Proceedings of The Physiological Society

Physiology 2016 (Dublin, Ireland) (2016) Proc Physiol Soc 37, PCA272

Poster Communications

Activation of spinal dorsal horn inhibitory networks by the C low-threshold Mechano Receptors derived chemokine tafa4

C. Kambrun1,2, O. Roca-Lapirot1,2, C. Salio3, M. Landry1,2, A. Moqrich4, Y. Le Feuvre1,2

1. University Bordeaux, Interdisciplinary Institute for Neuroscience, UMR 5297, Bordeaux, France. 2. CNRS, Interdisciplinary Institute for Neuroscience, UMR 5297, Bordeaux, France. 3. Department of Veterinary Sciences, University of Turin, Grugliasco, Italy. 4. Aix-Marseille-Université, CNRS, Institut de Biologie du Développement de Marseille, UMR 7288, Marseille, France.

Pain elaboration results from the integration within dorsal spinal cord networks of sensory and nociceptive information conveyed by primary afferents. Among these, C low-threshold Mechano Receptors (CLTMRs), expressing the chemokine TAFA4, were recently identified as modulators of pain. Although TAFA4 was previously demonstrated to modulate pain transmission, the functional repercussions of this regulation on sensory-nociceptive integration remains poorly understood. We investigated the effects of TAFA4 on synaptic transmission in Rexed lamina IIi in dorsal horn. Using in vitro patch clamp recording on acute spinal cord slices (mice 3-4 weeks), we demonstrate that in WT mice, application of TAFA4 (20nM) induces a reversible decrease in frequency of spontaneous excitatory post synaptic currents (EPSC) (means ± S.E.M, paired T-test n=12 control 10.2 ±0.9 vs.TAFA4 treatment 4.8±0.3 p<0.05). This decrease in excitatory activity is mirrored by an increase in frequency of spontaneous inhibitory synaptic events (IPSC) (n=7 control 1.2±0.2 vs. TAFA4 treatment 2.7±0.7 p<0.05), indicating a shift of the inhibition/excitation balance toward increased inhibition. This modulation of synaptic activity was preserved with tetrodotoxine (1μM) (mEPSC n=14 control 3.5±0.9 vs.TAFA4 treatment 2.5±0.6 p<0.05 mIPSC n=8 control 0.86±0.14 vs. TAFA4 treatment 2.3±0.4 p<0.05), indicating that TAFA4 alters synaptic transmission through presynaptic mechanisms. Moreover, by blocking inhibitory activity we demonstrate that the decrease of EPSC frequency is a consequence of the increase of IPSC frequency (n=9 control 19.4 ±6.3 vs. TAFA4 treatment 18.7±2.3 p<0.05), showing that TAFA4 releasing fibers mainly interact with inhibitory neurons. Using Electron Microscopy, we demonstrate the presence of direct synaptic contacts between CLTMR and GABAergic terminals within lamina IIi. In inflammatory condition (sub cutaneous injection of Complete Freund Adjuvant 1mg/ml in the right rear paw) there is a great tendency to relief of the CFA induced mechanic hypersensitivity by TAFA4. We also prove that the effect of TAFA4 on EPSC is preserved (T-test, control n=19 5.8 ±2.2 vs. TAFA4 treatment n=25 2.0±0.4 p<0.05). To go further in the study of modulation of sensory inputs integration within the spinal cord by TAFA4, we recorded the neuronal discharge of neurons responding to a mechanical stimulus. Using in vivo electrophysiology, we found a decrease of the neuronal discharge after a local injection of TAFA4 (200μg/ml) within the spinal cord indicating a decrease of nociceptive inputs transmission (ANOVA, N =5 ACSF 135.4±11.5 vs. TAFA4 treatment 62.7±11.2 p<0.05). We propose that CLTMR directly contact inhibitory interneurons in dorsal horn, and, through the liberation of TAFA4, reinforce inhibitory synaptic activity which may in turn promote their anti-nociceptive activity.

Where applicable, experiments conform with Society ethical requirements