Jean-Jacques Risso

• PhD DSc
• Head of Department at Armed Forces Biomedical Research Institute, France

Decompression sickness (DCS) with neurological disorders is the leading cause of major diving accidents treated in hyperbaric chambers. Exposure to high levels of CO2 during diving is a safety concern for occupational groups at risk of DCS. However, the effects of prior exposure to CO2 have never been evaluated. The purpose of this study was to eva...

Decompression sickness (DCS) with neurological disorders is the leading cause of diving accidents. Exposure to high levels of CO2 during diving is a safety concern for occupational , groups at risk of DCS. However, the effects of prior exposure to CO2 have never been evaluated. The purpose of this study was to evaluate the effect of CO2 breathing p...

Decompression sickness (DCS) with neurological disorders includes an inappropriate inflammatory response which degenerates slowly, even after the disappearance of the bubbles. There is high inter-individual variability in terms of the occurrence of DCS that could have been mastered by the selection and then the breeding of DCS-resistant rats. We hy...

On one side, decompression sickness (DCS) with neurological disorders lead to a reshuffle of the cecal metabolome of rats. On the other side, there is also a specific and different metabolomic signature in the cecum of a strain of DCS-resistant rats, that are not exposed to hyperbaric protocol. We decide to study a conventional strain of rats that...

Background: Diagnosing diaphragm dysfunction in the absence of complete paralysis remains difficult. The aim of the present study was to assess the normal values of the thickness and the inspiratory thickening of both hemidiaphragms as measured by ultrasonography in healthy volunteers while in a seated position. Methods: Healthy volunteers with a n...

On one side, decompression sickness (DCS) with neurological disorders lead to a reshuffle of the fecal metabolome from rat caecum. On the other side, there is high inter-individual variability in terms of occurrence of DCS. One could wonder whether the fecal metabolome could be linked to the DCS-susceptibility. We decided to study male and female r...

Purpose Long static or intense dynamic apnoea-like high-altitude exposure is inducing hypoxia. Adenosine is known to participate to the adaptive response to hypoxia leading to the control of heart rate, blood pressure and vasodilation. Extracellular adenosine level is controlled through the equilibrative nucleoside transporter 1 (ENT-1) and the enz...

Massive bubble formation after diving can lead to decompression sickness (DCS), which can result in neurological disorders. We demonstrated that hydrogen production from intestinal fermentation could exacerbate DCS in rats fed with a standard diet. The aim of this study is to identify a fecal metabolomic signature that may result from the effects o...

The prevention, prognosis and resolution of decompression sickness (DCS) are not satisfactory. The etiology of DCS has highlighted thrombotic and inflammatory phenomena that could cause severe neurological disorders or even death. Given the immunomodulatory effects described for minocycline, an antibiotic in widespread use, we have decided to explo...

Introduction: Previous studies have suggested that the circulatory system was involved in the production of circulatory bubbles after diving. This study was designed to research the cardio-vascular function characteristics related to the production of high bubble grades after diving. Methods: Thirty trained divers were investigated both at baseline...

Since the 1970s, although many studies have shown that the consumption of xylitol reduces the incidence of dental caries, others have not shown such a benefit. As a result, a Cochrane review published in 2005 states that the efficacy of xylitol against caries is not proven. However, dozens of public health authorities, learned societies, armies, et...

Circulating mitochondrial DNA (mtDNA) is receiving increasing attention as a danger-associated molecular pattern in conditions such as autoimmunity or trauma. In the context of decompression sickness (DCS), the course of which is sometimes erratic, we hypothesize that mtDNA plays a not insignificant role particularly in neurological type accidents....

In its severest forms, decompression sickness (DCS) may extend systemically and/or induce severe neurological deficits, including paralysis or even death. It seems that the sterile and ischemic inflammatory phenomena are consecutive to the reaction of the bubbles with the organism and that the blood platelet activation plays a determinant role in t...

Introduction: Periodontal diseases are caused by pathogenic microorganisms that induce increases in of local and systemic proinflammatory cytokines, resulting in periodontal damage. The onset and evolution of periodontal diseases are influenced by many local and systemic risk factors. Educational objective: In this article, we aim to review the res...

Objective: In the field of odontology, the objective of the military health service is to ensure that, during operations, the Armed Forces can rely on soldiers able to fulfill their missions without any loss of time and efficiency attributable to a dental cause. To achieve this aim, soldiers must comply with oral prevention recommendations (oral an...

