Joshua M. Gulley - US grants

DESCRIPTION: (Applicant's Abstract) Amphetamine (AMPH) elicits a species-specific pattern of motor activation that, in animals, has been shown to be mediated at least in part by the striatum. If the neuronal patters established in the striatum are critically involved in shaping the motor response to AMPH, as ample data suggest, then some aspect of these patterns should be communicated to its primary efferent structure the substantial nigra pars reticulate (SNr). Research in this application seeks to further understanding of the nigral mechanisms of AMPH-induced motor response in two ways. The first is to investigate the role of the SNr in the normal motor response of rats walking on a treadmill or performing a conditioned-reinforcement task. After surgery to implant microwire bundles for recording of single units in the SNr, rats will be placed in a chamber with a treadmill or one with two nose-poke holes and a spout for liquid sucrose delivery located on one wall. Single-unit activity will be monitored throughout performance of these tasks, which should yield numerous instances of head movements, oral behavior (e.g., licking) and locomotion. The second aim of the research proposed here is to correlate AMPH-induce changes in SNr activity and behavior the pre-drug behavioral response of the neuron. After performing the behavioral tasks, rats will be placed in an open-field environment where unit activity will be monitored after subcutaneous infections of either AMPH (1.0 or 5.0 mg/kg) or saline. These experiments will provide valuable information about the way in which the SNr influences motor- related target structures and how AMPH changes this output to produce its characteristic pattern of repetitive or stereotype movement.

[unreadable] DESCRIPTION (provided by applicant): [unreadable] Repeated exposure to psychostimulant drugs typically leads to behavioral sensitization, which refers to enhanced motor responsiveness after administration of the same or lower doses of the drug. This phenomenon, which persists well after drug taking ceases, has been suggested to contribute to various aspects of human drug addiction, including "craving" and relapse. In the research proposed here, I will investigate the role of dopamine transporter (DAT) function in the expression of behavioral sensitization. The DAT is responsible for clearing DA from the extracellular space. Using inbred Lewis and Fischer 344 rats, which have been described as addiction-prone and addiction-resistant, respectively, I will measure DAT number and function in the striatum and nucleus accumbens using quantitative autoradiography to measure in vitro radioligand binding and in vivo high-speed chronoamperometry to measure clearance of exogenous DA. Measurements will be made in untreated rats and those withdrawn from daily intravenous injections of saline or amphetamine (AMPH). These inbred rat strains exhibit basal differences in the number of DATs expressed in striatum and nucleus accumbens, but it is not clear if this leads to differences in DAT function. I will pay particular attention to correlation between individual differences in the susceptibility to express sensitization and all of the following: DAT number in dSTR, NAc and their respective subregions, basal DAT activity in these areas, and the ability of either frequent DA application and/or systemic AMPH to regulate DAT function. These experiments will help elucidate the role of the DAT in behavioral sensitization and further our understanding of the neuroadaptations associated with repeated drug intake. [unreadable] [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Repeated exposure to psychostimulant drugs such as amphetamine (AMPH) often leads to behavioral sensitization, which refers to enhanced motor responsiveness to subsequent drug administration. Alterations in brain anatomy and function parallel behavior changes and these adaptations have been hypothesized to contribute to the development and maintenance of human drug addiction. A large body of studies, mostly performed in rats, has implicated dopamine- and glutamate-containing brain areas within cortico-limbic and striatal pathways as important anatomical substrates for AMPH-induced behavioral sensitization. In particular, the medial prefrontal cortex (mPFC) appears to play an important role in the induction and expression of behavioral sensitization through its influence on the ventral tegmental area and nucleus accumbens, respectively. Thus, studies of mPFC function in awake, behaving subjects are necessary to verify if drug-induced plasticity in the mPFC is important for behavioral sensitization and if changes in neuronal responses correlate to its induction and/or expression. In the experiments proposed here, we will test the following hypotheses: (1) AMPH has acute effects on mPFC neurons that depend on the neuron's responsiveness during behavior and/or to a particular environmental context, and (2) Behavioral sensitization to repeated, intermittent administration of AMPH is correlated with changes in the firing rate and/or pattern of mPFC neurons and this relationship will differ in non-sensitized animals. We will use chronically implanted, multiwire electrodes to record single-neuron activity in the mPFC of rats that are allowed unrestricted movement in an open-field arena. Recordings will be obtained during baseline conditions, after saline administration, and after rats have undergone either acute or chronic treatment with AMPH. Ultimately, these experiments will help clarify the role of mPFC plasticity in behavioral sensitization and will further our understanding of the neuroadaptations associated with repeated drug intake.

