Endogenous glutamate within the prelimbic and infralimbic cortices regulates the incubation of cocaine-seeking in rats.

TitleEndogenous glutamate within the prelimbic and infralimbic cortices regulates the incubation of cocaine-seeking in rats.
Publication TypeJournal Article
Year of Publication2018
AuthorsShin CB, Templeton TJ, Chiu AS, Kim J, Gable ES, Vieira PA, Kippin TE, Szumlinski KK
JournalNeuropharmacology
Volume128
Pagination293-300
Date Published2018 Jan
ISSN1873-7064
KeywordsAmino Acids, Anesthetics, Local, Animals, Aspartic Acid, Bridged Bicyclo Compounds, Heterocyclic, Cerebral Cortex, Cocaine, Cocaine-Related Disorders, Conditioning, Operant, Drug-Seeking Behavior, Excitatory Amino Acid Agents, Glutamic Acid, Male, Microdialysis, Microinjections, Rats, Rats, Sprague-Dawley, Reinforcement (Psychology), Self Administration
Abstract

The incubation of cue-reinforced cocaine-seeking coincides with increased extracellular glutamate within the ventromedial prefrontal cortex (vmPFC). The vmPFC is comprised of two subregions that oppositely regulate drug-seeking, with infralimbic (IL) activity inhibiting, and prelimibic (PL) activity facilitating, drug-seeking. Thus, we hypothesized that increasing and decreasing endogenous glutamate within the IL would attenuate and potentiate, respectively, cue-reinforced drug-seeking behavior, with the converse effects observed upon manipulations of endogenous glutamate within the PL. Male Sprague-Dawley rats were trained to self-administer cocaine (0.25 mg/infusion; 6 h/day X 10 days), the delivery of which was signaled by a tone-light cue. Rats were then subdivided into 3 or 30 day withdrawal groups. For testing, rats were microinjected with vehicle, 20 mM of the mGlu2/3 agonist LY379268 (to lower endogenous glutamate), or 300 μM of the excitatory amino acid transporter inhibitor threo-β-benzyloxyaspartate (TBOA; to raise endogenous glutamate) into either the IL or PL (0.5 μl/side) and then given a 30-min test for cue-reinforced drug-seeking. Vehicle-infused rats exhibited incubated responding on the cocaine-associated lever. Neither LY379268 nor TBOA altered behavior at 3 days withdrawal, indicating that glutamate within neither subregion regulates cue-reinforced drug-seeking during early withdrawal. At 30 days withdrawal, intra-PL LY379268 microinjection significantly decreased drug-seeking behavior, while the effect was more modest when infused intra-IL. Interestingly, intra-IL TBOA attenuated incubated drug-seeking during protracted withdrawal, but did not affect behavior when infused intra-PL. These results argue that glutamate release within the PL in response to drug-seeking likely drives the manifestation of incubated cocaine-seeking during protracted withdrawal.

DOI10.1016/j.neuropharm.2017.10.024
Alternate JournalNeuropharmacology
PubMed ID29061508
Grant ListR01 DA024038 / DA / NIDA NIH HHS / United States