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Diagram of a synapse model summarizing the principal results demonstrated by a recent study. When a pre-synaptic terminal (in blue) is stimulated by a series of action potentials, the glutamate neurotransmitter is released into the synaptic cleft (red dots). It binds to glutamate receptors on the post-synaptic neuron (yellow). This triggers ionic currents (red tracings) which excite the post-synaptic neuron.
Paris, France. A neurotransmitter receptor is a protein on the surface of a cell that binds to receptors on the surface of another cell. The receptors move very rapidly, with a mobility that plays an essential role in the passage of nerve impulses from one neuron to another. It controls the reliability of data transfer ensuring the accurate transmission of neuronal information. Neurotransmitter receptors can also become unresponsive when exposed for extended periods of time (known as downregulation).
Information processing by the brain is mainly based on the coding of data by variations in the frequency of neuronal activity. "Good" communication thus implies the reliable transmission of this "code" by the connections between neurons, or synapses. Under normal circumstances, this junction comprises a pre-synaptic element from which the information arises, and a post-synaptic element which receives it.
Surface Mobility of Postsynaptic AMPARs Tunes Synaptic Transmission. Martin Heine, Laurent Groc, Renato Frischknecht, Jean-Claude Béïque, Brahim Lounis, Gavin Rumbaugh, Richard L. Huganir, Laurent Cognet, Daniel Choquet. Science 320(5873) 201-205. doi: 10.1126 / science.1152089
It is at this point that neuronal communication occurs. Once the pre-synaptic neuron has been stimulated by an electrical signal with a precise frequency, it releases chemical messengers into the synapse: neurotransmitters. The response is rapid as these neurotransmitters bind to specific receptors, thus provoking a change to the electrical activity of the post-synaptic neuron and hence the birth of a new signal.
Working at the interface between physics and biology, the teams in Bordeaux led by Choquet at CNRS, working in close collaboration with the group led by Brahim Lounis at the the CPMOH, have studied synaptic transmission and, more particularly, the role of certain receptors of glutamate, a neurotransmitter present in 80% of neurons in the brain.
Focusing on the dynamics of these receptors, the researchers revealed that a minor modification to their mobility has a major impact on high frequency synaptic transmission, i.e. at frequencies between 50 and 100 Hz. Those are the transmissions which intervene during memorization, learning or sensory stimulation processes.
More specifically, they established that this mobility enables the replacement in a few milliseconds of desensitized receptors by "naïve" receptors in the synapse. This phenomenon reduces synaptic depression and allows the neurons to transmit the information at a higher frequency. By contrast, if the receptors are immobilized, this depression is notably enhanced, preventing transmission of the nerve impulse in the synapses above around ten Hertz.
More profoundly, the scientists have demonstrated that prolonged series of high frequency stimulations, which induce an increase in calcium levels in the synapses, cause the immobilization of receptors. They have also proved that these series of stimulations diminish the ability of neurons to transmit an activity at high frequency.
When a pre-synaptic neuron is stimulated at very frequent intervals (high frequencies of around 50-100 Hertz), the post-synaptic response generally diminishes over time: this is called synaptic depression. The higher the stimulation frequency, the more this depression increases. Receptor mobility is thus correlated with the frequency of synaptic transmission and consequently, the reliability of this transmission.
A real advance for research. When the brain is functioning under normal conditions, we can suppose that the immobilization of receptors following a series of high frequency stimulations constitutes a safety mechanism. It will prevent subsequent series from overexciting the post-synaptic neuron. A reliable transmission of information between two neurons is obviously crucial to satisfactory functioning of the brain.
By enabling a clearer understanding of the mechanisms involved in neuronal transmissions, this work opens the way to new therapeutic targets for the neurological and psychiatric disorders that depend on poor neuronal communication (Parkinson's disease, Alzheimer's disease, OCD, etc.).
These results, of prime importance, suggest that some dysfunctions of neuronal transmission are due to a defect in receptor stabilization. However, high frequency electrical stimulation of certain regions of the brain is used to treat Parkinson's disease or obsessive-compulsive disorders (OCD). Its mechanism of action, still poorly understood, may therefore involve receptor mobility. This work has thus made it possible to identify new therapeutic targets and could augur well for potential drugs to treat neurological and psychiatric disorders which often result from poor communication between neurons.
Surface Mobility of Postsynaptic AMPARs Tunes Synaptic Transmission. Martin Heine, Laurent Groc, Renato Frischknecht, Jean-Claude Béïque, Brahim Lounis, Gavin Rumbaugh, Richard L. Huganir, Laurent Cognet, Daniel Choquet. Science 320(5873) 201-205. doi: 10.1126 / science.1152089
Abstract. AMPA glutamate receptors (AMPARs) mediate fast excitatory synaptic transmission. Upon fast consecutive synaptic stimulation, transmission can be depressed. Recuperation from fast synaptic depression has been attributed solely to recovery of transmitter release and/or AMPAR desensitization. We show that AMPAR lateral diffusion, observed in both intact hippocampi and cultured neurons, allows fast exchange of desensitized receptors with naïve functional ones within or near the postsynaptic density. Recovery from depression in the tens of millisecond time range can be explained in part by this fast receptor exchange. Preventing AMPAR surface movements through cross-linking, endogenous clustering, or calcium rise all slow recovery from depression. Physiological regulation of postsynaptic receptor mobility affects the fidelity of synaptic transmission by shaping the frequency dependence of synaptic responses.
Fluorescence image of a neuron labeled with three colors: a pre-synaptic marker (blue), a post-synaptic marker (red) and glutamate receptors (green). The white color at the tip of the dendritic spines indicates an accumulation of receptors. (Credit: Copyright Magali Mondin and Daniel Choquet / CNRS)
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Robot Violinist. A robot plays Pomp and Circumstance on the violin. The robot used its mechanical fingers to push the strings and bowed with its other arm.
The 152 cm (five foot) performer can perform a variety of tasks with its hands and arms, each of which has 17 joints.
Using precise control and coordination to achieve human-like agility, the robot could also be used to assist with domestic duties or nursing and medical care.
The mobility of receptors that control the reliability of neuronal transmission has been demonstrated by scientists in the 
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