Schizophrenia is a troubling and severe mental illness that is only incompletely treated by currently available drugs. New drug development is hindered by a scarcity of functionally relevant pharmacodynamic biomarkers that are translatable across preclinical and human subjects. Although psychosis is a major feature of schizophrenia, cognitive and negative symptoms determine the long-term functional outcomes for patients. Stimulus-evoked neural synchrony at gamma (~ 40 Hz) frequency plays an important role in the processing and integration of sensory information. Not surprisingly, schizophrenia patients show deficits in gamma oscillations. NMDA receptor (NMDAR) activation on fast-spiking parvalbumin-positive interneurons is deemed important for the generation of gamma oscillations. NMDA hypofunction has been proposed as an alternative hypothesis to the well-known dopamine dysregulation to explain the neurochemical abnormalities associated with schizophrenia. For this dissertation, we validated a preclinical model to pharmacologically probe NMDA-mediated gamma oscillations by further characterizing the auditory-steady state response (ASSR) in female Sprague Dawley rats. The ASSR is a measure of cortical neural synchrony evoked in response to periodic auditory stimuli. ASSR at 40 Hz is consistently disrupted in patients. First, we established the reliability of click train-evoked 40 Hz ASSR and tone-evoked gamma oscillations in 6 separate sessions, spread over a 3-week period. Then we established the sensitivity of these neural synchrony measures to acute NMDAR blockade using the high affinity NMDA channel blocker MK-801, using a repeated measures design. Next, we compared the reliability and sensitivity of the 40 Hz ASSR from two distinct recording sites. Results from this study showed that as compared to vertex, temporal recording showed a greater gamma synchrony. However, the temporal recording had poor test-retest reliability and lower sensitivity to MK-801-induced disruption. Lastly, we characterized the dose-response profiles of an NMDA co-agonist D-serine, an atypical (clozapine) and a typical (haloperidol) antipsychotic, on the 40 Hz ASSR. Results from these studies showed that only clozapine was effective in robustly augmenting 40 Hz ASSR. Furthermore, only clozapine pretreatment had partial protective effect against MK-801 induced ASSR disruption. Overall, this work establishes that vertex recorded 40 Hz ASSR is a reliable neural synchrony biomarker in female SD rats that is amenable for bidirectional pharmacodynamic modulation.

The ability of animals to sense, interpret, and respond appropriately to social stimuli in their environment is essential for identifying and distinguishing between members of their own species. In mammals, social interactions both within and across species play a key role in determining if an animal will live to pass on its genes to the next generation or else be removed from the gene pool. The result of this selection pressure can be observed in specialized neural circuits that respond to social stimuli and orchestrate appropriate behavioral responses. This highly conserved network of brain structures is often referred to as the Social Behavior Network (SBN). The medial amygdala (MeA) is a central node in the SBN and has been shown to be involved in transforming information from olfactory sensory systems into social and defensive behavioral responses. Previous research has shown that individual neurons in the MeA of anesthetized mice respond selectively to different chemosensory social cues, a characteristic not observed in its upstream relay, the accessory olfactory bulb (AOB). However, the cause of this stimulus selectivity in the MeA is not yet understood. Here, I hypothesize that a subpopulation of neurons in the MeA that express the enzyme aromatase are involved in the sensory representation of social stimuli in awake, behaving animals. To test this hypothesis, I designed and built a novel behavioral apparatus that allows for discrete presentations of social stimuli in a highly controllable and reproducible environment. I then injected the adeno-associated virus (AAV) AAV-Syn-Flex-GCAMP6s into the MeA of Aromatase:Cre transgenic mice and implanted a fiber optic cannula slightly above the injection site. The combination of this transgenic mouse line and conditional AAV caused GCaMP6s expression to be exclusive to aromatase-expressing neurons. By coupling my novel behavioral apparatus to a fiber photometry system, I successfully recorded the moment-to-moment activity of aromatase neurons in the MeA of awake, behaving animals as they investigated various social stimuli. Aromatase neurons in the MeA of adult male mice respond strongly to conspecific social stimuli, including live adult mice, mouse pups, and mouse urine samples. Sniffing and investigative behaviors correlated strongly with increased GCaMP6s signal in aromatase neurons, reflecting increases in their neural activity. Interestingly, after repeated investigations of the same stimuli the activity of aromatase neurons gradually diminished. Presenting a novel stimulus following repeated investigations of a familiar stimulus reinstated some, but not all of the initial GCaMP6s signal. This points to the potential role that aromatase neurons may play in the habituation to social stimuli that are consistently present in their environment. Investigations of predator stimuli did not evoke significant responses from aromatase neurons, nor did investigations of non-social stimuli. These results demonstrate that aromatase expressing neurons in the MeA of awake, behaving animals encode the sensory representation of conspecific social stimuli, and their responses are highly selective to the type of stimulus presented.

