Development of light response and GABAergic excitation‐to‐inhibition switch in zebrafish retinal ganglion cells

Abstract

The zebrafish retina has been an important model for studying morphological development of neural circuits in vivo. However, its functional development is not yet well understood. To investigate the functional development of zebrafish retina, we developed an in vivo patch-clamp whole-cell recording technique in intact zebrafish larvae. We first examined the developmental profile of light-evoked responses (LERs) in retinal ganglion cells (RGCs) from 2 to 9 days post-fertilization (dpf). Unstable LERs were first observed at 2.5 dpf. By 4 dpf, RGCs exhibited reliable light responses. As the GABAergic system is critical for retinal development, we then performed in vivo gramicidin perforated-patch whole-cell recording to characterize the developmental change of GABAergic action in RGCs. The reversal potential of GABA-induced currents (E GABA ) in RGCs gradually shifted from depolarized to hyperpolarized levels during 2-4 dpf and the excitation-to-inhibition (E-I) switch of GABAergic action occurred at around 2.5 dpf when RGCs became light sensitive. Meanwhile, GABAergic transmission upstream to RGCs also became inhibitory by 2.5 dpf. Furthermore, down-regulation of the K + /Cl − co-transporter (KCC2) by the morpholino oligonucleotide-based knockdown approach, which shifted RGC E GABA towards a more depolarized level and thus delayed the E-I switch by one day, postponed the appearance of RGC LERs by one day. In addition, RGCs exhibited correlated giant inward current (GICs) during 2.5-3.5 dpf. The period of GICs was shifted to 3-4.5 dpf by KCC2 knockdown. Taken together, the GABAergic E-I switch occurs coincidently with the emergence of light responses and GICs in zebrafish RGCs, and may contribute to the functional development of retinal circuits.

Non–cell-autonomous factor induces the transition from excitatory to inhibitory GABA signaling in retina independent of activity

“…Inhibition in the retina matures after the bulk of retinotopic refinement of retinocollicular projections is complete and retinocollicular glutamatergic synapses are strengthening (51). As inhibition plays a critical role in the formation of receptive fields, we suggest that the maturation of inhibition in the retina is completed in time for eye-opening and the onset of normal visual experience (24).…”

“…In vivo recordings in zebrafish demonstrate that the timing of the GABA switch is critical for the timing of the development of light responses (24) and therefore might be linked to the onset of visual experience. Chronic blockade of GABA A receptors (GABA A Rs) in turtle retina prevents the normal maturation of spontaneous firing patterns termed retinal waves and the maturation of adult-like chloride gradients, implicating early GABA signaling in the normal maturation of inhibitory circuits in retina (15).…”

GABA depolarizes immature neurons and inhibits network activity in the neonatal neocortex in vivo

“…In favour of a depolarizing GABA action in nonmammalian species in vivo, iontophoretic application of GABA or glycine was found to evoke somatic Ca 2 þ transients (CaTs) in spinal neurons of zebrafish larvae 34 . In addition, gramicidinperforated patch recordings showed that GABA depolarizes zebrafish retinal ganglion cells at an early developmental stage 35 . At present, only limited information is available on the intact mammalian brain.…”

Funktionen der GABAergen Übertragung im unreifen Gehirn

“…So gelang Zhang und Kollegen mittels Perforated-patch-clamp-Ableitungen der Nachweis einer depolarisierenden GABA-Wirkung in retinalen Ganglienzellen des Zebrafisches (Zhang et al, 2010). Hierbei zeigte sich ein Wechsel von de-zu hyperpolarisierender GABA-Wirkung zwischen Tag 2 und 3 nach Fertilisation, welcher zeitlich mit der Ausbildung sensorisch-evozierter PSC überlappte.…”