19: Cannabinoids

AEA is metabolized by (FAAH/MGL).

FAAH - Fatty Acid Amide Hydrolase; postsynaptic (we said in class that both of the enzymes were pre-synaptic, so not sure...)

True or False: There is currently no evidence-based pharmacotherapy available for cannabis users.

True. There's a high level of relapse for cannabis usage!

Are cannabinoid receptors generally excitatory or inhibitory?

inhibitory; they inhibit cAMP; close Ca2+ channels; open K+ channels (which is hyperpolarizing)

Endocannabinoids, such as anandamide (AEA) and 2-AG, are synthesized from __________________ in the cell membrane.

inositol phospholipids

A negative, psychopathological response to marijuana is more likely in _________________ users. Describe such a response.

first-time; -Anxiety (related to increased heart rate?) -Panic -Paranoia -Delirium

Where are CB1 receptors expressed?

in the brain! striatum, substantia nigra, cerebellum, hippocampus, and cortex *makes sense if you consider cannabinoids' effect on locomotor activity, coordination, and learning/memory

An endocannabinoid is made (inside/outside) the brain.

inside

What is cannabinol (CBN)?

(plant) metabolite of THC

What are some methods that have been used to treat cannabis use?

-Cognitive behavioral therapy -Contingency management -Family based interventions -Relapse prevention training -Psychotherapy -Antidepressants (some studies are promising)

There is some evidence of withdrawal and dependence involving THC...What are some withdrawal symptoms of THC?

-Irritability -Increased anxiety -Depressed mood -Sleep disturbances -Heightened aggressiveness -Decreased appetite (similar to nicotine withdrawal) -Symptoms begin within 48 hours, typically lasting a week; Some EEG changes persist at least 28 days

Describe some effects/impairments of cannabis in rodents that have been observed.

-Motor impairment -Catalepsy (trance or seizure with a loss of sensation and consciousness accompanied by rigidity of the body) -Hypothermia -Analgesia -Disruption in hippocampal dependent learning tasks

What are some therapeutic uses of cannabinoids?

-Reduction of nausea and vomiting in cancer chemotherapy patients (that don't respond to other drugs) -Appetite stimulant (AIDS-wasting disease) -Glaucoma (reduce intraocular pressure) -Analgesic (for spasticity, neuropathic pain, lower urinary tract symptoms associated with multiple sclerosis, inflammatory pain) -Neuroprotective following brain injury? (inhibits glutamate and free radicals) -Migraine? -Intractable hiccups?

What can you say about the behavior of the compound anandamide (AEA) based on its structure?

-immediate diffusion to presynaptic membrane (has hydrophobic portion and hydrophilic portion) -can pass through cell membranes -potential to be stored in fatty tissue -kind of contains fatty acid structure... *the same could be said for 2-AG

Describe the four stages of cannabis effects.

1. Buzz: light-headedness, dizziness 2. High: euphoria, exhilaration, disinhibition 3. Stoned: calmness, relaxed, dreamlike 4. Come-down

Describe the process of how endocannabinoids act on neurons (explain retrograde signaling).

1. Depolarization in the post-synaptic cell causes the synthesis of endocannabinoids (the enzymes are calcium-dependent). 2. Endocannabinoids travel "backwards" across the synapse and bind to CB receptors located on the pre-synaptic cell. 3. CBR binding activates the second messenger Ca2+. 4. Ca2+ release leads to vesicle release from the pre-synaptic cell, which then obviously affects the post-synaptic cell. *Recall: CB receptors usually have an inhibitory effect. AEA prefers binding to CB1, and 2-AG, which has a higher concentration in the brain than AEA, binds to CB1 and CB2.

Explain how consumption/metabolism of THC might lead to weight gain, and how might one counteract this?

A well-known effect of cannabis is increased appetite, particularly for sweet and palatable food, even when animals are sated. A CB1 antagonist might reduce increased appetite... Rimonabant (Acomplia) - CB1 antagonist, marketed as a diet drug (combined with a low-calorie diet)

Anandamide (AEA) has preferential action at the (CB1/CB2) receptor, acting as a partial agonist.

CB1

Which cannabinoid receptor is found in the brain, CB1 or CB2?

CB1

What are the cannabinoid receptors in the body?

CB1 and CB2

(CB1/CB2) receptors are expressed in immune cells (including microglia) and other peripheral tissues.

CB2

Anandamide (AEA) has less activity at the (CB1/CB2) receptor, acting as a partial agonist/antagonist.

CB2

What is the principle psychoactive cannabinoid that maintains the recreational use of marijuana?

Delta-9-Tetrahydrocannibinol (THC)

Both cannabidiol and cannabinol may modulate the activity of ______________.

THC

One study demonstrated that CB1 receptors mediate the subjective and physiological effects of smoking marijuana. Describe the different outcomes in the placebo + marijuana group and the Rimonabant + marijuana group in regards to rating of drug effect and heart rate. Recall that Rimonabant is a CB1 antagonist.

