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

Abstract

During development, the effect of activating GABA A receptors switches from depolarizing to hyperpolarizing. Several environmental factors have been implicated in the timing of this GABA switch, including neural activity, although these observations remain controversial. By using acutely isolated retinas from KO mice and pharmacological manipulations in retinal explants, we demonstrate that the timing of the GABA switch in retinal ganglion cells (RGCs) is unaffected by blockade of specific neurotransmitter receptors or global activity. In contrast to RGCs in the intact retina, purified RGCs remain depolarized by GABA, indicating that the GABA switch is not cell-autonomous. Indeed, purified RGCs cocultured with dissociated cells from the superior colliculus or cultured in media conditioned by superior collicular cells undergo a normal switch. Thus, a diffusible signal that acts independent of local circuit activity regulates the maturation of GABAergic inhibition in mouse RGCs.A lthough GABA is the principal inhibitory neurotransmitter in the mature CNS, it is a robust source of excitation during development that is important for many developmental processes (1-4). The transition from excitatory to inhibitory action of GABA has been observed in a number of neural circuits and in many vertebrate species (5, 6) and the primary mechanisms underlying the switch are fairly well understood (7-11; reviewed in refs. 12-14). However, whether the timing of the GABA switch is modulated by local circuit activity (8,(15)(16)(17)(18) or occurs independent of activity (19,20) and is therefore intrinsic to developmental program of the cell remains controversial.Retinal ganglion cells (RGCs) undergo a switch in their response to GABA during the first two postnatal weeks of development (21-23). 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). Based on these results, it has been proposed that the maturation of GABAergic inhibition is influenced by local network activity and is critical for the cessation of retinal waves (25).Here we explore factors that influence the timing of the GABA switch in mouse RGCs. By using three different preparations, we test whether the timing of the GABA switch is regulated by (i) local circuit activity in the retina, (ii) an intrinsic developmental program, or (iii) a diffusible, non-cell autonomous factor that operates independent of retinal activity. Results GABA Switch Occurs Normally in Nicotinic Acetylcholine Receptor-KORetinas. The timing of the GABA switch in retinal neurons in the ganglion cell layer (GCL) was determined by calcium imagi...

Correlated Spontaneous Activity Persists in Adult Retina and Is Suppressed by Inhibitory Inputs

“…GABA and glycine receptors are initially excitatory, but become inhibitory as the retina reaches maturity [14], [15] due to a change in the chloride equilibrium potential which coincides with an up-regulation of the chloride extruder KCC2 [59]. This is a gradual process, occuing throughout the course of stage II and stage III waves [14], [60]. In ferret, it has been shown that GABAARs become inhibitory after P18, while glycine receptors become inhibitory by P21 [10], ages where stage III waves are still active.…”

Assembly and disassembly of a retinal cholinergic network

“…Second, acetylcholinesterase, the enzyme that degrades ACh, is increased during this time window (Hutchins et al , 1995), which would decrease the spread of ACh. Third, the action of GABA becomes hyperpolarizing a few days before the onset of glutamatergic waves (Zhang et al , 2006b; Barkis et al , 2010). Intracellular chloride is reduced as the expression of the potassium-chloride transporter KCC2 is increased in ganglion cells (Zhang et al , 2006a).…”

“…References:(1) (Voinescu et al , 2009) (2) (Kim et al , 2000) (3) (Hinds & Hinds, 1983) (4) (Fisher, 1979) (5) (Bansal et al , 2000) (6) (Johnson et al , 2003) (7) (Xu & Tian, 2004) (8) (Barkis et al , 2010) (9) (Zheng et al , 2004) (approximate age from rabbit data)…”

Following the ontogeny of retinal waves: pan-retinal recordings of population dynamics in the neonatal mouse

“…They are first mediated by gap junctions (Stage I: late gestation) (Catsicas et al 1998;Bansal et al 2000;Syed et al 2004a), and then depend on cholinergic synaptic transmission (Stage II: until P9-10 in mouse) (Feller et al 1996;Sernagor & Grzywacz, 1996, 1999Catsicas et al 1998;Wong et al 1998;Bansal et al 2000;Sernagor et al 2000;Zhou & Zhao, 2000;Sernagor et al 2003;Syed et al 2004b). GABAergic signalling becomes involved in modulating waves at around P4-5 in mouse (Zhang et al 2006;Hennig et al 2011) and at these early stages is depolarizing, as it is elsewhere in the developing central nervous system (CNS) (Ben-Ari et al 2007), shifting polarity after P6 (Zhang et al 2006;Barkis et al 2010). Finally, glutamate signalling between bipolar cells takes over as the main driver of Stage III waves at around P10 in mouse (Bansal et al 2000;Zhou & Zhao, 2000;Syed et al 2004b;Blankenship et al 2009), although gap junctions between ON bipolar cells are also involved in lateral transmission (Akrouh & Kerschensteiner, 2013).…”