Riluzole normalizes early-life stress-induced visceral hypersensitivity in rats: role of spinal glutamate reuptake mechanisms.
OBJECTIVE
The molecular basis underlying visceral hypersensitivity in functional irritable bowel syndrome remains elusive, resulting in poor treatment effectiveness. Because alterations in spinal non-neuronal (astrocytic) glutamate reuptake are suspected to participate in chronic pain, we asked whether such processes occur in visceral hypersensitivity.


METHODS
Visceral hypersensitivity was induced in Sprague-Dawley rats by maternal separation. Separated adults were given a systemic administration of riluzole (5 mg/kg), an approved neuroprotective agent activating glutamate reuptake. Visceral hypersensitivity was assessed using colorectal distension (40 mm Hg). Somatic nociception was quantified using Hot Plate, Randall-Sellito, and Hargreaves tests. Spinal proteins were quantified using immunofluorescence and Western blot. The dependence of visceral sensory function upon spinal glutamate transport was evaluated by intrathecal injection of glutamate transport antagonist DL-threo-beta-benzyloxyaspartate (TBOA). For in vitro testing of riluzole and TBOA, primary cultures of astrocytes were used.


RESULTS
We show that riluzole counteracts stress-induced visceral hypersensitivity without affecting visceral response in nonseparated rats or altering nociceptive responses to somatic pain stimulation. In addition, maternal separation produces a reduction in glial excitatory amino acid transporter (EAAT)-1 with no change in EAAT-2 or gamma-amino butyric acid transporters. Stress was not associated with changes in glial fibrillary acidic protein or astrocytic morphology per se. Furthermore, visceral normosensitivity relies on spinal EAAT, as intrathecal TBOA is sufficient to induce hypersensitivity in normal rats.


CONCLUSIONS
We identify spinal EAAT as a therapeutic target, and establish riluzole as a candidate to counteract gastrointestinal hypersensitivity in disorders such as irritable bowel syndrome.
Laboratory of Neurogastroenterology, Alimentary Pharmabiotic Centre, University College Cork, Cork, Ireland.
Romain-Daniel
RD
Gosselin
Richard M
RM
O'Connor
Monica
M
Tramullas
Marcela
M
Julio-Pieper
Timothy G
TG
Dinan
John F
JF
Cryan
D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000627:therapeutic use*; D027341:Excitatory Amino Acid Transporter 1 / Q000032:analysis / Q000502:physiology; D027342:Excitatory Amino Acid Transporter 2 / Q000032:analysis / Q000502:physiology; D005904:Glial Fibrillary Acidic Protein / Q000032:analysis; D018698:Glutamic Acid / Q000378:metabolism*; D043183:Irritable Bowel Syndrome / Q000188:drug therapy*; D008297:Male; D008426:Maternal Deprivation; D009043:Motor Activity; D051381:Rats; D017207:Rats, Sprague-Dawley; D019782:Riluzole / Q000627:therapeutic use*; D013116:Spinal Cord / Q000378:metabolism*; D013315:Stress, Psychological / Q000150:complications*
D018691:Excitatory Amino Acid Antagonists; D027341:Excitatory Amino Acid Transporter 1; D027342:Excitatory Amino Acid Transporter 2; D005904:Glial Fibrillary Acidic Protein; C120673:benzyloxyaspartate; D001224:Aspartic Acid; D018698:Glutamic Acid; D019782:Riluzole