Comparative ultrastructure of the nerves innervating the muscle of the body of the bladder.

The distribution and structure of the nerves supplying the muscle of the body of the bladder in mammals such as the mouse, guinea-pig, rabbit, cat and dog was compared with that previously demonstrated in the rat. The muscle of the arterioles located between the muscle bundles is innervated by a fine perivascular plexus and the nerves forming the muscular plexus can be divided into inter- and intra-fascicular nerves and the intrafascicular nerves are characterised by large numbers of terminals with the features of those of cholinergic axons. In addition to many small clear vesicles, the cholinergic terminals contained some small dense-cored vesicles, and it is suggested that, as in the rat, these contain a second transmitter which is released with acetylcholine at the terminals during impulse transmission. Adrenergic term-nals are more common in the muscular plexuses of the guinea-pig, dog and cat than in those of the other animals studied and there is evidence for the presence of two types of such terminal in the nerves. Of these, one contains a much smaller proportion of small vesicles with dense cores and many more large dense-dored vesicles than the second, and the possibility of a relationship between such terminals and those of short adrenergic neurones and neurones associated with non-adrenergic patterns of impulse transmission is discussed.