John F. Marshall - US grants

DESCRIPTION:(provided by applicant) The globus pallidus (GP; external pallidum of primates) plays a key role in the circuitry of the basal ganglia. It receives synaptic input from all of the striatal spiny projection neurons and distributes axon collaterals to all structures of this circuit, including the striatum. Recent research highlights the diversity of its neurons, with many containing parvalbumin (PV) and others expressing preproenkephalin (PPE) mRNA. The dopaminergic innervation of the pallidum is functional, because intrapallidal infusions of dopamine (DA) or DA antagonists alter unit firing and affect GP immediate early gene expression. The influences of D2-class DA antagonists on immediate early gene expression occur predominantly within the PPE+/-/(PV-) pallidostriatal cells. The mRNA for the D2 dopamine receptor is expressed by many (48 percent) of the neurons in rodent GP, making this nucleus a likely target for actions of exogenously administered dopaminergic agents (e.g., L-dopa in Parkinson's disease). Four specific aims will address the issues of neuronal heterogeneity in GP neuron populations and the actions of DA on pallidal neuron function. These aims include: (1) studying pallidal immediate early gene response to local infusions of D2-, D3-, and D4-preferring DA antagonists and characterizing D3 mRNA-expressing neurons according to their axonal projections, their PPE mRNA, and their immediate early gene response; (2) investigating interactions between subthalamic nucleus activation or inactivation and local pallidal effects of D2-class agonists or antagonists, (3) determining the expression of GAD67 mRNA within identified populations of GP neurons after DA cell injury or DA antagonist treatment to determine cell type-specific regulation of this transmitter-related late gene; and (4) testing the hypothesis that the pallidostriatal axon collaterals influence gene expression within striatal PV interneurons. This last aim uses a paradigm of cortically-driven c-fos induction in striatal PV and enkephalin neurons to investigate whether intrapallidal GABA-A or D2 receptor drug infusions can suppress or enhance c-fos induction within these striatal interneuron and projection neuron populations. These experiments should substantially advance our understanding of (1) the phenotypic diversity of GP neurons, and (2) the actions of DA in the globus pallidus. The proposed research focuses on the GP neurons that contain D2 or D3 mRNA and/or are altered by the administration of DA antagonists. The significance of this work derives both from its relevance to basal ganglia disorders such as Parkinson's disease and also because of its potential to elucidate the significance of the pallidostriatal circuitry.

Damage to the dopaminergic innervation of the rat neostriatum results in impaired sensorimotor performance, including an inability to orient toward somatosensory stimuli. Many rats with such damage show a recovery from their initial sensorimotor impairments, and this recovery appears to be accomplished by a normalization of transmission at neostriatal dopamine terminals that escape injury. This recovery is mediated by presynaptic and postsynaptic changes at these surviving synapses. This proposal seeks to understand the cellular basis of this recovery by three experimental lines. (1) An important advance would be to determine which region of the neostriatum subserves orientation to touch, thereby restricting the neostriatal zones in which cellular correlates of the recovery would be sought. Experiments are proposed that use cats and rats to find the neostriatal locus of the somatonsensory orientation. (2) Postsynaptic changes that contribute to this recovery result from a proliferation of neostriatal dopamine receptors. Some of these receptors are labelled by incubation with 3H-spiroperidol. An autoradiographic approach to determine the binding of 3H-spiroperidol to forebrain sections through the neostriatum is described, as is the video imaging and analysis system used in the quantification of this binding. These methods will be used to determine the time course and topography of the proliferation of 3H-spiroperidol binding sites in the neostriatum of rats recovering sensorimotor functions after damage to the dopaminergic afferents. (3) The contribution that a loss of dopamine uptake sites may play to the early recovery of somatosensory function is determined using pharmacological approaches. The results will provide new evidence concerning the topographic organization of the caudate-putamen, which will guide research on the neuropathology and chemopathology of basal ganglia movement disorders. The 3H-spiroperidol autoradiography method to demonstrate dopamine receptor supersensitivity has important potential clinical applications.

