Two classes of sympathetic nerves with different dopa decarboxylase immunoreactivities exist in dog vas deferens.

To determine whether dihydroxyphenylalanine (DOPA) decarboxylase (DDC) activity in the terminal regions of noradrenergic axons varies with axonal length, we compared the pattern of immunohistochemical staining for DDC in the 'short' terminal nerves of dog vas deferens with that in the 'long' nerves of spleen and atrium. The terminal nerves supplying the muscular coats of the vas deferens were, like those in spleen and heart, devoid of DDC immunoreactivity. The presence of this enzyme is therefore not characteristic of either short or long noradrenergic axons, in support of previous evidence that it is a specific marker for dopaminergic terminal nerves. Many axons supplying the mucosal epithelial cells in the vas deferens were DDC-positive, suggesting the existence of a dopaminergic innervation.