Methods and Strategies of Research

Methods and Strategies of Research
Copyright 2001 by Allyn & Bacon

Experimental Ablation

* Ablation involves the destruction of brain tissue followed by an assessment of subsequent changes in behavior
* Ablation techniques include
o Electrolytic lesions/Radio Frequency lesions
o Excitotoxic lesions (kainic acid)
o Neurochemical lesions (6-OHDA)
o Aspiration
o Knife cuts
* Distinction between functions and behaviors
* Brain lesion studies are complicated by the fact that all regions of the brain are interconnected



Stereotaxic Surgery

* A stereotaxic instrument holds the head in a fixed position
o The instrument has an arm that can move in 3 dimensions
o The surgeon can thus position an electrode or other device within a particular sub-cortical structure
* A stereotaxic atlas provides a series of drawings of brain structures
o Each page is a section of brain relative to a landmark on the skull (such as bregma)

Using a Stereotaxic Atlas to Target a Brain Lesion

Histological Techniques

* Histological techniques are used to verify the placement of a lesion within brain
o Perfuse (to remove blood from brain)
+ Remove brain
o Fix brain in formalin to solidify tissue and to prevent autolysis
+ Slice brain into thin sections (10-80 microns thick)
o Use stains to highlight selective neural elements
+ Myelin (Weil stain)
+ Cell body (cresyl violet: Nissl substance in cytoplasm)
+ Membrane (Golgi stain)

Defining Neural Connections

* Neurons in a given region send axonal outputs (efferents) to other brain regions and receive axonal inputs (afferents)
o Tracing efferent connections is done using anterograde labels that are taken up by the cell bodies and transported to axons
+ “Forward: toward axons from cell bodies”
+ Inject the lectin PHA-L into a nucleus, wait several days, process brain tissue.
+ Immunocytochemistry uses a radioactive antibody to PHA-L in order to identify cells containing PHA-L
o Tracing afferent connections is done using retrograde labeling
+ “Backwards: from axons to cell bodies”
+ e.g. fluorogold is a retrograde tracer

Anterograde Tracing
Visualizing a Living Human Brain
Human MRI (Normal)
Images courtesy of Dr. Nancy Andreason
Recording Neural Activity

* Axons conduct action potentials and neurotransmitters elicit postsynaptic potentials
* The electrical events of a discrete region can be recorded using glass microelectrodes (acute recording) or tungsten wire (chronic recording)
* Macroelectrodes record the summated electrical activity of large regions of brain
o Surface electrodes placed on human scalp are used to record brain activity (electroencephalogram: EEG)

Recording Synaptic Activity
Human Brain Imaging
Microdialysis
Microdialysis Probe Details
Artificial Stimulation of Brain
Localization of Neurotransmitters
Receptor Localization Techniques

Genetic Methods
* Genetic research methods seek to demonstrate the linkage between genes and behavior
* Twin studies examine the impact of varying degrees of genetic similarity on behavioral similarity
o Identical twins (MZ) share 100% of their genes while fraternal twins (DZ) share about 50% of their genes
o Concordance rate examines the likelihood of whether a twin shares a behavioral trait with the other twin
o A higher concordance rate for MZ twins relative to DZ twins suggests a genetic influence for that characteristic
* Adoption studies examine the similarity with regard to a trait for an adopted person compared to their adopted parents and their biological parents
* Targeted mutations involve the insertion of defective (knockout) genes into the chromosomes of mice

Methods and Strategies of Research.ppt

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