Light and electron microscopic observations on noradrenergic nerves and striated muscle cells of the guinea pig urethra.

Neurohistochemical and electron microscopic techniques have been used to determine the arrangement and distribution of noradrenergic nerves and striated muscle in the wall of the guinea pig urethra. Fluorescent, catecholamine - containing nerves were observed among striated muscle cells only in the junctional zone between an inner layer of smooth muscle and an outer layer of striated cells. In this region considerable intermixing of the two types of muscle cell occurred. Electron microscopy has shown that noradrenergic terminal regions containing characteristic small dense-cored vesicles were invariable associated with smooth muscle cells; such nerves were never observed forming neuroeffector relationships with striated cells. These findings indicate that noradrenergic 'sympathetic' fibres are not directly involved in the functional control of urethral striated muscle.