The basal ganglia are critical for motor behavior, and a well-known deficit of basal ganglia disorders is the loss of voluntary control over movements. Many studies on the role of basal ganglia in saccadic eye movements have focused on the caudate and substantia nigra pars reticulata (SNr). It has remained unclear, however, whether neurons in other nuclei of the basal ganglia are active during oculomotor behavior and, if they are, whether their activity is preferential for voluntary saccades. We ventured beyond the caudate-SNr pathway to study the globus pallidus externa (GPe) and interna (GPi). First we recorded from neurons in GPe and GPi (and for comparison, in SNr) in monkeys that made memory-guided saccades. Neurons in all three structures had activity synchronized with saccade generation, visual stimulation, or reward. GPe activity was strongly visual-related while GPi activity was more reward-related. The distribution of signals in GPe, but not GPi, resembled that found in SNr. Response fields of neurons in all three structures were more spatially tuned early in trials (during visual and saccadic events) than later in trials (during reward). In our second study, we examined whether saccade-related activity in GPe and GPi was preferentially active for voluntary saccades as defined in two ways: made in the absence of visual stimulation and made in the absence of instructions. We designed tasks that covered all four permutations of presence or absence of visual stimulation and instruction, and analyzed neuronal activity associated with the same vectors of saccades across all the tasks. For about half of the saccade-related neurons in all three structures, saccade-related activity varied with task context. The most prominent factor accounting for differential saccade-related activity was instructional context. Surprisingly, we found higher activity for instructed saccades. Preferential activity for non-instructed (highly voluntary) tasks was rare in individual neurons and absent at the population level. We conclude that GPe and GPi, in addition to SNr, may contribute to oculomotor behavior, and that none of these structures are preferentially active for voluntary saccades. Both of these results provide new views on the role of basal ganglia in eye movements.

Adolescence is a developmental stage between childhood and adulthood associated with numerous brain and behavioral changes. It is also a period of vulnerability, as adolescents tend to take more risks, and various psychiatric problems first typically manifest at this time. Yet little is known about the neuronal basis of these vulnerabilities. Although extracellular electrophysiological recording is a useful technique for measuring the neural activity of awake behaving animals, it had not yet been used to address the neural correlates of adolescent motivated behavior. This dissertation therefore had two primary objectives. The first was to characterize a novel behavioral task suitable for testing adolescent and adult rats. The second was to record the neural activity of brain regions involved in motivated behavior, as adolescents and adults performed it. The behavioral task was a simple instrumental learning paradigm, in which rats associated poking into a hole with the delivery of a food pellet reward. While the learning and performance of this task was similar between the two groups, adolescents persisted in this activity more than adults when reward was withheld. It was determined that this was due to different age-related sensitivities to the presence of certain motivational factors. After characterizing the task, it was performed by adolescent and adult rats that had electrode arrays implanted in their orbitofrontal cortex (OFC), nucleus accumbens (NAc), or dorsal striatum (DS). Neural activity was examined in the context of similar instrumental behavior to determine whether adolescents processed salient events in a fundamentally different way from adults. Several interesting neural processing differences were observed, along with some notable similarities. The greatest phasic activity differences were found in the OFC and DS, particularly during the period immediately before reward. Local field potential oscillations also tended to differ, with particular disparities found in the DS. In contrast, NAc activity tended to look similar between adolescents and adults, with a few exceptions. In addition to demonstrating fundamental age-related neural processing differences during motivated behavior, these findings address existing hypotheses and raise new questions relevant to the neural basis of the increased vulnerabilities of adolescence.

Glucocorticoids (GCs) are administered to neonates and to pregnant mothers for the treatment of complications arising from premature birth and for congenital adrenal hyperplasia; however, antenatal exposure to GCs may trigger adverse neurological side effects due in part to reduced neural progenitor cell (NPC) proliferation. While many established cell cycle regulators impact NPC proliferation, other molecules also influence proliferation. An example is the gap junction protein connexin 43 (Cx43), although its precise role and mechanism of regulation remain unresolved. Gap junction intercellular communication (GJIC) is influenced by GCs in some cells, but such hormone effects and resulting functional consequences have not been examined in coupled stem cells. We found that both continuous and transient exposure of embryonic (E14.5) mouse neurosphere cultures to the glucocorticoid dexamethasone (DEX) limits proliferation of coupled NPCs, which is manifested by both a reduction in S phase progression and enhanced cell cycle exit. A short (i.e. 1hr) DEX treatment also reduced GJIC as measured by live cell fluorescence recovery after photobleaching (FRAP). GC effects on GJIC in NPCs are transcription-independent and mediated through plasma membrane glucocorticoid receptors (GRs). This non-classical pathway appears to operate through lipid-raft associated GRs through a site-specific, MAPK-dependent phosphorylation of Cx43, which is linked to GR via caveolin-1 and c-src. These effects were absent in caveolin-1 knockout NPCs indicating that caveolin-1 is an essential component for this signaling pathway. As transient pharmacologic inhibition of GJIC triggers reduced S phase progression but not enhanced cell cycle exit, the non-classical GR signaling pathway may operate via distinct downstream effectors to alter the proliferative capacity of NPCs.

