Functional Therapeutics in Neurology:  Oxidative Stress and the Nervous System

Catherine Willner, MD
Neurology and Pain Management (Board Certified)

The focus of this discussion is the role of oxidative stress and how it impacts neurological functioning in ways sometimes unique to the human nervous system.  It is important to understand initially some of the ways in which the nervous system is different from other organ systems in the body and the extent to which its failure to function can be a devastating consequence both to the individual and to society.  The cells and tissues of the human nervous system share many features in common with all other cellular structures in the body.  In this sense, all principles of functional medicine can be applied in situations where the predominant problem faced by a clinician seems to be one that is neurological.  In fact, it would be the most appropriate application of the principles of functional medicine to optimize functioning before a specific disease related to genomic or environmental risk can be identified.  However, getting to that ideal requires understanding the nervous system in terms of unique biochemistry, physiology and pathological states that sometimes set it apart from other systems and these issues deserve attention as we navigate the web of interconnectedness to apply the principles of functional medicine. Functional medicine approaches the nervous system as one part of a web of interconnectedness of all bodily systems and functions and assesses how to optimize processes that permit healthy functioning of the whole organism.  Functional neurology considers this web as it impacts the ability of the nervous system to perform optimally in all of its functions.  It is sometimes a struggle to make the leap between traditional neurology and these paradigms.  But it is also a very exciting challenge.  We will look briefly at some aspects of traditional neurological assessment, then explore the unique characteristics of the nervous system as they are impacted by oxidative stress.  The final sections of this monograph will deal with some specifics of the application of these principles to functional neurology.
Neurologists are taught very precisely to label in space (anatomy), function (physiology and pathology), time (pathophysiology of acute, subacute and chronic) and to consider genetics and the environment, though we are traditionally taught little in terms of how to impact the latter two.  For example, those disorders that we recognize as being impacted by environmental influences are often considered as irreversible or too delayed to alter when they result from certain toxic exposures or severe deficiencies.  More emphasis in traditional neurology is placed on naming and managing than on prevention or optimization of function or risk assessment. There are, of course, exceptions, such as disorders associated with B12 deficiencies, or metabolic changes that occur with acute or chronic alcohol exposure, or the cognitive and other neurological changes associated with altered thyroid status.  We are traditionally taught that these can be, at least in part, reversed by treatment if they are recognized early and their recognition is a core aspect in traditional neurological training.  However, in many circumstances, by the time these disorders have actually resulted in diagnosable conditions involving the nervous system, the damage is quite severe.  We are only beginning to respect the more subtle aspects of metabolic dysfunction or applying methods to assess early failure in the system.  For example, consider the longstanding awareness of neural tube defects, but the delay in appreciating other dysfunctions which can be reflected in dysfunction of the folate cycle and homocysteine metabolism.
Also quite traditional in neurological assessment is understanding of the temporal sequence of pathophysiological events, which is often useful in attempting to arrive at diagnostic considerations.  As such, acute events, those that occur suddenly, like stroke, migraine or seizure, are different than the subacute (infection, demyelinating disorders like multiple sclerosis) or the chronic progressive disorders that involve cognition and memory (dementias), movement or other bodily functions, usually considered the “system disorders” like Parkinsonism, cerebellar disorders, autonomic failure, peripheral neuropathies, and the combinations (multisystem diseases or atrophy).  Those disorders that cause progressive loss of the functions of the nervous system have been traditionally labeled as

Table 1: Neurodegenerative Disorders (traditional ones)

Dementias (Alzheimer’s, Pick’s, Lewy Body disorders)
Idiopathic Parkinson’s Disease
Parkinson Plus Syndromes (dementia, the most frequent)
Cerebellar degeneration (olivopontocerebellar atrophy)
Shy-Drager syndrome (autonomic failure)
Progressive supranuclear palsy
Motor neuron disorders (ALS)
Hereditary peripheral neuropathies

