Reflex plasticity between pelvic afferent and pudendal efferent nerve fibers was examined in anesthetized rats, Brief high-frequency electric stimulation (300 pulses at 100 Hz) of the pelvic nerve afferent fiber produced a long-lasting potentiation of the pelvic-to-pudendal reflex (PPR). This tetanization-induced potentiation was abolished by a selective N-methyl-D-aspartate (NMDA) receptor antagonist and attenuated by a non-NMDA excitatory amino acid receptor antagonist, However, the GABAA- receptor antagonist had no effect on this potentiation. Both intrathecal glutamate (0.1 mM, 2-5 μl it) and NMDA (0.1 mM, 2-5 μl it) induced a potentiation of PPR similar to that of tetanization. Agonist-induced potentiation was shorter than tetanization-induced potentiation. The duration of the contraction wave of intraurethral pressure, elicited by PPR, was elongated by tetanization-induced potentiation, whereas the peak pressure was not affected. All these results demonstrate that brief high-frequency stimulation of the pelvic nerve afferent fiber can induce a distinct and long-lasting modulation in PPR activity and this change may be involved in nociceptive C afferent-induced obstructive urinary dysfunctions.
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