Introduction to Neurotoxicology Introduction to the Health Effects of Chemicals Neurotoxicology Steven G. Gilbert, PhD, DABT & Non-Cancer Toxicology

A Small Dose of Toxicology Introduction to Neurotoxicology An adverse change in the chemistry, structure or function of the nervous system during development or at maturity, following exposure to a chemical or physical agent. What is Neurotoxicity

A Small Dose of Toxicology Introduction to Neurotoxicology Even minor changes in the structure or function of the nervous system may have profound consequences for neurological, behavioral, and related body functions. Nervous System Sensitivity

A Small Dose of Toxicology Introduction to Neurotoxicology  Interference with receptor-ligand interactions  Interference with membrane functions  Interference with cellular energy production  Binding to macromolecules  Perturbation of calcium regulation  Toxicity from selective cell loss  Non-lethal genetic alterations Are there general mechanisms?

A Small Dose of Toxicology Introduction to Neurotoxicology Rough Endoplasmic Reticulum Lysosomes Peroxisomes Mitochondria Membrane Protein NucleusGolgi Ribosomes Animal Cell

A Small Dose of Toxicology Introduction to Neurotoxicology Cell Lipid bilayer Channel Pump TransportProtein Hydrophilic head Hydrophobic tails Interference with Membrane Function

A Small Dose of Toxicology Introduction to Neurotoxicology  1930’s – Ginger-Jake Syndrome During prohibition, an alcohol beverage was contaminated with TOCP (triorthocresyl phosphate) causing paralysis in 5,000 with 20,000 to 100,000 affected.  1950’s – Mercury poisoning Methylmercury in fish cause death and sever nervous system damage in infants and adults. Historical Events

A Small Dose of Toxicology Introduction to Neurotoxicology Case Studies  Lead – damages developing brain  Alcohol – Fetal alcohol syndrome  MPTP – similar to Parkinson’s disease

A Small Dose of Toxicology Introduction to Neurotoxicology Alcohol (ethanol) C H H H OH Ethyl Alcohol C H H

A Small Dose of Toxicology Introduction to Neurotoxicology Vulnerability of Developing Nervous System FAS – Fetal Alcohol Syndrome FAE – Fetal Alcohol Effects What is a save level of consumption during pregnancy? Alcohol

A Small Dose of Toxicology Introduction to Neurotoxicology MPTP N CH 3 1-methyl-4-phenyl-1,2,3,6-tetrahydrophyridine

A Small Dose of Toxicology Introduction to Neurotoxicology 1980s – Designer Drug Caused effects similar to Parkinson’s disease Damaged neurons that secrete dopamine MPTP Effects

A Small Dose of Toxicology Introduction to Neurotoxicology MPTP – 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine: a contaminant in “synthetic heroin” Parkinson’s Disease-like symptoms in drug addicts Loss of neurons in the substantia nigra which synthesize and secrete dopamine MPTP-->MPP+ ---> oxidative stress MPTP

A Small Dose of Toxicology Introduction to Neurotoxicology MPTP – Real People

A Small Dose of Toxicology Introduction to Neurotoxicology PD Brain

A Small Dose of Toxicology Introduction to Neurotoxicology CNS – Central Nervous System PNS – Peripheral Nervous System Blood brain barrier Neuronal cells Neurotransmitters & receptors billion cells with connections Nervous System Biology

A Small Dose of Toxicology Introduction to Neurotoxicology Nervous System – CNS & PNS  Central Nervous System (CNS) Brain & Spinal Cord  Peripheral Nervous System (PNS) Afferent (sensory) Nerves – Carry sensory information to the CNS Efferent (motor) Nerves – Transmit information to muscles or glands

A Small Dose of Toxicology Introduction to Neurotoxicology Nervous System CNS Central Nervous System PNS Peripheral Nervous System AutonomicSomatic Sympathetic Parasympathetic

A Small Dose of Toxicology Introduction to Neurotoxicology Central Nervous System Central Nervous System (CNS) (Brain and Spinal Cord) Peripheral Nervous System (PNS) AutonomicSomatic Sympathetic Parasympathetic Afferent (sensory) Nerves (Carry sensory information to the CNS) Efferent (motor) Nerves (Transmit information to muscles or glands)

A Small Dose of Toxicology Introduction to Neurotoxicology Peripheral Nervous System  Peripheral Nervous System (PNS) Efferent (motor) Nerves – Transmit information to muscles or glands Somatic Nervous System Stimulates Skeletal muscles Autonomic Nervous System Stimulates Glands and Organs (e.g. heart) Sympathetic - Adrenergic – stress response Parasympathetic - Cholinergic – basic functions

