The role of cation-dependent chloride transporters in neuropathic pain following spinal cord injury.
BACKGROUND
Altered Cl- homeostasis and GABAergic function are associated with nociceptive input hypersensitivity. This study investigated the role of two major intracellular Cl- regulatory proteins, Na+-K+-Cl- cotransporter 1 (NKCC1) and K+-Cl- cotransporter 2 (KCC2), in neuropathic pain following spinal cord injury (SCI).


RESULTS
Sprague-Dawley rats underwent a contusive SCI at T9 using the MASCIS impactor. The rats developed hyperalgesia between days 21 and 42 post-SCI. Thermal hyperalgesia (TH) was determined by a decrease in hindpaw thermal withdrawal latency time (WLT) between days 21 and 42 post-SCI. Rats with TH were then treated with either vehicle (saline containing 0.25% NaOH) or NKCC1 inhibitor bumetanide (BU, 30 mg/kg, i.p.) in vehicle. TH was then re-measured at 1 h post-injection. Administration of BU significantly increased the mean WLT in rats (p < 0.05). The group administered with the vehicle alone showed no anti-hyperalgesic effects. Moreover, an increase in NKCC1 protein expression occurred in the lesion epicenter of the spinal cord during day 2-14 post-SCI and peaked on day 14 post-SCI (p < 0.05). Concurrently, a down-regulation of KCC2 protein was detected during day 2-14 post-SCI. The rats with TH exhibited a sustained loss of KCC2 protein during post-SCI days 21-42. No significant changes of these proteins were detected in the rostral region of the spinal cord.


CONCLUSIONS
Taken together, expression of NKCC1 and KCC2 proteins was differentially altered following SCI. The anti-hyperalgesic effect of NKCC1 inhibition suggests that normal or elevated NKCC1 function and loss of KCC2 function play a role in the development and maintenance of SCI-induced neuropathic pain.
Cramer
Samuel W
SW
Department of Neurosurgery, University of Wisconsin School of Medicine and Public Health, Madison, WI 53792, USA. cram0080@umn.edu
Baggott
Christopher
C
Cain
John
J
Tilghman
Jessica
J
Allcock
Bradley
B
Miranpuri
Gurwattan
G
Rajpal
Sharad
S
Sun
Dandan
D
Resnick
Daniel
D
D000818:Animals; D002034:Bumetanide / Q000494:pharmacology; D006930:Hyperalgesia / Q000378:metabolism; D008297:Male; D010146:Pain / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D049994:Sodium Potassium Chloride Symporter Inhibitors / Q000494:pharmacology; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism*; D064506:Solute Carrier Family 12, Member 2; D013116:Spinal Cord / Q000378:metabolism; D013119:Spinal Cord Injuries / Q000378:metabolism*; D027981:Symporters / Q000378:metabolism*; D000096922:K Cl- Cotransporters
D002034:Bumetanide; D049994:Sodium Potassium Chloride Symporter Inhibitors; D028021:Sodium-Potassium-Chloride Symporters; D064506:Solute Carrier Family 12, Member 2; D027981:Symporters; D000096922:K Cl- Cotransporters; C578879:Slc12a2 protein, rat
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