Methods in Behavioural Neurobiology

Question 1

direct measures of neuronal activity (6)

Answer 1

microdialysis, electrophysiological recording, EEG, fMRI, PET, immunohistochemisty/in-situ hybridization

Question 2

microdialysis

Answer 2

implant microdialysis probes to continuously sample the fluid around it. the volumes are very small and need to wait a long time to collect samples. the tip is a membrane that allows neurotransmitters to pass through. concentration of NT could be very low in that area so need to collect multiple samples. when the animal is exposed to a particular drug, cue or performing a particular behaviour - good to study this with microdialysis

Question 3

electrophysiological recording

Answer 3

measure the electrical activity of neurons and the changes in electrical potentials. can slice the brain into thick slices that have many neurons and put them in a solution that keeps the neurons alive for some time to measure electrical potentials. can record the change immediately - associate the change in function of neuron to the change in behaviour. can also use transcranial magnetic stimulation (TMS) which is less invasive - try to change brain activity from the outside using strong magnetic fields. usually minor side effects

Question 4

EEG (electroencephalography)

Answer 4

better resolution and better quality, can be placed on the brain itself - done for planned surgeries and not research. can also put electrodes on top of scalp. ex: someone suffers epilepsy. to find source of epileptic activity, probes are inserted to identify brain waves. different frequencies change depending on state. can identify the source - electrical disturbance.

Question 5

fMRI

Answer 5

non invasive. different molecules resonate differently when under strong magnetic field since every molecule has a magnetic field. under a magnetic field, it orients itself according to the magnetic field and when released, bounces back and releases specific radiofrequencies that are measured. if a particular brain activity is activated, needs more oxygen meaning it receives more oxygenated blood so can follow the change in oxygenation in blood as a proxy to the activation of particular areas. advantages = noninvasive, can do it many times, no radiation, shows pretty good spatial resolution. limitations = slight delay between actual activation and measurement of blood oxygenation, very sensitive to movement (even breathing could have an effect)

Question 6

PET (positron emission tomography)

Answer 6

non invasive. inject participant with labeled radioactive ligand solution that crosses BBB to a particular area in brain and bind to target (receptor or transporter). radioactivity is picked up and creates a picture. closer to red = higher radioactivity (more active). radioactivity doenst stay for a long time. cannot do this often. risk is very low.

Question 7

immunohistochemistry/in-situ hybridization

Answer 7

need to collect tissue, post mortem. very high resolution. develop antibodies against specific proteins. slice brain into thin slices to introduce antibodies by soaking slices in solutions of very high concentrations of antibodies. antibodies labelled with fluorescent colour. can study multiple proteins using different antibodies (different colours).
- use probe instead of antibodies to identify mRNA = in-situ hybridization. label the probe (usually radioactive). radioactive substance on top of film will make it black.

Question 8

behavioural evaluation

Answer 8

3 types = behavioural observations, unconditioned behaviour, conditioned behaviour

Question 9

behavioural observations

Answer 9

• catalepsy = placing an animal in an unusual position and measuring the time it takes to correct itself.
• locomotor activity chamber = test used to assess general behaviour such as locomotion activity, exploration activity. can be used to see effects of drugs on locomotor activity.

Question 10

unconditioned behaviour

Answer 10

not brought on by learning.

Question 11

conditioned behaviour

Answer 11

classical pavlovian conditioning (conditioned stimulus and unconditioned stimulus associations). operant (instrumental) conditioning includes positive reinforcement (response increase), negative reinforcement (response increase), punishment (response decrease), omission training (response decrease). operant conditioning involves schedules of reinforcement = ratio and interval (both can be fixed or variable).

Question 12

measurements of drug reward

Answer 12

2 ways = drug self administration and conditioned place preference

Question 13

drug self administration

Answer 13

increasing rate of response with the same dose. response should stop when drug is removed. response rate is sensitive to drug dose. cutting dose by half = double the number of responses. if drug dose is too low, take more of the drug. its rewarding/reinforcing. responses increase over time as the animal learns the task to self administer. to assess motivation to seek drug, use progressive ratio (PR). breakpoint = when the animal stops responding for an infusion, waits some time and respond again - changes with different doses of drug and between drugs. increasing dose = increases breakpoint. at one point, drug dose is too high they dont respond anymore. under progressive ratio they take less, more extreme if using fixed ratio. fixed ratio more sensitive to high doses.

Question 14

conditioned place preference (CPP)

Answer 14

classical conditioning procedure. apparatus is a box with 2 distinct sides with a central holding area. procedure is pavlovian = injects the animal with substance that has rewarding properties and puts the animal in one of the sides and keeps it there for a certain amount of time. the effects of the drug experienced is always in the same environment. on test day, dont inject the animals with anything, put the animal in the middle and lift the barriers, allow the animal to explore. if the substance has rewarding properties, the animal would spend more time in the environment it was conditioned in (drug environment). to get of bias, the animal was initially allowed to explore the environment and was conditioned on the side it showed less preference. higher CPP with higher doses. CPP is easier and simpler to do the study compared to self admin, the test can be done under drug free conditions. cons = exposure to drug isnt really high so not good for models of drug taking/seeking.

Question 15

4 ways to measure direct neuronal activation/inhibition

Answer 15

deep brain stimulation, TMS, optogenetics, DREADD

Question 16

optogenetics

Answer 16

extract a gene from an organism, inject virus in the gene and inject that virus into the brain of an animal. infect the cell and inject the genetic material and start translating these new proteins it did not before. these neurons with the newly expressed proteins are now sensitive to light (by shining light on it, it might be activated). implant an optical fibre into brain area and shine a light from a laser on that particular area, all the neurons in that area will be excited. can tweak the genetic material so that the protein gets expressed in specific cells. ex: injected this solution into nucleus accumbens leading to ACh neurons being inhibited. this inhibition was enough to block CPP. haloredalpsin reacts to yellow light and trenalredalspin reacts to blue light.

Question 17

DREADD (designer receptor exclusively activated by designer drug)

Answer 17

receptor that does not exist in nature, introduced through virus vector. its a non replicating virus so its only expressed in one area. carries a fluorescent protein allowing us to see where that special protein/receptor is actually expressed. if the infection is successful and the neurons starts replicating the code, it will also produce the fluorescent protein. DREADD different from optogenetics (DREADD looks at long term effects). designer drug activates the receptor and it can either be excitatory or inhibitory. the designer drugs act nowhere else but on those specific receptors.