Lecture 13: Cannabinoids Flashcards
1
Q
Central effects of THC
A
- Impairment of
- STM
- Motor coordination → drowsy
- Cognition
- Altered sense of time
- Mood changes (euphoria/dysphoria)
- Catalepsy (trance like state)
- Hypothermia
- Can be used as a measure of THC
- Analgesia
- Antiemetic
- Appetite increase
- Useful for cancer treatment
2
Q
Peripheral effects of THC
A
- Tachycardia
- Even modest doses 20 -30 BPM
- May increase the chance of MI esp in older people and those with heart problems are at higher risk.
- Intraocular pressure (IOP)
- Vasodilation → opens blood vessels in the eye → bloodshot eyes
- Fall in IOP
- Bronchodilation
3
Q
THC pharmacokinetics
A
- Long-lasting, takes a while to kick in
- Routes: smoking/oral (add to food, edibles)
- Orally → 30 minutes-2h to develop, lasts for 4-8h
- Subject to conjugation n enterohepatic circulation, prolonging duration
- Conjugation
- Phase 2 metabolism
- Grps added to it to to make it more polar
- Enterohepatic circulation
- Secreted in the bile
- Goes back into the gut n reabsorbed
- Prolongs the half life
- Conjugation
- Lipophilic
- Stored in the body fat THUS
- Can be detected weeks after smoking
- Company drug test
- Stored in the body fat THUS
4
Q
Describe the cannabis pilot experiment
A
- 9 pilots, current cannabis users, received a cigarette containing 20 mg THC.
- After smoking CHT cigarette, significant reduction in performance
- Long-lasting effects -> errors kept persisting even 24h after
- Pilots were unaware their performance is impaired
- Similar effects to ethanol
- Lasts much longer n won’t notice the errors
- Why?
- CONCLUSION: cannabis can impair complex tasks over long periods
5
Q
Describe the initial hypotheses regarding the mode of action of THC and the discovery of the first cannabinoid receptor
A
-
Mode of Action Hypotheses:
- THC is highly lipophilic → initially thought it might change membrane properties (similar to GA) or act at IC receptors.
- Initially considered possibilities:
- Dissolving in the membrane (lipid soluble) and affecting membrane fluidity.
- Passing through the membrane and acting on intracellular receptors within the cell.
-
Discovery of Cannabinoid Receptor:
- The first cannabinoid receptor was discovered in 1988.
- Originally, there was speculation about cannabinoids binding to receptors inside the cell.
6
Q
Explain the experimental approach used to identify cannabinoid receptors and the characteristics observed during the process.
A
- Study conducted using a tritium-labelled cannabinoid analogue CP-55,940 along with a cold ligand.
- THC (active compound) outcompeted the labelled ligand, indicating binding specificity.
- Binding was saturable, suggesting the presence of a specific binding site.
- If non-specific, binding would increase infinitely
- Can’t saturate if there isn’t a specific binding site
- No Vmax
- GTP analogs were used to alter the receptor’s affinity, indicating that the protein involved is a GPCR.
- The conversion of GTP or GDP changed the affinity of the receptor, providing additional evidence for GPCR involvement.
7
Q
Describe the characteristics of CB1 and CB2 receptors
A
- Both are GPCR
- CB2 has been cloned
- CB1 is primarily of interest [involvement in effects of the brain]
- CB2 involve din periphery n immune systems
- CB2 receptors inhibit adenyl cyclase activity
8
Q
Describe the distribution of CB1 and CB2 receptors
A
- CB1 Receptors:
- Expressed in various brain regions:
- Ventral Tegmental Area (VTA) and Locus Coeruleus (LC) involved in dopamine release and euphoria.
- Hypothalamus for autonomic activity, appetite regulation, and homeostasis control.
- Found in areas related to memory (hippocampus) and pain (Periaqueductal Gray - PAG).
- Expressed in various brain regions:
- CB2 Receptors: prominently expressed in immune cells.
9
Q
What are CB1’s signaling mechanisms?
A
- CB1 receptors are coupled with calcium channels, modulating calcium currents [it is a GPCR]
- Activates potassium channels → increased potassium currents.
- Inhibition of Protein Kinase A (PKA), influencing cAMP responses.
- Direct effects on vesicle release and neurotransmitter release.
10
Q
What are CB1’s regulatory mechanisms?
A
Beta-Arrestin:
- Involved in internalizing CB1 receptors.
- Contributes to the desensitization of CB1 receptor activity.
11
Q
Describe the physiological effects observed in mice with CB1 receptor knockout.
A
- Don’t live as long (significantly reduced in KO mice)
- Lose weight
- Resistant to obesity
- Enhanced leptin sensitivity
- Leptin is a hormone that tells you you’re full
- Loss of THC induced hypothermia
- Less pain sensitive in some tests of supraspinal pain responses
- No change in hypothermia
- Increase in catalepsy
- Analgesia assays
- Tail flick = how quickly it flicks
- Hotplate assay
- Formalin
- Reduced response
- CB1 receptor itself is pro-analgesic
- Induce less pain when KO
12
Q
What are the endogenous ligands that bind to cannabinoid receptors?
A
- Anandamide: endogenous lipid that can stimulate cannabinoid receptor-mediated signal transduction.
-
2-AG (2-Arachidonoylglycerol):
- Derived from the canine gut.
- Demonstrated in vivo effects similar to THC.
-
Other Endogenous Cannabinoids:
- Various other endogenous cannabinoids have been discovered.
13
Q
How is anandamide produced and released?
A
- Production on Demand:
- Anandamide is not stored in vesicles like classical neurotransmitters.
- Calcium-Sensitive Enzymes:
- Produced following the elevation of intracellular [Ca2+].
- Enzymes involved, such as N-acyl-phosphatidylethanolamine specific phospholipase D (NAPE-PLD), are calcium-sensitive.
- Source:
- Anandamide is obtained from the enzymatic hydrolysis of N-arachidonoyl-phosphatidylethanolamines (NArPE), a membrane phospholipids.
14
Q
What is the production mechanism of 2-AG?
A
-
Produced on demand
- Derived from sn-1-acyl-2-arachidonoylglycerols (DAGs) in the cell membrane
- Acts as a neurotransmitter
-
Calcium-Sensitive Enzymes:
- Production involves calcium-sensitive enzymes.
- sn-2-selective DAG lipases (DAGLs), specifically DAGL-α and DAGL-β, catalyze the conversion of DAGs into 2-AG.
15
Q
How are cannabinoids synthesized and released?
A
-
Production from Phospholipids:
- Endocannabinoids (e.g., anandamide, 2-AG) are produced from phospholipids in the cell membrane.
- Cleavage of phospholipids occurs when intracellular [Ca2+] increases.
-
On-Demand Production:
- Production of diacylglycerol (DAG) and subsequently 2-arachidonoylglycerol (2-AG) is calcium-dependent.
- These lipids are not stored but produced on demand.
-
Receptor Activation:
- Released endocannabinoids can activate receptors present in both post and presynaptic neurons.
- Cannabinoids can act in a normal or retrograde (backwards) fashion.
-
Enzymatic Breakdown:
- Once released, endocannabinoids are broken down by enzymes.
- Main enzymes involved: Monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH).
-
Presence in Glial Cells:
- Endocannabinoid receptors are also present in glial cells.
-
Transporter Involvement:
- Endocannabinoids may be released from cells through transporters like the endocannabinoid membrane transporter (EMT).
