OAA Medium Project Grant
Novel strategy in preventing the neurotoxicity of nitrous oxide when used for labour pain relief
Dr Daqing Ma
Background
Nitrous oxide (N2O) is a commonly used labour analgesic in the UK, with usage during labour as high as 60%. However, a body of research suggests that the gas may in fact be toxic to the brain. While this toxicity may not strongly affect the mother, N2O is known to cross the placenta and enter the blood stream of the foetus. Here, the foetal brain is more vulnerable than the mothers. This is of particular importance if there are complications in the neonatal period which may involve the infant needing surgery and further anaesthesia. In this case, the brain may already be primed for damage by N2O. Argon, on the other hand, is a noble gas, a completely inert chemical. Despite this chemical lack of action, it has been shown to be biologically active, protecting neurons from a range of damage including traumatic brain injury.
Aims
The aim of this study is to study the mechanisms by which the two gases interact to give toxicity or protection. By then manipulating cellular mechanisms in a culture model we can try to determine how the gases have their toxic or protective effects.
Methodology
A pure cortical neuronal culture can be obtained by removing the brain of an embryonic rat, separating the cells until they are single neurons, and plating these neurons on an optimised growth medium. After one week growth, the neurons grow processes and interact similar to neurons in the intact brain. Three treatment groups will be used; N2O and argon alone (50% N2O or 25% Argon +20% O2 + 5% CO2 balanced with nitrogen), and a third group with N2O and argon combined (50% N2O + 25% Argon + 20% O2 + 5% CO2). Cultures will be exposed to the gases for four hours, after which a subset will be collected for western blotting, flow cytometry for reactive oxygen species and immunofluorescent staining. A second set will be removed from the gas and returned to normal growth conditions for 24 hours, after which cell viability tests will be performed to assess longer term outcomes. A control group will be treated the same with the exception of exposure to any gas mixture.
By using inhibitors of various areas of the pathways thought to be involved in the mechanisms, a roadmap of the potential effects of the two gases can be built.
The in vivo model will involve treating 3 and 7 day old rat pups, similar in development to preterm and term human infants, to the same gas combinations. Levels of cell death will be measured and any structural changes to the brain will be analysed.
Expected outcomes
Preliminary data shows that N2O does indeed have neurotoxic effects on the
neuronal culture. This project will examine in vivo evidence of this fact, and strengthen the knowledge about mechanisms of argon neuroprotection.
Implications
If N2O can truly be neurotoxic, its use as a labour analgesic may be questionable due to the vulnerability of the neonatal brain. If a simple, cost effective gas could be introduced to counteract the neurotoxicity of N2O this could have positive effects on the further development of the brain.
Please see the NIAA's position statement on the use of animals in medical research.
