Neural mechanism underlying depressive-like state associated with social status loss.

Downward social mobility is a well-known mental risk factor for depression, but its neural mechanism remains elusive. Here, by forcing mice to lose against their subordinates in a non-violent social contest, we lower their social ranks stably and induce depressive-like behaviors. These rank-decline-associated depressive-like behaviors can be reversed by regaining social status. In vivo fiber photometry and single-unit electrophysiological recording show that forced loss, but not natural loss, generates negative reward prediction error (RPE). Through the lateral hypothalamus, the RPE strongly activates the brain's anti-reward center, the lateral habenula (LHb). LHb activation inhibits the medial prefrontal cortex (mPFC) that controls social competitiveness and reinforces retreats in contests. These results reveal the core neural mechanisms mutually promoting social status loss and depressive behaviors. The intertwined neuronal signaling controlling mPFC and LHb activities provides a mechanistic foundation for the crosstalk between social mobility and psychological disorder, unveiling a promising target for intervention.

Author Correction: Using the tube test to measure social hierarchy in mice.

In the version of this paper originally published, an affiliation for Zhengxiao Fan was omitted. In addition, the Reporting Summary incorrectly indicated that human research participants had been used in the study, instead of animal subjects. These errors have been corrected in the PDF and HTML versions of the protocol.

Using the tube test to measure social hierarchy in mice.

Investigation of the neural mechanisms underlying social hierarchy requires a reliable and effective behavioral test. The tube test is a simple and robust behavioral assay that we recently validated as a reliable measure of social hierarchy in mice. The test was demonstrated to produce results largely consistent with the results seen when using other dominance measures, including the warm spot test, territory urine marking or the courtship ultrasound vocalization test. Here, we describe a step-by-step procedure to use the tube test to measure dominance within a cage of four male C57/BL6 mice as an example application. The procedure comprises three stages: habituation, training to pass through the tube, and the tube test itself. The social rank of each mouse is determined by the number of wins it gains when competing against the other three cagemates. A stable rank is derived when all mice maintain the same ranking for 4 consecutive days. The time required to acquire a stable rank usually varies from 4 to 14 d. An additional 5 d is required for habituation and training.

History of winning remodels thalamo-PFC circuit to reinforce social dominance.

Mental strength and history of winning play an important role in the determination of social dominance. However, the neural circuits mediating these intrinsic and extrinsic factors have remained unclear. Working in mice, we identified a dorsomedial prefrontal cortex (dmPFC) neural population showing "effort"-related firing during moment-to-moment competition in the dominance tube test. Activation or inhibition of the dmPFC induces instant winning or losing, respectively. In vivo optogenetic-based long-term potentiation and depression experiments establish that the mediodorsal thalamic input to the dmPFC mediates long-lasting changes in the social dominance status that are affected by history of winning. The same neural circuit also underlies transfer of dominance between different social contests. These results provide a framework for understanding the circuit basis of adaptive and pathological social behaviors.