Transcript Russ Carpenter

Cannabinoid CB1 receptor
Role in extinction and
sensitization
Say it with me
• Kah nab a noid
• Ka banna boy
outline
• Receptor and receptor subtypes
– Location, function and distribution
• Endogenous ligand
• Kamprath paper
• Pamplona et al paper
– Results
– Clinical applications
CB receptor subtypes
• CB1-found in brain
• CB1A-very little info, but does exist
• CB2-found in immune cells (not in brain)
– CB1 is of most interest to us today
– acts via G-protein which, when activated,
inhibits adenylate cyclase as well as
voltage gated CA++ channels, stimulates K+
channels
Distribution of CB1
• Cerebellum– motor function
• Cortex– association
• Basal Ganglia
• Limbic system
– Hippocampus-learning
– Amygdala-fear
• NO CB1 in thalamus,medulla or brainstem
Limbic CB1 receptors
• Exclusively localized to GABA and
Cholecystokinin (CCK) containing
presynaptic terminals
– Receptor activates G-protein that
suppresses GABA release
• Less GABA=more anxiety?
– In hippocampus- release of ACh is inhibited
CB1 in a RAT BRAIN
Relative density of CB1R in select
brain regions
Anandamide
• Endogenous cannabinoid
– Synthesis not known
• When bound in high doses, behaviors
include: hypothermia, analgesia,
hypomobility, catalepsy
• LIPID NT, can pass membrane, thought to
be synthesized on demand
• Acts on membrane bound and intracellular
locations
Anandamide
• Brain levels rival that of DA (felder et al 96)
• Binds to both CB1 and CB2
– Acts as agonist
• Highest conc in hippo, striatum, ctx and
cerebellum
• THC acts as CB1 agonist
• Some diet drugs act as CB1 antagonist
– Rimonabant (aka SR141716)
Kamprath et al Neuroscience 06
• Sensitization: nonassociative learning
– General increase in reponse to potentially
harmful stimuli after aversive experience
– E.g. inescapable footshock=alter behav& cort
• Fear conditioning: tone paired with shock
– Re-exposure to tone activates memory of the
tone-punishment association and induces
response
– E.g. rats freeze upon re-exposure to tone
Extinction vs Habituation
• Extinction: new association btwn tone and
the nonappearance of predicted
punisment (safety learning)
– Suppresses the expression of the memory of
the tone-shock pairing
• Habituation: repeated non-reinforced tone
presentation will lead to a decrease in
response to the tone
Role of CB1
• CB1 role in extinction is limited to aversive
testing conditions
– Genetic ablation or pharmacological blockade
of CB1 impairs the extinction of fear
memories
• CB1 plays no role in conditioning to tasks
involving positive reinforcement
Goals of study
• Examine the role of CB1 in extinction and
habituation of acquired fear responses
– Utilize genetic mutant CB -/- and ‘wild type’
CB+/+
– Utilize SR selective CB1 antagonist
Cond
CB-/sensitized
Sens
No difference
in acquisition
CB-/- showed same freezing
Behavior with or without shock
conditioned
CB+/+
sensitized
conditioned
Conditioning: 80 dB tone with .7 mA footshock
next day tone only in novel envir
CB-/- show prolonged and stronger freezing to tone
Sensitization: .7 mA footshock only NO TONE
next day tone only in novel envir
CB-/- show prolonged and longer freezing to tone
Can CB-/- associate memories?
• Because no difference in freezing was
seen between tone-shock pair and tone
alone in CB-/- animals, authors wanted to
make sure that CB-/- animals could in fact
form an associative memory i.e. associate
the tone with the impending shock
• Utilize electrophysiology to record auditory
evoked potentials in CA1 region of hippo
• No significant differences between CB-/and CB+/+ in the potentiation of auditoryevoked potentials
• Both groups have similar activation in CA1
region when exposed to loud tone
Within session vs long term
• Next, authors wanted to see what changes
in extinction are seen over time between
the two groups
• Testing occurred as before, with the
addition of another testing round 5 days
after the first test
CB-/sensitized
conditioned
CB+/+
sensitized
conditioned
CB-/- again froze longer
And stronger both 1 day
and 6 days after conditioning
SR
CB+/+ animals treated with
SR show same trend as the
Mutant strain, even 5 days
later
CB1 controls both
within session and
long term
fear adaptation
Pamplona et al
Psychopharmacology 2006
The cannabinoid receptor agonist
WIN 55,212-2 facilitates the extinction of
contextual fear memory and spatial
memory in RATS
Main Objectives
• Examine whether admin of CB1 agonist
WIN could faciliate the extinction of recent
and/or remote contextual fear memory in
rats
• Investigate the role of CB1 antagonist SR
in the extinction process
• Determine if not only fear memory but also
spatial memory was affected by these
drugs
Methods
• Animals
– Male Wistar rats, group housed
• Behavorial testing occurred during light phase of
the day/night cycle….. Why?
