Activity of cytochrome oxidase in centers of tectofugal and thalamofugal tracts of the visual system of pigeon <Emphasis Type="Italic">Columbia livia</Emphasis>

By using a histochemical method of determination of activity of cytochrome oxidase (CO), the level of metabolic activity in pigeons has been shown to be higher in centers of the tectofugal visual tract (pretectal nuclei: Pr, SP, SP/IPS, thalamic nucleus Rot, end telencephalic entopallidum) than in centers of the thalamofugal visual tract (GLd of the thalamus, visual area of the hyperpallium Wulst). These data agree with the concept of dominating role of the tectofugal visual tract in organization of the bird everyday behavior. The high CO activity is also characteristic of the mesencephalic structures (EM, isthmic nuclei: IMc, IPc, and SLu) modulating transduction of visual information in tectum, Rot, and GLd. Similar differences in the metabolic activities between two visual system tracts were earlier shown in reptiles, which indicates the evolutionary conservatism of the tectofugal visual tract among the sauropside amniotes. However, in pigeons the level of the CO activity in some GLd nuclei approaches that in Rot, which allows us to suggest an increase in birds of role of the thalamofugal tract in processing of information necessary for performance of complex visual functions.