The Rimonabant + marijuana group had lower mean ratings of drug effect (feeling high; feeling stoned). The Rimonabant + marijuana group also demonstrated a lower mean heart rate.

In a study of cannabinoids' reinforcing effects, it was found that monkeys would self-administer THC. Interestingly, the monkeys did not make as many presses for a higher dose of THC. Why?

We don't know...but perhaps: The monkeys didn't require as much THC to achieve the desired effect OR the monkeys didn't like the higher dose...

In rats, blocking CB1 receptors after THC administration produces withdrawal signs. What are some of these signs?

Wet dog shakes, grooming, hyperactivity

What is cannabidiol (CBD)?

a precursor to THC

2-arachidonoylglycerol (2-AG) is a full (agonist/antagonist) to both CB1 and CB2 receptors.

agonist Hint: 2-"AG" => "AG"onist

Rimonabant is a cannabinoid receptor (agonist/antagonist). Why might this be useful?

antagonist Since blocking CB1 receptors can reduce the rewarding properties of many other drugs of abuse, decreasing overall reward, CB1 receptors might be a good target for treatments of different substance use disorders. Rimonabant is used to test the effects of blocking CB1 receptors.

Once synthesized and released, endocannabinoids travel to the (post-synaptic/pre-synaptic) cell, activating the second messenger _______________. The release of this second messenger causes the release of vesicles. What is contained in the vesicles depends on the cell type.

pre-synaptic (think opposite of what we've learned for every other signaling mechanism!); Ca2+

Wait, what the heck is inositol anyway??

(what I grabbed from online): Inositol phosphates are important intracellular second messengers in eukaryotic cells. Inositol, a cyclic molecule with six hydroxyl groups, forms the hydrophobic head group of membrane inositol phospholipids. The actions of lipid kinases and phosphatases on the inositol ring of inositol phospholipids generate a variety of phosphoinositol phospholipids. As a result of upstream signaling events, specific phospholipases are activated, cleave phosphoinositol phospholipids, and release intracellular inositol phosphate second messenger molecules.

What are some limitations/obstacles regarding what we know about therapeutic uses of cannabinoids?

-Currently a lack of research, primarily due to politics -Efficacy for some illnesses may be better if smoked; hence, long-term use might not be medically acceptable -Psychoactive, euphoric effects...thought to lead to dependency -Some research has argued that orally administered cannabinoids are unlikely to be abused...

Describe some effects of cannabis.

-Increased blood flow to skin (warmth, flushing) -Increased heart rate (pounding pulse); blood pressure effects vary -Cannabis causes brain arteries to constrict, may increase stroke risk -Dilation of corneal blood vessels leads to bloodshot eyes -Increased appetite -Immunosuppression (but little evidence that this causes disease) -Analgesic, especially with chronic inflammatory or neuropathic pain -Psychomotor effects: reduced coordination, reaction time and ability to divide attention can persist for several hours after "high"; Potentiated by alcohol use (hence, efforts to reduce driving under the influence of marijuana) ***Some effects of cannabis is likely due to expectation

How can you use CPP in a study of THC?

CPP = Conditioned Place Preference You can use CPP w/ rodents and see if they prefer the THC-associated place. ***You can only do this after an initial THC treatment (in home cage) => maybe b/c of common aversive experience experienced by 1st-time users

The enzymes that synthesize endocannabinoids are dependent on what ion?

Ca2+

Explain the mechanism behind cannabinoids leading to increased firing of dopamine neurons in the VTA.

Cannabinoids can inhibit GABA release in the VTA. This results in DISinhibition of dopamine neurons. Dopamine release increases (released in the Nucleus Accumbens).

Why use an ex-user in a study v. someone who has never taken the drug of interest?

Ex-users => presumed no longer tolerant; good control; they know what to expect; not a naïve user who might experience aversive effects; these people are more likely to agree to participate in your study, perhaps. Ask yourself: Is it reasonable to compare current users w/ people who NEVER used marijuana? There might be inherent difference(s) b/t these populations => b/c some of them chose to use and some of them did not.

True or False: Endocannabinoids are released in response to depolarization in the post-synaptic cell.

False! Endocannabinoids are SYNTHESIZED in response to depolarization in the post-synaptic cell. These enzymes act fast, and synthesis happens almost immediately. THEN endocannabinoids can bind to CB receptors on the pre-synaptic cell.

True or False: AEA is found at a higher concentration in the brain than 2-AG.

False. 2-AG is found at a higher concentration in the brain than AEA.

True or False: Endocannabinoids (such as AEA and 2-AG) can be transported via vesicles.

False. Because of the molecular structure, they would simply fuse with or diffuse through the membrane of the vesicle. Endocannabinoids simply diffuse passively.

True or False: Behavioral effects of cannabis take several hours to manifest.

False. Behavioral effects occur almost immediately. Effects seldom last longer than 2-3 hours.

Explain how research suggests that cannabinoid effects in the VTA (e.g., increased firing) depend on opioids.

