Pinel, M. | Search bioRxiv

bioRxiv2026

Lateral hypothalamic input engages a disinhibitory microcircuit in the dorsal raphe to promote behavior activation

Behavioral activation involves coordination between hypothalamic and brainstem systems that regulate movement and internal state, but the circuit logic underlying this interaction remains poorly defined. The dorsal raphe nucleus (DRN), a major serotonergic hub, integrates diverse inputs to influence behavioral inhibition and activation, yet how hypothalamic signals shape its activity is unclear. Here, we identify a disinhibitory pathway through which the lateral hypothalamus (LHA) promotes behavioral activation via DRN. Using intersectional viral tracing, electrophysiology, and single-nucleus RNA sequencing, we show that LHA inputs preferentially target GABAergic DRN neurons that locally inhibit 5-HT neurons. Silencing these DRN neurons innervated by LHA increased locomotor and repetitive behaviors, decreased local inhibition, and enhanced cFos activity in serotonergic neurons, consistent with circuit-level disinhibition. Molecular profiling revealed distinct transmitter identities and transcriptional signatures of LHA-targeted versus LHA-projecting DRN populations. Together, these findings delineate a hypothalamic-raphe circuit that transforms hypothalamic drive into serotonergic activation, revealing a mechanism by which the lateral hypothalamus promotes behavioral activation through local inhibitory control. HIGHLIGHTSO_LILHA inputs preferentially target non-serotonergic, transcriptionally distinct DRN neurons C_LIO_LILHA-innervated DRN neurons form extensive local inhibition C_LIO_LISilencing LHA-innervated DRN neurons reduced local inhibitory tone and activate serotonin neurons C_LIO_LIDisrupting this circuit drives behavioral activation with repetitive motor pattern, not anxiety C_LI

neuroscience↗

bioRxiv2025

The Lateral Habenula to Ventral Tegmental Area Pathway is Required for Aversive Learning and Defensive Behaviors

The lateral habenula (LHb) provides aversive signals to the ventral tegmental area (VTA), but its contribution to learning and behavior remains poorly understood. Using a retrograde viral strategy, we targeted VTA-projecting LHb neurons and monitored calcium activity during active avoidance training. These neurons were activated by aversive stimuli and predictive cues as animals acquired avoidance responses and showed increased activity at movement onset during the tail suspension test (TST). Silencing LHb[->]VTA transmission impaired avoidance learning, prolonged escape latency, and reduced the persistence and vigor of active coping in the TST, without affecting baseline locomotion. Anatomical and ex vivo electrophysiology revealed that LHb terminals innervate both dopaminergic (TH) and non-dopaminergic (TH-) VTA neurons, exhibiting session-specific synaptic adaptations during avoidance learning. Together, these findings identify the LHb[->]VTA pathway as a source of aversive predicting signals required for the acquisition of avoidance behavior and the persistence of active coping in aversive context. HighlightsO_LILHb[->]VTA neurons are required for aversive learning and adaptive avoidance C_LIO_LIThese neurons respond to aversive stimuli, predictive cues, and movement onset C_LIO_LISilencing the pathway impairs avoidance learning and reduces active coping in aversive contexts C_LIO_LILHb[->]VTA inputs innervate DA and non-DA neurons and undergo learning-related plasticity C_LI

neuroscience↗