A specific neurotransmitter receptor supports optimal information processing in the brain

March 30, 2015

Researchers have been fascinated for a long time by learning and memory formation, and many questions are still open. Bochum-based neuroscientists Prof Dr Denise Manahan-Vaughan and Dr Hardy Hagena have discovered a key building block for this complex process. A particular neurotransmitter receptor, namely the metabotropic glutamate receptor 5, is a switch for activating opposing forms of plasticity in the hippocampus, a brain region vital for memory forming. They reported in the current edition of the Journal of Neuroscience.

Synapses between neurons process different information

The brain region surrounding the hippocampus is crucial for forming and for processing of spatial information. The hippocampus itself can be subdivided into different regions: dentate gyrus, Cornu Ammonis (CA) 3 and CA1. The information that has to be processed passes these three regions successively like a traffic route with each region processing different spatial information of the environment. CA3 plays a significant role here. It receives information via the so-called mossy fibres (MF), which originate in dentate gyrus neurons and, together with pyramidal neurons, form synapses in CA3; in this case MF-CA3-synapses. "These synapses are likely to participate in the encoding of a new memory trace" says Prof Manahan-Vaughan. In addition, the neurons in the CA3 region of the same as well as the neighbouring brain hemisphere communicate via certain fibres – i.e. associative/commissural (AC) fibres via the AC-CA3 synapses, and are likely to support retrieval of established memories, a process that is called "pattern retrieval". "We have already demonstrated that these two synapses process different types of information that in turn is likely to comprise the cellular mechanisms  for memory encoding and retrieval at these synapses" explains Hardy Hagena.

Adapting to requirements: synaptic plasticity

But how is information at MF-CA3 synapses and AC-CA3 synapses processed differently? On the neural level, information processing triggers an adaptation to the requirements, i.e. essentially a memory effect. Researchers call this . It manifests itself in two forms: as long-term potentiation, LTP, a strengthening of synaptic efficacy, and as long-term depression, LTD, a weakening of synaptic efficacy. Both LTP and LTD encode different types of . Previous studies have shown for different brain regions that the 5 (mGlu5 receptor) plays a crucial role in this long-term form of synaptic plasticity.

How a receptor affects memory formation

"Based on these findings, it was particularly interesting to find out if and to what extent the mGlu5 receptor affects synaptic plasticity and, consequently, memory formation in the CA3 region," explains Hagena. The researchers switched off the receptor pharmacologically at MF-CA3 synapses and then stimulated the respective information-transmitting fibres. Subsequently, they did not detect any LTP anymore, but they continued to observe LTD. As opposed to this, after switching off the mGlu5 receptor at AC-CA3 synapses, LTD got blocked, but LTP did not. "These results show that once the mGlu5 receptor is activated, LTP is primarily triggered in the MF-CA3 synapses and LTD in the AC-CA3 synapses," conclude the researchers.

Fascinating insight into the mode of operation of the hippocampus region

"These results have granted us a fascinating insight into the mode of operation and regulation of synaptic plasticity in the CA3 region of the hippocampus," as the researchers sum up their findings. "The impact of the mGlu5 receptor is particularly interesting, which determines the direction of synaptic plasticity on activation, e.g. for learning processes, for processing of new information regarding the environment and during memory retrieval processes such as 'pattern completion', by triggering LTP primarily in MF-CA3 synapses and LTD in AC-CA3 ." This opposing regulation of synaptic plasticity supports optimal processing and storage and highlights the unique role this region plays in learning processes and .

Explore further: Newly found 'volume control' in the brain promotes learning, memory

More information: "mGlu5 acts as a switch for opposing forms of synaptic plasticity at mossy fiber-CA3 and commissural associational-CA3 Synapses," The Journal of Neuroscience, DOI: 10.1523/JNEUROSCI.3417-14.2015

Related Stories

Newly found 'volume control' in the brain promotes learning, memory

January 9, 2013
Scientists have long wondered how nerve cell activity in the brain's hippocampus, the epicenter for learning and memory, is controlled—too much synaptic communication between neurons can trigger a seizure, and too little ...

Research explains the formation of long-term motor memory

March 26, 2015
Recent studies of long-term motor memory have pointed out the involvement of synaptic plasticity at multiple sites in the cerebellum, but the physiological mechanism remains unclear. Now results from a collaboration of researchers ...

Novel combination of techniques reveals new details about the neuronal networks for memory

February 7, 2014
Learning and memory are believed to occur as a result of the strengthening of synaptic connections among neurons in a brain structure called the hippocampus. The hippocampus consists of five subregions, and a circuit formed ...

Blame it on the astrocytes

July 11, 2014
In the brains of all vertebrates, information is transmitted through synapses, a mechanism that allows an electric or chemical signal to be passed from one brain cell to another. Chemical synapses, which are the most abundant ...

New insights into underlying cellular mechanisms of information processing in the brain

February 18, 2015
Researchers at the Max Planck Florida Institute for Neuroscience and the Pasteur Institute have uncovered a key factor in regulating information transmittal during the early stages of auditory processing.

Memory in silent neurons

August 31, 2014
When we learn, we associate a sensory experience either with other stimuli or with a certain type of behavior. The neurons in the cerebral cortex that transmit the information modify the synaptic connections that they have ...

Recommended for you

Touching helps build the sexual brain

September 21, 2017
Hormones or sexual experience? Which of these is crucial for the onset of puberty? It seems that when rats are touched on their genitals, their brain changes and puberty accelerates. In a new study publishing September 21 ...

Gene immunotherapy protects against multiple sclerosis in mice

September 21, 2017
A potent and long-lasting gene immunotherapy approach prevents and reverses symptoms of multiple sclerosis in mice, according to a study published September 21st in the journal Molecular Therapy. Multiple sclerosis is an ...

Neuron types in brain are defined by gene activity shaping their communication patterns

September 21, 2017
In a major step forward in research, scientists at Cold Spring Harbor Laboratory (CSHL) today publish in Cell a discovery about the molecular-genetic basis of neuronal cell types. Neurons are the basic building blocks that ...

Highly precise wiring in the cerebral cortex

September 21, 2017
Our brains house extremely complex neuronal circuits whose detailed structures are still largely unknown. This is especially true for the cerebral cortex of mammals, where, among other things, vision, thoughts or spatial ...

Your neurons register familiar faces, whether you notice them or not

September 21, 2017
When people see an image of a person they recognize—the famous tennis player Roger Federer or actress Halle Berry, for instance—particular cells light up in the brain. Now, researchers reporting in Current Biology on ...

Faulty cell signaling derails cerebral cortex development, could it lead to autism?

September 20, 2017
As the embryonic brain develops, an incredibly complex cascade of cellular events occur, starting with progenitors - the originating cells that generate neurons and spur proper cortex development. If this cascade malfunctions ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.