Rapid neuronal labeling and functional imaging in the developing mouse brain with AAV-PHP.eB.

Neuronal labeling in the developing brain is essential for studying the formation and maturation of neural circuits. Among labeling techniques, adeno-associated virus (AAV)-based gene delivery offers high efficiency and versatility. However, whether AAV can effectively label neurons in the developing brain has not been fully determined. Here, we demonstrate that administration of AAV-PHP.eB in neonatal mice results in neuronal transduction as early as 3 days after injection. By titrating the AAVs, we achieve sparse neuronal labeling and facilitate high-resolution reconstruction of dendritic morphology during the critical developmental period. Then, we extend this method to functional imaging by delivering GCaMP, allowing longitudinal in vivo two-photon calcium imaging in the immature brain. Our findings show that AAV-PHP.eB-mediated early postnatal delivery offers a rapid, efficient, and minimally invasive approach for neuronal labeling and functional imaging in the developing brain, providing opportunities to investigate neural circuit development at both structural and functional levels.