Drugs of abuse 1 Flashcards
Outline the reward pathway
MESOLIMBIC DOPAMINE SYSTEM:
Dopaminergic cell bodies in the VTA, projects to the Nucleus Accumbens, releases dopamine
=EUPHORIA
T/F VTA/Nucleus Accumbens pwathway is only activated by drugs
F.. natural pathway, activated by food etc.
Drugs hi-jack this system ,and produce powerful rewards
Routes of administration of drugs of abuse
‘Snort’ – Intra-nasal
Eat’ - Oral
‘Smoke’ - Inhalational
‘Inject’ – Intra-venous
Outline the speed of absorption depending on the route of administration
‘Snort’ – Mucous membranes of nasal sinuses. Slow absorption
‘Eat’ – Gastrointestinal tract. Stomach to small intestine to portal system to liver to heart to brai
Very slow absorption
‘Smoke’ – Small airways and alveoli. Close to the heart Rapid absorption
‘Inject’ – Veins
Rapid absorption
Which route of administration of drugs of abuse is the fastest and why
Inhalation
Because if it goes far into the lungs, the alveoli have such thin walls,they allow really fast passage from lungs to blood…
if injecting, it has to go through the right side of the heart, through pulmonary system, then back to the heart then out to the body
With inhalation comes straight into the left side of the heart from the pulmonary system, then straight around the body
Classify drugs of abuse
Narcotics/Painkillers
Depressants
Stimulants
Miscellaneous
Give examples of narcotics/painkillers
Narcotics/Painkillers – opiate like drugs e.g. heroin
Give examples of depressants
Depressants – ‘downers’
e.g. alcohol, benzodiazepines (valium), barbiturates
Give examples of stimulants
Stimulants – ‘uppers’
e.g. cocaine, amphetamine (‘speed’), caffeine
metamphetamine (‘crystal meth’)
Give examples of the miscellaneous drugs classification
Miscellaneous – e.g. Cannabis (although predom. depressant), Ecstasy (MDMA) (predom. stimulant)
Where is the cannabis found in the cannabis plant
Hashish/Resin – Trichomes (the glandular hairs)
Hash Oil – Solvent extraction (this concentrates the THC etc found in the trichomes)
T/f there is only 1 type of cannabis compound
F > 400 compounds;
What is a cannabinoid and how many are there
Cannabis compound with pharmacological effect. 60 of the 400 cannabis compounds are cannabinoids
Name the cannabanoid responsible for most of the psychactive effects of cannabis
Detla 9 tetrahydrocannabinol
Which compound is responsible for the bad effects of cannabis
Detla 9 tetrahydrocannabinol
THC
Which compound actually can mitigate the effects of the Detla 9 tetrahydrocannabinol
Cannabidiol
What has been happening to THC concentration is hash over the years
It has significantyl increased
60’s + 70’s: ‘Reefer’ – 10mg THC
21st Century: ‘Skunkweed/Netherweed’
- 150mg THC - 300mg THC (+ hashish oil)
What can be found with increaseing THC
Increasing negative symptoms (e.g. suicidal thoughts, depression)
But much smaller difference in the positive experience (e.g. euphoria doesn’t increase much with THC concentration, compared to increase in negative effects)
Outline the two major routes of administration of cannabis, and how much of the drug that becomes bioavailable in each case
Oral – 5-15%
delayed onset/slow absorption
first pass metabolism
Inhalation – 25-35%
If inhalation is the fastest route of administration, why is only 25-35% becoming available
- Inhalation: 25-35% of dose enters bloodstream
- Anything inhaled suffers from about 50% loss automatically
- This is because only about 50% gets far enough down into the lungs to diffuse into the bloodstream
- Lots of it is breathed back out, much of it won’t be absorbed
Outline the solubility of cannabanoids. What are the implications of this
EXTREMELY lipid soluble (beaten only by GA)
Fatty acid conjugates build
up in fatty tissue
Why do drugs not usually accumulate in he fat
Most drugs not THAT lipid soluble, and very poor blood supply (only around 2% of CO)
What happens after drug is injected into the blood to the concentration of drug i the blood
It will decrease, as concentrations increase int he tissues as the drug diffuses out of the blood into the tissue
High perfursion tissues e.g. brain will have high THC concentration at first,
then just before 24hrs after administration, low perfusion tissue has higher concentration (as intensive accumulation occurs in less vascularised tissues and finally in body fat, the major long-term storage site, resulting in concentration ratios between fat and plasma of up to 104)
What can be the ration of drug in the plasma to drug in the fat in chronic cannabis users
104 : 1 fatty tissue vs plasma… then you get a slow leak back into the blood
T/f it is the active cannabanoid that stays in the fatty tissue
F… the metabolites
What is the metabolite of cananbanoid
11-hydroxy-THC
What is the problem with cannaboid metabolites
11-hydroxy-THC (metabolite) is actually more potent than the 9 delta THC! They are also very lipid soluble so they can accumulate in the fat
What is the problem with THC excretion
65% is excretd by the bile, but there is a lot of enterohepatic cycling because the cannabanoid is lipid soluble so after it is excreted into the small intestine in the bile, it just gets reabsorbed back into the bloodstream
Why is there poor correlation between plasma
cannabinoid concentration and degree
of intoxication
Due to the potent metaboite and the enterohepatic cycling, as well as that in chronic cannabis users a high amount builds up in the brain (as it is a fatty tissue).
