Key Markers for Neuronal Activity

Monitoring of neuronal activity is essential for both basic research on the function and health of the brain and for the clinical monitoring of neurological diseases.

Creative Biolabs has developed a range of advanced solutions and technologies that make large-scale, multi-modal neuronal activity monitoring possible. Their expertise supports researchers in capturing detailed neuronal signals across scales and conditions, enabling breakthroughs in neuroscience research and therapeutic development.

What Are Markers of Neuronal Activity?

Neuronal activity markers are proteins or gene expression products that specifically and visualizes the activation state of neurons under certain behaviors or stimuli. Neuronal activity markers can be labeled by using genetic engineering methods (fluorescent proteins) or expression of immediate early genes (IEGs) that label active neurons (examples: c-Fos, calcium indicators, GCaMP etc.).

General neuronal markers are the proteins or genes used to identify the type, structure and functional features of neurons. They are generally expressed in certain regions of the neuron (cell body, dendrites, or axons) to label different types of neurons, for example,

• Dopaminergic neurons can be marked by tyrosine hydroxylase TH
• GABAergic neurons can be marked by GABA etc.

General neuronal markers are widely used in the field of immunocytochemistry to study the morphology, distribution and function of neurons.

Common Neuronal Activity Markers

IEGs As Primary Neuronal Activity Markers

IEGs are a type of gene that is commonly used as a marker of neuronal activity. This is due to the fact that they are quickly and transiently induced upon neuronal stimulation. Furthermore, IEGs are often induced in a protein synthesis independent manner, allowing them to be rapidly expressed in response to neuronal activity.

Calcium ion influx signals and NMDA receptor dependent signaling cascades are some of the signaling pathways responsible for the induction of IEGs. The products of IEGs, which are often transcription factors, can in turn regulate the expression of other genes, allowing IEGs to ultimately influence neuronal function and behavior. IEG expression levels are also found to be highly correlated with neuronal activity.

However, neuronal activity is not always sufficient to induce IEG expression. As a result of this, IEGs are involved in long-term memory formation and synaptic plasticity, as well as acting as an immediate marker of neuronal activity.

The Specific Roles of Different IEGs

c-Fos, Arc, and Egr-1 are IEGs that are involved in neuronal activity and learning. Expression of these genes generally increases quickly after exogenous stimulation (like neuronal activity) and peaks within minutes to hours, after which it slowly decreases. Their temporal profiles and functional distinctions are as follows:

Table 1 Comparison of specific IEGs

Figure 1 Time course of IEG expression during the imaging paradigm and correlation of IEG expression with mean and maximum neuronal activity.^1,3

Fos Promoter as A Marker of Neuronal Activity

The molecular underpinnings of the Fos gene promoter as an activity marker involve both the gene's rapid expression in response to neural activity and its regulatory interactions with other transcription factors.

Neuronal stimulation, such as calcium ion influx through NMDA receptors and L-type voltage-sensitive calcium channels, leads to activation of the low-calcium-sensitive mitogen-activated protein kinase (MAPK) signaling pathway, resulting in c-Fos transcription.

The Fos protein can also form heterodimers with Jun family members to create the AP-1 complex, which can bind to the promoter regions of target genes to modulate gene expression. In addition to activity-dependent promoter usage, Fos has also been shown to work with other transcription factors to regulate enhancer regions and promote gene transcription through histone modifications and chromatin remodeling.

Figure 2 TGF-β1 activates c-Fos through the MAPK pathway.^2,3

Application of Neuronal Activity Markers in Neural Circuit Research

Single neuron analysis

By labeling neurons in specific brain regions, the organizational structure of their dendritic and axonal networks can be studied. For example, the dendritic and axonal networks in the mouse prefrontal cortex can be labeled with high brightness using a sparse labeling system, thereby mapping their axonal projections throughout the entire brain.

Axonal-specific calcium imaging

By measuring receptor activity in vivo, the calcium ion dynamics of neurons can be studied, thereby revealing their activity patterns.

Cholinergic neuron circuit research

By labeling cholinergic neurons in the ventral striatum, the plasticity of their derived circuits and their effects on chronic pain and depression-like behavior in male mice are studied.

Neurotropic virus labeling

Using neurotropic viruses (such as PRV-EGFP, HSV-tdTomato) for transsynaptic tracing, peripheral organ-to-central nervous system circuits can be labeled. For example, after intramuscular injection, the relevant regions of the central nervous system can be traced.

Optogenetic and chemogenetic labeling

Using the Gq-DREADD and Gi-DREADD systems, specific neurons can be activated or inhibited to study their roles in behavior and neural circuits.

Calcium ion probe labeling

For example, CaMPARI can permanently label neurons when they are activated, facilitating subsequent studies of their morphology and function.

Fluorescent gold labeling

Under UV or blue light excitation, labeled neuronal cell bodies emit bright golden-yellow fluorescence, enabling observation of neuronal morphology and location.

Viral vector labeling

Such as AAV-FLEX-HTB and AAV-FLEX-HB viral vectors, combined with Cre-dependent reporting systems, can specifically label specific neurons and their projection pathways.

Electroporation and fluorescence imaging

Using single-cell electroporation technology, fluorescent labels are introduced into neurons to observe their dynamic changes and dendritic growth in vivo.

Whole-brain c-Fos immunostaining

Combining viral labels with c-Fos expression, this method studies time-specific labeling of neuronal activity.

As a leading technology service provider in the field of neuroscience research, Creative Biolabs specializes in providing advanced neuronal activity monitoring solutions to help researchers gain deeper insights into brain function. Its advantages include:

• Multi-scale neural activity recording technology: covering multi-level monitoring from single neurons to brain networks, supporting various technical methods such as electrophysiology, optical imaging, and gene expression.
• Comprehensive analysis of multiple brain regions and cell types: Providing customized reagents and tools to help scientists collect and analyze neural activity data across regions and cell types.
• Time-dynamic monitoring of behavior and cognition: Combining behavioral experimental design to precisely capture neural activity changes closely related to cognitive function.
• Exploration of neuronal interaction mechanisms: Providing detection solutions for neuronal connections and signal transmission to advance understanding of neural network functions and disease mechanisms.

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References

1. Mahringer, David, et al. "Functional Correlates of Immediate Early Gene Expression in Mouse Visual Cortex." Peer Community Journal, vol. 2, July 2022, p. e45. DOI.org, https://doi.org/10.24072/pcjournal.156.
2. Hao, Yingying, et al. "C-Fos Mediates Α1, 2-Fucosyltransferase 1 and Lewis�y Expression in Response to TGF-Β1 in Ovarian Cancer." Oncology Reports, Oct. 2017. DOI.org, https://doi.org/10.3892/or.2017.6052.
3. Distributed under Open Access license CC BY 4.0, without modification.

Created June 2025

For Research Use Only. Not For Clinical Use.