The reestablishment of functional neural networks is vital to stroke recovery and readily occurs during the post-stroke critical period: a window of heightened neuroplasticity and training sensitivity. Although evidence suggests that neural repair processes are engaged as a part of the obligate response to stroke, the mechanisms of these processes remain unknown. Here, using widefield and 2-photon calcium imaging of awake, behaving mice, we determined that surviving neurons in the perilesional tissue are inactive after stroke. These neurons adapt to this prolonged inactivity after stroke by modifying excitatory synapses to include more NR2B-containing NMDA receptors. The inactivity-mediated increase in NR2B expression is critical for recovery since NR2B antagonism or chemogenetic activation prevents recovery. We extend this logic byalso demonstrating demonstrate that experimental neuronal inactivation can restore the post-stroke critical period in a NR2B-dependent manner. Together, our results identify a novel potential stroke therapy and provide a conceptual framework for post-stroke plasticity and functional recovery.

Drug addiction is a major global health problem, persisting due to a lack of effective treatments. This is largely due to insufficient understanding of the pathophysiology and neural circuitry underlying the progression of a healthy individual into drug addiction. Rodent models of cocaine addiction implicate the activity of medium spiny neurons (MSNs) in the nucleus accumbens (NAc) in the progression to addiction. MSNs of the NAc can be classified as dopamine receptor D1 or D2 expressing neurons, and cocaine exposure has previously been shown to induce many changes in these two cells types, including differential modifications of dendritic spine densities. While the neural substrates driving these changes remains unknown, these changes are likely due to synaptic changes driven by the neural adaptation in the regions upstream of the NAc in response to cocaine administration. Therefore, we seek to determine whether major excitatory projections to the NAc MSNs exhibit changes during the progression to addiction. In particular, previous work has shown the basolateral amygdala (BLA), prefrontal cortex (PFC), and the ventral hippocampus (VH) projections to the NAc as facilitating behavioral aspects of addiction. We utilized a method of monosynaptic retrograde tracing using an EnvA pseudotyped rabies virus that would allow us to label neurons in these areas that directly project to MSNs. The effect of cocaine on spine density was measured in multiple stages: initial use (5 days of cocaine exposure), withdrawal (5 days of cocaine followed by 2 week withdrawal period without cocaine), and relapse (5 days of cocaine followed by a single cocaine reinstatement shot at the end of 2 week withdrawal). Here, we characterize the distinct effects of cocaine exposure on dendritic modifications in a projection-, cell type-, and stage-specific manner. Our findings suggest cocaine differentially alters spine densities on neurons in brain areas that send excitatory projections to NAc MSNs. These neuroanatomical results establish a framework to further understand the circuit-basis of progression to drug addiction.

The external segment of the globus pallidus (GPe), a subcortical nucleus centrally located in the indirect pathway of the basal ganglia, plays a pivotal role in processing and broadcasting information received from the striatum and the subthalamic nucleus through its widespread projections across major basal ganglia nuclei. One of the largest neuronal populations of the GPe expresses the Ca2+-binding protein parvalbumin (PV) and projects to multiple nuclei of the basal ganglia and the thalamus and has been shown to be involved in movement disability in Parkinson’s disease (PD). However, most studies to date considered GPe PV neurons as a homogeneous population. We found that the GPe PV neurons can be further subdivided into two non-overlapping populations based on their projections to either the substantia nigra pars reticulata (SNr) or the parafascicular thalamus (PF) and their intrinsic electrophysiological properties. We further investigated the circuit-specific roles of these subpopulations in locomotion and reversal learning as well as their contributions to the impairments of motor and cognitive flexibility in a PD mouse model. Our findings establish the behavioral significance of two distinct GPe PV neuronal populations embedded in discrete neural pathways and their differential contributions to specific subdomains of Parkinsonian-like behaviors.

Cocaine addiction is one of the leading causes of drug-related deaths and overdose in the United States, and there are currently no cheap and effective treatments for this disease. To combat this problem, it is necessary to study the underlying neuronal circuits and populations that underlie cocaine seeking behavior. Previous studies have demonstrated that the prefrontal cortex (PFC) becomes hypoexcitable following chronic compulsive drug seeking (Chen et. al. 2013), so we decided to see how the inputs and outputs of the prefrontal cortex are modulated following chronic cocaine seeking. To answer both of these questions, we first designed a novel head-fixed cocaine self-administration behavioral setup. This thesis utilizes this model to answer two main questions: 1) how are the inputs to the prefrontal cortex modulated following cocaine addiction? 2) How are the downstream targets of the prefrontal cortex, the neocortex, modulated following cocaine seeking behavior?

