The effect of L-glutamate on the afferent resting activity in the cephalopod statocyst.
The effects of bath application of L-glutamate and of excitatory amino acid agonists and antagonists on the resting activity of afferent crista fibers were studied in isolated preparations of the statocyst of the cuttlefish, Sepia officinalis. L-Glutamate (threshold 10(-5) M) and its agonists quisqualate and kainate (thresholds 10(-6) M) increased the resting activity in a dose-dependent manner. Glutamine (threshold 10(-5) M) was also excitatory, while D-glutamate had no effect. Also, no obvious excitatory effects were seen for NMDA and L-aspartate, nor was any antagonistic effect seen for the selective NMDA-receptor antagonist D-2-amino-5-phosphonovaleric acid (D-AP-5). The spider toxin Argiotoxin636 (threshold 10(-11) M), 2-amino-4-phosphonobutyric acid (AP-4), glutamic acid diethyl ester (GDEE), gamma-D-glutamylaminomethyl-sulfonic acid (GAMS), and kynurenic acid decreased the resting activity and effectively blocked or reversed the effect of L-glutamate and its non-NMDA agonists. Preliminary experiments with statocysts from the squid Sepioteuthis lessoniana and the octopod Octopus bimaculoides gave comparable results. All data show that in cephalopod statocysts L-glutamate, via non-NMDA receptors, has an excitatory effect on the activity of afferent fibers, an effect consistent with its possible function as a hair cell transmitter.
Tu
Y
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Marine Biomedical Institute, University of Texas Medical Branch, Galveston 77555-0863.
Budelmann
B U
BU
D000200:Action Potentials / Q000187:drug effects; D000344:Afferent Pathways / Q000187:drug effects; D000818:Animals; D001224:Aspartic Acid / Q000037:antagonists & inhibitors / Q000494:pharmacology; D049832:Decapodiformes / Q000187:drug effects* / Q000648:ultrastructure; D018691:Excitatory Amino Acid Antagonists; D005260:Female; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D007608:Kainic Acid / Q000037:antagonists & inhibitors / Q000494:pharmacology; D008297:Male; D008974:Mollusca / Q000187:drug effects* / Q000648:ultrastructure; D016202:N-Methylaspartate / Q000037:antagonists & inhibitors / Q000494:pharmacology; D009412:Nerve Fibers / Q000187:drug effects; D049831:Octopodiformes / Q000187:drug effects* / Q000648:ultrastructure; D004856:Postural Balance / Q000187:drug effects*; D016318:Quisqualic Acid / Q000037:antagonists & inhibitors / Q000494:pharmacology; D013045:Species Specificity
D018691:Excitatory Amino Acid Antagonists; D005971:Glutamates; D001224:Aspartic Acid; D018698:Glutamic Acid; D016202:N-Methylaspartate; D016318:Quisqualic Acid; D007608:Kainic Acid