Human model of central sensitization using high-frequency conditioning electrical stimulation: Psychophysical and electrophysiological assessment using reflex receptive fields

J.A. BIURRUN MANRESA; R.W. HORUP; R.K. NIELSEN; D. SIMONSEN; L. SØRENSEN; D. HE; O.K. ANDERSEN

Washington D.C.

Conferencia; Neuroscience 2011; 2011

Introduction: Central sensitization (CS) denotes an increased responsiveness of nociceptive neurons in the central nervous system to their normal or subthreshold afferent input. CS can be experimentally induced by conditioning electrical stimulation (CES). Quantification of CS can be performed by subjective psychophysical parameters and objective electrophysiological measures, such as the nociceptive withdrawal reflex (NWR). Reflex receptive fields (RRF), derived from NWR, provide essential information about the state of the nociceptive system and are expected to enlarge after CES due to expansion of neuronal receptive fields. The aim of this study was to establish a human model of CS applying high-frequency CES and assess it using psychophysical and electrophysiological descriptors.Materials and methods: Nine subjects participated in two sessions: control and conditioning. In the conditioning session, high-frequency CES was applied using a special electrode located in the center of the sole of the foot. CES consisted of 5 trains of 100 pulses (2 ms pulse width) delivered at 100 Hz and repeated at 10 s intervals, with an intensity of 5 times detection threshold for a single-pulse stimulus. Eight stimulation electrodes were mounted on the foot sole to evoke NWR. Each NWR stimulation consisted of a train of 5 pulses (1 ms pulse width) delivered at 200 Hz. Each train was repeated 5 times at 3 Hz to elicit temporal summation. Electromyographic responses were recorded from tibialis anterior muscle, and RRF sensitivity and probability maps were derived. Primary and secondary hyperalgesia were assessed on the conditioned and non-conditioned foot using single-pulse electrical stimuli and calibrated punctuate probes. Pain ratings were quantified using a Visual Analogue Scale. All measurements were assessed 6 times in each session (2 pre-conditioning and 4 post-conditioning tests). Two- or three-way ANOVA (Session, Time, Stimulation number) were used to analyze the data.Results: High-frequency CES evoked a significant increase in pain ratings to single-pulse electrical stimuli on both conditioned (P