and consequently plays a hyperalgesia role in CNS.Apelin may have interaction with morphine and display its hyperalgesia effect through the intracellular second messenger cAMP. Key words: Apelin; Caudate; Hyperalgesia; cAMP