Dopamine/BDNF loss underscores narcosis cognitive impairment in divers: a proof of concept in a dry condition

Eur J Appl Physiol. 2023 Jan;123(1):143-158. doi: 10.1007/s00421-022-05055-6. Epub 2022 Oct 10.

Abstract

Purpose: Divers can experience cognitive impairment due to inert gas narcosis (IGN) at depth. Brain-derived neurotrophic factor (BDNF) rules neuronal connectivity/metabolism to maintain cognitive function and protect tissues against oxidative stress (OxS). Dopamine and glutamate enhance BDNF bioavailability. Thus, we hypothesized that lower circulating BDNF levels (via lessened dopamine and/or glutamate release) underpin IGN in divers, while testing if BDNF loss is associated with increased OxS.

Methods: To mimic IGN, we administered a deep narcosis test via a dry dive test (DDT) at 48 msw in a multiplace hyperbaric chamber to six well-trained divers. We collected: (1) saliva samples before DDT (T0), 25 msw (descending, T1), 48 msw (depth, T2), 25 msw (ascending, T3), 10 min after decompression (T4) to dopamine and/or reactive oxygen species (ROS) levels; (2) blood and urine samples at T0 and T4 for OxS too. We administered cognitive tests at T0, T2, and re-evaluated the divers at T4.

Results: At 48 msw, all subjects experienced IGN, as revealed by the cognitive test failure. Dopamine and total antioxidant capacity (TAC) reached a nadir at T2 when ROS emission was maximal. At decompression (T4), a marked drop of BDNF/glutamate content was evidenced, coinciding with a persisting decline in dopamine and cognitive capacity.

Conclusions: Divers encounter IGN at - 48 msw, exhibiting a marked loss in circulating dopamine levels, likely accounting for BDNF-dependent impairment of mental capacity and heightened OxS. The decline in dopamine and BDNF appears to persist at decompression; thus, boosting dopamine/BDNF signaling via pharmacological or other intervention types might attenuate IGN in deep dives.

Keywords: Brain-derived neurotrophic factor (BDNF); Deep diving; Dopamine; Narcosis; Reactive oxygen species (ROS).

MeSH terms

  • Brain-Derived Neurotrophic Factor / metabolism
  • Cognitive Dysfunction* / etiology
  • Decompression / adverse effects
  • Diving* / adverse effects
  • Dopamine / metabolism
  • Glutamates
  • Humans
  • Inert Gas Narcosis* / complications
  • Reactive Oxygen Species
  • Stupor* / etiology

Substances

  • Brain-Derived Neurotrophic Factor
  • Dopamine
  • Glutamates
  • Reactive Oxygen Species