• We are sorry, but NCBI web applications do not support your browser and may not function properly. More information
Logo of pnasPNASInfo for AuthorsSubscriptionsAboutThis Article
Proc Natl Acad Sci U S A. Aug 1, 1993; 90(15): 7163–7167.

L-glutamate may be the fast excitatory transmitter of Aplysia sensory neurons.


Although modulation of synaptic transmission between Aplysia mechanosensory and motor neurons has been an important model for processes thought to underlie simple forms of learning and memory, the nature of the fast excitatory transmitter utilized by the sensory neurons has remained obscure. To identify the sensory neuron transmitter, we first examined the detailed properties of the synaptic response evoked in motor neurons cocultured with pleural sensory neurons. The excitatory postsynaptic current had a nonlinear current-voltage relation with a reversal potential between 0 and 10 mV and a plateau region between -40 and -70 mV. When the concentration of Mg2+ in the artificial sea water was lowered to 5 mM, the current-voltage relation of the excitatory postsynaptic current became linear, suggesting that Mg2+ blocks the postsynaptic receptor in a voltage-dependent manner. After screening a variety of small molecules, we found that L-glutamate could mimic the actions of the sensory neuron transmitter: responses to L-glutamate also had a reversal potential between 0 and 10 mV and a nonlinear current-voltage relation that could be made linear by lowering external Mg2+. To demonstrate further similarity of action between L-glutamate and the endogenous transmitter, we utilized four antagonists (kynurenate, 6,7-dinitroquinoxaline-2,3-dione, D-aspartate, and D-glutamate) to block in a dose-dependent manner the actions of L-glutamate and the natural transmitter. We therefore suggest that the sensory neurons use a glutamate-like transmitter and favor L-glutamate itself, because no other naturally occurring amino acid that we have studied has had similar actions. As the postsynaptic receptor for the sensory neuron transmitter is weakly blocked in a voltage-dependent manner by Mg2+, the excitatory receptors innervated by the Aplysia sensory neuron may represent a distant precursor of the vertebrate N-methyl-D-aspartate receptor.

Full text

Full text is available as a scanned copy of the original print version. Get a printable copy (PDF file) of the complete article (884K), or click on a page image below to browse page by page. Links to PubMed are also available for Selected References.

Selected References

These references are in PubMed. This may not be the complete list of references from this article.
  • Castellucci VF, Kandel ER. A quantal analysis of the synaptic depression underlying habituation of the gill-withdrawal reflex in Aplysia. Proc Natl Acad Sci U S A. 1974 Dec;71(12):5004–5008. [PMC free article] [PubMed]
  • Castellucci V, Kandel ER. Presynaptic facilitation as a mechanism for behavioral sensitization in Aplysia. Science. 1976 Dec 10;194(4270):1176–1178. [PubMed]
  • Watkins JC, Evans RH. Excitatory amino acid transmitters. Annu Rev Pharmacol Toxicol. 1981;21:165–204. [PubMed]
  • Collingridge GL, Kehl SJ, McLennan H. Excitatory amino acids in synaptic transmission in the Schaffer collateral-commissural pathway of the rat hippocampus. J Physiol. 1983 Jan;334:33–46. [PMC free article] [PubMed]
  • Dale N, Kandel ER. Facilitatory and inhibitory transmitters modulate spontaneous transmitter release at cultured Aplysia sensorimotor synapses. J Physiol. 1990 Feb;421:203–222. [PMC free article] [PubMed]
  • Nowak L, Bregestovski P, Ascher P, Herbet A, Prochiantz A. Magnesium gates glutamate-activated channels in mouse central neurones. Nature. 1984 Feb 2;307(5950):462–465. [PubMed]
  • Mayer ML, Westbrook GL, Guthrie PB. Voltage-dependent block by Mg2+ of NMDA responses in spinal cord neurones. Nature. 1984 May 17;309(5965):261–263. [PubMed]
  • Szczepaniak AC, Cottrell GA. Biphasic action of glutamic acid and synpatic inhibition in an identified serotonin-containing neurone. Nat New Biol. 1973 Jan 10;241(106):62–64. [PubMed]
  • Yarowsky PJ, Carpenter DO. Aspartate: distinct receptors on Aplysia neurons. Science. 1976 May 21;192(4241):807–809. [PubMed]
  • Pfeiffer-Linn C, Glantz RM. An arthropod NMDA receptor. Synapse. 1991 Sep;9(1):35–42. [PubMed]

Articles from Proceedings of the National Academy of Sciences of the United States of America are provided here courtesy of National Academy of Sciences


Related citations in PubMed

See reviews...See all...

Cited by other articles in PMC

See all...


Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...