Abstract
l-Glutamate (Glu) is the main excitatory neurotransmitter in the mammalian central nervous system, and it is involved in most aspects of normal brain function, including cognition, memory and learning, plasticity, and motor movement. Although microdialysis techniques have been used to study Glu, the slow temporal resolution of the technique may be inadequate to properly examine tonic and phasic Glu. Thus, our laboratory has developed an enzyme-based microelectrode array (MEA) with fast response time and low detection limits for Glu. We have modified the MEA design to allow for reliable measures in the brain of awake, freely moving mice. In this study, we chronically implanted the MEA in prefrontal cortex (PFC) or striatum (Str) of awake, freely moving C57BL/6 mice. We successfully measured Glu levels 7 days postimplantation without loss of MEA sensitivity. In addition, we determined resting (tonic) Glu levels to be 3.3 μM in the PFC and 5.0 μM in the Str. Resting Glu levels were subjected to pharmacological manipulation with tetrodotoxin (TTX) and dl-threo-β-hydroxyaspartate (THA). TTX significantly (p < 0.05) decreased resting Glu by 20%, whereas THA significantly (p < 0.05) increased resting Glu by 60%. Taken together, our data show that chronic recordings of tonic and phasic clearance of exogenously applied Glu can be carried out in awake mice for at least 7 days in vivo, allowing for longer term studies of Glu regulation.
Footnotes
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This work was supported by DARPA Grant N66001-02-C-8085, National Science Foundation Grant DBI-0352848, U.S. Public Health Service Grant DA017186, and National Institute of Health training Grant 1 T32 DA022738-01.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.107.131698.
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ABBREVIATIONS: Glu, l-glutamate; TTX, tetrodotoxin; MEA, microelectrode array; DOPAC, 3,4-dihydroxyphenylacetic acid; AA, ascorbic acid; PFC, prefrontal cortex; Str, striatum; THA, dl-threo-β-hydroxyaspartate; EAAT, excitatory amino acid transporter; GluOx, l-glutamate oxidase; BSA, bovine serum albumin; FAST, fast analytical sensing technology.
- Received September 17, 2007.
- Accepted November 15, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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