26_08_0130_Approaches.ppt

26_08_0130_Approaches.ppt

• 1.
  HOW WE STUDYBRAIN & BEHAVIOR (CONT.) AMHERST COLLEGE INTRODUCTION TO NEUROSCIENCE WEDNESDAY, JANUARY 30, 2008 Reading: Chapter 1 & 2 Friday: Chapter 7: 168-180; 193-199; 205-235 Chapter 15 (490-497) Chen, Sandi S. Coombs, Angela A. Guha, Pallabi Gutierrez, Christina Hopkins, Christina C. Howard, Clare E. Kativhu, Chido L. Kim, Daniel W. LaMontagne, Laurel Mattison, Jamie E. Montgomery, Tracy Navarro, Yasmin Rivera, Ashley M. Salgado, Sanjay M. Thein, Thuzar Tsareva, Alina Zhang, Wen Zhu, Victor Tuesday lab Anderson, Nicolle Cai, Sophia L Cameron, Rachel Dalton, Elizabeth D. Dier, Kirsten N. Gladstone, Alexandra Glick, Michelle S. Hartley, Iris R. Holaday, Eric J. Jeppson, Pamela Jiang, Debbie C. Kundu, Surya Lim, Tiffany M. Ludwig, Susannah W. Moin, Emily E. O'Loughlin, Kerry Romanowicz, Jennifer Waskom, Michael L Wednesday lab
• 2.
  Neuroscience definition &history – Chapter 1 • Neuroscience: The study of behavior and the mind through the study of the nervous system. • Mind and brain: – “Today, some people still believe that there is a ‘mind-brain problem,’ that somehow the human mind is distinct from the brain. However, as we shall see…, modern neuroscience research supports another conclusion: The mind has a physical basis, which is the brain.” – Combustion of gasoline is the physical basis of a car’s movement, but the car’s movement is distinct from the combustion of gasoline.
• 3.
  Chapter 1 questions •Before it was understood that nerves signal using electricity, what mode of signalling was attributed to nerves? • What is the earliest experiment (as distinct from observation) cited in Chapter 1? • What are the arguments that experiments on animals such as rats can be relevant to understanding human behavior, human mental life, and human brain diseases? What is the brain made of? • Cells: individual or syncytium? • Cell types • Extracellular space in brain tissue • Ventricles
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  How we study… A.Nerve cell structure B. Neurons in isolation C. Connections between different parts of the nervous system D. Electrical activity E. Chemical signalling between neurons F. Relation between brain activity and behavior
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  A. Nerve cellstructure: 1. Nissl and other traditional stains 100 m
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  2. Golgi method Silveror mercury salts, precipitate within neurons -Camilo Golgi, 1870s -used by Santiago Ramon y Cajal, 1880s-1920s The “Neuron Doctrine” Dendrites Soma (cell body) Axon
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  3. Fluorescence labelling Neuronsvs. glia (University of Florida) Fused neurons (Institute of Biophysics, Beijing)
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  …with computer processing
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  4. Electron microscopy Shorterwavelength = higher resolution 1 m Cell membrane
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  Neurons: a compositepicture The neuron: your typical cell, and more! Text Fig. 2.7
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  B. Studying livingnerve cells in isolation from their normal surroundings • Gray vs. white matter – are axons a separate type of cell? • Cell and tissue culture – Invented by Ross Harrison in 1909 to study this question
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  C. Tracing connectionsbetween different parts of the nervous system Pathway tracing: • Dye transport along axons, e.g. Fast Blue • Lesion + degeneration-specific staining • Radioactive tracers (3H-proline) • Other chemical tracing: horseradish peroxidase (anterograde or retrograde) Inject into one eye, observe in visual cortex Text, Fig. 22.18
• 13.
  Horseradish peroxidase HRP isa plant enzyme. It is transported down nerve axons, and it creates colored product when tissue exposed to hydrogen peroxide (H2O2) (H2O2 H2O + O, O + chromogen color) Inject HRP into left eye From: Kay Fite, UMass
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  D. Studying theelectrical activity of neurons “Electrophysiology:” • Surface recording – evoked potentials, EEG – Populations of neurons – Can be done in humans • Single neuron recording • Patch clamp recording
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  Single neuron recording:intracellular Fig. 3.11 Glass micropipette: - Tip diameter 0.5 um - Filled with salt solution - Records electrical difference across the cell membrane
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  Single neuron recording:extracellular Sharpened metal probe, tip diameter 1 – 5 um Records electrical currents flowing outside neurons Voltage Time
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  E. Studying chemicalsignalling: Pharmacology • How can chemicals have effects in the body at very low concentrations? • Concepts: – Receptors – Specific binding – Multiple subtypes for a single neurotransmitter – Agonists, antagonists
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  Measuring chemicals andchemical signals (1) Immunological methods – Antibody to specific protein, e.g. receptor – Single brain section: Immunohistochemistry – Piece of brain tissue: Western blotting – ‘gel’ (2) Receptor autoradiography - Radioactively labelled neurotransmitter (or chemical analog of the transmitter molecule) binds to receptor (3) In situ hybridization – radioactively labelled nucleic acid “probe” detects specific messenger RNAs C-fos immunohistochemistry
• 19.
  F. Studying therelationship between behavior and brain activity • Observe brain correlates of behavior (electrical activity, fMRI, 2-deoxyglucose) • Change brain activity and see effect on behavior – Decrease activity: lesions, chemical block – Increase activity: electrical or chemical stimulation • Need for animal experiments: – Electroencephalogram vs. single neuron recording – Accidental vs. experimental lesions
• 20.
  Brain imaging • CAT(CT) scan – computed tomography • Magnetic Resonance imaging – Spin of atomic nuclei perturbed by a pulse of strong magnetic field; when the nuclei return to normal spin they send a signal – Regular MRI: Regions of different water composition give a different signal – Functional MRI: detects metabolic differences (hemoglobin when oxygenated vs. unoxygenated) From: Scott Rauch ’80 (MGH)
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  Example 1: 2-deoxyglucose •Radioactively labelled 2DG is taken up by cells as glucose is, but isn’t metabolized. – Highly active cells take up lots of 2DG – After desired stimulation or behavioral observation, look for labelled regions Example 2: lesions • Cut, freeze, heat (via high electrical frequency), toxic chemical (as in our lab later this semester) • Problems: • Not always precisely specific to desired region • Fibers of passage
• 22.
  Example 3: Braininjections of neurochemicals • Neuropeptide-Y (NPY) and Melanin Concentrating Hormone (MCH) both increase food intake. • NPY neurons project to MCH neurons. – Hypothesis: MCH neurons mediate the downstream effects or “commands” of NPY on feeding.