Research news in brief

Gut feeling: anxiety may be linked to gut bacteria

Irish research published in the open access journal Microbiome has investigated how gut bacteria may influence anxiety-like behaviours. Investigators from University College Cork found that a significant number of biological molecules called microRNAs were changed in the brains of microbe-free mice. These mice, known as germ-free (GF) mice, are reared in a germ-free bubble and typically display abnormal anxiety, deficits in sociability and cognition, and increased depressive-like behaviours. MicroRNAs are short sequences of nucleotides, which can act to control how genes are expressed. They have been shown to be involved in a wide range of biological processes, and microRNA dysregulation or dysfunction is believed to be an underlying factor contributing to stress-related psychiatric disorders, neurodegenerative diseases and neurodevelopmental abnormalities. MicroRNA changes in the brain have been implicated in anxiety-like behaviours. The researchers found that levels of 103 microRNAs in the amygdala and 31 microRNAs in the prefrontal cortex were different in GF mice compared with conventional mice. Adding back the gut microbiome later in life normalised some of the changes to microRNAs in the brain. The findings suggest that a healthy microbiome is necessary for appropriate regulation of microRNAs in these brain regions. Previous research had shown that manipulation of the gut microbiome affects anxiety-like behaviours, but this is the first time that the gut microbiome has been linked to microRNAs in both the amygdala and the prefrontal cortex, according to the authors. They found that depleting the microbiota of adult rats with antibiotics affected some microRNAs in the brain in a similar way to the GF mice. According to the authors, this finding suggests that even if a healthy microbiota is present in early life, subsequent changes in adulthood may affect microRNAs in the brain relevant to anxiety-like behaviours.

Improvised explosive devices more damaging than landmines

The types of close contact injuries inflicted by improvised explosive devices (IEDs) are much more serious than the injuries associated with land mines, according to Canadian research published in the online journal BMJ Open. After a high profile campaign, 162 countries signed the 1997 Ottawa Treaty pledging to stop the production and use of landmines. However, they have increasingly been replaced in modern warfare with IEDs. The mechanism of injury is the same for landmines and IEDs, while the seriousness of injuries for either device depends on how close the victim is to the centre of the explosion, say the researchers. But they suspected that pattern 1 injuries — those where the victim suffers the full effects of the explosion at close quarters — would be more serious when they involved IEDs. They therefore assessed pattern 1 injuries sustained by 100 people during IED attacks in Afghanistan over 18 months in 2010–11 and compared them with pattern 1 injuries previously described for landmines. All the casualties, who comprised both local civilians and military personnel, were male and aged between 6 and 44 years. Their average age was 25 years; nine were under the age of 18 years. They were all treated at the North Atlantic Treaty Organization Role 3 Multinational Medical Unit at Kandahar Air Field, Afghanistan, a facility equivalent to a level II civilian trauma centre. Eleven people were dead on arrival; a further eight subsequently died of their wounds in hospital, giving a fatality rate of one in five (19%). IED victims were more likely than people similarly injured by landmines to have more than one amputation (70% v 10.5%). Five out of the 70 multiple amputees had four amputations, 27 had three amputations and 38 had a double amputation. Among the nine children and teenagers, three had a triple amputation and five had a double amputation. IED victims were also twice as likely to sustain genital and gluteal injuries (26% v 13.4%). Pelvic fracture was more common among IED victims who had multiple amputations and genital and gluteal injuries than it was among landmine victims with similar injuries (28.6% v 3.3%). And IED victims with this pattern of injuries were also nearly four times more likely to die than similarly injured landmine victims (24.3% v 6.7%). IEDs are sometimes portrayed as a primitive or crude weapon crafted from locally available resources because of a lack of access to conventional weapons, but they have evolved and are now more sophisticated, directed and destructive, say the researchers.

Methamphetamine use linked to stroke in young people

The stimulant methamphetamine, also known as “speed”, “ice” and “meth” is linked to a heightened risk of stroke among young people, according to a review of the available evidence by authors from the National Drug and Alcohol Research Centre, published in the Journal of Neurology, Neurosurgery and Psychiatry. Haemorrhagic stroke is more commonly associated with the use of this drug than ischaemic stroke, with men twice as likely to succumb as women, the findings show. The authors were looking for a potential link between methamphetamine use and associated stroke risk in young people (under the age of 45 years), and their findings were based on a review of 370 articles published up to February 2017 of which 77 case reports and series were selected for inclusion. Some 81 haemorrhagic and 17 ischaemic strokes were reported. Both types were around twice as common in men as they were in women. In the case reports and series, eight out of ten strokes associated with the use of methamphetamine among young people were haemorrhagic. This rate is much higher than reported rates of this type of stroke in people under the age of 45 years (40–50%) or in older people (15–20%), the researchers point out. Methamphetamine can be swallowed, inhaled or injected. Haemorrhagic strokes were equally associated with swallowing the drug and injecting it, while inhalation was the most common route associated with ischaemic stroke. Haemorrhagic stroke was associated with vascular abnormalities, such as high blood pressure and vasculitis, in a third of cases. Repeated use of methamphetamine can drive up blood pressure even in people whose blood pressure is normal to start with, say the researchers. Risk of death was also higher after a haemorrhagic stroke: one in four people recovered completely, but a third died. This compares with complete recovery for one in five people and death in one in five after an ischaemic stroke.

Less REM sleep associated with greater risk of dementia

Research from Swinburne University of Technology in Melbourne has found that dementia in the elderly may be predicted by measuring rapid eye movement (REM) sleep. The study, published in Neurology, found that for every percentage that REM sleep was reduced in an elderly person, there was a nine-fold increase in the risk of them developing dementia. Researchers looked at 321 people with an average age of 67 years who participated in the United States-based Framingham Heart Study. During the study, their sleep cycles were measured. Researchers then followed the participants for an average of 12 years. During that time, 32 people were diagnosed with some form of dementia and of those, 24 were determined to have Alzheimer’s disease. The participants who developed dementia spent an average of 17% of their sleep time in REM sleep, compared with 20% for the people who did not develop dementia. After adjusting for age and sex, researchers found that a lower percentage of REM sleep and a longer time to get to the REM sleep stage were both linked to a greater risk of dementia. The results were similar after researchers adjusted for other factors that could affect dementia risk or sleep, such as heart disease factors, depression symptoms and medication use. Other stages of sleep were not associated with an increased dementia risk.

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