Temporal changes in the expression of the translocator protein TSPO and the steroidogenic enzyme 5α-reductase in the dorsal spinal cord of animals with neuropathic pain: Effects of progesterone administration

Neuropathic pain is a frequent complication of spinal cord injury (SCI), still refractory to conventional treatment. The presence and biological activity of steroidogenic regulatory proteins and enzymes in the spinal cord suggests that neurosteroids locally generated could modulate pain messages. In this study we explored temporal changes in the spinal expression of the 18 kDa translocator protein TSPO, the steroidogenic acute regulatory protein (StAr) and the steroidogenic enzyme 5 alpha-reductase (5 alpha-RI/II) in an experimental model of central chronic pain. Male Sprague-Dawley rats were subjected to a SCI and sacrificed at different time points (1,14 or 28 days). The development of mechanical and cold allodynia was assessed. Injured animals showed an early increase in the mRNA levels of TSPO and 5 alpha-RII, whereas in the chronic phase a significant decrease in the expression of 5 alpha-RI and 5 alpha-RII was observed, coinciding with the presence of allodynic behaviors. Furthermore, since we have shown that progesterone (PG) administration may offer a promising perspective in pain modulation, we also-evaluated the expression of steroidogenic proteins and enzymes in injured animals receiving daily injections of the steroid. PG-treated did not develop allodynia and showed a marked increase in the mRNA levels of TSPO, StAR, 5 alpha-RI and 5 alpha-RII 28 days after injury. Our results suggest that in the acute phase after SCI, the increased