David Lyons - US grants

DESCRIPTION: (Applicant's Abstract) Studies of the living human brain indicate that long-term cocaine abuse alters brain function, and this change may be permanent. Human studies are difficult to interpret, however, because they are often confounded by incomplete and varied drug histories, polydrug abuse, and comorbid psychopathology. Many of these problems can be obviated by the use of animals. Past studies of the functional consequences of cocaine administration in non-human primates have focused on the immediate response to an acute administration of cocaine, whereas long-term changes in functional activity have not been adequately described. Cytochrome oxidase (CO) is an essential enzyme of the mitochondrial electron transport chain that converts fuels into ATP via oxidative phosphorylation. The regional capacity of tissue for oxidative phosphorylation is modified by sustained levels of energy demand that take place over a period of hours, days or weeks and has been repeatedly shown to be linked to persistent changes in neural activity. This activity can be quantitatively visualized in brain tissue sections, and regional values can be determined by quantitative densitometry. Histochemical assessment of cytochrome oxidase activity is an index of long-term cerebral energy metabolism that complements other metabolic mapping techniques such as 2[14C]deoxyglucose that measures short-term, stimulus-evoked changes in metabolic rates. The overall goal of the proposed study is to investigate the long-term effect of cocaine intake on brain function as evaluated in post-mortem tissue from non-human primates that have chronically self-administered cocaine. To that end, the quantitative method of assessing cytochrome oxidase activity that has been developed in the rat will be adapted to non-human primates. Furthermore, the pattern of cerebral energy metabolism resulting from a high and a low dose of self-administered cocaine will be determined in regions of non-human primate brain associated with the effects of cocaine: the striatum and two of its primary limbic inputs, the amygdala and orbitofrontal cortex. The results of the proposed studies will provide a clearer understanding of the comprehensive changes in brain function that result from long-term cocaine abuse.

The proposed study will evaluate the neurobiological consequences of prolonged ethanol drinking. Such studies will identify the regions of the brain that are sensitive to ethanol and potentially help to focus treatment strategies to combat abuse and the neurologic complications of chronic alcoholism. It is known that the magnitude and topography of ethanol's effects on brain function are modified by long-term ethanol exposure. Human studies are limited, however, by the spatial resolution of current methods and the various confounds associated with human research on alcoholism. Animal studies are needed, therefore, to directly link ethanol drinking to changes in brain function within specific sites. To date, imaging studies of ethanol's effects in the brains of animals have used methods that were specifically designed to identify the regional pattern of brain function within a small time window. Accordingly, they have been very useful in defining, the response to acute ethanol intake or acute withdrawal. These methods are, however, less well equipped to evaluate long-term changes in brain function which are modified over a period of hours to weeks. It is not sensitive to short-lived phenomena such as acute ethanol intake and withdrawal. Furthermore, quantitative methods have been recently devised. Therefore, the present proposal will first establish the quantitative method of assessing cytochrome oxidase histochemistry in this laboratory. These procedures involve the use of internal standards and quantitative densitometry. Next, the consequences of ethanol self- administration in rodents will be assessed using this method. This effort will serve as an initial evaluation of the long-term effects of ethanol intake. A self-administration paradigm was specifically chosen to most closely model human alcohol drinking. The use of the CO method will be particularly useful because it avoids confounds associated with acute alcohol intake or withdrawal. There are clear indications that changes in brain function result from chronic alcohol intake in humans and animals; this approach is likely to identify key sites that manifest long-term changes associated with ethanol drinking.

The effects of ethanol are biphasic with respect to administration time. Positive reinforcement occurs early as blood ethanol levels rise. As these levels fall, the depressant and aversive properties predominate. This time-dependency supports a multi-phasic view of ethanol's effects in the CNS in which ethanol has distinct actions within independent brain systems as a function of time after ethanol administration. Seeking evidence of ethanol-induced changes in disparate neural systems as a function of time, the present proposal will determine whether ethanol affects different neural substrates at different times after ethanol administration and whether these systems adapt to chronic ethanol exposure at different rates. Brain mapping studies are in a unique position to contribute significantly in this regard because they determine levels of activity throughout the brain simultaneously. This laboratory has recently shown that ethanol's effects on functional brain activity in the rat are also time-dependent. Activity was altered immediately after ethanol administration in one set of structures, and activity was altered in a completely different set of structures as blood ethanol levels fell. Therefore, it appears that different neural circuits subserve the effects of ethanol when concentrations are rising and falling. The proposed studies will first extend our previous findings obtained at a single dose to a range of relevant doses in order to establish the conditions of dose and time under which each of these two patterns of brain energy metabolism occur. We also present preliminary data which suggest that functional activity adapts differently to chronic ethanol in distinct sets of brain structures in the rat. Therefore, the present studies will also determine how regional neural activity along the rising and falling phases of the blood ethanol curve change in response to chronic exposure to ethanol. These finding swill contribute to the body of work that supports a concept of tolerance which recognizes that integrated activity among various neural circuits are responsible for the time-dependent effects of ethanol.