– N of 7-10 animals per group
• Drugs
– Win and SR dissolved in 0.9% saline with
10% DMSO and 0.1% Tween 80
– Controls received vehicle only
• Animals injected IP 0.2mL per 100 g BW
– Win given 30 min before testing
– SR given 20 minutes before testing
Behavioral Procedures
• Fear Conditioning
– Contextual fear: 3 min in cond chamber and
then received 1 sec 1.5 mA shock, 60
seconds after shock they were removed
– Tone fear: 3 min in cond chamber and then 10
sec of 80 dB tone that co-terminated with 1
sec 1.5 mA shock, 60 seconds after shock
they were removed
• Freezing was the behavior measured
during subsequent testing
Effects of CB1R on extinction of
recent contextual fear memory
• Successive exposures to conditioning
chamber were used to assess short term
(within exposure) and long term (between
exposure) extinction of cond fear
• 24, 48 and 72 hours after contextual
conditioning animals were placed back in
chamber and freezing recorded
– WIN or SR treatment before each session
Control animals froze less on each
successive re-exposure
1.0 mg/Kg dose of SR disrupted this
extinction (they froze more than
control group)
Low dose of WIN facilitated
extinction (they froze less than
controls); high dose of WIN
disrupted extinction
Mid dose of WIN mimicked control
group
Dose Dependant Effects!
In the first 3 minutes (retrieval) of the
9 minute test block SR had no effect
But WIN at the mid dose showed
Decreased freezing time, this means
That there is no effect of WIN on
Memory retrieval
• Effects of WIN on extinction
of remote contextual fear
memory
5 days of exposure to context
shows that WIN treated rats
freeze less, extinction is
facilitated in short term fear
memory by WIN
Drug free rats 48 hours after
the 5 day extinction protocol
WIN treated, contextual cond
rats froze less than control and
SR treated rats
WIN facilitates extinction of
remote fear memory
Unconditioned freezing behavior
• Day 1 rats placed in cond chamber for 3
minutes, shocked (1 sec 1.5mA), 60
seconds later they were removed
• Day 2 rats treated with WIN or SR, placed
in novel environment and freezing
behavior was measured
• Also, separate group of rats treated with
WIN and SR and placed in open field to
measure effects on locomotion
No effect of WIN or SR on unconditioned freezing or
on locomotion in open field test
Day 1 and 2 were training,
6 trials each day
Drug admin on day 3, platform
moved to opposite side, and
6 trials followed
WIN treated animals had
decreased latency to find
platform on first trial, no diff
from controls after that
SR treated animals showed
increased latency on trial 2
Compared to control, no diff
from controls after that
Discussion
• Disruption of CB1 cannabinoid signaling
decreases the ability of rodents to
extinguish fear memories
• WIN acting as a CB1 agonist facilitates
fear extinction
– WIN also facilitates spatial memory
– Not by disrupting acquisition, memory
retrieval or affecting sensory-motor ability
CB1 antagonists
• Administration of selective CB1
antagonists (SR or rimonabant) or genetic
ablation of CB1 gene leads to a
pronounced deficit in the extinction of
conditioned fear
– Also leads to deficits in previously learned
spatial information
• In Rats!
• Administration of CB1 agonist WIN
facilitates the extinction of contextual fear
and may have long term implications
• In humans, pharmacotherapies directed at
the endocannabinoid system may help
treat psychiatric disorders such as retrival
of fear memories, panic, phobias (like
being afraid of russians) and PTSD
You may cease learning…….
………………….now!
The End
Pat Ronan
Rules!