Abstract
Underwater divers are susceptible to neurological risks due to their exposure to increased pressure. Absorption of elevated partial pressure of inert gases such as helium and nitrogen may lead to nitrogen narcosis. Although the symptoms of nitrogen narcosis are known, the molecular mechanisms underlying these symptoms have not been elucidated. Here, we examined the behaviour of the soil nematode Caenorhabditis elegans under scuba diving conditions. We analysed wild-type animals and mutants in the dopamine pathway under hyperbaric conditions, using several gas compositions and under varying pressure levels. We found that the animals changed their speed on a flat bacterial surface in response to pressure in a biphasic mode that depended on dopamine. Dopamine-deficient cat-2 mutant animals did not exhibit a biphasic response in high pressure, while the extracellular accumulation of dopamine in dat-1 mutant animals mildly influenced this response. Our data demonstrate that in C. elegans, similarly to mammalian systems, dopamine signalling is involved in the response to high pressure. This study establishes C. elegans as a powerful system to elucidate the molecular mechanisms that underly nitrogen toxicity in response to high pressure.
Highlights
When humans are exposed to compressed air or a nitrogen–oxygen mixture at a pressure of 3–4 atmospheres (0.3–0.4 MPa) or in a depth of 10–30 m during diving, they may experience nitrogen narcosis which is a life-threatening condition
To test if dopamine plays a role in a simple model organism under pressure, we examined the response to air pressure in two C. elegans mutants, both defective in the dopamine pathway, cat-2(e1112) and dat-1(ok157)
We examined C. elegans behaviour in deepdiving conditions, aiming to establish it as a multicellular model system that will enable the molecular mechanisms underlying nitrogen narcosis to be deciphered
Summary
When humans are exposed to compressed air or a nitrogen–oxygen mixture at a pressure of 3–4 atmospheres (0.3–0.4 MPa) or in a depth of 10–30 m during diving, they may experience nitrogen narcosis which is a life-threatening condition. Decrease in dopamine levels in rats is suppressed by recurrent exposure to nitrogen narcosis conditions, suggesting an adaptation mechanism [4,8] This adaptive phenomenon has been examined recently in expert scuba divers at 0.6 MPa [9]. The cat-2 mutant animals have reduced levels of dopamine (9% compared to WT) [23] and these low dopamine levels are probably maintained by the activity of tyrosinase enzymes that are expressed in the dopaminergic neurons [15]. Our study revealed that in C. elegans, dopamine controls locomotion speed in response to high pressure. 0.044 0.140 0.220 0.100 0.220 0.050 0.055 compressed nitrogen induced changes in animal speed while compressed oxygen did not affect locomotion speed in both WT and dopamine mutant animals
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