Role for Hypocretin in Mediating Stress-Induced Reinstatement of Cocaine-Seeking Behavior
description
Transcript of Role for Hypocretin in Mediating Stress-Induced Reinstatement of Cocaine-Seeking Behavior
Role for Hypocretin in Mediating Stress-Induced Reinstatement of
Cocaine-Seeking Behavior
Investigating the effects of Hypocretin-1+2(Hcrt-1 / Hcrt-2)
on reinstatement of drug seekingbehavior through stress pathways
Hypocretin-1 and -2(Hcrt-1 & -2)
Recently discovered Lateral Hypothalmic Neuropeptides (1996) also known as Orexins
1+2 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
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?
Hypocretin (background)
Foot shock (FS) and Restraint (RS) induce c-Fos expression in Hypocretin neurons
Less so in neurons with CRF-R knockouts
Materials and Methods
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.
1
2
3
4
(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”
(1)Cocaine extinction
Active lever Light but no cocaine
2h sessions for minimum of 14 days
(1)Drugs administered
1. After extinction, rats were given various amounts of hypocretin icv
2. Various drugs that interfere with the stress pathway were then given and active levers were again introduced. Clonidine – α2 agonists (NE agonist) inhibits CRF
by neg feed back D-Phe-CRF12-41 – CRF antagonist
(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
(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.
(3)Food Reinforcement
A similar group was brought up without food reinforcement. Active lever pushed turned light on but did not
deliver food.
(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
Results
(1)Varied amount of Hypocretin and
reinstatement
(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.
(1)Stress Pathway Antagonists
(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
(2)Foot shock
Hypocretin receptor blocker (SB 334867)No added Hcrt
(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.
(3)Food Training
(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
(4)Inter Cerebral Self Stimulation
(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
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.