Genetic Targeting of Neural Circuit Elements Underlying Anxiety-Like Behavioral States

Exposure to uncontrollable stress or acute trauma is a critical etiological factor in the onset of anxiety-like behavioral states in humans and rats. Serotonergic (5-HT) neurons in the dorsal raphe nucleus (DRN) are activated during uncontrollable (inescapable) tailshock (IS), but not during controllable (escapable) tailshock (ES). This activation leads to sensitization of the DRN, resulting in acute anxiety-like behavior in rats. Moreover, activation of the DRN is both necessary and sufficient for the behavioral and neurochemical consequences of IS. The lateral habenula (LHb) provides the primary glutamatergic input to the DRN and dysregulation of the LHb and DRN is implicated in stress-related psychiatric disorders. In the present study, the role of the LHb in regulating the behavioral response to acute stress was examined. First, it was necessary to determine whether stress-induced activation of the LHb is modulated by the controllability of the stressor. ES and IS resulted in an equivalent increase in Fos protein in the LHb, as compared to home cage controls (HC). Next, Fos expression restricted to the LHb-DRN pathway was measured. The retrograde tracer Fluorogold (FG) was injected into the DRN and Fos immunoreactivity (Fos-ir) was quantified in FG-positive (FG-ir) cells in the LHb following ES, IS or HC. ES and IS yielded a similar increase in activation of the LHb-DRN pathway, with no effect of controllability of the stressor. Finally, an optogenetic strategy was implemented to determine whether silencing the LHb during IS would protect against the behavioral consequences of IS. Halorhodopsin silencing of the LHb during IS produced resistance to the anxiety-like behavioral outcome of IS, as measured in a juvenile social investigation test. These data suggest that the LHb modulates DRN activity during stress, and that silencing this pathway during uncontrollable stress may protect against stress-related psychiatric disorders.