Cerebral Cortex 1995; 5:363-375
© Oxford University Press 1995
Feature Article |
Patterns of Connectivity in the Neocortex of the Echidna (Tachyglossus aculeatus)
1Physiology Department, The University of Western Australia Nedlands, Perth, Western Australia, 6009, 2MRC Anatomical Neurophannacology Unit Oxford OX1 3TH, United Kingdom
Correspondence should be addressed to Dr. J. F. Dann, Zoology Department, The University of Western Australia, Nedlands, Perth, Western Australia, 6907
Patchy connections were traced in the visual and auditory cortex of the echidna (Tachyglossus aculeatus). Labeled neurons and clusters of axon collaterals were distributed in regular arrays after the application of a small crystal (
100–300 µm diameter) of the carbocyanine dye Dil (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocart)ocyanine par-chlorate) into the upper cortical layers. In general, the anterograde and retrograde labels were in register, but whereas the anterograde label was distributed throughout all six layers, the retrogradely filled neurons were absent from layer 1 and the highest density of labeled cells was in layers 5 and 6. The cells contained within the patches were all pyramidal or pyramid-like and contained long spines on their dendrites. Therefore, despite their unusual location within the lateral posterior cortex, the internal structure of the echidna visual and auditory cortices resembled that of eutherian mammals in containing a regular columnar array of connections that may represent the corti-cocortical projections.