neurodegenerative.  We have struggled to name them by the tools that we use in classification (anatomy, physiology and pathophysiology) with consideration of both the genome and the environment.  A list of some of these traditional diagnoses of the chronically progressive disorders appears in Table 1.  Precisely because we are living longer as a population, and because our population is aging as a whole, many people are surviving longer with these diagnoses which impact the quality of life and extract a large economic burden on our society.  However, it is important to take into consideration that the other disorders, not specifically considered neurodegenerative, also are costly to manage.  For example, the toll in terms of work attendance, activities of daily living, and pain and suffering, caused by migraine alone is quite high.1  The availability of progressively more expensive pharmaceuticals to treat this disorder has not completely, at least in any satisfactory way, solved this problem.  And, as with almost every other traditionally labeled “neurological disease” or disorder, prevention of stroke, migraine, epilepsy, multiple sclerosis, peripheral neuropathy, the dementias and the degenerative system disorders should be as much or more of a focus than their management.  And oxidative stress plays a role in every one of these disorders.  We will first deal with some of the unique features of the nervous system related to its structure and function.

Function and Structure: The Nervous System
Probably the most important task performed by the nervous system in a general sense is communication which permits coordination of adaptive responses both within the brain and throughout the entire organism.  This permits, for example, awareness (perception) of both internal and external environments, and performance and the adjustment or fine tuning that can occur fairly rapidly because of the unique features of that communication.  Though such processes are present in most other organ systems, the nervous system is unique because of the rapidity with which it can alter function in these very systems and also because of the distances that can be involved from the origin of signals.  It is also unique because it permits awareness of, and interaction with the environment (consciousness, memory, cognition). This system of communication requires electrical potentials as well as chemical interactions from neurotransmitters or substances more traditionally considered hormonal.  And, the nervous system allows us to perceive and to react both at a conscious level and in the sense of autonomic activity, without the requirement of conscious awareness.  When one actually attempts to discuss this system in depth, the concept of neuroendocrinology becomes apparent.
With respect to anatomy and physiology, there are several unique features of the nervous system that warrant consideration.  Some of the more obvious are as follows, though they are not discussed in any rank order of importance.  First of all, the nervous system has unique energy requirements that include fairly consistent access to oxygen and to glucose, though other carbon-based fuels can be accommodated.  It is a demanding metabolic environment with high energy requirements partly because of the generalized need to maintain electrochemical gradients to allow generation of action potentials appropriately and to allow receptors to function normally.  Mitochondrial function, as the source of this energy, is key to optimization of function.  Second is the method of communication at synapses by transmitters and receptors, which requires continuous recycling of both the chemicals and their receptors involved in this process.  This requires a normally functioning genome as well as access to substrate to make the enzymes, the transmitters and the receptors.  Third, maintenance of membrane structure system is paramount to normal performance of neurons and the surrounding complex cellular system of glial cells. Discussion of their complex functions is beyond our scope, but one of the major functions is to provide insulation by forming myelin which permits electrical activity that is sequestered to travel appropriately to the correct destination at speeds in the range of 100 m/s.  Because of the need for insulation related to such highly complex communications between cells (both in the brain and at a distance, through the fiber tracts and peripheral nervous system), the concentration of lipid is unique and high, both as cell membrane components and in the myelin which insulates axons, the processes sent out by cells to accomplish this communication. The relatively high content of polyunsaturated fatty acid (PUFA) places the brain at significant risk for lipid peroxidation secondary to free radical damage. Fourth, when considering neurological uniqueness, it is important to remember that the neurons are, for the most part, postmitotic tissues.  Though potential for regeneration (especially in the periphery) and plasticity of surviving neurons is one of the strong points of the system, the limited ability of the nervous system to regenerate or replace damaged cells does have serious consequences.  Fifth, certain regions of the brain, specifically the substantia nigra and the striatum, have very high concentrations of iron which also increases risk of peroxidation.  Finally, though less unique, the nervous system is relatively segregated from the rest of the body - from the blood stream by the blood brain and blood nerve barriers, and this portends a separate source for immunological protection and defense, mostly provided in the CNS by the glial cells.  When the system fails, the consequences can be devastating.  Neuroimmunology is a very complicated and fascinating subject which we will not be covering in this monograph.  The gut, with its unique role of interaction with the external environment has similar types of barriers and unique defenses and many of the same principles of functional medicine can be applied.

