Nitric oxide plays a vital role in the formation of long-term memory in snails

Snails can teach us a great deal about how we form memories, according to a group of neuroscientists at the University of Sussex.

Research by Dr Ildikó Kemenes, Professor Paul Benjamin, Professor Michael O’Shea and colleagues shows that nitric oxide plays a vital role in the formation of long-term memory in snails. This is of crucial importance because the gas has already been shown to play such a role in humans and other mammals.

Ideally, scientists would like to use mammals to study the mechanism of memory formation, but mammalian brains are too complex. So, instead, they have to study animals with simpler brains. Snails are an ideal choice because they have unusually large neurons (nerve cells). But, until now no one had conclusively shown that nitric oxide plays a role in the formation of long-term memory in snails.

So, the Sussex team carried out experiments to see whether interfering with nitric oxide, in ways known to prevent mammals forming long-term memory, would have a similar effect on snails.

The experiments made use of a smell-taste association. Snails can be taught to associate the smell of amyl acetate, a chemical that smells like pear drops, with a tasty sugar solution. Subsequently, whenever they smell ‘pear drops’, they begin to make mouth movements in anticipation of food.

The Sussex team injected snails with chemicals that either blocked the production of nitric oxide, or prevented it passing to other neurones, or blocked its action. They found that in each case the snails failed to memorise the association if the injection had been made within five hours after training – the time in which long-term memory is laid down.

This is the best evidence so far that nitric oxide plays a role in the formation of long-term memory in snails. Moreover, this is the first time that anyone has demonstrated such a role in any animal at both the neuronal and the behavioural level.

The findings are published in the current Journal of Neuroscience, issued on February 15.