Optogenetics Flashcards
define optogenetics:
- use of light to regulate activity of neurons
optogenetics: how does it work?
- cells genetically engineered to possess light responsive ion channels= control neuronal activity
- these ion channels cloned from organisms responsive to light
optogenetics: eg. used (2) and ions
green algae: channelrhodopsins (+ve ions)
halobacteria: archaerhodopsins (proton pumps- remove +ve ions)
optogenetics: method to inject
- virus carrying specific opsin (channelrhodopsin) and identifier for specific neuron type (promoter) injected into brain area to infect cells of interest
optogenetics: how to activate ion channels
- using lasers
- alters activity of infected neurons
optogenetics: light wave/ freq and which commonly used?
- electromagnetic radiation many freq, can only see small proportion
- common colours used: blue, yellow, green
optogenetics: to activate use which light and action caused- channelrhodopsin (ChR2)
- blue light
- lets +ve ions into cell
- cell stimulated
optogenetics: to activate use which light and action caused- halorhodopsin (NpHR)
- orange/yellow light
- lets Cl- ions in
- cell inhibited
optogenetics: to activate use which light and action caused- achaerhodopsin (Arch)
- orange/yellow light
- pumps +ve ions out
- inhibits cell
optogenetics: opsins tagged w wat? eg.
- tagged w fluorescent protein so visualise infected neurons under microscope
- ensures labelled correct cells w channels
eg. green fluorescent protein (GFR) or mCherry
optogenetics: how to check functioning of channel
- electrophysiology
optogenetics: why use it?
- electrical stimulation affects all neurons in area, incl fibres of passage
- neuropharm: all neurons w that type of receptor in area drug is administered
- optogenetics: specific to neuron/circuit u r targeting (others not affected)
optogenetics: process of using opsin to find circuitry
- virus injected into B
- opsin expressed through B (also fibres to A and C)
- by laser activating B axons on A, corresponding B cell bodies r affected
- by activating terminals at A only affecting neurons that come from B (where virus was injected)
optogenetics: process involving locus coeruleus (LC) and amygdala
- virus w photosensitive channels in LC
- while plant optrode (holds optic fibre in place) in amygdala
= only neurons from LC to amygdala will be stimulated
optogenetics: bidirectional control of neurons process
- mixed viral injection of opsins w diff lightwave spctrum into mixed pop of B (activator, inhibitor opsins)
- opsin expression in B cell bodies to A and C
- differentiate which opsin activated by using diff coloured lasers, due to photosensitivity of ion channels to diff wavelengths of light
optogenetics: use in humans and eg. (4)
- possibly used
- similar invasive procedure of deep brain stimulation, optic tech to target particular neuron type
- schizophrenia
- anxiety
- depression
- drug addiction
anxiety vs fear response features
- universal human emotion, necessary to adapt to env
fear: defensive behaviours, arousal, -ve emotions
anxiety: reactions due to anticipation of -ve event
fear: subcortical and features- immediate response to a threat
- subcortical
- visual, auditory stimuli reach thalamus, travel to amygdala
- amyg alerts other brain structures (hypothalamus- HPA axis and locus coeruleus: LC)
- surge in cortisol and nAd = sweaty palms, tachycardia, increased BP
fight or flight response
fear: cortical and features- cognitive processing immediate response to a threat
- cortical
- info sent from thalamus - cortex and basal ganglia for cognitive processing
- regions analyse raw data from sensory organs and decide dis/continue fear response
- if maintained response: amyg remains on alert (helps make further appropriate behavioural responses)
amygdala: function
- key area in processing fear, anxiety
- esp basolateral (BLA) and central nuclei
- alerted when emotional processing, or emotional response required
amygdala: name subregions and sig
- BLA: basolateral
- CeM: central medial amyg believed to drive fear response
- CeL: central lateral amyg
no amygdala=
no fear!
amygdala: experiment to test how portions connected- activating BLA-CeL? results
- blue light
- reduced anxiety in elevated + maze
- reduced anxiety in open field test (rat crossed through box vs. staying towards edges)
- anxiolytic (reduce anxiety) effect = BLA activates CeL, reducing CeM output
amygdala: experiment to test how portions connected- inhibiting BLA-CeL?
