Simultaneous real-time measurement of EEG/EMG and l-glutamate in mice: A biosensor study of neuronal activity during sleep

Abstract

We report on electroencephalograph (EEG) and electromyograph (EMG) measurements concurrently with real-time changes in L-glutamate concentration. These data reveal a link between sleep state and extracellular neurotransmitter changes in a freely-moving (tethered) mouse. This study reveals, for the first time in mice, that the extracellular L-glutamate concentration in the pre-frontal cortex (PFC) increases during periods of extended wakefulness, decreases during extended sleep episodes and spikes during periods of REM sleep. Individual sleep epochs (10 s in duration) were scored as wake, slow-wave (SW) sleep or rapid eye movement (REM) sleep, and then correlated as a function of time with measured changes in L-glutamate concentrations. The observed L-glutamate levels show a statistically significant increase of 0.86 ± 0.26 μM (p < 0.05) over 37 wake episodes recorded from all mice (n = 6). Over the course of 49 measured sleep periods longer than 15 min, L-glutamate concentrations decline by a similar amount (0.88 ± 0.37 μM, p < 0.08). The analysis of 163 individual REM sleep episodes greater than one min in length across all mice (n = 6) demonstrates a significant rise in L-glutamate levels as compared to the 1 min preceding REM sleep onset (RM-ANOVA, DF = 20, F = 6.458, p < 0.001). The observed rapid changes in L-glutamate concentration during REM sleep last only between 1 and 3 min. The approach described can also be extended to other regions of the brain which are hypothesized to play a role in sleep. This study highlights the importance of obtaining simultaneous measurements of neurotransmitter levels in conjunction with sleep markers to help elucidate the underlying physiological and ultimately the genetic components of sleep.

Rapid changes in extracellular glutamate induced by natural arousing stimuli and intravenous cocaine in the nucleus accumbens shell and core

“…1A) revealed a significant decrease in basal currents (Pre ϭ 2.60 Ϯ 0.24 nA vs. Post ϭ 0.51 Ϯ 0.06 nA; P Ͻ 0.01) coupled with an approximately twofold decrease in their sensitivity to both Glu (1.54 Ϯ 0.08 nA/10 M) and ascorbate (0.35 Ϯ 0.04 nA/250 M). This decrease in sensitivity is consistent with other studies using sensors of similar design (Behrend et al 2009;Naylor et al 2011) and may be due in part to fouling of the active surface (Kulagina et al 1999) or perturbation of the enzyme layer during sensor removal from the brain. Despite decreases in sensitivity to both substances, the Glu-ascorbate Fig.…”

“…Traditionally, the development of a highly substrate-sensitive and -selective biosensor has been viewed as the most critical factor determining the accuracy of electrochemical measurement of neuroactive substances. With respect to Glu, such sensors were developed in the 1990s (Cooper and Pritchard 1994;Hu et al 1994;Qin et al 2008;Wilson and Gifford 2005) and their use was validated by further in vivo work (Hascup et al 2010;Oldenziel et al 2006), including experiments in awake, behaving animals (Dash et al 2009;John et al 2008;Naylor et al 2011;Uslaner et al 2011). As confirmed in this study, Glu sensors produced by Pinnacle Technology showed in vitro high substrate sensitivity (ϳ0.6 nA/1 M) and reasonably high selectivity against possible interferents, particularly ascorbate and dopamine.…”

“…In contrast, electrochemistry has excellent temporal resolution, but its measurement selectivity in vivo has always been problematic; concomitant changes in physical and chemical factors in the environment can confound the current changes induced by the oxidation of the substance of interest. While Gluselective, enzyme-based electrochemical sensors have been developed (Cooper and Pritchard 1994;Hu et al 1994;Wilson and Gifford 2005) and their selectivity validated by further work (Agnesi et al 2010;Hascup et al 2010;Oldenziel et al 2006;Rutherford et al 2007), the use of this technique in awake, behaving animals has thus far been limited (Dash et al 2009;John et al 2008;Naylor et al 2011). …”

An implantable microelectrode array for simultaneous L-glutamate and electrophysiological recordings in vivo

“…Using separate electrodes to examine glutamate and electrophysiological signals within the same preparation has been a commonly employed method [19][20][21][22] ; however, it is problematic when the separate microelectrodes are not located within the same microenvironment. Several reports delivered external glutamate or drugs that could affect glutamate release into the rat brain and recorded only electrophysiological signal changes [23][24][25][26][27][28] ; however, this method can serve in only a limited capacity for glutamate change is not quantitative.…”

Multifunctional lab-on-a-tube (LOT) probe for simultaneous neurochemical and electrophysiological activity measurements

“…Current approach is to insert multiple monitoring probes which either limits spatial or time resolution [5]. To overcome these issues, a multifunctional LOT probe was proposed as shown in Fig.…”