Transplant restoration of spinal cord inhibitory controls ameliorates neuropathic itch

The transmission of pruritoceptive (itch) messages involves specific neural circuits within the spinal cord that are distinct from those that transmit pain messages. These itch-specific circuits are tonically regulated by inhibitory interneurons in the dorsal horn. Consistent with these findings, it has previously been reported that loss of GABAergic interneurons in mice harboring a deletion of the transcription factor Bhlhb5 generates a severe, nonremitting condition of chronic itch. Here, we tested the hypothesis that the neuropathic itch in BHLHB5-deficient animals can be treated by restoring inhibitory controls through spinal cord transplantation and integration of precursors of cortical inhibitory interneurons derived from the embryonic medial ganglionic eminence. We specifically targeted the transplants to segments of the spinal cord innervated by areas of the body that were most severely affected. BHLHB5-deficient mice that received transplants demonstrated a substantial reduction of excessive scratching and dramatic resolution of skin lesions. In contrast, the scratching persisted and skin lesions worsened over time in sham-treated mice. Together, these results indicate that cell-mediated restoration of inhibitory controls has potential as a powerful, cell-based therapy for neuropathic itch that not only ameliorates symptoms of chronic itch, but also may modify disease.