Microglial In Central Nucleus Of Amygdala Involved In Acetic Acid-elicited Anxiety-like Behavior

Objective : Accumulated data showed that patients and experimental animals with acute or chronic pathologic pain are likely to comorbid anxiety or depression,however,few attention has been taken to acute visceral pain in this area.Ethological methods in this experiment were used to examine whether acetic acid-elicited visceral pain mice were anxious,and then observed the influence of minocycline,and studied the expression of ionized calcium binding adapter molecule 1(IBA-1)in microglial and immediate-early gene protein product c-fos in neuro in different time point subjected to acetic acid in central nucleus of amygdala,exploring the possible mechanisms of acute visceral pain related anxiety.Method:this experiment was carried out on male Kunming mice when the weight arrived 22 g to 25 g The animal models of acute acetic acid visceral pain were established by intraperitoneal(i.p)injection of acetic acid(1.0%,10 ml/kg),and the same amount of normal saline was administered to another cohort of mice in the same method as normal saline group,and the degree of visceral pain sensation was assessed by the amount of abdominal constrictions in the first or second or twenty-fourth hour subjected to acetic acid,besides,the open file test and elevated plus maze test and light/dark box paradigm were utilized to evaluate the anxiety-like behavior in the second or twenty-fourth hour subjected to acetic acid.What’s more,mice were sacrificed for thedetermination of c-fos and IBA-1 in central nucleus of amygdala by immunohistochemistry in the second or twenty-fourth hour subjected to acetic acid.To examine the effect of minocycline,1 hour before the tests of anxiety-like behavior minocycline(40 ml/kg)was intraperitoneal(i.p)injected and then anxiety-like behavior was examined.Results:1.The development of visceral pain sensation in different time point subjected to acetic acid: intraperitoneal injection of acetic acid could lead to abdominal constriction frequently and immediately,but from the first to the second hour animals,abdominal constrictions decreased significantly,and mice in contrast group showed no abdominal constrictions in all time points,indicating that visceral pain relieved from the second hour.2.The result of anxiety-like behavior testing in different time point subjected to acetic acid: open file test showed that the time spent in the inner square and the number of crossing in the center significantly decreased in the second or twenty-fourth hour subjected to acetic acid,but the locomotive activity showed no statistically difference.Similarly,elevated plus maze tests showed that the percentage of time spent in open arms and number of open arm entrance significantly decreased in the second or twenty-fourth hour subjected to acetic acid.Light/dark box tests also showed that the time spent in light cubicle and number of entering to the light cubicles significantly decreased in the second or twenty-fourth hour subjected to acetic acid,indicating that acetic acid could induced anxiety-like behavior even when acute visceral pain relieved.3.The effect of minocycline pretreatment on anxiety-like behavior: minocycline intraperitoneal injection significantly alleviated animals’ decrease in the time spent in the inner square and the number of crossing in the center in open file test in the second and twenty-fourth hour subjected to acetic acid,and showed no effect on animals,locomotive activity.Similar to the results in the open file tests,minocycline pretreatment almost reversibly inhibited of animal’s decrease in percentage of time spent in open arms and percentage of open arm entrance number in the elevated plus maze test and the time spent in light cubicle and number of entering to the light cubicles in the light/dark box test.4.The result of c-fos expression in central nucleus of amygdala in different time point subjected to acetic acid: compared with normal saline group,the second and twenty-fourth hour after acute visceral pain showed significantly increased number of c-fos positive cell in central nucleus of amygdala respectively.5.The result of IBA-1 expression in central nucleus of amygdala in different time point subjected to acetic acid: compared with normal saline group,the second and twenty-fourth hour after acute visceral pain showed significantly increased number of IBA-1 positive cell in central nucleus of amygdala.Conclusion:acute visceral pain induced by acetic acid accompany with anxiety-like behavior.The activation of microglial and exaggeration of neuron in central nucleus of amygdala,probably play a key role in acute visceral pain associated anxiety.