The ontogeny of GABA- and glutamate-like immunoreactivity in the embryonic Australian freshwater crayfish, Cherax destructor

The distribution and ontogeny of GABA- and glutamate-like immunoreactivity in embryos of the Australian freshwater crayfish Cherax destructor were investigated over the period from 30% development until hatching. GABA-like immunoreactive cells and fibres appeared fast in the brain at 40-45% development. By 70% development, GABA-like immunoreactive cells were present in almost all ganglia, and GABA-like immunoreactive fibres were distributed extensively throughout the neuropil, commissures and connectives of the central nervous system, and were also found in peripheral nerve roots supplying the appendages and the abdominal musculature. In contrast, glutamate-like immunoreactivity did not appear in the central nervous system until 60-65% development. By the time of hatching, the distribution of glutamate-like immunoreactivity was restricted to discrete regions of neuropil and fibre staining in the thoracic and abdominal nerve cord, the abdominal musculature and the appendages. The precocious establishment of the extensive distribution of GABA-like immunoreactive neurons in the developing crayfish embryo is consistent with the possibility that these neurons play a trophic role in controlling or modulating the development of the nervous system.