Response of a parasympathetic neuroeffector system to motor nerve stimulation

Abstract

The pressure response of the feline urinary bladder to motor nerve stimulation was measured by a strain gauge connected to a urethral catheter. In lightly anesthetized cats the magnitude of the responses produced was a hyperbolic function of the stimulation frequency within the range of .5–20 impulses/sec. Blockade of the ChE system by the administration of 1 mg/kg of prostigmine with or without arrest of the bladder circulation failed to alter the characteristics of this response. Our findings suggest that these graded responses of bladder smooth muscle at different stimulation frequencies is dependent upon a mechanical summation of individual ‘twitch’ responses. The response magnitude is in a way proportional to the concentration of ACh. Contractions resulting from repetitive stimulation at rates of 10–15/sec., achieved optimal summation. At stimulation frequencies below 5/sec. the efficiency of mechanical summation in the bladder smooth muscle diminished. When the interval between stimuli was increased to 200 msec. (5/sec.) the summated response of the smooth muscle established a lower plateau. It is suggested that the smaller responses found at the lower frequencies may be related in part to the tendency of smooth muscle units to restore themselves to the resting state independently of high ACh concentrations.