Table 2: The Nervous System – Unique Features

High Energy Requirements, Mitochondrial Dependence
High Metabolic Turnover, Excitatory Transmitters
Post-mitotic State
High Lipid Content (specialized membranes, PUFA)
Transmembrane Electrochemical Gradient
Region specific mineral concentration (Fe)
Sequestration (BBB / BNB / myelin)

The list of these features discussed above is presented in Table 2.  Now, let’s consider some of the consequences of these features and how functional neurology might approach the task of enhancing or protecting these functions in the setting of dysfunction, where the nervous system might be vulnerable. The specific focus will be on oxidative stress the consequence of free radical damage and the link to neurotoxicity and apoptosis or cell death.

NEUROLOGICAL VULNERABILITY: Oxidative Dependence, Free Radical Stress
The nervous system with its high metabolic requirements, uses about 20% of the oxygen provided from ventilation.  Oxygen and oxygen species are used in the body for several different functions including the role in the respiratory chain in energy production as ATP is manufactured by alteration of carbon bonds to form water and carbon dioxide.  Oxidation also plays a role in defense related to destruction of damaged or foreign substances by free radical attack. There are elaborate mechanisms of protection for the brain and body, related to free radical damage: enzymes such as SOD (superoxide dismutase – requiring Zn, Cu, Mn), glutathione peroxidase (requiring Se), and catalase (requiring Fe); dietary antioxidants (Vitamins C, E, among others); and endogenous antioxidants (coenzyme Q10, carnitine, lipoic acid).  But as will be discussed below, free radical formation is a necessary and essential function of these systems.  It is when the system is not balanced, that function fails.  There are risks in this setting that are both genetic and environmental.  The genetic risks of one of the chronic disorders, Parkinsonism, are well discussed in a recent review.2 And, in both acute and chronic disorders there exist evidence-based hypotheses that both energy metabolism deficits and glutamate-mediated excitatory transmitter dysfunction may be causative and integral to these processes and related to damage by reactive oxygen and nitrogen species.
The Basics of Oxidative Stress and Neuronal Function
Mitochondrial function and the respiratory chain provide the mechanism for production of energy through the formation of high-energy phosphate bonds.  This system is a complex one consisting of membrane, enzymes, cofactors and substrates and the cellular organelles that perform this function are the mitochondria, which are maternally inherited and contain their own DNA (mitochondrial or mtDNA).  A schematic of the system is presented in Figure 1.  Getting down to absolute basics, in the neurons, like every other cell in the body that utilizes carbon based atoms and oxygen to produce energy, this complicated system is necessary to maintain cell function.  In addition to providing the energy necessary to produce enzymes or neurotransmitters, or structural components for the cell, including complex receptors, one of the most important functions which is maintained in cells of the nervous system is an electrochemical gradient or membrane potential, which is unique for cell systems that can generate an “action potential” or other electrical charge which is the basis for the rapid fire communication possible in the nervous system.  As mentioned above, the necessity to provide insulation or sequestration in this system is supported by the formation of myelin, which is a complicated lipid structure produced by glial cells in the central nervous system and by Schwann cells in the periphery.  These “supporting cells” including the glia perform many other protective functions as well by processing or storing many of the neurotransmitters in the system when they are not acting at receptors.  Obviously, energy is required to accomplish all of these tasks.  It seems obvious that when the mitochondria fail to produce adequate energy, the result will be suboptimal function at many levels in the cell, and hence the system in general.  However, in addition to the impact that might be caused by inadequate energy availability for normal functioning, there is also the risk posed by the process of extracting such energy in the first place.

Table 2 Free Radical Targets

Lipid Cell Membranes
Cell Receptor Complexes
Structural Proteins (neurofilaments)
Mitochondrial buffering*
Viruses, bacteria*

*Normal functions
The work of producing energy via the mitochondria has a price that includes generating free radicals and other products that have to be handled by the system.  The free radicals are dangerous to many targets, especially the mitochondrial DNA itself but also to lipid laden membranes (which are especially available in the nervous system) but the generation of free radicals is required by the mitochondrial system or the system cannot function.  Free radical damage might either imply impaired function of the mitochondria, or it might be the consequence of too high a demand on the system in the absence of the complement of metabolic factors necessary for the system to function.  The general concept is described as “oxidative stress.”  A list of common targets for free radical damage is presented in Table 2.  Typical sources of oxygen radicals are depicted in Figure 2.