DESCRIPTION (provided by applicant): Growth and development of prefrontal cortex extends across childhood into adulthood in humans and nonhuman primates. Based on indications that stressful conditions alter developing brain systems in rats, the proposed research investigates chronic early stress effects on subsequent prefrontal correlates of cognitive control, novelty-seeking behavior, dopamine neurochemistry, and sensitivity to cocaine in adolescent squirrel monkeys. Specific Aim 1: Test the hypothesis that early chronic stress increases perseverative tendencies and impairs cognitive control of behavior on tests previously shown to reflect prefrontal cortical dopamine related dysfunctions. Specific Aim 2: Test the hypothesis that early chronic stress enhances voluntary novelty seeking behavior in "stress-free" conditions that do not elicit increases in plasma levels of cortisol or adrenocorticotropic hormone. Specific Aim 3: Test the hypothesis that early chronic stress selectively impairs sensitivity to low but not high doses of cocaine as demonstrated by place preference conditioning. Specific Aim 4: Test the hypothesis that early chronic stress induces baseline hypocortisolism and attenuates baseline levels of cisternal cerebrospinal fluid dopamine and its metabolite HVA. Specific Aim 5: Determine the effects of early chronic stress on prefrontal growth and development assessed longitudinally in vivo by high resolution magnetic resonance imaging. Our hypotheses predict that stress-related group differences in behavioral, hormonal, and neurochemical measures in monkeys correspond with diminished peri-pubertal reductions in right ventromedial gray matter volumes, and diminished maturation of white matter integrity and connectivity as measured by diffusion anisotropy. The data collected to address these hypotheses are analyzed with respect to theories that consider psychostimulant drug-use, risk-taking, and novelty seeking as attempts to alleviate underarousal produced by neuroadaptations trigger in development by chronic stress.

Abstract Not Provided.

[unreadable] DESCRIPTION (provided by applicant): The negative consequences of stress are well-recognized in mental health research. Interestingly, however, prior stress exposure has also been linked to the subsequent development of resilience. Variously described as inoculating, immunizing, steeling, toughening, or thriving, the notion that prior stress exposure facilitates the development of subsequent resilience is tested in the proposed research using alprazolam to diminish key aspects of stress inoculation that are thought to foster resilience. Alprazolam is a benzodiazepine medication that reduces acute anxiety and attenuates hypothalamic-pituitary-adrenal (HPA) axis activation by stress. In animal models, benzodiazepines also interfere with learned extinction of conditioned fear. Conversely, the anxiogenic compound yohimbine activates the HPA axis and accelerates learned extinction of conditioned fear. These findings are consistent with evidence that cognitive and emotional processing of acute anxiety and HPA axis activation promote recovery from stress-related psychiatric disorders. The proposed research tests the hypothesis that acute anxiety and HPA axis activation facilitate the development of stress inoculation-induced resilience. Animals randomized to receive alprazolam or the vehicle control before each weekly stress inoculation training session are compared to non-inoculated animals administered alprazolam or vehicle and assessed at later ages on established behavioral and neuroendocrine measures of resilience. If cognitive and emotional processing of acute anxiety and HPA axis activation are necessary for the development of stress inoculation-induced resilience, then animals administered alprazolam before stress inoculation training sessions will subsequently resemble animals from both non-inoculated treatment conditions with diminished indications of resilience compared to the stress inoculated vehicle treatment condition. This research will extend our understanding of the capacity for enhancing mental health, with the goal of advancing preventative strategies designed to most efficiently foster the development of resilience. Results from these studies will also provide insights on whether benzodiazepines aid or interfere with behavioral therapies, and will help to clarify the role of re-experiencing stressors during therapeutic interventions. These issues are important because of concerns that re-experiencing stressors may exacerbate psychiatric symptoms and impede recovery instead of fostering the development of resilience. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Novelty seeking behavior promotes the ability to discover and construct new knowledge about the environment. Greater preferences for novelty during infancy predict higher scores on tests of intelligence, language, memory, and speed of information processing in children and young adults. Novelty seeking can be costly, however, as it increases the prevalence of reckless driving, pathological gambling, unprotected sex, under-age drinking, and other forms of alcohol and drug abuse. Recently, we discovered that novelty seeking in an animal model mediates the effects of early social stress on subsequent resistance to extinction of a conditioned place preference for cocaine. Our preliminary evidence further suggests that early exposure to social stress induces long-lasting downregulation of dopamine D2 receptor (DRD2) gene expression in ventral but not dorsal striatum. Diminished ventral striatal DRD2 availability determined in vivo by positron emission tomography (PET) has been linked in humans and animal models to novelty seeking and related maladaptive forms of anticipatory impulsivity, but not in the context of early social stress. Therefore, we plan to test the hypothesis that early social stress downregulates DRD2 gene expression in ventral striatum via epigenetic mechanisms (i.e., increased DNA methylation) and thereby increases anticipatory impulsivity. Specifically, we address the following three aims. Aim 1. Determine whether early social stress increases DRD2 gene promoter methylation in ventral but not dorsal striatum assessed by bisulfite sequencing of DNA from striatal brain tissues. Aim 2. Determine whether early social stress decreases DRD2 availability in ventral but not dorsal striatum assessed in vivo by positron emission tomography. Aim 3. Determine whether early social stress increases anticipatory impulsivity without impairing non-anticipatory forms of impulsive behavior. The studies designed to address these aims will provide mechanistic insights for understanding the pathways that mediate the long-term effects of early social stress on broadly important health-related aspects of behavior.