ELECTROPHYSIOLOGICAL ANALYSIS OF THE LATERAL HABENULA UNDER ACUTE STRESS

Major depressive disorder (MDD) is a leading cause of global disability, marked by persistent low mood, anhedonia, and cognitive impairment. Lateral habenula (LHb) hyperactivity contributes to the pathophysiology of MDD, and its suppression alleviates depressive-like behaviors. Yet, the precise subthreshold dynamics and temporal evolution of LHb activity during affective transitions are unclear, due to its deep location and technical challenges. Here, we examined the progression of LHb activity during acute stress to pinpoint early electrophysiological markers of depressive vulnerability. Using in vivo whole-cell patch-clamp recordings from LHb neurons in head-fixed mice alongside high-density Neuropixels recordings for ensemble monitoring, we tracked activity longitudinally before, during, and after acute restraint stress. Patch-clamp recordings identified three phenotypes: silent, burst-firing, and tonic-firing neurons. Basally, burst-firing cells had higher excitatory postsynaptic potential (EPSP) frequencies, whereas tonic-firing cells displayed larger EPSP amplitudes, indicating distinct modes of synaptic integration. Neuropixels revealed stress-induced LHb hyperactivation: compared with controls, stressed mice exhibited progressive rises in firing rates, burst rates, and population synchrony (as measured by population firing rate variance). Burst firing increased most rapidly and robustly in early stress phases, preceding the peaks in mean firing and synchrony. LHb burst firing thus emerges as a sensitive early indicator of stress, likely driving network hyperactivity toward depressive pathology. This temporal mapping refines models of MDD onset and proposes early suppression of bursting as a preventive strategy. Future work will assess pharmacological targeting, including psychedelics like psilocybin, to normalize these dynamics and lower the risk of depression.