Gary L. Wenk - US grants

This research program is directed towards an understanding of the neurochemical and behavioral correlates of the decline in cognition and memory with age and in Alzheimer's Disease (AD). The ultimate goal is the development of preventative or ameliorative treatments for this decline. The investigations focus on age-associated changes in the rat nucleus basalis magnocellularis (NBM), an area analogous to the nucleus basalis of Meynert in humans. During normal aging and in AD the brain develops a complicated pattern of degenerative changes including, but not limited to, the loss of specific neural systems that underlie the normal mechanisms associated with memory. The loss of cells in the nucleus basalis of Meynert may be responsible for this memory impairment. The nature of the selection process that leads to the degeneration of cells within the NBM is unknown, although endogenous excitatory amino acids have been implicated. In addition, the identity of the cell, or cells, in this nucleus whose degeneration leads to the development of the memory impairment, is also unknown. The assumption has been that the loss of cholinergic cells is sufficient to produce the memory deficit. Previous research from this laboratory has raised significant doubt about the validity of this assumption. However, the NBM region contains many noncholinergic neurotransmitter systems and their role in age- and dementia-associated memory deficits has not been investigated. This project addresses the following hypothesis related to the mechanisms of NBM neuronal cell death associated with aging: if neurons in the NBM demonstrate an age-related differential vulnerability to excitatory amino acid neurotoxins, such as 2-amino-3-hydroxy-5-methylisoxazole-4- proprionicacid (AMPA) or N-methyl-d-aspartate (NMDA), then these neurotoxins should produce differential behavioral and biochemical consequences in young, adult and old rats. This hypothesis will be tested by producing lesions within the basal forebrain of rats; studying the behavioral changes that develop; examining the histological and biochemical changes in the brain following the lesions; and correlating the changes in specific neuronal markers with performance in the behavioral tasks. These experiments have significant implications for our understanding of the differential vulnerability of specific NBM neurons with aging.

Rett Syndrome (RS) is a neurodevelopmental disorder affecting almost exclusively female children with an incidence rate of approximately one in 1O,OO-15,OOO live births. Its most characteristic clinical manifestations are severe developmental and cognitive deterioration, sterotypic movements, irregular respiration, autistic behavior and seizures. Neurochemical evaluations have demonstrated a decrease in cholinergic function in cortical and subcortical regions that may underlie some of these symptoms. The goal of this proposal is to investigate the neural mechanisms responsible for this impaired cholinergic function. The elucidation of these mechanisms will provide information that is central to our understanding of the neurobiology of RS. The results will lay the foundation for the development of an entirely new approach to the study of RS and will determine whether the underlying problem in RS is one of neuronal apoptosis or impaired trophic factor function. The proposed biochemical studies will provide important information on regional levels of trophic factors in the brains of RS cases and female controls. The chronic lack of this trophic-factor, and possibly others, would have an enormous impact upon the normal function (and possibly development) of forebrain cholinergic neurons in the RS brain. The proposed histological studies will investigate for evidence of programmed cell death. In addition, these studies will provide quantitative information on the functional integrity of the acetylcholinergic neurons located within the brain of RS girls. The successful completion of these studies will provide fundamental insights into the neurological bases for the decline in cognitive function seen in RS. In addition, a better understanding of the neurochemical and pathological changes that underlie changes in this neural system, and how these changes underlie the specific clinical symptoms associated with RS, may lead to improved diagnostic and/or therapeutic approaches.

DESCRIPTION (provided by applicant): An important questions in research on Alzheimer's Disease (AD) is to define why specific brain regions and neural systems are affected with the progression of the symptoms of dementia and to determine what mechanisms will slow the progression of these processes. This proposal is a continuation of my previous studies aimed at understanding the role of neuro-inflammation in the degeneration of the AD brain. The degeneration or dysfunction of the temporal lobe and forebrain cholinergic neurons are responsible for aspects of the dementia associated with AD and my preliminary studies indicate that temporal lobe and basal forebrain acetylcholine neurons are selectively vulnerable to the neurotoxic effects of chronic neuroinflammation. The current series of studies will examine the effects of chronic neuroinflammation within the brain of four different types of mice: 1) non-transgenic control mice, or transgenic mice that express either, 2) the Swedish mutant amyloid precursor protein, APP (Tg2576; K670N/M671L; Hsiao, et al., 1996), 3) the mutant presenilin type1 (PS1 line 5.1; M146L; Duff, et al, 1996) gene or, 4) both genes simultaneously. The Alzheimer's-like phenotype present in these mice has already been well characterized. The proposed specific aims will test the overall hypothesis that inflammatory proteins influence the pathophysiological processes that underlie the degeneration of neurons in brains of people with AD. I further predict that the extent of pathology induced by the chronic neuroinflammation will be exacerbated in the combined presence of the Beta-amyloid and PS1 mutations. In the present proposal, the biochemical, pathological and behavioral consequences of chronic neuroinflammation produced by the infusion of Iipopolysaccharide (LPS). LPS is a component of the cell wall of gram-negative bacteria and has been used experimentally to stimulate the production of the endogenous cytokines and other inflammatory proteins. Our preliminary studies using LPS infusion into the 4th ventricle, found that the greatest inflammatory response was contained within the basal forebrain, hippocampus, particularly the dentate gyrus, as well as within the entorhinal and piriforin cortexes. The proposed studies will explore the hypothesis that inflammatory processes are involved in the initial stages of cellular and molecular dysfunction that may alter cellular vulnerability and that these changes may in turn lead to cell death and cognitive impairments. In addition, these studies will investigate whether there is an age-associated increase in the vulnerability to these processes. Finally, because the cascade of biochemical processes that leads to neuronal degeneration may involve the production of prostaglandins the proposed studies will also investigate whether it is possible to antagonize these processes and provide neuroprotection. Once accomplished, the research will significantly enhance our understanding of the role of inflammation in neurodegeneration in the AD brain and will greatly improve my ability to reproduce, and then manipulate with potential pharmacotherapies, important steps in the degeneration of neurons in the brain of AD patients.