The generally recognized diseases associated with mitochondrial disorders, which were traditionally referred to as “mitochondrial encephalomyopathies” are now more commonly called “mitochondrial cytopathies” to emphasize the multisystem nature of the dysfunction. The most common of these are summarized in Table 3.  There are disorders now known to be associated with defects in each of the five complexes classically described within the mitochondria.  Though most of the proteins and subunits of the mitochondria are actually encoded by nuclear DNA, there are 13 critical polypeptide subunits of the electron transport complexes which are formed by mitochondrial DNA.3  The actual mitochondrial dysfunction can be anything from a specific point mutation in mitochondrial DNA to large scale deletions or duplications.  The inheritance is variable from maternal, both dominant and recessive, to acquired or sporadic mutations.  Many changes in function that occur with aging are usually hypothesized to be related to the consequences of oxidative stress or various toxic insults, to which the mitochondria seem to be particularly predisposed because of their relative absence of DNA-repairing enzymes.4
The heterogeneity of these disorders is related to the specific dysfunction but the major organ systems involved are those that are most dependent on oxidative metabolism, hence the brain, and muscle (skeletal and heart) are the most frequently affected, though other tissues like the kidney and liver are also clearly at risk.  The abnormality most often discussed in the skeletal muscle is the development of mitochondrial proliferation with abnormal morphology (which along with patchy atrophy gives the appearance of “ragged red” fibers on trichrome staining.  Interestingly these changes are not seen frequently with nuclear DNA changes but are quite common with disorders produced by abnormalities of the mitochondrial DNA.

Table 3 Mitochondrial Disorders

Kearns-Sayre syndrome (ophthalmoplegia, retinal pigmentation, conduction block, dementia)
LHON (Leber’s hereditary optic neuropathy - subacute blindness in young adult)
MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes)
MERRF (myoclonic epilepsy, ragged red fibers)
CPEO (chronic progressive external ophthalmoplegia)
Pearson’s syndrome (sideroblastic anemia, pancreatic dysfunction, death in infancy)
NARP (neuropathy, ataxia, retinitis pigmentosa syndrome)
Maternally inherited myopathy with cardiomyopathy (spares the CNS)

MPTP Induced Parkinsonism as a Model – The Mitochondrial Link

In neurology, the most widely known model that resulted in elucidation of at least some of the hypothesis about the role of mitochondrial dysfunction in the neurodegenerative disorders is that of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) - induced Parkinsonism.  MPTP is an analog of meperidine (a synthetic narcotic). This model serves as a classic example to explain a link between the failure of oxidative metabolism in the mitochondria and metabolite mediated neurotoxicity.  The model of MPTP toxicity is detailed in Figure 3 and the hypothesis about excitatory receptor activation that links this to cell destruction, discussed in further detail below, is presented in Figure 4.  As a direct outgrowth of understanding this model, investigations have led to the delineation of similar pathology in the so-called “idiopathic” disorders involving degeneration of the nervous system.  There has been evidence identified for low complex I activity found in brain, muscle, and platelets of patients with idiopathic Parkinson’s disease.5  Low complex IV activity has been reported in patients with Alzheimer’s disease.6  And importantly, several mitochondrial DNA deletions and point mutations have been reported in both Parkinson’s and Alzheimer’s tissues, supporting the hypothesis that failure of oxidative phosphorylation is important as an etiology for the neurodegenerative disorders.  In addition to specific disorders of mitochondrial function, there is also evidence that those enzyme systems providing protection from free radicals can be identified as abnormal in certain familial disorders.  Mutations of the gene of cytosolic copper-zinc superoxide dismutase (SOD1) was discovered in patients with familial ALS (amyotrophic lateral sclerosis) and identified as causative in approximately 20% of all the cases of familial ALS, making it therefore responsible for about 1-2 % of all cases of ALS.7
These are some of the many examples of disorders of the nervous system which relate to dysfunction of the mitochondria in general, but the significance is amplified exponentially when the system to accommodate generation of free radicals fails, which will be discussed briefly below.  The major producer of such unstable intermediate products is the mitochondrial electron transport chain.  It is estimated that 2-4% of the oxygen used by mitochondria is for the generation of free radical species.  Studies have suggested that oxidative damage to mitochondrial DNA might be as much as 10 times higher than damage to nuclear DNA.8   Progressive damage to mitochondrial DNA is part of this process and this probably contributes to aging because of progressive dysfunction of oxidative metabolism.   In aging mitochondria, there is evidence for lowered electron transport complex activity and large mitochondrial deletions are increased in tissues of older individuals.8  Interestingly these findings are identified in normal aging hearts but there is evidence for specifically common deletions that occur with aging, found to be even more prominent in hearts that have suffered ischemic insults.  And, because of the unduplicated role of mitochondrial DNA in production of subcomplexes discussed above, the finding that mutations of mtDNA can be as much as 17 times higher than the rate of damage of nuclear DNA emphasizes the importance of providing mitochondrial support.9

