<p style="text-align: center;">CHEN Lizhen, KAN Yu, WANG Yili, ZHANG Xiaoning, WANG Xiaoyu, HE Wei, JING Xianghong&nbsp;</p><p style="text-align: center;">（Institute of Acupuncture and Moxibustion, China Academy of Chinese Medical Sciences, Beijing 100700）</p><p style="text-align: justify;"><strong>Abstract</strong>:&nbsp; <strong>Objective</strong>:&nbsp; Transcutaneous&nbsp; electrical&nbsp; acupuncture&nbsp; stimulation&nbsp; (TEAS)&nbsp; has&nbsp; been gradually applied in clinic for its easy-operation, non-invasive and painless procedures.Increasing evidence&nbsp; has&nbsp; demonstrated&nbsp; that&nbsp; TEAS&nbsp; are&nbsp; effective&nbsp; in&nbsp; regulating&nbsp; some&nbsp; disorders&nbsp; instead&nbsp; of inserting needles.Previous studies have shown that local cutaneous nerve fibers and mast cells responded to manual acupuncture (MA).However, the reaction of TEAS remains unknown. The aim of this study was to investigate the local response of TEAS in Hegu (LI4) acupoint. <strong>Methods</strong>:TEAS was applied in left LI4 of rats, while the contralateral LI4 of the same rats was as a nonstimulated control. Immunohistochemistry analyses were carried out to observe the mast cells by tryptase antibody and nociceptive neuropeptides by calcitonin gene-related peptide (CGRP) or substance&nbsp; P&nbsp; (SP)&nbsp; in&nbsp; the&nbsp; LI4&nbsp; area.The&nbsp; co-expression&nbsp; between&nbsp; CGRP&nbsp; or&nbsp; SP&nbsp; and&nbsp; mast&nbsp; cells&nbsp; was observed as well. Mast cells were also labeled with serotonin (5-HT) primary antibodies to observe their&nbsp; co-expression.Furthermore,mast&nbsp; cells&nbsp; were&nbsp; stained&nbsp; by&nbsp; toluidine-blue&nbsp; for&nbsp; observing morphological&nbsp; changes&nbsp; and&nbsp; cell&nbsp; counting.&nbsp; <strong>Results</strong>:&nbsp; The&nbsp; results&nbsp; showed&nbsp; that&nbsp; CGRP&nbsp; and&nbsp; SP immune-reactive nerve fibers（CGRP-IR&nbsp; or&nbsp; SP-IR）of LI14 were expressed more highly after TEAS than that of the non-stimulated control. The CGRP-IR or SP-IR fibers distributed in intraepidermis and dermis and most of them concentrated in local dermis.There were a few intact mast cells labeled by tryptase located in dermis in the control while deformed and aggregated mast cells distributed near the CGRP-IR or SP-IR nerve fibers after TEAS.In addition, some of mast cells aggregated near the blood vessels with degranulation of 5-HT granules after TEAS.The number of mast&nbsp; cells&nbsp; and&nbsp; the&nbsp; degranulation&nbsp; rate&nbsp; significantly&nbsp; increased&nbsp; as&nbsp; well.&nbsp;<strong> Conclusion</strong>:&nbsp; The&nbsp; results indicated&nbsp; an&nbsp; “acupuncture-like”&nbsp; reaction&nbsp; that local higher expression of CGRP and SP-IR nerve fibers responded to TEAS at L14. In addition, mast cells aggregated near the nerve fibers and blood vessels with degranulation of 5-HT after TEAS.</p><p style="text-align: justify;"><strong>Key words</strong>: Acupuncture, LI14, Transcutaneous electrical acupoint stimulation, Calcitonin generelated peptide, Substance P, Mast cells, Serotonin</p><p><br/></p>