Epilepsy can be both a primary pathology and a secondary effect of many neurological conditions. Many papers show that neuroinflammation is a product of epilepsy, and that in pathological conditions characterized by neuroinflammation, there is a higher probability to develop epilepsy. However, the bidirectional mechanism of the reciprocal interaction between epilepsy and neuroinflammation remains to be fully understood. Here, we attempt to explore and discuss the relationship between epilepsy and inflammation in some paradigmatic neurological and systemic disorders associated with epilepsy. In particular, we have chosen one representative form of epilepsy for each one of its actual known etiologies. A better understanding of the mechanistic link between neuroinflammation and epilepsy would be important to improve subject-based therapies, both for prophylaxis and for the treatment of epilepsy.

Cortical activity patterns are strongly modulated by fast synaptic inhibition mediated through ionotropic, chloride-conducting receptors. Consequently, chloride homeostasis is ideally placed to regulate activity. We therefore investigated the stability of baseline [Cl^-]_i in adult mouse neocortex, using in vivo two-photon imaging. We found a two-fold increase in baseline [Cl^-]_i in layer 2/3 pyramidal neurons, from day to night, with marked effects upon both physiological cortical processing and seizure susceptibility. Importantly, the night-time activity can be converted to the day-time pattern by local inhibition of NKCC1, while inhibition of KCC2 converts day-time [Cl^-]_i towards night-time levels. Changes in the surface expression and phosphorylation of the cation-chloride cotransporters, NKCC1 and KCC2, matched these pharmacological effects. When we extended the dark period by 4 h, mice remained active, but [Cl^-]_i was modulated as for animals in normal light cycles. Our data thus demonstrate a daily [Cl^-]_i modulation with complex effects on cortical excitability.

PCDH19 epilepsy (DEE9) is an X-linked syndrome associated with cognitive and behavioral disturbances. Since heterozygous females are affected, while mutant males are spared, it is likely that DEE9 pathogenesis is related to disturbed cell-to-cell communication associated with mosaicism. However, the effects of mosaic PCDH19 expression on cortical networks are unknown. We mimicked the pathology of DEE9 by introducing a patch of mosaic protein expression in one hemisphere of the cortex of conditional PCDH19 knockout mice one day after birth. In the contralateral area, PCDH19 expression was unaffected, thus providing an internal control. In this model, we characterized the physiology of the disrupted network using local field recordings and two photon Ca²⁺ imaging in urethane anesthetized mice. We found transient episodes of hyperexcitability in the form of brief hypersynchronous spikes or bursts of field potential oscillations in the 9–25 Hz range. Furthermore, we observed a strong disruption of slow wave activity, a crucial component of NREM sleep. This phenotype was present also when PCDH19 loss occurred in adult mice, demonstrating that PCDH19 exerts a function on cortical circuitry outside of early development. Our results indicate that a focal mosaic mutation of PCDH19 disrupts cortical networks and broaden our understanding of DEE9.

Glioblastoma (GBM) is the most common and aggressive malignant brain tumor in adults, accounting for more than 60% of all cases.¹ Current treatment options at diagnosis include surgical resection, radiation, and chemotherapy² but—despite advances in this field—it remains largely incurable; its 5-year survival rate³ is $<5\%$. Extensive and complete surgical resection of GBM is difficult due to the high invasiveness of these tumors. However, multiple studies^4,5 have demonstrated the importance of aggressive surgical resection—when possible—with trends toward better outcomes in those patients with a greater extent of resection.

Summary: The main inhibitory synaptic currents, gated by gamma-aminobutyric acid (GABA), are mediated by Cl ^- -conducting channels ^1–3 , and are therefore sensitive to changes in the chloride electrochemical gradient. GABAergic activity dictates the neuronal firing range ^4,5 and timing ^6–9 , which in turn influences the rhythms of the brain, synaptic plasticity, and flow of information in neuronal networks ^7,10–12 . The intracellular chloride concentration [Cl ^- ] _i is, therefore, ideally placed to be a regulator of neuronal activity. Chloride levels have been thought to be stable in adult cortical networks, except when associated with pathological activation ^13–16 . Here, we used 2-photon LSSmClopHensor imaging, in anaesthetized young adult mice ¹³ , to show that [Cl ^- ] inside pyramidal cells shows a physiological diurnal rhythm, with an approximately 1.8-fold range, equating to an ~15mV positive shift in ECl at times when mice are typically awake (midnight), relative to when they are usually asleep (midday). This change of [Cl ^- ] _i alters the stability of cortical networks, as demonstrated by a greater than 3-fold longer latency to seizures induced by 4-aminopyridine at midday, compared to midnight. Importantly, both [Cl ^- ] _i and latency to seizure, in night-time experiments, were shifted in line with day-time measures, by inhibition of NKCC1. The redistribution of [Cl ^- ] _i reflects diurnal changes in surface expression and phosphorylation states of the cation-chloride-co-transporters, KCC2 and NKCC1, leading to a greatly reduced chloride-extrusion capacity at night (awake period). Our data demonstrate a means by which changes in the biochemical state of neurons are transduced into altered brain states.

Background: Glioblastoma (GB), is an incurable brain tumor characterized by extreme malignancy and invasiveness, and the cellular mechanisms underlying such a severe phenotype are not completely understood. Although calcium (Ca2+) plays an important part in tumor proliferation and infiltration, it remains unclear whether Ca2+ signaling in GB cells is related to its location within the tumor and on the infiltrative potential of the cells. Methods: In this study, we developed a stably transfected GL261 cell line that coexpresses a red fluorescent protein for actin cytoskeleton staining and the intracellular Ca2+ sensor, GCaMP6s. By means of intravital 2-photon imaging, we have characterized the morphological and functional properties of cells at different locations within the tumor. Results: Our results showed that cells located at the tumor core are densely packed and rounded in shape, contrasting sharply with the polarized morphology observed in the peripheral cells. This anatomical heterogeneity corresponded to notable variations of the physiological phenotype: cells at the tumor core displayed low Ca2+ activity and very limited motility, while peripheral cells displayed intense Ca2+ activity and increased migration rates. Moreover, peripheral cells formed a cellular ensemble characterized by synchronized Ca2+ activity accompanied by a directionally biased collective motility. Conclusions: These findings suggest that GB cells manifest activity patterns depending upon their spatial location within the tumor and that these correlate with their migration.