A normally laminated afferent projection to an abnormally laminated cortex: some olfactory connections in the reeler mouse.

The relative positions of pyramidal and polymorphic cell classes are inverted in the central olfactory cortical structures of the reeler mutant mouse. Each cell class is generated at the normal embryonic time. The polymorphic cells of the mutant, like those of the normal, are generated between E11-E13. The pyramidal cells are formed between E11-E16 in both. Despite the anomalous positions of their somata deep in the cortex the apical dendrites of many pyramidal cells reach and ramify at a superficial cortical level subjacent to the lateral olfactory tract. The main and accessory olfactory bulbs are cytoarchitectonically normal in the mutant and project normally upon the anterior olfactory nucleus, the olfactory tubercle, the hippocampal rudiment, the piriform cortex, the amygdaloid region and the entorhinal cortex. As in the normal animal the axons transverse layer Ialpha, and their terminals are concentrated in the immediately subjacent laminar zone. The rostrally directed cortic-cortical association system of the piriform cortex projects upon the anterior olfactory nucleus in the mutant just as in the normal with a relative concentration of terminals in a lamina subjacent and complementary to the zone of termination afferent systems in the abnormally laminated olfactory cortex of the mutant syggests that, in this system at least, the developmental mechanisms which determine relative position of neuron somata and those which govern axon trajectories and the distribution of axon terminals are largely independent.