Can physiological signals estimation improve fMRI connectivity assessment in anesthetized rats?

International audienceResting-state functional magnetic resonance imaging (fMRI) is a common translational method to evaluate brain functional connectivity (FC) in preclinical neurologic applications. However, unlike human studies, preclinical fMRI studies are usually performed under anesthetic condition. The confounding effect of the anesthesia on fMRI measurements is not clear. Indeed, a controversy exists between those who claim that anesthesia change FC (Paasonen et al., 2018) and other who maintain that FC is preserved (Becq et al., 2020). Our hypothesis is that physiological changes induced by anesthesia could explain this discrepancy. While in human studies, fMRI analysis generally includes cleaning of physiological-noise (Glover et al., 2000; Kassinopoulos & Mitsis, 2019), preclinical study processing is rather often limited to a low-pass temporal filtering. We aimed first to demonstrate that the global MRI signal of animal brain includes, like in human, a physiological component. Second, that a normalization of this component based on global signal can reduce variability of FC assessment

Can physiological signals estimation improve fMRI connectivity assessment in anesthetized rats?

International audienceResting-state functional magnetic resonance imaging (fMRI) is a common translational method to evaluate brain functional connectivity (FC) in preclinical neurologic applications. However, unlike human studies, preclinical fMRI studies are usually performed under anesthetic condition. The confounding effect of the anesthesia on fMRI measurements is not clear. Indeed, a controversy exists between those who claim that anesthesia change FC (Paasonen et al., 2018) and other who maintain that FC is preserved (Becq et al., 2020). Our hypothesis is that physiological changes induced by anesthesia could explain this discrepancy. While in human studies, fMRI analysis generally includes cleaning of physiological-noise (Glover et al., 2000; Kassinopoulos & Mitsis, 2019), preclinical study processing is rather often limited to a low-pass temporal filtering. We aimed first to demonstrate that the global MRI signal of animal brain includes, like in human, a physiological component. Second, that a normalization of this component based on global signal can reduce variability of FC assessment

High resolution 3T fMRI in anesthetized monkeys

International audienceAlthough there are numerous 3 T MRI research devices all over the world, only a few functional studies at 3 T have been done in anesthetized monkeys. In the past, anesthetized preparations were reported to be misleading when exploring cortical brain regions outside the primary sensory areas. Nonetheless, a great improvement has been achieved in the limited effect of anesthetic agents on the reactivity of the brain.Here, we re-address the feasibility and potential applications of the brain oxygen level dependent (BOLD) fMRI signal in Macaca mulatta monkeys that have been lightly anesthetized with sevoflurane and curarized. The monkeys were studied with commercially available coils and sequences using a 3 T clinical magnet. We obtained sagittal T1 scout images, gray matter double inversion recovery, standard gradient echo sequences and gradient echo functional imaging sequences. Given that fMRI signals are most readily identified in the cerebral cortices, we optimized Echo Planar Imaging sequences to reproduce significant changes in the BOLD signal subsequent to a visual stimulation paradigm.Our results provide a satisfactory signal to noise ratio with a limited standard deviation range, when compared with studies on alert macaques.We suggest that the 3 T magnet remains a valuable tool to analyze neural pathways in the macaque brain under light anesthesia and report the use of spatially resolved fMRI in higher visual areas of anesthetized monkeys. This methodology avoids the need for time-consuming training of awake monkeys, is stable over many hours, provides reproducible data and could be applied successfully to future functional studies

Delayed hypoxic postconditioning protects against cerebral ischemia in the mouse.

