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FASEB J
2022 Mar 01;363:e22203. doi: 10.1096/fj.202101815R.
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Lipid mediator n-3 docosapentaenoic acid-derived protectin D1 enhances synaptic inhibition of hippocampal principal neurons by interaction with a G-protein-coupled receptor.
Mikroulis A
,
Ledri M
,
Ruffolo G
,
Palma E
,
Sperk G
,
Dalli J
,
Vezzani A
,
Kokaia M
.
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Epilepsy is a severe neurological disease manifested by spontaneous recurrent seizures due to abnormal hyper-synchronization of neuronal activity. Epilepsy affects about 1% of the population and up to 40% of patients experience seizures that are resistant to currently available drugs, thus highlighting an urgent need for novel treatments. In this regard, anti-inflammatory drugs emerged as potential therapeutic candidates. In particular, specific molecules apt to resolve the neuroinflammatory response occurring in acquired epilepsies have been proven to counteract seizures in experimental models, and humans. One candidate investigational molecule has been recently identified as the lipid mediator n-3 docosapentaenoic acid-derived protectin D1 (PD1n-3DPA ) which significantly reduced seizures, cell loss, and cognitive deficit in a mouse model of acquired epilepsy. However, the mechanisms that mediate the PD1n-3DPA effect remain elusive. We here addressed whether PD1n-3DPA has direct effects on neuronal activity independent of its anti-inflammatory action. We incubated, therefore, hippocampal slices with PD1n-3DPA and investigated its effect on excitatory and inhibitory synaptic inputs to the CA1 pyramidal neurons. We demonstrate that inhibitory drive onto the perisomatic region of the pyramidal neurons is increased by PD1n-3DPA , and this effect is mediated by pertussis toxin-sensitive G-protein coupled receptors. Our data indicate that PD1n-3DPA acts directly on inhibitory transmission, most likely at the presynaptic site of inhibitory synapses as also supported by Xenopus oocytes and immunohistochemical experiments. Thus, in addition to its anti-inflammatory effects, PD1n-3DPA anti-seizure and neuroprotective effects may be mediated by its direct action on neuronal excitability by modulating their synaptic inputs.
FIGURE 1. Images illustrating hippocampal slicing. (A and B) Approximate slicing location, according to the Allen Mouse Brain Atlas. Squares in B indicate the area of the slices kept. Images generated with the Allen Institute Brain Explorer 2 software, using the Allen Mouse Brain Atlas. (C) Example of slice section after electrophysiology (DAPI staining in blue)
FIGURE 2. PD1n‐3DPA incubation increases the frequency and amplitude of IPSCs recorded in CA1 pyramidal neurons. (A) sIPSC interevent interval (IEI) presented as cumulative probability curves (Kolmogorov‐Smirnov test D = .098, p < .01) and cell‐based averages (insert) of sIPSC frequency. (B) mIPSCs, same presentation as (A), IEI (Kolmogorov‐Smirnov test D = .102, p < .01) and average frequencies. (C and D) sIPSC and mIPSC amplitudes, respectively, presented as cumulative probability curves (Kolmogorov‐Smirnov test sIPSCS: D = .272, p < .01; mIPSCs: D = .181, p < .01) and cell‐based averages (insert). (E and F) Rise‐times of sIPSCs and mIPSCs, respectively, presented as cumulative probability curves (Kolmogorov‐Smirnov test sIPSCS: D = .029, p > .01; mIPSCs: D = .101, p < .01) and cell‐based averages (inserts). Arrows denote 2 distinct distribution peaks around 1 and 3 ms. Insets display the median and range of cell averages. * Mann‐Whitney p < .05 for cell averages. (G) representative traces of sIPSCs with and without PD1n‐3DPA. Highlighted segment (green) shows 10‐fold time‐stretched recording. (H) magnification of amplitude‐normalized averaged fast (black) and slow (grey) rise‐time events in cells from control slices (n = 125 sIPSCs per group)
FIGURE 3. Effect of PD1n‐3DPA incubation on EPSCs recorded in CA1 pyramidal neurons. (A and B) sEPSCs and mEPSCs, respectively, are presented as cumulative probability curves for IEI (sEPSCs: Kolmogorov‐Smirnov test D = .014, p < .01; mEPSCs: D = .045, p < .01) and cell‐based averages for sEPSC frequencies (inserts). (C and D) sEPSCs and mEPSCs, respectively, are presented as cumulative probability curves (sEPSCs: Kolmogorov‐Smirnov test D = .045, p < .01; mEPSCs: D = .089, p < .01) for amplitudes and cell‐based averages (inserts). (E and F) sEPSC and mEPSC rise‐times, respectively, are presented as cumulative probability curves (sEPSCs: Kolmogorov‐Smirnov test D = .028, p > .01; mEPSCs: D = .062, p < .01) and cell‐based averages. Insets display the median and range of cell average. Arrows denote much less pronounced peaks as compared to those in Figure 1. (G) representative traces with and without PD1n‐3DPA. Highlighted segment (green) shows 10‐fold time‐stretched recording. (H) magnification of amplitude‐normalized averaged fast (black) and slow (grey) rise‐time events in cells from control slices (n = 42 sEPSCs per group)
FIGURE 4. Rise time/amplitude distribution of IPSCs. Spontaneous (A) and miniature (B) IPSCs, after vehicle (green) and PD1n‐3DPA incubation (magenta). Fisher's exact test ns (sIPSCs), p < .05 (mIPSCs)
FIGURE 5. Examples of slices and the subfields CA1 and CA3 examined by immunofluorescence for GABAA receptor γ2‐subunit. Panels A and C show immunofluorescence images of representative slices incubated with aCSF (A) or PD1n3DPA in aCSF (D). Panels B and E show respective details of Sector CA1 and panels C and F of sector CA3 of the same sections. GABAA receptor γ2‐immunofluorescence labels primarily dendrites (note punctate labeling in B and E). Pericarya of pyramidal cells and interneurons are mostly unlabeled and appear dark. Note that in CA3 some interneurons show immunoreactivity at their cell bodies (arrow heads). Panel E indicates somewhat more intensive labeling for the γ2‐subunit as observed in some sections. CA1, CA3, cornu ammonis, sectors 1 and 3; ML, dentate molecular layer; pcl, pyramidal cell layer; slm, stratum lacunosum moleculare; so, stratum oriens; sr, stratum radiatum
FIGURE 6. PD1n‐3DPA effect on IEI of IPSC in CA1 pyramidal neurons was reverted by pertussis toxin. Cumulative distribution curves of IEI (A), amplitudes (B) and rise times (C) of IPSCs were recorded after incubation with PD1n‐3DPA or with PD1n‐3DPA + PTX. The control (vehicle) group is displayed as a reference. Insets display the median and range of cell averages. * Mann‐Whitney p < .05 for cell averages (PD1n‐3DPA vs. PD1n‐3DPA + PTX), Kolmogorov‐Smirnov p < .01, D > .1 for all PD1n‐3DPA vs. PD1n‐3DPA + PTX distribution comparisons
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