Submitted on April 15, 2008
Revised on July 10, 2008
Accepted on July 10, 2008
Acute anal distension inhibits NMDA-dependent pelvic-urethra reflex potentiation via spinal GABAergic inhibition in anesthetized rats
Sung-Lang Chen, Yu-Hui Huang, Yu-Lin Kao, Gin-Den Chen, Chen-Li Cheng1, Hsien-Yu Peng2, Jiuan-Miaw Liao2, Pei-Chen Huang, Shih-Jei Tsai, and Tzer-Bin Lin2*
1 Taichung Veterans General Hospital
2 Chung-Shan Medical University
* To whom correspondence should be addressed. E-mail: tblin{at}csmu.edu.tw.
The impact of acute anal stretch on the pelvic-urethra reflex potentiation was examined in urethane-anesthetized rats by recording the external urethra sphincter electromyogram (EUSE) activity evoked by the pelvic afferent stimulation. Test stimulation (TS, 1 stimulation/30 sec) evoked a baseline reflex activity with a single action potential that was abolished by gallamine (5 mg/kg, i.v.). On the other hand, the repetitive stimulation (RS, 1 stimulation/1 sec) induced spinal reflex potentiation (SRP) that was attenuated by intrathecal CNQX (a glutamatergic AMPA receptor antagonist, 100 µM, 10 µl) and APV (a glutamatergic NMDA antagonist, 100 µM, 10 µl). Acute anal stretch using a mosquito clamp with a distance of 4 mm exhibited no effect, while with distances of 8 mm attenuated and of 12 mm abolished the repetitive stimulation-induced SRP. Intrathecal NMDA (100 µM, 10 µl) reversed the abolition on SRP caused by anal stretch. On the other hand, pretreated bicuculline (GABA A receptor antagonist, 100 µM, 10 µl) but not hydroxysaclofen (GABA B receptor antagonist) counteracted the abolition on the repetitive stimulation-induced SRP caused by the anal stretch. All the results suggested that anal stretch may be used as an adjunct to assist voiding dysfunction in patients with overactive urethra sphincter, and that GABAergic neurotransmission is important in the neural mechanisms underlying external urethra sphincter activity inhibited by anal stretch.
