Second-by-Second Measures of l-Glutamate in the Prefrontal Cortex and Striatum of Freely Moving Mice

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 M in the PFC and 5.0 M in the Str. Resting Glu levels were subjected to pharmacological manipulation with tetrodotoxin (TTX) and DL-threo-␤-hydroxyaspartate (THA). TTX significantly (p Ͻ 0.05) decreased resting Glu by 20%, whereas THA significantly (p Ͻ 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.

p11 modulates L-DOPA therapeutic effects and dyskinesia via distinct cell types in experimental Parkinsonism

“…Small cranial windows were drilled over the striata (AP: +1.3; ML: ±1.5; DV: −2.5 versus bregma), and microelectrode arrays (MEAs) were inserted into dorsal striatum of the intact and dopaminedepleted hemispheres. As previously described (17,25), glutamate dynamics were assessed on a subsecond timescale by MEA recordings with two of four electrode sites coated with L-glutamate oxidase enzyme, which breaks down L-glutamate into α-ketoglutarate and peroxide (H 2 O 2 ). By using constant voltage amperometry with application of a fixed potential, the H 2 O 2 was oxidized, with electron loss, and the resulting current was recorded using a Fast Analytical Sensing Technology-16 electrochemistry instrument (Quanteon).…”

Resting Glutamate Levels and Rapid Glutamate Transients in the Prefrontal Cortex of the Flinders Sensitive Line Rat: A Genetic Rodent Model of Depression

“…The MEA paddle was modified for use in freely moving animals as extensively described in previous literature (Hascup et al, 2008;Rutherford et al, 2007, Hascup et al, 2006. Briefly, the pedestal was the portion of the system that was chronically implanted on the rat's head and contained the MEA.…”

“…MEAs were calibrated to determine their sensitivity and selectivity against ascorbic acid as previously described (Hascup et al, 2010(Hascup et al, , 2009(Hascup et al, , 2008(Hascup et al, , 2006Nickell et al, 2005). Selectivity ratios for glutamate over ascorbic acid were calculated in addition to the slope (sensitivity), limit of detection (LOD), and linearity (R 2 ) for glutamate for all MEAs.…”

“…Furthermore, preapplication of tetrodotoxin (TTX) completely abolishes the physiological glutamate response to a tail-pinch stressor (Hascup et al, 2010). These MEAs were chronically implanted into the PFC of young (3-to 6-month) and old (12-to 15-month) FSL and FRL rats allowing us to measure extracellular levels of resting glutamate over several days (Hascup et al, 2008;Rutherford et al, 2007) in a clinically relevant brain structure implicated in depression (Canbeyli, 2010).…”

Soluble Amyloid-β42 Stimulates Glutamate Release through Activation of the α7 Nicotinic Acetylcholine Receptor

“…Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by progressive memory loss and hippocampal atrophy. Soluble amyloid-␤ (A␤) 42 and plaque accumulation is implicated as the neurotoxic species in this disorder; however, at physiological concentrations (pM-nM), A␤ 42 contributes to neurogenesis, long-term potentiation, and neuromodulation. Because A␤ 42 binds the ␣7 nicotinic acetylcholine receptors (␣7nAChRs) located presynaptically on glutamatergic terminals, involved with hippocampal dependent learning and memory, we examined the effects of the human, monomeric isoform of A␤ 42 on glutamate release in the dentate gyrus (DG), CA3, and CA1, of isoflurane anesthetized, 6-9 month old male C57BL/6J mice.…”