Social anxiety disorder (SAD), also known as social phobia, is a major physical and mental health concern with a high lifetime prevalence. Despite being the most common anxiety disorder, current treatment options available are unsatisfactory among SAD patients. Therefore, we adapted a social fear conditioning (SFC) paradigm to mimic the main behavioral symptoms of SAD of humans in mice. In this protocol, social fear is induced by administering foot shocks during social interaction with an unknown conspecific. This form of conditioning did not induce any other behavioral alterations such as general anxiety. The negative social experience inducing social fear in this animal model and SAD patients satisfies construct validity, whereas the similarity in behavioral phenotypes satisfies face validity. After establishing that our model of social fear has face and construct validity, we aim to assess 1) whether this model has predictive validity, and 2) test the therapeutic efficacies of three novel therapeutic strategies: cognitive behavioral therapy, pharmacological selective-serotonin reuptake inhibitor, and targeted brain stimulation.

Thyrotropin-releasing hormone-degrading ectoenzyme (TRH-DE) specifically hydrolyzes released thyrotropin-releasing hormone (TRH), limiting TRH action. Past studies suggest released TRH exerts an anxiolytic- and antidepressant-like effect, Additionally, increased TRH promotes negative energy balance. TRH-DE has been shown to be highly expressed in brain regions that subserve emotional behavior. Furthermore, a past study in our lab found central trhde overexpression was associated with vulnerability to obesity. The following studies in this thesis tested the hypothesis that reducing TRH-DE function by targeted gene knockout in mice would show an antidepressant- or anxiolytic-like effect, and would be leaner and less fatty. Adult male and female mice of wild type (WT), heterozygous and trhde knock-out (KO) genotypes were analyzed for whole-body energy expenditure, food intake and body composition after chow or high fat-diet challenge. To assess anxiety-like and antidepressant-like phenotypes, adult male and female mice were tested in the elevated plus maze, light-dark box, and forced swim behavioral tests. Adult female and male mice of WT and KO genotypes were then compared for operant self-administration of food+water and a highly reinforcing sucrose(3%)-saccharin(0.125%) solution.

Energy expenditure (EE) analysis at 2 months old revealed KO mice have an altered circadian profile compared to WT, where KO have higher EE, with the greatest difference in the later half of the dark cycle. Body composition analysis after six weeks of high fat diet challenge revealed a significant Genotype (p<0.05) and Sex (p<0.05) effect where KO and HET gained less body fat than WT mice, with no difference in weight gained throughout the 6 weeks. Furthermore, the KO have a reduced high fat intake across all weeks compared to HET (p=0.038) and WT (p=0.006). Body composition analysis of adult mice weaned on chow showed that WT were heavier, fatter and had more lean mass than KO littermates (p<0.0001). This Genotype effect in body weight was more pronounced in older males than females.

The time spent in the open arm and light box for EPM and LD, respectively, did not differ by genotype, suggesting similar anxiety-like behavior. A main effect of Genotype was observed for forced swim immobility, however, whereby KO (p=0.01) and HET (p=0.02) mice were significantly less immobile than WT littermates. A main effect of Sex for climbing reflected that males climbed more than females (p<0.005).

With respect to operant self-administration behavior, Sex x Genotype interactions reflected that male, but not female, TRH-DE KO mice self-administered more food and water than WT controls following acquisition. Although there were no differences in later self-administration sessions with super-sac, males had exaggerated response after deprivation, but females had absent response. In conclusion, knocking out TRH-DE function had an anti-depressant-like effect on the FST, but did not show an anxiolytic-like effect, nor impair learning or memory in self-administration testing. Furthermore, even a partial trhde knockout resulted in less fat gain compared to WT on a high fat diet, even though there was no significant difference in amount of weight gained.

In modern society, an increased availability of palatable food has promoted obesity, leading some to diet and restrict oneself from certain “desired” foods. This restriction leads to under-acceptance of alternative diets, followed by an overconsumption of palatable food when one can no longer withstand dieting. Here, we modeled this behavior of “fasting” and “binging” in mice, based off our previous free-feeding rat model. In this mouse model, female mice were assigned one of three diet groups (ad libitum chow diet, ad libitum palatable, sucrose-rich, chocolate-flavored diet, and intermittent access to chocolate diet). To assess binge eating behavior, the mice in these three diet groups were compared on operant-self administration (fixed/progressive ratio), and daily energy consumption. Operant self-administration results revealed that intermittent mice were significantly more motivated and compulsive than ad libitum mice, and demonstrated significant rejection of non-palatable chow diet, showing that intermittent access to a palatable diet promotes compulsive eating behavior, allowing for the establishment of a mouse binge eating model. Binge eating has been shown by various studies to cause neurological changes in the brain, similar those caused by drug addiction. The following studies on the mouse model tested the hypothesis that compulsive eating may alter various neurological mechanisms in a similar manner as drugs of addiction. BBP-02, a sigma-1 receptor antagonist, was treated in mice but showed no effect on self-administration, suggesting that sigma-1 by itself may not play a role in the modulation of compulsive eating. Another drug, 14-methyoxymetoponin, a mu-opioid receptor agonist, resulted in a significant decrease in self administration with intermittent mice at the two highest doses, suggesting that the opioid system may be altered in mice with compulsive eating behavior.

