Experimental Ablation

Experimental Ablation
Aleem Ashraf
Department of Psychology
University of Sindh.
Methods & Strategies in
Biological Psychology

Contents
1. Evaluating the Behavioral Effects of
Brain Damage
2. Producing Brain Lesions
3. Stereotaxic Surgery
4. Histological Methods
5. Tracing Neural Connections
6. Studying the Structure of the Living
Human Brain
7. Reference
2

Experimental Ablation
 Experiments in which part of the brain
is damaged and the animal’s behavior
is subsequently observed are called
lesion studies or Experimental
ablation.
3

 All regions of the brain are
interconnected, it’s hard to interpret
the results of such studies.
 Damage to structure X doesn’t for sure
affect structureY.
Evaluating the Behavioral
Effects of Brain Damage
4

Producing Brain Lesions
 Brain lesions of subcortical regions are
usually produced by passing electrical
current through a stainless steel wire that
is coated with an insulating varnish
except for the very tip.
 The heat of the current kills the cell in the
tissue.
 All nearby cells including the axons of the
passing neurons are destroyed.
 Called Radio Frequency Lesions.
5

Figure 1. Radio Frequency Lesions in rat brain
6

 A more selective method of producing
brain lesions employs an excitatory
amino acid such as kainic acid, which kills
neurons by stimulating them to death.
 Amino acid is injected through a cannula.
 Lesions produced in this way are
referred to as excitotoxic lesions.
 Does not affect the nearby axons.
7

 This selectivity permits the
investigator to determine whether the
behavioral effects of destroying a
particular brain structure are caused
by the death of neurons located there
or by the destruction of axons that
pass nearby.
8

Figure 2. Ecitotoxic Lesion in hippocampus of rat brain
9

 When we pass an electrode or a
cannula through the brain to get to our
target, we inevitably cause a small
amount of damage to other areas as
well.
 Which makes causal inferences
implausible.
 Sham lesion is produced in the control
group to avoid this problem.
10

 Sham lesion A placebo procedure
that dupli-cates all the steps of
producing a brain lesion except the
one that actually causes the brain
damage.
 Sometimes researchers don’t cause
permanent brain damage to animals.
 The inject local anesthetic to the
target area blocking action
11

Stereotaxic Surgery
 The process by which an electrode or a
cannula is precisely located and
produces lesions in a brain is called
stereotaxic surgery.
 Done with an apparatus called
stereotaxic apparatus.
 For precise measurements of brain
stereotaxic atlas is used.
12

 Stereotaxic atlas is a collection of
drawings of sections of the brain of a
particular animal with
that provide coordinates for stereo-
taxic surgery.
13

Figure 3. Stereotaxic Apparatus
14

Figure 4. Stereotaxic Surgery on human brain
15

Histological Methods
 Fixing, slicing, staining, and exami-
ning the brain under microscope.
These methods are called histological
methods.
 Fixation:To preserve the tissue from
decomposing it is placed in a fixative
chemical such as formaline.
 To obtain clear view, the blood is
drained prior to fixation (Perfusion).
16

 Sectioning: A tissue is then sliced into
thin sections to place under
 Slicing is done with a microtome.
17

 After the tissue is cut, the slices are
attached to glass microscope slides.
 The slides are then put in various chem-
ical solutions, the process known as
staining.
 Staining is done to give contrast to the
tissues under microscope to make the
smaller structures clearly visible.
 The most frequently used is cresyl violet.
18

Figure 6. Frontal Section of a cat brain stained with cresyl violet
19

Electron Microscopy
 Transmission electron microscope is
used to see the small details of the
cells such as synaptic vesicles.
Figure 7. Electron
Photomicrograph
This electron
photomicrograph shows
a section through
an axodendritic synapse.
20

Scanning Electron Microscope
 It provides the images in three
dimensions.
Figure 8.
Neurons &
Glial Cells
21

Confocal Laser Scanning Micro-
scopy
 It doesn’t require
slides. It can
work on exposed
tissue in living
brains
 Requires
florescent dye
for staining cells
Figure 8. Branches of dendrites of a
living mouse
22

Tracing Neural Connections
 Studying isolated brain tissues is not
enough.
 It’s important to understand its
connection with other neural circuits.
 Tracing Efferent Axons:The output
from the tissue of interest.
 Tracing Afferent Axons:The input to
the tissue of interest.
23

Tracing Efferent Axons
 A chemical is injected into a tissue of
interest.
 Which is taken up by dendrites and cell
bodies and transported through axons
to other neurons.
 The process known anterograde
labelling (moving forward).
 After few days the animal is killed and
examined under a microscope.
24

Once we know that a particular brain region is involved in a
particular function, we may ask what structures provide
inputs to the region and what structures receive outputs
from it.
25

 The antibody molecules are attached
to various types of dye molecules.
 The body’s immune system attacks
these antigens.
 The antibodies attach themselves to
their antigens becoming visible under
a microscope.
 This way researcher can trace where
the output goes from the tissue of
interest.
26

Using PHA-L (kidney protein) forTracing Efferent Axons
27

Anterograde Tracing Method.
PHA-L was injected into the ventromedial nucleus
(VMH) of the hypothalamus, where it was taken up by
dendrites and carried through the cells’ axons to their
terminal buttons. The section shows labeled axons and
terminal buttons in the periaqueductal gray matter
(PAG).
28

Tracing Afferent Axons
 It is also important to know from
where the tissue of interest receives its
input from.
 The process called retrograde label-
ling method (moving backward).
 Chemicals that are taken up by
terminal buttons and carried back
through the axons toward the cell
bodies.
29

Tracing Afferent Axons
 The chemical commonly used in this
method (fluorogold) is injected into a
tissue of interest.
 Which is taken up by terminal buttons
and carried back through the axons
toward the cell bodies.
 After few days the animal is killed and
examined under a microscope.
30

Retrograde Tracing Method
Fluorogold was injected in the VMH, where it was taken
up by terminal buttons and transported back through
the axons to their cell bodies. The photograph shows
these cell bodies, located in the medial amygdala.
31

Results of Tracing
The figure shows one
of the inputs to the
VMH and one of the
outputs, as revealed by
anterograde and
retrograde labeling
methods.
32

Studying the living brain
 The living brain can be examined with:
 Computerized tomography (CT
scanners)
 Magnetic resonance imaging (MRI
scanners).
 Diffusion tensor imaging (DTI)
33

Computerized Tomography
The use of a device that uses a computer to
analyze data obtained by a scanning beam of X-
rays to produce a two-dimensional picture.
The patient has a lesion
in the right occipital-
parietal area (scan 5).
34

Magnetic Resonance Imaging
 A technique by
which the interior
of the body can be
accurately
imaged; involves
the interaction
between radio
waves and a
strong magnetic
field.
35

Diffusion Tensor Imaging
 It can measure macroscopic axonal
organization in nervous system tissues.
 The computer adds colors to distin-
guish different bundles of axons.
36

Reference
Carlson, N.R. (2011). Physiology of
Behavior. (11th Ed).
37

Experimental Ablation

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Experimental Ablation