Glutamate as an inhibitory transmitter in the crayfish local circuit

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Not only GABA but also glutamate is revealed to act as an inhibitory neurotransmitter at synaptic interactions between local circuit neurones in the terminal abdominal ganglion that is a centre controlling uropod movements of the crayfish Procambarus clarkii Girard by using electrophysiological, morphological, pharmacological and neurochemical analyzes. Local circuit controlling uropod movements is consisted of ascending intersegmental interneurones, spiking local interneurones and nonspiking local interneurones and sensory information from the mechanosensory afferents innervating hairs on the tailfan is transmitted to the motor neurones innervating uropod muscles via these local circtrit neurones. Double labelling method that is a combination of intracellular staining with Lucifer yellow and immunocytochemical staining against glutamate suggested many motor neurones innervating the uropods and the telson and some spiking local interneurones were glutamatergic. Many local circuit neurones showed inhibitory response and were hyperpolarized their membrane in response to local pressure ejection of both GABA and glutamate and the inhibitory response of the uropod motor neurones to the sensory stimulation was mediated by GABA since membrane hyperpolarization of the motor neurones induced by either sensory stimulation or GABA ejection was unaffected by bath application of picrotoxin (PTX) although the amplitude of membrane hyperpolarization of the motor neurones mediated by glutamate was reversely reduced by PTX. Membrane hyperpolarization of the nonspiking local interneurones was therefore seemed to mediate by both GABA released from the nonspiking local interneurones and glutamate released from spiking local interneurones.