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Abstract Background Development of neurodegeneration in older people has been associated with microglial cell activation triggered by systemic infection. We hypothesize that α7 nicotinic acetylcholine receptor (α7nAChR) plays an important role in regulation of this process. Methods 8- to 10-week-old male wild-type (WT) and α7nAChR knock-out (α7nAChR −/−) mice were intraperitoneally inoculated with live Escherichia (E.) coli or saline. After inoculation, all mice were treated with ceftriaxone (an antimicrobial drug) at 12 and 24 h and killed at 2 or 3 days. The microglial response was characterized by immunohistochemical staining with an ionized calcium-binding adaptor molecule 1 (Iba-1) antibody and flow cytometry. To quantify inflammatory response, mRNA expression of pro- and anti-inflammatory mediators was measured in brain and spleen. Results We observed no differences in Iba-1 positive cell number or morphology and flow cytometry (CD11b, CD45 and CD14) of microglial cells between WT and α7nAChR −/− mice after systemic infection. Infected α7nAChR −/− mice showed significantly higher mRNA expression in brain for tumor necrosis factor alpha (TNF-α) at day 2 and 3, interleukin 6 (IL-6) at day 2 and monocyte chemotactic protein 1 (MCP-1) and suppressor of cytokine signaling 1 (SOCS1) at day 3, there was significantly lower mRNA expression in brain for mitogen-activated protein kinase 1 (MAPK1) at day 2 and 3, high-mobility group 1 (HMGB-1) and CD11b at day 2, and deubiquitinase protein A20 (A20) at day 3 compared to infected WT mice. Interpretation Loss of function of α7nAChR during systemic infection led to an increased expression of TNF-α and IL-6 in brain after systemic infection with E. coli, but not to distinct differences in microglial cell number or morphological activation of microglia.

Background: Development of neurodegeneration in older people has been associated with microglial cell activation triggered by systemic infection. We hypothesize that α7 nicotinic acetylcholine receptor (α7nAChR) plays an important role in regulation of this process.Methods: 8- to 10-week-old male wild-type (WT) and α7nAChR knock-out (α7nAChR-/-) mice were intraperitoneally inoculated with live Escherichia (E.) coli or saline. After inoculation, all mice were treated with ceftriaxone (an antimicrobial drug) at 12 and 24 h and killed at 2 or 3 days. The microglial response was characterized by immunohistochemical staining with an ionized calcium-binding adaptor molecule 1 (Iba-1) antibody and flow cytometry. To quantify inflammatory response, mRNA expression of pro- and anti-inflammatory mediators was measured in brain and spleen.Results: We observed no differences in Iba-1 positive cell number or morphology and flow cytometry (CD11b, CD45 and CD14) of microglial cells between WT and α7nAChR-/- mice after systemic infection. Infected α7nAChR-/- mice showed significantly higher mRNA expression in brain for tumor necrosis factor alpha (TNF-α) at day 2 and 3, interleukin 6 (IL-6) at day 2 and monocyte chemotactic protein 1 (MCP-1) and suppressor of cytokine signaling 1 (SOCS1) at day 3, there was significantly lower mRNA expression in brain for mitogen-activated protein kinase 1 (MAPK1) at day 2 and 3, high-mobility group 1 (HMGB-1) and CD11b at day 2, and deubiquitinase protein A20 (A20) at day 3 compared to infected WT mice.Interpretation: Loss of function of α7nAChR during systemic infection led to an increased expression of TNF-α and IL-6 in brain after systemic infection with E. coli, but not to distinct differences in microglial cell number or morphological activation of microglia. [ABSTRACT FROM AUTHOR]

