Figure 7. Selective naloxone effect on recurrent inhibition.

A, sample records of bladder C fibre reflexes inhibited by antidromic activation of contralateral preganglionic neurones (After contra; upper pair) or orthodromic activation of ipsilateral dorsal clitoris afferents (D clit, lower pair). The latter induced a shortlasting inhibition, so each test reflex was conditioned by a brief stimulus train to the dorsal clitoris nerve (50 Hz, 200 ms, starting 50 ms before test stimulation). The recurrent inhibition was assed as usual in the period after contralateral BPN stimulation (20 Hz, 20 s). The two conditioning stimuli were adjusted to give roughly similar inhibition of the bladder C fibre reflex. B, similar responses after naloxone (0.5 mg kg⁻¹i.v.). The recurrent inhibition was abolished by the drug while the afferent inhibition remained unchanged. C and D, effects of the two conditioning stimuli on bladder C fibre reflexes of different sizes evoked by varying the test stimulation intensity. Each point represents the size of the conditioned reflex plotted against the size of its control reflex, before (○) and after naloxone (•). Hatched lines indicate conditioned reflexes equal in size to their controls, thin dotted and continuous lines are best fits for data points from before and after naloxone. The diagrams show pooled data from three naloxone sessions in the same experiment (same as in Fig. 6). For the naloxone effect, only reflexes sampled during the first 20 min after injections are included. Naloxone clearly suppressed the recurrent inhibition at all test reflex sizes while leaving the inhibition from dorsal clitoris afferents unchanged.