Search

The electrographic hallmark of childhood absence epilepsy (CAE) and other idiopathic forms of epilepsy are 2.5–4 Hz spike and wave discharges (SWDs) originating from abnormal electrical oscillations of the cortico-thalamo-cortical network. SWDs are generally associated with sudden and brief non-convulsive epileptic events mostly generating impairment of consciousness and correlating with attention and learning as well as cognitive deficits. To date, SWDs are known to arise from locally restricted imbalances of excitation and inhibition in the deep layers of the primary somatosensory cortex. SWDs propagate to the mostly GABAergic nucleus reticularis thalami (NRT) and the somatosensory thalamic nuclei that project back to the cortex, leading to the typical generalized spike and wave oscillations. Given their shared anatomical basis, SWDs have been originally considered the pathological transition of 11–16 Hz bursts of neural oscillatory activity (the so-called sleep spindles) occurring during Non-Rapid Eye Movement (NREM) sleep, but more recent research revealed fundamental functional differences between sleep spindles and SWDs, suggesting the latter could be more closely related to the slow (+ clearance and neurotransmitter uptake from the extracellular space and the synaptic cleft, (iii) gap junction mechanical and functional coupling as well as hemichannel function, (iv) gliotransmission, (v) astroglial Ca2+ signaling and downstream effectors, (vi) reactive astrogliosis and cytokine release.

Astrocytes play crucial roles in brain homeostasis and are regulatory elements of neuronal and synaptic physiology. Astrocytic alterations have been found in Major Depressive Disorder (MDD) patients; however, the consequences of astrocyte Ca2+ signaling in MDD are poorly understood. Here, we found that corticosterone-treated mice (Cort-mice) showed altered astrocytic Ca2+ dynamics in mPFC both in resting conditions and during social interactions, in line with altered mice behavior. Additionally, Cort-mice displayed reduced serotonin (5-HT)-mediated Ca2+ signaling in mPFC astrocytes, and aberrant 5-HT-driven synaptic plasticity in layer 2/3 mPFC neurons. Downregulation of astrocyte Ca2+ signaling in naïve animals mimicked the synaptic deficits found in Cort-mice. Remarkably, boosting astrocyte Ca2+ signaling with Gq-DREADDS restored mood and cognitive deficits in Cort-mice to control levels. This study highlights the important role of astrocyte Ca2+ signaling for homeostatic control of brain circuits and behavior, but also reveals its potential therapeutic value for depressive-like states.

Fluorescent dyes and genetically encoded fluorescence indicators (GEFI) are common tools for visualizing concentration changes of specific ions and messenger molecules during intra-as well as intercellular communication. Using advanced imaging technologies, fluorescence indicators are a prerequisite for the analysis of physiological molecular signaling. Automated detection and avnalysis of fluorescence signals requires to overcome several challenges, including correct estimation of fluorescence fluctuations at basal concentrations of messenger molecules, detection and extraction of events themselves as well as proper segmentation of neighboring events. Moreover, event detection algorithms need to be sensitive enough to accurately capture localized and low amplitude events exhibiting a limited spatial extent. Here, we present two algorithms (PBasE and CoRoDe) for accurate baseline estimation of fluorescent detection of messenger molecules and automated detection of fluorescence fluctuations.Author summaryAnalyzing molecular signalling is crucial in understanding intra- and intercellular communication. These signals are visualized using fluorescent dyes or genetically encoded fluorescence indicators. In the brain, Ca2+ signals of glial cells are essential in deciphering complex regulatory functions in health and disease. Due to signal heterogeneity, detection and analysis are highly challenging. They can be stationary, with low amplitude and localized in cell processes, occur as prominent somatic signals or propagate as waves across cellular networks.We have developed two algorithms to analyze fluorescence transients, each tackling a specific problem. PBasE performs automatic and adaptive background correction, removing basal fluorescence fluctuations. CoRoDe automatically extracts regions of interest, explicitly including temporal information to obtain a precise segmentation, which is essential for accurate transient extraction. Combined, these algorithms are able to detect regions exhibiting low amplitude transients with small spatial extent as well as large, high amplitude signals. Extracted transients are categorized based on their peak amplitude, allowing detailed analyses by comparing changes of specific properties. In order to make these algorithms accessible, an interactive application, called Msparkles, has been designed.

