title: Muscarinic acetylcholine receptor activation blocks long-term potentiation at cerebellar parallel fiber-Purkinje cell synapses via cannabinoid signaling.
abstract: Muscarinic acetylcholine receptors (mAChRs) are known to modulate synaptic plasticity in various brain areas. A signaling pathway triggered by mAChR activation is the production and release of endocannabinoids that bind to type 1 cannabinoid receptors (CB1R) located on synaptic terminals. Using whole-cell patch-clamp recordings from rat cerebellar slices, we have demonstrated that the muscarinic agonist oxotremorine-m (oxo-m) blocks the induction of presynaptic long-term potentiation (LTP) at parallel fiber (PF)-Purkinje cell synapses in a CB1R-dependent manner. Under control conditions, LTP was induced by delivering 120 PF stimuli at 8 Hz. In contrast, no LTP was observed when oxo-m was present during tetanization. PF-LTP was restored when the CB1R antagonist N-1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide (AM251) was coapplied with oxo-m. Furthermore, the suppressive effect of oxo-m on PF-LTP was abrogated by the GDP analog GDP-β-S (applied intracellularly), the phospholipase C inhibitor U-73122, and the diacylglycerol lipase inhibitor tetrahydrolipstatin (THL), suggesting that cannabinoid synthesis results from the activation of Gq-coupled mAChRs present on Purkinje cells. The oxo-m-mediated suppression of LTP was also prevented in the presence of the M3 receptor antagonist DAU 5884, and was absent in M1/M3 receptor double-KO mice, identifying M3 receptors as primary oxo-m targets. Our findings allow for the possibility that cholinergic signaling in the cerebellum--which may result from long-term depression (LTD)-related disinhibition of cholinergic neurons in the vestibular nuclei--suppresses presynaptic LTP to prevent an up-regulation of transmitter release that opposes the reduction of postsynaptic responsiveness. This modulatory capacity of mAChR signaling could promote the functional penetrance of LTD.
authors.affiliation: Department of Neurobiology, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Rinaldo
authors.forename: Christian
authors.initials: C
authors.lastname: Hansel
mesh_terms: D000818:Animals; D002186:Cannabinoids / Q000737:chemistry* / Q000494:pharmacology; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D017774:Long-Term Potentiation / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D018721:Muscarinic Agonists / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D010095:Oxotremorine / Q000031:analogs & derivatives / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011689:Purkinje Cells / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043884:Receptor, Cannabinoid, CB1 / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics; D013569:Synapses / Q000187:drug effects / Q000502:physiology*
chemical_list: D002186:Cannabinoids; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D043884:Receptor, Cannabinoid, CB1; D011976:Receptors, Muscarinic; D010095:Oxotremorine; C042743:oxotremorine M
keywords: learning; retrograde signaling; vestibulocerebellum