GABAergic TH2 Amacrine Cells Participate in Spontaneous Wave Activity in the Developing Retina

Amacrine cells (ACs) are retinal interneurons that regulate synaptic transmission from bipolar cells to retinal ganglion cells (RGCs) and play essential roles in object motion detection, contrast sensitivity, and light adaptation. A subtype of GABAergic ACs identified using a tyrosine hydroxylase (TH) promoter-driven green fluorescent protein (GFP) mouse line has been termed TH2 amacrine cells (TH2-ACs). Although TH2-ACs contribute to the feature selectivity of object-motion signals in the adult retina, their functional properties during early postnatal development remain unclear. Using genetic mouse models, electrophysiology, immunohistochemistry, and calcium imaging, we show that TH2-ACs exhibit spontaneous rhythmic depolarizations during development. In the first postnatal week, these depolarizations were abolished by acetylcholine receptor antagonists, indicating that TH2-ACs are excited by starburst amacrine cells (SACs) via spontaneous cholinergic retinal waves. During the second postnatal week, rhythmic depolarizations persisted but were blocked by glutamate receptor antagonists, demonstrating that TH2-ACs are subsequently driven by bipolar cells through glutamatergic waves. Calcium imaging further revealed that this activity propagates across the TH2-AC network in a wave-like manner, potentially resulting in spatially and temporally patterned GABA release. Pharmacological blockades of GABA _A receptors significantly enhanced glutamatergic wave activity in SACs and RGCs, indicating that GABAergic signaling from TH2-ACs participates in exerting inhibitory control over retinal waves. Together, these findings identify TH2-ACs as active participants in the development of retinal wave circuits and suggest that this participation via GABA signaling could contribute to activity-dependent refinement of retinal circuits underlying object motion processing.

TH2 amacrine cells are excited by starburst amacrine cells through cholinergic retinal wave activity during the first postnatal week.During the second postnatal week, TH2 amacrine cells are driven by bipolar cells via glutamatergic retinal wave activity.The dense dendritic arborization of TH2 amacrine cells enables their participation in the propagation of both cholinergic and glutamatergic waves. Wave-like GABA release from TH2 amacrine cells contributes to the modulation of retinal wave activity through activation of GABA _A receptors.