Objectif : dans le domaine de l’odontologie, l’objectif du Service de santé est de permettre aux armées de disposer en opération de militaires capables d’effectuer leurs missions sans perte de temps ni d’efficacité attribuable à une cause dentaire. Pour atteindre cet objectif, les militaires doivent respecter les recommandations en matière de préve...

Objective: The frequent occurrence of dental caries among soldiers has a deleterious impact on the operational capability of the Armed Forces. The consumption of chewing-gums sweetened with xylitol has proved its efficiency in the prevention of dental caries among children. The objective of our study is to assess its efficiency among soldiers. Met...

According to the OECD statistical base for 2014, anti-depressants will, on average, be distributed at a rate of 62 daily doses per 1,000 inhabitants for the 25 countries surveyed (Health at a glance: Europe 2014; OECD Health Statistics; World Health Organization and OECD Health Statistics, 2014). Divers must be concerned. On another hand, divers ar...

Xenon (Xe) is considered to be the golden standard neuroprotective gas. However, Xe has a higher molecular weight and lower thermal conductivity and specific heat than those of nitrogen, the main diluent of oxygen in air. These physical characteristics could impair or at least reduce the intrinsic neuroprotective action of Xe by increasing the pati...

The noble gases xenon (Xe) and helium (He) are known to possess neuroprotective properties. Xe is considered the golden standard neuroprotective gas. However, Xe has a higher molecular weight and lower thermal conductivity and specific heat than those of nitrogen, the main diluent of oxygen (O2) in air, conditions that could impair or at least redu...

Hyperbaric oxygen induced in rats a decrease in striatal dopamine levels. Such decrease could be a result of changes in glutamatergic and GABAergic controls of the dopaminergic neurons into the Substantia Nigra Pars Compacta. The aim of this study was to determine the role of gluatamatergic and Gama-Amino-Butyric-Acid neurotransmissions in this alt...

Introduction: Since their appearance in the 1890s, mouthguards have been the subject of numerous research studies. Based on the results of these studies, the use of mouthguard is recommended for the prevention of orofacial lesions in some sports. Since the mid-1960, a new type of mouthguard appeared: the performance mouthguard. According to its man...

Objective. The objective of our study is to determine if the pressure changes generated by the practice of scuba diving can cause the fracture of teeth temporarily filled between two sessions of an endodontic treatment and if the filling material and the obturation techniques have an impact on the risk of dental fracture. Method. 60 extracted maxil...

Introduction: In the army, the occurrence of orofacial lesions related to military and sport activities can have a deleterious impact on the operational capability of soldiers and their units. While mouthguards, also called Intrabuccal Guards ( IBGs), are used in a civilian context to decrease the incidence and severity of orofacial lesions of trau...

Investigation of the use of a mouthguard for decreasing the incidence and/or severity of sportrelated concussions. Introduction: Concussion in sport, so-called sport-related concussion (SRC), is a complex pathophysiological process resulting in the impairment of the brain. Its incidence is increasing due to the uncertainty surrounding SRC (diagnos...

The results of our study show that the consumption of chewing-gums sweetened with xylitol has a major interest for the diminution of dental caries in mainland France for high caries risk soldiers and during deployments for all the soldiers exposed to a deterioration of oral hygiene and dietary habits. A daily consumption of 6 to 10 grams of xylitol...

Les résultats de l’étude XYLIMIL montrent que la consommation de chewing-gums au xylitol a un intérêt majeur pour la diminution de la survenue de caries dentaires en métropole pour les militaires à risque carieux élevé et au cours des missions pour tous les militaires exposés à une dégradation de leur hygiène alimentaire et bucco-dentaire. Une cons...

Recent data have shown that normobaric oxygen (NBO) increases the catalytic and thrombolytic efficiency of recombinant tissue plasminogen activator (rtPA) in vitro, and is as efficient as rtPA at restoring cerebral blood flow in rats subjected to thromboembolic brain ischemia. Therefore, in the present study, we studied the effects of hyperbaric ox...

Normobaric oxygen (NBO) and hyperbaric oxygen (HBO) are emerging as a possible co-treatment of acute ischemic stroke. Both have been shown to reduce infarct volume, to improve neurologic outcome, to promote endogenous tissue plasminogen activator-induced thrombolysis and cerebral blood flow, and to improve tissue oxygenation through oxygen diffusio...

The occurrence of paroxysmal narcotic episodes including psychotic-like symptoms in divers participating to experimental deep diving programs with various gas mixtures has constituted, beyond the classical symptoms of the high-pressure neurological syndrome, the major limitation for deep diving. With the development of new saturation deep diving pr...

