Expression changes of the neuregulin 1 isoforms in neuropathic pain model rats

The neuregulin1 (Nrg1) gene that is expressed in the dorsal root ganglion (DRG) contains an EGF-like domain, which is known to be a direct ligand for ErbB3 and ErbB4. Multiple splice variants of the Nrg1 gene are broadly classified into 3 groups by structural features (type I, type II and type III) and their functions differ in various tissues. The Nrg1 gene has emerged as a key mediator of axon-Schwann cell interactions and as a regulator of Schwann cell development. The Nrg1 gene is indicated as a promising growth factor for neuronal development. However, the function of the Nrg1 in pain has not been clarified. We therefore, examined the expression profiles of each type of the Nrg1 transcript in the bilateral L4/L5 DRGs using L5 spinal nerve ligation (SNL) model rats and complete Freund's adjuvant (CFA) model rats. Behavior tests have shown typical mechanical hyperalgesia in both the L5SNL model and the CFA model. In the L5SNL model, expression of the Nrg1 type I and type II were significantly increased in the L5 DRG. On the other hand, the expression of the Nrg1 type III was decreased in the L5 DRG. We demonstrated that the expression changes of the Nrg1 isoforms in the ipsilateral DRGs were preferentially related to the response to nerve injury. Our findings suggest that the aberrant expression may play an important role in nerve injury, regeneration and subsequent neuropathic pain on the L5SNL.