used optogenetics (controlling neural activity with light) along with chemogenetics (controlling neural activity with chemicals). To interrogate how important the pathway connecting the PBN to the PVT is to emotional processing, Zhu et al. Further viral tracing experiments also showed that the density of PBN axonal fibers was higher in the middle and posterior regions of the PVT, consistent with the notion that the posterior of the PVT is particularly sensitive to aversion ( Gao et al., 2020). Moreover, more connections were observed between the PBN and the medial and posterior (back) regions of the PVT than with the anterior (front) area of the PVT. also demonstrated that these synapses use glutamate as a neurotransmitter, since the synaptic responses can be completely blocked by a glutamate receptor antagonist. The results showed that PBN neurons send direct excitatory synaptic projections to the PVT. expressed an optogenetic tool that allowed them to activate neurons in the PBN using light and record the synaptic response in PVT neurons.

To examine the functional connectivity between the PBN and the PVT, Zhu et al. This suggests that these cells are a newly identified population of PBN neurons. examined several genetic markers for subpopulations of PBN neurons from mice, and found that most of the PBN neurons that project into the PVT do not express these genes. This revealed that the neurons from the PBN that project into the PVT are located laterally (on the sides) in the PBN and can rarely be found medially (in the middle).

used retrograde adeno-associated viruses to characterize the anatomic connections between the PBN and the PVT. Their observations describe important details of the previously uncharacterized brain circuit that connects the PBN and the PVT.įirst, Zhu et al. Now, in eLife, Ling Zhang and Di Mu, along with colleagues from Shanghai Jiao Tong University, Tongji University School of Medicine, Guangzhou Medical University and Southern University of Science and Technology – with Ya-Bing Zhu, Yan Wang and Xiao-Xiao Hua as joint first authors – report that, in mice, projections from the PBN into the PVT regulate aversive states, such as fear and anxiety ( Zhu et al., 2022). However, even through our understanding of the neurocircuitry in the PVT has improved, the region of the brain that relays aversive information to the PVT is not well studied. The PVT is activated by various stressors (such as electric foot shock) and contributes to memories of fear ( Do-Monte et al., 2015 Penzo et al., 2015 Zhu et al., 2016). One of the projection targets of the PBN is the thalamic paraventricular nucleus (PVT), a brain region crucial for regulating emotional processing. A recent study found that subpopulations of neurons in the PBN have different roles, and that their axons – which the neurons use to relay signals – project away from the PBN in distinct patterns ( Chiang et al., 2020). Aversive states are essential for survival, but not much is known about how the brain processes and modulates these negative emotions.Ī region of the brainstem called the parabrachial nucleus (PBN) plays a critical role in encoding danger signals, such as threats ( Campos et al., 2018). When an animal perceives a threat, this triggers an ‘aversive state’ in its brain, making the animal want to run away or hide from the threat.

Part of the brain that controls emotion