Cannabis - endocannabinoids and G proteins Flashcards
uses of cannabis
industrial - hemp
religious rituals
recreational use
recreational use of cannabis §
smoked or injested
widely used but usage going down
(dried flowers, resin or liquid extracts)
types of effects of cannabis
psychotropic (mainly)
somatic
psychotropic effects of cannabis
change in perception euphoria increase in appetite relaxation increased appreciation of music Introspection enhanced episodic memory increased awareness of sensation
At higher doses
auditory and/or visual illusions
hallucinations
ataxia
euphoria
heightened mood
episodic memory
recollection
ataxia
lack of voluntary control of muscle movement
somatic effects of cannabis
increased HR dry mouth reddening of the eyes reduction in intra-ocular pressure muscle relaxation Electroencephalography or EEG: more persistent alpha waves
cannabis used to treat glaucoma due to
its ability to reduce intra-ocular pressure
how can cannabis be used in treatment of bronchial asthma
cannabis causes bronchial dilation
how can the antiemetic effect of cannabis be used as a therapeutic
treats the nausea/vomiting caused by anti cancer drugs
other therapeutic uses of cannabis
apetite stimulant
analgesia
ataxia - to treat muscular sclerosis etc
mental health risks of cannabis
Triggering psychotic episodes and psychosis Increase risk of schizophrenia Anxiety Paranoia Substance abuse disorders
physical health risks of cannabis
Lung problems (due to ingestion by smoking) Lung cancer (cannabis often combined with tobacco) Increased heart rate/blood pressure --> heart problems Foetal developmental (if consumed when pregnant)
legal/societal risks
prison sentence
fine
criminal record
how many cannabinoids found in recreational cannabis
66
example of cannabinoids found in cannabis
delta9-tetrahydrocannabinol
cannabinol
2 canonical cannabinoid receptors
CB1
CB2
known about for ages
other possible non-canonical cannabinoid receptors
GPR55
GPR119
GPR18
recently discovered
CB1 receptor expression
mainly in the brain, kidneys, liver and lungs
CB2 receptor expression
immune cells and macrophages
which cannabinoid receptor is a potential therapeutic target
CB2
structure of CB1 receptor
7 transmembrane domain
extracellular N terminal binds to agonist
intracelular C terminal associated with downstream signalling
when ligand eg THC binds to CB1 receptor
moves from resting state (Ga bound to GDP)
conformational change
GTP then binds to Ga
Ga dissociates from GB/y complex
which G protein subunits are CB1 receptors coupled to
Gi/o
what happens when Gai/o dissociates from GB/y
Gai/o:
- shuts Ca2+ channels into the cell
- inhibits adenyl cyclase –> decreased cAMP
GB/y:
- positively regulates GIRK channels –> increased K+
CB1 receptor location
ubiquitous across the brain but more densely located in higher functioning areas e.g. neocortex, hippocampus
presynaptic
use of binding assays
tell us how well the radioactive ligand binds to its receptor
assays for measuring receptor pharmacology
binding assays
functional assays
use of functional assay
determines how activated the receptor is
measure EC50
Ki
binding affinity
constant
Ki of THC
10-50nM
why does THC have a low efficacy
it is a partial agonist
compared to synthetic ligands
features of synthetic ligands
much higher efficacy and potency
effect of cannabidiol at CB1 receptors
functional antagonist
shifts the curve to the right (concentration-response curve)
role of CB1 receptors at synapses
modulate inhibitory synaptic transmission
effect of CB1 agonists
inhibit GABA-mediated synaptic transmission
possible post synaptic mechanism of CB1 R agonist
reduce postsynaptic sensitivity to GABA
possible pre synaptic mechanism of CB1 R agonist
reduce presynaptic release probability
each quantal release
corresponds to each miniature IPSC
If amplitude of events reduced …
then the neurotransmitter has had a postsynaptic effect
Infrequent quantal events
– likely to be driven by single vesicle release (no APs) – simplified system
Evidence for amplitude effect
No. of neurotransmitter in each vesicle taken to be the same
effects of CB1 agonists of miniature IPSCs
CB1 agonists do NOT affect:
mIPSC frequency or mIPSC amplitude
But DO reduce evoked IPSCs
Therefore, they reduce action potential-dependant GABA release (via inhibition of Ca2+ channels)
2 examples of endocannabinoids
2-AG - (2-arachidonylglycerol)
Anandamide (AEA)
how do endocannabinoids diffuse through membranes
they are lipid soluble
not stored in vesicles
DSI
Depolarisation-induced Suppression of Inhibition
can be mediated by CB1 receptors
retrograde signalling
signalling from post-synaptic cell back to pre-synaptic
Evidence that DSI is mediated via a retrograde messenger
- Increase in postsynaptic [Ca2+]i is necessary and sufficient for the induction of DSI
- The frequency of spontaneous inhibitory synaptic vesicles released from pre-synaptic is reduced
- Postsynaptic sensitivity to exogenously applied GABA (e.g. from pipette) is not affected by depolarisation – therefore effect must be pre-synaptic
- Not blocked by classical neurotransmitter receptor antagonists
- DSI is not synapse or cell specific
effect of Ca2+ on DSI
if you block Ca2+, you block DSI
DSI is mediated by endocannabinoids
endocannabinoids synthesis/release is dependant on Ca2+
in response to postsynaptic depolarisation
causes suppression of GABA release
DSI is mimicked by blocking endocannabinoid uptake
psychotropic effects of cannabis mediated by which receptor
CB1
main effect of CB1 receptor activation
reduced inhibitory synaptic transmission
form of short term plasticity
DSI
define Ki
the concentration required to produce half maximum inhibition
lower Ki
means the inhibitor is more potent
greater binding affinity
less required to produce inhibition in 50% o
higher Ki
inhibitor is less potent
less binding affinity
more required to produce half maximum inhibition
