Effects of central nervous system-acting drugs on urinary bladder contraction in unanesthetized rats

We studied the effects of drugs on urinary bladder contraction in unanesthetized (UA) rats using the same method as that previously employed to investigate similar effects in urethane and alpha-chloralose-anesthetized (A) rats. The surgical procedure was performed under halothane anesthesia, and after the recovery, the rats were restricted in a Ballman cage during the experiment. The pattern of the cystometrogram obtained in UA rats was very similar to that in A rats, and almost the same pattern was maintained for at least three hours. Baclofen (10 mg/kg, i.p.), morphine (10 mg/kg, i.p.) and pentobarbital (20 mg/kg, i.p.) completely inhibited the bladder contraction at doses only double those at which the same drugs inhibited the bladder contraction in A rats when i.v. injected. When the bladder pressure rose almost to the level of the peak pressure existing before injection of these drugs, the instilled solution leaked from the penis. On the other hand, even after injection of diazepam (5 mg/kg, i.p.) at a dose five times greater than the minimum amount necessary for complete inhibition of bladder contraction in A rats, the bladder contraction accompanying micturition continued in UA rats. It appears that the inhibitory effect of diazepam on bladder contraction in rats is potentiated by anesthesia.