Different Molecular Events Underly Experience-Dependent Loss And Gain Of The Function Of The Developing Brain

May 14, 1998

Sensory experience is capable of modifying neuronal connectivities in the brain, either by enhancing or diminishing the flow of information. Scientists from the Max Planck Institute for Developmental Biology (Tübingen, Germany) report in "Nature Neuroscience" (May 1998) that these two forms of plasticity differ in their molecular machinery.

Sensory experience during early postnatal development is essential for the optimization of neuronal connections in the brain. While genetic information is only sufficient for the development of the coarse pattern of connections between nerve cells, use-dependent modifications lead to the adaptation of neuronal connectivities to the individuals¹ needs. The basic rules for these modifications are that connections which are rarely used are eliminated, and the flow of information along pathways which are regularily used are strengthened by addition of connections. These modifications of brain circuitries are also believed to underly the mechanisms of learning and forgetting in the mature brain.

The developing visual cortex is an excellent model system to study both forms of plasticity. In this structure the information of both eyes converges and thereby allows depth-vision through a comparison of the pictures seen by either eye. As shown by the pioneering studies by Drs. Hubel and Wiesel in the 1970¹s, impairment of vision in one eye in infants leads to a severe loss of connections from this eye to the cortex. This can result in almost complete blindness of the affected eye within a short period of time. During early development, this loss of function can be recovered by restoring vision in the deprived eye, leading to new formation of connections carrying the according information to the cortex.

Christian M. Müller and Claudius B. Griesinger from the Max Planck Institute for Developmental Biology used this model system to address the mechanisms underlying both consequences of brain plasticity (Nature Neuroscience, vol. 1, 1998). They focussed on the putative role of proteases in the remodelling of connections between nerve cells. Recent data from different laboratories has provided evidence that certain proteases are essential for the development of nerve processes, most likely by digesting proteins in the vicinity of the growing structures. By applying inhibitors against different proteases into the cortex, Müller and Griesinger show that the recovery of function after restoration of vision with a formerly deprived eye can be fully abolished. When protease activity is blocked during impairement of vision through one eye, however, the loss of connections proceeds normally. Therefore it is concluded that proteases are neccessary for only one form of plasticity in the brain, namely the gain of function. By using a variety of different inhibitors it is shown that a cascade of two proteases is essential for brain plasticity. These proteases are Œtissue plasminogen activator¹ and Œplasmin¹, both known to be present and important in the cardiovascular system, where they participate in wound healing.

The study has several implications for the understanding of brain development and experience-dependent plasticity in the brain. As interference with the mechanism underlying the improvement of brain function does not affect the loss of function resulting from disuse, it has to be concluded that the two forms of plasticity proceed independently of each other. The essential role of proteases - known to be involved in growth mechanisms of neurons - for the gain of function through experience strongly suggests that the growth of connections between nerve cells underlies the enhancement of information flow through experience. The knowledge of a molecular mechanism being specific for the improvement of brain function might be useful for the development of therapeutic tools to support the long-term strengthening of connectivities in the brain.
-end-


Max-Planck-Gesellschaft

Related Nerve Cells Articles from Brightsurf:

Nerve cells let others "listen in"
How many ''listeners'' a nerve cell has in the brain is strictly regulated.

Nerve cells with energy saving program
Thanks to a metabolic adjustment, the cells can remain functional despite damage to the mitochondria.

Why developing nerve cells can take a wrong turn
Loss of ubiquitin-conjugating enzyme leads to impediment in growth of nerve cells / Link found between cellular machineries of protein degradation and regulation of the epigenetic landscape in human embryonic stem cells

Unique fingerprint: What makes nerve cells unmistakable?
Protein variations that result from the process of alternative splicing control the identity and function of nerve cells in the brain.

Ragweed compounds could protect nerve cells from Alzheimer's
As spring arrives in the northern hemisphere, many people are cursing ragweed, a primary culprit in seasonal allergies.

Fooling nerve cells into acting normal
In a new study, scientists at the University of Missouri have discovered that a neuron's own electrical signal, or voltage, can indicate whether the neuron is functioning normally.

How nerve cells control misfolded proteins
Researchers have identified a protein complex that marks misfolded proteins, stops them from interacting with other proteins in the cell and directs them towards disposal.

The development of brain stem cells into new nerve cells and why this can lead to cancer
Stem cells are true Jacks-of-all-trades of our bodies, as they can turn into the many different cell types of all organs.

Research confirms nerve cells made from skin cells are a valid lab model for studying disease
Researchers from the Salk Institute, along with collaborators at Stanford University and Baylor College of Medicine, have shown that cells from mice that have been induced to grow into nerve cells using a previously published method have molecular signatures matching neurons that developed naturally in the brain.

Bees can count with just four nerve cells in their brains
Bees can solve seemingly clever counting tasks with very small numbers of nerve cells in their brains, according to researchers at Queen Mary University of London.

Read More: Nerve Cells News and Nerve Cells Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.