SPIKING DYNAMICS IN LATERAL HABENULA AND RAPHE NUCLEI REVEALED BY HIGH-DENSITY RECORDINGS

The Lateral Habenula (LHb) and the Raphe Nuclei – comprising the Dorsal (DRN) and Median Raphe (MRN) – are critical nodes in the neural circuitry governing emotional valence, stress adaptation, and decision-making. While the LHb is well-established as a center for encoding negative affect, the Raphe nuclei are pivotal in modulating mood and behavioral coping strategies via widespread serotonergic projections. Although anatomical studies have delineated robust, topographically organized glutamatergic inputs from the LHb to the Raphe, the real-time neuronal dynamics of such a projection remain poorly understood. Existing evidence relies on bulk activation of LHb inputs onto the Raphe to establish both functional and behavioral causalities. This method, while powerful, imposes artificial synchrony and masks the naturalistic temporal structure of inter-regional communication. To bridge this gap, we employed in-vivo electrophysiological recordings of neuronal activity using Neuropixels 2.0 probes, in adult C57Bl6j male mice under isoflurane anesthesia. Initial recordings of Raphe neurons during electrical stimulation of the LHb revealed heterogeneous excitatory and inhibitory responses, confirming functional connectivity in-vivo. To capture naturalistic, spontaneous interaction between these neuronal networks we utilized simultaneous dual-probe recordings. Preliminary analysis identified a subset of units in the Raphe nuclei whose firing dynamics can be modeled based on preceding LHb activity. Ultimately, this work aims to dissect the precise temporal codes the LHb uses to modulate Raphe output (and consequently serotonin release) providing a granular view of this essential neural circuit of affect.