Background & Aims
Hyperalgesia is a hallmark feature of the sickness state during a systemic infection yet the central neural circuits orchestrating this phenomenon remain unclear. My preliminary studies identified several key brain regions containing neurons activated by both systemic inflammation and noxious stimuli, suggesting a node of intersection between sickness and pain circuitry. One region located adjacent to the preoptic area of the hypothalamus has previously been linked to the emotional regulation of pain: the ventral bed nucleus stria terminalis (vBNST). I aim to [1] investigate the role of vBNS-TLPS neurons in sickness-induced hyperalgesia and motivated pain behaviors, and [2] determine whether vBNST-LPS neurons are activated by local immune molecules during sickness. My research will shed new light on the pain modulation strategies and could ultimately improve outcomes for patients suffering from hyperalgesia due to acute or chronic inflammatory conditions.
Methods
Our lab induces sickness by administering pro-inflammatory lipopolysaccharide (LPS). We used a transgenic mouse line (Fos2A-iCreER) to genetically label LPS-activated neurons during sickness. Two weeks later, mice were subjected to a pain assay consisting of a noxious pinprick stimulus applied every 30 seconds for 10 minutes followed by immunohistochemical staining to asses Fos protein expression induced by the noxious stimulus. Co-localized cells of separate Fos-dependent labeling of sickness-activated neurons and pain-activated neurons in the same tissue sections were counted using a semi-automated approach (QuPath). Pain sensitivity to mechanical pain was measured by injecting mice (IP) with LPS, waiting 2 hours to take effect, followed by using a series of von Frey filaments (0.2g to 2.0g) and a sharp 25G syringe needle (noxious stimuli). Paw withdrawal height and velocity are averaged for each stimulus strength level during the session. Studies were conducted in males and females.
Results
My results showed that some neuronal populations activated by LPS also responded to painful stimuli, suggesting a key intersection where sickness and pain pathways meet in the brain. These areas could serve as entry points for understanding how sickness increases pain sensitivity. Interestingly, my quantification analysis revealed very little overlap of LPS-sensitive TRAP’d cells and Fos protein expression (noxious stimulus) within regions involved in pain processing, suggesting that sickness-induced hyperalgesia is likely controlled in brain areas outside of canonical pain pathways. Instead, my analysis revealed several brain regions with a significant degree of overlap between cells activated by LPS and pain, including a region in the preoptic area of the hypothalamus, an area previously linked to sickness-induced hyperalgesia. Interestingly, Crh+ neurons in the vBNST have been found to encode painful stimuli. However, I found that LPS-sensitive neurons in the vBNST are largely Crh negative, suggesting a previously undescribed function for these neurons. Additionally, reflexive pain behavior results indicate that LPS-injected mice require less applied force for paw withdrawal and are more sensitive to lighter mechanical stimuli than saline-injected controls.
Conclusions
I have identified several brain regions, including the ventral bed nucleus of the stria terminalis (vBNST), which are activated by both systemic inflammation and noxious stimuli, suggesting a critical intersection between sickness and pain pathways. Additionally, I found that LPS-injected mice are more sensitive to lighter mechanical stimuli, confirming previous findings that LPS induces hyperalgesia in mice. My ongoing studies involve the use of chemogenetic tools to manipulate vBNST-LPS neurons and assess their role in pain sensitivity and related behaviors. By selectively activating or inhibiting these neurons, I aim to determine how their activity influences reflexive pain responses and motivated pain behaviors. These experiments are expected to further elucidate the specific functions of vBNST-LPS neurons in mediating sickness-induced hyperalgesia and contribute to a deeper understanding of the neural circuits involved in the intersection of immune signaling and pain perception.
References
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Presenting Author
Jacklyn Nguyen
Poster Authors
Jacklyn Nguyen
BS Biological Sciences
University of Utah
Lead Author
Topics
- Gender/Sex Differences