Capsaicin-induced central sensitization in spinal cord injured humans assessed by nociceptive withdrawal reflex receptive fields

J.A. BIURRUN MANRESA; N.S. FINNERUP; I.L. JOHANNESEN; F. BIERING-SØRENSEN; T.S. JENSEN; L. ARENDT-NIELSEN; O.K. ANDERSEN

Barcelona

Conferencia; 8th FENS Forum of Neuroscience; 2012

Introduction and aimThe underlying mechanisms associated with central sensitization are commonly investigated using human surrogate models applied to healthy volunteers. However, these models have not been extensively studied in cases where a clinical condition that affects the central nervous system is already present. In particular, patients with complete spinal cord injury (SCI) already present signs of sensitization caudal to the spinal injury, so it is crucial to determine if the protective plastic mechanisms triggered after intense nociceptive activation are still functional, and to investigate if central sensitization models can still be established in the presence of adaptive/maladaptive changes in synaptic plasticity and complete lack of descending control. MethodsFifteen volunteers with complete spinal cord injury (SCI) and fourteen non-injured (NI) volunteers participated in a single experimental session, where the RRF was assessed before, 1 min after and 60 min after an intramuscular injection of capsaicin in the foot sole for induction of central sensitization. Repeated electrical stimulation was applied on eight sites on the foot sole in order to elicit the nociceptive withdrawal reflex (NWR). EMG responses from tibialis anterior muscle were recorded, and reflex receptive field (RRF) maps were derived using two-dimensional interpolation. ResultsBoth groups presented RRF expansion immediately after capsaicin injection (RRF areas were 28% larger in SCI volunteers and 48% larger in NI volunteers right after capsaicin injection, p = 0.007). Moreover, the RRF topography was significantly different in SCI volunteers compared to NI volunteers in terms of size and shape (RRF areas were in average 56% larger in SCI volunteers compared to NI volunteers, p = 0.007). ConclusionIt is possible to induce central sensitization in volunteers with complete spinal cord injury, despite adaptive/maladaptive changes in synaptic plasticity and lack of descending control. Moreover, central sensitization can significantly expand the RRF and this modulation is under strong influence of descending control.