Expression of Corticotropin Releasing Factor in Amygdala by Visceral Pain Induced by Colorectal Distension in Rats

초록

Objective: Commonly used stressful stimuli for animal study were restraint, immobilization, forced swimming, maternal separation, electric shock, single prolonged stress and predator exposure. Among them, electric shock, single prolonged stress and predator exposure are especially used for post-traumatic stress disorder. Previous animal studies observed increases of CRF in amygdala by various stresses. This study tried to observe changes of CRF in amygdala by pain due to colorectal distension(CRD) and to test if visceral pain increases CRF expression in amygdala as previous studies. Methods: Nine week-old male Sprague-Dawley white rats were used as experimental subjects to induce visceral pain by ballooning with 80mmHg for 5 minutes. Such procedure was repeated 3 times with 1 minute resting between each ballooning without anesthetizing the rats. Visceral pains were induced for 1 day for the first experimental group and 5 days for the second experimental group. For the control group only tube was inserted without ballooning. In order to compare the CRF immune responses, serial sections of amygdala were photographed by fluorescence microscope and an image analysis program was used to measure the surface area(㎛2) of CRF immune response. Results: CRF expression of amygdala increased both in control group and experimental groups and more CRF was expressed in experimental groups than control group. Variation of CRF expression between individual subjects in same group was larger in experimental groups than control group and the experimental group with 5 days of stimulus showed larger variation between individual subjects than other groups. Conclusions: Difference from previous studies which reported hormones in HPA axis were suppressed under same repeated stimulus to experimental animals, this study showed the increase of CRF expression in amygdala. This increase of CRF expression was higher in 5 day experimental group than 1 day experimental group. Such difference was probably caused by length of stimulus, genetic factor, conditions of stress, or histological changes due to CRD. In conclusion, visceral pain by CRD increased CRF expression in amygdala. In addition, the finding of continuous increase in CRF expression for 5 days indicates that 5 days of pain acts as subacute stressor.