It has been found that blocking opioid receptors in the VTA blocks the rewarding effects of cannabinoids.

2-AG is metabolized (FAAH/MGL).

MGL - monoacylglycerol; presynaptic

Describe the metabolism of cannabis.

Metabolism: Liver (cytochrome P450 enzymes) First metabolite of THC (11-hydroxy-delta-9-THC) is active Elimination is long (20-30 hours) due to fat absorption

Describe different routes of administration of cannabis.

Oral: poor absorption; prolonged action Smoked: faster acting; 5-60% absorbed, depending on a variety of factors

Precipitated withdrawal

Producing immediate acute withdrawal by administering an antagonist to the drug Ex: In rats, blocking CB1 receptors after THC administration produces withdrawal signs

In one study of cannabis effects, subjects performed a recall task. They listened to a short passage of prose and were tested on their ability to remember details of the story later. There were 3 groups: 1) placebo, 2) small dose of THC, and 3) larger dose of THC. Describe the results.

The placebo group scored the highest (difference in recall score compared to baseline). There might not have been a signif difference between the low THC dose and the placebo group. What is striking on the plot is the score for the large THC dose group. They had a MUCH lower recall score than the other two groups.

What is unique about the CB1 and CB2 receptors?

The signaling molecules are lipids; mechanism is retrograde signaling!

Describe the Conditioned Place Preference paradigm.

There are two different compartments w/ different stimuli (ex: horizontal bars v. vertical bars on walls of chamber). The rodent learns to associate specific cues w/ specific drug administration in corresponding environment. You test in extinction: where does animal spend most of its time? Which compartment does it prefer? => infer which drug/treatment it prefers

True or False: There are evidence-based, significant impairments due to cannabinoid use.

True! Impairments have been observed in verbal memory; spatial memory; time estimation; and reaction time

True or False: Anandamide (AEA) is an endocannabinoid that is found in nearly all tissues.

True.

True or False: Cannabinoids are reinforcing.

True.

True or False: Cannabis can be tested and found in samples weeks after use.

True.

True or False: Endocannabinoids can modulate any type of neuron.

True.

True or False: Unlike THC, cannabidiol (CBD) is not psychoactive.

True.

True or False: Cannabis is very fat soluble.

True. Remember the structure of endocannabinoid compounds (contains hydrocarbon chain). It will accumulate in fatty parts of the body, like the brain and placenta.

Blocking CB1 receptors can reduce the rewarding properties of many other drugs of abuse, not just cannabinoids. What does this suggest?

brain cannabinoid systems may be critical for reward processing generally (like dopamine)

Because of the concern of cannabinoids' psychoactive effects (which could lead to dependency...), researchers have looked into the potential use of _______________ for therapeutics. This compound is active, but not psychoactive.

cannabidiol (CBD) - think about the paper we discussed in class!

In a study that compared withdrawal discomfort scores of current marijuana users v. ex-users, the (current users/ex-users) had consistently higher scores.

current users

In rats, withdrawal is associated with (increased/decreased) VTA dopamine activity, and (increased/decreased) CRF release in the amygdala.

decreased; increased

The synthesis of endocannabinoids is dependent on (hyperpolarization/depolarization) of the post-synaptic cell.

depolarization

Endocannabinoids are synthesized and released in response to (hyperpolarization/depolarization) of the (post-synaptic/pre-synaptic) cell due to the influx of Ca2+.

depolarization; post-synaptic

Cannabinoids increase the firing of VTA ______________ neurons (which neurotransmitter), activating the brain's reward system.

dopamine

Anandamide and 2-AG are examples of ________________.

endocannabinoids

Are cannabinoid receptors ionotropic or metabotropic?

metabotropic

Research suggests that cannabinoid effects in the VTA depend on _____________ (what drug class).

opioids

Cannabis plants contain _________________, which can have psychoactive properties.

phytocannabinoids (more than 70 unique kinds!)

CB receptors are (post-synaptic/pre-synaptic) and lead to (inhibition/excitation) of further neurotransmitter release (e.g., GABA, glutamate).

pre-synaptic; inhibition *recall that CB receptors involve retrograde signaling *also, if you INHIBIT, for example, a GABA interneuron, then you're going to DISinhibit the neuron that the interneuron synapses on, leading to excitation

Down-regulation and desensitization of CB1 receptors in response to chronic THC use has been shown in both rodents and humans. This is evidence of pharmacodynamic _______________.

tolerance; repeated use of THC leads to new allostatic state

What are some effects of cannabis at high doses?

profound personality changes, perceptual distortions, and hallucinations have been reported

Why is oral administration of cannabis slow acting?

stomach degradation and first-pass metabolism => a lot of the drug is never absorbed; longer action but slower onset of effects

What does Endocannabinoid Membrane Transporter (EMT) do?

terminates action of endocannabinoids (if they're not already passively diffused through the membrane); located on pre-synaptic neuron

In a study of cannabinoids' reinforcing effects, it was found that monkeys (would not/would) self-administer THC.

would