Environmental stress and threat influence feeding behavior in animals, but how that interaction occurs is still largely unclear. Neurons in the bed nucleus of the stria terminalis (BNST), part of the extended amygdala, have dense projections to the parabrachial nucleus (PBN) in the brainstem. We have uncovered projections in these neural circuits that link the modulation of feeding and threat assessment in mice. This project aims to investigate and characterize these previously unrecognized neural circuits with the incorporation of a variety of optogenetic, surgical, and histological techniques. We used Cre-dependent anterograde and retrograde viral tracers in order to trace the anatomy of these neural circuits, and found functional projections from inhibitory (GABA) and excitatory (glutamate) populations in the BNST to neurons in the PBN. We also used translating ribosome affinity purification (TRAP) to isolate the mRNA of these projections. This proved useful in separating and identifying the molecular expression profile of different GABAergic and glutamatergic subpopulations. Furthermore, we used a variety of behavioral assays to determine the BNST-PBN circuits’ role in feeding and threat-response behavior. We used fiber photometry to track the activity of GABAergic (vGAT) and glutamatergic (vGLUT2) populations during these behaviors, and found that vGAT and vGLUT2 populations have differing roles in threat and feeding behaviors. vGAT neurons increase their activity during feeding and decrease in response to threat, while vGLUT2 neurons decrease their activity during feeding and increase in response to threat. We also used optogenetic activation of these neurons to determine their causal role in behavior. With activation, vGAT populations drive place preference, operant positive reinforcement, and increased feeding. Conversely, vGLUT2 populations drive place aversion, operant negative reinforcement, and reduced feeding. These findings characterize the distinct nature of BNST-PBN neural circuits and the mechanism behind the evaluation of threatful stimuli and the integration of feeding.

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide and has been established as a risk factor for neurodegenerative diseases such as Alzheimer’s disease (AD). The progression of AD is characterized by intracellular aggregates of phosphorylated tau protein, which is mainly found in neurons and plays an important role in the stabilization of microtubules. One of the mechanisms that may contribute to tau aggregation is decreased tau clearance by the glymphatic system, a pathway that clears solutes from the brain. This fluid movement is facilitated by the astrocytic water channel aquaporin-4 (AQP4) which is primarily localized to the astrocytic endfeet that line perivascular channels surrounding the brain vasculature. Prior studies demonstrate that solute clearance along these pathways is slowed following TBI, and that there is a loss of perivascular localization of AQP4. Based on these findings we hypothesized the loss of perivascular localization of AQP4 may impair interstitial tau clearance and promote neurodegeneration. We first tested this hypothesis by examining whether loss of perivascular AQP4 following TBI promotes tau pathology in a transgenic PS19 mouse that spontaneously develops tau pathology. We then evaluated whether deletion of perivascular AQP4 in an alpha-syntrophin knock-out mouse promotes tau pathology both in the presence and absence of TBI, and when crossed with a PS19 tauopathy mouse. Alpha-syntrophin is a protein that anchors AQP4 and is important in perivascular localization; therefore, deletion of alpha-syntrophin results in loss of localization of AQP4 and impairment of clearance. We assessed levels of pathological tau using histology on the transgenic mice and crosses both with and without TBI. If validated, our findings may suggest that loss of perivascular AQP4 may increase the brain’s vulnerability to tau aggregation and neurodegeneration following TBI and provide the basis for potential treatment to prevent the development of post-traumatic neurodegeneration.

Amyloid β (Aβ) plaques are a hallmark of Alzheimer’s disease (AD), the most common form of dementia that afflicts over 5 million Americans. Soluble proteins, including Aβ, are cleared from the brain by the glymphatic system, a brain wide network of perivascular spaces that facilitates the intermixing of cerebrospinal fluid and interstitial fluid. Prior studies report that aquaporin-4 (AQP4), a water channel polarized to perivascular astrocyte endfeet, supports glymphatic clearance of soluble proteins from the brain. In the aging brain, glymphatic clearance becomes impaired and AQP4 becomes depolarized from astrocytic endfeet. Such loss of perivascular AQP4 localization is correlated with AD status and Aβ plaque burden in the human brain. In the present study, we test whether such AQP4 depolarization promotes Aβ plaque formation. AQP4 is anchored to astrocytic endfeet via the dystrophin protein complex that includes the adaptor protein α-syntrophin (α-Syn). We crossed the α-Syn knockout mouse, which lacks perivascular AQP4 localization, with the 5XFAD mouse line which spontaneously develops Aβ plaques. Our preliminary analysis suggests that loss of perivascular AQP4 localization with α-Syn knockout increases Aβ burden relative to controls. These findings demonstrate that loss of perivascular AQP4 localization, such as occurs in the human brain in the setting of AD, contributes to the development of Aβ pathology. In the future, it may be possible that targeting the localization of AQP4 may be the basis for new therapeutics that can slow or even reverse AD pathology.

 Mu-opioid receptors (MOR) are expressed on populations of neurons within the brain. Exogenous activation of these receptors by drugs of abuse, such as heroin and fentanyl, causes feelings of euphoria and can be highly addictive. During natural behavior, MORs in the brain are activated by the endogenous ligand enkephalin. Spiny projection neurons (SPN) in the nucleus accumbens (NAc) are known to express enkephalin and likely release it during neural activity. It is known that these enkephalin SPNs can be either excited or inhibited while animals consume natural rewards. However, it remains unclear whether these functionally distinct enkephalin SPN populations are anatomically intermixed or are anatomically separated within NAc. In this study, we used 2-photon calcium imaging through endoscopic lenses to examine the neural activity of enkephalin SPNs in NAc while mice consumed sucrose rewards. We characterized the reward-excitations or reward-inhibitions of individual enkephalin SPNs over multiple imaging sessions. Through precise post-mortem histological examination, we then verified the anatomical placements of our endoscopic lenses and associated the relative anatomical location of neuronal populations to their reward-related neural activity. We found that enkephalin SPNs in anterior NAc were consistently reward-inhibited while enkephalin SPNs in posterior NAc were reward-excited. This is the first demonstration of anterior-posterior axis differences in the reward-related modulation of enkephalin SPNs and is a key step to understanding how opioidergic neurons function in natural reward behavior.

