Hippocampal cholinergic receptors and the mTOR participation in fear-motivated inhibitory avoidance extinction memory

• Published in: Behavioural brain research 2023-02, Vol.437, p.114129-114129, Article 114129
• Main Authors: Rosa, Jessica, de Carvalho Myskiw, Jociane, Fiorenza, Natalia Gindri, Furini, Cristiane Regina Guerino, Sapiras, Gerson Guilherme, Izquierdo, Ivan
• Format: Article
• Language: English
• Subjects: Animals; Avoidance Learning - physiology; Extinction memory; Extinction, Psychological - physiology; Fear - physiology; Hippocampus; Hippocampus - metabolism; Male; Memory - physiology; mTOR; Muscarine - pharmacology; Muscarinic Antagonists - pharmacology; Muscarinic receptors; Nicotine - pharmacology; Nicotinic receptors; Rats; Rats, Wistar; Receptors, Cholinergic - metabolism; Sirolimus - pharmacology; Step-down inhibitory avoidance; TOR Serine-Threonine Kinases - metabolism
• ISSN: 0166-4328; 1872-7549
• DOI: 10.1016/j.bbr.2022.114129

Evidence has demonstrated the hippocampal cholinergic system and the mammalian target of rapamycin (mTOR) participation during the memory formation of aversive events. This study assessed the role of these systems in the hippocampus for the extinction memory process by submitting male Wistar rats to fear-motivated step-down inhibitory avoidance (IA). The post-extinction session administration of the nicotinic and muscarinic cholinergic receptor antagonists, mecamylamine and scopolamine, respectively, both at doses of 2 µg/µl/side, and rapamycin, an mTOR inhibitor (0.02 µg/µl/side), into the CA1 region of the dorsal hippocampus, impaired the IA extinction memory. Furthermore, the nicotinic and muscarinic cholinergic receptor agonists, nicotine and muscarine, respectively, had a dose-dependent effect on the IA extinction memory when administered intra-CA1, immediately after the extinction session. Nicotine (0.6 µg/µl/side) and muscarine (0.02 µg/µl/side), respectively, had no effect, while the higher doses (6 and 2 µg/µl/side, respectively) impaired the IA extinction memory. Interestingly, the co-administration of muscarine at the lower dose blocked the impairment that was induced by rapamycin. This effect was not observed when nicotine at the lower dose was co-administered. These results have demonstrated the participation of the cholinergic receptors and mTOR in the hippocampus for IA extinction, and that the cholinergic agonists had a dose-dependent effect on the IA extinction memory. This study provides insights related to the behavioural aspects and the neurobiological properties underlying the early stage of fear-motivated IA extinction memory consolidation and suggests that there is hippocampal muscarinic receptor participation independent of mTOR in this memory process. •The cholinergic system in the hippocampus is required for IA extinction memory.•Hippocampal mTOR is necessary for IA extinction memory.•Muscarinic receptors might involve an mTOR-independent pathway for IA extinction.•The results bear on the behavioural and neural properties of the IA extinction.