Role for Hypocretin in Mediating Stress-Induced Reinstatement of Cocaine-Seeking Behavior - PowerPoint PPT Presentation

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Role for Hypocretin in Mediating Stress-Induced Reinstatement of Cocaine-Seeking Behavior

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Role for Hypocretin in Mediating Stress-Induced Reinstatement of Cocaine-Seeking Behavior Investigating the effects of Hypocretin-1+2 (Hcrt-1 / Hcrt-2) – PowerPoint PPT presentation

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Title: Role for Hypocretin in Mediating Stress-Induced Reinstatement of Cocaine-Seeking Behavior


1
Role for Hypocretin in Mediating Stress-Induced
Reinstatement of Cocaine-Seeking Behavior
  • Investigating the effects of Hypocretin-12
  • (Hcrt-1 / Hcrt-2)?
  • on reinstatement of drug seeking
  • behavior through stress pathways

2
Hypocretin-1 and -2(Hcrt-1 -2)?
  • Recently discovered Lateral Hypothalmic
    Neuropeptides (1996) also known as Orexins
  • 12 bind equally at Hcrt-R
  • Projections
  • Locus Ceruleus (Major) - NE
  • Dorsal Raphe Nuclei - 5-HT
  • Amygdala
  • Suprachiasmatic Nucleus biological clock
  • Basal Forebrain
  • Cholinergic Brainstem
  • Spinal Cord

3
Hypocretin
  • Evidence points to excitatory function
  • ?energy expenditure, ?feeding behavior,
    ?locomotor activity.
  • Evidence indicates that Hcrt neurons drive
    hyper-arousal through modulation of stress
  • Stress? ?CRF? ?Hypocretin
  • Role for Hcrt in reward seeking?

4
Hypocretin (background)
  • Foot shock (FS) and Restraint (RS) induce c-Fos
    expression in Hypocretin neurons
  • Less so in neurons with CRF-R knockouts

5
Materials and Methods
6
Animals
  • Male Wistar rats 250-350 grams
  • 12 hr light/dark cycle (lights off 10AM)?
  • Testing during dark cycle except during
    intracranial-self stimulation testing.

7
1
2
3
4
8
(1)Cocaine self-administration training
  • Two lever system
  • Active lever light .25 mg cocaine in saline
    iv. over 4s
  • 20s timeout pushes recorded but no cocaine
    delivered
  • 7days 1hr sessions, then 5-7days 2hr session
  • When there was 20 variation in cocaine use for
    three days the rats were considered trained

9
(1)Cocaine extinction
  • Active lever
  • Light but no cocaine
  • 2h sessions for minimum of 14 days

10
(1)Drugs administered
  • After extinction, rats were given various amounts
    of hypocretin icv
  • Various drugs that interfere with the stress
    pathway were then given and active levers were
    again introduced.
  • Clonidine a2 agonists (NE agonist) inhibits CRF
    by neg feed back
  • D-Phe-CRF12-41 CRF antagonist

11
(2)Footshock
  • Some rats from the previous groups were given
    another extinction session similar to the
    first.(!)
  • Rats were given a Hcrt-Receptor antagonist,
    SB-334867, then shocked
  • 0.5mA for 0.5s intermittent for 15 min
  • Cocaine administration levers were then introduced

12
(3)Food Reinforcement
  • Similar to first experiment except with active
    lever dispensing food pellets instead of cocaine.
  • During testing rats were food restricted to 14g
    of food pellets/day
  • Self administered pellets were 45g
  • Training until stable intake, extinction, then
    reinstatement with Hcrt.
  • Experiment was done with one and two levers.

13
(3)Food Reinforcement
  • A similar group was brought up without food
    reinforcement.
  • Active lever pushed turned light on but did not
    deliver food.

14
(4)Intra cerebral self stimulation
  • Electrode was implanted in medial fore brain
    bundle.
  • Stimulation causes Nucleus accumbens activity
  • Turns on measolimbic system
  • Three trials were preformed for each current
    intensity
  • Stimulus was applied in 5 micro Amp steps, in for
    alternating and descending series.
  • Rat had 7.5s to respond on wheel to get an equal
    stimulus.
  • If rat responded to two out of the three stimuli,
    it was counted as the threshold

15
Results
16
(1)Varied amount of Hypocretin and reinstatement
17
(1)Amount of Hypocretin
  • Increased in dose dependent fashion
  • 0.3 nmol did not produce significantly different
    results from saline control.
  • Pulls on inactive lever were never significantly
    different suggesting increased locomotor activity
    had to do with increasing active lever pushes.

18
(1)Stress Pathway Antagonists
19
(1)Stress Pathway Antagonists
  • Evidence Suggests Hcrt CRF interact during
    stress response
  • Stress pathway is a major cause of drug relapse
  • Both Clonidine and D-Phe-CRF12-41 reduced active
    lever hits in Hcrt treated mice.
  • When combined, drug seeking behavior was
    extinguished

20
(2)Foot shock
Hypocretin receptor blocker (SB 334867) No added
Hcrt
21
(2)Foot shock
  • Used to test endogenous Hcrt systems and their
    role in stress-induced drug relapse
  • Control rats display strong drug seeking relapse
    after footshock
  • Rats treated with HcrtR-antagonist showed a
    marked decrease in relapse proportional with
    amount of inhibitor.

22
(3)Food Training
23
(3)Food Training
  • Hcrt increased lever responses in extinguished
    rats previously trained to respond to food
    reinforces
  • Hcrt only reinstated lever pushing in rats that
    previously had the active lever paired with food
    reward
  • Inactive levers were insignificant
  • Parallel results to drug seeking experiment

24
(4)Inter Cerebral Self Stimulation
25
(4)Inter Cerebral Self Stimulation
  • Mean thresholds
  • Saline 104.5 /- 11.4 µA
  • Hcrt-1 129.9 /- 13.6 µA
  • Hcrt produced long lasting increase in response
    thresholds (between 24-36h)?
  • Shows that the response Hcrt has on brain reward
    center is negative unlike priming

26
Conclusions
  • Icv Infusions of Hcrt reinstated extinguished
    cocaine-seeking behavior.
  • Hcrt-R antagonist blocks relapse.
  • Hcrt increases ICSS stimulation threshold,
    suppressing the brain reward system. Cocaine
    priming typically lowers this threshold
  • These data suggest that Hcrt reinstates cocaine
    seeking through stress pathways and not dopamine
    release
  • Similar to glucocoticoids, 5-HT3, Egr1, CRF
  • Because the CRF antagonist can also block relapse
    in Hcrt treated mice, the system must work in
    conjunction with the stress pathways.
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