Stroke is a leading cause of disability; but no pharmacological therapy is currently available for promoting recovery. The brain region adjacent to stroke damage, the peri-infarct zone, is critical for rehabilitation, as it exhibits heightened neuroplasticity, allowing sensorimotor functions to re-map from damaged areas1–3. Thus, understanding the neuronal properties constraining this plasticity is important to developing new treatments. Here we show that after a stroke in mice, tonic neuronal inhibition is increased in the peri-infarct zone. This increased tonic inhibition is mediated by extrasynaptic GABAA receptors (GABAARs) and is caused by an impairment in GABA transporter (GAT-3/4) function. To counteract the heightened inhibition, we administered in vivo a benzodiazepine inverse agonist specific for the α5-subunit-containing extrasynaptic GABAARs at a delay after stroke. This treatment produced an early and sustained recovery of motor function. Genetically lowering the number of α5 or δ-subunit-containing GABAARs responsible for tonic inhibition also proved beneficial for post-stroke recovery, consistent with the therapeutic potential of diminishing extrasynaptic GABAAR function. Together, our results identify new pharmacological targets and provide the rationale for a novel strategy to promote recovery after stroke and possibly other brain injuries.

Intracellular Ca2+ signaling is considered important for multiple astrocyte functions in neural circuits. However, mice devoid of inositol triphosphate type 2 receptors (IP3R2) reportedly lack all astrocyte Ca2+ signaling, but display no neuronal or neurovascular deficits, implying that astrocyte Ca2+ fluctuations play no role(s) in these functions. An assumption has been that loss of somatic Ca2+ fluctuations also reflects similar loss within astrocyte processes. Here, we tested this assumption and found diverse types of Ca2+ fluctuations within astrocytes, with most occurring within processes rather than in somata. These fluctuations were preserved in IP3R2−/− mice in brain slices and in vivo, occurred in endfeet, were increased by G-protein coupled receptor activation and by startle-induced neuromodulatory responses. Our data reveal novel Ca2+ fluctuations within astrocytes and highlight limitations of studies that used IP3R2−/− mice to evaluate astrocyte contributions to neural circuit function and mouse behavior.

Summary Astrocytes exist throughout the nervous system and are proposed to affect neural circuits and behavior. However, studying astrocytes has proven difficult because of the lack of tools permitting astrocyte selective genetic manipulations. Here, we report the generation of Aldh1l1-Cre/ERT2 transgenic mice to selectively target astrocytes in vivo. We characterised Aldh1l1-Cre/ERT2 mice using imaging, immunohistochemistry, AAV-FLEX-GFP microinjections and crosses to RiboTag, Ai95 and new Cre-dependent membrane tethered Lck-GCaMP6f knock-in mice that we also generated. Two-to-three weeks after tamoxifen induction, Aldh1l1-Cre/ERT2 selectively targeted essentially all adult (P80) brain astrocytes with no detectable neuronal contamination, resulting in expression of cytosolic and Lck-GCaMP6f and permitting subcellular astrocyte calcium imaging during startle responses in vivo. Crosses with RiboTag mice allowed sequencing of actively translated mRNAs and determination of the adult cortical astrocyte transcriptome. Thus, we provide well characterised, easy-to-use resources with which to selectively study astrocytes in situ and in vivo in multiple experimental scenarios.

Why is ketamine an antidepressant? A better understanding of the mechanisms underlying the action of antidepressants is urgently needed. Moda-Sava et al. explored a possible mode of action for the drug ketamine, which has recently been shown to help patients recover from depression (see the Perspective by Beyeler). Ketamine rescued behavior in mice that was associated with depression-like phenotypes by selectively reversing stress-induced spine loss and restoring coordinated multicellular ensemble activity in prefrontal microcircuits. The initial induction of ketamine's antidepressant effect on mouse behavior occurred independently of effects on spine formation. Instead, synaptogenesis in the prefrontal region played a critical role in nourishing these effects over time. Interventions aimed at enhancing the survival of restored synapses may thus be useful for sustaining the behavioral effects of fast-acting antidepressants. Science , this issue p. eaat8078 ; see also p. 129

