Sharp wave ripple coupling in zebrafish hippocampus and basolateral amygdala

The mammalian hippocampus exhibits sharp wave events (1-30 Hz) with an often-present superimposed fast ripple oscillation (120-200 Hz) forming a sharp wave ripple (SWR) complex. During slow wave sleep or consummatory behaviors, SWRs result from the sequential spiking of hippocampal cell assemblies initially activated during imagined or learned experiences. SWRs occur in tandem with cortical/subcortical assemblies critical to the long-term storage of specific memory types. Leveraging juvenile zebrafish, we show that SWR events in their hippocampal homologue, the anterodorsolateral lobe (ADL), in ex vivo whole-brains are locally generated and maintained. SWR events were also recorded in the basolateral amygdala (BLA). Concomitant single cell calcium imaging and local field potential (LFP) recordings showed that BLA SWs couple to ADL SWs. Calcium imaging recordings of whole-brains demonstrated that ADL and BLA SWRs are endogenously and spontaneously silenced by the activation of a more caudal population of putative cholinergic cells. Electrical stimulation of this caudal region silenced ADL SWs. Our results suggest that the SWR-generating circuit is evolutionarily conserved through shared acetylcholine modulating mechanisms. These findings further our understanding of neuronal population dynamics in the zebrafish brain and highlights their advantage for simultaneously recording SW/SWRs and single cell activity in diverse brain regions.