In mice, disseminated coagulation, inflammation, and ischemia induce neurological damage that can lead to death. These symptoms result from circulating bubbles generated by a pathogenic decompression. Acute fluoxetine treatment or the presence of the TREK-1 potassium channel increases the survival rate when mice are subjected to an experimental div...

Interventions: Helium has been shown to provide neuroprotection in mechanical model of acute ischemic stroke by inducing hypothermia, a condition shown by itself to reduce the thrombolytic and proteolytic properties of tissue plasminogen activator. However, whether or not helium interacts with the thrombolytic drug tissue plasminogen activator, th...

Despite state-of-the-art hyperbaric oxygen (HBO) treatment, about 30% of patients suffering neurologic decompression sickness (DCS) exhibit incomplete recovery. Since the mechanisms of neurologic DCS involve ischemic processes which result in excitotoxicity, it is likely that HBO in combination with an anti-excitotoxic treatment would improve the o...

Objective: The aim of the study MoCoDeS (reasons for dental emergency care during operation Serval) is to identify the types of dental pathologies encountered during deployments in order to prevent them in the future by implementing adapted measures and in doing so, enable soldiers to be available without any loss of time and efficiency attributabl...

We investigated the effects of the noble gas argon on the expression of locomotor sensitization to amphetamine and amphetamine-induced changes in dopamine release and mu-opioid neurotransmission in the nucleus accumbens. We found (1) argon blocked the increase in carrier-mediated dopamine release induced by amphetamine in brain slices, but, in cont...

Objectif : L’objectif de l’étude POP (Problèmes Odontologiques des Plongeurs) est d’étudier les conséquences odontologiques de l’exposition des militaires au milieu subaquatique. Méthode : Un questionnaire relatif aux problèmes bucco-dentaires pouvant être rencontrés par les plongeurs sous-marins a été complété par tous les plongeurs se présentant...

La plongée militaire totalise 2 200 personnels dont certains sont spécialisés en opérations de déminage ou en contreterrorisme maritime. En parallèle, la plongée civile s’est considérablement développée ; de nombreux accidents surviennent malgré le respect des procédures et de nouvelles entités cliniques émergent. Ainsi la médecine de la plongée ci...

Au cours du XIXe siècle, le développement du travail en air comprimé est à l’origine des premières observations cliniques attribuables aux effets de l’élévation de la pression sur l’organisme. En parallèle, la plongée en scaphandre devient une activité routinière. La conséquence est que de nombreux cas d’accidents de désaturation sont rapportés en...

Dans un sous-marin en détresse avec une voie d’eau, la compression de l’air présent dans un compartiment augmente la pression partielle d’azote, soumettant ainsi l’équipage à un risque de narcose. Afin de pouvoir se connecter à ce sousmarin, le véhicule de secours doit être à la même pression. L’équipe médicale intervenante est ainsi soumise au mêm...

Systemic administration of γ-amino-butyric acid type A (GABA-A) and benzodiazepine receptor agonists has been reported to block the development of locomotor sensitization to amphetamine. Here, we investigated whether the non-anesthetic noble gas argon, shown to possess agonistic properties at these receptors, may block the acquisition of amphetamin...

Background: Current in vivo methods cannot distinguish between the roles of vascular and stationary tissular gas bubbles in the mechanisms of decompression sickness (DCS). New method: To answer this question, we designed a normobaric-hyperbaric chamber for studying specifically the contribution of stationary tissular gas bubbles in the mechanism...

Certain underwater circumstances carry risk of inert gas narcosis. Impairment of sensorimotor information processing due to narcosis, induced by normobaric nitrous oxide or high partial nitrogen pressure, has been broadly evidenced, by a lengthening of the reaction time (RT). However, the locus of this effect remains a matter of debate. We examined...

The purpose of this study was to investigate the change in the striatal dopamine (DA) level in freely-moving rat exposed to different partial pressure of oxygen (from 1 to 5 ATA). Some works have suggested that DA release by the substantia nigra pars compacta (SNc) neurons in the striatum could be disturbed by hyperbaric oxygen (HBO) exposure, alte...

En odontostomatologie, face à une perte de substance osseuse dont le comblement ne peut intervenir spontanément du fait des seules capacités physiologiques du patient (défaut osseux de taille critique), le praticien peut avoir recours à de nombreux matériaux de comblement osseux. Actuellement, le matériau de référence reste l’os du patient (greffe...

Ischemia and metabolic crisis are frequent post-traumatic secondary brain insults that negatively influence outcome. Clinicians commonly mix up these two types of insults, mainly because high lactate/pyruvate ratio (LPR) is the common marker for both ischemia and metabolic crisis. However, LPR elevations during ischemia and metabolic crisis reflect...

