Objective: To determine whether glutamate release in the nucleus accumbens core is necessary for heroin seeking induced by cue presentation or heroin priming after extinction of heroin self-administration
Materials & Equipment Checklist
8 items
Gather these items before starting the experiment. Check off items as you prepare.
Equipment3
Not specified • Not mentioned • Not mentioned • Not mentioned
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Protocol Steps
View Abstract
Long-term changes in glutamate transmission in the nucleus accumbens core (NAcore) contribute to the reinstatement of drug seeking after extinction of cocaine self-administration. Whether similar adaptations in glutamate transmission occur during heroin and cue-induced reinstatement of heroin seeking is unknown. After 2 weeks of heroin self-administration and 2 weeks of subsequent extinction training, heroin seeking was induced by a noncontingent injection of heroin or by presentation of light/tone cues previously paired with heroin infusions. Microdialysis was conducted in the NAcore during reinstatement of heroin seeking in animals extinguished from heroin self-administration or in subjects receiving parallel (yoked) noncontingent saline or heroin. Reinstatement by either heroin or cue increased extracellular glutamate in the NAcore in the self-administration group, but no increase was elicited during heroin-induced reinstatement in the yoked control groups. The increase in glutamate during heroin-induced drug seeking was abolished by inhibiting synaptic transmission in the NAcore with tetrodotoxin or by inhibiting glutamatergic afferents to the NAcore from the prelimbic cortex. Supporting critical involvement of glutamate release, heroin seeking induced by cue or heroin was blocked by inhibiting AMPA/kainate glutamate receptors in the NAcore. Interestingly, although a heroin-priming injection increased dopamine equally in animals trained to self-administer heroin and in yoked-saline subjects, inhibition of dopamine receptors in the NAcore also blocked heroin- and cue-induced drug seeking. Together, these findings show that recruitment of the glutamatergic projection from the prelimbic cortex to NAcore is necessary to initiate the reinstatement of heroin seeking.
1
Heroin self-administration training
Animals were trained to self-administer heroin for 2 weeks
2 weeksNot specified
Note: Self-administration group only
View evidence from paper
“After 2 weeks of heroin self-administration and 2 weeks of subsequent extinction training”
2
Extinction training
Animals underwent extinction training where heroin was no longer available following the self-administration period
2 weeksNot specified
Note: Self-administration group only
View evidence from paper
“After 2 weeks of heroin self-administration and 2 weeks of subsequent extinction training”
3
Cue-induced reinstatement testing
Heroin seeking was induced by presentation of light and tone cues that were previously paired with heroin infusions during self-administration
Not specifiedNot specified
Note: Conducted in self-administration group and yoked control groups
View evidence from paper
“heroin seeking was induced by a noncontingent injection of heroin or by presentation of light/tone cues previously paired with heroin infusions”
4
Heroin-induced reinstatement testing
Heroin seeking was induced by a noncontingent injection of heroin
Not specifiedNot specified
Note: Conducted in self-administration group and yoked control groups
View evidence from paper
“heroin seeking was induced by a noncontingent injection of heroin or by presentation of light/tone cues previously paired with heroin infusions”
5
Microdialysis sampling during reinstatement
Microdialysis was conducted in the nucleus accumbens core to measure extracellular glutamate during reinstatement testing
Not specifiedNot specified
Note: Conducted simultaneously with reinstatement testing
View evidence from paper
“Microdialysis was conducted in the NAcore during reinstatement of heroin seeking in animals extinguished from heroin self-administration”
6
Tetrodotoxin inhibition test
Synaptic transmission in the nucleus accumbens core was inhibited with tetrodotoxin to test its effect on glutamate increase during heroin-induced drug seeking
Not specifiedNot specified
Note: Tetrodotoxin abolished the increase in glutamate during heroin-induced drug seeking
View evidence from paper
“The increase in glutamate during heroin-induced drug seeking was abolished by inhibiting synaptic transmission in the NAcore with tetrodotoxin”
7
Prelimbic cortex glutamatergic afferent inhibition test
Glutamatergic afferents to the nucleus accumbens core from the prelimbic cortex were inhibited to test their necessity for heroin-induced drug seeking
Not specifiedNot specified
Note: Inhibition of these afferents abolished the increase in glutamate during heroin-induced drug seeking
View evidence from paper
“The increase in glutamate during heroin-induced drug seeking was abolished by inhibiting synaptic transmission in the NAcore with tetrodotoxin or by inhibiting glutamatergic afferents to the NAcore from the prelimbic cortex”
8
AMPA/kainate receptor antagonist test
AMPA/kainate glutamate receptors in the nucleus accumbens core were inhibited to test their role in heroin and cue-induced drug seeking
Not specifiedNot specified
Note: Inhibition of these receptors blocked both heroin-induced and cue-induced heroin seeking
View evidence from paper
“heroin seeking induced by cue or heroin was blocked by inhibiting AMPA/kainate glutamate receptors in the NAcore”
9
Dopamine receptor antagonist test
Dopamine receptors in the nucleus accumbens core were inhibited to test their role in heroin and cue-induced drug seeking
Not specifiedNot specified
Note: Inhibition of dopamine receptors blocked both heroin-induced and cue-induced heroin seeking despite equal dopamine increase in both self-administration and yoked-saline groups
View evidence from paper
“inhibition of dopamine receptors in the NAcore also blocked heroin- and cue-induced drug seeking”
Subjects / Specimens
Species
rat
Strain
Not specified
Age
Not specified
Sex
unknown
Weight
Not specified
Animals were divided into self-administration group, yoked-saline control group, and yoked-heroin control group