Major depressive disorder and cardiovascular disease are highly comorbid, and the presence of one disorder greatly increases the likelihood of the other. Remarkably, depressed but otherwise healthy patients with no history of cardiovascular disease are as likely to have a heart attack as patients with established cardiovascular disease. Experimental studies have used chronic mild stress (CMS), a rodent model of depression that uses a series of unpredictable, intermittent, and variable mild stressors to induce anhedonia, one of the core diagnostic criteria for major depression. CMS also induces a constellation of behavioral, physiological, and neuroendocrine responses that closely resemble those observed in depressed patients, including alterations in autonomic control of the heart marked by decreased heart rate variability (HRV). Commonly prescribed antidepressants might not improve cardiovascular alterations associated with depression, even when depressive signs are ameliorated. There is evidence, however, that candesartan, an angiotensin type 1 receptor (AT1R) antagonist (ARB) often prescribed for cardiovascular disorders, has anxiolytic and possibly antidepressant effects in animal models. To study the possible antidepressant effects of candesartan, we first established a robust rodent model of vulnerability to depression, since severity of depression is correlated with severity of cardiovascular changes in humans. We found that rats selectively-bred for low locomotor responses to a novel environment (bLR) were especially vulnerable to CMS-induced anhedonia and cardiovascular changes. Conversely, selectively-bred high-responder rats (bHR) were resilient to the behavioral and cardiovascular changes induced by CMS. Finally, we compared the effects of candesartan and the SSRI fluoxetine on CMS-induced anhedonia and cardiovascular changes. We found that candesartan has profound antidepressant effects, including rapid reversal of anhedonia, and attenuated anxiety-like behavior. Furthermore, candesartan reversed cardiovascular changes, including clinically relevant markers of risk for cardiac mortality. Thus the major findings of these studies are twofold: (1) bHR/bLR rats exposed to CMS offer a robust model of the interactions of predisposition and environmental stress that may contribute to depression and comorbid cardiovascular disease and (2) candesartan and other ARBs may be novel therapies for the treatment of comorbid depression and cardiovascular disease, and may be more effective than traditionally-prescribed antidepressants such as SSRIs.

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterized by deficits in social behavior. It is unclear if deficits are due to disinterest in social stimuli, or to an elevated stress response. The autonomic nervous system and hypothalamic pituitary adrenal axis facilitate arousal, as well as approach and avoidance behavior in response to sensory information, including social stimuli. Research in our lab has shown blunted responsivity to social judgment in children with ASD. Previous work has also demonstrated alterations in autonomic regulation, including respiratory sinus arrhythmia (RSA), a measure of PNS function. The majority of prior work has focused on children with ASD, but adolescents with ASD have been understudied. The adolescent period is of interest, as this developmental epoch is associated with increased salience of social judgment in typically developing (TD) populations. In this study, we employed the Trier Social Stress Test (TSST) to study RSA and salivary cortisol response to social judgment in ASD compared to TD adolescents. Participants underwent a modified version of the TSST, in which one of the raters was replaced with an age-matched peer. At arrival and during the TSST, ECG was obtained. Salivary cortisol data was obtained prior to and following the TSST. Operationalized behavior coding was collected using video recordings of the TSST. RSA was calculated from ECG. We performed repeated measures ANOVA to determine group differences in RSA, as well as for behaviors. Paired sample t-tests were used to calculate within-group cortisol response to the TSST. TD participants showed higher mean RSA values than ASD participants at all time points. Cortisol data showed a significant increase in response to the TSST in the TD group but not the ASD group. The TD group showed more displacement behaviors than the ASD group. Our findings indicated reduced regulatory capacity as indexed by RSA in ASD adolescents compared to TD peers. The lack of a cortisol response to the TSST in the ASD group could suggest that the TSST is not interpreted as stressful or salient for ASD participants, as does the reduced displacement behaviors in the ASD group.

Due to the escalating obesity epidemic in the United States, an important public health concern is the comorbidity of metabolic disorders and mental illness. Mounting clinical evidence supports the comorbid nature of mental illness with metabolic disorders such as diabetes and obesity. Human epidemiologic data as well as studies in animal models showed that aberrant metabolic mTORC2/Akt signaling is linked to monoamine related neuropsychiatric disorders, particularly DA-associated brain dysfunctions, which manifest in many mental diseases including schizophrenia. Of utmost interest and relevance to this thesis was to elucidate how fine-tuning of Akt activity, particularly its upstream mTORC2/rictor signaling, regulates striatal DA homeostasis and subcortical DA-dependent behaviors. Collectively, our studies reveal that disrupted central mTORC2/Akt signaling results in aberrant subcortical DA neurotransmission and disrupted DA-dependent behaviors. We utilized transgenic mouse models and viral intervention techniques to induce whole brain or region-specific deletion of protein rictor, an essential mTORC2 component. Here, we demonstrate how disruption of mTORC2/Akt signaling in brain-region specific manner results in altered subcortical DA neurotransmission. Importantly, we show that these genetic alterations manifest in neurochemical and biochemical changes in the brain that influence neurophysiological behaviors as well as peripheral metabolic phenotype.