International audienceBACKGROUND AND PURPOSE: Inspired from preconditioning studies, ischemic postconditioning, consisting of the application of intermittent interruptions of blood flow shortly after reperfusion, has been described in cardiac ischemia and recently in stroke. It is well known that ischemic tolerance can be achieved in the brain not only by ischemic preconditioning, but also by hypoxic preconditioning. However, the existence of hypoxic postconditioning has never been reported in cerebral ischemia. METHODS: Adult mice subjected to transient middle cerebral artery occlusion underwent chronic intermittent hypoxia starting either 1 or 5 days after ischemia and brain damage was assessed by T2-weighted MRI at 43 days. In addition, we investigated the potential neuroprotective effect of hypoxia applied after oxygen glucose deprivation in primary neuronal cultures. RESULTS: The present study shows for the first time that a late application of hypoxia (5 days) after ischemia reduced delayed thalamic atrophy. Furthermore, hypoxia performed 14 hours after oxygen glucose deprivation induced neuroprotection in primary neuronal cultures. We found that hypoxia-inducible factor-1alpha expression as well as those of its target genes erythropoietin and adrenomedullin is increased by hypoxic postconditioning. Further studies with pharmacological inhibitors or recombinant proteins for erythropoietin and adrenomedullin revealed that these molecules participate in this hypoxia postconditioning-induced neuroprotection. CONCLUSIONS: Altogether, this study demonstrates for the first time the existence of a delayed hypoxic postconditioning in cerebral ischemia and in vitro studies highlight hypoxia-inducible factor-1alpha and its target genes, erythropoietin and adrenomedullin, as potential effectors of postconditioning

Delayed administration of deferoxamine reduces brain damage and promotes functional recovery after transient focal cerebral ischemia in the rat.

International audienceThe mechanisms underlying functional recovery after stroke are poorly understood. Brain-adaptive responses to the hypoxic stress elicited by ischemia could contribute to these mechanisms. Indeed, hypoxia-inducible factor-1 (HIF-1), one of the main transcriptional factors regulated by oxygen level, increases the expression of several beneficial genes such as erythropoietin, glucose transporter-1 and vascular endothelial growth factor. In order to strengthen the expression of these hypoxia-inducible factors, we administered deferoxamine, an iron chelator known to stabilize HIF-1alpha protein expression, and examined its effects on the functional deficits induced by ischemia. Anesthetized Sprague-Dawley rats were subjected to 60 min of intraluminal occlusion of the middle cerebral artery. Chronic deferoxamine treatment (300 mg/kg, s.c.), or its vehicle, started 24 h after ischemia and was continued bi-weekly until the animals were killed. Sensorimotor deficits were periodically assessed over 2 months, and at this end point, the lesion volume was determined by histology. Treatment with deferoxamine significantly decreased the size of brain damage (-28%) after ischemia and improved behavioral recovery. Indeed, neurological score and sensorimotor performances in the adhesive removal test recovered earlier in the deferoxamine-treated animals. Moreover, the long-lasting skilled forepaw reaching deficits were attenuated by deferoxamine. Although an antioxidant effect of deferoxamine cannot be excluded, the hypothesis that its beneficial effects could be mediated by an increase in HIF-1 target genes merits further investigations. Our data suggest that delayed administration of deferoxamine could represent an interesting therapeutical approach to treat focal cerebral ischemia

Comparison of the effects of erythropoietin and its carbamylated derivative on behaviour and hippocampal neurogenesis in mice.

International audienceErythropoietin (EPO), a well known haematopoietic growth factor, possesses neuroprotective and neurotrophic effects which have been recently reported to improve cognition and to modulate emotional processing. We investigated the effects of EPO and of its non-erythropoietic carbamylated derivative (CEPO) on memory- and emotion-related behaviour in the adult mouse. Locomotor activity, memory performances (place and object recognition tasks), anxiety- (light/dark transition test) and despair-like behaviours (tail suspension test) were assessed over 6 weeks of repeated EPO or CEPO administration (40 μg/kg, twice a week). Given the potential involvement of hippocampal neurogenesis in memory, we also assessed the effects of EPO and CEPO on neurogenesis in the dentate gyrus. Both treatments improved spatial and non-spatial recognition memory and increased the number of NeuN/BrdU double-labeled cells in the dentate gyrus. These effects seem to be, at least partly, independent from an haematopoietic action since administration of CEPO leads to the similar results. Moreover, CEPO decreased, albeit modestly, despair-related behaviour and tended to decrease anxiety-like behaviour. These results suggest that CEPO is as an attractive molecule for the treatment of neuropsychiatric diseases associating memory and/or emotional disorders