DESCRIPTION (provided by applicant): The overall goal of this project is to define the glia phenotype that promotes the establishment of neurodegenerative disease states. The proposed experiments will establish a detailed understanding of age-related changes in glial activation states and how they are influenced by a neuroinflammatory stimulus. The primary focus of these studies is the interaction of microglia with neurons. Cross-talk among brain cells may be key for the understanding of inflammatory mechanisms involved in pathogenesis of neurodegenerative diseases. Subtle micro-environmental alterations can induce microglia to react rapidly, change morphology and acquire an array of functions, including phagocytosis and the secretion of inflammatory molecules. The consequences of this activation must be tightly regulated because both inadequate and excessive responses can result in pathological consequences. The balance of these processes, operating across a time scale of decades, are carefully orchestrated and regulated until, due to normal aging, there is a gradual shift to a non-equilibrium state that is permissive for neurodegenerative processes. Aim 1 will determine the time course and regional changes in phenotype profile of the microglial activation associated with normal aging or the intraventricular infusion of LPS using a series of markers that discriminate pro- or anti-inflammatory microglia states. Aim 2 will investigate three specific mechanisms by which neurons regulate the microglial cytokine profile, the response of these mechanisms to challenge by LPS and how they are altered by normal aging. Aim 3 will examine the ability of caffeine to restore cytokine balance and promote an anti-inflammatory cytokine profile in young and aged male rats and improve spatial memory. Aim 4 will investigate the consequences of inflammation-induced alterations in NMDA-type glutamate receptor- dependent calcium ion signaling. We hypothesize that the pattern of these changes, and the degenerative changes that subsequently develop, may be due to regional variations in the micro-environment that are a direct consequence of the ability of activated microglia or injured neurons to release pro- and anti-inflammatory molecules in response to their age and ability to communicate with neurons.

DESCRIPTION (provided by applicant): The overall goal of this project is to determine the pathological consequences of chronic neuroinflammation associated with normal aging or enhanced by the infusion of lipopolysaccharide (LPS) upon ascending aminergic and cholinergic neurons within the brainstem of rats. A pro-inflammatory state has been described in the brains of patients with Alzheimer's disease, viral encephalitis, multiple sclerosis, AIDS and Parkinson's disease. The principle hypothesis of the current proposal is that the consequences of chronic neuroinflammation also underlie numerous other age-related degenerative diseases that involve the dopamine neurons in the SN, norepinephrine neurons in the LC, serotonergic neurons in the RN and the acetylcholine neurons in the LPT. The current proposal is designed to advance our understanding of the selective vulnerability of these brainstem regions to conditions that characterize age-associated disorders of these neural systems. The proposed studies are based upon the hypothesis that a major underlying problem in the age-associated loss of these neurons is the inflammation-induced elevation in extracellular glutamate and action of glutamate at NMDA channels. Clinical benefits would be achieved if one could modify the ability of glutamate to injure or destroy vulnerable neural systems. These studies will provide evidence that targeting the regulation of glutamate release or its actions within the synapse or calcium channels may produce clinical benefit for acute and chronic neurodegenerative disorders attributable to or exacerbated by brain inflammation. Aim 1 will determine the time course and regional changes pro-inflammatory biomarkers and pathology. Aim 2 will investigate the role of glutamate in the inflammation-induced degeneration of neurons within these brainstem nuclei. Aim 3 will monitor second-by-second changes in extracellular glutamate levels within the discrete nuclei of the ascending systems following infusion of LPS into the 4th ventricle of young, adult and aged rats;these changes will be related to the degree of pathology expressed by each aminergic brainstem nuclei. PUBLIC HEALTH RELEVANCE: A pro-inflammatory state has been described in the brains of patients with Alzheimer's disease, viral encephalitis, multiple sclerosis, AIDS, and Parkinson's disease. The principle hypothesis of the current proposal is that the consequences of chronic neuroinflammation underlie the progression of these age-related degenerative diseases. The experiments proposed will investigate the consequences of long term brain inflammation on specific nuclei that are critical for normal cognitive processes, particularly those that fail with normal aging. In addition, these experiments will investigate potential ways to reverse the effects of the inflammation.