Contrary to popular belief neuronal ageing is not associated with significant neuronal loss but appears to be primarily due to changes in the way in which nerve cells talk to one another.
Molluscs have relatively simple nervous systems (»25000 nerve cells). The nerve cells are large (up to 100µm in diameter) and individual nerve cells can be reproducibly identified from one animal to the next.
CNS of the pond snail, Lymnaea Stagnalis
Their simplicity of the system means we can examine individual nerve cells and their connections across the lifespan of the animal and determine the changes that occur and the mechanisms driving the changes.
Modulatory Cerebral Giant Cells
This pair of cells regulates the frequency at which the animal feeds (Yeoman et al 1994) and is also vital in allowing the formation of long term memories associated with food stimuli (see work of Sussex Group; Professors Benjamin, Kemenes and O’Shea).
Fluorescent image of the CNS of Lymnaea labelled with an antibody against serotonin. Arrows indicate the location of the paired CGC cell bodies.
Effects of Age on the CGCs
With increasing age the excitability of the CGCs is attenuated and there are clear changes in their connectivity. Some connections are strengthened whilst others are weakened, providing us with a unique simple model to determine the factors that make some connections age-sensitive.
Analysing the effects of age on transmitter release
The CGCs have been shown to contain 3 types of putative neurotransmitters. A classical transmitter serotonin (5-HT), a range of peptide transmitters and a gaseous transmitter nitric oxide (NO). In collaboration with Imperial College we have used electrochemical techniques to start to examine changes in the release of 5-HT and NO. Below is a photograph and diagram of the basic carbon fibre sensor used to record 5-HT release.
This basic sensor can be treated with eugenol to make it sensitive to NO (see Patel et al. 2007).