The hippocampus is a medial temporal lobe structure involved in learning and memory. Several magnetic resonance imaging methods exist to investigate hippocampal structure and function in vivo. Some of these methods provide information about the anterior and posterior hippocampus while other methods can examine its subfields. In this study, we applied several imaging techniques to study hippocampal structure, blood volume (CBV), and blood flow (CBF) in early psychosis and chronic schizophrenia. We characterized CBV gradients in the hippocampus and its subfields and found increased anterior CA1 CBV in chronic schizophrenia. Hippocampal CBF was normal in the same cohort of chronic, medicated patients. When we studied patients in early psychosis, we found no hippocampal volume and CBF differences. However, we found an inverse relationship between hippocampal volume and CBF and a trend towards increased anterior hippocampal CBV. This study provides comprehensive, multi-modal imaging to characterize hippocampal structural and functional alternations in a clinical population.

Rapid habituation to repeated presentations of stimuli that are neither threatening nor rewarding is crucial for effectively navigating the constantly changing environment. Failure to habituate has been proposed as a neuronal mechanism underlying social anxiety. In this study, we test the hypothesis that social fearfulness is associated with reduced neural habituation to social stimuli. Twenty-nine individuals representing the full dimension of social fearfulness (low to high) viewed repeated presentations (up to 7) of neutral social and nonsocial stimuli during an fMRI study. Percent signal change was extracted from a priori regions of interestincluding the amygdala, hippocampus, medial orbitofrontal cortex (mOFC), ventromedial prefrontal cortex (vmPFC), fusiform face area (FFA), extrastriate cortex, and primary visual cortex (V1)areas that have been previously implicated in social anxiety disorder. Social fearfulness was correlated with elevated initial response to faces in the hippocampus and vmPFC, and habituation differences to faces in the amygdala, hippocampus, mOFC, vmPFC, extrastriate, and V1 (p < .05). Higher social fear was associated with a sustained response relative to individuals with low social fear, who showed rapid habituation to repeated social stimuli. Social fearfulness was also correlated with sustained functional connectivity between the amygdala and two visual cortex regionsthe extrastriate cortex and V1. Importantly, social fearfulness findings were similar when controlling for neural response to non-social stimuli (objects), suggesting that differences were specific to social stimuli. Individual differences in habituation to social stimuli may provide an important neurobiological marker for risk for psychiatric illness, such as social anxiety disorder.

Fos and Jun are transcription factors that heterodimerize to form AP-1, a transcriptional activator complex. They are two among many important candidate immediate early genes long hypothesized to function as transcriptional gatekeepers between the short-term and long-term modifications of synaptic efficacy postulated to underlie learning and memory. In normally active Drosophila motor neurons, overexpression of AP-1, induces cAMP- and CREB- dependent forms of synaptic enhancement. The activities of immediate early genes such as fos, jun, and CREB have long been assumed to achieve synaptic enhancement by increasing synapse number. We show that at the Drosophila neuromuscular junction (NMJ), an AP-1- and CREB- dependent form of presynaptic strengthening is mediated by increasing the weights of unitary synapses and not through the insertion of additional release sites. Post-tetanic potentiation (PTP) is reduced at these synapses, suggesting that the mechanisms underlying this short-term form of synaptic enhancement may be stably recruited by pathways activated downstream of AP-1 overexpression. Electrophysiological and FM1-43 based measurements further demonstrate that enhanced neurotransmitter release is accompanied by an increase in the actively cycling synaptic-vesicle pool at the expense of the reserve pool. Increases in both transmitter release and cycling-pool size are blocked under conditions of CREB inhibition arguing that: a) AP-1 and CREB are required for reserve-pool mobilization; and b) that sustained reserve pool mobilization may underlie this form of plasticity. These findings together suggest transcriptional mechanisms believed to participate in long-term forms of synaptic enhancement may, in some instances, be accomplished by the stable recruitment of mechanisms that normally underlie short-term synaptic change.

GABA-ergic disturbances are hallmark features of many brain disorders. Two transgenic mouse lines were generated to suppress GAD1 in non-overlapping cell types that express cholecystokinin (CCK) or neuropeptide Y (NPY). In situ lipidomic and proteomic analyses on brain tissue sections revealed distinct, brain region specific profiles in each transgenic line. Behavioral analyses revealed that suppression of GAD1 in CCK+ interneurons resulted in locomotor and olfactory sensory changes while suppression in NPY+ interneurons affected anxiety-related behaviors and social interaction. Both transgenic mouse lines had altered sensitivity to amphetamine albeit in opposite directions. Together, these data argue that reduced GAD1 expression leads to altered molecular and behavioral profiles in a cell type-dependent manner, and that these two subpopulations of interneurons are strong and opposing modulators of dopamine system function. Furthermore, our findings also support the hypothesis that neuronal networks are differentially controlled by diverse inhibitory subnetworks.