Treatment of animals with the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-- tetrahydropyridine (MPTP) results in movement disorders and signs of injury to striatal dopamine nerve terminals that are similar to those observed in patients with Parkinson's Disease (PD). Patients with PD, like MPTP-treated animals, suffer regionally heterogeneous injury to striatal dopaminergic terminals. That is, the extent of damage is greater in dorsal striatum than ventrally, and the nucleus accumbens septi (NAc) dopamine inputs are largely spared. Preliminary data indicate that mice, rats, rabbits, and humans have a higher density of dopamine uptake sites (determined by [3H]DA uptake kinetics or [3H]mazindol binding to the associated recognition site) in dorsal striatum than ventrally, with particularly low levels observed in NAc. The present studies seek to determine whether regional striatal [3H]mazindol binding densities in young adult and mid-age mice are predictive of regional MPTP-induced injury to the dopamine systems of the striatum, as well as of extrastriatal structures. Further, an analysis will be undertaken of the distribution of [3H]mazindol binding sites in human striatal tissue obtained postmortem. These studies should (i) contribute to an understanding of the mechanism of MPTP neurotoxicity in animals, (ii) add to our knowledge of the physiological and pathophysiological significance of high-affinity dopamine uptake, and (iii) provide novel information regarding the hypothesis that the incorporation of environmental neurotoxins via the high-affinity DA uptake system contributes to the etiology of PD.

The long-term objective of this proposal is to characterize neurobiological processes that contribute to behavioral recovery from cortical injury. Injury to the prefrontal area termed medial agranular (AGm) cortex of rats results in a well-characterized neglect of stimuli, in which animals fail to orient toward visual, auditory, or tactile stimuli on the side contralateral to the lesion. These symptoms are similar to neglect in humans. However, rats show a remarkable spontaneous recovery from this neglect, and by several weeks postoperatively they typically respond to stimuli on either body side. While the processes responsible for this recovery are only beginning to be understood, current evidence indicates that adaptations within striatal dopaminergic synapses contribute importantly to time-dependent restoration of orientation. The effects of striatal dopaminergic neurotransmission on recovery from cortical neglect will be interpreted with reference to a neurobiological model of the striatum in which corticostriatal (excitatory amino acid- using) and nigrostriatal (dopaminergic) afferents converge on individual medium spiny neurons. This proposal will investigate neurobiological compensations occurring within the striatum of animals given unilateral AGm ablations. The overall strategy is to study indexes of dopaminergic or excitatory amino acid transmission, or of medium spiny neurons' responses, within the striatum of rats given AGm ablations, comparing short-term (5 days post surgery) effects in animals with neglect to long-term (greater than or equal to 3 weeks) changes in recovered animals. Specific experiments will investigate whether recovery from AGm injury is associated with presynaptic, postsynaptic, or intracellular adaptations occurring within striatum by examining: (1) extracellular dopamine, glutamate, or aspartate concentrations, (2) numbers or affinities of dopamine or excitatory amino acid receptors, (3) dopamine-stimulated adenylate cyclase activity and G(olf) immunoreactivity, or (4) immediate early gene expression stimulated by dopamine or NMDA agonists. A role for striatal excitatory amino acid transmission in recovery from neglect will be tested further by determining the effects on orientation of intrastriatal infusion of NMDA or non-NMDA antagonists in recovered AGm- lesioned rats. Finally, studies will examine changes in immediate early gene expression of non-striatal regions (superior colliculus, subthalamus, and thalamus) in relation to recovery from AGm ablations.