[unreadable] DESCRIPTION (provided by applicant): Adolescence in humans is a period of life when alcohol use is often initiated. Unfortunately, it is also a time when some individuals develop long-lasting patterns of alcohol abuse and alcoholism. Human and animal studies have revealed that during adolescence, brain areas such as the prefrontal cortex (PFC) are undergoing significant, yet normal, changes in synaptic connectivity. These changes in synaptic organization have important implications in the adolescent and adult PFC. For example, in a recent report (Markam et al., 2007), we demonstrated region- and sex-specific decreases in the number of neurons in the medial PFC (mPFC) of adolescent compared to adult rats. It is possible that alcohol alters these normal patterns of adolescent-to adult changes in mPFC and thereby produces a particularly susceptible nervous system. Furthermore, pubertal hormones may interact with alcohol's effects in the mPFC, and this might contribute to sex differences in drinking behavior. In the research proposed here, we will use animal models to explore the effects of alcohol exposure during adolescence on the mPFC and on the operant self-administration of alcohol in adulthood. This will be accomplished by: (1) examining whether alcohol exposure during adolescence alters decreases in neuron number in the rat mPFC and if gonadal hormones contribute to alcohol's effects; and (2) investigate whether alcohol exposure during adolescence alters alcohol drinking behavior in adulthood and if there is an influence of sex and hormonal status. Rats will be divided into eight different groups (n = 10/group) based on sex (male or female), hormone status (intact or pre-pubertal gonadectomy), and adolescent exposure to alcohol (saline or 3.0 g/kg ethanol). As adults (PND 90), rats will be either euthanized for brain removal and subsequent stereological analysis of the number of neurons in the mPFC (Aim 1) or they will begin training for operant self-administration of alcohol (Aim 2). Ultimately, the information learned in these studies will help us understand if alcohol-induced brain changes are a contributing factor to the high rates of alcoholism in individuals who begin drinking at an early age. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Adolescence is a developmental stage in humans that is characterized by dramatic changes in an individual's biology and their behavior. It is also a period during which individuals may begin using psychostimulant drugs, whether for therapeutic or recreational purposes. Repeated exposure to these drugs is associated with deficits in memory, decision making, impulse control, and reward processing, and these adverse consequences on cognition may persist through extended periods of drug abstinence. Thus, it is critically important to understand the neurobiological processes that mediate drug-induced changes in behavior and to determine how adolescents, compared to adults, are particularly vulnerable. Our long-term goal in these studies is to understand the neuroadaptations induced by amphetamine in corticolimbic regions of the adolescent brain and determine how these changes can be prevented or reversed. In the proposed studies, we will use behavioral, pharmacological, and electrophysiological techniques in animal models of adolescence and adulthood to address two aims. In Aim 1, we will determine if changes in dopamine and NMDA receptor function in the mPFC are responsible for the enduring deficits in cognitive behavior induced by amphetamine exposure during adolescence. In Aim 2, we will determine the basis of the long-lasting functional changes in mPFC neurons that are observed in adolescent- compared to adult-exposed individuals. Our working hypotheses are that, 1) adolescent-exposed rats, when tested as adults, will be more sensitive to drug-induced deficits in cognitive function and to selective manipulations of dopamine and NMDA receptors, compared to those exposed as adults;2) the effects of repeated amphetamine treatment on the intrinsic firing properties, NMDA-dependent long term potentiation, and dopamine receptor-mediated responses of mPFC neurons are enhanced in adolescent- compared to adult-exposed individuals;and 3) the effects of this exposure on the in vivo responses of mPFC neurons to amphetamine and dopamine or NMDA receptor selective drugs will be greater in adolescent- compared to adult-exposed individuals. These