High-frequency conditioning electrical stimulation of glabrous skin failed to induce heterotopic long-term potentiation (LTP)

M. B. JENSEN; J. A. BIURRUN MANRESA; O. K. ANDERSEN

Vienna

Congreso; 9th Congress of the European Pain Federation EFIC; 2015

European Pain Federation EFIC

Background and aims: High-frequency electrical stimulation (HFS) can induce perceptual correlates of long-term potentiation (LTP) of nociceptive synaptic transmission causing hyperalgesia at both homo- and heterotopic zones of hairy skin [1]. This study investigated if similar effects can be induced in thick glabrous skin underneath the foot sole. Methods: HFS was applied through a circular pin electrode placed at the metatarsal region in 21 healthy subjects (large anode on the foot dorsum). HFS consisted of 5 trains of 50 constant current pulses (2 ms, 100 Hz) felt as 5 individual 1 s stimuli with 9 s interstimulus intervals. Stimulation intensity was 10 times the detection threshold [1]. Somatosensory perception was tested by pinprick stimuli using a Von Frey hair (4 sites around the conditioning electrode) and electrical stimuli (stimulation intensity of 1.3´pain threshold through the conditioning electrode), delivered immediately before and 5 minutes after HFS. In addition, nociceptive withdrawal reflex thresholds were estimated to electrical stimulation of the sural nerve and through the conditioning electrode before and after HFS. Two sessions were performed 48 h apart (conditioning and control) in randomized order. Two-way repeated measures ANOVA was used for statistical analysis (factors: time and session).Results: Pain sensitivity to electrical stimulation was significantly higher after HFS (p=0.01). No significant results were identified for the remaining tests.Conclusions: Results indicate that HFS induced homotopic hyperalgesia in the glabrous skin. However, lack of significant heterotopic effects challenge the role of heterosynaptic facilitation inLTP