GLT-1 overexpression attenuates bladder nociception and local/cross-organ sensitization of bladder nociception

Abstract

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.

Fig. 1.

A: comparison of GLT-1 expression in lumbosacral (LS) spinal cord of mice administered 1-wk vehicle (Veh; n = 3) or ceftriaxone (CTX; 200 mg/kg daily; n = 3). *P < 0.05. B: glutamate uptake activity comparison from LS spinal cord of mice administered 1-wk Veh (n = 7) or CTX (200 mg/kg daily; n = 7). *P < 0.05.

Fig. 2.

A: visceromotor responses to graded bladder distension in female mice treated with 1-wk CTX (200 mg/kg daily) were compared with mice treated with 1-wk Veh. CTX-treated animals showed a diminished visceromotor response compared with littermates treated with Veh. *P < 0.05. B: raw representative electromyographic recordings elicited after graded bladder distension in 1-wk Veh vs. 1-wk CTX-treated female mice.

Fig. 3.

Effect of selective glutamate transporter (GLT-1) antagonist dihydrokainate (DHK) on the blunted visceromotor response to graded bladder distension caused by GLT-1 overexpression. CTX (200 mg/kg daily) or Veh were each administered in 2 separate groups of animals for 7 days. One hour before graded bladder distension, one 1-wk Veh (●) and 1-wk CTX group (▲) was treated with DHK (10 mg/kg ip). One-week CTX + Veh (▵) produced a significantly reduced visceromotor response to bladder distension compared with the 1-wk Veh + Veh group (○) with the 0.1- and 0.15-ml volumes. DHK pretreatment 1 h before the study reversed the significantly blunted responses. *P < 0.01 compared with 1-wk Veh + 1-h Veh group.

Fig. 4.

A: effects of GLT-1 overexpression on bladder irritant-sensitized visceromotor response to graded bladder distension were compared in female mice. In animals treated with 1-wk Veh and then intravesicular acrolein (●), administered 1 h before the study, significant increased (30–83%) visceromotor response to bladder distension (*P < 0.05) was observed, compared with intravesicular Veh-treated mice (○). One-week CTX treatment abolishes the enhanced visceromotor response to bladder distension caused by intravesicular acrolein (▲). *P < 0.01 compared with 1-wk Veh + intracolonic Veh group. B: raw representative electromyographic recordings elicited after graded bladder distension in animals treated with intravesicular Veh or acrolein (0.4 mM, 100 μl) 1 h before the study. Cohorts pretreated with 1-wk Veh or 1-wk CTX were compared.

Fig. 5.

A: effects of GLT-1 overexpression on the cross-organ-sensitized visceromotor response to graded bladder distension were compared in female mice. In animals administered 1-wk Veh and then treated with intracolonic trinitrobenzene sulfonic acid (TNBS; ●), administered 1 h before the study, a significant increase in the visceromotor response to bladder distension (*P < 0.05) was observed, compared with intracolonic Veh-treated mice (○). CTX treatment (200 mg/kg daily for 1 wk) abolished the enhanced visceromotor response to bladder distension caused by intracolonic TNBS (▲). *P < 0.01 compared with 1-wk Veh + intracolonic Veh group. B: raw representative electromyographic recordings elicited after graded bladder distension in animals treated with intracolonic vehicle or TNBS (35 mg/ml, 50 μl) 1 h before the study. Cohorts pretreated with 1-wk Veh or 1-wk CTX were compared.