[Distribution of serotonin-positive cells in local cutaneous tissues of different acupuncture points at hindlimbs in rats]

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.