BNST PKCδ neurons are activated by specific aversive conditions to promote anxiety-like behavior

The bed nucleus of the stria terminalis (BNST) is a critical mediator of stress responses and anxiety-like behaviors. Neurons expressing protein kinase C delta (BNSTPKCδ) are an abundant but understudied subpopulation implicated in inhibiting feeding, but which have conflicting reports about their role in anxiety-like behaviors. We have previously shown that expression of PKCδ is dynamically regulated by stress and that BNSTPKCδ cells are recruited during bouts of active stress coping. Here, we first show that in vivo activation of this population is mildly aversive. This aversion was insensitive to prior restraint stress exposure. Further investigation revealed that unlike other BNST subpopulations, BNSTPKCδ cells do not exhibit increased cfos expression following restraint stress. Ex vivo current clamp recordings also indicate they are resistant to firing. To elucidate their afferent control, we next used rabies tracing with whole-brain imaging and channelrhodopsin-assisted circuit mapping, finding that BNSTPKCδ cells receive abundant input from affective, arousal, and sensory regions including the basolateral amygdala (BLA) paraventricular thalamus (PVT) and central amygdala PKCδ-expressing cells (CeAPKCδ). Given these findings, we used in vivo optogenetics and fiber photometry to further examine BNSTPKCδ cells in the context of stress and anxiety-like behavior. We found that BNSTPKCδ cell activity is associated with increased anxiety-like behavior in the elevated plus maze, increases following footshock, and unlike other BNST subpopulations, does not desensitize to repeated stress exposure. Taken together, we propose a model in which BNSTPKCδ cells may serve as threat detectors, integrating exteroceptive and interoceptive information to inform stress coping behaviors.

Acute restraint stress redirects prefrontal cortex circuit function through mGlu5 receptor plasticity on somatostatin-expressing interneurons

Inhibitory interneurons orchestrate prefrontal cortex (PFC) activity, but we have a limited understanding of the molecular and experience-dependent mechanisms that regulate synaptic plasticity across PFC microcircuits. We discovered that mGlu5 receptor activation facilitates long-term potentiation at synapses from the basolateral amygdala (BLA) onto somatostatin-expressing interneurons (SST-INs) in mice. This plasticity appeared to be recruited during acute restraint stress, which induced intracellular calcium mobilization within SST-INs and rapidly potentiated postsynaptic strength onto SST-INs. Restraint stress and mGlu5 receptor activation each augmented BLA recruitment of SST-IN phasic feedforward inhibition, shunting information from other excitatory inputs, including the mediodorsal thalamus. Finally, studies using cell-type-specific mGlu5 receptor knockout mice revealed that mGlu5 receptor function in SST-expressing cells is necessary for restraint stress-induced changes to PFC physiology and related behaviors. These findings provide new insights into interneuron-specific synaptic plasticity mechanisms and suggest that SST-IN microcircuits may be promising targets for treating stress-induced psychiatric diseases.

Delineation of an insula-BNST circuit engaged by struggling behavior that regulates avoidance in mice

Active responses to stressors involve motor planning, execution, and feedback. Here we identify an insular cortex to BNST (insula→BNST) circuit recruited during restraint stress-induced active struggling that modulates affective behavior. We demonstrate that activity in this circuit tightly follows struggling behavioral events and that the size of the fluorescent sensor transient reports the duration of the struggle event, an effect that fades with repeated exposure to the homotypic stressor. Struggle events are associated with enhanced glutamatergic- and decreased GABAergic signaling in the insular cortex, indicating the involvement of a larger circuit. We delineate the afferent network for this pathway, identifying substantial input from motor- and premotor cortex, somatosensory cortex, and the amygdala. To begin to dissect these incoming signals, we examine the motor cortex input, and show that the cells projecting from motor regions to insular cortex are engaged shortly before struggle event onset. This study thus demonstrates a role for the insula→BNST pathway in monitoring struggling activity and regulating affective behavior.