EFFECTS OF GYKI-52466 AND CNQX, AMPA-KAINATE RECEPTOR ANTAGONISTS, ON THE MICTURITION REFLEX IN THE RAT

GYKT 52466, a non-competitive AMPA/kainate glutamate receptor antagonist, administered in graded doses (0.5-8 mg/kg, i.v.) at 10 min intervals, decreased the amplitude and duration of reflex bladder contractions (maximal inhibition = 63%), the intercontraction interval (maximal inhibition = 83%) and external urethral sphincter activity (maximal inhibition = 91%) in urethane-anesthetized (1.2 g/kg, s.c.) intact rats during continuous transurethral cystometrograms. On the other hand, in unanesthetized decerebrate rats, the drug did not alter reflex bladder activity but did produce a significant depression of sphincter activity (maximal inhibition = 59%). The depressant effects of single doses of GYKI 52466 (4 mg/kg, i.v.) on external urethral sphincter EMG activity occurred with similar time courses in both urethane-anesthetized (1.2 g/kg, s.c.) intact and unanesthetized decerebrate rats during continuous transurethral cystometrograms. In urethane-treated (0.6 g/kg, i.p.) decerebrate rats, GYKI 52466 (0.5-4 mg/kg, i.v.) depressed bladder contraction amplitude and sphincter EMG activity, similar to the effects in urethane-anesthetized (1.2 g/kg, s.c.) intact rats. CNQX (0.01-1 mg/kg, i.v.), a competitive AMPA/kainate receptor antagonist, administered to urethane-anesthetized (1.2 g/kg, s.c.) intact or unanesthetized decerebrate rats did not alter the bladder or the external urethral sphincter activity during continuous transurethral cystometrograms, possibly due to the inability of the drug to readily cross the blood-brain barrier. The present results indicate that glutamatergic excitatory transmission mediated by AMPA/kainate receptors is essential for the activation of external urethral sphincter activity during micturition in anesthetized and unanesthetized preparation. However, the depressant effect of GYKI 52466 on reflex bladder activity is only unmasked by urethane anesthesia, raising the possibility that urethane interacts with AMPA/kainate glutamate receptors in the spinobulbospinal micturition reflex pathway.