Glutamate as a putative neurotransmitter in the mollusc, Lymnaea stagnalis.
Bath-applied glutamate (10-1000 microM) produced excitatory and inhibitory responses on numerous identified neurons of the mollusc Lymnaea stagnalis. Using both in situ and in vitro preparations, glutamate or glutamate agonists produced a depolarization in identified neurons right pedal dorsal 1 and right pedal dorsal 2 and 3. However, attempts to block glutamate-evoked responses with glutamate antagonists were unsuccessful. We examined a potential glutamatergic neuron, visceral dorsal 4. Exogenous application of the peptides (GDPFLRFamide and SDPFLRFamide) could mimic the inhibitory, but not the excitatory effects of visceral dorsal 4 on its postsynaptic cells, implying the presence of a second transmitter. We tested the possibility that glutamate is this second neurotransmitter by using excitatory synapses between visceral dorsal 4 and postsynaptic cells right pedal dorsal 2 and 3, right pedal dorsal 1, visceral F group and right parietal B group neurons. Of all the putative neurotransmitters tested, only glutamate had consistent excitatory effects on these postsynaptic cells. Also, the amplitude of the right pedal dorsal 2 and 3 excitatory postsynaptic potentials was reduced in the presence of N-methyl-D-aspartate and other glutamate agonists, suggesting desensitization of the endogenous transmitter receptor. In conclusion, some identified Lymnaea neurons respond to glutamate via a receptor with novel pharmacological properties. Furthermore, a Lymnaea interneuron may employ glutamate as a transmitter at excitatory synapses.
Nesic
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OB
Department of Medical Physiology, Faculty of Medicine, University of Calgary, Alberta, Canada.
Magoski
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NS
McKenney
K K
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Syed
N I
NI
Lukowiak
K
K
Bulloch
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AG
D000818:Animals; D002478:Cells, Cultured; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology*; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D007608:Kainic Acid / Q000494:pharmacology; D008195:Lymnaea; D008564:Membrane Potentials / Q000187:drug effects; D016202:N-Methylaspartate / Q000494:pharmacology; D009424:Nervous System Physiological Phenomena; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009479:Neuropeptides / Q000494:pharmacology; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D016318:Quisqualic Acid / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D013873:Thionucleotides / Q000494:pharmacology; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology
D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D013873:Thionucleotides; C067840:GDPFLRFamide; D006153:Guanosine Diphosphate; D018698:Glutamic Acid; D016202:N-Methylaspartate; C023427:guanosine 5'-O-(2-thiodiphosphate); D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D016318:Quisqualic Acid; D007608:Kainic Acid