Authors: Courtney Johnson
A new study, conducted by researchers at UCLA School of Nursing (CA, USA) has demonstrated that increased levels of the neurotransmitter glutamate and decreased levels of the neurotransmitter gamma-aminobutyric acid (GABA) are present in patients with obstructive sleep apnea (OSA) when compared with healthy controls. The findings were published recently in the Journal of Sleep Research and may offer explanations for the various neurological symptoms observed in the disorder
“In previous studies, we’ve seen structural changes in the brain due to sleep apnea, but in this study we actually found substantial differences in these two chemicals that influence how the brain is working,” commented Paul Macey (UCLA School of Nursing).
One in 15 people suffer from moderate to severe OSA – the most common type of sleep apnea and a disorder involving interruptions in respiration during sleep of up to 30 times per hour. Beyond symptoms experienced during sleep, patients also report impacts on their daily lives, such as memory issues, difficulties with concentration, reduced decision-making capabilities, stress and depression.
In the current study, researchers examinedthe insular cortices, an area of the brain which is impaired in OSA. The insular cortices integrate signals from higher brain regions to regulate emotion, thinking and physical functions such as blood pressure and perspiration. Using MRI scans of 14 OSA patients and 22 healthy individuals, higher levels of glutamate and lower levels of GABA were observed in OSA sufferers.
GABA acts as an inhibitory neurotransmitter for many neural processes as well as playing a role in endorphin generation. In contrast glutamate acts as a stimulatory neurotransmitter, implying that the brains of OSA individuals are working at high stress levels. High levels of glutamate are also known to be potentially toxic to nerves and neurons.
“It is rare to have this size of difference in biological measures,” Macey remarked. “We expected an increase in the glutamate, because it is a chemical that causes damage in high doses and we have already seen brain damage from sleep apnea. What we were surprised to see was the drop in GABA. That made us realize that there must be a reorganization of how the brain is working.”
The results are in some ways promising though: “In contrast with damage, if something is working differently, we can potentially fix it.”
Researchers hypothesize that changes in these neurotransmitter levels could alter the regulation of the autonomic nervous system and in particular cardiovascular regulation, which is impaired in OSA.
In the future, the team aim to examine if treatments such as continuous positive airway pressure restore such chemical levels within the brain and if not, to investigate what treatments might be available to restore these levels. Current research is also underway examining the effectiveness of mindfulness exercises in reducing glutamate levels within the brain.
“What comes with sleep apnea are these changes in the brain, so in addition to prescribing continuous positive airway pressure, or CPAP – a machine used to help an individual sleep easier, which is the gold standard treatment for sleep disturbance – physicians now know to pay attention to helping their patients who have these other symptoms,” Macey concluded. “Stress, concentration, memory loss – these are the things people want fixed.”
Sources: UCLA Press Release; Macey PM, Sarma MK, Nagarajan R et al. Obstructive sleep apnea is associated with low GABA and high glutamate in the insular cortex. J. Sleep Res. doi:10.1111/jsr.12392 (2016) (Epub ahead of print).