Glutamate Excitotoxicity and Cell Dysfunction
The relevance of these findings to progressive degenerative disorders of the nervous system requires an understanding of the consequences of disrupted oxidative metabolism.  Recall that one reason that the nervous system has such high energy demands is the need to maintain electrochemical gradients across the cell membrane.  In the absence of adequate energy or substrate to maintain this potential energy barrier, there are alterations in cell membrane receptors.  The most well understood actors in this story are the excitatory amino acids, (EAA’s).  Glutamate, probably the most abundant free amino acid in the central nervous system, is one of the excitatory amino acid neurotransmitters. Though the majority of glutamate is actually housed within the neuronal storage vesicles, there are high quantities in the extracellular space. The other major excitatory substance is aspartate.  Analogous to the double-edged sword of mitochondrial respiratory chain free radical production, these EAA neurotransmitters are paramount to the brain’s plasiticity of function.  However, in excess, they are toxic to neurons.  There are two major receptor types for glutamate, ionotropic and metabotropic.  Ionotropic receptors are grouped into two major subtypes: NMDA (N-methyl-D-aspartate) and non-NMDA receptors (the AMPA-kainate receptor).  The metabotropic receptor is coupled to cyclic GMP and modulates production of intracelluar messengers which also influences the ionotropic glutamate receptors.  Under normal circumstances, when adequate energy and cell function permit the electrochemical gradiant to maintain a normal membrane potential, the NMDA receptor is blocked by magnesium.  Loss of the gradient results in loss of the magnesium ion blocking the NMDA receptor, which when activated by glutamate, results in influx of calcium into the neuron. Under normal circumstances, this reaction is self limiting.  In models of neurotoxicity, there is an escalating cascade of damage leading to cell death.
This same scenerio of excitatory neurotoxicity is postulated in the mechanism of ischemic and hypoxic damage as seen with stroke or hemorrhage.  In this setting, rather than a clear cut loss of energy and change in gradient potential, altering the receptor for glutamate, it is suspected that there might actually be increases in the amount of glutamate because of failure of the surround to modulate the substance.10  The consequence is overactivation of the receptor due to excess amounts of glutamate, then ultimately cell failure secondary to the same processes discussed above related to primary gradient potential failure.  Both sodium and calcium are increased intracellularly in this setting.  
Exogenous glutamate receptor agonists are known to produce neurotoxicity.  One of the best understood models comes from clinical insight about lathyrism which results from an AMPA glutamate receptor agonist found in the foods (chick peas) known to be associated with this condition, which produces a clinical syndrome similar or mimicking ALS predominantly with upper motor neuron changes.  Glutamate, once the receptor cell is activated, is normally recycled by active transport back into glial cells or is it to some extent sequestered in neurons.  Its elevation extracellularly can cause continued reactivation of the both NMDA and non-NMDA receptors which then allows increased levels of calcium to enter the neuron.  Calcium is normally buffered by intracellular buffering proteins, such as calbindin or parvalbumin, among others.  However, when the buffering capacity is exceeded, the excess calcium ions may catalyze activity in specific destructive enzymes that are not normally activated .  These include in the setting of ALS above, xanthine oxidase, nitric oxide synthase, and phospholipase, all of which produce free radicals, including reactive oxygen and also reactive nitrogen species.11
