Using Micro-Electro-Mechanical-Systems (MEMS) technologies, we have developed silicon wafer-based platinum microelectrode arrays (MEAs) modified with glutamate oxidase (GluOx) for electroenzymatic detection of glutamate in vivo. These MEAs were designed to have optimal spatial resolution for in vivo recordings. Selective detection of glutamate in the presence of the electroactive interferents, dopamine and ascorbic acid, was attained by deposition of polypyrrole and Nafion. The sensors responded to glutamate with a limit of detection under 1μM and a sub-1-second response time in solution. In addition to extensive in vitro characterization, the utility of these MEA glutamate biosensors was also established in vivo. In the anesthetized rat, these MEA glutamate biosensors were used for detection of cortically-evoked glutamate release in the ventral striatum. The MEA biosensors also were applied to the detection of stress-induced glutamate release in the dorsal striatum of the freely-moving rat.

Implantable aptamer transistor probes for in vivo neurotransmitter monitoring advance brain activity recording.

Environmental stimuli have the ability to generate specific representations of the rewards they predict and in so doing alter the selection and performance of reward-seeking actions. The basolateral amygdala participates in this process, but precisely how is unknown. To rectify this, we monitored, in near-real time, basolateral amygdala glutamate concentration changes during a test of the ability of reward-predictive cues to influence reward-seeking actions (Pavlovian-instrumental transfer). Glutamate concentration was found to be transiently elevated around instrumental reward seeking. During the Pavlovian-instrumental transfer test these glutamate transients were time-locked to and correlated with only those actions invigorated by outcome-specific motivational information provided by the reward-predictive stimulus (i.e., actions earning the same specific outcome as predicted by the presented CS). In addition, basolateral amygdala AMPA, but not NMDA glutamate receptor inactivation abolished the selective excitatory influence of reward-predictive cues over reward seeking. These data support the hypothesis that transient glutamate release in the BLA can encode the outcome-specific motivational information provided by reward-predictive stimuli.Adaptive reward seeking is critical to survival and is disrupted in a variety of neuropsychiatric disorders, including substance abuse, overeating and depression. The basolateral amygdala (BLA) has been implicated in these disorders [1][2][3][4] and is involved in reward processing 5,6 , but much is unknown about its precise contribution. The BLA receives dense cortical and thalamic glutamatergic input [7][8][9] . Based on the results of BLA lesions [10][11][12][13] , these excitatory chemical messages may be thought to convey a sustained emotional valence signal in response to reward-predictive stimuli. However, it is also possible that BLA signaling represents the motivational value of specific reward expectations generated by such cues. Here we investigate the latter.Assessment of this hypothesis requires a method to selectively measure BLA glutamate signaling with fast temporal resolution in order to distinguish chemical messages related to individual reward-seeking behaviors. Microdialysis allows for selective measurement of extracellular neurochemical concentration changes, but the typical 10-20 min (or even rapid 14-20 s [14][15][16] ) sampling window does not provide the

The separation method, flow field-flow fractionation (flow FFF), is coupled on-line with multiangle laser light scattering (MALLS) for simultaneous measurement of the size and concentration of vesicles eluting continuously from the fractionator. These size and concentration data, gathered as a function of elution time, may be used to construct both number- and mass-weighted vesicle size distributions. Unlike most competing, noninvasive methods, this flow FFF/MALLS technique enables measurement of vesicle size distributions without a separate refractive index detector, calibration using particle size standards, or prior assumptions about the shape of the size distribution. Experimentally measured size distributions of vesicles formed by extrusion and detergent removal are non-Gaussian and are fit well by the Weibull distribution. Flow FFF/MALLS reveals that both the extrusion and detergent dialysis vesicle formation methods can yield nearly size monodisperse populations with standard deviations of approximately 8% about the mean diameter. In contrast to the rather low resolution of dynamic light scattering in analyzing bimodal systems, flow FFF/MALLS is shown to resolve vesicle subpopulations that differ by much less than a factor of two in mean size.