Brain cells that control where worms wander identified
3 July 2008
Research on the patterns of brain activity in Caenorhabditis elegans, the humble nematode worm, has identified how they taste salt and crawl toward high salt concentrations. The discovery hints at how the brains of animals that navigate using taste and smell might work.
The transparent worm’s nervous system, gut and muscle tissues are similar to those of humans and other mammals though there is a huge different in brain complexity. A human brain holds billions of neurones; C.elegans is guided by just 302. This simplicity is a bonus for medical researchers as it enables them to link neurone stimulation to behavioural actions in the worm. Understanding how a worm’s brain governs its behaviour can help to unravel how controls in the more sophisticated human brain work.
In research published in Nature, Dr William Schafer of the MRC Laboratory of Molecular Biology and colleagues from Oregon and California investigated the action of two worm neurons called ASEL and ASER. Both are involved in chemotaxis, the worm’s movement either towards or away from a source of a chemical.
They discovered that ASEL is an ‘on’ cell meaning that it is stimulated by increases in salt concentration. ASER is ASEL’s opposite - an ‘off’ cell that springs into action when salt concentration in the worm’s immediate environment drops.
By placing the worms in environments with differing salt concentrations and observing which neuron acted when, Dr Schafer and his team have been able to confirm that when the ASEL neurone kicks in a worm will move forward for longer stretches and the ASER neuron tells the worm to change direction.
Commenting on the findings Dr Schafer said:
‘‘We have learned how taste sensory neurons detect and respond to salts, as well as the computational strategy the worm brain uses to determine how salt concentrations are changing in time. The two neurones function asymmetrically, but their combined activity patterns allow the worm to process chemosensory information like changes in salt concentration in soil This provides a fundamental control mechanism in C.elegans chemotaxsis. This motif of brain activity, with a simple pattern of on and off responses, occurs in other sensory networks such as the human eye, and our work suggests this motif may also be common to all animals that navigate by taste and smell.’’
Dr Schafer and his team will be at the Royal Society Summer Science Exhibition from Monday 30 – Thursday 3 July with their exhibit ‘Can worms unlock the secrets of our mind?’ The display includes live worms (viewable under a microscope) and a one metre long model of a worm that shows its internal structure.
Original research paper: Functional asymmetry in Caenorhabditis elegans taste neurons and its computational role in chemotaxis is published in Nature.
Link to Royal Society Summer Science Exhibition
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