Serotonin is a gap junction-permeable neuronal tracer in the mouse retina

Gergely Szarka; Gyula Hoffmann; Tamás Kovács-Öller; Béla Völgyi

doi:10.3389/fopht.2023.1151024

Serotonin is a gap junction-permeable neuronal tracer in the mouse retina

Front Ophthalmol (Lausanne). 2023 Mar 22:3:1151024. doi: 10.3389/fopht.2023.1151024. eCollection 2023.

Authors

Gergely Szarka^{1

2

3

4}, Gyula Hoffmann^{1

2

3}, Tamás Kovács-Öller^{1

2

3

4}, Béla Völgyi^{1

2

3

4}

Affiliations

¹ Szentágothai Research Centre, University of Pécs, Pécs, Hungary.
² Department of Comparative Anatomy and Developmental Biology, University of Pécs, Pécs, Hungary.
³ Center for Neuroscience, University of Pécs, Pécs, Hungary.
⁴ NEURON-066 Rethealthsi Research Group, Pécs, Hungary.

Abstract

Introduction: Gap junctions are dynamically modulated bridges allowing the transcellular passage of ions and small molecules with a molecular mass of up to 1 kDa, a mechanism utilized for molecular communication purposes by living cells. This same mechanism is also exploited by scientists to reveal the existence of gap junction contacts by the cell-to-cell movement of tracers. However, multiple labeling experiments require the availability of multiple gap junction-permeable tracers.

Methods: To this end, we utilized the well-known transient OFF alpha retinal ganglion cell (RGC)-coupled array as a model system to study and compare the transjunctional movement of neurobiotin (NB), a commonly used tracer, and serotonin, a recently identified tracer.

Results: Although the transjunctional movement of serotonin has been established in cell cultures, here we show, for the first time, that serotonin is also a potent tracer in in vitro tissue. In addition, serotonin is lighter than the classical gap junction-permeable NB, and thus, we expected that tracer movement would be comparable to or better than that of serotonin. We found that intracellular serotonin injections result in the labeling of the coupled transient OFF alpha RGC array very similar to those of the classical NB-labeled arrays. Both serotonin and NB-injected transient OFF alpha RGCs displayed the well-known pattern with coupled RGCs and a cohort of coupled wide-field amacrine cells (ACs).

Discussion: By using morphological characteristics, we confirm that the serotonin and the NB-coupled AC arrays are identical, and thereby confirm that serotonin is a potent gap junction-permeable tracer and can be readily used as an alternative to NB in in vitro tissue. Moreover, serotonin can be utilized in parallel with other dyes or tracers, enabling the use of multiple labels in the same material.

Keywords: Neurobiotin; amacrine cell; electrical synapse; ganglion cell; gap junction; retina; serotonin.

Grants and funding

This study was supported by the NKFIH and the European Union under the action of the ERA-NET COFUND (2019-2.1.7-ERANET-2021–00018; NEURON (NEURON-066 Rethealthsi) to BV. The study was also financially supported by the NKFI (OTKA NN128293) (BV) from the European Union and the State of Hungary, co-financed by the European Social Fund in the framework of TKP2020 IKA-07 National Excellence Program (BV, TK-Ö). This research was also financed by the Thematic Excellence Program 2021 Health Sub-programme of the Ministry for Innovation and Technology in Hungary, within the framework of the EGA-16 project of the University of Pécs. Supported by the ÚNKP-22-3-II-PTE-1414 (GS) New National Excellence Program of the Ministry of Human Capacities.