A decarboxylated form of L-arginine, agmatine, preferentially antagonizes NMDArs containing Glun2B subunits within the spinal cord and lacks motor side effects commonly associated with non-subunit-selective NMDAr antagonism, namely sedation and motor impairment. Spinally delivered agmatine has been previously shown to reduce the development of tactile hypersensitivity arising from spinal nerve ligation. The present study interrogated the dependence of agmatine’s alleviation of neuropathic pain (spared nerve injury (SNI) model) on GluN2B-containing NMDArs. SNI-induced hypersensitivity was induced in mice with significant reduction of levels of spinal GluN2B subunit of the NMDAr and their floxed controls. Agmatine reduced development of SNI-induced tactile hypersensitivity in controls but had no effect in subjects with reduced levels of GluN2B subunits. Ifenprodil, a known GluN2B-subunit-selective antagonist, similarly reduced tactile hypersensitivity in controls but not in the GluN2B-deficient mice. In contrast, MK-801, an NMDA receptor channel blocker, reduced hypersensitivity in both control and GluN2B-deficient mice, consistent with a pharmacological pattern expected from a NMDAr antagonist that does not have preference for GluN2B subtypes. Additionally, we observed that spinally delivered agmatine, ifenprodil and MK-801 inhibited nociceptive behaviors following intrathecal delivery of NMDA in control mice. By contrast, in GluN2B-deficient mice, MK-801 reduced NMDA-evoked nociceptive behaviors, but agmatine had a blunted effect and ifenprodil had no effect. These results demonstrate that agmatine requires the GluN2B subunit of the NMDA receptor for inhibitory pharmacological actions in pre-clinical models of NMDA receptor-dependent hypersensitivity.
Bibliographical noteFunding Information:
Generation of the GluN2B knock-down (KD) mouse was initiated by Dr. E. Delpire (Vanderbilt University), as previously described. The GluN2B-mutant mouse was generated by the Gene-Targeted Mouse Core of the INIA-stress consortium. They are on a C57Bl/6 genetic background. This Integrative Neuroscience Initiative on Alcoholism examines the link between stress and alcohol. The consortium is supported by the National Institute on Alcohol Abuse and Alcoholism. The Gene-Targeted Mouse Core is supported by NIH grant U01 AA013514 (to E.D.). A breeding colony of homogenous GluN2B-floxed mice was established. At time of weaning (p21), all subjects received either an intrathecal injection of 5 microliters of 0.9% saline (floxed control subjects) or AAV9.hSYN.HI.eGFP-Cre.WPRE.SV40 (GluN2B-KD subjects) (Penn Vector Core, University of Pennsylvania).
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by R01DA035931 (CAF), R01DA015438 (GLW), NIDA training grant T32-DA007097 supported CDP, and NIDA training grant T32-DA07234 supported KP. The NR2B-flox mouse was generated by the Gene-Targeted Mouse Core of the INIA-stress consortium (supported by NIH grant U01 AA013514 to ED).
© The Author(s) 2021.
- chronic pain
- neuropathic pain