hypotheses are consistent with our preliminary studies, which show that that exposure to amphetamine during adolescence impairs behavior on an mPFC-sensitive working memory task and alters the intrinsic firing properties of layer V pyramidal cells recorded in vitro. Through the research proposed in this application, we seek to fill the large gaps in our knowledge about what makes the brain and behavior of adolescence so uniquely different from adults and increases their vulnerability to the adverse consequences of repeated drug exposure. By understanding the unique plasticity of the adolescent brain, we will likely identify targets for preventative or therapeutic strategies aimed at ameliorating the adverse consequences of repeated amphetamine exposure during adolescence. In addition, we anticipate our results will move the field towards a clearer understanding of the unique effects of psychostimulants during this critical period of neural and behavioral development. PUBLIC HEALTH RELEVANCE: The results of these experiments in animal models will help clarify the neurobiological underpinnings of the heightened vulnerability of adolescents to the detrimental consequences of amphetamine exposure. By understanding the unique neural and behavioral processes of adolescence, neuroscience we will be able to make significant advances in our attempts to more effectively prevent and treat the behavioral adaptations, including cognitive deficits, that result from drug exposure early in life.

Project Summary   Alcohol and cannabis are the most commonly abused drugs and they are often used in combination, especially  by adolescents. Previous work has revealed that the frequent use of either drug alone is associated with  cognitive impairments, including loss of memory function, impulsivity, poor decision making, and lack of  behavioral flexibility. These cognitive problems, which likely contribute to the persistence of drug addiction and  poor treatment outcomes, may be heightened in those who use both drugs in combination.  Metabolic  dysfunction is also seen in drug abusers and the mechanisms underlying these effects may contribute to those  that underlie drug-­induced cognitive impairment. However, the potentially shared mechanisms for drug-­induced  metabolic and cognitive dysfunction have been largely unexplored.  Here, we use a rat model of adolescence  to investigate the co-­use of alcohol and ?9-­tetrahydrocannibinol (THC), the primary psychoactive drug in  cannabis, and the role of the Akt-­GSK3? signaling pathway in drug-­induced changes in metabolic activity,  synaptic plasticity and behavioral flexibility. Our preliminary data show that adolescent rats who drank  moderate levels of alcohol and were exposed to synthetic THC (dronabinol), either via s.c. injection or oral self-­ administration, had significant changes in glucose metabolism and impaired synaptic plasticity in the prefrontal  cortex (PFC) that were not observed in rats exposed to either drug alone. Accordingly, we hypothesized that  co-­use of alcohol and THC causes dysregulation of the Akt-­GSK3? signaling pathway in the mediobasal  hypothalamus, which plays a critical role in insulin-­mediated metabolism, and in the PFC, which is critical for  normal cognition. We will test this hypothesis in both male and female rats by identifying the unique impact of  adolescent alcohol and THC co-­use on (1) Akt-­GSK3? signaling in response to metabolic challenge in  adulthood, (2) operant behavior tests of behavioral flexibility, and (3) high frequency stimulation-­induced  synaptic plasticity in the PFC. We expect that our results will provide new insights into how mechanisms of  metabolic and synaptic signaling are integrated to control cognition, how combined use of alcohol and THC  influence the developing brain to produce long term negative outcomes, and how these mechanisms are  differently regulated to produce sex differences in the effects of alcohol and THC co-­use. The successful  completion of this research project will shape our future plans for a collaborative research program that is  focused on identifying a specific hypothalamic-­corticolimbic circuitry that is altered by alcohol and THC  exposure. Our long-­term goal is to elucidate how this circuitry mediates normal energy metabolism and  cognition and how the effects of adolescent alcohol and THC co-­use may be heightened compared to drug  exposure in adulthood.