Postsynaptic M1 and M3 receptors are responsible for the muscarinic enhancement of retrograde endocannabinoid signalling in the hippocampus.
The cholinergic system is crucial for higher brain functions including learning and memory. These functions are mediated primarily by muscarinic acetylcholine receptors (mAChRs) that consist of five subtypes (M(1)-M(5)). A recent study suggested a novel role of acetylcholine as a potent enhancer of endocannabinoid signalling that acts retrogradely from postsynaptic to presynaptic neurons. In the present study, we further investigated the mechanisms of this cholinergic effect on endocannabinoid signalling. We made paired whole-cell recordings from cultured hippocampal neurons, and monitored inhibitory postsynaptic currents (IPSCs). The postsynaptic depolarization induced a transient suppression of IPSCs (DSI), a phenomenon known to involve retrograde signalling by endocannabinoids. The cholinergic agonist carbachol (CCh) markedly enhanced DSI at 0.01-0.3 microM without changing the presynaptic cannabinoid sensitivity. The facilitating effect of CCh on DSI was mimicked by the muscarinic agonist oxotremorine-M, whereas it was eliminated by the muscarinic antagonist atropine. It was also blocked by a non-hydrolizable analogue of GDP (GDP-beta-S) that was applied intracellularly to postsynaptic neurons. The muscarinic enhancement of DSI persisted to a substantial degree in the neurons prepared from M1-knockout and M3-knockout mice, but was virtually eliminated in the neurons from M1/M3-compound-knockout mice. CCh still enhanced DSI significantly under the blockade of postsynatpic K(+) conductance, and did not significantly influence the depolarization-induced Ca(2+) transients. These results indicate that the activation of postsynaptic M1 and M3 receptors facilitates the depolarization-induced release of endocannabinoids.
Ohno-Shosaku
Takako
T
Department of Cellular Neurophysiology, Graduate School of Medical Science, Kanazawa University, 13-1 Takara-machi, Kanazawa 920-8640, Japan.
Matsui
Minoru
M
Fukudome
Yuko
Y
Shosaku
Jumpei
J
Tsubokawa
Hiroshi
H
Taketo
Makoto M
MM
Manabe
Toshiya
T
Kano
Masanobu
M
D000818:Animals; D000831:Animals, Newborn; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D063385:Cannabinoid Receptor Modulators; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D004594:Electrophysiology; D063388:Endocannabinoids; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D005231:Fatty Acids, Unsaturated / Q000378:metabolism*; D005703:Gallamine Triethiodide / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D018721:Muscarinic Agonists / Q000494:pharmacology; D009154:Mutation / Q000235:genetics; D018733:Nicotinic Antagonists / Q000494:pharmacology; D010275:Parasympathetic Nervous System / Q000502:physiology*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects; D051381:Rats; D043643:Receptor, Muscarinic M1; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*
D063385:Cannabinoid Receptor Modulators; D063388:Endocannabinoids; D005231:Fatty Acids, Unsaturated; D018721:Muscarinic Agonists; D018733:Nicotinic Antagonists; D015221:Potassium Channels; D043643:Receptor, Muscarinic M1; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic; D002217:Carbachol; D005703:Gallamine Triethiodide