Sustained elevation of calcium in particular is thought to initiate toxic consequences including activation of catabolic enzymes such as proteases, phospholipases, and endonucleases which will damage enzymes, membranes and DNA.12  ¬These can be rapidly lethal.  High intracellular calcium also leads to uncoupling of the mitochondrial reactions which results in further production of free radicals as well as energy failure.  Other activations including initiation of protein kinase and lipid kinase cascades, which include for example, activation of calcium calmodulin kinase (CaMK) and other kinases will modify the function of ion channels, including the NMDA and AMPA/kainate receptors.13  And, high intracellular calcium leads to formation of free radicals by several other mechanisms including calcium dependent activation of phospholipase A2 which liberates arachidonic acid which then leads to further free radical production and lipid peroxidation.  
Glutamate Excitotoxicity and Free Radical Production: The Feed Forward Loop
During normal cell function,  stimulation of the NMDA receptors leads to activation of nitric oxide synthase (NOS) with release of nitric oxide which occurs as L-arginine is oxidized to citrulline by NOS.  This is a short lived reaction and self limiting under normal circumstances.  Nitric oxide is a potent vasodilator and is a free radical species itself but it is not thought to cause severe damage in normal physiology, and as seen with other reactions, its normal role in metabolism is necessary for health.  Once increased excitotoxicity leads to calcium altered enzyme systems and free radical generation, there is damage of all the cell components mentioned in our opening discussion.  Superoxide (O2-) produced by xanthine oxidase, and nitric oxide (NO) produced by NO synthase react to form peroxynitrite (ONOO-), one of the most potent reactive nitrogen species which causes nitration of intracelluar proteins containing tyrosine.14  These changes result in further damage to structural and enzyme proteins.  The changes also increase the demand on the mitochondria which further upregulate but cannot adequately counter the production of their own free radicals which then results in more damage.  Peroxynitirite is also indicted in other reactions within neurons including DNA deamination, strand breaks, and damage to the mitochondrial complexes I, II and mitochhondrial aconitase.  Ultimately cell death occurs as a result of multiple system failures.
Because of the significant toxicity posed by peroxnitrite, a great deal of research is ongoing related to the potential roles for the nitric oxide and NOS systems as they might be pathological in the neurodegenerative disorders and possible candidates for manipulation to prevent this cascade of damage.  There are a number of disease models where induction of NOS is suspected as participating in the progression of pathology.  Such changes have been seen in the experimental model of multiple sclerosis (EAE, experiemental autoimmune encephalomyelitis) and are widely demonstrated in models of cerebral ischemia for stroke.  Aminoguanidine, an inhibitor of NOS, used in the model of EAE resulted in a dose dependent reduction of disease expression.15 Using the MPTP model, researchers have shown that pretreatment with an inhibitor of NOS (7-nitosindazole) prevented development of Parkinsonism and typical cognitive changes seen in this model in baboons exposed to MPTP.16   Application of NOS synthase inhibitors also provided protection in cortical neuron cell cultures against the toxic effect of beta-amyloid which is the altered protein structure known to be associated with the plaques of Alzheimer’s disease.18 It is also known that exposure of rat microglial cells in culture to beta-amyloid results in the release of nitric oxide especially in conditions of inflammatory upregulation.17  
Use of arginine analogs has been attempted to interfere with this NOS pathway, however, most of the substances studied are potent vasoconstrictors and as such, they interfere with normal function making clinical application elusive.14
Similar problems have been encountered in attempts to identify pharmacological substances that block the NMDA receptors.  Though in theory, this might be protective in many settings, including acute brain injury or ischemia, or in situations of stress during surgeries, and some of the newer anticonvulsant type medications have some degree of NMDA blocking activity, when direct application of NMDA inhibitors has been attempted, significant problems with memory, learning and overall functioning have resulted. Clinical application has remained elusive for the most part.

