Infragranular excitatory projection to granular neurons in neonatal rodent somatosensory neocortex
- Authors: Idzhilova O.S.1, Simonova N.A.1, Minlebaev M.G.2,3, Malyshev A.Y.1
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Affiliations:
- Institute of Higher Nervous Activity and Neurophysiology of RAS (IHNA&NPh RAS)
- Mediterranean Institute of Neurobiology, Aix-Marseille University
- Kazan (Volga Region) Federal University
- Issue: Vol 18, No 4 (2023)
- Pages: 771-773
- Section: Conference proceedings
- URL: https://journal-vniispk.ru/2313-1829/article/view/256342
- DOI: https://doi.org/10.17816/gc623337
- ID: 256342
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Abstract
Though the principles of central nervous system development are genetically encoded, the cortical activity is also critically involved in these processes. While this question is quite important, up to now we are limited in our understanding of the role that neuronal activity plays in formation of functionally linked cellular ensembles in the developing cortex. Recently, transient inhibitory neuronal projections were shown in the barrel cortex during the critical period of its development. Expression of interneuronal connections from infragranular to other cortical layers exactly during the period of barrel formation suggests their critical role in establishment of adult-like columnar organization of the barrel cortex. While the inhibitory connections were demonstrated, the question remains, whether the transient connectivity is restricted by emergence of inhibitory projections, or both types (including excitatory connections) could be expressed during the critical period of the barrel cortex development.
Here, we aimed to answer this question using in vitro optogenetic stimulation of the neurons in the infragranular layers of the neonatal mouse barrel cortex. A viral vector of serotype AAV.PHP.eB containing channelrhodopsin-2 along with a fluorescent Venus tag sequence under the hSyn promoter was delivered via intraventricular injection into the neonatal mouse brain at P0. This transduction protocol resulted in neuron-specific expression of the construct primarily in the L2/3, L5 and L6 cortical layers at P7. At P7, acute coronal brain slices containing the barrel cortical field were prepared. For a given cortical column, the infragranular layers were optogenetically mapped while simultaneous whole-cell electrophysiological registration of a pyramidal cell in the barrel was performed. Holding potential was varied to discriminate between light-evoked EPSCs and IPSCs.
The results of our preliminary recordings in the neonatal somatosensory cortex showed presence of neuronal projections from infra- to granular layer, which is in agreement with the already demonstrated data. However, L4 EPSCs evoked by infragranular layer stimulation were also recorded, suggesting the expression of the excitatory connections from infra- to granular layers early in development. Though we require to continue our recordings, our findings suggest an even more complex network interactions that shape the barrel cortex L4 during the early postnatal stages.
Full Text
Although central nervous system development is genetically encoded, cortical activity also plays a critical role in these processes. While the question of the role that neuronal activity plays in the formation of functionally linked cellular ensembles in the developing cortex is important, our current understanding on this matter is limited. Transient inhibitory neuronal projections were recently observed in the barrel cortex during its critical development period. The expression of interneuronal connections from infragranular to other cortical layers during the barrel formation period implies their essential role in establishing a columnar organization similar to that of adult barrel cortex. While inhibitory connections have been demonstrated, it remains unclear whether the transient connectivity is limited by the emergence of inhibitory projections, or if both types of connections (including excitatory) could be expressed during the critical period of barrel cortex development.
Here, our aim is to address this query by conducting in vitro optogenetic stimulation on the neurons present in the infragranular layers of the neonatal mouse barrel cortex. We delivered a viral vector of serotype AAV.PHP.eB, which contained channelrhodopsin-2 and a fluorescent Venus tag sequence under the hSyn promoter, through an intraventricular injection into the neonatal mouse brain at P0. This transduction protocol yielded neuron-centric expression of the construct chiefly in the cortical layers L2/3, L5, and L6 at P7. At postnatal day 7 (P7), acute coronal brain slices that contained the barrel cortical field were prepared. We optogenetically mapped the infragranular layers of a given cortical column, while simultaneously performing whole-cell electrophysiological registration on a pyramidal cell within the barrel. The holding potential was varied to distinguish between light-evoked excitatory post-synaptic currents (EPSCs) and inhibitory post-synaptic currents (IPSCs).
The initial recordings in the neonatal somatosensory cortex displayed the existence of neuronal projections from infra- to granular layer, in alignment with formerly demonstrated data. In addition, recordings of L4 EPSCs evoked by infragranular layer stimulation were also observed, suggesting the manifestation of excitatory connections from infra- to granular layers in the early stage of development. Although further recordings are necessary, our findings indicate that there are highly intricate network interactions that influence the development of the barrel cortex L4 in the early postnatal stages.
ADDITIONAL INFORMATION
Authors’ contribution. All authors made a substantial contribution to the conception of the work, acquisition, analysis, interpretation of data for the work, drafting and revising the work, final approval of the version to be published and agree to be accountable for all aspects of the work.
Funding sources. This study was not supported by any external sources of funding.
Competing interests. The authors declare that they have no competing interests.
About the authors
O. S. Idzhilova
Institute of Higher Nervous Activity and Neurophysiology of RAS (IHNA&NPh RAS)
Author for correspondence.
Email: olgaidzh@gmail.com
Russian Federation, Moscow
N. A. Simonova
Institute of Higher Nervous Activity and Neurophysiology of RAS (IHNA&NPh RAS)
Email: olgaidzh@gmail.com
Russian Federation, Moscow
M. G. Minlebaev
Mediterranean Institute of Neurobiology, Aix-Marseille University; Kazan (Volga Region) Federal University
Email: olgaidzh@gmail.com
France, Marseille; Kazan, Russian Federation
A. Yu. Malyshev
Institute of Higher Nervous Activity and Neurophysiology of RAS (IHNA&NPh RAS)
Email: olgaidzh@gmail.com
Russian Federation, Moscow
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