Priming of microglia with IFN-γ slows neuronal gamma oscillations in situ

Abstract

Type II IFN (IFN-γ) is a proinflammatory T lymphocyte cytokine that serves in priming of microglia-resident CNS macrophagesduring the complex microglial activation process under pathological conditions. Priming generally permits an exaggerated microglial response to a secondary inflammatory stimulus. The impact of primed microglia on physiological neuronal function in intact cortical tissue (in situ) is widely unknown, however. We explored the effects of chronic IFN-γ exposure on microglia in hippocampal slice cultures, i.e., postnatal parenchyma lacking leukocyte infiltration (adaptive immunity). We focused on fast neuronal network waves in the gamma-band (30-70 Hz). Such gamma oscillations are fundamental to higher brain functions, such as perception, attention, and memory, and are exquisitely sensitive to metabolic and oxidative stress. IFN-γ induced substantial morphological changes and cell population expansion in microglia as well as moderate upregulation of activation markers, MHC-II, CD86, IL-6, and inducible nitric oxide synthase (iNOS), but not TNF-α. Cytoarchitecture and morphology of pyramidal neurons and parvalbumin-positive inhibitory interneurons were well-preserved. Notably, gamma oscillations showed a specific decline in frequency of up to 8 Hz, which was not mimicked by IFN-α or IL-17 exposure. The rhythm disturbance was caused by moderate microglial nitric oxide (NO) release demonstrated by pharmacological microglia depletion and iNOS inhibition. In conclusion, IFN-γ priming induces substantial proliferation and moderate activation of microglia that is capable of slowing neural information processing. This mechanism might contribute to cognitive impairment in chronic brain disease featuring elevated IFN-γ levels, blood-brain barrier leakage, and/or T cell infiltration, well before neurodegeneration occurs.interferon-gamma | microglia | neuroinflammation | neuronal electrical activity | nitric oxide synthase

Interferon-γ potentiates GABAA receptor-mediated inhibitory currents in rat hippocampal CA1 pyramidal neurons

“…janelia.org) (Cembrowski et al, 2016) and found that both Ifngr1 and Ifngr2 gene transcripts are constitutively expressed in glutamatergic neurons of CA1-3 and dentate gyrus as well as parvalbumin (PV) or somatostatin (SST) expressing interneurons of mouse hippocampus. Furthermore, the presence of IFN-γ receptor in hippocampal microglia and astrocytes has been demonstrated, although the levels of expression differ depending on species and in vivo/in vitro conditions (Hashioka et al, 2010;Papageorgiou et al, 2016;Ta et al, 2019). Thus, the constitutive expression of IFN-γ receptors in several hippocampal cell There was no significant difference in mIPSC median amplitude (+TTX, 20.9 ± 1.36 pA, n = 11; IFN-γ + TTX, 24.34 ± 1.68 pA, n = 8; unpaired student t-test, p = .1281), or median rise time (10-90%) (+TTX, 2.42 ± 0.2 ms, n = 11; IFNγ + TTX, 1.93 ± 0.13 ms, n = 8; unpaired student ttest, p = .073), or median decay time (90-37%) (+TTX, 22.25 ± 1.05 ms, n = 11; IFN-γ + TTX, 20.23 ± 1.3 ms, n = 8; unpaired student t-test, p = .2369) in aCSF with IFN-γ (100 ng/ml) as compared to aCSF alone.…”

“…IFN-γ levels can increase under many pathological conditions particularly neuroinflammation (Ottum et al, 2015). In this study, we have pre-incubated the rat hippocampal slices with IFN-γ for 1-4 h at a concentration of 100 ng/ml, which has been shown to evoke maximal effects in microglia (Hausler et al, 2002;Ta et al, 2019). Notably, the actual IFN-γ concentration within the slices may be lower due to lack of blood flow, longer diffusion distance and limited extracellular space in hippocampal slices (McBain et al, 1990;Ta et al, 2019).…”

“…In this study, we have pre-incubated the rat hippocampal slices with IFN-γ for 1-4 h at a concentration of 100 ng/ml, which has been shown to evoke maximal effects in microglia (Hausler et al, 2002;Ta et al, 2019). Notably, the actual IFN-γ concentration within the slices may be lower due to lack of blood flow, longer diffusion distance and limited extracellular space in hippocampal slices (McBain et al, 1990;Ta et al, 2019). The studies of the effects of IFN-γ on the neurotransmission have been mainly focused on the glutamatergic system (Mizuno et al, 2008;Sonekatsu et al, 2016;Vikman et al, 2001).…”

“…Indeed, the increased sIPSC and mIPSC frequencies could be explained by an enhancement in interneuron excitability and activity-independent quantal release of GABA, respectively. Additionally, the pre-incubation of hippocampal slices with IFN-γ could first activate microglia and astrocytes and secondly affect the GABAergic neurotransmission by mechanisms such as the release of other cytokines and modulation of GABA reuptake (Losi et al, 2014;Ta et al, 2019).…”

“…To date, little is known about the effects of IFN-γ on hippocampal excitability. In vitro experiments have revealed that the acute application of IFN-γ on cultured rat hippocampal slices increased the excitability of CA3 neurons (Muller et al, 1993) whereas the chronic IFN-γ treatment reduced the gamma oscillations in the CA3 region (Ta et al, 2019). In fact, the excitability of neuronal network is critically dependent on the balance between excitatory glutamatergic transmission and inhibitory GABAergic (γ-aminobutyric acid) transmission.…”