Objective To investigate the expression of serotonin(5-HT)in local tissue of different acupoint regions at the hind limbs of rats.Methods A total of 6 male SD rats were used in the present study. The local tissues of"Neiting"(ST44)

"Zusanli"(ST36)and"Futu"(ST32)at the hindlimbs were dissected after transcardiac perfusion with fixative solution containing 4% paraformaldehyde

phosphate buffer

etc.

fixed again in 4% paraformaldehyde and cut into sections(at 20 μm thick). Then

the tissue sections were subjective into immunofluorescence stain for displaying 5-HT positive cells and calcitonin gene-related peptide(CGRP)-positive fibers

vessel-like structure(labelled with phalloidin)and cellular nucleus(labelled with DAPI)

separately. After that

the tissue samples were observed and recorded using a laser confocal microscope.Results The 5-HT labeled cells presented flat or round form in the local tissues of the 3 acupoint regions. These cells were mainly located in the dermis and subcutaneous tissue

and concentrated around the vessel-like structure and CGRP-positive nerve fibers. The number of cutaneous 5-HT positive cells was most in ST44(156. 6±12. 1)

and fewer in ST36(83. 5±18. 2)and ST32(53. 3±5. 2)in turn.Conclusion 5-HT-positive cell is an important member in local tissue of acupoints(ST44

ST36 and ST32)

and varies in number according to their locations

suggesting an involvement of different densities of 5-HT-positive cells in different levels of regulatory effects of acupuncture stimulation of these acupoints.