Morphology of pyramidal neurones in cytochrome oxidase modules of the S-I bill representation of the platypus

The primary somatosensory cortex of the platypus (Ornithorhynchus anatinus) is characterized by a distinct array of functionally specific cytochrome o xidase (CO) modules, forming alternate GO-rich and GO-poor bands. In the cu rrent study, we undertook to establish whether the cellular morphology of l ayer V pyramidal neurones reflects this modular organization, To this end, we injected neurones with Lucifer Yellow in 250 mu m thick, flat-mounted co rtical slices and processed the tissue to reveal a light-stable reaction pr oduct, By aligning blood vessels in serial sections in which we injected in dividual neurones with sections processed for CO, we were able to establish the exact location of injected cells with respect to the pattern of CO ban ds, Pyramidal neurones in the GO-poor bands (which are responsive to both m echano- and electroreceptive stimuli) had basal dendritic fields that were larger than those in the GO-rich bands, The large basal dendritic fields of layer V pyramidal neurones in the GO-poor bands may allow for integration of a greater number of more diverse inputs, thus allowing for averaging of stimuli to improve the signal-to-noise ratio or enhance spatial discriminat ion of peripheral stimuli, In some instances, neurones located within appro ximately 100 mu m of the boundaries of the CO bands had dendritic fields th at appeared to conform to the CO bands, the dendrites preferentially arbori zing within a single band and avoiding the neighbouring band. However, the bias was not absolute, as we observed many examples of cells with dendrites that crossed the boundary between bands. Furthermore, many cells had dendr ites that showed distinct dendritic bias that bore no obvious relationship to the CO boundaries.