Viral-Mediated Gene Expression Restricted to GABAergic Interneurons and Parvalbumin Subclass in Marmoset Primary Visual Cortex

Conceitos essenciais

Viral vectors can selectively and efficiently target GABAergic and parvalbumin-expressing inhibitory neurons in the primate visual cortex, enabling the study of their connectivity and function.

Resumo

The authors thoroughly validated and characterized several recently-developed viral vectors designed to restrict transgene expression to GABAergic cells or their parvalbumin (PV) subtype in the primary visual cortex (V1) of the marmoset, a non-human primate model.

They found that the AAV-h56D virus induces transgene expression in GABAergic cells with up to 91-94% specificity and 80% efficiency, depending on viral serotype and cortical layer. The AAV-PHP.eB-S5E2 virus induces transgene expression in PV cells across all cortical layers with up to 98% specificity and 86-90% efficiency.

The authors compared the laminar distribution of GABA+ and PV+ cells in marmoset V1 with previous findings in mouse V1, revealing some species differences. They also observed that the viral injections caused a reduction in GABA and PV immunoreactivity at the injection sites, suggesting the specificity of the viruses may be even higher than measured.

These viral vectors represent promising tools for studying the function and connectivity of GABAergic and PV inhibitory neuron subtypes in the primate cortex, which is critical for understanding cortical function and dysfunction in the model system closest to humans.

Estatísticas

The density of GABA+ cells peaks in layers 2/3 and 4C of marmoset V1, with no significant difference between these two layers.
The density of PV+ cells peaks in layer 4C of marmoset V1, and is significantly higher than in all other layers.
92.3% of PV+ cells in marmoset V1 are GABA+, and PV+ cells represent 61.4% of all GABA+ cells on average.

Citações

"Understanding cortical inhibitory neuron function in the primate is critical for understanding cortical function and dysfunction in the model system closest to humans."
"These viral vectors represent promising tools for studying GABAergic and PV neuron connectivity and function in primate cortex."

Principais Insights Extraídos De

Laminar specificity and coverage of viral-mediated gene expression restricted to GABAergic interneurons and their parvalbumin subclass in marmoset primary visual cortex

by Federer,F., ... às www.biorxiv.org 03-11-2024

https://www.biorxiv.org/content/10.1101/2024.03.07.583998v1

Perguntas Mais Profundas

How do the functional properties of GABAergic and PV interneurons in primate visual cortex differ from those observed in rodents?

In the primate visual cortex, the functional properties of GABAergic and PV interneurons exhibit some differences compared to rodents. One key difference is the laminar distribution of these interneurons. In primates, including marmosets, GABA+ and PV+ cells peak in layers 2/3 and 4C, whereas in rodents, these cells peak in layers 4 and 5. This difference in laminar distribution suggests potential variations in the functional organization of inhibitory circuits between the two species.
Moreover, the proportion of PV cells among GABAergic neurons is higher in primate visual cortex compared to rodents. In marmoset V1, PV cells represent on average 61% of all GABAergic cells, with peaks reaching up to 79% in certain layers. This is higher than the proportion observed in mouse V1, where PV cells represent about 40% of all GABA cells. This difference in the proportion of PV cells suggests potential species-specific roles and functional contributions of PV interneurons in primate cortical processing.
Additionally, the connectivity patterns and network properties of inhibitory neurons may differ between primates and rodents. Studies in mice have provided insights into the connectivity and function of distinct classes of inhibitory neurons, but it remains unknown whether these findings fully apply to inhibitory neurons in higher species such as primates. Understanding the specific functional properties and connectivity of GABAergic and PV interneurons in the primate visual cortex is crucial for elucidating cortical function and dysfunction in a model system closer to humans.

What are the potential limitations or caveats of using viral vectors to study inhibitory neuron function in the primate brain?

While viral vectors offer a powerful tool for studying inhibitory neuron function in the primate brain, there are several limitations and caveats that researchers need to consider:

Specificity and Off-Target Effects: Although viral vectors can be engineered to target specific cell types, there is always a possibility of off-target effects. Viral-mediated transgene expression may inadvertently affect non-target cells or alter the expression of endogenous genes in the host neurons. This can lead to unintended changes in neuronal function and circuit dynamics.

Immunoreactivity Alterations: As observed in the study, viral injections can lead to reduced GABA and PV immunoreactivity at the injection sites. This reduction in marker expression may affect the accuracy of specificity measurements, potentially underestimating the true specificity of the viral vectors.

Dose-Dependent Effects: The dose and volume of viral injections can impact the specificity and coverage of transgene expression. Higher injection volumes may lead to a dose-dependent reduction in specificity, possibly due to increased off-target effects or alterations in marker expression.

Inflammatory Response: Viral vectors can elicit an immune response in the host brain, potentially causing inflammation and tissue damage. This immune response may influence the behavior of inhibitory neurons and affect the interpretation of experimental results.

Temporal Dynamics: The temporal dynamics of viral-mediated gene expression should be carefully considered. The timing of transgene expression and its persistence may impact the interpretation of results, especially in studies investigating dynamic changes in inhibitory neuron function over time.

Integration and Spread: Viral vectors can integrate into the host genome and spread beyond the intended injection site. This spread of viral particles may lead to unintended transduction of neighboring cells or distant brain regions, affecting the specificity of transgene expression.

What insights could be gained by combining the use of these viral tools with other techniques, such as electrophysiology or calcium imaging, to further elucidate the role of inhibitory neurons in primate cortical processing?

Combining viral tools with complementary techniques like electrophysiology and calcium imaging can provide a more comprehensive understanding of the role of inhibitory neurons in primate cortical processing. Here are some insights that could be gained from such integrative approaches:

Functional Connectivity: By combining viral-mediated transgene expression with electrophysiological recordings, researchers can investigate the functional connectivity between inhibitory neurons and excitatory neurons in the primate cortex. Recording the activity of specific inhibitory neuron subtypes while manipulating their gene expression can reveal how these neurons contribute to cortical circuit dynamics.

Network Dynamics: Calcium imaging techniques can be used to monitor the activity of inhibitory neuron populations in real-time. By correlating the activity patterns of GABAergic and PV interneurons with viral-induced transgene expression, researchers can elucidate the network dynamics and information processing mechanisms in the primate visual cortex.

Behavioral Correlates: Integrating viral tools with behavioral paradigms allows researchers to link the activity of inhibitory neurons to specific cognitive functions or sensory processing tasks. By manipulating the gene expression of inhibitory neuron subtypes and monitoring their activity during behavioral tasks, insights into the functional relevance of these neurons in primate behavior can be gained.

Plasticity and Adaptation: Studying the plasticity of inhibitory circuits in response to sensory stimuli or learning tasks can provide insights into how inhibitory neurons contribute to cortical adaptation and flexibility. Combining viral tools with longitudinal calcium imaging can reveal changes in inhibitory neuron activity patterns over time, shedding light on the mechanisms underlying cortical plasticity.

Cell-Type Specific Effects: By selectively manipulating the gene expression of GABAergic and PV interneurons using viral vectors, researchers can dissect the cell-type specific effects of these inhibitory neurons on cortical processing. Integrating these manipulations with functional readouts from electrophysiology and calcium imaging allows for a more precise characterization of the contributions of different inhibitory neuron subtypes to primate cortical function.