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. 2016 Sep 29;11(9):e0163784.
doi: 10.1371/journal.pone.0163784. eCollection 2016.

Behavioral History of Withdrawal Influences Regulation of Cocaine Seeking by Glutamate Re-Uptake

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Free PMC article

Behavioral History of Withdrawal Influences Regulation of Cocaine Seeking by Glutamate Re-Uptake

Luyi Zhou et al. PLoS One. .
Free PMC article

Abstract

Withdrawal from cocaine regulates expression of distinct glutamate re-uptake transporters in the nucleus accumbens (NAc). In this study, we examined the cumulative effect of glutamate re-uptake by multiple excitatory amino acid transporters (EAATs) on drug-seeking at two different stages of withdrawal from self-administered cocaine. Rats were trained on fixed ratio 1 (FR1), progressing to FR5 schedule of reinforcement. After one day of withdrawal, microinfusion of a broad non-transportable EAAT antagonist, DL-threo-beta-benzyloxyaspartate (DL-TBOA), into the NAc shell dose-dependently attenuated self-administration of cocaine. Sucrose self-administration was not affected by DL-TBOA, indicating an effect specific to reinforcing properties of cocaine. The attenuating effect on cocaine seeking was not due to suppression of locomotor response, as DL-TBOA was found to transiently increase spontaneous locomotor activity. Previous studies have established a role for EAAT2-mediated re-uptake on reinstatement of cocaine seeking following extended withdrawal and extinction training. We found that blockade of NAc shell EAATs did not affect cocaine-primed reinstatement of cocaine seeking. These results indicate that behavioral history of withdrawal influences the effect of re-uptake mediated glutamate clearance on cocaine seeking. Dynamic regulation of glutamate availability by re-uptake mechanisms may impact other glutamate signaling pathways to account for such differences.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Cannulae placement verification.
Left, A schematic of the brain section from Paxinos and Watson [40]. Right, A representative photomicrograph of cresyl violet-stained brain slice (75 μm-thick) used to confirm cannulae placements in the NAc shell. Dotted circle (1 mm diameter) represents the maximal diffusion area for a 0.5 μl solution volume [41]. Black arrow–tip of the guide cannula. White arrow–tip of the microinjector. White arrowhead–lateral ventricle. AC–anterior commissure. Scale bar, 0.5 mm.
Fig 2
Fig 2. Microinjection of DL-TBOA into the NAc shell dose-dependently attenuated cocaine self-administration.
A),B) Total number of responses (mean ± SEM) on the active and inactive levers following microinfusion of vehicle (n = 11), 3 mM (n = 4), and 5 mM (n = 7) of DL-TBOA into the NAc shell bilaterally (Bonferroni, *p<0.05 relative to vehicle controls). C) Total number of cocaine infusions (mean±SEM) earned during the two-hour self-administration sessions (Bonferroni, *p<0.05 relative to vehicle controls).
Fig 3
Fig 3. Microinjection of DL-TBOA did not affect cocaine priming-induced reinstatement of cocaine seeking.
A), B) Total number of responses (mean ± SEM) on the active and inactive levers during extinction training (average of 3 sessions preceding the reinstatement test, n = 7) and following bi-lateral NAc shell infusion of vehicle or DL-TBOA. DL-TBOA was microinfused ten minutes prior to the priming injection of cocaine (10 mg/kg, i.p.). No significant differences were found.
Fig 4
Fig 4. Microinjection of DL-TBOA did not affect sucrose self-administration.
Total numbers (mean±SEM) of active lever responses (A), inactive lever responses (B), and sucrose pellets earned (C) were not different between animals that received a bilateral NAc shell microinfusion of vehicle and DL-TBOA, ten minutes prior to a 2 hour sucrose self-administration session (n = 6).
Fig 5
Fig 5. DL-TBOA transiently increased locomotor activity.
Two groups of naïve animals habituated to a locomotor chamber during a 30-minute session with no difference between groups. Bilateral microinfusion (inf.) of vehicle or DL-TBOA into the NAc shell potentiated locomotor activity in the DL-TBOA group during the first ten minutes of the test session (Bonferroni, **p<0.01; n = 5). AU, arbitrary units.

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