While whole-organism calcium imaging in small and semi-transparent animals has been demonstrated, capturing the functional dynamics of large-scale neuronal circuits in awake, behaving mammals at high speed and resolution has remained one of the main frontiers in systems neuroscience. Here we present a novel method based on light sculpting that enables unbiased single and dual-plane high-speed (up to 160 Hz) calcium imaging, as well as in vivo volumetric calcium imaging of a mouse cortical column (0.5 × 0.5 × 0.5 mm) at single-cell resolution and fast volume rates (3 – 6 Hz). This is achieved by tailoring the point-spread function of our microscope to the structures of interest, and by maximizing the signal-to-noise ratio by using a home-built fiber laser amplifier and synchronizing its pulses to the imaging voxel speed. This has enabled in-vivo recording of calcium dynamics of several thousand neurons across cortical layers and in the hippocampus of awake behaving mice.

Transsynaptic interactions between neurons are essential during both developmental and learning-related synaptic growth. We have used Aplysia neuronal cultures to examine the contribution of transsynaptic signals in both types of synapse formation. We find that during de novo synaptogenesis, specific presynaptic innervation is required for the clustering of postsynaptic AMPA-like but not NMDA-like receptors. We further find that the cell adhesion molecule Dscam is involved in these transsynaptic interactions. Inhibition of Dscam either pre- or postsynaptically abolishes the emergence of synaptic transmission and the clustering of AMPA-like receptors. Remodeling of both AMPA-like and NMDA-like receptors also occurs during learning-related synapse formation and again requires the reactivation of Dscam-mediated transsynaptic interactions. Taken together, these findings suggest that learning-induced synapse formation recapitulates, at least in part, aspects of the mechanisms that govern de novo synaptogenesis.

Mouse models have demonstrated utility in delineating the mechanisms underlying many aspects of malaria immunology and physiology. The most common mouse models of malaria employ the rodent-specific parasite species Plasmodium berghei, P. yoelii, and P. chabaudi, which elicit distinct pathologies and immune responses and are used to model different manifestations of human disease. In vitro culture methods are not well developed for rodent Plasmodium parasites, which thus require in vivo maintenance. Moreover, physiologically relevant immunological processes are best studied in vivo. Here, we detail the processes of infecting mice with Plasmodium, maintaining the parasite in vivo, and monitoring parasite levels and health parameters throughout infection.

Facilitating the development of alternative targeted therapeutic strategies is urgently required to improve outcome or circumvent chemotherapy resistance in children, adolescents, and adults with recurrent/refractory de novo mature B-cell (CD20) non-Hodgkin lymphoma, including Burkitt lymphoma (BL). Romidepsin, a histone deacetylase inhibitor (HDACi), has been used to treat cutaneous T-cell lymphoma. We have demonstrated the significant anti-tumor effect of anti-CD20 chimeric antigen receptor (CAR) modified expanded peripheral blood natural killer (exPBNK) against rituximab-sensitive and -resistant BL. This study examined the anti-tumor activity of romidepsin alone and in combination with anti-CD20 CAR exPBNKs against rituximab-sensitive and -resistant BL and. We found that romidepsin significantly inhibited both rituximab-sensitive and -resistant BL cell proliferation (P< 0.001) and induced cell death in rituximab-sensitive Raji (P < 0.001) and cell cycle arrest in rituximab-resistant Raji-2R and Raji-4RH (P < 0.001). Consistent with observations, we also found romidepsin significantly inhibited the growth of rituximab-sensitive and -resistant BL in BL xenografted NSG mice. We also demonstrated that romidpesin significantly induced the expression of Natural Killer Group 2, Member D (NKG2D) ligands MICA/B in both rituximab-sensitive and -resistant BL cells (P< 0.001) resulting in enhancement of exPBNK cytotoxicity through NKG2D. Finally, we observed the combination of romidepsin and anti-CD20 CAR exPBNK significantly induced cell death in BL cells, reduced tumor burden and enhanced survival in humanized BL xenografted NSG mice (p < 0.05). Our data suggests that romidepsin is an active HDAC inhibitor that also potentiates expanded NK and anti-CD20 CAR exPBNK activity against rituximab-sensitive and -resistant BL.