Evidence against the presence of NMDA receptors at a central glutamatergic synapse in leeches.
The N-methyl- D-aspartate (NMDA) receptor, able to detect the coincidence of pre- and postsynaptic events, is considered to be the molecular analogue of associative learning. Associative learning is well known in leeches, particularly for reflexive shortening. The neuronal circuits underlying shortening have been documented and include neurons that release glutamate. Is this type of learning in leeches also mediated by NMDA receptors? The synapse between the P sensory neuron and the motoneuron-like AP cell was examined and: (1) NMDA failed to elicit a response in the AP cell, (2) the NMDA receptor antagonist 2-amino-5-phosphopentanoic acid affected synaptic transmission only at high, non-specific levels, and (3) the antagonist for the glycine-binding site 7-chloro-kynurenic acid at 20 microM did not inhibit transmission. Therefore, there are evidently no NMDA receptors at the P to AP synapse, suggesting other mechanisms of associative learning in leeches.
Wu
Eric
E
Neuroscience Program, Department of Physiology and Biophysics, University of Miami School of Medicine, 1600 NW 10th Avenue, Miami, FL 33136, USA. ewu001@fiu.edu
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000818:Animals; D001245:Association Learning / Q000502:physiology; D002490:Central Nervous System / Q000378:metabolism*; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism*; D005998:Glycine / Q000494:pharmacology; D007736:Kynurenic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D007865:Leeches / Q000378:metabolism* / Q000502:physiology; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology; D016202:N-Methylaspartate / Q000494:pharmacology; D009475:Neurons, Afferent / Q000502:physiology; D018009:Receptors, Glycine / Q000037:antagonists & inhibitors; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012018:Reflex / Q000502:physiology; D013569:Synapses / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects
D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D018009:Receptors, Glycine; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D016202:N-Methylaspartate; D015763:2-Amino-5-phosphonovalerate; D007736:Kynurenic Acid; C057013:7-chlorokynurenic acid; D005998:Glycine