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Tsotsokou G, Kouri V, Papatheodoropoulos C. α7 nicotinic acetylcholine receptors induce long-term synaptic enhancement in the dorsal but not ventral hippocampus. Synapse 2024; 78:e22285. [PMID: 38287475 DOI: 10.1002/syn.22285] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2023] [Revised: 11/08/2023] [Accepted: 12/04/2023] [Indexed: 01/31/2024]
Abstract
Agents that positively modulate the activity of α7nAChRs are used as cognitive enhancers and for the treatment of hippocampus-dependent functional decline. However, it is not known whether the expression and the effects of α7nAChRs apply to the entire longitudinal axis of the hippocampus equally. Given that cholinergic system-involving hippocampal functions are not equally distributed along the hippocampus, we comparatively examined the expression and the effects of α7nAChRs on excitatory synaptic transmission between the dorsal and the ventral hippocampal slices from adult rats. We found that α7nAChRs are equally expressed in the CA1 field of the two segments of the hippocampus. However, activation of α7nAChRs by their highly selective agonist PNU 282987 induced a gradually developing increase in field excitatory postsynaptic potential only in the dorsal hippocampus. This long-term potentiation was not reversed upon application of nonselective nicotinic receptor antagonist mecamylamine, but the induction of potentiation was prevented by prior blockade of α7nAChRs by their antagonist MG 624. In contrast to the long-term synaptic plasticity, we found that α7nAChRs did not modulate short-term synaptic plasticity in either the dorsal or the ventral hippocampus. These results may have implications for the role that α7nAChRs play in specifically modulating functions that depend on the normal function of the dorsal hippocampus. We propose that hippocampal functions that rely on a direct α7 nAChR-mediated persistent enhancement of glutamatergic synaptic transmission are preferably supported by dorsal but not ventral hippocampal synapses.
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Affiliation(s)
- Giota Tsotsokou
- Department of Medicine, Laboratory of Physiology, University of Patras, Rion, Greece
| | - Vasiliki Kouri
- Department of Medicine, Laboratory of Physiology, University of Patras, Rion, Greece
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Rosa J, de Carvalho Myskiw J, Fiorenza NG, Furini CRG, Sapiras GG, Izquierdo I. Hippocampal cholinergic receptors and the mTOR participation in fear-motivated inhibitory avoidance extinction memory. Behav Brain Res 2023; 437:114129. [PMID: 36179804 DOI: 10.1016/j.bbr.2022.114129] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2022] [Revised: 09/07/2022] [Accepted: 09/24/2022] [Indexed: 10/14/2022]
Abstract
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.
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Affiliation(s)
- Jessica Rosa
- Memory Center, Brain Institute of Rio Grande do Sul, Pontifical Catholic University of Rio Grande do Sul (PUCRS), Ipiranga 6690, Floor 2, 90610-600 Porto Alegre, RS, Brazil; Department of Pharmacology, School of Medicine of Ribeirao Preto, University of Sao Paulo (USP), Bandeirantes 3900, 14049-900 Ribeirao Preto, SP, Brazil.
| | - Jociane de Carvalho Myskiw
- Memory Center, Brain Institute of Rio Grande do Sul, Pontifical Catholic University of Rio Grande do Sul (PUCRS), Ipiranga 6690, Floor 2, 90610-600 Porto Alegre, RS, Brazil; National Institute of Translational Neuroscience (INNT), National Research Council of Brazil, Federal University of Rio de Janeiro, 21941-902 Rio de Janeiro, RJ, Brazil; Department of Biophysics, Institute of Biosciences, Federal University of Rio Grande do Sul (UFRGS), Bento Gonçalves 9500, Building 43422, Room 208 A, 91501-970 Porto Alegre, RS, Brazil
| | - Natalia Gindri Fiorenza
- Memory Center, Brain Institute of Rio Grande do Sul, Pontifical Catholic University of Rio Grande do Sul (PUCRS), Ipiranga 6690, Floor 2, 90610-600 Porto Alegre, RS, Brazil; Oswaldo Cruz Foundation (FIOCRUZ), Branch Ceara, 60760-000 Eusebio, CE, Brazil
| | - Cristiane Regina Guerino Furini
- Memory Center, Brain Institute of Rio Grande do Sul, Pontifical Catholic University of Rio Grande do Sul (PUCRS), Ipiranga 6690, Floor 2, 90610-600 Porto Alegre, RS, Brazil; National Institute of Translational Neuroscience (INNT), National Research Council of Brazil, Federal University of Rio de Janeiro, 21941-902 Rio de Janeiro, RJ, Brazil; Laboratory of Cognition and Memory Neurobiology, Brain Institute, Pontifical Catholic University of Rio Grande do Sul (PUCRS), Ipiranga 6690, 3rd Floor, 90610-000 Porto Alegre, RS, Brazil
| | - Gerson Guilherme Sapiras
- Memory Center, Brain Institute of Rio Grande do Sul, Pontifical Catholic University of Rio Grande do Sul (PUCRS), Ipiranga 6690, Floor 2, 90610-600 Porto Alegre, RS, Brazil; Clinical Hospital of Passo Fundo (HCPF), Tiradentes 295, 99010-260 Passo Fundo, RS, Brazil
| | - Ivan Izquierdo
- Memory Center, Brain Institute of Rio Grande do Sul, Pontifical Catholic University of Rio Grande do Sul (PUCRS), Ipiranga 6690, Floor 2, 90610-600 Porto Alegre, RS, Brazil; National Institute of Translational Neuroscience (INNT), National Research Council of Brazil, Federal University of Rio de Janeiro, 21941-902 Rio de Janeiro, RJ, Brazil
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