Chronic second‐by‐second measures of l‐glutamate in the central nervous system of freely moving rats

Abstract

L-glutamate (Glu) is the main excitatory neurotransmitter in the central nervous system (CNS) and is associated with motor behavior and sensory perception. While microdialysis methods have been used to record tonic levels of Glu, little is known about the more rapid changes in Glu signals that may be observed in awake rats. We have reported acute recording methods using enzyme-based microelectrode arrays (MEA) with fast response time and low detection levels of Glu in anesthetized animals with minimal interference. The current paper concerns modification of the MEA design to allow for reliable measures in the brain of conscious rats. In this study, we characterized the effects of chronic implantation of the MEA into the brains of rats. We were capable of measuring Glu levels for 7 days without loss of sensitivity. We performed studies of tail-pinch induced stress, which caused a robust biphasic increase in Glu. Histological data show chronic implantation of the MEAs caused minimal injury to the CNS. Taken together, our data show that chronic recordings of tonic and phasic Glu can be carried out in awake rats for up to 17 days in vivo allowing longer term studies of Glu regulation in behaving rats.

Decreased Dopamine D4 Receptor Expression Increases Extracellular Glutamate and Alters Its Regulation in Mouse Striatum

“…anesthetized animal studies, microdialysis shows evidence of tissue disruption of at least 220-250 mm away from the probe (Borland et al, 2005), whereas the MEA showed evidence of some neuroinflammation only 50-100 mm away in a chronic study following 8 weeks in vivo (Rutherford et al, 2007). The temporal resolution of our MEA is an order of magnitude faster than the most sophisticated microdialysis techniques designed for measurement of aminoacid neurotransmitters (Kennedy et al, 2002).…”

Glutaraldehyde Cross-Linked Glutamate Oxidase Coated Microelectrode Arrays: Selectivity and Resting Levels of Glutamate in the CNS

“…Although electroactive amino acids could be detected at microelectrode Pt surfaces without selective coatings (e.g., mPD), such exclusion coatings are used for in vivo experiments to minimize or eliminate interfering agents. 25,26 16 The mPD effectively blocked potentially interfering electroactive species including amino acids. The published resting levels of amino acids range from 1 to 10 μM for most amino acids and 41 μM for glutamine.…”

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.…”

“…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).…”

“…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).…”