Bubble formation can occur in the vascular system after diving leading to decompression sickness (DCS). DCS signs and symptoms range from minor to death. Too often, patients are admitted to hyperbaric centre with atypical symptoms while bubbles cannot be detected anymore. In absence of relevant biomarker for humans, the therapeutic management remai...

Vascular bubble formation after decompression contributes to endothelial injuries which form the basis for the development of decompression sickness (DCS). Nitric oxide (NO) is a powerful vasodilator that contributes to vessel homeostasis. It has been shown that NO-releasing agent may reduce bubble formation and prevent serious decompression sickne...

Interest of hyperbaric oxygen therapy in the prevention and treatment of bisphosphonate-related osteonecrosis of the jaws. Bisphosphonates (BP) have been used since 1960s for their capability to alter the mechanism of bone resorption and remodeling. Intravenous (IV) BP are effective in the treatment and management of cancer-related conditions inclu...

Argon has been shown to provide cortical as well as, under certain conditions, subcortical neuroprotection in all models so far (middle cerebral artery occlusion, trauma, neonatal asphyxia, etc.). This has led to the suggestion that argon could be a cost-efficient alternative to xenon, a metabolically inert gas thought to be gold standard in gas ph...

Massive bubble formation after diving can lead to decompression sickness (DCS) that can result in central nervous system disorders or even death. Bubbles alter the vascular endothelium and activate blood cells and inflammatory pathways, leading to a systemic pathophysiological process that promotes ischemic damage. Fluoxetine, a well-known antidepr...

The potential benefit of 100 vol% normobaric oxygen (NBO) for the treatment of acute ischemic stroke patients is still a matter of debate. To advance this critical question, we studied the effects of intraischemic normobaric oxygen alone or in combination with recombinant tissue-plasminogen activator (rtPA) on cerebral blood flow and ischemic brain...

In vitro studies have well established the neuroprotective action of the noble gas argon. However, only limited data from in vivo models are available, and particularly whether postexcitotoxic or postischemic argon can provide neuroprotection in vivo still remains to be demonstrated. Here, we investigated the possible neuroprotective effect of post...

Nitrogen supersaturation and bubble formation can occur in the vascular system after diving, leading to death and nervous disorders from decompression sickness (DCS). Bubbles alter the vascular endothelium, activate platelets, and lead to focal ischemia with neurological damage mediated by the mechanosensitive TREK-1 neuronal potassium ion channel...

In rats, a single exposure to 3 MPa nitrogen induces change in motor processes, a sedative action and a decrease in dopamine release in the striatum. These changes due to a narcotic effect of nitrogen have been attributed to a decrease in glutamatergic control and the facilitation of GABAergic neurotransmission involving NMDA and GABA(A) receptors,...

Preclinical evidence in rodents has suggested that inert gases, such as xenon or nitrous oxide, may be promising neuroprotective agents for treating acute ischemic stroke. This has led to many thinking that clinical trials could be initiated in the near future. However, a recent study has shown that xenon interacts with tissue-type plasminogen acti...

We previously demonstrated that vitamin D₂ (ergocalciferol) triggers axon regeneration in a rat model of peripheral nerve transection. In order to confirm the regenerative potential of this neuroactive steroid, we performed a study in which vitamin D₃ (cholecalciferol) was delivered at various doses to paralytic rats. After spinal cord compression...

Previous studies performed in the laboratory have shown that nitrogen narcosis induces a decrease in striatal glutamate and dopamine levels. Although we stimulated the N-methyl-D-aspartate (NMDA) receptor, an important glutamate receptor required for motor and locomotor activity managed by the striatum, and demonstrated that the receptor was effect...

Olfactory ensheathing cells (OECs) are unique glia found only in the olfactory system. They retain exceptional plasticity and support olfactory neurogenesis and retargeting across the PNS:CNS boundary in the olfactory system. OECs have been shown to improve functional outcome when transplanted into rodents with spinal cord injury. The growth-promot...

The use and benefits of normobaric oxygen (NBO) in patients suffering acute ischemic stroke is still controversial. Here we show for the first time to the best of our knowledge that NBO reduces both NMDA-induced calcium influxes in vitro and NMDA-induced neuronal degeneration in vivo, but increases oxygen and glucose deprivation-induced cell injury...

The effects of anesthetics on central energetic metabolism remain poorly documented. In this study, the authors have investigated changes in energetic metabolism in the rat striatum following the systemic administration of either pentobarbital or ketamine. Changes in subcortical energetic homeostasis were compared to those in peripheral adipocyte t...