<p>Temporal order judgment (TOJ) refers to one’s ability to successively report the temporal order of two tactile stimuli delivered to independent skin sites. The brain regions involved in processing TOJ remain unclear. Research has shown that TOJ performance can be impaired with a conditioning background stimuli and this phenomenon, known as TOJ synchronization (TOJ-S), is suggested to be mediated by inhibitory neural mechanisms within the primary somatosensory cortex (SI) that create perceptual binding across the two skin sites. Continuous theta-burst stimulation (cTBS) over SI impairs tactile spatial and temporal acuity. This dissertation examines the effects of cTBS on TOJ and TOJ-S performance on the hand. In Experiment 1, TOJ and TOJ-S were measured from the right hand before and for up to 34 minutes following 50 Hz cTBS over SI. In Experiment 2, same measurements were obtained bilaterally for up to 42 minutes following 30 Hz cTBS over SI. Compared to pre-cTBS values, TOJ was impaired for up to 42 minutes on the right hand following 30 Hz cTBS. TOJ-S performance was improved for up to 18 minutes on the right hand following 50 Hz cTBS. These experiments reveal two major findings. First, cTBS act upon different inhibitory circuits that are suggested to mediate TOJ and TOJ-S. Second, cTBS parameters may dictate cTBS effects over SI excitability. The findings of this work not only emphasize the significant contributions of SI on tactile temporal perception, it provides novel insight of the underlying neural mechanisms of cTBS effects on SI cortical excitability.</p> / Master of Science in Kinesiology

Parkinson’s disease and Essential tremor are the two most prevalent movement disorders in the world, but due to overlapping clinical symptoms, accurate differential diagnosis is difficult. As a result, approximately 60% of patients with movement disorders symptoms will have their diagnosis changed at least once before death. By their subjective nature, clinical exams are inherently imprecise, leading to the desire to create an objective, quantifiable test for movement disorders; a test that currently is elusive. Eye movements have been studied for a century, and are widely appreciated to be quantifiably affected in those with neurological disease. Through a collaborative effort between the VA hospital and VCU, over 1,000 movement disorder subjects had their eye movements recorded, utilizing an SR Research Eyelink 2. Patients with Parkinson’s disease exhibited an ocular gaze tremor during fixation, normal reflexive saccades, and reduced blink rate. Subjects with Essential tremor exhibited slowed saccadic dynamics, with increased latencies, in addition to a larger number of square wave jerk interruptions of otherwise stable fixation. After diagnostic features of each disorder were identified, prospective data collection could occur in a blinded fashion, and oculomotor features used to predict clinical diagnoses. It was determined that measures of fixation stability were capable of almost perfectly differentiating subjects with PD, and a novel, combined parameter was capable of similar results in ET. As a group, it appears as if these symptoms do not progress as the disease does, but subanalyses show that individual patients on constant pharmaceutical doses tracked over time do slightly change and progress. The near perfect separation of disease states suggest the ability of oculomotor recording to be a powerful biomarker to be used for the differential diagnosis of movement disorders. This tool could potentially impact and improve the lives of millions of people the world over.

