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Following stroke, the survival of neurons and their ability to re-establish 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 GABAA receptors (GABAAR). Conversely, in the late phase, negative allosteric modulation of GABAAR can correct the sub-optimal excitability and improves both sensory and motor recovery. Here, we hypothesized that octadecaneuropeptide (ODN), an endogenous allosteric modulator of the GABAAR 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 make 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 sub-acute period after stroke, the repairing cortex can be treated with ODN by means of a single hydrogel deposit into the stroke cavity.SIGNIFICANCE STATEMENTStroke 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 (ODN), can be used as a delayed treatment, to safely correct cortical excitability and facilitate sensorimotor recovery after stroke.

Days and weeks after an ischemic stroke, the peri-infarct area adjacent to the necrotic tissue exhibits very intense synaptic reorganization aimed at regaining lost functions. In order to enhance functional recovery, it is important to understand the mechanisms supporting neural repair and neuroplasticity in the cortex surrounding the lesion. Brain oscillations of the local field potential (LFP) are rhythmic fluctuations of neuronal excitability aimed at synchronizing neuronal activity to organize information processing and plasticity. Although the oscillatory activity of the brain has been probed after stroke in both animals and humans using electroencephalography (EEG), the latter is ineffective to precisely map the oscillatory changes in the peri-infarct zone where synaptic plasticity potential is high. Here, we worked on the hypothesis that brain oscillatory system is altered in the surviving peri-infarct cortex, which may slow down functional repair and reduce the capacity to recovery. In order to document the relevance of this hypothesis, oscillatory power was measured at various distances from the necrotic core at 7 and 21 days after a permanent cortical ischemia induced in mice. Delta and theta oscillations remained at a normal power in the peri-infarct cortex, in contrast to gamma oscillations that displayed a rapid decrease, the closer we get to the lesion core. A broadband increase of power was also observed in the homotopic contralateral sites. Thus, the proximal peri-infarct cortex could become a target of therapeutic interventions aimed at correcting the oscillatory regimen. These results argue for the usefulness of therapeutic intervention aimed at boosting gamma oscillations in order to improve post-stroke functional recovery.

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(A)Rs). Conversely, in the late phase, negative allosteric modulation of GABA(A)R 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(A)R 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.

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.

Background and Purpose The neuropeptide 26RFa and its cognate receptor GPR103 are involved in the control of food intake and bone mineralization. Here, we have tested, experimentally, the predicted ligand-receptor interactions by site-directed mutagenesis of GPR103 and designed point-substituted 26RFa analogues. Experimental Approach Using the X-ray structure of the β2-adrenoceptor, a 3-D molecular model of GPR103 has been built. The bioactive C-terminal octapeptide 26RFa(19–26), KGGFSFRF-NH2, was docked in this GPR103 model and the ligand-receptor complex was submitted to energy minimization. Key Results In the most stable complex, the Phe-Arg-Phe-NH2 part was oriented inside the receptor cavity, whereas the N-terminal Lys residue remained outside. A strong intermolecular interaction was predicted between the Arg25 residue of 26RFa and the Gln125 residue located in the third transmembrane helix of GPR103. To confirm this interaction experimentally, we tested the ability of 26RFa and Arg-modified 26RFa analogues to activate the wild-type and the Q125A mutant receptors transiently expressed in CHO cells. 26RFa (10−6 M) enhanced [Ca2+]i in wild-type GPR103-transfected cells, but failed to increase [Ca2+]i in Q125A mutant receptor-expressing cells. Moreover, asymmetric dimethylation of the side chain of arginine led to a 26RFa analogue, [ADMA25]26RFa(20–26), that was unable to activate the wild-type GPR103, but antagonized 26RFa-evoked [Ca2+]i increase. Conclusion and Implications Altogether, these data provide strong evidence for a functional interaction between the Arg25 residue of 26RFa and the Gln125 residue of GPR103 upon ligand-receptor activation, which can be exploited for the rational design of potent GPR103 agonists and antagonists.