Pharmacological agents that limit secondary tissue loss and/or improve functional outcomes after stroke are still limited. Cannabidiol, the major non-psychoactive component of Cannabis sativa, has been proposed as a neuroprotective agent against experimental focal cerebral ischemia. The effects of cannabidiol have generally been related to the modulation of neuroinflammation, including the control of glial activation and the toxicity exerted by pro-inflammatory mediators. However, so far, most information concerning cannabidiol neuroprotective effects was obtained from histological and biochemical post-mortem assays. To test whether the effects of cannabidiol on glial cells could be also detected in vivo, we performed time-lapse imaging of microglial activity and astrocytic calcium signaling in the subacute phase of stroke using two-photon laser-scanning microscopy. First, C57BL/6N wild-type mice underwent either sham or transient middle cerebral artery occlusion surgery. The animals received intraperitoneal injection of vehicle or cannabidiol (10 mg/kg) 30 min, 24 h, and 48 h after surgery. One day later the neurological score test was performed. Brain tissue was processed to evaluate the neuronal loss and microglial activation. Transgenic mice with microglial expression of the enhanced green fluorescent protein and astrocyte-specific expression of the calcium sensor GCaMP3 were used to access in vivo microglial activity and astrocytic calcium signaling, respectively. The animals were submitted to the same experimental design described above and to imaging sessions before, 30 min, 24 h and, 48 h after surgery. Astrocytic calcium signaling was also assessed in acutely isolated slices 5 h after transient middle cerebral artery occlusion surgery in the presence of perfusion or cannabidiol solution. Cannabidiol prevented ischemia-induced neurological impairments as well as protected against neuronal loss in ischemic mice. Cannabidiol also reduced ischemia-induced microglial activation, as demonstrated in fixed tissue as well in in vivo conditions. No difference in the amplitude and duration of astrocytic calcium signals was detected before and after the middle cerebral artery occlusion in vivo. Similarly, no significant difference was found in the astrocytic calcium signals between contra and ipsilateral side of acutely isolated brain slices. The present results suggest that the neuroprotective effects of cannabidiol after stroke may occur in the subacute phase of ischemia and reinforce the strong anti-inflammatory property of this compound.

Astrocytes from the cerebral cortex (CTX) and cerebellum (CB) share basic molecular programs, but also form distinct spatial and functional subtypes. The regulatory epigenetic layers controlling such regional diversity have not been comprehensively investigated so far. Here, we present an integrated epigenome analysis of methylomes, open chromatin, and transcriptomes of astroglia populations isolated from the cortex or cerebellum of young adult mice. Besides a basic overall similarity in their epigenomic programs, cortical astrocytes and cerebellar astrocytes exhibit substantial differences in their overall open chromatin structure and in gene-specific DNA methylation. Regional epigenetic differences are linked to differences in transcriptional programs encompassing genes of region-specific transcription factor networks centered around Lhx2/Foxg1 in CTX astrocytes and the Zic/Irx families in CB astrocytes. The distinct epigenetic signatures around these transcription factor networks point to a complex interconnected and combinatorial regulation of region-specific transcriptomes. These findings suggest that key transcription factors, previously linked to temporal, regional, and spatial control of neurogenesis, also form combinatorial networks important for astrocytes. Our study provides a valuable resource for the molecular basis of regional astrocyte identity and physiology.

The spinal cord is the main pathway connecting brain and peripheral nervous system. Its functionality relies on the orchestrated activity of both neurons and glial cells. To date, most advancement in understanding the spinal cord inner mechanisms has been made either by