Background: Cortical spreading depolarization (CSD) is a massive neuro-glial depolarization wave, which propagates across the cerebral cortex. In stroke, CSD is a necessary and ubiquitous mechanism for the development of neuronal lesions that initiates in the ischemic core and propagates through the penumbra extending the tissue injury. Although CSD propagation induces dramatic changes in cerebral blood flow, the vascular responses in different ischemic regions and their consequences on reperfusion and recovery remain to be defined. Methods: Ischemia was performed using the thrombin model of stroke and reperfusion was induced by r-tPA (recombinant tissue-type plasminogen activator) administration in mice. We used in vivo electrophysiology and laser speckle contrast imaging simultaneously to assess both electrophysiological and hemodynamic characteristics of CSD after ischemia onset. Neurological deficits were assessed on day 1, 3, and 7. Furthermore, infarct sizes were quantified using 2,3,5-triphenyltetrazolium chloride on day 7. Results: After ischemia, CSDs were evidenced by the characteristic propagating DC shift extending far beyond the ischemic area. On the vascular level, we observed 2 types of responses: some mice showed spreading hyperemia confined to the penumbra area (penumbral spreading hyperemia) while other showed spreading hyperemia propagating in the full hemisphere (full hemisphere spreading hyperemia). Penumbral spreading hyperemia was associated with severe stroke-induced damage, while full hemisphere spreading hyperemia indicated beneficial infarct outcome and potential viability of the infarct core. In all animals, thrombolysis with r-tPA modified the shape of the vascular response to CSD and reduced lesion volume. Conclusions: Our results show that different types of spreading hyperemia occur spontaneously after the onset of ischemia. Depending on their shape and distribution, they predict severity of injury and outcome. Furthermore, our data show that modulating the hemodynamic response to CSD may be a promising therapeutic strategy to attenuate stroke outcome.

Following stroke, the survival of neurons and their ability to reestablish connections is critical to functional recovery. This is strongly influenced by the balance between neuronal excitation and inhibition. In the acute phase of experimental stroke, lethal hyperexcitability can be attenuated by positive allosteric modulation of GABA_A receptors (GABA_ARs). Conversely, in the late phase, negative allosteric modulation of GABA_AR can correct the suboptimal excitability and improves both sensory and motor recovery. Here, we hypothesized that octadecaneuropeptide (ODN), an endogenous allosteric modulator of the GABA_AR synthesized by astrocytes, influences the outcome of ischemic brain tissue and subsequent functional recovery. We show that ODN boosts the excitability of cortical neurons, which makes it deleterious in the acute phase of stroke. However, if delivered after day 3, ODN is safe and improves motor recovery over the following month in two different paradigms of experimental stroke in mice. Furthermore, we bring evidence that, during the subacute period after stroke, the repairing cortex can be treated with ODN by means of a single hydrogel deposit into the stroke cavity. SIGNIFICANCE STATEMENT Stroke remains a devastating clinical challenge because there is no efficient therapy to either minimize neuronal death with neuroprotective drugs or to enhance spontaneous recovery with neurorepair drugs. Around the brain damage, the peri-infarct cortex can be viewed as a reservoir of plasticity. However, the potential of wiring new circuits in these areas is restrained by a chronic excess of GABAergic inhibition. Here we show that an astrocyte-derived peptide, can be used as a delayed treatment, to safely correct cortical excitability and facilitate sensorimotor recovery after stroke.

The cortex immediately surrounding a brain ischemic lesion, the peri-infarct cortex (PIC), harbors a large part of the potential to recover lost functions. However, our understanding of the neurophysiological conditions in which synaptic plasticity operates remains limited. Here we hypothesized that the chronic imbalance between excitation and inhibition of the PIC prevents the normalization of the gamma rhythm, a waveband of neural oscillations thought to orchestrate action potential trafficking. Probing the local field potential activity of the forelimb primary sensory cortex (S1FL) located in the PIC of male adult mice, we found a constant, deep reduction of low-gamma oscillation power (L-gamma; 30–50 Hz) precisely during the critical time window for recovery (1–3 weeks after stroke). The collapse of L-gamma power negatively correlated with behavioral progress in affected forelimb use. Mapping astrocyte reactivity and GABA-like immunoreactivity in the PIC revealed a parallel high signal, which gradually increased when approaching the lesion. Increasing tonic inhibition with local infusion of GABA or by blocking its recapture reduced L-gamma oscillation power in a magnitude similar to stroke. Conversely, the negative allosteric modulation of tonic GABA conductance using L655,708 or the gliopeptide ODN rescued the L-gamma power of the PIC. Altogether the present data point out that the chronic excess of ambient GABA in the PIC limits the generation of L-gamma oscillations in the repairing cortex and suggests that rehabilitative interventions aimed at normalizing low-gamma power within the critical period of stroke recovery could optimize the restitution of lost functions.

26RFa is a neuropeptide that activates the rhodopsin-like G protein-coupled receptor QRFPR/GPR103. This peptidergic system is involved in the regulation of a wide array of physiological processes including feeding behavior and glucose homeostasis. Herein, the pharmacological profile of a homogenous library of QRFPR-targeting peptide derivatives was investigated in vitro on human QRFPR-transfected cells with the aim to provide possible insights into the structural determinants of the Phe residues to govern receptor activation. Our work advocates to include in next generations of 26RFa_(20–26)-based QRFPR agonists effective substitutions for each Phe unit, i.e., replacement of the Phe²² residue by a constrained 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid moiety, and substitution of both Phe²⁴ and Phe²⁶ by their para-chloro counterpart. Taken as a whole, this study emphasizes that optimized modifications in the C-terminal part of 26RFa are mandatory to design selective and potent peptide agonists for human QRFPR.

Endozepines, known as the endogenous ligands of benzodiazepine-binding sites, include the diazepam binding inhibitor (DBI) and its processing products, the triakontatetraneuropeptide (TTN) and the octadecaneuropeptide (ODN). Despite indisputable evidences of the binding of ODN on GABA _A R-BZ-binding sites, their action on this receptor lacks compelling electrophysiological observations, some studies reporting that ODN acts as a negative allosteric modulator (NAM) of GABA _A R while others suggest the opposite (positive allosteric modulation, PAM effect). All these studies were carried out in vitro with various neuronal cell types. To further elucidate the role of ODN on neuronal excitability, we tested its effect in vivo in the cortex of the anesthetized mouse. Spontaneous neuronal spikes were recorded by the mean of an extracellular pipette in the vicinity of which ODN was micro-infused, either at high dose (10 ^-5 M) or low dose (10 ^-11 M). ODN at high dose induced a significant increase of neuronal spiking. This effect could be antagonized by the GABA _A R-BZ-binding sites blocker flumazenil. In sharp contrast, at low concentration, ODN reduced neuronal spiking in a magnitude similar to GABA itself. Interestingly, this decrease of neuronal activity by low dose of ODN was not flumazenil dependent suggesting that this effect is mediated by another receptor. Finally, we show that astrocytes in culture, known to be stimulated by picomolar dose of ODN via a GPCR, increased their export of GABA when stimulated by low dose of ODN. Our results confirm the versatility of ODN in the control of GABA transmission, but suggest that its PAM-like effect is, at least in part, mediated via an astrocytic non-GABA _A R ODN receptor.