The effect of genotype on sensitivity to electroacupuncture analgesia

Individual differences in sensitivity to pain and analgesia are well apprec iated, and increasing evidence has pointed towards a role of inherited gene tic factors in explaining some proportion of such variability. It has long been known by practitioners of acupuncture, an ancient modality of analgesi a, that some patients are 'responders' and others 'non-responders.' The pre sent research was aimed at defining the inherited genetic influence on acup uncture analgesia in the mouse, using 10 common inbred strains. Two pairs o f metallic needles were inserted into acupoints ST 36 and SP 6, fixed in si tu and then connected to the output channel of an electric pulse generator. Electroacupuncture (EA) parameters were set as constant current output (in tensity: 1.0-1.5-2.0 mA, 10 min each; frequency. 2 or 100 Hz) with alterati on of a positive and negative square wave, 0.3 ms in pulse width. Tail-flic k latencies evoked by radiant heat were measured before, during and after E A stimulation. Narrow-sense heritability estimates of 2 and 100 Hz EA were 0.37 and 0.16, respectively. We found that the C57BL/10 strain was the most sensitive, and the SM strain was the least sensitive to both 2 and 100 Hz EA. However, the relative sensitivities of other strains to these two EA fr equencies suggested some genetic dissociation between them as well. These r esults demonstrate a role of inherited genetic factors in EA sensitivity il l the mouse, although the low-to-moderate heritability estimates suggest th at environmental factors may be of greater importance in predicting who wil l benefit from this analgesic modality. (C) 2001 International Association for the Study of Pain. Published by Elsevier Science B.V. All rights reserv ed.