- inhibiting w eNpHR3 (halorhodopsin)
- 👷🏻
- enhanced anxiety
amygdala: experiment to test how portions connected- activation of BLA result, summary
- activating BLA released glutamate in CeL to stimulate GABA cells and inhibit fear response of CeM
- optogenetic activation of BLA terminals in CeL reduces anxiety stopping output of CeM
oxytocin: features (6)
- social neuropeptide
- social interaction w peers
- form monogamous pair bonding
- sexual arousal, orgasm
- maternal behaviour
- social memory, anxiety reduction (anxyiolytic)
oxytocin: where in brain
- produced in magnocellular neurosecretory cells of hypothalamus
- magnocellular cells in paraventricular nuclus (PVN) of hypothalamus (lateral/medial section) and supraoptic nucleus of hypothalamus (near optic tracts)
oxytocin: where to- from supraoptic nucleus
- volume transmission
- not so much neuron to neuron contact
oxytocin: where to- from paraventricular nucleus (PVN)
- classic neuron to neuron contact and vol transmission
- oxytocin receptors in brain aka OT receptors
neurons to:
- nucleus accumbens (NAS)
- bed nucleus stria terminalis
- amyg (CeA, MeA)
- dopamine cells of VTA
oxy release in central amyg reduce fear response? experiment features general
- link of opsin ChR2 to oxytocin promoter so only oxy cells targeted
oxy release in central amyg reduce fear response? result
- yes
- activating ChR2 on oxy terminals of CeL of amyg reduced fear in rats
list core brain regions receiving dopamine from VTA: (7)
- subthalamic nucleus
- striatum
- orbitofrontal cortex
- prelimbic cortex
- nucleus accumbens
- amygdala
- hippocampus
dopamine received from VTA function: striatum
habit
dopamine received from VTA function: orbitofrontal cortex
impulsivity
dopamine received from VTA function: prelimbic cortex
decision making
dopamine received from VTA function: nucleus accumbens
saliency/ motivation
dopamine received from VTA function: hippocampus
context/ memory of drug use
PFC-NAc connection: for dopamine
- prelimbic cortex (PL) of prefrontal cortex. (PFC) has glutamate (+ve) connections back to VTA dopamine cells and nucleus accumbens (NAc)
cocaine: method for rats
- intravenous drug self-administration (lever press)
cocaine: function at synapses
- DAT = dopamine transporter
- cocaine blocks DAT, modulation of DAT increases dopamine in synaptic cleft
reinstatement of cocaine seeking: list 3 tests done
- inject ArchT opsin/virus at PFC, laser via optrode on PFC
- inject ArchT on NAc, and laser too
- inject ArchT on PFC, laser on NAc
reinstatement of cocaine seeking: inhibition of PL (prelimbic) cortex-
- prevents drug seeking behaviour produced by re-exposure to cocaine
function of PFC neurons in rats displaying addiction phenotype: type of cell, features
- pyramidal neuron
- cocaine use resistant to inhibition by -ve consequence
function of PFC neurons in rats displaying addiction phenotype: hypoactive neurons result
- willing to keep taking cocaine despite shock (-ve consequence)
function of PFC neurons in rats displaying addiction phenotype: activation of PL cortex (somatic method) in shock resistant rats?
- reduced cocaine seeking in shock resistant rats
function of PFC neurons in rats displaying addiction phenotype: inhibition of PL cortex (somatic method) in shock sensitive rats?
- increases compulsive cocaine seeking in shock sensitive rats
summary: CeL function
- act as modulator of neuronal output of CeM
- CeL stops anxiety output of CeM
summary: oxy release in CeL causes
reduces fear responses
DREADDS: define
designer receptors exclusively activated by a designer drug
- targets specific brain cells if virus targets promoter
