Abstract
OBJECTIVE: The aim of this study was to determine if the non-convulsant delta-opioid receptor (DOR) agonist, KNT-127, could inhibit migraine-associated endpoints. BACKGROUND: The DOR has been identified as a therapeutic target for migraine. However, the development of delta agonists is limited as some ligands have seizurogenic properties, which may be related to their ability to induce receptor internalization. While both pro- and non-convulsant delta agonists can reduce migraine-associated allodynia, only the proconvulsant agonist, SNC80, has been shown to decrease cortical spreading depression (CSD). It is unclear if the ability of delta agonists to modulate cortical activity is related to the same signaling mechanisms that produce proconvulsant effects. METHODS: The effects of the non-convulsant delta agonist, KNT-127, were examined. Repetitive CSD was induced in female C57BL6/J (n = 6/group) mice by continuous application of KCl and the effect of KNT-127/vehicle (Veh) on both local field potentials and optical intrinsic signals was determined. To assess the effect of KNT-127 on established chronic migraine-associated pain, male and female C57BL6/J mice were treated with nitroglycerin (NTG; 10 mg/kg, ip) every other day for 9 days and tested with KNT-127 (5 mg/kg, sc) or Veh on day 10 (n = 6/group). DOR-enhanced green fluorescent protein mice (n = 4/group) were used to confirm the internalization properties of KNT-127 in the trigeminal ganglia, trigeminal nucleus caudalis, and somatosensory cortex. RESULTS: KNT-127 inhibited CSD events (t((10)) = 3.570, p = 0.0051). In addition, this delta agonist also reversed established cephalic allodynia in the NTG model of chronic migraine (F((1, 20)) = 12.80, p < 0.01). Furthermore, KNT-127 caused limited internalization of DOR in key migraine processing regions. CONCLUSIONS: This study shows that the antimigraine effects of DOR agonists can be separated from their proconvulsant effects. This data provides valuable information for the continued development of delta agonists for the treatment of migraine.