Comparative study of proton versus X-rays on circulating leukocytes in a context of brain irradiation: a preclinical study

CERVOXYNational audienceIntroduction: Although radiotherapy based on X-ray improves the survival of patients suffering brain tumours, it also leads to deleterious effects on the inflammatory system such as lymphopenia, which in turn decreases the immunotherapeutic response and is associated to a poor prognosis. Proton therapy has recently emerged as a new radiation strategy for brain tumours. Thanks to its precise dose deposition, it enables to spare healthy tissue. Moreover, due to its different biological effects on the irradiated tissue, it could results in less harmful effects for systemic inflammation. In this project, we aim to evaluate if brain radiation with proton therapy is less deleterious for circulating leukocytes than conventional brain radiotherapy as a function of other variables.Materials & Methods: Tumour-free mice were irradiated twice a day (2.5 Gy/session) for four consecutive days for a total dose of 20Gy with X-rays (X-rad 225 Cx GIP CYCERON, Caen) or protons beam (25MeV PRECy platform, Strasbourg). Groups of mice were defined according to spatial coverage (whole-brain or hemisphere) and dose rate (1 or 2Gy/min). Blood samples were collected before, during and after radiation and circulating leukocytes populations and cytokines were analyzed by flow cytometry. Results: Mice weight decreased after whole-brain radiation with X-rays but not with protons beam. Blood sampling confirmed radiation-induced profound decrease in leukocytes early after irradiation with X-rays, especially for CD3+ lymphocytes and the CD4+ lymphocytes subpopulation. Results seem to show an opposite effect in CD45+ CD11b+ myeloid cells. Interestingly, we noticed that whole-brain irradiation induced a more pronounced effect than hemispheric irradiation. Changes in leukocytes after proton irradiation suggest a conservative effect on circulating lymphocytes.Conclusion: Proton therapy appears as a better radiotherapy strategy for brain tumours to spare circulating leukocytes. The mechanisms behind these observations are under investigation

Comparative study of proton versus X-rays on circulating leukocytes in a context of brain irradiation: a preclinical study

CERVOXYNational audienceIntroduction: Although radiotherapy based on X-ray improves the survival of patients suffering brain tumours, it also leads to deleterious effects on the inflammatory system such as lymphopenia, which in turn decreases the immunotherapeutic response and is associated to a poor prognosis. Proton therapy has recently emerged as a new radiation strategy for brain tumours. Thanks to its precise dose deposition, it enables to spare healthy tissue. Moreover, due to its different biological effects on the irradiated tissue, it could results in less harmful effects for systemic inflammation. In this project, we aim to evaluate if brain radiation with proton therapy is less deleterious for circulating leukocytes than conventional brain radiotherapy as a function of other variables.Materials & Methods: Tumour-free mice were irradiated twice a day (2.5 Gy/session) for four consecutive days for a total dose of 20Gy with X-rays (X-rad 225 Cx GIP CYCERON, Caen) or protons beam (25MeV PRECy platform, Strasbourg). Groups of mice were defined according to spatial coverage (whole-brain or hemisphere) and dose rate (1 or 2Gy/min). Blood samples were collected before, during and after radiation and circulating leukocytes populations and cytokines were analyzed by flow cytometry. Results: Mice weight decreased after whole-brain radiation with X-rays but not with protons beam. Blood sampling confirmed radiation-induced profound decrease in leukocytes early after irradiation with X-rays, especially for CD3+ lymphocytes and the CD4+ lymphocytes subpopulation. Results seem to show an opposite effect in CD45+ CD11b+ myeloid cells. Interestingly, we noticed that whole-brain irradiation induced a more pronounced effect than hemispheric irradiation. Changes in leukocytes after proton irradiation suggest a conservative effect on circulating lymphocytes.Conclusion: Proton therapy appears as a better radiotherapy strategy for brain tumours to spare circulating leukocytes. The mechanisms behind these observations are under investigation