Complex connections from simple rules

Using stem cells to repair spinal injuries may be a step closer thanks to research which has revealed spinal nerve cell networks may develop using much simpler rules than expected.

In the first study of its kind, researchers from the Universities of Bristol and Plymouth studied the anatomy and physiology of young frog tadpoles and from the results built the first reconstruction of a nerve cell network that can produce complex behaviour in a whole vertebrate organism.

They observed imprecise connections between nerve cell fibres depending on where in the brain and spinal cord they were located, and built these into their computer model of nerve growth. Their model contained nearly 100,000 connections and can make a model of the tadpole nervous system ‘swim’ when stimulated.

“Adult animal nervous systems are highly complex with billions of connections, however since humans evolved from simple vertebrates like fish and frogs our results imply that early in development, simple rules may lay out the first functional nerve cell networks in our brains,” said Professor Alan Roberts from Bristol’s School of Biological Sciences.

The findings – published in the Journal of Neuroscience – challenge the generally accepted notion that nerve cell connections in developing embryonic animals are only made using highly specific recognition processes, like those used when nerve cells in the eye find the correct part of the brain.

“The next step is to investigate how imprecise the connections can be while still allowing the correct behaviour to be displayed and to understand how the networks controlling other aspects of tadpole behaviour are constructed,” Roberts said.

Building the early nervous system: can simple rules control development of a pioneer vertebrate network generating behaviour?