Astrocytes communicate with synapses by means of intracellular calcium ([Ca(2+)](i)) elevations, but local calcium dynamics in astrocytic processes have never been thoroughly investigated. By taking advantage of high-resolution two-photon microscopy, we identify the characteristics of local astrocyte calcium activity in the adult mouse hippocampus. Astrocytic processes showed intense activity, triggered by physiological transmission at neighboring synapses. They encoded synchronous synaptic events generated by sparse action potentials into robust regional (∼12 μm) [Ca(2+)](i) elevations. Unexpectedly, they also sensed spontaneous synaptic events, producing highly confined (∼4 μm), fast (millisecond-scale) miniature Ca(2+) responses. This Ca(2+) activity in astrocytic processes is generated through GTP- and inositol-1,4,5-trisphosphate-dependent signaling and is relevant for basal synaptic function. Thus, buffering astrocyte [Ca(2+)](i) or blocking a receptor mediating local astrocyte Ca(2+) signals decreased synaptic transmission reliability in minimal stimulation experiments. These data provide direct evidence that astrocytes are integrated in local synaptic functioning in adult brain.

Glucose is the primary energetic substrate of the brain, and measurements of its metabolism are the basis of major functional cerebral imaging methods. Contrary to the general view that neurons are fueled solely by glucose in proportion to their energetic needs, recentin vitroandex vivoanalyses suggest that glucose preferentially feeds astrocytes. However, the cellular fate of glucose in the intact brain has not yet been directly observed. We have used a real-time method for measuring glucose uptake in astrocytes and neuronsin vivoin male rats by imaging the trafficking of the nonmetabolizable glucose analog 6-deoxy-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-aminoglucose (6-NBDG) using two-photon microscopy. During resting conditions we found that astrocytes and neurons both take up 6-NBDG at the same rate in the barrel cortex of the rat. However, during intense neuronal activity triggered by whisker stimulation, astrocytes rapidly accelerated their uptake, whereas neuronal uptake remained almost unchanged. After the stimulation period, astrocytes returned to their preactivation rates of uptake paralleling the neuronal rate of uptake. These observations suggest that glucose is taken up primarily by astrocytes, supporting the view that functional imaging experiments based on glucose analogs extraction may predominantly reflect the metabolic activity of the astrocytic network.

Background and Purpose— Whereas the effects of chronic arterial hypertension on the cerebral vasculature have been widely studied, its effects on brain tissue have been studied less so. Here we examined if spontaneously hypertensive rats (SHRs) or the normotensive control Wistar Kyoto rats (WKYs) made hypertensive by renal artery stenosis (R-WKYs) are vulnerable to an excitotoxic brain lesion provoked by an overactivation of glutamate receptors. Methods— Lesion volumes were quantified by histology in WKYs and SHRs subjected to striatal administration of N -methyl- d -aspartate (NMDA) or α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA). The expression of AMPA receptors subunits and calcium/calmodulin kinase-IIα was analyzed by real-time polymerase chain reaction and Western blot. Results— NMDA (50 and 75 nmol) induced similar lesions in both SHRs (10±2 mm 3 and 16±4 mm 3 , respectively) and WKYs (11±2 mm 3 and 19±7 mm 3 , respectively). However, AMPA-induced (2.5 and 5 nmol) lesions were significantly greater in 14-week-old SHRs (14±3 mm 3 and 20±5 mm 3 , respectively) than WKYs (4±2 mm 3 , P 3 , P 3 vs 6±3 mm 3 ; P 3 and 5±4 mm 3 , respectively) compared with WKYs. Striatal levels of AMPA receptors subunits, GluR1 and GluR2, were not different between SHRs and WKYs. However, SHRs displayed an increase in phosphorylated form of GluR1 at Ser-831 ( P P P Conclusions— These findings show that an increase in phosphorylated GluR1, which increases AMPA receptor conductance, may be involved in the vulnerability of SHRs to AMPA.

