Effect of high or low frequency electroacupuncture on the cellular activity of catecholaminergic neurons in the brain stem

Although the opioid system plays a pivotal role in the analgesic effect of electroacupuncture (EA), it has been suggested that other peptidergic syste ms also may be involved in the therapeutic effect of EA. Among several pept ides for EA-induced analgesia, catecholamine (CA) is associated with the de scending pain inhibitory system. We evaluated whether the different frequen cies of EA modified the cellular activity of central CA synthesizing neuron s using double labeling immunohistochemistry between Fos-like immunoreactiv e (FLI) neurons and dopamine-beta-hydroxylase (DBH)/tyrosine hydroxylase (T H)-positive neurons. We observed that different frequencies of EA increased the number of FLI neurons in catecholaminergic neurons, such as the dorsal raphe (DR), hypothalamic arcuate nucleus (Arc), locus coeruleus (LC), A5 n oradrenaline cells (A5), and A7 noradrenaline cells (A7). In addition, diff erent frequencies of EA significantly increased the ratio of colocalization between FLI neurons and TH positive neurons in DR, LC and Are. Only low fr equency EA increased the neuronal activity in Are. The ratio of double labe ling between FLI and DBH positive neurons was also elevated at both LC and AS. These data demonstrate that different frequencies of EA increase the ce llular activity of central CA synthesizing neurons, suggesting that the CA system plays an important role in EA-induced analgesia.