Sacral glutamatergic transmission in the descending limb of the micturition reflex in the cat.

This study was undertaken to clarify the location of glutamatergic synaptic transmission in the descending pathway of the micturition reflex in decerebrate cats. Contractions of the urinary bladder evoked by stimulating the pontine micturition center were completely inhibited by the broad-spectrum excitatory amino acid antagonist, kynurenic acid (KYN) and the selective N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801, that were applied intrathecally to the sacral cord, while such contractions were not attenuated by the non-NMDA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). An iontophoretic application of KYN remarkably inhibited discharges of the sacral parasympathetic preganglionic neurons innervating the urinary bladder (bladder motoneurons) elicited by pontine stimulation. Our results suggest that glutamatergic synaptic transmission is located at the level of the sacral cord in the descending limb of the micturition reflex and is mediated via NMDA receptor on the bladder motoneurons.