Nitrogen at raised pressure interacts with the GABAA receptor to produce its narcotic pharmacological effect in the rat

Background: Strong evidence supports the concept that conventional anesthetics, including inhalational agents and inert gases, such as xenon and nitrous oxide, interact directly with ion channel neurotransmitter receptors. However, there is no evidence that nitrogen, which only exhibits narcotic potency at increased pressure, may act by a similar mechanism. Methods: We compared the inhibitory and sedative effects of ␥-aminobutyric acid (GABA) and nitrogen pressure on locomotor activity and striatal dopamine release in freely moving rats and investigated the pharmacologic properties of the GABAinduced and nitrogen pressure-induced narcotic action using the highly selective competitive GABA A receptor antagonist bicuculline. Results: Intracerebroventricular GABA infusion up to 60 mol or exposure to nitrogen pressure up to 3 MPa decreased to a similar extent striatal dopamine release (

La plongée : pression barométrique et mécanismes neurochimiques

Les travaux de Paul Bert regroupés dans son ouvrage "La Pression Barométrique" en 1878 ont été à l'origine de la physiologie hyperbare moderne en démontrant 1) que l'on devait dissocier les effets de la pression de ceux de la décompression, 2) les effets de l'oxygène sous pression et 3) que les accidents neurologiques et mortels des plongeurs étaient dus à des décompressions trop rapides. Cependant, il fallut attendre les travaux de Behnke et al. en 1935, pour que l'on attribue les troubles observés en air comprimé ou en mélange azote-oxygène à partir de 3 bars de pression, à l'augmentation de pression partielle d'azote entraînant une narcose à l'azote. On connaît peu de chose sur les origines et les mécanismes de la narcose que l'on retrouve avec tous les gaz dits inertes. La conception traditionnelle était de relier, comme en anesthésie, l'apparition de la narcose à l'expansion des sites hydrophobiques membranaires au delà d'un volume critique du fait de l'adsorption des molécules du gaz. L'observation d'un effet inverse de la pression sur l'anesthésie générale a longtemps conforté cette théorie lipidique. Cependant, depuis peu, on considère à nouveau les hypothèses protéiques depuis que des résultats avec des anesthésiques gazeux ont été interprétés comme l'évidence d'une interaction directe gaz - protéine. La question est de savoir si les gaz inertes qui perturbent notamment la neurotransmission dopaminergique et GABAergique et probablement glutamatergique, agissent par des processus de liaison sur les protéines des récepteurs aux neurotransmetteurs

Opposing effects of narcotic gases and pressure on the striatal dopamine release in rats

International audienceNitrogen-oxygen breathing mixtures, for pressures higher than 0.5 MPa, decrease the release of dopamine in the rat striatum, due to the narcotic potency of nitrogen. In contrast, high pressures of helium-oxygen breathing mixtures of more than 1-2 MPa induce an increase of the striatal dopamine release and an enhancement of motor activity, referred to as the high pressure nervous syndrome (HPNS), and attributed to the effect of pressure per se. It has been demonstrated that the effect of pressure could be antagonized by narcotic gas in a ternary mixture, but most of the narcotic gas studies measuring DA release were executed below the threshold for pressure effect. To examine the effect of narcotic gases at pressure on the rat striatal dopamine release, we have used two gases, with different narcotic potency, at sublethargic pressure, nitrogen at 3 MPa and argon at 2 MPa. In addition, to dissociate the effect of the pressure, we have used nitrous oxide at 0.1 MPa to induce narcosis at very low pressure, and helium at 8 MPa to study the effect of pressure per se. In all the narcotic conditions we have recorded a decrease of the striatal dopamine release. In contrast, helium pressure induced an increase of DA release. For the pressures used, the results suggest that the decrease of dopamine release was independent of such an effect of the pressure. However, for the same narcotic gas, the measurements of the extracellular DA performed in the striatum seem to reflect an opposing effect of pressure, since the decrease in DA release is lower with increasing pressure

Opposing effects of narcotic gases and pressure on the striatal dopamine release in rats

International audienceNitrogen-oxygen breathing mixtures, for pressures higher than 0.5 MPa, decrease the release of dopamine in the rat striatum, due to the narcotic potency of nitrogen. In contrast, high pressures of helium-oxygen breathing mixtures of more than 1-2 MPa induce an increase of the striatal dopamine release and an enhancement of motor activity, referred to as the high pressure nervous syndrome (HPNS), and attributed to the effect of pressure per se. It has been demonstrated that the effect of pressure could be antagonized by narcotic gas in a ternary mixture, but most of the narcotic gas studies measuring DA release were executed below the threshold for pressure effect. To examine the effect of narcotic gases at pressure on the rat striatal dopamine release, we have used two gases, with different narcotic potency, at sublethargic pressure, nitrogen at 3 MPa and argon at 2 MPa. In addition, to dissociate the effect of the pressure, we have used nitrous oxide at 0.1 MPa to induce narcosis at very low pressure, and helium at 8 MPa to study the effect of pressure per se. In all the narcotic conditions we have recorded a decrease of the striatal dopamine release. In contrast, helium pressure induced an increase of DA release. For the pressures used, the results suggest that the decrease of dopamine release was independent of such an effect of the pressure. However, for the same narcotic gas, the measurements of the extracellular DA performed in the striatum seem to reflect an opposing effect of pressure, since the decrease in DA release is lower with increasing pressure

Human cord blood-derived hematopoietic and neural-like stem/progenitor cells are attracted by the neurotransmitter GABA.

