Objective To investigate the distribution of substance P(SP)-positive nerve fibers in local skin tissues of the five shu-points of the Pericardium Meridian in rats for revealing the differential innervations of the five acupoints.MethodsSix adult male SD rats were used in the present study.Under deep anesthesia

the rats received transcardiac perfusion with 4%polyformaldehyde+phosphate buffered solution

followed by dissecting the local skin tissues from the sites corresponding to five shu-points"Zhongchong"(PC 9)

"Laogong"(PC 8)

"Daling"(PC 7)

"Jianshi"(PC 5)

and "Quze"(PC 3)in the human body.The tissues were sagittally cut into sections(20μm)using a freezing microtome

followed by fluorescent immunohistochemical and histochemical staining with SP

phalloidin and DAPI

respectively.The distribution of SP-positive fibers were observed under fluorescent microscope and laser confocal microscope.Results In general

SP expressed on the thin sensory fibers in the skin tissue.SP-positive nerve fibers distributed in a free single style in the epidermis and dermis

and gathered together to form a bundle in the subcutaneous layer.After counting the number and length of free single fibers in the epidermis and dermis of each of the five shu-points

we found that no significant differences existed in the density between the PC 9and PC 8regions

as well as among the PC 7

PC 5

and PC 3regions(P>0.05).In contrast

the density of SP-positive nerve fibers in the former two acupoints(PC 9and PC 8)was significantly higher than that of anyone of the latter three acupoints(P<0.01).In addition

SP positive nerve fibers mainly ran in parallel to the vessel-like structure.Conclusion The local skin tissues of acupoint PC 9

PC 8

PC 7

PC 5

and PC 3of the Pericardium Meridian express SP-positive fibers

which presents a decreasing tendency in the density from the distal to the proximal part of the forelimb

reflecting a relative specificity of the innervations of the five shu-points.