An abundance of studies from different international groups have demonstrated tracers
along linear pathways resembling meridians over the body surface of humans. All experiments of
the studies have been conducted by injection of a radiotracer solution or tracer dyes in a volume of
solution into acupuncture points (acupoints). The solution injected into acupoints produces much
stronger mechanical stimuli than acupuncture, which causes axon reflex. Anatomical studies have
demonstrated that acupoints/meridians exist higher number of small nerve fibers and blood vessels
with rich nitric oxide (NO) and neuropeptides in the cutaneous tissues as structures for the biomolecules
mediated axon reflexes. Recent advances have determined that NO and calcitonin generelated
peptides play crucial roles in the comprehension of the axon reflex. The stimuli-evoked axon
reflex and NOergic biomolecules/neuropeptides increase local blood flow with higher levels in
acupoints/meridians, which move radioactive substances or tracer dyes in the skin and subcutaneous
tissue under a linear path resembling acupoints and meridians, the important phenomena of
meridians induced by the stimuli. The evidence and understanding of the biomolecular processes
of the tracers along linear pathways resembling meridians have been summarized with an emphasis
on recent developments of NO and neuropeptides mediating stimuli-evoked axon reflexes to increase
local blood flow with higher levels in acupoints/meridians, which move radioactive substances
or tracer dyes in the skin and subcutaneous tissue contributing to tracers along linear pathways
resembling meridians in this mini-review.