Reflex plasticity between pelvic afferent nerve (PAN) and pudendal efferent nerve (PEN), as well as external-urethral sphinctor (EUS) activity was examined in anesthetized rats. A progressive increase in the number of evoked action potentials per stimulus occurred in PEN and EUS activity when PAN was repetitively stimulated (1 Hz). This potentiation in pelvic-pudendal reflex (PPR) activity induced by repetitive stimulation was abolished by APV (D-2-amino-5-phosphonoraleric acid, i.t. 100 μM, 2-5 μl) and attenuated by the NBQX (2, 3-dihydroxy-6-nitro-7-sulfamoyl-benzo (F) quinoxaline, i.t. 20 μM, 2-5 μl) but was not affected by the presence of bicuculline (i.t. 10 μM, 2-5 μl). The duration of contraction wave of intra-urethral pressure (IUP) elicited by a single electric shock was elongated by potentiated PPR, while the peak pressure was not affected. Both intrathecal application of glutamate (i.t. 0.1 mM, 2-5 μl) and NMDA (N-methyl-D-aspartic acid, i.t. 0.1 mM, 2-5 μl) induced spontaneous repetitive (0.31±0.02 Hz) burst discharges in PEN and EUSE and produced small contraction wave in IUP, which is similar to the high frequency oscillation phase during a voiding cycle of urinary bladder in rats. All these results demonstrate that repetitive stimulation of PAN can induce a distinct and long-lasting modulation in PPR activity and this change may be physiologically relevant in urinary continence.
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