Central complex in the brain of crayfish and its possible homology with that of insects

A small, medial heterolateral neuropil in the brain of crustaceans has long been regarded as the central body of the crustacean brain. Its simplicity and the absence of clear layers within its neuropil have led to the question of its homology with the more complex central body that occupies an approximately equivalent position in the brain of insects. We have labelled neurons in the central body of the Australian freshwater crayfish Cherax destructor by the extracellular application of dextrans and by treating the brain with antibodies to anti-CCAP, anti-locustatachykinin, anti-perisulfakinin, anti-proctolin, anti-dip-allatostatin AI, anti-PEA-head-peptide, anti-serotonin, and anti-rabbit anti-substance P, all of which label neurons in the insect brain. The dextran and immunocytochemical labelling have revealed a neural complex associated with the crayfish central body that is very similar in overall anatomical architecture to the subset of neuropils that are incorporated in the central complex of the insects, and in particular to that of the locust. Similarities between the crayfish and locust central complexes extend to the number and position of the neuropils, the location of the cell body clusters of the neurons that belong to the central complex, the numbers of tracts that link some of the constituent neuropils together, and the form and immunoreactivity of many of the individual neuron classes. These similarities are taken as evidence to support a possible homology between the crustacean central complex and that of the insects.