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ABSTRACT In self-amplifying RNA (saRNA), substitution of cytidine with 5-hydroxymethylcytidine (hm5C) reduces innate immune responses and prolongs protein expression. When formulated as a vaccine and administered intramuscularly, lipid nanoparticles (LNPs) loaded with modified saRNA (saRNA-LNPs) afford robust and long-term protein expression. Here we report the protein expression and cell type tropism of modified saRNA-LNPs, encoding fluorescent proteins, when injected in the mammalian brain. saRNA encapsulated in an LNP formulation comprising ALC-0315 (present in Comirnaty®) efficiently mediates robust and long-lasting protein expression in brain cells beyond five weeks, with detectable expression in some neurons at three months. hm5C saRNA substantially outperforms N1mΨ mRNA. Intriguingly, in addition to transfecting astrocytes and neurons at the injection site, saRNA-LNPs labels neurons retrogradely. Thus, saRNA-LNPs are an exciting nonviral gene transduction method that effectively transduces brain cells with excellent potency and mediates prolonged gene expression. 

ABSTRACT The timing of spikes dictates a neuron’s impact on downstream circuits and behavior, and spike timing is determined by the membrane potential (Vm). However, due to technical challenges, it has been impossible to analyze the relative timing of Vm dynamics between neurons during behavior. Using large scale membrane voltage imaging, we simultaneously recorded Vm from many individual hippocampal neurons in animals engaged in a virtual spatial task. We found that relative phase of Vm theta oscillations across neurons exhibit gradual or discrete shifts depending on spatial position. This finding extends beyond previous studies showing Vm dynamics in single neurons or spiking activity in multiple neurons, revealing previously unknown evidence for consistent coding of space by spike-independent relative phase of Vm theta dynamics between neurons.