When you measure the blood concentration of THC, the active metabolite and the inactive metabolite, it may be quite low. But if you look in the brain, there could be high levels of THC and 11OH-THC (active metabolite), because of accumulation in the brain, which is quite a fatty tissue, and this may be very intoxicating.
What is the inactive metabolite of cannabanoid
THC-COOH (glucoronidated form).. then goes into the bile and is subject to enterohepatic cycling
Other than fat, which other tissue is very fatty
The brain (there is an increase in cannabis concentraiton in the blood for the first few hours after taking the drug, and this does fall so effects most potent at the start)
What is the problem with chronic users of cannabis in terms of the amount in the brain
There can be a huge times more in the brain than in the plasma
How long does 1 cannabis cigarette effects persist in the body
30 days (accumulates in the fatty tissue over 5 days, and then remains and very slowly exits
What is the mechanism of action of cannabanoids
There are GPCR….
CB1 and CB2….
depressant so the GPCR is Gi/o
What is the effect of cannabis on cell activity and why
GPCR is Gi/o so cAMP is reduced
Which endogenous compounds act on the cannabanoid receptors
Endogenous Anandamide
What is the most prevalent GPCR in the brain
CB receptors
Where are CB1
receptors located
Hippocampus/cerebellum/
cerebral cortex/basal ganglia
Where are CB2 receptros located
Immune cells
What is the usual inhibitor of the mesolimbic pathway to keep this system shut off until it needs to be activted due to a reward
GABA mediated inhibition
How does cannabanoid receptor work in euphoria
As they are depressant, they reduce the GABA neuron which inhibits the dopaminerigc neurons coming from the VTA….
Act via CB1 rceptors on the GABA inhibitory neurons on the dopaminergic neurons.
Called dysinhibition
What is the Anterior Cingulate
Cortex (ACC) involved in
error detection
performance monitoring with behaviour adjustment in order to avoid losses
e.g. if you driving on a big wide road, and you’re chatting, and then you go on a tight road, then you’re concentration will be refocused to the road… ACC responible for this to maintain perofmrance
What is noticed about the ACC in cannabis (improve)
Hypoactivity in cannabis users
could lead to schizophrenia
What is the effect of cannabis on food intake
Review the hypothalamic control of food
Ventromedial hypothalamus is catabolic and reduces feeding (MC4R)
Lateral hypothalamus is anabolic and increases feeding (Orexin and MCH)
- Presynaptic inhibition of GABA increases MCH neuronal activity
- Increased orexin production, which increases appetite
What is the effect of cannabis on the immune system
Cannabis is IMMUNOSUPRESSANT.
CB2 receptors present on NK, macrophage, B cell, T cell and mast cells
Cannabanoid reduces all of these
Review the function of immune cells on the diagram…
….
Why do some people use cannabis in disease
To suppress inflammatory response due to the effect on immune cells
What are the peripheral effects of cannabis and what is the effect mediated by
Immunosuppressant
AND
Tachycardia/vasodilation of (Conjunctivae!)-(not mediated by CB receptors… by TRPV1!)
Could lead to bloodshot eyes
Effect of cannabis on memory
Memory loss – Limbic regions (Amnestic effects/↓ BDNF)
Why is it difficult to overdose on cannabis to the point of death
They don’t have profound effects on the medulla, as there is low CB1 receptor expression
Because it shuts down the cardiorespiratory centre in the medulla
What is the medical application of cannabis
CB receptors seem to go up in diseases like MS, pain and stroke….
this seems to be the body’s own response to pain etc to reduce these effects
Also in stroke, post-stroke iscahemia can be improved by reducing inflammation by the CB2 receptors
What is the effect of cabbanoid receptors for obesity and/fertility
As adipose tissue increases etc. CB seems to increase which may be negative
Fertility has less evidence
When would you want agonist of cannabanoid receptor
During MS/pain/stoke it’s regulatory so you’d want agonist
MS: neuropathic pain + spasticity
Stroke: post-stroke ischaemia can cause damage driven by inflammatory processes
When would you want antagnist of cannabanoid receptor
To reduce pathalogical effect associated with obesity /fertility
Give examples of antagonst drugs
Rimonabant…. obesity drug… suppresses appetite and reduced weight gain
but some committed suicide so not on market
Give examples of agonist drugs and their use
You’’ want to use an agonist to increase cannabanoid receptor stimulation for things like post stroke ischaemia etc (where there is pain, this reduces pain)
Explain the the nasal route of administration
- Snort (intranasal) –> drug enters nasal sinus –> venous drainage –> lung –> heart –> brain
o Mucous membranes of the nasal sinuses will slow absorption
What is the clinical use of Dronabinol
Used in AIDS patients and cachexia (appetite stimulate)
What is nabilone used
Anti-nausea in cancer therapy
When is sativex used
MS… control the pain and spasticity in this condition
What other kind of drug could be used with cannabanoid like effect
Fatty acid amide hydrolase inhibitor… prevents breakdown of endogenous anandamide…. used in chronic pain
What do the following drugs contain:
Dronabinol
Nabilone
Sativex
Dronabinol: delta 9 THC
Nabilone: delta 9 THC
Sativex: delta 9 THC + CBD
Autoprotection’ – Dronabinol, Sativex
‘Autoimpairment’ - Rimonabant
