SUMMARY Defensive behaviors are essential for survival, with risk assessment enabling organisms to evaluate and respond to potential threats. The dorsal raphe nucleus (DRN), a key neuromodulatory center, is crucial for encoding motivational salience and regulating arousal and sleep-wake states through its diverse neuronal populations, including dopaminergic neurons (DRN DA ). While the roles of DRN DA neurons have been studied, their specific contributions to threat evaluation are less understood. Recent research identifies a distinct subset of DRN DA neurons that express vasoactive intestinal peptide (VIP) and project to the central amygdala (CeA) and the oval nucleus of the bed nucleus of the stria terminalis (ovBNST). Together, these two regions comprise the central extended amygdala, a key network regulating adaptive responses to threats. We hypothesized that distinct DRN DA subpopulations exert diverging effects on sleep-wake regulation and that DRN VIP neurons play a pivotal role in coordinating activity between the CeA and ovBNST, thereby influencing risk assessment and defensive response. To test this hypothesis, we used a combination of in situ hybridization, immunochemistry, whole-brain mapping, electrophysiology, and cell-specific genetic tools in mice and non-human primates. Our findings reveal that DRN VIP neurons form a key DRN DA neuronal subset, uniquely positioned to regulate the central extended amygdala through a feedback loop. These neurons receive inputs from Protein Kinase C delta (PKC-δ) neurons in the ovBNST and CeA and send glutamate-releasing projections back to these regions, modulating PKC-δ neuron excitability. Selective ablation of DRN VIP neurons increases activity in both the BNST and CeA, disrupting active-phase sleep architecture and impairing risk assessment and defensive behaviors. Together, these findings suggest DRN VIP neurons control specific phases of sleep and orchestrate the central extended amygdala’s role in risk assessment and defensive responses. HIGHLIGHTS DRN VIP neurons form a subset of DRN DA neurons in mice and non-human primates. DRN VIP receive inputs from Protein Kinase C delta (PKC-δ) neurons in the ovBNST and CeA and project back to both. By releasing glutamate, DRN VIP neurons regulate PKC-δ neuron excitability in the ovBNST and CeA. Ablating DRN VIP neurons increases BNST and CeA activity, disrupts active-phase sleep architecture, and impairs threat responses. IN BRIEF DRN VIP neurons, a key subset of DRN DA neurons in mice and primates, are strategically positioned to influence the central extended amygdala via feedback loops. They regulate PKC-δ neuron excitability in the ovBNST and CeA through glutamate release, with their ablation heightening activity in these regions and altering active-phase sleep architecture, risk assessment and defensive behaviors.

The central amygdala (CeA) plays a crucial role in defensive and appetitive behaviours. It contains genetically defined GABAergic neuron subpopulations distributed over three anatomical subregions, capsular (CeC), lateral (CeL), and medial (CeM). The roles that these molecularly- and anatomically-defined CeA neurons play in appetitive behavior remain unclear. Using intersectional genetics in mice, we found that neurons driving food or water consumption are confined to the CeM. Separate CeM subpopulations exist for water only versus water or food consumption. In vivo calcium imaging revealed that CeMHtr2a neurons promoting feeding are responsive towards appetitive cues with little regard for their physical attributes. CeMSst neurons involved in drinking are sensitive to the physical properties of salient stimuli. Both CeM subtypes receive inhibitory input from CeL and send projections to the parabrachial nucleus to promote appetitive behavior. These results suggest that distinct CeM microcircuits evaluate liquid and solid appetitive stimuli to drive the appropriate behavioral responses.
© 2025. The Author(s).

The cortico-basal ganglia loop has traditionally been conceptualized as consisting of three distinct information networks: motor, limbic, and associative. However, this three-loop concept is insufficient to comprehensively explain the diverse functions of the cortico-basal ganglia system, as emerging evidence suggests its involvement in sensory processing, including the auditory systems. In the present study, we demonstrate the auditory cortico-basal ganglia loop by using transgenic mice and viral-assisted labelings. The caudal part of the external globus pallidus (GPe) emerged as a major output nucleus of the auditory cortico-basal ganglia loop with the cortico-striato-pallidal projections as its input pathway and pallido-cortical and pallido-thalamo-cortical projections as its output pathway. GABAergic neurons in the caudal GPe dominantly innervated the nonlemniscal auditory pathway. They also projected to various regions, including the substantia nigra pars lateralis, cuneiform nucleus, and periaqueductal gray. Considering the functions associated with these GPe-projecting regions, auditory cortico-basal ganglia circuits may play a pivotal role in eliciting defensive behaviors against acoustic stimuli.
Copyright © 2024 Tomioka et al.

Maladaptive plasticity is linked to the chronification of diseases such as pain, but the transition from acute to chronic pain is not well understood mechanistically. Neuroplasticity in the central nucleus of the amygdala (CeA) has emerged as a mechanism for sensory and emotional-affective aspects of injury-induced pain, although evidence comes from studies conducted almost exclusively in acute pain conditions and agnostic to cell type specificity. Here, we report time-dependent changes in genetically distinct and projection-specific CeA neurons in neuropathic pain. Hyperexcitability of CRF projection neurons and synaptic plasticity of parabrachial (PB) input at the acute stage shifted to hyperexcitability without synaptic plasticity in non-CRF neurons at the chronic phase. Accordingly, chemogenetic inhibition of the PB→CeA pathway mitigated pain-related behaviors in acute, but not chronic, neuropathic pain. Cell-type-specific temporal changes in neuroplasticity provide neurobiological evidence for the clinical observation that chronic pain is not simply the prolonged persistence of acute pain.
Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.

Activity of central amygdala (CeA) PKCδ expressing neurons has been linked to appetite regulation, anxiety-like behaviors, pain sensitivity, and addiction-related behaviors. Studies of the role that CeA PKCδ+ neurons play in these behaviors have largely been carried out in mice, and genetic tools that would allow selective manipulation of PKCδ+ cells in rats have been lacking. Here, we used a CRISPR/Cas9 strategy to generate a transgenic Prkcd-cre knock-in rat and characterized this model using anatomical, electrophysiological, and behavioral approaches in both sexes. In the CeA, Cre was selectively expressed in PKCδ+ cells. Anterograde projections of PKCδ+ neurons to cortical regions, subcortical regions, several hypothalamic nuclei, the amygdala complex, and midbrain dopaminergic regions were largely consistent with published mouse data. In a behavioral screen, we found no differences between Cre+ rats and Cre- wild-type littermates. Optogenetic stimulation of CeA PKCδ+ neurons in a palatable food intake assay resulted in an increased latency to first feeding and decreased total food intake, once again replicating published mouse findings. Lastly, using a real-time place preference task, we found that stimulation of PKCδ+ neurons promoted aversion, without affecting locomotor activity. Collectively, these findings establish the novel Prkcd-Cre rat line as a valuable tool that complements available mouse lines for investigating the functional role of PKCδ+ neurons.
Copyright © 2024 Toivainen et al.