Conclusions and Insights

The unique attributes of the nervous system discussed above, in combination with the complexities and “double-edged” sword of mitochondrial function, and generation of free radical species as part of normal  metabolic function lead to the recognition of a delicate balance that must be fostered to permit healthy human functioning.  But these insights also offer the opportunity to apply scientific evidence based principles to the optimization of these systems in an effort to minimize genetic and environmental risk which have resulted in a myriad of neurological disorders, from migraine to stroke to MS and to parkinsonism and dementia.

1.    Lipton R, Stewart W, Von Korff M. Burden of migraine: societal costs and therapeutic opportunities. Neurology 1997; 48 (suppl 3): S4–S9
2.    Mouradian MM. Recent advances in the genetics and pathogenesis of Parkinson disease. Neurology 2002; 58 (2): 179-185.
3.    DiMauro S, Moraes T. Mitochondrial encephalomyopathies. Arch Neurol 1993;50:1197-1208.
4.    Shigenaga MK, Hagen TM, Ames BN.  Oxidative damage and mitochondrial decay in aging.  Proc Natl Acad Sci 1994; 91 (23): 10771-10778.
5.    Janetzky B, et al. Unaltered aconitase activity, but decreased complex I activity in substantia nigra pars compacta of patients with Parkinson’s disease.  Neurosci Lett 1994; 169 (1-2) 126-128.
6.    Parker WD Jr, Parks JK, Filey CM. Cytochrome oxidase deficiency in Alzheimer’s disease. Neurol 1990; 40: 1302-1303.
7.    Rosen, DR. Mutations in Cu/Zn superoxide dismutase gene are associated with familial amyotrophic lateral sclerosis. Nature 1993; 362: 59-62.
8.    Mecocci P, et al. Oxidative damage to mitochondrial DNA shows marked age-dependent increases in human brain. Ann Neurol 1993; 34(4): 609-616.
9.    Wallace DC, et al. Sequence analysis of cDNA’s for the human and bovine ATP synthase beta unit: mitochondrial DNA genes sustain seventeen times more mutations.  Curr Genet 1987;12 (2): 81-90.
10.    Nicholls D, Atwell D. The release and uptake of excitatory amino acids.  Trends Pharmacol Sci 1990: 11: 462-468.
11.    Brown RH Jr. Superoxide dismutase and familial amyotrophic lateral sclerosis: new insights into mechanisms and treatments.  Ann Neurol 1996; 39: 145-146.
12.    Choi DW, Calcium: Still center-stage in hypoxic-ischemic neuronal death. Trends Neurosci.  1995; 18: 58-60.
13.    Smart TG. Regulation of excitatory and inhibitory neurotransmitter-gated ion channels by protein phosphorylation.  Curr. Opin. Neurobiol. 1997; 7: 358-367.
14.    Beckman JS. The double-edged role of nitric oxide in brain function and superoxide-mediated injury.  J Dev Physiol 1991; 15(1): 53-59.
15.    Cross AH, et al. Aminoguanidine, an inhibitor of inducible nitric oxide synthase, ameliorates experimental autoimmune encephalomyelitis in SJL mice.  J Clin Invest 1994; 93: 2684-2690.
16.    Hantraye  P, et al. Inhibition of neuronal nitric oxide synthase prevents MPTP-induced parkinsonism in baboons.  Nat Med 1996; 2(9): 1017-1021.
17.    Resink AM, Brahmbhatt HP, Cordell B, Dawson VL, Dawson DM. Nitric oxide mediates a component of B-amyloid neurotoxicity in cortical neuronal cell cultures.  Soc Neurosci Abstr 1995; 21: 1010.
18.    Goodwin JL, Uemura E, Cunnick JE.  Microglial release of nitric oxide by the synergistic action of beta-amyloid and IFN-gamma.  Bran Res 1995; 692: 207-214.

Applying Functional Medicine in Clinical Practice