Typical effects of naloxone on prolonged TNS inhibition of micturition reflex. Naloxone (1 mg/kg, i.v.) either restored the inhibited micturition reflex (A) or reduced the bladder capacity (B). However, additional 30-min TNS removed the naloxone effect by either completely suppressing the micturition reflex (A) or increasing the bladder capacity (B). Repeated TNS before naloxone in A: 5 Hz, 0.2 ms, 30 min at 4T applied three times followed by 6T two times, T = 1.2 V. Repeated TNS before naloxone in B: 5 Hz, 0.2 ms, 30 min at 4T applied three times followed by 6T five times, T = 0.5 V. TNS after naloxone in both A and B: 5 Hz, 0.2 ms, 30 min at 6T applied one time. T—intensity threshold for inducing toe twitch