Two forms of long-term depression in a polysynaptic pathway in the leech CNS: one NMDA receptor-dependent and the other cannabinoid-dependent.
Although long-term depression (LTD) is a well-studied form of synaptic plasticity, it is clear that multiple cellular mechanisms are involved in its induction. In the leech, LTD is observed in a polysynaptic connection between touch mechanosensory neurons (T cells) and the S interneuron following low frequency stimulation. LTD elicited by 450 s low frequency stimulation was blocked by N-methyl-D-aspartic acid (NMDA) receptor antagonists. However, LTD elicited by 900 s low frequency stimulation was insensitive to NMDA receptor antagonists and was instead dependent on cannabinoid signaling. This LTD was blocked by both a cannabinoid receptor antagonist and by inhibition of diacylglycerol lipase, which is necessary for the synthesis of the cannabinoid transmitter 2-arachidonyl glycerol (2-AG). Bath application of 2-AG or the cannabinoid receptor agonist CP55 940 also induced LTD at this synapse. These results indicate that two forms of LTD coexist at the leech T-to-S polysynaptic pathway: one that is NMDA receptor-dependent and another that is cannabinoid-dependent and that activation of either form of LTD is dependent on the level of activity in this circuit.
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Qin
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Division of Basic Biomedical Sciences, Sanford School of Medicine at the University of South Dakota, Vermillion, SD 57069, USA.
Burrell
Brian D
BD
D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism; D002186:Cannabinoids / Q000378:metabolism*; D002490:Central Nervous System / Q000187:drug effects / Q000378:metabolism*; D004558:Electric Stimulation; D063388:Endocannabinoids; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials; D005989:Glycerides / Q000378:metabolism; D007865:Leeches / Q000187:drug effects / Q000378:metabolism*; D008071:Lipoprotein Lipase / Q000037:antagonists & inhibitors / Q000378:metabolism; D036881:Long-Term Synaptic Depression / Q000187:drug effects; D040542:Mechanotransduction, Cellular; D009434:Neural Pathways / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D043882:Receptors, Cannabinoid / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects
D001095:Arachidonic Acids; D002186:Cannabinoids; D063388:Endocannabinoids; D004791:Enzyme Inhibitors; D018691:Excitatory Amino Acid Antagonists; D005989:Glycerides; D043882:Receptors, Cannabinoid; D016194:Receptors, N-Methyl-D-Aspartate; C094503:glyceryl 2-arachidonate; D008071:Lipoprotein Lipase