PRESSURE, VOLUME, AND CHEMOSENSITIVITY IN AFFERENT INNERVATION OF URINARY-BLADDER IN RATS

Bladder afferent nerve activity was recorded from the pelvic and hypog astric nerves of rats anesthetized with pentobarbital sodium. Bladder filling with isotonic NaCl at a rate of 250 mu l/min excited multiunit afferent activity in the hypogastric nerve by 190 +/- 38% over backgr ound at a pressure of 30 mmHg, whereas 150 meq/l KCI at the same filli ng rate excited hypogastric nerve activity by 498 +/- 103% (P < 0.0001 ). This difference was localized to a group of chemosensitive fibers t hat are excited by bladder filling with KCl in a concentration-depende nt fashion but are insensitive to bladder filling with NaCl. Bladder f illing with 200 meq/l KCl at different filling rates caused a bursting pattern of discharge in these fibers at consistent bladder volumes bu t with a pressure threshold that increased proportionately with fillin g rate. Other hypogastric bladder afferent fibers were activated to a similar extent by NaCl and KCl solutions. Chemoreceptive bladder affer ent fibers were rare in the pelvic nerve (1 of 15 units), and multiuni t preparations showed comparable excitations during bladder filling wi th NaCl and KCl solutions. The bursting activation of bladder chemorec eptive afferent nerves in hypogastric nerves could signal noxious over distension and/or inflammation of the bladder.