Sensory collaterals, intramural ganglia and motor nerves in the guinea-pig bladder: evidence for intramural neural circuits

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Abstract
The afferent output from the bladder is important for triggering micturition. This study identifies different types of afferent nerve and explores the connections of their collateral fibres on intramural ganglia and potential ganglionic targets. The experiments were performed on tissues from male guinea-pigs (n=16). Fibres positive for choline acetyl transferase (ChAT+) were found to originate close to the urothelium, to transit the sub-urothelial interstitial cell layer and to pass into the lamina propria. A different population of fibres, immunopositive for calcitonin gene-related peptide (CGRP), capsaicin receptors or neurofilament protein (NF), were seen to intertwine with the ChAT+ fibres in the lamina propria. The ChAT+ fibres did not express NF. Ganglia with ChAT+ and NF+ neurones were found in the lamina propria and muscle. ChAT+ fibres, with pronounced terminal varicosities, were present on the nerve cell bodies. Two types were noted: NF+ terminals and those with little or no NF (NF−) suggesting that their origins were the ChAT+ afferent collaterals and the adjacent ganglia. Fibres containing CGRP or substance P were seen on the ganglionic cells. α1B adrenergic receptors were also found on the neurones indicative of adrenergic synapses. Thus, the ganglia had multiple inputs. Different types of ChAT+ nerves were seen in the muscle: NF+ and NF−. The ChAT+/NF+ nerves may represent a ganglionic output to the muscle. This complex neuronal network may therefore represent the elements generating and modulating bladder sensations. The role of such a scheme in bladder pathology and the therapeutic sites of action of anticholinergic and sympathomimetic drugs are discussed.