Lecture 7 - Cannabis

Question 1

Name some of the psychotropic effects of cannabis intoxication

Answer 1

Euphoria 
Changes in perception
Increased appetite
Relaxation
Introspection
Increased appreciation of music 
Enhanced episodic memory recollection
Increased awareness of sensations

Question 2

Name some of the somatic effects of cannabis intoxication

Answer 2

Increased heart rate
Dry mouth
Red/swollen eyes
Reduced intra-ocular pressure
Muscle relaxation
More persistent alpha waves on EEG

Question 3

What are some of the beneficial effects of cannabis and what illnesses might this be used to treat?

Answer 3

Bronchodilation - bronchial asthma
Antiemetic effect - nausea/vomiting
Appetite stimulation - anorexia
Analgesia - post operative pain, chronic pain conditions, phantom limb pain
Muscle relaxation - cerebral palsy
Decreased intraocular pressure - glaucoma

Question 4

What are the risks of cannabis intoxication?

Answer 4

Mental health risks - psychosis, schizophrenia, anxiety, paranoia
Physical health risks - lung cancer, heart problems, foetal development problems
Societal risks - imprisonment, fines, criminal record

Question 5

Name the cannabinoid receptors and explain what kind of receptors they are

Answer 5

Canonical: CB1 and CB2
Non canonical: GPR18, GPR55, GPR119

All GPCRs coupled to Gi/o

Question 6

Where in the body are the canonical cannabinoid receptors expressed?

Answer 6

CB1 - brain, kidneys, liver, lungs

CB2 - immune cells

Question 7

How are GPCRs inactivated?

Answer 7

The Galpha subunit is a GTPase which hydrolyses GTP to GDP

The Galpha and Gby dimer reassociate

Question 8

What are the intracellular effects of CB1 receptor activation?

Answer 8

Activation of Gi/o subunit
Upregulation of GIRK potassium channels, hyperpolarisation
Reduced cAMP, downregulation of calcium channels, preventing neurotransmitter release and other biochemical changes

Question 9

What regions of the brain are CB1 receptors located in and what effect of cannabis intoxication is this linked to?

Answer 9

Basal ganglia - reduced motor control
Cerebellum - reduced motor control and coordination
Hippocampus - reduced memory formation
Hypothalamus - increased appetite and sexual behaviour
Ventral striatum - feeling of reward
Amygdala - anxiety
Brain stem and spinal cord - antiemetic, analgesic
Neocortex - changes in sensory information and higher cognitive function

Question 10

What is the mechanism of action and effects of THC?

Answer 10

Partial agonist of cannabinoid receptors

Strong psychotropic effects

Question 11

What is the mechanism of action of cannabidiol?

Answer 11

Inverse agonist

Sometimes this can appear to be functioning as an antagonist, ‘functional antagonist’

Question 12

Name the two methods by which receptor pharmacology can be investigated

Answer 12

1. Binding assay with a radioligand

2. Functional assay with radioactive GTP

Question 13

Describe how a binding assay works

Answer 13

High concentrations of radioactive ligand is applied and binds to the receptor
Measure the radioactivity
Attempt to displace it with an unlabelled ligand
Measure the loss of radioactivity
Tells you how well the ligands are binding to the receptor

Question 14

Describe how a functional assay works

Answer 14

A radioactive GTP (GTP-gamma-S) binds irreversibly to the Galpha subunit
When the receptor agonist binds, GDP is exchanged for the radioactive GTP
Measure the radioactivity - tells you how activated the receptors are

Question 15

What effect does CB1 activation have on neurotransmitter release?

Answer 15

CB1 receptors are inhibitory autoreceptors
Activation suppresses neurotransmitter release
They do this by inhibiting calcium channels

Question 16

What are spontaneous quantal events?

Answer 16

Every so often, a single vesicle releases its neurotransmitter unprompted
Binds to postsynaptic membrane, resulting in a miniature EPSC (or IPSC if GABA)
As the amount of neurotransmitter in each vesicle is the same, quantal release is always consistent in amplitude and frequency

Question 17

Describe the experimental design that led to the discovery of how CB1 receptors exert neuromodulatory effects

Answer 17

Block presynaptic sodium channels so all postsynaptic potentials are now the result of quantal events
Activate CB1 receptors
Measure the miniature EPSCs/IPSCs
If the amplitude changes, you know its a postsynaptic mechanism
If the frequency changes, you know its a presynaptic mechanism
If there is no change in amplitude or frequency, it’s an action-potential dependent mechanism

Question 18

What is DSI?

Answer 18

Depolarisation induced Suppression of Inhibition

Form of short term synaptic plasticity mediated by CB1 receptors

Question 19

Where on neurons are cannabinoid receptors present?

Answer 19

Always presynaptically

Question 20

What were the results of the investigation into how CB1 receptors work?

Answer 20

There was no change in frequency or amplitude of the miniature IPSCS (so must be action potential dependent)
However IPSCs that are evoked by action potentials were reduced in frequency (so must be presynaptic)
Shows that the effect of CB1 receptors is presynaptic and action potential-dependent i.e. inhibition of VOCCS

Question 21

Name two examples of endogenously produced cannabinoids (endocannabinoids)

Answer 21

Anandamide (AEA)

2-Arachidonylglycerol (2-AG)

Question 22

Where are the areas of the brain with the highest density of CB1 receptors?

Answer 22

Basal ganglia
Cerebellum
Hippocampus

Question 23

What kind of values can a binding assay and a functional assay tell you about a ligand and a receptor?

Answer 23

Binding assay: Binding affinity (Ki)

Potency: inhibitory EC50

Question 24

How do endocannabinoids differ from exogenous cannabinoids?

Answer 24

They are lipid soluble so cannot be stored in vesicles

Diffuse through membranes instead

Question 25

Where does DSI occur?

Answer 25

Hippocampus

Question 26

What is the mechanism of DSI?

Answer 26

1. Prolonged depolarisation triggers endocannabinoid release
2. This is calcium dependent
3. Retrograde messengers - bind presynaptic membrane
4. Bind CB1 receptors on inhibitory GABAergic interneurons
5. CB1 coupled to Gi/o
6. Inhibition of N-type calcium channels
7. Suppression of inhibition