Alcohol Dependence (AD) is a chronic substance use disorder with moderate heritability (60%). Linkage and genome-wide association studies (GWAS) have implicated a number of loci; however, the molecular mechanisms underlying AD are unclear. Advances in systems biology allow genome-wide expression data to be integrated with genetic data to detect expression quantitative trait loci (eQTL), polymorphisms that regulate gene expression levels, influence phenotypes and are significantly enriched among validated genetic signals for many commonly studied traits including AD. We integrated genome-wide mRNA and miRNA expression data with genotypic data from the nucleus accumbens (NAc), a major addiction-related brain region, of 36 subjects (18 AD cases, 18 matched controls). We applied weighted gene co-expression network analysis (WGCNA) to identify mRNA and miRNA gene co-expression modules significantly associated with AD. We identified six mRNA modules, two of which were downregulated in AD and were enriched for neuronal marker gene expression. The remaining four modules were upregulated in AD and enriched for astrocyte and microglial marker gene expressions. After performing gene set enrichment analysis (GSEA), we found that neuronal-specific modules enriched for oxidative phosphorylation, mitochondrial dysfunction and MAPK signaling pathways and glial-specific modules enriched for immune related processes, cell adhesion molecules and cell signaling pathways. WGCNA was also applied to miRNA data and identified two downregulated and one upregulated modules in AD. We intersected computationally predicted miRNA:mRNA interactions with miRNA and mRNA expression correlations to identify 481 significant (FDR<0.10) miRNA:mRNA targeting pairs. Over half (54%) of the mRNAs were targeted cooperatively by more than one miRNA suggesting a potentially important cellular mechanism relevant to AD. After integrating our expression and genetic data we identified 591 significant mRNA and 68 significant miRNA cis-eQTLs (<1 megabase) (FDR<0.10). After querying against GWAS data from the Colaborative Study on Genetics of Alcohol and Study of Addiction: Gentics and Environment, eQTLs for neuronatin (NNAT; rs1780705), proteosome subunit type 5 (PSMB5; rs10137082), long non-coding RNA (PKI55; rs13392737), adaptor related protein complex 1 sigma one subunit (AP1S1; rs12079545) and translocation associate membrane protein 1 (TRAM1; rs13277972) were associated with AD or alcohol related phenotypes at p<10-4.

The model of basal ganglia function proposed by Albin, Young and Penney (1989) describes two anatomically independent motor pathways, the direct and indirect. However, under normal conditions striatal dopamine (DA) is required for the expression of motor behavior, and DAergic control of the two pathways (via D1 and D2 receptors, respectively) is dependent on co-activation. We tested for a possible breakdown of D1/D2 synergism using transgenic R6/1 mice bearing the human huntingtin allele (Htt). Motor stereotypy, observed prior to the onset of HD-related symptoms, was rated on a 5-point scale following activation of: A) D1 receptors alone, B) D2 receptors alone, and C) stimulation of both D1 and D2 receptors. Results revealed that mice with the HD allele, like their WT litter mates, depend on the co-activation of the indirect and direct motor pathways to facilitate deliberate behavior.

Implicit association of racial stereotypes is brought about by social conditioning (Greenwald & Krieger, 2006). This conditioning can be explained by attractor networks (Sharp, 2011). Reducing implicit bias through meditation can show the effectiveness of reducing the rigidity of attractor networks, thereby reducing subjectivity. Mindfulness meditation has shown to reduce bias from the use of one single guided session conducted before performing an Implicit Association Test (Lueke & Gibson, 2015). Attachment to socially conditioned racial bias should become less prevalent through practicing meditation over time. An experimental model is proposed to test this claim along with a reconceptualization of consciousness based in meditative practice.

