RESPONSES OF FELINE RAPHESPINAL NEURONS TO URINARY-BLADDER DISTENSION

Effects of distending the urinary bladder were studied on extracellula r activity of 77 raphespinal neurons in 19 alpha-chloralose anesthetiz ed cats. Neurons were activated antidromically from thoracic spinal co rd; recording sites were located in nucleus raphe magnus (NRM). Mean c onduction velocity was 48 +/- 2 m/s. Urinary bladder distension (UBD) increased activity in 12 cells and decreased activity in 17 cells. Spo ntaneous bladder contractions also affected activity in raphespinal ne urons responsive to UBD. Noxious pinch stimulus applied to proximal hi ndlimbs or forelimbs either increased or decreased activity in 28 raph espinal neurons. No cells were excited both by UBD and pinching of ski n and deep tissues of the limbs. Thus, excitatory viscerosomatic conve rgence was not observed with the stimuli tested in raphespinal neurons examined in this study. Urinary bladder input to descending projectio n neurons in NRM might participate in descending modulation of dorsal horn neurons. In addition, micturition reflexes might be affected by u rinary bladder input to these neurons.