A Small Dose of Toxicology Introduction to Neurotoxicology Cells of the Nervous System  Neurons Information conductors  Supporting Cells (Glia cells) Astrocytes (CNS – blood brain barrier) Oligodendrocytes (CNS – link cells) Schwann cells (PNS – wrap cells)

A Small Dose of Toxicology Introduction to Neurotoxicology Blood-brain Barrier  Not an absolute barrier Caffeine (small) Methylmercury cysteine complex Lipids (brain is a ball of fat)  Anatomic Characteristics Capillary endothelial cells are tightly joined – no pores between cells Capillaries in CNS surrounded by astrocytes Low protein concentration in CNS fluid Active ATP-dependent transporter – moves chemicals into the blood

A Small Dose of Toxicology Introduction to Neurotoxicology Neuronal Cells Axon Myelin (Schwann cell) Synapse Dendrite Cell Body Nucleus

A Small Dose of Toxicology Introduction to Neurotoxicology Dopamine Transmitter Cell (Excitatory Neuron) Dopamine Receptor Cell (Post-synaptic receptor) Dopamine Receptor Synaptic Cleft Synaptic Vesicles Neurotransmission

A Small Dose of Toxicology Introduction to Neurotoxicology Inhalation (e.g. solvents, nicotine) Ingestions (e.g. lead, alcohol) Skin (e.g. pesticides, nicotine) Physical (e.g. load noise) Exposure Issues

A Small Dose of Toxicology Introduction to Neurotoxicology What causes neurotoxicity? Wide ranged of agents – chemical and physical

A Small Dose of Toxicology Introduction to Neurotoxicology Types Of Neurotoxicity  Neuronopathy Cell Death. Irreversible – cells not replaced. MPTP, Trimethytin  Axonopathy Degeneration of axon. Reversible. Hexane, Acrylamide  Myelinopathy Damage to myelin (e.g. Schwann cells) Lead, Hexachlorophene  Transmission Toxicity Disruption of neurotransmission Organophosphate pesticides, Cocaine, DDT

A Small Dose of Toxicology Introduction to Neurotoxicology Neurotoxic Injury Neuron Normal Neuronopathy Axonopathy Myelinopathy Transmission Axon Synapse Myelin

A Small Dose of Toxicology Introduction to Neurotoxicology Examples of Neurotoxicology  Diseases Parkinson's, Alzheimer's, MS, ALS..  Environmental Lead, Methylmercury, PCBs  Occupational Solvents, Pesticides  Drugs - Clinical Vincristine, cisplatin  Drugs - Social Alcohol, cocaine, nicotine

A Small Dose of Toxicology Introduction to Neurotoxicology  Cognitive Effects - memory, learning, confusion  Motor Effects - weakness, convulsion, paralysis  Sensory Effects - vision, auditory, touch, balance  Mood and Personality Effects - sleep, depression, irritability, excitability  General Effects - loss of appetite, fatigue Neurotoxic Effects

A Small Dose of Toxicology Introduction to Neurotoxicology Classification of Neurotoxicant  Temporary inhibition of nerve function Agents which alter membrane function Agents with interfere with synaptic transmission Mechanism of action

A Small Dose of Toxicology Introduction to Neurotoxicology Classification of Neurotoxicant  Permanent inhibition of nerve function Agents which cause Anoxia Anoxic anoxia (e.g. CO 2 asphyxiation) Ischemic anoxia (e.g. blood clot) Cytotoxic anoxia (e.g. cyanide) Agents which damage myelin formation Oligodendroglia (CNS) Schwann cells (PNS) Agents which damage peripheral axons Agents which damage nerve cell body Agents which cause localized CNS lesions Mechanism of action

A Small Dose of Toxicology Introduction to Neurotoxicology 1. Autonomic function (lacrimation and salivation, piloerection and exophthalmus, urination and defecation, pupillary function, palpebral closure) 2. Convulsions, tremors, or abnormal motor movements 3. Reactivity to general stimuli such as removal from the cage or handling (no reaction to hyperreactivity) 4. Arousal level (from coma to hyperalertness) 5. Posture and gait abnormalities (home cage and open field) 6. Forelimb and hindlimb grip strength 7. Landing foot splay 8. Sensorimotor responses to stimuli (a tail-pinch, tailflick, hot-plate, acoustic startle response ) 9. Body weight 10. Any unusual or abnormal behaviors, excessive or repetitive actions (stereotypies), emaciation, dehydration, hypotonia or hypertonia, altered fur appearance, red or crusty deposits around the eyes, nose, or mouth, and any other observations that may facilitate interpretation of the data. Functional Observational Battery (FOB)

