Comparative Physiology of the Vertebrate Autonomic Nervous System. I. Innervation of the Urinary Bladder of the Toad (Bufo Marinus)

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Abstract
I. The anatomy, physiology and pharmacology of the innervation of the bladder of the toad (Bufo marinus) have been studied. 2. Motor fibres only have been demonstrated to innervate the toad bladder. These fibres travel mainly in the 9th spinal nerve, but may also be present in the 10th, 7th and occasionally in the 8th spinal nerves. Usually, all these fibres reach the bladder via the pelvic nerves. 3. The response of the bladder to nerve stimulation was qualitatively the same whichever nerve was stimulated and whatever parameters of stimulating pulse were applied. The optimal frequency at 20° C. was about 20 pulses/sec. 4. ACh causes contraction of the toad bladder. Adrenaline and noradrenaline usually cause relaxation, but dopamine and low concentrations of noradrenaline can cause weak excitation. The bladder is insensitive to both histamine and 5-HT. 5. Atropine reduced the response of the bladder to pelvic nerve stimulation by up to 50%. Eserine did not potentiate the nerve-mediated response, but nor did it potentiate the direct action of ACh. 6. All the adrenergic blocking agents used reduced or completely blocked the nervemediated response, but the response to applied ACh is also reduced under these conditions. 7. All the ganglionic blocking agents tested reduced the nerve-mediated response. However, only mecamylamine markedly reduced the response without affecting the action of applied ACh. 8. It was concluded that a division into sympathetic and parasympathetic innervation of the toad bladder was not justified, and that the nerve fibres which innervate this organ are probably all of one type, regardless of their origin, with at least 50 % of the pelvic nerve fibres being pre-ganglionic. 9. The pharmacological evidence presented favours the view that these nerves are cholinergic rather than adrenergic. 10. The evolutionary implications of these results have been discussed.