Individuals who self-administer stimulant drugs repeatedly at closely spaced intervals can develop psychoses. Attempts to understand athe neurobiology of psychoses by mimicking this pattern of stimulant treatment in experimental animals have been few in number and have not employed recently developed neurochemical, immunologic, or molecular neurobiologic techniques. Experiments performed in this laboratory have suggested that repeated administration of methamphetamine to rats has consequences for striatal dopaminergic terminal overflow that differ from those of acute administration of this drug. Further experiments have revealed that Fos, the protein product of the proto-oncogene, c-fos, has a qualitatively different localization in brain regions of rats undergoing repeated versus acute methamphetamine treatments. Of particular interest is the finding that rats given repeated methamphetamine treatments displayed increased numbers of Fos=immunoreactive nuclei in two interconnected limbic cortical regions (postsubiculum and retrosplenial cortex), the anterodorsal thalamic nucleus (which innervates both these limbic cortices) and in paraventricular thalamic nucleus (which innervates subiculum and prelimbic cortex). This proposal is designed (i) to characterize alterations in Fos immunoreactivity during a course of chronic methamphetamine administration to rats, and (ii) to begin studying how the limbic cortex and anterodorsal and paraventricular thalamic nuclei become activated during chronic methamphetamine treatment. The specific aims of this proposal include: (i) development of a chronic methamphetamine regimen in rats what minimizes injury to monoaminergic neurons, (ii) characterization of the pattern of brain Fos immunoreactivity in rats exposed to this chronic treatment regimen, (iii) comparison between the brain Fos immunoreactivity of rats exposed acutely to NMDA antagonists (phencyclidine, MK-801) versus chronically to methamphetamine, (iv) characterization of the effects of chronic methamphetamine or acute NMDA antagonist administration on the induction of the heat shock protein, HSP72, in these same brain regions, (v) assessment of time-dependent alterations in the dopamine overflow occurring in limbic cortex during the regimen of chronic methamphetamine administration, (vi) determination of the effects of injury to specific dopamine terminal fields ont he methamphetamine- or NMDA antagonist-induced pattern of Fos immunoreactivity, and (vii) identification of populations of Fos-immunoreactive neurons in chronic methamphetamine-treated animals, based on their axonal projections.

DESCRIPTION (provided by applicant): Although psychostimulant drug abuse poses several potential health risks, the chronic abuse of amphetamines carries the danger of permanent brain injury. In animals, repeated administration of methamphetamine during the course of a single day produces long lasting damage to striatal dopamine and forebrain serotonin terminals. In addition, this drug produces a degeneration of pyramidal and stellate cells in the rat somatosensory cortex. Moreover, the degeneration of somatosensory cortical neurons appears to represent only the most visible form of methamphetamine's long term deleterious effects on cerebral cortex. Recent findings indicate that exposure to methamphetamine in animals reduces the immediate early gene responses of neurons in widespread cortical areas to dopaminergic agents, even long after the methamphetamine exposure. These findings agree with results from human methamphetamine abusers, indicating long lasting functional abnormalities in the cerebral cortex of abstinent addicts. The mechanisms underlying the long term suppression of cortical cell response are of particular interest because prior research concerning long term effects of methamphetamine has focused almost exclusively on mechanisms of injury to dopamine and serotonin terminals. The hypothesis underlying this application is that the long term reductions in cortical immediate early gene response of animals given methamphetamine relate to diminished basal ganglia gating of cortical function. Four specific aims are proposed to test this hypothesis: (i) to test the role of dopamine D1 and D2 receptors in the methamphetamine induced reductions in basal ganglia gating of cortical function; (ii) to establish the role of the striatum in the actions of dopamine in gating of cortical function; (iii) to determine whether methamphetamine affects the density or function of G proteins that couple dopamine with specific second messengers; and (iv) to investigate the effects of methamphetamine on signal transduction pathways leading to reduced cortical function. In aggregate, these experiments should provide a body of novel evidence concerning how methamphetamine addiction can alter cortical functions.