• Identification of a cholinergic nerve projecting to the spleen. • Identification of a T cell-independent anti-inflammatory pathway in the spleen. • Inhibition of inflammation by apical nerve relies on b2-ARs and a7-AchRs signaling. • Collagen-induced arthritis is inhibited by apical splenic nerve electrostimulation. The autonomic nervous system innervates all lymphoid tissues including the spleen therefore providing a link between the central nervous system and the immune system. The only known mechanism of neural inhibition of inflammation in the spleen relies on the production of norepinephrine by splenic catecholaminergic fibers which binds to β2-adrenergic receptors (β 2-ARs) of CD4+ T cells. These CD4+ T cells trigger the release of acetylcholine that inhibits the secretion of inflammatory cytokines by macrophages through α7 nicotinic acetylcholine receptor (α7nAchRs) signaling. While the vagal anti-inflammatory pathway has been extensively studied in rodents, it remains to be determined whether it coexists with other neural pathways. Here, we have found that three nerve branches project to the spleen in mice. While two of these nerves are associated with an artery and contain catecholaminergic fibers, the third is located at the apex of the spleen and contain both catecholaminergic and cholinergic fibers. We found that electrical stimulation of the apical nerve, but not the arterial nerves, inhibited inflammation independently of lymphocytes. In striking contrast to the anti-inflammatory pathway mechanism described so far, we also found that the inhibition of inflammation by apical nerve electrical stimulation relied on signaling by both β 2-ARs and α7nAchRs in myeloid cells, with these two signaling pathways acting in parallel. Most importantly, apical splenic nerve electrical stimulation mitigated clinical symptoms in a mouse model of rheumatoid arthritis further providing the proof-of-concept that such an approach could be beneficial in patients with Immune-mediated inflammatory diseases. [ABSTRACT FROM AUTHOR]

The alpha7 (α7) nicotinic acetylcholine receptor is a therapeutic target for cognitive disorders. Here we describe 3-(3,4-difluorophenyl)-N-(1-(6-(4-(pyridin-2-yl)piperazin-1-yl)pyrazin-2-yl)ethyl)propanamide (B-973), a novel piperazine-containing molecule that acts as a positive allosteric modulator of the α7 receptor. We characterize the action of B-973 on the α7 receptor using electrophysiology and radioligand binding. At 0.1 mM acetylcholine, 1 μM B-973 potentiated peak acetylcholine-induced currents 6-fold relative to maximal acetylcholine (3 mM) and slowed channel desensitization, resulting in a 6900-fold increase in charge transfer. The EC 50 of B-973 was approximately 0.3 μM at acetylcholine concentrations ranging from 0.03 to 3 mM. At a concentration of 1 μM, B-973 shifted the acetylcholine EC 50 of peak currents from 0.30 mM in control to 0.007 mM. B-973 slowed channel deactivation upon acetylcholine removal (τ=50 s) and increased the affinity of the α7 agonist [ 3 H]A-585539. In the absence of exogenously added acetylcholine, application of B-973 at concentrations >1 μM induced large methyllycaconitine-sensitive currents, suggesting B-973 can function as an Ago-PAM at high concentrations. B-973 will be a useful probe for investigating the biological consequences of increasing α7 receptor activity through allosteric modulation. [ABSTRACT FROM AUTHOR]

In yeast two-hybrid screening, protein 4.1N, a scaffolding protein, was identified as a binding partner of the α7 ACh (acetylcholine) receptor. For rat hippocampal slices, the linoleic acid derivative DCP-LA {8-[2-(2-pentyl-cyclopropylmethyl)- cyclopropyl]-octanoic acid} increased the association of the α7 ACh receptor with 4.1N, and the effect was inhibited by GF109203X, an inhibitor of PKC (protein kinase C), although DCP-LA did not induce PKC phosphorylation of 4.1N. For PC-12 cells, the presence of the α7ACh receptor in the plasma membrane fraction was significantly suppressed by knocking down 4.1N. DCP-LA increased the presence of the α7 ACh receptor in the plasma membrane fraction, and the effect was still inhibited by knocking down 4.1N. In the monitoring of α7 ACh receptor mobilization, DCP-LA enhanced signal intensities for the α7 ACh receptor at the membrane surface in PC-12 cells, which was clearly prevented by knocking down 4.1N. Taken together, the results of the present study show that 4.1N interacts with the α7 ACh receptor and participates in the receptor tethering to the plasma membrane. The results also indicate that DCP-LA increases membrane surface localization of the α7 ACh receptor in a 4.1N-dependent manner under the control of PKC, but without phosphorylating 4.1N. [ABSTRACT FROM AUTHOR]

