The pain-relieving effect of acupuncture is known to involve primary afferent nerves (PANs) via their roles in signal transmission to the CNS.Using single-unit recording in rats,we characterized the generation and transmission of electrical signals in Aβ and Aδ fibers induced by acupuncture-like stimuli.Acupuncture-like signals were elicited in PANs using three techniques:manual acupuncture (MAc),emulated acupuncture (EAc),and electro-acupuncture (EA)-like peripheral electrical stimulation (PES).The discharges evoked by MAc and EAc were mostly in a burst pattern with average intra-burst and inter-burst firing rates of 90 Hz and 2 Hz,respectively.The frequency of discharges in PANs was correlated with the frequency of PES.The highest discharge frequency was 246 Hz in Aβ fibers and 180 Hz in Aδ fibers.Therefore,EA in a dense-disperse mode (at alternating frequency between 2 Hz and 15 Hz or between 2 Hz and 100 Hz) best mimics MAc.Frequencies of EA output ＞250 Hz appear to be obsolete for pain relief.