Glutamatergic pathways mediate transmission of pain. Strategies to reduce glutamatergic neurotransmission may have beneficial effects to mitigate nociception. Recent work revealed that overexpression of the astrocytic glutamate transporter (GLT-1) by transgenic or pharmacologic approaches produced a diminished visceral nociceptive response to colonic distension. The purpose of this study was to determine the effect of GLT-1 overexpression on the visceromotor response to bladder distension. Increased glutamate uptake activity produced by 1-wk ceftriaxone (CTX) treatment attenuated 60-64% the visceromotor response to graded bladder distension compared with vehicle-treated mice. One-hour pretreatment with selective GLT-1 antagonist dihydrokainate reversed the blunted visceromotor response to bladder distension produced by 1-wk CTX, suggesting that GLT-1 overexpression mediated the analgesic effect of CTX. Moreover, sensitization of the visceromotor response to bladder distension produced by local bladder irritation (acrolein) was also attenuated by 1-wk CTX treatment. A model of cross-organ sensitization of bladder visceromotor response to distension was next studied to determine whether increased expression of GLT-1 can mitigate colon to bladder sensitization. Intracolonic trinitrobenzene sulfonic acid (TNBS) administered 1 h before eliciting the visceromotor response to graded bladder distension produced a 75- 138% increase in visceromotor response compared with animals receiving intracolonic vehicle. In marked contrast, animals treated with 1-wk CTX + intracolonic TNBS showed no enhanced visceromotor response compared with the 1-wk vehicle + intracolonic vehicle group. The study suggests that GLT-1 overexpression attenuates the visceromotor response to bladder distension and both local irritant-induced and cross-organ-sensitized visceromotor response to bladder distension.
- Excitatory amino acids
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