Responses of feline raphespinal neurons to urinary bladder distension

Effects of distending the urinary bladder were studied on extracellular activity of 77 raphespinal neurons in 19 alpha-chloralose anesthetized cats. Neurons were activated antidromically from thoracic spinal cord; recording sites were located in nucleus raphe magnus (NRM). Mean conduction velocity was 48 +/- 2 m/s. Urinary bladder distension (UBD) increased activity in 12 cells and decreased activity in 17 cells. Spontaneous bladder contractions also affected activity in raphespinal neurons responsive to UBD. Noxious pinch stimulus applied to proximal hindlimbs or forelimbs either increased or decreased activity in 28 raphespinal neurons. No cells were excited both by UBD and pinching of skin and deep tissues of the limbs. Thus, excitatory viscerosomatic convergence was not observed with the stimuli tested in raphespinal neurons examined in this study. Urinary bladder input to descending projection neurons in NRM might participate in descending modulation of dorsal horn neurons. In addition, micturition reflexes might be affected by urinary bladder input to these neurons.