Kouvaros S, Papatheodoropoulos C
Laboratory of Physiology, Department of Medicine, School of Health Sciences, University of Patras, 26504 Rion, Greece.
Laboratory of Physiology, Department of Medicine, School of Health Sciences, University of Patras, 26504 Rion, Greece.
Neuroscience. 2016 Mar 11;317:47-64. doi: 10.1016/j.neuroscience.2015.12.059. Epub 2016 Jan 5.
Recent research points to diversification in the local neuronal circuitry between dorsal (DH) and ventral (VH) hippocampus that may be involved in the large-scale functional segregation along the long axis of the hippocampus. Here, using CA1 field recordings from rat hippocampal slices, we show that activation of N-methyl-d-aspartate receptors (NMDARs) reduced excitatory transmission more in VH than in DH, with an adenosine A1 receptor-independent mechanism, and reduced inhibition and enhanced postsynaptic excitability only in DH. Strikingly, co-activation of metabotropic glutamate receptor-5 (mGluR5) with NMDAR, by CHPG and NMDA respectively, strongly potentiated the effects of NMDAR in DH but had not any potentiating effect in VH. Furthermore, the synergistic actions in DH were occluded by blockade of adenosine A2A receptors (A2ARs) by their antagonist ZM 241385 demonstrating a tonic action of these receptors in DH. Exogenous activation of A2ARs by 4-[2-[[6-amino-9-(N-ethyl-β-D-ribofuranuronamidosyl)-9H-purin-2-yl]amino]ethyl]benzenepropanoic acid hydrochloride (CGS 21680) did not change the effects of mGluR5-NMDAR co-activation in either hippocampal pole. Importantly, blockade of cannabinoid CB1 receptors (CB1Rs) by their antagonist 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-4-morpholinyl-1H-pyrazole-3-carboxamide (AM 281) restricted the synergistic actions of mGluR5-NMDARs on excitatory synaptic transmission and postsynaptic excitability and abolished their effect on inhibition. Furthermore, AM 281 increased the excitatory transmission only in DH indicating that CB1Rs were tonically active in DH but not VH. Removing the magnesium ions from the perfusion medium neither stimulated the interaction between mGluR5 and NMDAR in VH nor augmented the synergy of the two receptors in DH. These findings show that the NMDAR-dependent modulation of fundamental parameters of the local neuronal network, by mGluR5, A2AR and CB1R, markedly differs between DH and VH. We propose that the higher modulatory role of A2AR and mGluR5, in combination with the role of CB1Rs, provide DH with higher functional flexibility of its NMDARs, compared with VH.
近期研究表明,背侧(DH)和腹侧(VH)海马体之间的局部神经元回路存在差异,这可能与海马体长轴上的大规模功能分离有关。在此,我们利用大鼠海马体切片的CA1区记录,发现N-甲基-D-天冬氨酸受体(NMDARs)激活后,通过一种不依赖腺苷A1受体的机制,在VH中比在DH中更能降低兴奋性传递,且仅在DH中降低抑制作用并增强突触后兴奋性。令人惊讶的是,分别用CHPG和NMDA使代谢型谷氨酸受体5(mGluR5)与NMDAR共同激活时,在DH中强烈增强了NMDAR的作用,但在VH中没有任何增强作用。此外,腺苷A2A受体(A2ARs)拮抗剂ZM 241385阻断A2ARs后,DH中的协同作用被消除,表明这些受体在DH中具有紧张性作用。用盐酸4-[2-[[[6-氨基-9-(N-乙基-β-D-呋喃核糖酰胺基)-9H-嘌呤-2-基]氨基]乙基]苯丙酸(CGS 21680)外源性激活A2ARs,在两个海马极中均未改变mGluR5-NMDAR共同激活的作用。重要的是,其拮抗剂1-(2,4-二氯苯基)-5-(4-碘苯基)-4-甲基-N-4-吗啉基-1H-吡唑-3-甲酰胺(AM 281)阻断大麻素CB1受体(CB1Rs)后,限制了mGluR5-NMDARs对兴奋性突触传递和突触后兴奋性的协同作用,并消除了它们对抑制作用的影响。此外,AM 281仅在DH中增加兴奋性传递,表明CB1Rs在DH中具有紧张性活性,而在VH中没有。从灌流介质中去除镁离子既未刺激VH中mGluR5与NMDAR之间的相互作用,也未增强DH中这两种受体的协同作用。这些发现表明NMDAR依赖的局部神经元网络基本参数的调节,在mGluR5、A2AR和CB1R的作用下,在DH和VH之间存在显著差异。我们认为,与VH相比,A2AR和mGluR5更高的调节作用,与CB1Rs的作用相结合,为DH的NMDARs提供了更高的功能灵活性。