Non-cholinergic transmission by post-ganglionic motor neurones in the mammalian bladder

1. In mucosa-free preparations of the detrusor muscle electrical stimulation with 0.1 msec pulses has been utilized to reveal the non-cholinergic nature of most, if not all, of the post-ganglionic motor neurones in the guinea-pig bladder.2. The twitches elicited by 0.1 msec pulses were abolished by tetrodotoxin, but were not reduced by dimethyltubocurarine or by hexamethonium. Hexamethonium was nevertheless present in all the experiments in order to restrict acetylcholine action to ;muscarinic' receptors in the muscle fibres.3. There was little or no diminution in the twitches after prolonged exposure to atropine, 10(-8)-10(-5) g/ml., although the twitch-matching dose of acetylcholine was raised 1000-2500 times. Hence, there was no anomalous refractoriness to atropine in these ;muscarinic' receptors.4. Despite massive atropinization, the recruitment of unoccupied transmitter-receptors by means of extra pulses remained unaffected.5. Eserine failed to potentiate the atropine-resistant twitches.6. The twitches were not depressed by morphine.7. Noradrenaline produced relaxation and twitch reduction. The twitches persisted after alpha + beta adrenoceptor blockade with phentolamine + pronethalol and were unaffected by the monoamine oxidase and catecholamine-O-methyl transferase inhibitors, tranylcypromine and pyrogallol.8. Rapid contractions were elicited by 5-HT and by histamine but the twitches remained unaltered after antagonism of 5-HT by methysergide and of histamine by mepyramine.9. The twitches could be mimicked by injections of ATP, but after desensitization of the preparation to ATP the response to electrical stimulation remained unaltered.10. Prostaglandins E(2) and F(2alpha), only in large doses, produced delayed, sluggish contractions which persisted after the wash; these contractions were quite different from the responses to electrical stimulation, which were immediate, sharp and brief.11. The non-cholinergic nature of the post-ganglionic motor neurones was confirmed in the bladder of two other species, the cat and the rabbit.