Nitrogen narcosis occurs in humans at around 0.4 MPa (4 ATA). Hydrogen narcosis occurs between 2.6 and 3.0 MPa. In rats, nitrogen disturbances occur from 1 MPa and a loss of righting reflex around 4 MPa. Neurochemical studies in striatum of rats with nitrogen at 3 MPa (75% of anesthesia threshold) with differential pulse voltammetry have demonstrat...

Previous microdialysis studies performed in rats have revealed a decrease of striatal dopamine and glutamate induced by nitrogen narcosis. We sought to establish the hypothetical role of the glutamatergic corticostriatal pathway because of the glutamate deficiency which occurs in the basal ganglia in this hyperbaric syndrome. Retrodialysis with 1 m...

High pressure of helium-oxygen (He-O2) increases the extracellular levels in both serotonine and dopamine in the rat striatum. Some motor symptoms evoked by high pressure (i.e., LMA) are known to be reduced by intrastriatal infusions of D1-like (SCH23390, 1 microM) or D2-like (Sulpiride, 1 microM) dopaminergic antagonists. Other studies have also r...

Preclinical evidence in rodents has proven that xenon may be a very promising neuroprotective agent for treating acute ischemic stroke. This has led to the general thinking that clinical trials with xenon could be initiated in acute stroke patients in a next future. However, an unappreciated physicochemical property of xenon has been that this gas...

Since a pioneer work that has shown in vitro that the rat's fibrinolytic system is 10-fold less sensitive to recombinant tissue-plasminogen activator (rtPA) than the human system, most preclinical studies are performed with 10 instead of 0.9 mg/kg rtPA (the clinical dose in stroke patients). In this study, we compared the effects of these doses on...

Absence of axo-dendritic differentiation in cortical neurons 24 h after seeding. Fluorescent microphotographs showing immunolabelling for Tau-1 (green) and MAP2 (red) specific markers of axons and dendrites, respectively. Hoechst #33258 stained the nuclei (blue). At 24 h post-seeding, tau expression is low and essentially colocalised with MAP2, ind...

TIMP-1/GFP transfection and actin cytoskeleton labelling. Fluorescent microphtographs showing anti-GFP immunostaining (green) and F-actin phallodin labelling (red). Hoechst #33258 stained the nuclei (blue). Note that transfected neurons appear well integrated in the neuronal circuitry and most neurites and growth cones are intermingled with neuriti...

Inhibitory effect of mrTIMP on hrMMP-2 proteolytic activity. Fluorescence generated by cleavage of the fluorescein quenched substrate (Mcmat, 0.5 µg) is expressed as arbitrary fluorescence units (AFU). Mcmat cleavage by human recombinant MMP-2 (hr MMP-2, 20 ng) was inhibited by mouse recombinant TIMP-1 (mrTIMP-1, 100 ng) diluted in TCNB (Tris, CaCl...

TIMP-1/GFP is not detected in the supernatant of transfected cortical neurons. Western blot from supernatants (S) and lysates (L) of N2a cells and neurons 24 or 48 h after transfection with TIMP-1/GFP constructs. The transgene is detected in N2a cells, where transfection rates are over 30%, whereas it is not detected in transfected neuronal culture...

Tissue inhibitor of metalloproteinases-1 (TIMP-1) displays pleiotropic activities, both dependent and independent of its inhibitory activity on matrix metalloproteinases (MMPs). In the central nervous system (CNS), TIMP-1 is strongly upregulated in reactive astrocytes and cortical neurons following excitotoxic/inflammatory stimuli, but no informati...

Astrocytes play an active role in the central nervous system and are critically involved in astrogliosis, a homotypic response of these cells to disease, injury, and associated neuroinflammation. Among the numerous molecules involved in these processes are the matrix metalloproteinases (MMPs), a family of zinc-dependent endopeptidases, secreted or...

Previous neurochemical studies performed in rats have revealed a decrease of striatal dopamine and glutamate induced by inert gas narcosis. We sought to establish the hypothetical role of glutamate and its main receptor, the N-methyl-d-aspartate (NMDA) receptor, in this syndrome. We aimed to counteract the nitrogen narcosis-induced glutamate and do...

Erythropoietin receptor (EpoR) binding mediates neuroprotection by endogenous Epo or by exogenous recombinant human (rh)Epo. The level of EpoR gene expression may determine tissue responsiveness to Epo. Thus, harnessing the neuroprotective power of Epo requires an understanding of the Epo-EpoR system and its regulation. We tested the hypothesis tha...