A putative non-cholinergic mechanism in urinary bladders of New but not Old World primates

The effects of atropine on bladder contractions evoked by sacral ventral root stimulation were investigated in two species of New World monkey (marmoset and cebus) and in paraplegic man. The findings were then compared to those previously obtained for the cat and two species of Old World monkey (rhesus and baboon). The results show the marmoset and cebus to represent a transitional stage between the complete sensitivity of the bladders of Old World monkeys to atropine and the relative insensitivity of the cat bladder. The bladder response is shown to comprise two components, an atropine sensitive component which is slow in onset and an atropine resistant component which is easily fatigued. The experiments in paraplegic people confirm that the parasympathetic innervation of the bladder of man is, like that of Old World monkeys, exclusively cholinergic. A behavioural interpretation is tentatively offered to explain the two types of innervation.