brain plasticity: more on axon growth and connections (Introduction)

by David Turell , Saturday, February 06, 2016, 01:02 (2994 days ago) @ David Turell

A study which looks at axon growth and how that contributes to plasticity:-http://medicalxpress.com/news/2016-02-amazing-axon-adventure.html-"For an axon in a growing embryo, the journey from retina to brain is not a straightforward one. It's a very long way for a tiny axon, through a constantly changing series of environments that it has never encountered before. So how do axons know where to go, and what can it tell us about how the brain is made and maintained?-***-"On the pathway through this patchwork quilt, there is a set of distinct beacons, breaking the axon's journey down into separate steps. Every time the growing axon reaches a new beacon, it has to make a decision about which way to go. At the tip of the axon is a growth cone, which 'sniffs out' certain chemical signals emitted from the beacons, helping it to steer in the right direction.-"The growth cones are receptive to certain signals and blind to others, so depending on what the axon encounters when it reaches a particular beacon, it will behave in a certain way. Holt's research group uses a variety of techniques to determine what the signals are at the steering points where axons alter their direction of growth or their behaviour.-***-"'It had been thought that if we built a model and took out all of the guidance molecules, there would be no topographic order whatsoever," says Eglen. "But instead we found that there is still residual order in how the neurons are wired up, so there must be extra molecules or mechanisms that we don't know about. What we're trying to do is to take biology and put it into computers so that we can really test it."-***-"Holt's group has found that the same guidance molecule can have different roles depending on what aspect of growth is going on - but the question then becomes how do you wire the brain with so few molecules?-"Adding to the complexity was another puzzling discovery - that the growth cones of axons can make proteins. Previous knowledge held that new proteins could be synthesised only within the main cellular part of each neuron, the cell body (where the nucleus is located), and then transported into axons. However, Holt's group found that the growth cones of axons are also capable of synthesising proteins 'on demand' when they encounter new guidance beacons, suggesting that messenger RNA (mRNA) molecules play a role in helping axons to navigate to their correct destinations. mRNAs are the molecules from which new proteins are synthesised, and further experiments found that axons contain hundreds or even thousands of different types of this nuclear material.-"In addition to their role in axon growth when the brain is wiring itself up during development, certain types of mRNA are also important in maintaining the connections in the adult brain, by keeping mitochondria - the energy-producing 'batteries' of cells - healthy, which, in turn, keeps axons healthy."-Comment: These axons follow automatic orders from various proteins and RNAs, and once formed, develop connections following how the individual organisms uses its brain.