Motivation directs and guides an organisms interaction with their environment and is profoundly influenced by internal brain states in conjunction with external environmental stimuli. Motivated behaviors can range from survival-based actions such as foraging for food or avoiding potentially deadly conflict to pursuit of pleasure or sex. Proper maintenance of every day motivation is essential for guiding behavior to preserve homeostatic balance and stable functioning.

However, states of pathological motivation result when proper motivational control is lost. Instances of hyper-motivation misdirected towards harmful or negative stimuli can manifest as addiction, and conversely loss of motivation and extreme apathy is a hallmark of major depressive disorder (MDD). How then, does the brain regulate motivation and what kind of adaptations lead to conditions such as addiction and depression?

Components of the reward circuitry in the brain such as the nucleus accumbens (NAc) has been heavily studied in the context of addiction and MDD. As a central node in the reward circuitry, the NAc receives dopaminergic input from the ventral tegmental area (VTA) in the midbrain and sends its primary output to the ventral pallidum (VP) and back to the VTA. While structural and electrophysiological changes in neurons within the NAc have been well described in addiction and MDD, much less is known how the NAc interacts with the reward circuitry as a whole. In particular, how do the various interconnections within the reward circuit relate to the complex behaviors characteristic of neuropsychiatric conditions such as MDD and addiction? This dissertation aims to shed light on how discrete aspects of circuits involving the NAc and VP contribute to discrete behavioral aspects of addiction and MDD. Chapter I illustrates that discrete components of the ventral pallidal circuit mediates separate depressive-like behaviors in a mouse model of depression. In chapter II, we outline discrete structural changes in separate input structures of the NAc at different stages of addiction. In all, this dissertation hopes to illuminate the circuit-specific changes governing neuropsychiatric disorders that may provide a platform for more specific treatments.

Binge eating is characterized by eating a large amount of food within a short period of time with the feeling of loss of control. We applied the principles of behavioral economics, which separate consumption into unconstrained demand (Q0) and elasticity of demand (α) to study binge eating. We found that rats with intermittent access to palatable diet (INT) had increased Q0 and decreased α comparing to rats with ad-libitum chow (CHOW) or palatable diet (CHOC), which correlated with greater palatable food intake and consumption during self- administration. Within INT group, Q0 positively correlated with fixed ratio self-administration responses. Initial chow intake, initial body weight, and first-day palatable diet intake predicted higher α. Results show behavioral economic measures have predictive values in assessing compulsive eating.

Drug dependence has been implicated with the change in glucocorticoid receptor (GR) levels in the central amygdala (CeA), where its elevation relates to negative affect upon abstinence, increasing likelihood of relapse through negative reinforcement. Here we accessed change in GR mRNA expression in rats after intermittent access to palatable diet. Results showed that female, but not male, INT rats had higher expression comparing controls; female INT rats had higher expression than male counterparts; and female INT rats with substantially high progressive-ratio response showed significantly higher expression comparing to controls, while other female INT rats did not. Results show sex and individual-level differences in the development of compulsive eating, suggesting differences in neuroadaptation in response to intermittent access diet schedule.

Alzheimer’s disease (AD) is a neurodegenerative disease that causes a reduction in brain-derived neurotrophic factor (BDNF) in multiple animal models, and delivery of BDNF provides neuroprotective effects in those disease models. BDNF regulates a wide range of biological functions in the human body, and therapeutic delivery requires effective delivery routes and targeting specificity.

Adeno-associated viral (AAV) vector systems have recently become popularized for targeted gene delivery. AAVs are non-pathogenic in humans, provide long-term gene expression,

and do not integrate into the host genome. Despite the advancements in viral gene therapy over the past decades, AAV vector systems are limited by the lack of regulation.

Here, we developed a novel regulatable dual AAV vector system for therapeutic delivery of BDNF that can be turned off by oral administration of tamoxifen to adult mice. Our dual AAV vector system contains two co-dependent AAV vectors. One vector carries a pancellular promoter and the BDNF transgene. The second vector carries a drug-inducible Cre recombinase enzyme (Cre) that we hypothesize will result in degradation of the AAV genome and elimination of gene expression.

We found that our dual vector system provides a modest reduction in AAV gene expression following administration of tamoxifen. Further optimization of the system could lead to the first regulatable AAV system suitable for clinical applications. This regulation could act as an “off” switch for eliminating gene expression in the event of adverse side-effects. Moreover, this regulation could allow for transient gene delivery for treating medical conditions such as traumatic brain injury and spinal cord injury. The ability to tightly regulate AAV gene expression is potentially applicable to all 105 on-going clinical trials involving AAV gene therapy.