Functional evidence for sprouting or decentralized parasympathetic neurons in rat urinary bladder

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Abstract
The pelvic nerve, carrying parasympathetic nerve fibers, distributes bilaterally in the rat urinary bladder. Preganglionic parasympathetic denervation (decentralization) on 1 side and postganglionic parasympathetic denervation on the other are followed by an initial decrease in acetylcholine [ACh] forming capacity and in number of acetylcholinesterase positive nerves in the bladder. Within a few weeks a marked recovery in ACh synthesis and in number of nerves, based on collateral sprouting, occurs. Muscle strips of the rat urinary bladder exposed to the combined surgical procedure was studied. The strips were taken from denervated and decentralized halves of the bladder. Their contractile responses to methacholine and transmural electrical field stimulation were isometrically recorded in vitro. A supersensitivity to methacholine developed, of about the same degree, in the 2 halves 1 wk postoperatively. In the denervated halves 4 wk postoperatively, the supersensitivity was even more marked, whereas in the decentralized halves it tended to be less than after 1 wk. The responses of denervated halves to electrical stimulation were reduced 1 wk postoperatively. This was also the case for decentralized halves, although the reduction was not large enough to be significant. When examined 4 wk postoperatively the responses, in particular in denervated halves, were enlarged compared to those 1 wk postoperatively. The atropine-sensitive portion of the responses increased with time. Increases in contractile responses to electrical stimulation accompanied by a tendency to desensitization to methacholine are taken as functional evidence for outgrowth of decentralized parasympathetic neurons in the decentralized halves. The gradual development of sensitization with time may in part explain the increasing responses to electrical stimulation in the denervated halves.