[unreadable] DESCRIPTION (provided by applicant): Relapse into drug-taking among abstinent addicts represents the major obstacle to successful long-term treatment of addiction. Exposure to people, places and objects associated with their drug-taking often precipitates renewed substance abuse. Human and animal research indicates exposure to drug-associated cues activates a set of interconnected brain regions (accumbens area, prefrontal cortex, amygdala) and elicits strong craving. Research from the investigator's laboratory has identified the specific neuron populations of this circuit that show increased gene expression when rodents seek drugs as a result of being exposed to contextual cues previously paired with cocaine delivery. More recently, the principal investigator has demonstrated that the long-term memory for such cues that predict cocaine delivery depends upon the extracellular signal-regulated kinase (ERK) pathway of the accumbens. Inhibitors of this ERK pathway (i.e., MEK inhibitors) infused into the core of the nucleus accumbens of animals immediately after they recall the cocaine-cue memory interfere with the reconsolidation of the cocaine-cue memory, such that animals show no preference for cocaine- associated contextual cues for at least two weeks after memory reactivation. The project's long-term objective is to characterize the role of the ERK signaling pathway in the accumbens-prefrontal cortex- amygdala circuit during reconsolidation of drug-cue memories. Four specific aims will provide novel information relevant to this objective: (1) to characterize more fully the ability of MEK inhibitors to block reconsolidation of memories for cocaine-paired contexts, (2) to investigate whether interference with the ERK pathway in the amygdala and prefrontal cortical regions has a similar effect on cocaine- cue memories as does accumbens inhibition, (3) to identify the specific cell populations in these brain regions expressing activated ERK during recall of cocaine-related memories, and (4) to investigate the contribution of dopamine and glutamate transmitter receptors, and of receptor tyrosine kinase transactivation, in cue-elicited activation of the accumbens ERK pathway. Relevance. A greater understanding of the neurobiology of reconsolidation of drug-cue memories holds the potential to provide new avenues for preventing relapse into substance abuse among the addicted population. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Methamphetamine (mAMPH) abusers experience several long-term changes in their brains, including abnormalities in basal ganglia dopamine and cortical structure/function, as detected by neural imaging methods. Also, mAMPH abusers perform less well than controls on several measures of cognitive function, including recognition memory and executive functions. Together, these mAMPH-induced brain structural, neurochemical, and cognitive changes may predispose abusers to failure in escaping their compulsive drug use. These mAMPH-induced changes have been modeled in rodents exposed repeatedly to moderate doses of mAMPH in a binge pattern, producing long-lasting injury to brain monoamine pathways, diminished cortical function, and impairments in memory and executive function that are strikingly similar to impairments of human mAMPH abusers. Notably, in both humans and rodents, mAMPH-induced damage slowly recovers toward normal values. The current application examines the influence of voluntary exercise in counteracting mAMPH-induced injury and behavioral impairments in rats. Exercise induces long-term brain changes of potential therapeutic value in treatment after neural injury, and voluntary wheel running has been shown by the applicant to counteract the monoaminergic damage induced by binge mAMPH. Here we hypothesize that the angiogenesis stimulated by chronic exercise may promote a neural environment that can either diminish the initial damage cause by mAMPH treatment or accelerate regrowth and plasticity of the damaged monoamine fibers thus producing behavioral recovery. In three specific aims, this application tests a role for voluntar exercise mitigating mAMPH-induced neurochemical and behavioral deficits. First, we propose a time course experiment to determine whether exercise acts as an initial neuroprotectant or enhances recovery after mAMPH-induced neural injury. Second, we propose to determine whether mAMPH-induced cognitive deficits are long-lasting, whether they recover over time in parallel with normalization of monoaminergic markers, and whether wheel running accelerates their recovery. Third, we will examine the effects of both exercise and binge mAMPH administration on the levels of the angiogenic growth factor vascular endothelial growth factor (VEGF) and its primary angiogenic receptor as a possible signaling pathway mediating the beneficial effects of exercise on recovery from mAMPH-induced damage. In addition, we will investigate the ability of exercise in control and mAMPH-treated animals to increase striatal, cortical and hippocampal neurovascular density and whether these increases in vascularization are necessary for exercise-induced amelioration of mAMPH-induced damage and cognitive changes. We anticipate that the results of these experiments, when taken together, will provide the basis for a novel avenue of therapy for mAMPH addiction that can be rapidly translated to use in humans.