Science: Tastes so good it will leave you twitching: Glutamate helps to flavour Chinese food, but it also has a role in strokes and Alzheimer's disease, writes Ruth McKernan

Within half an hour of finishing lunch, I had a pounding headache, felt weak, was unsteady on my feet and had difficulty breathing. I crawled out of the World Conference on Pharmacology, held in one of the plushest hotels in Tokyo, and lay for the next two hours squirming on the floor of the hotel's palatial 'ladies' rest room'.

People stepped over me with the sympathy usually reserved for English football fans abroad. It was my first trip to the Orient, my first delicious thick and spicy soup, and my first encounter with 'Chinese restaurant syndrome'.

The syndrome is caused by glutamate, which is added to oriental food as the flavour enhancer monosodium glutamate (MSG). But Chinese restaurant syndrome is the least serious of the conditions associated with this molecule: glutamate is responsible for the brain damage that can result from strokes, which rank as the third-largest cause of death in Western Europe and North America, after cancer and heart disease.

Glutamate is also a primary factor in the memory loss suffered in Alzheimer's disease, and the hallucinations experienced by those who take the illicit drug PCP.

Glutamate is one of the chemical messengers present in the brain responsible for transmitting information from one cell to another. It works by binding to 'receptors' - specific sites on the surface of the brain cell that recognise the chemical - rather as a key fits into a lock. For years, biochemists have known that glutamate acts as a pass key - it can open four types of lock.

Last month, however, they discovered that there is a much richer variety of receptors than they had thought. By analysing how these receptors differ from one another, they hope to develop new drugs to prevent the sort of paralysing brain damage that results from strokes. It may even be possible to slow the loss of memory characteristic in those suffering from Alzheimer's disease.

German researchers have isolated the genes responsible for the receptors and, by inserting the genes into cells cultured in the laboratory, can now study each receptor individually.

Glutamate is present in small amounts in every cell in the body and brain cells make their own glutamate. Normally, it does not get from the blood into the brain unless present in excessive amounts; it was only because the meal I ate in Tokyo contained so much MSG that concentrations in my blood were high enough for some of it to pass into my brain, causing me to be ill. Even then it only reaches one specialised region, the hypothalamus, a cherry- sized structure at the front of the brain responsible for many functions, including muscle control and blood pressure. The glutamate I ingested, albeit deliciously disguised, may have caused my symptoms by overstimulating cells in the hypothalamus.

Overstimulation is also the key to the brain damage suffered when someone has a stroke. Glutamate is normally released from brain cells only in small, controlled amounts. A stroke, or a severe head injury, interferes with the blood supply to the brain, reducing the supply of essential nutrients, oxygen and glucose, to the cells. Without a continuous supply of energy, the cell cannot hold in its glutamate and it pours out, overstimulating the adjacent cells and triggering a series of internal chemical reactions. Ultimately, the cells are made to work so hard that they burn out - they are literally excited to death.

Jim McCulloch, whose team at Glasgow University comprises world leaders in the search for possible treatments for stroke, says: 'Dead brain cells can never be replaced and we have no drugs at present that can protect them.' But Professor McCulloch believes there may be ways of blocking the action of glutamate and so preventing brain damage.

Although there are four types of glutamate receptor, one of them - the NMDA receptor - is the most important in cell death. Pharmaceutical companies are developing drugs that will block this one type of receptor but still allow glutamate to act on the others. 'By using receptor-selective drugs, we can take out the lethal system but leave others unaffected,' says Professor McCulloch.

Drugs that block the NMDA receptor are undergoing clinical trials in the US and Britain. 'They undoubtedly save brain cells, even if given a few hours after a stroke. But you would take these drugs only for a few days in an emergency,' warns Professor McCulloch, because the side-effects can be severe. NMDA receptors normally control memory, thought processing and movement. Patients who take drugs to block these receptors could experience side-effects ranging from drowsiness to hallucinations.

The side-effects came as little surprise to researchers. About five years ago American scientists realised that PCP, also known as 'angel dust', which has been much abused in the US for its mind-bending properties, blocks the NMDA receptors.

'We now know enough about how glutamate can cause brain damage to see where drugs will work,' says Professor McCulloch. 'This is one of the areas where Britain has been at the forefront of research internationally.'

Drugs that block glutamate receptors impair memory. If it were possible to do the opposite - make glutamate receptors work a bit better - this might offer a mechanism for improving memory and a treatment for some of the symptoms of Alzheimer's disease.

In Alzheimer's disease, 'many cells that use glutamate degenerate', says David Bowen, Reader in Neurochemistry at the Institute of Neurology in London.

This causes two problems. First, as the cells die, the outflow of glutamate can kill their neighbours. Second, once the original cells have disappeared, the opposite problem ensues - there is too little glutamate. At a biochemical level, memory depends on cells being regularly stimulated by glutamate, but surviving neighbouring cells get too little stimulation and normal processes of memory are lost.

'It may be that the loss of some cells is particularly important - either because of their location, or they may have a type of receptor which makes them more vulnerable than most,' suggests Dr Bowen, who has been studying the involvement of glutamate in Alzheimer's disease for 10 years.

