The present study was designed to investigate the effect of different patterns 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 treated group. These different patterns of low frequency EA were applied to Zusanli point of experimental animals for Lwo hours. The distribution and the number of Fos positive neurons were evaluated in the spinal cord and brainstem. The second objective was to test the effect of stimulus-duration of low frequency EA on the fos expression in the spinal cord and brainstem. The results were summerized as follows :
1. The patterns of low frequency EA increased the number of Fos immunoreactive neurons in the spinal cord dorsal and ventral horn compared to that of anesthetic control group (P<0.05). Among the different patterns of EA treatment, biphasic rectangular wave EA treatment showed dramatic increase in the number of Fos positive neurons of the spinal cord dorsal horn (P<0.05).
2. In the low frequency biphasic and monophasic EA treated groups, the increased neuronal activities were observed in all parts of brainstem except RMg(P<0.05). The biphasic EA stimulation is more effective to the Fos expression than the positive and the negative
monophasic EA stimulation.
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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