To correlate brain metabolic status with the molecular events during cerebral ischemia, a cDNA array was performed after positron emission tomography scanning in a model of focal cerebral ischemia in baboons. Cluster analysis for the expression of 74 genes allowed the identification of 4 groups of genes. In each of the distinct groups, the authors observed a marked inflection in the pattern of gene expression when the CMRo2 was reduced by 48% to 66%. These patterns of coordinated modifications in gene expression could define molecular checkpoints for the development of an ischemic infarct and a molecular definition of the penumbra.

Spreading depression (SD) is a propagating wave of neuronal depolarization and ionic shifts, seen in stroke and migraine.In vitro, SD is associated with astrocytic [Ca2+] waves, but it is unclear what role they play and whether they influence cerebral blood flow, which is altered in SD. Here we show that SDin vivois associated with [Ca2+] waves in astrocytes and neurons and with constriction of intracortical arterioles severe enough to result in arrest of capillary perfusion. The vasoconstriction is correlated with fast astrocytic [Ca2+] waves and is inhibited when they are reduced. [Ca2+] waves appear in neurons before astrocytes, and inhibition of astrocytic [Ca2+] waves does not depress SD propagation. This suggests that astrocytes do not drive SD propagation but are responsible for the hemodynamic failure seen deep in the cortex. Similar waves occur in anoxic depolarizations (AD), supporting the notion that SD and AD are related processes.

Background— Accumulating evidence demonstrates a critical involvement of tissue-type plasminogen activator (tPA) in pathological and physiological brain conditions. Determining whether and how vascular tPA can cross the blood-brain barrier (BBB) to enter the brain is thus important, not only during stroke but also in physiological conditions. Methods and Results— In the present work, we provide evidence in vivo that intravenous injection of tPA increases NMDA-induced striatal lesion in the absence of BBB leakage. Accordingly, we show that tPA crosses the BBB both after excitotoxic lesion and in control conditions. Indeed, vascular injected tPA can be detected within the brain parenchyma and in the cerebrospinal fluid. By using an in vitro model of BBB, we have confirmed that tPA can cross the intact BBB. Its passage was blocked at 4°C, was saturable, and was independent of its proteolytic activity. We have shown that tPA crosses the BBB by transcytosis, mediated by a member of the LDL receptor–related protein family. Conclusions— We demonstrate that blood-derived tPA can reach the brain parenchyma without alteration of the BBB. The molecular mechanism of the passage of tPA from blood to brain described here could represent an interesting target to improve thrombolysis in stroke

Background and Purpose— Endothelins act through 2 receptors, namely, ET A and ET B . In the cerebral circulation, ET A mediates marked and prolonged vasoconstriction, and its blockade increases cerebral blood flow (CBF) and reduces ischemic brain damage. However, the role of ET B receptors remains unclear. In this study we examined, in rats, the kinetics of expression of ET B and the effects of ET B blockade on changes in CBF and brain damage after focal cerebral ischemia and N -methyl- d -aspartate (NMDA)–induced excitotoxic injury. Methods— Rats were subjected to transient (60 minutes) focal cerebral ischemia or cortical injection of NMDA. The selective ET B antagonist BQ-788 was injected intracerebroventricularly 30 minutes before and 30 minutes after the onset of ischemia. Cortical perfusion was monitored by laser-Doppler flowmetry. The volume of infarction or NMDA-induced cortical lesion was assessed at 24 hours after the insult. The reverse transcription–polymerase chain reaction technique was used to assess ET B expression. Results— Cerebral ischemia failed to alter the expression of ET B mRNA in both acute and chronic stages. Administration of BQ-788 resulted in an increase in infarction volume (178%; P P Conclusions— Our results suggest that the ET B antagonist BQ-788 induces deleterious effects that are mediated by the reduction of residual blood flow after ischemia and argue that the optimal therapeutic strategy in stroke would be to target the use of selective ET A antagonists and not mixed ET A /ET B antagonists.