Alzheimer’s Disease (AD) is a neurodegenerative disease, characterized by amyloid-ß plaque deposition in the brain, that affects more than 5 million Americans. The glymphatic system is a network of perivascular spaces that facilitates fluid movement and solute clearance from the brain, and its dysfunction in aging has been implicated in the development of AD. The water channel aquaporin-4 (AQP4), located in astrocytic endfeet bordering the perivascular spaces, supports glymphatic function. In the aging rodent and human AD brain, loss of perivascular AQP4 localization is associated with impaired glymphatic function and increased amyloid-ß deposition. Yet the molecular basis for this loss of perivascular AQP4 localization is unknown. Aquaporin-4ex (AQP4ex) is a novel translational readthrough variant of AQP4. Selective deletion of AQP4ex results in the mislocalization of AQP4 all over the astrocytic membrane, indicating that AQP4ex is a crucial element in the perivascular localization of AQP4. In this study, we quantitatively analyze the expression and localization of AQP4ex to determine whether changes in AQP4ex associate with aging, AD status, or AD pathology. Using immunofluorescent double-labeling, confocal microscopy, and custom digital image analysis techniques, we define AQP4ex expression and localization between young and aged mice, and compare these changes between wild-type animals and transgenic animals that spontaneously form amyloid-ß plaques. Using a case series of post mortem human frontal cortical tissue, we compare AQP4ex expression between healthy young adults, cognitively intact aged subjects, and aged subjects with an AD diagnosis. This is the first characterization of AQP4ex expression in the murine brain and in a human case series, and these data will contribute to the small but growing body of research on AQP4ex and its relationship with AQP4 localization, creating opportunities to identify a new novel mechanism and novel target in AD pathology.

Mild traumatic brain injury (mTBI), otherwise known as concussion, is the most prevalent form of brain injury and is a risk factor for the development of Alzheimer’s disease (AD). AD is characterized by deposition of proteins, such as amyloid β and tau, that accumulate in the brain due to impaired protein clearance. However, mechanisms driving clearance reduction are poorly understood. The glymphatic system, a brain-wide clearance system that facilitates the movement and exchange of cerebrospinal fluid and interstitial fluid throughout the brain, has been implicated in both amyloid β and tau clearance. Prior studies in animal models of mTBI suggest that glymphatic function is impaired after mTBI. The negative impacts of mTBI are well documented, but the pathological differences between various forms of mTBI, such as impact vs blast injuries, are not well understood. Similarly, difference in the effect of glymphatic function between these two mTBI types has never been explored. Here, we hypothesize that glymphatic function is differentially impaired as a result of blast or impact mTBI. We measured glymphatic function in repetitive impact and repetitive blast mTBI murine models by injecting fluorescent tracers into a CSF-filled space surrounding the brain, measuring the fluorescent intensity within the tissue as a measure of cerebrospinal fluid influx. Using these data, we define the differences in CSF tracer dynamics in the impact and blast injured mouse brain. By increasing our understanding of how different types of injuries impact CSF dynamics, we can better understand the possible mechanisms that render the post-traumatic brain vulnerable to neurodegeneration and target treatments for different mTBI patients accordingly.

Δ⁹-tetrahydrocannabinol (THC) is the primary psychoactive compound found in Cannabis sativa. The psychoactive and cannabimimetic behaviors associated with THC have been well described as being dependent on the partial agonist activity of THC at the endogenous cannabinoid 1 receptor (CB₁R). We are investigating the direct action of THC on the medial prefrontal cortex (mPFC, a brain region primarily responsible for executive function), and the effects of adolescent THC exposure on µ-opioid receptor (MOR) expression in adult periaqueductal grey (PAG, a brain region involved in opioid-mediated pain inhibition). To increase our understanding of the cannabimimetic behavioral effects of THC, and its direct pharmacological action in the brain, it is important to map the neuro-anatomical expression of target proteins. We examined expression patterns of CB₁R and MOR in the mPFC and the PAG, respectively. To do this, we utilized a form of in situ hybridization, RNAscope. We leveraged RNAscope by preparing tissue samples from brain regions of interest for treatment with mRNA-specific probes, allowing us to target CB₁R and MOR mRNA. After a series of washes and incubations, these fluorescent probes hybridize to our target mRNAs and allow us to visualize their expression under a confocal microscope. Analysis of mRNA expression informs us on the localization of the CB1R/MOR and known neuron types within our brain regions of interest. After imaging, we are able to utilize HALO software to analyze the levels of expression and co-localization of CB₁R/MORs with neuronal markers for glutamatergic and GABAergic neuron types. By creating and optimizing a workflow for extraction, preparation, hybridization, and analysis, we determined CB₁R mRNA is primarily co-localized with glutamatergic neurons in the mPFC. Moving forward, we are utilizing this RNAscope technique to investigate differential CB₁R expression GABA interneuron subpopulations in the mPFC. (Funded by DA051558)