Glutamate depresses release by activating non-conventional glutamate receptors at crayfish nerve terminals.
The present study shows that release of glutamate from crayfish nerve terminals is inhibited at low depolarizing current pulses by glutamate, N-methyl-D-aspartate (NMDA) and quisqualate. These agonists elicit inhibitory effects at concentrations as low as 10(-8) M (quisqualate) and 10(-7) M (glutamate and NMDA). The NMDA-mediated inhibition is blocked by (+/-)-2-amino-5-phosphonovaleric acid (APV). The quisqualate-mediated inhibition is blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Both CNQX and APV are needed to block glutamate-mediated inhibition. The inhibition of release is not accompanied by a detectable change in presynaptic membrane conductance at the secondary branch. Using fura-2, Ca2+ accumulation during repetitive stimulation (100 Hz) was monitored in single release boutons. Inhibition of release, elicited by 10(-4) M glutamate, was not associated with a reduction in the accumulation of Ca2+. We show that the glutamate released from a single or a few release boutons during normal activity acts similarly to glutamate added externally, i.e. it inhibits its own release.
Parnas
I
I
Otto Loewi Center for Cellular and Molecular Neurobiology, Hebrew University of Jerusalem, Israel.
Dudel
J
J
Parnas
H
H
Ravin
R
R
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D003400:Astacoidea; D001369:Axons / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000502:physiology; D004553:Electric Conductivity; D004558:Electric Stimulation; D016257:Fura-2; D018698:Glutamic Acid / Q000494:pharmacology*; D009132:Muscles / Q000294:innervation; D016202:N-Methylaspartate / Q000494:pharmacology; D009411:Nerve Endings / Q000187:drug effects / Q000502:physiology*; D010477:Perfusion; D016318:Quisqualic Acid / Q000494:pharmacology; D017470:Receptors, Glutamate / Q000187:drug effects / Q000502:physiology*; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D013997:Time Factors
D017470:Receptors, Glutamate; D018698:Glutamic Acid; D016202:N-Methylaspartate; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate; D016318:Quisqualic Acid; D002118:Calcium; D016257:Fura-2