A Small Dose of Toxicology Introduction to Neurotoxicology 1. Count of rearing activity on the open field. 2.Ranking of righting ability. 3.Body temperature. 4.Excessive or spontaneous vocalizations. 5.Alterations in rate and ease of respiration, e.g., rales or dyspnea. 6.Sensorimotor responses to visual or proprioceptive stimuli. Functional Observational Battery (FOB)

A Small Dose of Toxicology Introduction to Neurotoxicology Memory and learning tests (e.g. radial maze, Morris water maze) Conditioned stimulus/responses Other supportive techniques: Histopathology/Quantitative Stereology EEG, EMG, Functional MRI: CBV-fMRI of rat brain induced by electrical stimulation of both forepaws. T. Reese, A. Sauter, N. Beckmann, M. Rudin et al. Novartis Pharmaceutical, Basel, Switzerland Other measures

A Small Dose of Toxicology Introduction to Neurotoxicology  Structure Long cell requires extensive intracellular transport  Blood-Brain Barrier  Developmental stage (lead and alcohol) Physiological Sensitivity

A Small Dose of Toxicology Introduction to Neurotoxicology  Neurons CANNOT divide and replace themselves  Neurons CAN repair limited axonal damage  Most Recovery Redundancy of Function Plasticity of Organization Reversibility of Damage

A Small Dose of Toxicology Introduction to Neurotoxicology Classification of neurotoxicants by mechanism of action  Permanent inhibition of nerve function Agents which cause Anoxia Anoxic anoxia Ischemic anoxia Cytotoxic anoxia Agents which damage myelin formation Oligodendroglia (CNS) Schwann cells (PNS) Agents which damage peripheral axons Agents which damage nerve cell body Agents which cause localized CNS lesions

A Small Dose of Toxicology Introduction to Neurotoxicology Neurological and Behavioral Effects of Exposure to Toxic Substances  Motor Effects - Convulsions, weakness, tremor, twitching, lack of coordination, unsteadiness, paralysis, reflex abnormalities, activity changes  Sensory Effects - Equilibrium changes, vision disorders, pain disorders, tactile disorders, auditory disorders  Cognitive Effects - Memory problems, confusion, speech impairment, learning impairment  Mood and personality effects - Sleep disturbances, excitability, depression, irritability, restlessness, nervousness, tension, delirium, hallucinations  General effects - Loss of appetite, depression of neuronal activity, narcosis stupor, fatigue, nerve damage

A Small Dose of Toxicology Introduction to Neurotoxicology Receptor Ligand Cell Membrane Signal Protein Positive Response Outside Cell Inside Cell Ligand binds to receptor Normal Receptor-Ligand Interaction

A Small Dose of Toxicology Introduction to Neurotoxicology Toxicant 11 inactivates receptor Toxicant inactivates receptor No Response Inactivation of Receptor by Toxicant

A Small Dose of Toxicology Introduction to Neurotoxicology Toxicant 1 No Response 3 2 Ligand Toxicant out competes normal ligand Ligand cannot bind receptor Competition For Receptor

A Small Dose of Toxicology Introduction to Neurotoxicology Who Is Vulnerable? Young or Old Male or Female Genetics - Individual Diff. Species

A Small Dose of Toxicology Introduction to Neurotoxicology Fetal Nervous System Developing Nervous System Mature Nervous System Aging Nervous System Vulnerability / Sensitivity

A Small Dose of Toxicology Introduction to Neurotoxicology Additional Information  Web Sites U.S. National Institute of Health - National Institute of Neurological Disorders and Stroke (NINDS). Online. Available HTTP: (accessed: 10 April 2003). Natural Resources Defense Council (NRDC). Online. Available HTTP: (accessed: 10 April 2003). NRDC site provides information on children’s health and neurotoxicology.  Other Chapters Mercury, lead, pesticides

A Small Dose of Toxicology Introduction to Neurotoxicology Authorship Information For Additional Information Contact Steven G. Gilbert, PhD, DABT Web: This presentation is supplement to “A Small Dose of Toxicology”