Abstract: In the assay of glutamate and γ-aminobutyric acid (GABA) with a high-performance liquid chromatography, spontaneous release of glutamate and GABA from rat hippocampal slices was significantly enhanced by mecamylamine, an inhibitor of non-α7 ACh receptors, or α-bungarotoxin, an inhibitor of α7 ACh receptors in the absence of tetrodotoxin (TTX), but not in the presence of TTX. Nicotine significantly enhanced glutamate and GABA release in the absence of TTX, that is abolished by mecamylamine or α-bungarotoxin, while it had no effect on the release in the presence of TTX. In the recording of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor-mediated excitatory postsynaptic currents (AMPA-EPSCs) and GABAA receptor-mediated inhibitory postsynaptic currents (GABAA-IPSCs) from CA1 pyramidal neurons of rat hippocampal slices, nicotine did not affect the rate and amplitude of AMPA-EPSCs and AMPA-miniature EPSCs. In contrast, nicotine significantly increased the rate of GABAA-IPSCs, without affecting the amplitude, but such effect was not obtained with GABAA-miniature IPSCs. The collective results suggest that α7 and non-α7 ACh receptors expressed in the hippocampus, activated under the basal conditions, inhibit release of glutamate and GABA controlled through multi-synaptic relays, but that otherwise, those receptors, highly activated by nicotine, stimulate both the release, with a part of GABA released from interneurons transmitting to CA1 pyramidal neurons. Furthermore, the results also suggest that α7 and non-α7 ACh receptors do not have potency sufficiently to modulate glutamate and GABA release controlled by single synapses. [Copyright &y& Elsevier]

Nicotinic acetylcholine (ACh) receptors, such as α7, α3β4 and α4β2 receptors in the hippocampus, are suggested to modulate neurotransmitter release. 8-[2-(2-Pentyl-cyclopropylmethyl)-cyclopropyl]-octanoic acid (DCP-LA) (100 n m), a linoleic acid derivative, potentiated responses of α7, α3β4 and α4β2 ACh receptors expressed in Xenopus oocytes that are blocked by 3-(1-[dimethylaminopropyl] indol-3-yl)-4-[indol-3-yl] maleimide (GF109203X), a selective inhibitor of protein kinase C (PKC), except for α3β4 ACh receptors. DCP-LA enhanced the nicotine-triggered release of GABA from rat hippocampal slices in the presence of tetrodotoxin in a bell-shaped dose-dependent manner at concentrations ranging from 10 n m to 10 µ m, although DCP-LA by itself had no effect on GABA release. The DCP-LA action was inhibited by GF109203X or α-bungarotoxin, an inhibitor of α7 ACh receptors, but not by mecamylamine or dihydro-β-erithroidine, an inhibitor of α3β4 and α4β2 ACh receptors. A similar effect on GABA release was obtained with 12- O-tetradecanoylphorbol 13-acetate, a PKC activator. DCP-LA (100 n m) also enhanced GABA release triggered by choline, an agonist of α7 ACh receptors, but not 3-[2(s)-azetidinylmethoxy] pyridine, an agonist of α4β2 ACh receptors. In addition, DCP-LA (100 n m) increased the rate of nicotine-triggered GABAA receptor-mediated miniature inhibitory post-synaptic currents, monitored from CA1 pyramidal neurons of rat hippocampal slices, and the effect was also inhibited by GF109203X or α-bungarotoxin but not by mecamylamine. Thus, the results of the present study indicate that DCP-LA stimulates GABA release by enhancing activity of pre-synaptic α7 ACh receptors present on the GABAergic terminals of interneurons that transmit to CA1 pyramidal neurons via a PKC pathway. [ABSTRACT FROM AUTHOR]

Abstract: The present study aimed at understanding the effect of FR236924, a newly synthesized linoleic acid derivative with cyclopropane rings instead of cis-double bonds, on hippocampal synaptic transmission in both the in vitro and in vivo systems. FR236924 increased the rate of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor-mediated miniature excitatory postsynaptic currents, without affecting the amplitude, triggered by nicotine in CA1 pyramidal neurons of rat hippocampal slices, that is inhibited by GF109203X, a selective protein kinase C (PKC) inhibitor or α-bungarotoxin, an inhibitor of α7 acetylcholine (ACh) receptors. FR236924 stimulated glutamate release from rat hippocampal slices and in the hippocampus of freely behaving rats, and the effect was also inhibited by GF109203X or α-bungarotoxin. FR236924 induced a transient huge potentiation followed by a long-lasting potentiation in the slope of field excitatory postsynaptic potentials recorded from the CA1 region of rat hippocampal slices, and the latter effect was blocked by GF109203X or α-bungarotoxin. Likewise, the compound persistently facilitated hippocampal synaptic transmission in the CA1 region of the intact rat hippocampus. It is concluded from these results that FR236924 stimulates glutamate release by functionally targeting presynaptic α7 ACh receptors on the glutamatergic terminals under the influence of PKC, responsible for the facilitatory action on hippocampal synaptic transmission. This may provide evidence for a link between cis-unsaturated free fatty acids and presynaptic α7 ACh receptors in hippocampal synaptic plasticity. [Copyright &y& Elsevier]