Synaptic transmission is a key process that fuels the nervous system. Without it, cells would not be able to communicate – meaning there would be no way to, say, pull your hand away from a hot stove. Now, scientists from Japan’s esteemed RIKEN Center for Brain Science have discovered a new development in synaptic activity with the help of cell culture models taken from mice.
What Is Synaptic Activity?
Synaptic activity is key to any operations of the nervous system. Synapses are the sites of nerve impulse transmission between cells – either between two neurons or between a neuron and a gland or muscle cell. The latter sends messages that coordinate essential body functions like reactive movement. However, the former can contribute to learning and memory formation. Scientists are continually studying the processes behind this neuronal activity. Now, Medical XPress reports that RIKEN neuroscientists have discovered a surprising mechanism for how neuronal activity in mice is “dynamically tuned.” Specifically, the researchers witnessed some synapses activating while other synapses went quiet, a process that seemed to promote memory formation.
Studying Synaptic Activity and Astrocytes
Per Medical XPress, researcher Yukiko Goda led the RIKEN team in an effort to understand the neural processes behind learning and memory formation – in other words, the communication between neurons mentioned above. Goda has long been engaged in efforts to understand the strengths of individual synapses. For example, in a 2016 study, Goda’s team used cell cultures from rat brains to study synaptic connections between distinct types of neurons. During that study, the team determined that astrocytes played a key role in this process. But what are astrocytes, exactly?
How Astrocytes Impact Synaptic Connections
Astrocytes are cells that support essential functions in the brain. These cells are also highly abundant, far outnumbering neurons. In the 2016 study, Goda’s team found that astrocytes are responsible for certain synaptic activity, including the strengthening of active synapses and the weakening of less-active synaptic connections. But the team needed to know more – which is how their most recent study, published in the fall of 2021, came about. To understand how astrocytes impact synaptic connections, the team explored receptors for the neurotransmitter N-methyl-D-aspartate (NMDA). To accomplish this, the researchers used cell cultures taken from mouse models – specifically, cultures taken from the hippocampus, which is where memories are formed.
Manipulating Astrocytes in Cell Culture Models
To explore the effect of astrocytes on synaptic activity, Goda’s team interfered with NMDA receptor activity in the mouse astrocytes. The researchers saw clear effects on the presynaptic side of synapses. First, the team observed that altering NMDA receptor activity in astrocytes helped modulate the terminals of input neurons. Additionally, they noticed more uniform synaptic activity between astrocytic input and recipient neurons. Ultimately, this suggests that NMDA receptors ensure the broad distribution of presynaptic strengths in hippocampal astrocytes. In other words, these changes in synaptic function could promote the reinforcement of memories via synaptic transmission.
Goda’s team is now working to further understand their findings, exploring the activity of NMDA receptors in hippocampal astrocytes on a broader scale. With further research, the team could draw conclusions about the impact of ensuring the broad distribution of presynaptic strengths in animal behavior, particularly as it pertains to spatial and contextual learning.
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