Activation of the spinal sigma-1 receptor enhances NMDA-induced pain via PKC- and PKA-dependent phosphorylation of the NR1 subunit in mice.
OBJECTIVE
Previously we demonstrated that the spinal sigma-1 receptor (Sig-1 R) plays an important role in pain transmission, although the exact mechanism is still unclear. It has been suggested that Sig-1 R agonists increase glutamate-induced calcium influx through N-methyl-D-aspartate (NMDA) receptors. Despite data suggesting a link between Sig-1 Rs and NMDA receptors, there are no studies addressing whether Sig-1 R activation directly affects NMDA receptor sensitivity.


METHODS
We studied the effect of intrathecal (i.t.) administration of Sig-1 R agonists on protein kinase C (PKC) and protein kinase A (PKA) dependent phosphorylation of the NMDA receptor subunit NR1 (pNR1) as a marker of NMDA receptor sensitization. In addition, we examined whether this Sig-1 R mediated phosphorylation of NR1 plays an important role in sensory function using a model of NMDA-induced pain.


RESULTS
Both Western blot assays and image analysis of pNR1 immunohistochemical staining in the spinal cord indicated that i.t. injection of the Sig-1 R agonists, PRE-084 or carbetapentane dose dependently enhanced pNR1 expression in the murine dorsal horn. This increased pNR1 expression was significantly reduced by pretreatment with the specific Sig-1 R antagonist, BD-1047. In another set of experiments Sig-1 R agonists further potentiated NMDA-induced pain behaviour and pNR1 immunoreactivity and this was also reversed with BD-1047.


CONCLUSIONS
The results of this study suggest that the activation of spinal Sig-1 R enhances NMDA-induced pain via PKC- and PKA-dependent phosphorylation of the NMDA receptor NR 1 subunit.
Kim
H-W
HW
Department of Physiology, College of Medicine and Research Institute for Medical Sciences, Chungnam National University, Daejeon, South Korea.
Roh
D-H
DH
Yoon
S-Y
SY
Seo
H-S
HS
Kwon
Y-B
YB
Han
H-J
HJ
Kim
K-W
KW
Beitz
A J
AJ
Lee
J-H
JH
D000818:Animals; D001522:Behavior, Animal; D015153:Blotting, Western; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D003517:Cyclopentanes / Q000008:administration & dosage; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D005029:Ethylenediamines / Q000008:administration & dosage; D007150:Immunohistochemistry; D007278:Injections, Spinal; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009025:Morpholines / Q000008:administration & dosage; D016202:N-Methylaspartate / Q000008:administration & dosage; D010146:Pain / Q000139:chemically induced / Q000201:enzymology*; D010147:Pain Measurement; D010766:Phosphorylation; D020671:Posterior Horn Cells / Q000201:enzymology; D011493:Protein Kinase C / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D017480:Receptors, sigma / Q000187:drug effects / Q000378:metabolism*; D012694:Serine; D012815:Signal Processing, Computer-Assisted; D015398:Signal Transduction; D013116:Spinal Cord / Q000201:enzymology*; D013997:Time Factors; D000097605:Sigma-1 Receptor
D017868:Cyclic AMP-Dependent Protein Kinases; D003517:Cyclopentanes; D005029:Ethylenediamines; D009025:Morpholines; D016202:N-Methylaspartate; D011493:Protein Kinase C; D016194:Receptors, N-Methyl-D-Aspartate; D017480:Receptors, sigma; D012694:Serine; D000097605:Sigma-1 Receptor; C409466:NR1 NMDA receptor; C071738:2-(4-morpholino)ethyl-1-phenylcyclohexane-1-carboxylate; C097963:N-(2-(3,4-Dichlorphenyl)ethyl)-N,N',N'-trimethyl-1,2-ethandiamin; C018861:carbetapentane