Temporal profile of spinal neuropeptides expression and neuropathic behaviour after spinal cord injury and progesterone administration

M.F. CORONEL; F. LABOMBARDA; M.J. VILLAR; P.R. BRUMOVSKY; S.L. GONZALEZ

Congreso; XV World Congress on Pain; 2014

International Association for the Study of Pain (IASP)

Aim of Investigation: Spinal cord injury (SCI) results in the development of chronic pain that severely compromises the quality of life in nearly 70% of patients. We have previously reported that progesterone (PG), a neuroprotective steroid, may offer a promising perspective in pain modulation. Using a model of central pain, we have shown that PG administration prevents the injury-induced proinflammatory cascade and the activation of the transcription factor NF-kB, key players in nociceptive processing at the spinal level. NF-kB-dependent proinflammatoy mediators can modulate neuropeptide expression, including galanin (Gal), strongly involved in the modulation of neuropathic pain. However, the expression of neuropeptide systems during pain development after SCI remains less explored. Thus, in the present study we have evaluated the temporal profile of mRNA expression for Gal, Gal receptors 1 and 2 (GalR1 and GalR2), neuropeptide Y (NPY) and NPY receptor 1 (Y1) in the injured dorsal spinal cord and the impact of steroid administration on neuropathic behavior and neuropeptide systems after SCI. Methods: Sprague-Dawley male rats subjected to spinal hemisection at T13 level received daily subcutaneous injections of PG (Hx+PG; 16 mg/kg) or vehicle (Hx) until tissue extraction. Uninjured rats were used as control animals (CTL). Mechanical and thermal cold allodynia of the hindpaws were assessed with the von Frey and Choi tests, respectively. Real-time PCR was used to determine the relative mRNA levels (expressed as fold-increase relative to CTL levels) of Gal, NPY and their receptors in the dorsal spinal cord using cyclophilin as housekeeping gene. Results: One day after SCI, a significant increase in Y1 mRNA levels was observed in the spinal cord as compared to CTL (Hx: 1.778±0.108, p menor 0.05 vs. CTL). At this time point, no changes were detected in Gal, GalR1 and NPY mRNA levels. However, a significant down-regulation in GalR2 was observed (Hx: 0.752±0.045, p menor 0.05 vs CTL). Interestingly, treatment with PG prevented the upregulation of the Y1 mRNA and even downregulated GalR1 mRNA after Hx (GalR1:0.829±0.093; Y1:1.036±0.138; p mayor 0.05 vs CTL, p menor 0.05 vs Hx in both cases). Twenty-eight days after injury, Hx rats showed well-established mechanical and cold allodynia, a significant increase in Gal (1.857±0.223), GalR1 (1.619±1.255), NPY (1.581±0.159) and Y1 (1.792±0.213) mRNAs (p menor 0.05 vs CTL in all cases) and down-regulation of GalR2 (0.634±0.055; p menor 0.05 vs CTL). At this time point, PG prevented the injury-induced increase in the mRNA levels for both neuropeptides and receptors, resulting in similar values as compared to the CTL group (Gal:1.352±0.098; GalR1:0.873±0.074; NPY:1.027±0.094 and Y1:0.865±0.036, p mayor 0.05 vs CTL, p menor 0.05 vs Hx in all cases). In line with previously published observations, Hx+PG animals did not develop mechanical allodynia and showed reduced sensitivity to cold stimulation. Conclusions: Spinal cord injury leads to considerable changes in the expression of Gal, NPY and their associated receptors. Our results suggest that by modulating inflammatory responses after injury, PG prevents the triggering of spinal neuropeptide-associated protective mechanisms against painful states. Thus, PG emerges as an attractive strategy to impede the development of central chronic pain.