Last month, a team of researchers in Heidelberg, led by Peter Seeberg, applied the latest techniques of modern genetics to discover that there are several different types of NMDA receptors. Dr Ralf Schoepfer, a senior member of the German team, says: 'So far there are four forms, but we are convinced that there are more, we do not yet know how many.' The beauty of the Germans' procedure is that it opens the way to insert individual receptors into cells cultured in the laboratory and then use these designer receptors for testing potentially active drugs.

By sorting out the different types of receptors and studying how different compounds interact with them, it should be possible to develop drugs that are precise in their mode of action and which have fewer unwanted side-effects.

(Photograph omitted)

Start your day with The Independent, sign up for daily news emails
News
i100 In this video, the late actor Leonard Nimoy explains how he decided to use the gesture for his character
News
Robert De Niro has walked off the set of Edge of Darkness
news The Godfather Part II actor has an estimated wealth of over $200m
Arts and Entertainment
Fearne Cotton is leaving Radio 1 after a decade
radio The popular DJ is leaving for 'family and new adventures'
Sport
Robbie Savage will not face a driving ban
football
Voices
voices
Life and Style
Nearly half of all young people in middle and high income countries were putting themselves at risk of tinnitus and, in extreme cases, irreversible hearing loss
health Nearly half of all young people in middle and high income countries are at risk of tinnitus
News
It was only when he left his post Tony Blair's director of communications that Alastair Campbell has published books
people The most notorious spin doctor in UK politics has reinvented himself
ebooks
ebooksA special investigation by Andy McSmith
Arts and Entertainment
arts + ents
Life and Style
fashion
Arts and Entertainment
James Franco and Zachary Quinto in ‘I Am Michael’
filmJustin Kelly's latest film tells the story of a man who 'healed' his homosexuality and turned to God
News
i100
Arts and Entertainment
Public Service Broadcasting are going it alone
music
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Sauce Recruitment: Retail Planning Manager - Home Entertainment UK

salary equal to £40K pro-rata: Sauce Recruitment: Are you available to start a...

Ashdown Group: Front-End Developer - London - up to £40,000

£35000 - £40000 per annum: Ashdown Group: Creative Front-End Developer - Claph...

Recruitment Genius: Product Quality Assurance Technologist - Hardline & Electric

£18000 - £24000 per annum: Recruitment Genius: The role in this successful eco...

Ashdown Group: QA Tester - London - £30,000

£28000 - £30000 per annum: Ashdown Group: QA Tester - London - £30,000 QA Tes...

Day In a Page

HIV pill: Scientists hail discovery of 'game-changer' that cuts the risk of infection among gay men by 86%

Scientists hail daily pill that protects against HIV infection

Breakthrough in battle against global scourge – but will the NHS pay for it?
How we must adjust our lifestyles to nature: Welcome to the 'Anthropocene', the human epoch

Time to play God

Welcome to the 'Anthropocene', the human epoch where we may need to redefine nature itself
MacGyver returns, but with a difference: Handyman hero of classic 1980s TV series to be recast as a woman

MacGyver returns, but with a difference

Handyman hero of classic 1980s TV series to be recast as a woman
Tunnel renaissance: Why cities are hiding roads down in the ground

Tunnel renaissance

Why cities are hiding roads underground
'Backstreet Boys - Show 'Em What You're Made Of': An affectionate look at five middle-aged men

Boys to men

The Backstreet Boys might be middle-aged, married and have dodgy knees, but a heartfelt documentary reveals they’re not going gently into pop’s good night
Crufts 2015: Should foreign dogs be allowed to compete?

Crufts 2015

Should foreign dogs be allowed to compete?
10 best projectors

How to make your home cinema more cinematic: 10 best projectors

Want to recreate the big-screen experience in your sitting room? IndyBest sizes up gadgets to form your film-watching
Manchester City 1 Barcelona 2 player ratings: Luis Suarez? Lionel Messi? Joe Hart? Who was the star man?

Manchester City vs Barcelona player ratings

Luis Suarez? Lionel Messi? Joe Hart? Who was the star man at the Etihad?
Arsenal vs Monaco: Monaco - the making of Gunners' manager Arsene Wenger

Monaco: the making of Wenger

Jack Pitt-Brooke speaks to former players and learns the Frenchman’s man-management has always been one of his best skills
Cricket World Cup 2015: Chris Gayle - the West Indies' enigma lives up to his reputation

Chris Gayle: The West Indies' enigma

Some said the game's eternal rebel was washed up. As ever, he proved he writes the scripts by producing a blistering World Cup innings
In Ukraine a dark world of hybrid warfare and murky loyalties prevails

In Ukraine a dark world of hybrid warfare

This war in the shadows has been going on since the fall of Mr Yanukovych
'Birdman' and 'Bullets Over Broadway': Homage or plagiarism?

Homage or plagiarism?

'Birdman' shares much DNA with Woody Allen's 'Bullets Over Broadway'
Broadchurch ends as damp squib not even David Tennant can revive

A damp squib not even David Tennant can revive

Broadchurch, Series 2 finale, review
A Koi carp breeding pond, wall-mounted iPads and a bathroom with a 'wellness' shower: inside the mansion of Germany's 'Bishop of Bling'

Inside the mansion of Germany's 'Bishop of Bling'

A Koi carp breeding pond, wall-mounted iPads and a bathroom with a 'wellness' shower