GABA and glutamate-like immunoreactivity at synapses on depressor motorneurones of the leg of the crayfish, Procambarus clarkii

To investigate their synaptic relationships, depressor motorneurones of the crayfish leg were impaled with microelectrodes, intracellularly injected w ith horseradish peroxidase, and prepared for electron microscopy. Post-embe dding immunogold labelling with antibodies against gamma-aminobutyric acid (GABA) or glutamate was carried out either alone or together on the same se ction and allowed the identification of three classes of input synapses: 51 % were immunoreactive for glutamate and contained round agranular vesicles, 31% were immunoreactive for GABA and contained pleomorphic agranular vesic les, and the remainder were immunoreactive for neither and also predominant ly contained pleomorphic agranular vesicles. Output synapses were abundant in some of the motorneurones but were not seen in others, suggesting that m embers of the motor pool differ in their connectivity. (C) 2000 Wiley-Liss, Inc.