Lecture 7: Neurophysiology Flashcards
log time
time of phenomenon
in brain studies: ms-s
log size
brain area to look at
synapse, dendrite, layer neuron, column, map, brain etc
What are different levels at which you can study brain?
single channel level, single cell level, population level
single channel level
single receptor information (effects of acetylcholine)
single cell level
figure out what cell is doing in relation to other effects
population level
for example: hippocampus role
from where we record activity in single channel/cell level?
soma! not so much dendrites
how can we record from cells?
membrane ensures potential difference between inside and outside
membrane potential
current flows by the virtue of potential difference (between outside and inside of the cell), negative inside with respect to outside
what maintains membrane potential?
sodium-potassium pump (dependent on ATP)
what are channel types?
active transporters and ion channels
active transporters
actively move selected ions against concentration gradient; create ion concentration gradients
ion channels
allow ions to diffuse down concentration gradient, selectively permeable to certain ions
patch clamp technique
used to study electrical properties of excitable cells and ion channels
enables isolating patch of membrane through which different currents pass
2 types: voltage clamp, current clamp
voltage clamp
clamping (controlling) the voltage across the membrane and measuring current passing through it
current clamp
clamping (controlling) the current across the membrane and measuring the voltage passing through it
what is a difference between current and voltage?
Voltage is the force that makes electrons flow. It’s a difference in potential energy between two different points in a circuit. = CAUSE
Current: Current is the rate of the flow of electrons. = EFFECT
How to most easily identify single channel of interest in patch clamp technique?
apply substance to the patch of membrane to which receptors in channel are the most responsive to
What happens when you apply benzodiazepines/barbiturates?
increase frequency of GABA channels opening - more inhibition - sleeping agent
why barbiturates are dangerous?
because they open -by themselves- all GABA channels - may be deadly
Where is serotonin synthesized and projected to?
synthesis: raphe nucleus
projections: all over the brain
What is the effect of ecstacy on serotonin?
ecstacy (MDMA) induces reverse reuptake of serotonin = so serotonin is taken outside of presynapse
In what serotonin is involved?
gut motility (most serotonin in the gut), vasculatum
mood, anxiety, arousal, circadian rhythms, eating disorders, migraine, pain, drug abuse
What reuptakes serotonin?
SERT
What converts tryptophan to serotonin?
5-hydrooxytryptophan
Why eating chocolate is important?
because it contains tryptophan which 5-hydrooxytryptophan coverts into serotonin
What is function of serotonin?
modulation of basic psychological functions (mood, appetitie, sleep, sexuality)
implied in depression
implicated in aggression (high serotonin levels)
What most antidepressants do?
block serotonin reuptake
usually it takes around 2-3 weeks to see effects because new neurons need to grow
What are different types of antidepressants?
MAO inhibitors: inhibit breakdown of all monoamines
tricyclic: inhibit reuptake of serotonin and norepinephrine
SSRI: inhibit reuptake only of serotonin
How does mood disorder treatment look like? What areas are targeted?
antidepressants SSRI - update activity of dorsal raphe nucleus
CBT - puts medial PFcortex back in business
what happens in voltage clamp (more in detail)?
Voltage is controlled. So we record how ion flows across cell membrane and we measure CURRENT. You look at neuron’s channel openings over time.
What is equivalent to voltage (V)?
I (current) x R(estistence)
How do receptors react to drug application?
firstly, all of them start to open
then you see some fluctuations: some open fast, some open later, fluctuations
sum of all channels opening is recorded
then you get a profile of how neuron responds to drug
What does it mean when neuron has long curve of channels opening?
activity of the neuron signals prolonged change - it means it is important for the system
What can you investigate with voltage clamp?
characteristics of cell within the network; effects of drugs on network; communication within the network; also possible in vivo - entire anesthesized animal
Why injections are usually applied to brain slices?
because brain slices don’t breathe - and breathing may disrupt easy injection
what happens in current clamp (more in detail)?
Current is controlled. So we record VOLTAGE. We are mainly interested in membrane potential (which is consequence of ion channels activities - depolarization, hyperpolarization etc.). If we spikes reaching particular threshold - action potential is reached and neuron fires.
When you can examine if cell is firing?
when you do current clamp - because you examine voltage changes
How can we study single cell neurophysiology? For example: effects of norepinephrine?
We can use current clamp to record voltage of membrane potential. We do it in a slice of prefrontal cortex. Then we inject the norepinephrine (noradrenaline) and we examine the effects.
Results: noradrenaline brings membrane potential about 5 mV up (you still need extra input to pass firing threshold, but it still helps)
Why would you like to create knock-out mice?
to make models of certain diseases
What is a knock-out mice?
A knockout mouse is an animal model in which a gene of interest is disrupted or inactivated. The goal of making knockout mice is to completely deactivate a certain gene in order to study its effect on the body. Without the gene, certain physiological functions may be impaired, which can give insight into the development of various diseases.
What if you want to study the whole communication network of neurons?
you need an animal and stereotaxic surgery
stereotaxic surgery
drilling hole inside animal’s skull and placing electrodes inside -> animals are then investigated - enables recording from many neurons with different action potential profiles
Why there is jitter when you record from the brain?
action potentials don’t happen at fixated rate
fusion of neurotransmitters with membrane and bindind to post-synaptic neurons causes jitter
Why recorded activity goes up and down?
because you record outside membrane -> as soma depolarizes (becomes more positive, activity up), outside becomes more negative (activity down)
Where would you put electrodes if you were interested in motivated, reward related behavior?
neurons in nucleus accumbens which respond both to hippocampus and amygdala stimulation
What are two types of channels used in optogenetics?
channelrhodopsin = causes channels to open - Na goes into cell
halorhodopsin = switches neuron off - negative ions flow in
How is optogenetics performed?
via genetic engineering -> you take protein-encoding gene from algae and you put it into virus -> then you inject virus into mouse brain -> neurons get infected -> some neurons will have characteristics enabling them to express algae protein in cell membrane - then upon flashing the light, you can activate the whole area
Optogenetics study in nucleus accumbens
cells are infused with channel rhodopsin -> if you flash blue light, you can activate cells in nucleus accumbens
for example: mouse despite its natural dark preference, will go to the light area because NA is stimulated (reward)
deep brain stimulation
last-resort treatment when medication doesn’t help
useful in Parkinson’s disease - you stick electrodes into subthalamic nucleus which drives basal ganglia system - particularly effective for tremors
