In vivo voltammetry and concomitant electrophysiology at a single micro-biosensor to analyse ischaemia, depression and drug dependence

In vivo real time non invasive monitoring of brain penetration of chemicals with near-infrared spectroscopy: Concomitant PK/PD analysis

BACKGROUND

Near-infrared spectroscopy (NIRS) is a non-invasive technique that monitors changes in oxygenation of haemoglobin. The absorption spectra of near-infrared light differ for the oxygenation-deoxygenation states of haemoglobin (oxygenate (HbO2) and deoxygenate (Hb), respectively) so that these two states can be directly monitored.

COMPARISON WITH EXISTING METHOD(S)

Different methodologies report different basal values of HbO2 and Hb absolute concentrations in brain. Here, we attempt to calculate basal HbO2 levels in rat CNS via evaluation of the influence of exogenous oxygen or exogenous carbon dioxide on the NIRS parameters measured in vivo.

NEW METHOD

Furthermore the possibility that changes of haemoglobin oxygenation in rat brain as measured by NIRS might be a useful index of brain penetration of chemical entities has been investigated. Different compounds from different chemical classes were selected on the basis of parallel ex vivo and in vivo pharmacokinetic (PK/PD) studies of brain penetration and overall pharmacokinetic profile.

RESULTS

It appeared that NIRS might contribute to assess brain penetration of chemical entities, i.e. significant changes in NIRS signals could be related to brain exposure, conversely the lack of significant changes in relevant NIRS parameters could be indicative of low brain exposure.

CONCLUSIONS

This work is proposing a further innovation on NIRS preclinical applications i.e. a "chemical" NIRS [chNIRS] approach for determining penetration of drugs in animal brain. Therefore, chNIRS could became a non invasive methodology for studies on neurobiological processes and psychiatric diseases in preclinical but also a translational strategy from preclinical to clinical investigations.

Infralimbic cortex Rho-kinase inhibition causes antidepressant-like activity in rats

Depression is one of the most common psychiatric disorders in the world; however, its mechanisms remain unclear. Recently, a new signal-transduction pathway, namely Rho/Rho-kinase signalling, has been suggested to be involved in diverse cellular events in the central nervous system; such as epilepsy, anxiety-related behaviors, regulation of dendritic and axonal morphology, antinociception, subarachnoid haemorrhage, spinal cord injury and amyotrophic lateral sclerosis. However there is no evidence showing the involvement of Rho-kinase pathway in depression. In addition, the infralimbic cortex, rodent equivalent to subgenual cingulate cortex has been shown to be responsible for emotional responses. Thus, in the present study, intracranial guide cannulae were stereotaxically implanted bilaterally into the infralimbic cortex, and the effects of repeated microinjections of a Rho-kinase (ROCK) inhibitor Y-27632 (10 nmol) were investigated in rats. Y-27632 significantly decreased immobility time and increased swimming and climbing behaviors when compared to fluoxetine (10 μg) and saline groups in the forced swim test. In addition, Y-27632 treatment did not affect spontaneous locomotor activity and forelimb use in the open-field and cylinder tests respectively; but it enhanced limb placing accuracy in the ladder rung walking test. Our results suggest that Y-27632 could be a potentially active antidepressant agent.

Influence of melatonin or its antagonism on alcohol consumption in ethanol drinking rats: a behavioral and in vivo voltammetric study

Melatonin, an indoleamine hormone synthesized in the pinealocytes, has been implicated as influencing the intake of alcohol in rats. It has been shown that this hormone is voltammetrically electroactive at the surface of pretreated carbon fiber microelectrodes in vitro and in vivo, in rat cerebral melatonergic regions such the pineal gland. The aim of this work consisted in the study of the influence of melatonin on spontaneously ethanol drinking or ethanol avoiding rats selected throughout a free choice two bottle test. It appeared that only the water preferring rats were affected by treatment with the hormone and that in vivo voltammetric related levels of melatonin were higher in the pineal gland of ethanol drinking rats versus water preferring rats. In addition, when treated with the melatonin antagonist GR128107 ethanol drinking rats significantly reduced the spontaneous consumption of alcohol.

