Lecture 6 Flashcards
What justifies animal studies?
- Minimized pain and discomfort
- The value of the information gained from the research
- The importance of science for understanding ourselves and animals
What is experimental ablation?
- it involves the destruction of brain tissue followed by an assessment of subsequent changes in behavior
What do ablation techniques include?
- Electrolytic lesions/radio frequency
- excitotoxic lesions
- temporary ‘lesions’ by muscimol injection
What happens during ablation studies?
- brain lesions are studied in order to determine which behaviors have been inhibited
What is stereotaxic surgery?
- type of surgery done with animals in order to place electrodes on lesions of the brain to determine what behaviors have been inhibited
What is the sterotaxic instrument?
- holds the head in a fixed position
- allows the surgeon to position an electrode or other device within a particular sub-cortical structure
What is the stereotaxic atlas?
- provides a series of drawings of brain structures
- each page is a section of the brain relative to a landmark on the skull (such as bregma)
How does the stereotaxic atlas to target a brain region?
- hole will be drilled here above target of lesion
- page indicates distance from bregma
- once we have the bregma, then we have the landmark
What are Histological techniques?
- used to verify the placement of a lesion within the brain
What is the Histological technique process?
1) Prefuse the brain
2) Fix the brain
3) Use different strains
What is Prefuse?
- Remove blood from the brain
What is fixing the brain in the histological technique?
- fix brain in formalin to solidify tissue and to prevent autolysis
- slice the brain into thin sections and then freeze the rest
What doe we mean by “use stains” in the histological technique?
- use stains to highlight selective neural elements
- Myelin (Weil stain)
- cell body (cresyl violet)
- membrane (golgi stain)
Tracing Neural connections?
- neurons in a given regon send axonal (efferents) to other brain regions and receive axonal inputs (afferents)
How are efferent connections done?
- done by using anterograde labels that are taken up by the cell bodies and transported to axons
- “forward: toward the axons from the cell bodies”
- Inject PHA-L into a nucleus, wait a few days, process the brain tissue
- Immunocytochemistry uses a radioactive antibody to PHA-L in order to identify cells contaning PHA-L
How are afferent connections done?
- done by using retrograde labeling
- “Backwards: from the terminal buttons to the cell bodies”
- flurogold is a retrograde tracer
What are the results of Tracing methods?
- Anterograde tracing: Inject PHA-L in VMH
- Then see axons and terminals in PAG
- Retrograde tracing inject flurogold in VMH
- Then see cell bodies in medial amygdala
What the two types of neuroimaging techniques?
- structural and functional methods
What are the types of structural neuro imaging techniques?
- Computerized tomography (CT)
- Magnetic Resonance Imaging (MRI)
What are the types of functional neuroimaging techniques?
- Position emission tomography (PET)
- Functional Magnetic Resonance Imaging (fMRI)
- Electrical Methods (EEG, ERG)
Property measured, strengths, and weakness of CT scan?
- amount of radioactivity that passes through tissue
- Cheap and quick
- Spatial resolution is poor and there is radiation exposure
Property measured, strengths, and weakness of MRI?
- Energy released by hydrogen atoms in response to radio frequency
- High spatial resolution
& Distinction between different tissue ‘compartments’ - Discomfort for participant
Property measured, strengths, and weakness PET scan?
- uptake of radiotracer (e.g., fluoxyglucose)
- Can image energy consumption or neurotransmission & good spatial resolution
- COSTS, ionizing radiation, temporal resolution poor
Property measured, strengths, and weakness of fMRI?
- changes in blood-oxygen dependent (BOLD) response
- No radiation, excellent spatial radiation
- Temporal resolution modest, discomfort for participant
Property measured, strengths, and weakness of EEG and ERP?
- Fluctuations in electrical activity over time or in response to specific stimulus
- Costs, no radiation, excellent temporal resolution (w/in milliseconds)
- Poor spatial resolution
What is a CT scan?
- uses an x-ray beam to scan the brain from all angles, these scans are then summarized in an image of skull and brain (in horizontal plane)
What is an MRI?
- uses a magnetic field and radio waves to excite hydrogen molecules, the resting information is combined to form an image of tissue
- can see both white and gray matter
What is DTI?
- This is a sensitive probe of cellular structure measured by diffusion of water molecules
- the diffusion of molecules is generally isotopic (equal in all directions)
What is the key to DTI?
- anistropy: variability of diffusion directionally in relation to tissue structure.
- 3 dimensional vector that measures the direction of the water
- the higher the fraction, the more they interact with matter fibers
What is the PET can a variation of?
- the animal 2-DG technique
- What is the 2-DG technique?
- Human subject is injected with radioactive 2-DG, which is taken up by brian cells
- As the radioactive molecules decay they emit positrons that can be detected by scanner
What are PET scans be used for?
- PET scans be used to characterize neurological disease, monitor treatment, and depict task-related activation patterns. PET is highly sensitive to preclinical disease