International audienceMigration of stem/progenitor cells is a crucial event for homing toward tissue where cells need to be renewed. The neurotransmitter gamma-aminobutyric acid (GABA) has been shown to have a crucial role in migration of neuronal stem/progenitor cells. Since human umbilical cord blood (HUCB) contains stem/progenitor cells able to generate either neuronal or hematopoietic cells, we evaluated the effect of GABA on this type of cells. While whole fraction of mononuclear cells expressed GABA(A) and GABA(B) receptor subunits (GABA-R), only GABA(B)R subunits were found to be expressed on immature CD133+ cells. Functional experiments revealed that both cell fractions of HUCB were attracted by a gradient of GABA concentration and furthermore were blocked by specific antagonists of GABA(A)R and GABA(B)R bicuculline and saclofen, respectively. Moreover, through GABA(B)R activation the migrating fraction was highly enriched by both hematopoietic progenitors and cells able to generate neuron- like cells in culture. Therefore, GABA is a potent chemoattractant of HUCB stem/progenitor cells specifically through GABA(B)R activation

Cord blood-derived neurons are originated from CD133+/CD34 stem/progenitor cells in a cell-to-cell contact dependent manner.

International audiencePrevious studies described that neurons could be generated in vitro from human umbilical cord blood cells. However, there are few data concerning their origin. Notably, cells generating neurons are not well characterized. The present study deals with the origin of cord blood cells generating neurons and mechanisms allowing the neuronal differentiation. We studied neuronal markers of both total fractions of cord blood and stem/progenitor cord blood cells before and after selections and cultures. We also compared neuronal commitment of cord blood cells to that observed for the neuronal cell line SK-N-BE(2). Before cultures, neuronal markers are found within the total fraction of cord blood cells. In CD133+ stem/progenitor cell fraction only immature neuronal markers are detected. However, CD133+ cells are unable to give rise to neurons in cultures, whereas this is achieved when total fraction of cord blood cells is used. In fact, mature functional neurons can be generated from CD133+ cells only in cell-to-cell close contact with either CD133- fraction or a neurogenic epithelium. Furthermore, since CD133+ fraction is heterogenous, we used several selections to precisely identify the phenotype of cord blood-derived neuronal stem/progenitor cells. Results reveal that only CD34- cells from CD133+ fraction possess neuronal potential. These data show the phenotype of cord blood neuronal stem/progenitor cells and the crucial role of direct cell-to-cell contact to achieve their commitment. Identifying the neuron supporting factors may be beneficial to the use of cord blood neuronal stem/progenitor cells for regenerative medicine

Neonatal maternal separation and enhancement of the hypoxic ventilatory response in rat: the role of GABAergic modulation within the paraventricular nucleus of the hypothalamus

Neonatal maternal separation (NMS) affects respiratory control development as adult male (but not female) rats previously subjected to NMS show a hypoxic ventilatory response 25% greater than controls. The paraventricular nucleus of the hypothalamus (PVN) is an important modulator of respiratory activity. In the present study, we hypothesized that in awake rats, altered GABAergic inhibition within the PVN contributes to the enhancement of hypoxic ventilatory response observed in rats previously subjected to NMS. During normoxia, the increase in minute ventilation following microinjection of bicuculline (1 mm) within the PVN is greater in NMS versus control rats. These data show that regulation of ventilatory activity related to tonic inhibition of the PVN is more important in NMS than control rats. Microinjection of GABA or muscimol (1 mm) attenuated the ventilatory response to hypoxia (12% O2) in NMS rats only. The higher efficiency of microinjections in NMS rats is supported by results from GABAA receptor autoradiography which revealed a 22% increase in GABAA receptor binding sites within the PVN of NMS rats versus controls. Despite this increase, however, NMS rats still show a larger hypoxic ventilatory response than controls, suggesting that within the PVN the larger number of GABAA receptors either compensate for (1) a deficient GABAergic modulation, (2) an increase in the efficacy of excitatory inputs converging onto this structure, or (3) both. Together, these results show that the life-long consequences of NMS are far reaching as they can compromise the development of vital homeostatic function in a way that may predispose to respiratory disorders