Kat Arney

Does Pregnancy Make You Smell More ?

No, I don't mean smell in the stinky sense - unless you happen to develop cravings for boiled eggs, cabbage and baked beans - but new research has revealed that part of the brain responsible for smelling grows during pregnancy, at least in rats. This discovery has exciting implications for our understanding of brain function and learning in adults, principally because instances where scientists have managed to track down newly forming brain cells (neurones) in adults are relatively rare.

Until the 1980's it was thought that neurones were only created

in the developing embryonic brain, and if they subsequently died

in the adult then that was that. Game over, no second chances. This

dogma was challenged by studies on songbirds, when researchers discovered

that certain types of birds grew more brain cells at the time of

year when they had to learn new songs. Presumably, it was argued,

the increased number of neurones helped them cope with the learning

task. But could this apply to animals? Many were sceptical, until

American scientists showed that new neurones could be born in the

brains of adult mice and humans. Interestingly, two sites where

the new cells were found were the hippocampus (the area of the brain

associated with learning and memory) and the olfactory bulb (the

"smelling zone"), which is where the pregnant rodents

come into the picture.

Researchers in Calgary, Canada, injected pregnant rats with a chemical

that specifically labelled newly formed neurones. Intriguingly they

found a burst of neurone "birth" amongst cells that contribute

to the olfactory bulb, about a third of the way into the pregnancy

and also just after the pups were born. The trigger for the increase

in cell numbers was found to be the hormone prolactin, which increases

during pregnancy.

So what is the purpose of this brain expansion? Other researchers

have found that female mice that cannot use the hormone properly

also fail to recognise their babies. Some have speculated that this

could be because they cannot identify their offspring by smell,

a common mechanism in many animal species. Perhaps the increased

number of neurones in the pregnant rats helps them to learn the

smell of their babies. Even more fascinating, is the observation

that levels of prolactin increase in males and females immediately

after sexual activity. Maybe this also stimulates the production

of brain cells - although nothing has yet been proven. It's certainly

worth a try as a chat-up line, though.

But how can such studies help us? One of the most keenly sought

Holy Grails of modern medical science is the ability to rejuvenate

the human brain and body. By studying the sort of things that can

stimulate growth of new neurones, we may be able to repair or enhance

our ageing brains. Other groups of researchers have shown that if

you place rats in an exciting environment, with toys and physical

activities, they will increase in mental power and brain size. Exposure

to certain anti-depressant drugs can also lead to the birth of new

neurones, while stress and depression prevent this. Sadly, the complexities

of the mammalian brain make such experiments difficult to interpret,

despite the exciting speculation that can be made from even the

simplest results. We are a long way from understanding the signals

that cause this new growth, but if we can harness the process, the

potential for novel therapies could be enormous.

- May 2004

About the Author

Kat Arney is a writer and member of the naked scientists radio programme. She is based at Cancer Research UK