Rapid microelectrode measurements and the origin and regulation of extracellular glutamate in rat prefrontal cortex

Abstract

J. Neurochem. (2010) 115, 1608–1620. Abstract Glutamate in the prefrontal cortex (PFC) plays a significant role in several mental illnesses, including schizophrenia, addiction and anxiety. Previous studies on PFC glutamate‐mediated function have used techniques that raise questions on the neuronal versus astrocytic origin of glutamate. The present studies used enzyme‐based microelectrode arrays to monitor second‐by‐second resting glutamate levels in the PFC of awake rats. Locally applied drugs were employed in an attempt to discriminate between the neuronal or glial components of the resting glutamate signal. Local application of tetrodotoxin (sodium channel blocker), produced a significant (∼40%) decline in resting glutamate levels. In addition significant reductions in extracellular glutamate were seen with locally applied ω‐conotoxin (MVIIC; ∼50%; calcium channel blocker), and the mGluR2/3 agonist, LY379268 (∼20%), and a significant increase with the mGluR2/3 antagonist LY341495 (∼40%), effects all consistent with a large neuronal contribution to the resting glutamate levels. Local administration of D,L‐threo‐β‐benzyloxyaspartate (glutamate transporter inhibitor) produced an ∼120% increase in extracellular glutamate levels, supporting that excitatory amino acid transporters, which are largely located on glia, modulate clearance of extracellular glutamate. Interestingly, local application of (S)‐4‐carboxyphenylglycine (cystine/glutamate antiporter inhibitor), produced small, non‐significant bi‐phasic changes in extracellular glutamate versus vehicle control. Finally, pre‐administration of tetrodotoxin completely blocked the glutamate response to tail pinch stress. Taken together, these results support that PFC resting glutamate levels in rats as measured by the microelectrode array technology are at least 40–50% derived from neurons. Furthermore, these data support that the impulse flow‐dependent glutamate release from a physiologically ‐evoked event is entirely neuronally derived.

Linking kindling to increased glutamate release in the dentate gyrus of the hippocampus through the STXBP5/tomosyn‐1 gene

“…This effect could be a compensatory response acting through presynaptic mGluR 2/3 autoreceptors (Rohde et al., 2012; Watanabe et al., 2011). In support of this explanation, we previously showed that resting glutamate levels are modulated with an mGluR 2/3 agonist and antagonist in freely moving animals (Hascup et al., 2010). Alternatively, there is also evidence that kindling may increase neuropeptide Y which has been shown to decrease resting glutamate levels in the hippocampus (Botterill, Guskjolen, Marks, Caruncho, & Kalynchuk, 2015; Klapstein & Colmers, 1997; Patrylo, van den Pol, Specer, & Williamson, 1999).…”

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

“…This meant the sentinel sites could not record any converted glutamate but could record any electroactive interferents (at + 0.7 V vs a Ag/AgCl reference electrode) not repelled by Nafion. When the current recorded on the sentinel sites was subtracted from the current on the glutamate recording sites, the resulting signal represents the resting glutamate levels in brain tissue (Hascup et al, 2010;Burmeister et al, 2002;Burmeister and Gerhardt, 2001). …”

“…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.…”

“…MEA implantation has been extensively described in previous literature (Hascup et al, 2010(Hascup et al, , 2009Rutherford et al, 2007). The MEA pedal assembly was implanted in the right PFC (MEA tip coordinates: AP: + 3.2 mm; ML: 0.8 mm, DV: À5.0 mm vs bregma), with the incisor bar set so that the skull was level (À2.3 mm), which was based on the atlas of Paxinos and Watson (1998).…”

“…Using these MEAs in combination with pharmacological treatments, we have shown that resting glutamate levels in the medial prefrontal cortex (PFC) are at least 50% neuronally derived. 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).…”