Regional distribution of catecholaminergic terminals in the pigeon visual system.

A glyoxilic acid histofluorescence technique was used in this study to determine the distribution of catecholaminergic (CA) terminals in the pigeon visual areas. Our results show that the main visual structures are under the influence of CA nuclei of the brain stem. In particular, the pigeon Wulst, like the mammalian visual cortex, is profusely innervated by CA terminals. In fact, dense CA afferents, most likely noradrenergic (NA) terminals, were found in the hyperstriatum intercalatus superior and the nucleus intercalatus hyperstriati accessorii; area which represent the terminal zone of the retino-thalamo-hyperstriatal pathway. These results suggest a possible convergence of NA terminals and visual fibers on common target cells in the Wulst.