Electrochemical biosensors in pharmaceutical analysis

Given the increasing demand for practical and low-cost analytical techniques, biosensors have attracted attention for use in the quality analysis of drugs, medicines, and other analytes of interest in the pharmaceutical area. Biosensors allow quantification not only of the active component in pharmaceutical formulations, but also the analysis of degradation products and metabolites in biological fluids. Thus, this article presents a brief review of biosensor use in pharmaceutical analysis, focusing on enzymatic electrochemical sensors.

Neural Probes for Concurrent Detection of Neurochemical and Electrophysiological Signals in vivo

Electrochemical sensing with microelectrode arrays provides a means for monitoring neurotransmitter dynamics across multiple locations within a micro-scale region of brain tissue. Here we present a multi-modal neural probe design for concurrent recording of neurochemical and electrophysiological signals in vivo. Prior to implantation, platinum sites on each array underwent platinum-black electroplating and Nafion electropolymerization, which increased sensitivity to dopamine by 74% and decreased sensitivity to common interferents by at least 89%. In a series of three rats, we applied various electrochemical waveforms to platinum sites and monitored neural activity on adjacent iridium sites. We found that chronoamperometry and constant-potential amperometry did not alter firing rates at +0.25, +0.50, and +0.75 V. In addition, we have demonstrated multi-modal recordings of striatal neurons in response to medial forebrain bundle stimulation.

Non-invasive in vivo infrared laser spectroscopy to analyse endogenous oxy-haemoglobin, deoxy-haemoglobin, and blood volume in the rat CNS

Oxy-haemoglobin (HbO2) and deoxy-haemoglobin (Hb) are chromophores present in biological tissues. Near infrared spectroscopy (NIRS) is a non-invasive methodology based on the low extinction coefficient of tissue in the near infrared region. NIRS can be used to measure changes in the concentration of these chromophores, i.e., haemoglobin, in muscular tissue. In the present work, NIRS has been used for the non-invasive monitoring of HbO2, Hb, and blood volume (V: representing total haemoglobin, i.e., HbO2+Hb) in vivo in the whole rat brain. This has been performed by means of prototype instrumentation based on optic fibre probes placed in contact with the head of anaesthetised rats held in a stereotaxic frame. A preliminary test of the instrument has been performed on human muscle, i.e., lateral gastrocnemius, in order to evaluate the ability of the instrument to detect oxygenation changes. Afterwards, the effects of pharmacological treatments, such as systemic amphetamine and nicotine treatments on the CNS have been detected.

In vivo voltammetry: from wire to wireless measurements

A novel telemetric system based on either differential pulse voltammetry (DPV) or direct current amperometry (DCA) by using a diffused infrared transmission channel is presented. Unlike similar pre-existing instruments based on infrared transmission, the present system works on a single-way communication, thus avoiding problems related to cross-talking between two-way channels. The infrared channel is also immune from electromagnetic interferences from the surrounding environment. Further advancement is the development of an original miniaturised system (dimension 1cm x 1.2 cm x 0.5 cm) with reduced weight (5-6 g), suitable for affixing to the rat head and allowing real time telemetric monitoring using DCA sampling of neurotransmitters such as dopamine or serotonin every 100 ms. The set-up is based on a transmitter (TX) circuit mounted on the animal's head and connected to the electrodes inserted into its brain. The TX circuit generates the proper electrical signals for DPV or DCA, collects the electrical response of the brain and transmits it, via an infrared channel, to a receiving station (RX) interfaced with a personal computer. The PC performs the sampling and elaboration of polarographic traces in a flexible and programmable way.

