Characteristics of the New Mast Cell-Rich Nodal Structure in the Rat Skin Surface

: Acupuncture, practiced for millennia, lacks a clear anatomical definition for acupoints. A prevailing theory suggests that acupoints overlap with skin areas with higher mast cell density. Skin spots stained with intravenously infused Evans blue (EB), indicative of neurogenic inflammation, have recently been posited as acupoints in rats.

: To demonstrate the concordance between EB-reactive skin spots and mast cell-enriched acupoints.

: We employed staining and RNA-seq analysis to delineate the morphological characteristics and gene expression profiles of EB-reactive skin spots in rats.

: EB infusion revealed a novel nodal structure on the rat skin surface, visible to the naked eye, with dimensions of approximately 1 mm in both diameter and height. Around 30 such nodes were identified on one side of the abdominal area, spaced roughly 3 mm apart, excluding the linea alba. RNA-seq analysis indicated that the gene expression patterns within these nodes markedly differed from both non-nodal skin areas and lymph nodes. Histological examination using toluidine blue revealed a significantly greater mast cell count in the nodes than in non-nodal skin regions. Additionally, the nodes stained positively with Alcian blue and Hemacolor, reagents known to mark primo vascular tissues.

: Our findings suggest that EB-reactive nodes are indeed rich in mast cells. Further research is warranted to establish these skin nodes as surface primo nodes.