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Although acupuncture has a long history of analgesic effects, the mechanisms underlying its effects are still unclear. Somatosensory evoked potential (SEP) methodology has been adopted in the research of acupuncture since the 1970s. In research on the effects of acupuncture on the conventional SEP, variable results have been observed, and two different opinions concerning the presence or absence of acupuncture effects on the conventional SEP are discussed. Since the conventional SEP is mediated mainly by fast conducting sensory nerve fibers, the conventional SEP methodology, especially that for recording short-latency SEP, may be inadequate for studying acupuncture mechanisms. In the case of the long-latency cortical SEP, there are too few data available to judge the effects of acupuncture analgesia (AA). Studies on the effects of AA on pain SEPs demonstrated that AA has a suppressive effect on amplitude of the pain SEP (and affecting the latency as well in some experiments) in both animals and humans, being accompanied by increased pain threshold. Thus, acupuncture seems to have analgesic effects that are probably related to activation of the antinociceptive system, and application of the pain SEP methodology to the study of mechanisms of AA may be promising.

There is currently accumulating evidence for bidirectional communication between the neuroendocrine and immune systems. Various cytokines have been suggested to be involved in the stimulation of stress hormone secretion during the times of infection and inflammation. To assess the possible involvement and pathophysiologic significance of cytokines in the mechanisms responsible for the perioperative stress response of the hypothalamo-pituitary-adrenal axis, we observed the changes of plasma adrenocorticotropic hormone and cortisol levels together with those of plasma endotoxin and cytokine levels. In patients undergoing pancreatoduodenectomy, perioperative stimulation of adrenocorticotropic hormone and cortisol secretion was accompanied by a significant elevation of plasma cytokine levels. Application of epidural block up to the upper thoracic levels failed to suppress this stress response effectively. In patients undergoing unilateral total hip replacement, the response of plasma hormone levels was smaller and briefer with no significant increase of plasma cytokine levels. Application of epidural block up to the lower thoracic levels suppressed this hormonal response almost completely. In patients undergoing pancreatoduodenectomy, a significant elevation of plasma endotoxin level was followed by a gradual but significant elevation of plasma tumor necrosis factor alpha and interleukin-6 levels. It seems likely that the stimulatory effects of these cytokines on the secretion of adrenocorticotropic hormone and cortisol might be involved in the development of the greater and more prolonged stress response of hypothalamo-pituitary-adrenal axis. Our present study suggests that not only neural input from the surgical wound but also stimulation of cytokine production were responsible for the development of the stress response of the hypothalamo-pituitary-adrenal axis during and after upper abdominal surgery.(ABSTRACT TRUNCATED AT 250 WORDS)