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Scientific Frontline: Extended "At a Glance" Summary: The Paradoxical Role of GABA
The Core Concept: Gamma-aminobutyric acid (GABA), typically known as the brain's primary inhibitory neurotransmitter that quiets neuronal activity, can under certain conditions act as an excitatory agent that enhances brain signaling.
Key Distinction/Mechanism: While most GABA receptors suppress neural firing, specific interactions with GABA-alpha-5 receptors produce a paradoxical effect. Inhibiting the electrical activity at these specific receptors unexpectedly increases the likelihood that a neuron will draw in calcium ions during its next firing, effectively amplifying calcium-dependent neural plasticity instead of silencing the circuit.
Major Frameworks/Components:
- Gamma-aminobutyric acid (GABA): The major chemical messenger historically categorized strictly as the central nervous system's "brakes."
- GABA-alpha-5 Receptors: One of 19 identified subtypes of GABA-alpha receptors, uniquely responsible for this unexpected excitatory signaling pathway.
- Calcium-Dependent Neural Plasticity: The process by which calcium ion influx strengthens synaptic connections, serving as a fundamental mechanism for learning and memory formation.
- Two-Photon Microscopy: An advanced imaging technique utilized to track the real-time concentration and movement of calcium ions within living mouse neurons.
Branch of Science: Neuroscience, Neurobiology, and Psychiatry.
Future Application: The discovery opens novel therapeutic avenues for developing or refining treatments for psychiatric and neurological conditions, including anxiety, depression, schizophrenia, and epilepsy, by explicitly targeting the GABA-alpha-5 receptor pathway to promote cognitive flexibility.
Why It Matters: This finding forces a reevaluation of how current psychiatric medications function. It suggests that existing GABA-targeting therapies might alleviate symptoms not merely by dampening overactive brain circuits, but by actively promoting the neural plasticity required to establish new behaviors and cognitive habits.
An important chemical messenger that typically inhibits brain activity might sometimes do the opposite, according to new Yale School of Medicine (YSM) research.
Brain cells communicate through chemical messengers called neurotransmitters. Most research indicates that the neurotransmitter gamma-aminobutyric acid (GABA) quiets brain signals, serving as the system's brakes.
Now, a new study published May 12 in Neuron suggests that this story might not be so simple. Yale researchers have found that GABA can, under certain circumstances, enhance neuronal activity.
Promoting GABA signaling is a common target for treatments of anxiety and other psychiatric conditions. Scientists have long assumed that these therapies work by dampening overactive brain circuits. Now, this research suggests that “there may be more going on,” says Michael Higley, MD, PhD, professor of neuroscience at YSM.
The work is a reminder that “the most unexpected results, the ones that are really surprising, are very often those worth following,” he says.
Certain GABA Signals Can Boost Calcium Influx
The nervous system uses electrical signals to tell our bodies what to do. Whether a neuron broadcasts a signal—helping to move an arm, store a memory, or learn a new skill—is controlled by neurotransmitters.
Neurons release GABA and other neurotransmitters into the tiny spaces called synapses that separate them. The neurotransmitters then bind to receptors on the receiving neuron, increasing or decreasing the likelihood that the neuron will fire. While decades of research have shown that GABA largely inhibits neuronal firing, several recent studies suggest that GABA might sometimes do just the opposite.
How this happens, however, remains unclear.
A few years ago, Higley and his colleagues were running an experiment when they noticed some unusual results. The researchers blocked GABA from binding to receptors in brain tissue, which normally causes neurons to exhibit increased activity. Instead, the team observed a “surprising and robust decrease in signals corresponding to activity,” Higley says.
In the new study, the researchers used an imaging technique called two-photon microscopy to track the concentration of calcium ions in mouse (Mus musculus) neurons. A brief influx of calcium into the cell typically indicates that it has fired, or activated, in response to input. Several earlier studies, including those from the Higley lab, found that GABA could suppress these calcium signals, as expected for a classic inhibitor.
Surprisingly, in this new study, when the researchers blocked GABA transmission in both brain slices and living mice, they observed a decrease in calcium influx—suggesting that neurons had become less active, rather than more active.
The team also found that not all GABA receptors were involved. Only \(\alpha\)5-containing GABA receptors—incorporating one of nineteen identified types of GABA receptor subunits—acted in this unusual way.
A New Perspective on GABA in Health and Disease
Computer models created by the researchers suggest that GABA is still acting as expected for the most part, quieting neuronal activity. But for \(\alpha\)5 receptors, inhibiting electrical activity comes with an unexpected side effect: it makes neurons more likely to draw in calcium ions the next time the cell fires. The team then showed that this "paradoxical effect," could enhance calcium-dependent neural plasticity, which is one way that the brain learns and develops memories, Higley says.
GABA-based therapies are used to treat many psychiatric and neural conditions, including schizophrenia, depression, and epilepsy. For some of these conditions, the secondary effect on neural plasticity—which can help people develop new habits and attitudes—might help explain why these therapies work. Targeting this pathway could even provide new avenues for developing therapies, Higley says.
Overall, this research does not undermine researchers’ understanding of GABA and how it inhibits brain function, he says. “But it does add an interesting and unexpected spin to it,” Higley says. “And it could open up totally new perspectives on the role of GABA signaling in health and disease.”
Reference material: What Is: Biological Plasticity
Funding: The research reported in this news article was supported by the National Institutes of Health (awards R01MH099045, R01MH113852, DP1EY033975, and K01MH097961) and Yale University. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. Additional support was provided by funding agencies in Chile and Roche Pharmaceutical.
Published in journal: Neuron
Title: SST interneurons facilitate dendritic calcium signaling via tonic activation of α5-GABA receptors
Authors: Chiayu Q. Chiu, Thomas M. Morse, Karima AitOuares, Lauren C. Panzera, Paras A. Patel, Francesca Nani, Frederic Knoflach, Maria-Clemencia Hernandez, Monika Jadi, and Michael J. Higley
Source/Credit: Yale School of Medicine | Freda Kreier
Edited by: Scientific Frontline
Reference Number: ns052026_01
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