Cannabinoid CB1 receptor

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Cannabinoid CB1 receptor

• Role in extinction and sensitization

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Say it with me

• Kah nab a noid
• Ka banna boy

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outline

• Receptor and receptor subtypes
• Location, function and distribution
• Endogenous ligand
• Kamprath paper
• Pamplona et al paper
• Results
• Clinical applications

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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

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Distribution of CB1

• Cerebellum-
• motor function
• Cortex-
• association
• Basal Ganglia
• Limbic system
• Hippocampus-learning
• Amygdala-fear
• NO CB1 in thalamus,medulla or brainstem

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Limbic CB1 receptors

• Exclusively localized to GABA and Cholecystokinin
  (CCK) containing presynaptic terminals
• Receptor activates G-protein that suppresses GABA
  release
• Less GABAmore anxiety?
• In hippocampus- release of ACh is inhibited

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CB1 in a RAT BRAIN
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Relative density of CB1R in select brain regions
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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

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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)

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Kamprath et al Neuroscience 06

• Sensitization nonassociative learning
• General increase in reponse to potentially
  harmful stimuli after aversive experience
• E.g. inescapable footshockalter 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

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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

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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

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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

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Cond
Sens
CB-/- showed same freezing Behavior with or
without shock
CB-/-
No difference in acquisition
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
CB/
sensitized
conditioned
Sensitization .7 mA footshock only NO TONE
next day tone only in novel envir CB-/- show
prolonged and longer freezing to tone
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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

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• No significant differences between CB-/- and
  CB/ in the potentiation of auditory-evoked
  potentials
• Both groups have similar activation in CA1 region
  when exposed to loud tone

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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

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CB-/-
sensitized
conditioned
CB/
sensitized
conditioned
CB-/- again froze longer And stronger both 1 day
and 6 days after conditioning
CB/ animals treated with SR show same trend as
the Mutant strain, even 5 days later
SR
CB1 controls both within session and long term
fear adaptation
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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

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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

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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

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• 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

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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

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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

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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!
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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
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• Effects of WIN on extinction of remote contextual
  fear memory

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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
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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

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No effect of WIN or SR on unconditioned freezing
or on locomotion in open field test
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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
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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

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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!

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• 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

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• You may cease learning.
• .now!
• The End

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• Pat Ronan
• Rules!