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Fluctuations in nucleus accumbens extracellular glutamate and glucose during motivated glucose‐drinking behavior: dissecting the neurochemistry of reward
Author(s) -
Wakabayashi Ken T.,
Myal Stephanie E.,
Kiyatkin Eugene A.
Publication year - 2015
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/jnc.12993
Subject(s) - glutamate receptor , nucleus accumbens , microdialysis , neurochemical , habituation , medicine , extracellular , neuroscience , neurochemistry , neurotransmitter , endocrinology , chemistry , biochemistry , dopamine , biology , central nervous system , neurology , receptor
While motivated behavior involves multiple neurochemical systems, few studies have focused on the role of glutamate, the brain's excitatory neurotransmitter, and glucose, the energetic substrate of neural activity in reward‐related neural processes. Here, we used high‐speed amperometry with enzyme‐based substrate‐sensitive and control, enzyme‐free biosensors to examine second‐scale fluctuations in the extracellular levels of these substances in the nucleus accumbens shell during glucose‐drinking behavior in trained rats. Glutamate rose rapidly after the presentation of a glucose‐containing cup and before the initiation of drinking (reward seeking), decreased more slowly to levels below baseline during consumption (sensory reward), and returned to baseline when the ingested glucose reached the brain (metabolic reward). When water was substituted for glucose, glutamate rapidly increased with cup presentation and in contrast to glucose drinking, increased above baseline after rats tasted the water and refused to drink further. Therefore, extracellular glutamate show distinct changes associated with key events of motivated drinking behavior and opposite dynamics during sensory and metabolic components of reward. In contrast to glutamate, glucose increased at each stimulus and behavioral event, showing a sustained elevation during the entire behavior and a robust post‐ingestion rise that correlated with the gradual return of glutamate levels to their baseline. By comparing active drinking with passive intra‐gastric glucose delivery, we revealed that fluctuations in extracellular glucose are highly dynamic, reflecting a balance between rapid delivery because of neural activity, intense metabolism, and the influence of ingested glucose reaching the brain.By using enzyme‐based biosensors coupled with high‐speed amperometry, we examined the pattern of dynamic fluctuations in extracellular levels of glutamate and glucose in the nucleus accumbens during glucose‐drinking behavior in trained rats. These fluctuations are considered with respect to their functional significance in motivated behavior and their relation to sensory and metabolic aspects of reward.