The present study characterized two fiber pathways important for language, the superior longitudinal fasciculus/arcuate fasciculus (SLF/AF) and the frontal aslant tract (FAT), and related these tracts to speech, language, and literacy skill in children five to eight years old. We used Diffusion Tensor Imaging (DTI) to characterize the fiber pathways and administered several language assessments. The FAT was identified for the first time in children. Results showed no age-related change in integrity of the FAT, but did show age-related change in the left (but not right) SLF/AF. Moreover, only the integrity of the right FAT was related to phonology but not audiovisual speech perception, articulation, language, or literacy. Both the left and right SLF/AF related to language measures, specifically receptive and expressive language, and language content. These findings are important for understanding the neurobiology of language in the developing brain, and can be incorporated within contemporary dorsal-ventral-motor models for language.

Anxiety is an affective state defined by heightened arousal and unease in the absence of a clear and present fear-inducing stimulus. Chronic and inappropriate anxiety leads to anxiety disorders, the most common class of human mental disorder. Recent work suggests projections to the ventral tegmental area (VTA), are critical for anxiety behavior expression. However, the relationship between efferent VTA projections and anxiety is unclear. This thesis resolves anxiety circuitry connecting the dopaminergic (DAergic) VTA to the interpeduncular nucleus (IPN), coined the mesointerpeduncular circuit. I hypothesize the mesointerpeduncular circuit affects anxiety through the release of anxiogenic corticotropin releasing factor (CRF) during nicotine withdrawal and anxiolytic dopamine (DA) during drug naïve behavior. Electrophysiological and pharmacological data suggest CRF release from the DAergic VTA during nicotine withdrawal activates CRF receptor 1 (CRFR1) potentiating the glutamatergic activation of “Type 2” neurons and anxiety-like behavior in mice. However, in nicotine naïve conditions CRF production is negligible. Instead, in vivo DA release is anticorrelated with anxiety-like behaviors. Optogenetic stimulation and inhibition drives decreased and increased anxiety-like behaviors, respectively. Electrophysiological experiments reveal a complex interpeduncular microcircuit where D1-like DA receptor expressing “Type C” neurons in the caudal IPN (cIPN) regulate glutamatergic release in the ventral IPN (vIPN) through presynaptic GABA receptors. The result is propagation of the signal to excite “Type A” and inhibit “Type B” vIPN neurons. Finally, pharmacological activation or inhibition of interpeduncular D1-like DA receptors is sufficient to decrease and increase anxiety-like behaviors respectively. Thus, this circuit is important for modulating anxiety-like behavior.

Depression and related disorders are characterized by motivational dysfunctions, including deficits in behavioral activation and exertion of effort. Animal models of relevance to depression represent a critical starting point in elucidating the neurobiological mechanisms underlying motivational dysfunctions. The present study explored the use of the Wistar-Kyoto (WKY) animal model of depression to examine effort-related functions as measured by voluntary wheel running and performance on a mixed fixed ratio 5/progressive ratio (FR5/PR) operant task. Given the known link between activational aspects of motivation and the mesocorticolimbic dopamine (DA) system, the behavioral effects of d-amphetamine (0.5 and 1.0 mg/kg, IP), a psychostimulant that increases DA release, were evaluated in WKY and control Sprague-Dawley (SD) male and female rats responding on a mixed FR5/PR task. An additional experiment assessed intracellular content of monoamine neurotransmitters and their metabolites in relevant mesocorticolimbic brain regions, including the medial prefrontal cortex, the nucleus accumbens and the ventrolateral striatum using HPLC-ED. WKY rats demonstrated initial effort-related deficits in FR5/PR responding compared to SD controls, which ameliorated with training. Amphetamine significantly decreased FR5 work output, but increased responding on the PR phase in both SD and WKY rats. This effect was more pronounced in SD rats compare to WKY rats. In addition, sex differences were evident both in FR5/PR performance and in the behavioral response to amphetamine treatment. Moreover, females demonstrated higher levels of voluntary wheel-running than males. Finally, tissue concentrations of dopamine were lower in the NA and VLS of WKY compared to SD rats. Taken together, results suggest dysfunctions in mesolimbic DA neurotransmission in the WKY strain, likely underlying the depressive phenotype. The present study represents an important initial step in validating the WKY strain as a rat model of effort-related dysfunctions relevant to depression and other neuropsychiatric disorders.