Demonstration of spontaneous and stretch induced urinary bladder EMG in the living rabbit

Spontaneous bladder EMG was recorded in the living rabbit from an isovolumetric bladder without chemical or electrical stimulation. Mechanical intervention, either by lifting the bladder out of the abdomen or by rapid filling, resulted in stretch induced bladder EMG. A self made epoxy resin electrode device that embedded 32 EMG recording electrodes in a matrix like pattern, each electrode Ag/AgCl, d = 0.6 mm with an interdistance of 2.3 mm, was used for registration. The recorder used a common average reference technique and a sample frequency of 400 Hz. A signal bandwidth of 0.05 to 108 Hz was available for analysis. Spontaneous EMG consisted of single spikes and bursts (2-20 spikes), but not of continuous activity. The shape of spikes was triphasic. Single spikes appeared with and without burst activity. Small (2-5 spikes) and large bursts (6-20 spikes) were discerned; small bursts not necessarily propagated across electrodes, large bursts did and were able to organize, suggesting that they were under short neuron system control. Spontaneous EMG was probably related to both contraction and relaxation. Stretch induced EMG was characterised by continuous activity on all electrodes, spikes that followed each other immediately, slowly fading away. The spikes had an elongated third phase when compared to the shape of spontaneous activity. Highest activity and amplitudes were found after lifting the bladder out of the abdomen and placing it on the electrode device. A concept is put forward in which the continuous activity is not unequivocally related to muscle shortening, but where the current stress and strain situation of the bladder tissue can cause a muscle fibre elongation upon the appearance of electrical activity. The EMG activity found was in many aspects similar to results of a previous study using mortalized rabbits. Artifact sources like the heart, respiration, or local movement between electrode and bladder could easily be identified due to the new experimental methodology used.