Organization of sympathetic responses to distension of urinary bladder

Distension of the urinary bladder can cause reflex pressor responses, which appear to be mediated by increased sympathetic activity. However, preganglionic upper thoracic sympathetic activity is excited inconsistently by bladder distension in intact and spinal animals. The objective of this investigation was to determine if any of the postganglionic nerves originating from thoracic and lumbar spinal segments are consistently excited by vesical afferent nerves. Responses of external carotid, renal, and splenic sympathetic nerves to distension of the urinary bladder were evaluated in chloralose-anesthetized cats. In addition, the potential preferential spinal segmental distribution of vesico-sympathetic reflexes was assessed by comparing the magnitudes of external carotid, renal, and splenic nerve responses. Distension of the urinary bladder with 5-35 ml saline initiated vesical contractions to pressures of 45-90 cmH2O and caused inconsistent changes in arterial pressure and activity of renal and splenic sympathetic nerves. External carotid nerves were excited by this stimulus. Vesical distension with 12-50 ml saline caused contractions to vesical pressures of 135-175 cmH2O and produced consistent increases in arterial pressure and activity of all three nerves. Thus activation of vesical afferent nerves by high pressure produced excitation of upper thoracic vasomotor neurons and of two major components of splanchnic and lumbar sympathetic outflow. The magnitudes of external carotid, renal, and splenic sympathetic responses were not different, illustrating that propriospinal circuits thought to mediate vesicosympathetic responses are not organized segmentally.