Activation of muscarinic receptors induces protein synthesis-dependent long-lasting depression in the perirhinal cortex.
There is strong evidence that decrements in neuronal activation in perirhinal cortex when a novel stimulus is repeated provide a neural substrate of visual recognition memory. There is also strong evidence that muscarinic acetylcholine (ACh) receptors are involved in learning and memory. However, the mechanisms underlying neuronal decrements in the perirhinal cortex and the basis of ACh involvement in learning and memory are not understood. In an in vitro preparation of rat perirhinal cortex we now demonstrate that activation of ACh receptors by carbachol (CCh) produces long-lasting depression (LLD) of synaptic transmission that is dependent on muscarinic M1 receptor activation. Crucially, the induction of this form of LLD requires neither N-methyl-D-aspartate receptor activation nor synaptic stimulation. CCh-induced LLD was not blocked by the protein kinase C inhibitors staurosporine or BIM, or by the protein phosphatase inhibitor okadaic acid. However, each of cyclopiazonic acid (an agent that depletes intracellular calcium stores) and anisomycin (an inhibitor of protein synthesis) significantly reduced the magnitude of CCh-induced LLD. These mechanisms triggered by muscarinic receptor activation could play a role in the induction and/or expression of certain forms of activity-dependent long-term depression in perirhinal cortex. An understanding of CCh-induced LLD may thus provide clues to the mechanisms underlying lasting neuronal decrements that occur in the perirhinal cortex and hence for neural substrates of visual recognition memory.
Massey
P V
PV
MRC Centre for Synaptic Plasticity, Department of Anatomy, University of Bristol, University Walk, Bristol BS8 1TD, UK.
Bhabra
G
G
Cho
K
K
Brown
M W
MW
Bashir
Z I
ZI
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology; D018680:Cholinergic Antagonists / Q000494:pharmacology; D013181:Cortical Spreading Depression / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008568:Memory / Q000187:drug effects / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000096:biosynthesis* / Q000187:drug effects; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009924:Organ Culture Techniques; D020534:Parahippocampal Gyrus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
D018679:Cholinergic Agonists; D018680:Cholinergic Antagonists; D004791:Enzyme Inhibitors; D018691:Excitatory Amino Acid Antagonists; D009419:Nerve Tissue Proteins; D011976:Receptors, Muscarinic; D016194:Receptors, N-Methyl-D-Aspartate; D002217:Carbachol; D000109:Acetylcholine; D002118:Calcium