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Lecture 2

PSYC 211 Lecture Notes - Lecture 2: Ct Scan, Bregma, ExcitotoxicityPremium

5 pages74 viewsFall 2017

Department
Psychology
Course Code
PSYC 211
Professor
Gary Brouhard
Lecture
2

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Experimental and Research Methods in psychology:
Woman complains after stroke that she doesn’t enjoy sex.
Computerized Tomography (CT scan): cheap, fast, effective, not super
resolution in images. Large problems jump out at viewer. X-ray does this.
Magnetic Resonance Imaging (MRI): NOT X-RAYS, uses strong magnetic
fields. Protons orient themselves in a particular direction in strong magnetic
fields. You shine radiowaves into the body, when they hit a proton, it’ll get
knocked out of place but when it jumps back to its proper orientation it
releases radiowaves relative to the amount. More brain matter = more
protons release radio waves.
Sex drive: ventral lateral portion of the ventromedial nucleus of the
hypothalamus.
Experimental ablation: do a radiofrequency lesion (most common way) that
heats up a metal wire using a current and slicing that part of the brain and
see if the female rat has a sex drive. But you do a lot of glial damage there.
OR you can inject glutamate or an excitatory drug that causes so much
excitation that the most active neurons (ex: seizure-causing cells) undergo
apoptosis. It kills entire cell bodies, because those are what have glutamate
receptors. Passing axons are thoroughly unaffected.
Visualizing the human brain:
o MRI: expensive, takes a couple of hours, gives high-quality pictures.
Brain Lesions (Experimental Ablation):
o Excitotoxic: only targets cells bodies, not passing axons. Which is good, it
doesn’t destroy everything.
o Reversible lesion: You insert a drug into the brain, usually a cocktail of GABA
receptor agonists (hyperpolarize cells so that nothing will happen in that
area, that area of the brain is temporarily quiet until the drugs are
processed). Lidocaine is an example. Temporary inactivation of part of the
brain to analyze behaviour.
o How to Lesion:
o Stereotaxic apparatus: clamps the head. Then you cut open the skin,
drill a hole in the scull above the area you want to deal with. There is
also a stereotaxic atlas which is a map of the brain for different
animals. These maps are based on a part of the skull called bregma,
this is the soft spot during fetal development, where the foreplates
fuse together. This is a consistent spot for all species. Every number in
the atlas is based on its relation to bregma.
o Sometimes a chemical or virus is used to lesion a VERY specific part of
the brain, for a brain area we use excitotoxic lesion and for a specific
type of cell will kill the dopamine neurons in that area (dopamine cells
have their own transporters which can be targeted).
To stop a specific protein from working, you use viral-
mediated gene delivery.
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We insert a tube in the brain (cannula) which can be used to
insert chemicals in the brain. We put a cap on it throughout the
day to protect the brain, but can inject drugs through it too.
Microelectrodes can be cemented onto the rain to record which
neurons spike.
Cement fiber optic cables (new approach), we control neurons
with a laser pointer. We put specific DNA into a neuron that
makes it respond to light. This is so that when we point at it
with a laser pointer, the cell will turn on and work. We can also
add fluorescent proteins sensitive to the voltage potential
across the membrane so that, every time the cell fires, it emits
light.
Histological Methods:
o After producing a brain lesion, we cut the brain open and stain the
brain to show where we did the lesion.
The brain is mushy, so to slice it, we add a chemical fixative, ex:
formaldehyde. Its reactive with proteins, makes proteins form
covalent bonds with each other, cross-link to each other,
becomes a fixed solid mass. No more movement of proteins.
Microtome: fancy deli slicer. Makes thin cuts of a rat brain and
helps you figure out where the lesion is.
Missl stain: It’s a particular type of blue dye. Generic term for
any dye that stains the nucleus of stain, has an affinity for
nucleic acids. Most common: cresyl violet stain, makes cell
bodies turn purple. Light regions are mostly axons.
Electron microscopy: uses electron microscope to see small
structure, ex: terminal buttons. A mitochondrion is exactly one
micron in length. The black dots in the picture on the slide are
proteins.
VMH:
Why is this nucleus involved in sexual behaviour?
To figure this out, we’ll use:
o Retrograde labeling: tracking where the information is coming from,
what are the afferent neurons. Chemical used is fluorogold, taken up
by axon terminals and sent to cell body.
o Anterograde labeling: tracking efferent axons, where is this nucleus
sending info. Chemicals used: PHA-L, taken up by cell bodies.
o Picture shows that the amygdala is where the fluorogold showed up,
those are the afferent neurons.
o So, Medial amygdala sends to the VMH and then the VMH to the PAG.
Medial amygdala: in rodents, if you interfere with this, it causes them
to either have sex or start fighting with each other.
Genetics:
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