Somatostatin and neuropeptide Y are almost exclusively found in the same neurons in the telencephalon of turtles.

In mammals, somatostatin and neuropeptide Y (NPY) are largely found in the same neurons of the telencephalon. To determine if this is a phylogenetically ancient feature of telencephalic organization, the brain of red-eared turtles was examined using immunofluorescence double-labeling procedures. The results showed that somatostatin and NPY are found almost exclusively in the same neurons in the telencephalon of turtles, but these neuropeptides rarely co-occur in neurons outside the telencephalon. Thus, the extensive co-occurrence of NPY and somatostatin appears to be a feature of telencephalic organization that was present in the reptilian common ancestors of mammals and modern reptiles.