Behaviour of the urethral striated sphincter and of the bladder in the chronic spinal cat

Nine cats were spinalized at the thoraco-lumbar junction (T12-L7) and the subsequent behaviour of the bladder and urethral striated sphincter was observed during periods of up to 27 days after spinalization by means of bladder manometry and of urethral electromyography. On the day following operation, the urethral sphincter responds to stimulation of its intact motor nerve, the pudic nerve by reflex (R) and direct (M) responses analogous to those of the intact animal anaesthetized with chloralose. The ratio R/M lies between 1 and 0.6 in the chronic spinal cat whereas it is generally less than 0.5 in the intact chloralose-anaesthetized cat. The tonic activity of the sphincter is weak or not present. The continence, however, is well maintained. The bladder activity appears only 4 to 8 days after spinalization. The bladder can thus void urine during brief contractions. These micturitions are always incomplete. The urethral reflex activity, either spontaneous or triggered by stimulation of the pudic nerve, may be inhibited, i: to a moderate degree by passive bladder distension; ii: almost completely by activation of vesicomotor neurones which provoke the bladder contraction. The first inhibition is seen the day after spinalization and is probably a protective reflex against vesical hypertension. The second inhibition develops progressively and in parallel to the functional recovery of vesical preganglionic neurones. It takes place on a background of antagnostic equilibrium of bladder and of urethral sphincter activities during micturition.