Figure 7.

Urethane-anaesthetized female rat: traces showing the effects of i.v. Phenol red (0.1 μmol kg⁻¹) on bladder and urethra pressure (mmHg) and on raw external urethral sphincter (EUS-EMG) activity during the micturition reflex evoked by distension of the urinary bladder by saline (0.05 ml min⁻¹). The first panel shows the control effects of infusion of saline into the bladder (infusion on) to evoke contractions (increases in bladder pressure); after three similar contractions the infusion was stopped (infusion off) and the bladder allowed to contract isovolumetrically. At 5 min after the saline infusion had been switched off, the bladder was emptied. There is also an inset showing an expanded time base of the period it took for the saline infusion to initiate a bladder contraction. The second panel shows the same scenario 5 min after administration i.v. of the low dose of phenol red. It should be noted that the time to initiate the first bladder contraction by the saline infusion was delayed. This is better illustrated by comparing the expanded time base inserted with that in the control panel.