In vivo autofluorescence spectrofluorometry of central serotonin

The autofluorescence properties of serotonin (5-HT) were investigated by light spectrofluorometry in in vitro, ex vivo and in vivo experiments. Ex vivo samples were prepared from rat brain regions containing serotonin (5-HT) i.e. cortex, striatum, hippocampus. Rats were untreated (controls) or previously submitted to chronic behavioural or pharmacological treatments known to affect endogenous 5-HT levels. Autofluorescence analysis (excitation: 366 nm) on hippocampus homogenates supplied with exogenous 5-HT revealed spectral alterations attributable to changes of endogenous 5-HT levels. In vivo, real time fluorescence studies were performed via a 50 microm diameter optic fiber probe stereotaxically implanted into selected brain areas of anaesthetised rats treated with fluoxetine or 5-OH-tryptophan. All autofluorescence data were consistent with those obtained in parallel experiments performed with ex vivo or in vivo voltammetry, confirming that auto-fluorescence spectroscopy is a suitable technique for the direct assessment of fluorescent neurotransmitters. This is a reliable evidence of the in vivo application of spectroscopy together with optic fiber probe for in vivo, in situ and real time measurement of 5-HT in discrete brain areas.

Autofluorescence Spectrofluorometry of central nervous system (CNS) neuromediators

BACKGROUND AND OBJECTIVES

Changes in the neurotransmitter 5-hydroxytriptamine (5-HT) are related to psychiatric diseases such as depression and anxiety. In this study, 5-HT autofluorescence properties were investigated in solution and in biological tissues.

STUDY DESIGN/MATERIALS AND METHODS

Spectrofluorometric characterization was performed on ex vivo samples (tissue sections, homogenates) of the 5-HT-rich brain region hippocampus from rats untreated or treated to affect endogenous 5-HT levels; in vivo, with a 50 solidus in circle optic fiber probe positioned via stereotaxis.

RESULTS

5-HT exhibited minor excitation and emission bands at wavelengths longer than the well known excitation and emission bands in the UV region, 250-320 nm. Spectrofluorometric measurements under 366 nm excitation on homogenates supplied with 5-HT or belonging to treated rats revealed spectral alterations attributable to changes in the amount of 5-HT. Ex vivo and in vivo autofluorescence data were consistent with those obtained by conventional voltammetry.

CONCLUSIONS

Autofluorescence spectroscopy potential is confirmed as a suitable technique for the direct measurement of neurotransmitters.

Evidence that the metabotropic glutamate receptor 5 antagonist MPEP may act as an inhibitor of the norepinephrine transporter in vitro and in vivo

The mechanisms through which blockade of metabotropic glutamate receptors 5 (mGluR5) results in anxiolytic and antidepressant effects are currently unknown. In the present study, we therefore hypothesized that the anxiolytic- and antidepressant-like profile of the noncompetitive mGluR5 receptor antagonist 2-ethyl-6-(phenylethynyl)-pyridine (MPEP) may be mediated by inhibition of the norepinephrine transporter (NET). Accordingly, we first examined the potency of MPEP to bind to or inhibit uptake at the NET as well as the dopamine and serotonin transporters (DAT and SERT, respectively). We also examined the simultaneous in vivo effects of MPEP and desipramine (DMI) on both NE-like oxidation current in the amygdala (AMY) and cell firing in the locus coeruleus (LC) by means of differential pulse voltammetry (DPV) coupled with electrophysiology. MPEP completely displaced the binding of [3H]-nisoxetine on human NET with a pKi of 6.63 +/- 0.02. In addition, MPEP was able to inhibit [3H]-NE uptake in LLCPK cells expressing human NET, with a pIC50 of 5.55 +/- 0.09. In vivo DPV data revealed that both MPEP (30 mg/kg i.p.) and DMI (10 mg/kg i.p.) significantly increased NE-like voltammetric responses levels in the AMY, whereas both compounds also significantly decreased cell firing monitored concomitantly from the second microelectrode in the LC. Collectively, the results of the present study provide potential new mechanisms through which MPEP exerts its anxiolytic and antidepressant effects.