Hippocampal long term memory: effect of the cholinergic system on local protein synthesis.
The present study was aimed at establishing a link between the cholinergic system and the pathway of mTOR and its downstream effector p70S6K, likely actors in long term memory encoding. We performed in vivo behavioral experiments using the step down inhibitory avoidance test (IA) in adult Wistar rats to evaluate memory formation under different conditions, and immunohistochemistry on hippocampal slices to evaluate the level and the time-course of mTOR and p70S6K activation. We also examined the effect of RAPA, inhibitor of mTORC1 formation, and of the acetylcholine (ACh) muscarinic receptor antagonist scopolamine (SCOP) or ACh nicotinic receptor antagonist mecamylamine (MECA) on short and long term memory formation and on the functionality of the mTOR pathway. Acquisition test was performed 30 min after i.c.v. injection of RAPA, a time sufficient for the drug to diffuse to CA1 pyramidal neurons, as demonstrated by MALDI-TOF-TOF imaging. Recall test was performed 1 h, 4 h or 24 h after acquisition. To confirm our results we performed in vitro experiments on live hippocampal slices: we evaluated whether stimulation of the cholinergic system with the cholinergic receptor agonist carbachol (CCh) activated the mTOR pathway and whether the administration of the above-mentioned antagonists together with CCh could revert this activation. We found that (1) mTOR and p70S6K activation in the hippocampus were involved in long term memory formation; (2) RAPA administration caused inhibition of mTOR activation at 1 h and 4 h and of p70S6K activation at 4 h, and long term memory impairment at 24 h after acquisition; (3) scopolamine treatment caused short but not long term memory impairment with an early increase of mTOR/p70S6K activation at 1 h followed by stabilization at longer times; (4) mecamylamine plus scopolamine treatment caused short term memory impairment at 1 h and 4 h and reduced the scopolamine-induced increase of mTOR/p70S6K activation at 1 h and 4 h; (5) mecamylamine plus scopolamine treatment did not impair long term memory formation; (6) in vitro treatment with carbachol activated mTOR and p70S6K and this effect was blocked by scopolamine and mecamylamine. Taken together our data reinforce the idea that distinct molecular mechanisms are at the basis of the two different forms of memory and are in accordance with data presented by other groups that there exist molecular mechanisms that underlie short term memory, others that underlie long term memories, but some mechanisms are involved in both.
Department of Health Sciences, Section of Pharmacology and Clinical Oncology, University of Florence, Viale Pieraccini 6, 50139 Firenze, Italy.
Daniele
D
Lana
Francesca
F
Cerbai
Jacopo
J
Di Russo
Francesca
F
Boscaro
Ambra
A
Giannetti
Polina
P
Petkova-Kirova
Anna Maria
AM
Pugliese
Maria Grazia
MG
Giovannini
D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects* / Q000502:physiology; D006624:Hippocampus / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008464:Mecamylamine / Q000494:pharmacology; D057567:Memory, Long-Term / Q000187:drug effects* / Q000502:physiology; D008570:Memory, Short-Term / Q000187:drug effects / Q000502:physiology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D018733:Nicotinic Antagonists / Q000494:pharmacology; D014176:Protein Biosynthesis / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D011976:Receptors, Muscarinic / Q000378:metabolism*; D011978:Receptors, Nicotinic / Q000378:metabolism*; D012601:Scopolamine / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism
D018727:Muscarinic Antagonists; D018733:Nicotinic Antagonists; D011976:Receptors, Muscarinic; D011978:Receptors, Nicotinic; D008464:Mecamylamine; D012601:Scopolamine; D058570:TOR Serine-Threonine Kinases
ACQ; ACh; Acetylcholine; CCh; IA; Inhibitory avoidance; Long term memory; M; MALDI-TOF-TOF; MECA; Mecamylamine; RAPA; REC; Rapamycin; SCOP; SEM; Scopolamine; aCSF; acetylcholine; acquisition; artificial cerebrospinal fluid; carbachol; mAChR; mTOR; mTORC1; mammalian target of rapamycin; mammalian target of rapamycin complex 1; matrix assited laser desorption ionization-time of flight-time of flight; mean; mecamylamine; muscarinic acetylcholine receptors; nAChR; nicotinic acetylcholine receptors; p70S6K; p70S6Kinase; rapamycin; recall; scopolamine; standard error of the mean; step-down inhibitory avoidance