The present study was designed to investigate the effect of different patterns and stimulation-duration of low frequency electroacupuncture(EA) treatment on the neuronal activities in the spinal cord and brainstem using Fos immunohistochemical technique. First, to analyze the effect of patterns of low frequency EA, the experimental animals were divided into three groups ; low frequency biphasic rectangular wave treated group, low frequency positive monophasic rectangular wave treated group and low frequency negative monophasic rectangular wave ixeated group. These different times of low frequency EA were applied to Zusanli point of experimental animals. The distribution and the number of Fos positive neurons were evaluated in the spinal cord and brainstem. The objective was to test the effect of stimulus-duration of low frequency EA on the fos expression in the spinal cord and brainstem. Three different stimulus-durations were used in this experiment ; 30minutes, 1 hour and 2 hours. The results were summerized as follows :
1. The number of Fos expression was significantly increased in the spinal cord dorsal and ventral horn depending upon the increase of stimulus-duration ; 30mins, 1h, 2h (P<0.05).
2. Low frequency EA biphasic stimulation significantly enhanced the Fos expression in the DR, LC, caudal portion of PAG D after 1 hour treatment. Low frequency EA biphasic stimulation after 2 hours treatment significantly increased the Fos expression in all parts of brainstem except RMg. There was no significant difference in 30 mins EA treated group.
3. The ratio of colocalization between serotonin containing neuron and Fos positive neuron in the brainstem was markedly increased in DR in biphasic and positive monophasic EA stimulation and in PAG LV Mid in all three different patterns. There was no significant difference in RMg
These results indicate that low frequency biphasic EA stimulation is the most effective method to increase the neuronal activities in the spinal cord and brainstem for inducing analgesic effect of EA. In addition, the ratio of colocalization of serotoninergic neuron and Fos positive neurons is effectively increased by treatment of low frequency biphasic EA, suggesting that the analgesic effect of low frequency EA depends on the serotoninergic pathway of endogenous pain control system. Furthermore, at least 1 hour EA treatment was necessary to increase the neuronal activities in the spinal cord and brainstem. Those basic data from this study can be applied to establish the effective treatment of EA For pain control in the clinical field.
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