Extensive evidence supports an important role for soluble oligomers of the amyloid β-protein (Aβ) in Alzheimer’s Disease pathogenesis. In the present study we combined intracerebroventricular (icv) injections with brain microdialysis technology in the fully conscious rat to assess the effects of icv administered SDS-stable low-n Aβ oligomers (principally dimers and trimers) on excitatory and inhibitory amino acid transmission in the ipsilateral dorsal hippocampus. Microdialysis was employed to assess the effect of icv administration of Aβ monomers and Aβ oligomers on dialysate glutamate, aspartate and GABA levels in the dorsal hippocampus. Administration of Aβ oligomers was associated with a +183% increase (p<0.0001 vs. Aβ monomer-injected control) in dorsal hippocampal glutamate levels which was still increasing at the end of the experiment (260 min), whereas aspartate and GABA levels were unaffected throughout. These findings demonstrate that icv administration and microdialysis technology can be successfully combined in the awake rat and suggests that altered dorsal hippocampal glutamate transmission may be a useful target for pharmacological intervention in Alzheimer’s Disease. Full article

Dopamine (DA) D3 receptors have been associated with drug intake and abuse and selectively distribute in the brain circuits responding to drug administration. Here we examined the effects of an acute systemic administration of cocaine (15 mg/kg) alone or preceded by treatment with the selective D3 receptor antagonist SB-277011-A (10 mg/kg) on DA levels concurrently in the rat nucleus accumbens shell and core sub-regions (NAcshell and NAccore, respectively). It is shown that cocaine increases extracellular DA in both compartments and that blocking D3 receptors with SB-277011-A, although the latter is devoid of dopaminergic effects per se, potentiates these effects. No differences in the amplitude of the response were observed between NAcshell and NAccore compartments, though the dopaminergic response in the NAcshell was transient whereas that in the NAccore rose slowly to reach a plateau. These results demonstrate the feasibility to use multiprobe voltammetry to measure discrete monoaminergic responses in discrete areas of the brain and confirm the effect of D3 receptors antagonist at modifying the neurochemical effects of cocaine. Full article

Liquid chromatography with amperometric detection remains the most widely used method for acetylcholine quantification in microdialysis samples. Separation of acetylcholine from choline and other matrix components on a microbore chromatographic column (1 mm internal diameter), conversion of acetylcholine in an immobilized enzyme reactor and detection of the produced hydrogen peroxide on a horseradish peroxidase redox polymer coated glassy carbon electrode, achieves sufficient sensitivity for acetylcholine quantification in rat brain microdialysates. However, a thourough validation within the concentration range required for this application has not been carried out before. Furthermore, a rapid degradation of the chromatographic columns and enzyme systems have been reported. In the present study an ion-pair liquid chromatography assay with amperometric detection was validated and its long-term stability evaluated. Working at pH 6.5 dramatically increased chromatographic stability without a loss in sensitivity compared to higher pH values. The lower limit of quantification of the method was 0.3 nM. At this concentration the repeatability was 15.7%, the inter-day precision 8.7% and the accuracy 103.6%. The chromatographic column was stable over 4 months, the immobilized enzyme reactor up to 2-3 months and the enzyme coating of the amperometric detector up to 1-2 months. The concentration of acetylcholine in 30 μl microdialysates obtained under basal conditions from the hippocampus of freely moving rats was 0.40 ± 0.12 nM (mean ± SD, n = 30). The present method is therefore suitable for acetylcholine determination in rat brain microdialysates. Full article

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. Full article

Reports that globular proteins could enhance the interference blocking ability ofthe PPD (poly(o-phenylenediamine) layer used as a permselective barrier in biosensordesign, prompted this study where a variety of modifying agents were incorporated into PPDduring its electrosynthesis on Pt-Ir electrodes. Trapped molecules, including fibrous proteinsand β-cyclodextrin, altered the polymer/modifier composite selectivity by affecting thesensitivity to both H₂O₂ (signal molecule in many enzyme-based biosensors) and thearchetypal interference species, ascorbic acid. A comparison of electrochemical properties ofPt and a Pt-Ir alloy suggests that the benefits of the latter, more rigid, metal can be exploitedin PPD-based biosensor design without significant loss of backward compatibility withstudies involving pure Pt. Full article

An improvement of selectivity for electrochemical detection of dopamine (DA)with differential pulse voltammetry is achieved by covalently modifying a glassy carbonelectrode (GCE) with O-carboxymethylchitosan (OCMCS). The amphiphilic chitosanprovides electrostatic accumulation of DA onto the electrode surface. In a phosphate buffersolution (pH 6.0), a pair of well-defined reversible redox waves of DA was observed at theOCMCS/GCE with a δE_p of 52 mV. The anodic peak current obtained from thedifferential pulse voltammetry of dopamine was linearly dependent on its concentration inthe range of 6.0 × 10^-8 to 7.0 × 10^-6 M, with a correlation coefficient of 0.998. Thedetection limit (S/N = 3) was found to be 1.5 × 10^-9 M. The modified electrode had beenapplied to the determination of DA in human serum samples with satisfactory results. Full article

Fluorescence spectroscopy and ultraviolet (UV) spectroscopy techniques coupled with cyclic voltammetry (CV) were used to study the interaction between salmon sperm DNA and 1,10-Phenanthroline cobalt(II) complex, [Co(phen)₂(Cl)(H₂O)]Cl·H₂O, where phen = 1,10-phenanthroline. The interaction between [Co(phen)₂(Cl)(H₂O)]⁺ and double-strand DNA (dsDNA) was identified to be intercalative mode. An electrochemical DNA biosensor was developed by covalent immobilization of probe single-strand DNA (ssDNA) related to human immunodeficiency virus (HIV) on the activated glassy carbon electrode (GCE). With [Co(phen)₂(Cl)(H₂O)]⁺ being the novel electrochemical hybridization indicator, the selectivity of ssDNA-modified electrode was investigated and selective detection of complementary ssDNA was achieved using differential pulse voltammetry (DPV). Full article

The changes in blood flow, blood volume and oxygenation that accompany focal increases in neural activity are collectively referred to as the hemodynamic response and form the basis of non-invasive neuroimaging techniques such as blood oxygen level dependent (BOLD) functional magnetic resonance imaging. A principle factor influencing blood oxygenation, the cerebral metabolic rate of oxygen consumption is poorly understood and as such, data from imaging techniques are difficult to interpret in terms of the underlying neural activity. In particular how neurometabolic changes vary temporally, spatially and in magnitude remains uncertain. Furthermore knowledge of which aspects of neural activity are closely reflected by metabolic changes is essential for the correct interpretation of cognitive neuroscience studies in terms of information processing. Polarographic electrode measurements of cerebral tissue oxygenation in animal models following presentation of sensory stimuli have started to address these issues. Early studies demonstrated both increases and decreases in tissue oxygenation following neural activation. However a recent series of elegant studies in the cat visual system demonstrated a tight spatial and temporal coupling between evoked peri-synaptic activity and oxygen consumption following presentation of visual stimuli. Full article