Summary: Researchers report that the SLK protein is a key regulator of neuronal excitability and sensitivity.
Source: University of Bonn
Neurons are capable of adjusting their responsiveness to incoming signals on their own. A new study led by the University of Bonn identifies a molecular mechanism that enables this autonomous tuning. Researchers from the German Center for Neurodegenerative Diseases and the Max Planck Institute for Neurobiology of Behavior also contributed to the work.
The findings are published in the journal Cell Reports.
Anyone who has recorded audio knows how important gain control is: shouting into a microphone produces distorted sound, while speaking too softly yields an inaudible recording. Sound engineers compensate by adjusting each microphone’s gain to match the signal. In a similar way, neurons adjust how strongly they respond to incoming signals to ensure reliable information transmission.
In this study, researchers examined neural circuits involved in sensory processing—pathways that underlie vision, hearing and touch. Sensory input first reaches the thalamus, a deep brain structure, and from there it is relayed to the cerebral cortex for more complex processing.
Each neuron calibrates its own sensitivity
“Neurons in the cerebral cortex respond to thalamic input by generating action potentials,” explains Prof. Dr. Heinz Beck from the Institute of Experimental Epileptology and Cognition Research at the University Hospital Bonn. Action potentials are brief electrical impulses that convey information to other parts of the brain. For accurate signaling, cortical neurons must adapt their responsiveness to the strength of incoming excitatory signals.
When inputs are particularly strong, neurons reduce their sensitivity to prevent overexcitation. The new study shows that the enzyme Ste20-like kinase (SLK) is a critical factor in this self-regulation. “SLK allows individual neurons to calibrate their own excitability,” Beck says. In other words, rather than relying on an external “sound engineer,” neurons use an intrinsic molecular mechanism to keep their activity within an optimal range.
Interneurons—specialized inhibitory neurons—play a central role in this process. Dr. Pedro Royero from Beck’s group, who conducted most of the experiments as part of his doctoral work, explains that interneurons send inhibitory signals to excited neurons and thereby reduce their responsiveness. SLK determines how effectively these inhibitory interneurons can tune down a neuron’s excitability.
The researchers distinguish two types of interneurons. One type is activated directly by thalamic input and provides inhibition at the same time the thalamus excites cortical neurons—this is called feedforward inhibition. The second type is activated only by activity within the cortex itself, forming a negative feedback loop that inhibits the very neurons that triggered it.
Importantly, SLK selectively influences feedforward inhibition: it regulates inhibition provided by interneurons that are directly driven by thalamic input but does not affect inhibition arising from the feedback circuit. This specificity shapes how excitation and inhibition are balanced across cortical neurons.
Implications for disease and future research
The team also identified genes whose expression changes when SLK is altered. These genes are linked to transsynaptic signaling and cytoskeletal dynamics, processes that can modify synaptic strength and neuronal connectivity. The researchers plan to study these genes further to understand how they contribute to the homeostatic adjustments controlled by SLK.
Maintaining a proper balance between excitation and inhibition is vital for normal brain function. Disorders such as epilepsy illustrate the consequences of disrupted balance: seizures can arise when widespread networks become excessively excited. Prior studies have reported reduced SLK levels in neurons from some epilepsy patients, suggesting that the current findings may help illuminate disease mechanisms and point to potential targets for intervention.
About this neuroscience research news
Author: Press Office
Source: University of Bonn
Contact: Press Office – University of Bonn
Image: The image is in the public domain
Original Research: Open access. “Circuit-selective cell-autonomous regulation of inhibition in pyramidal neurons by Ste20-like kinase” by Heinz Beck et al. Cell Reports
Abstract
Circuit-selective cell-autonomous regulation of inhibition in pyramidal neurons by Ste20-like kinase
Highlights
- SLK enables neurons to maintain excitation–inhibition balance through cell-autonomous mechanisms
- SLK in cortical neurons regulates feedforward inhibition but not feedback inhibition
- SLK selectively influences inhibition delivered by parvalbumin-expressing interneurons
Summary
Balancing excitation and inhibition is essential for accurate neuronal information processing. Cortical neurons can independently adjust the amount of inhibition they receive in response to varying levels of excitatory input, but the mechanisms behind this capacity were previously unclear.
This study demonstrates that Ste20-like kinase (SLK) mediates cell-autonomous regulation of excitation–inhibition balance specifically within the thalamocortical feedforward circuit, while leaving feedback inhibition intact. The effect is driven by changes in inhibition from parvalbumin-expressing interneurons; inhibition from somatostatin-expressing interneurons remains unaffected.
Computational modeling indicates that SLK-dependent regulation supports stable excitation–inhibition ratios across pyramidal cells and promotes robust, sparse coding in cortical networks. Patch-clamp RNA sequencing identified genes whose expression is altered by SLK knockdown, including transcripts involved in transsynaptic communication and cytoskeletal organization—processes relevant to synaptic function and network stability.
Together, these data reveal a mechanism by which individual cortical pyramidal neurons autonomously regulate a specific inhibitory circuit. This circuit-selective regulation helps ensure that most cortical pyramidal cells can participate effectively in sensory coding and other neural computations.