Comparative Physiology of the Vertebrate Autonomic Nervous System

Abstract

1. A histological study of the structure of the urinary bladder of the ringtail possum has been made. The innervation of the bladder has been studied in vitro, using the technique of analytical pharmacology. 2. The bladder has well-defined inner longitudinal and outer circular muscle layers. Nerves supplying the bladder are found both in the pelvic nerves and in the vesical nerves which run with the vascular supply of the bladder fundus. Ganglia have been demonstrated along the trunks of the vesical nerves and also aggregated at the bladder neck. 3. The response of the bladder to stimulation of either nerve supply in situ or in vitro is always a simultaneous contraction of both longitudinal and circular muscles. Inhibitory responses to nerve stimulation have never been observed. The optimal frequency for stimulation of these nerves at 30° C. is 50 pulses/sec. 4. The bladder is contracted by ACh and 5-hydroxytryptamine, but is relaxed by adrenaline, noradrenaline and histamine. 5. The response to nerve stimulation is reduced by atropine and potentiated by eserine. Adrenergic blocking agents do not affect the nerve-mediated response unless they also affect the response to applied ACh in a similar manner. 6. Ganglionic blocking agents, in concentrations which do not reduce the response to ACh, cause up to a 40% reduction of the response to stimulation of either the vesical or the pelvic nerves. 7. It is concluded that the nerve fibres supplying the possum bladder are cholinergic, perhaps 40 % of them being stimulated pre-ganglionically. 8. The evolutionary significance of these observations is discussed. 9. Some points of pharmacological interest have been discussed in relation to drug actions on placental mammal preparations.