Simultaneous wireless and high-resolution detection of nucleus accumbens shell ethanol concentrations and free motion of rats upon voluntary ethanol intake

Highly sensitive detection of ethanol concentrations in discrete brain regions of rats voluntarily accessing ethanol, with high temporal resolution, would represent a source of greatly desirable data in studies devoted to understanding the kinetics of the neurobiological basis of ethanol's ability to impact behavior. In the present study, we present a series of experiments aiming to validate and apply an original high-tech implantable device, consisting of the coupling, for the first time, of an amperometric biosensor for brain ethanol detection, with a sensor for detecting the microvibrations of the animal. This device allows the real-time comparison between the ethanol intake, its cerebral concentrations, and their effect on the motion when the animal is in the condition of voluntary drinking. To this end, we assessed in vitro the efficiency of three different biosensor designs loading diverse alcohol oxidase enzymes (AOx) obtained from three different AOx-donor strains: Hansenula polymorpha, Candida boidinii, and Pichia pastoris. In vitro data disclosed that the devices loading H. polymorpha and C. boidinii were similarly efficient (respectively, linear region slope [LRS]: 1.98 ± 0.07 and 1.38 ± 0.04 nA/mM) but significantly less than the P. pastoris-loaded one (LRS: 7.57 ± 0.12 nA/mM). The in vivo results indicate that this last biosensor design detected the rise of ethanol in the nucleus accumbens shell (AcbSh) after 15 minutes of voluntary 10% ethanol solution intake. At the same time, the microvibration sensor detected a significant increase in the rat's motion signal. Notably, both the biosensor and microvibration sensor described similar and parallel time-dependent U-shaped curves, thus providing a highly sensitive and time-locked high-resolution detection of the neurochemical and behavioral kinetics upon voluntary ethanol intake. The results overall indicate that such a dual telemetry unit represents a powerful device which, implanted in different brain areas, may boost further investigations on the neurobiological mechanisms that underlie ethanol-induced motor activity and reward.

Is catalase involved in the effects of systemic and pVTA administration of 4-methylpyrazole on ethanol self-administration?

The oxidative metabolism of ethanol into acetaldehyde involves several enzymes, including alcohol dehydrogenase (ADH) and catalase-hydrogen peroxide (H₂O₂). In this regard, while it is well known that 4-methylpyrazole (4-MP) acts by inhibiting ADH in the liver, little attention has been placed on its ability to interfere with fatty acid oxidation-mediated generation of H₂O₂, a mechanism that may indirectly affect catalase whose enzymatic activity requires H₂O₂. The aim of our investigation was twofold: 1) to evaluate the effect of systemic (i.p. [intraperitoneal]) and local (into the posterior ventral tegmental area, pVTA) administration of 4-MP on oral ethanol self-administration, and 2) to assess ex vivo whether or not systemic 4-MP affects liver and brain H₂O₂ availability. The results show that systemic 4-MP reduced ethanol but not acetaldehyde or saccharin self-administration, and decreased the ethanol deprivation effect. Moreover, local intra-pVTA administration of 4-MP reduced ethanol but not saccharin self-administration. In addition, although unable to affect basal catalase activity, systemic administration of 4-MP decreased H₂O₂ availability both in liver and in brain. Overall, these results indicate that 4-MP interferes with ethanol self-administration and suggest that its behavioral effects could be due to a decline in catalase-H₂O₂ system activity as a result of a reduction of H₂O₂ availability, thus highlighting the role of central catalase-mediated metabolism of ethanol and further supporting the key role of acetaldehyde in the reinforcing properties of ethanol.

Microdialysis as a New Technique for Extracting Phenolic Compounds from Extra Virgin Olive Oil

The amount and composition of the phenolic components play a major role in determining the quality of olive oil. The traditional liquid-liquid extraction (LLE) method requires a time-consuming sample preparation to obtain the "phenolic profile" of extra virgin olive oil (EVOO). This study aimed to develop a microdialysis extraction (MDE) as an alternative to the LLE method to evaluate the phenolic components of EVOO. To this purpose, a microdialysis device and dialysis procedure were developed. "Dynamic-oil" microdialysis was performed using an extracting solution (80:20 methanol/water) flow rate of 2 μL min^-1 and a constant EVOO stream of 4 μL min^-1. The results indicated a strong positive correlation between MDE and the LLE method, providing a very similar phenolic profile obtained with traditional LLE. In conclusion, the MDE approach, easier and quicker in comparison to LLE, provided a reliable procedure to determine the phenolic components used as a marker of the quality and traceability of EVOO.

Implantable (Bio)sensors as new tools for wireless monitoring of brain neurochemistry in real time

Implantable electrochemical microsensors are characterized by high sensitivity, while amperometric biosensors are very selective in virtue of the biological detecting element. Each sensor, specific for every neurochemical species, is a miniaturized high-technology device resulting from the combination of several factors: electrode material, shielding polymers, applied electrochemical technique, and in the case of biosensors, biological sensing material, stabilizers, and entrapping chemical nets. In this paper, we summarize the available technology for the in vivo electrochemical monitoring of neurotransmitters (dopamine, norepinephrine, serotonin, acetylcholine, and glutamate), bioenergetic substrates (glucose, lactate, and oxygen), neuromodulators (ascorbic acid and nitric oxide), and exogenous molecules such as ethanol. We also describe the most represented biotelemetric technologies in order to wirelessly transmit the signals of the above-listed neurochemicals. Implantable (Bio)sensors, integrated into miniaturized telemetry systems, represent a new generation of analytical tools that could be used for studying the brain’s physiology and pathophysiology and the effects of different drugs (or toxic chemicals such as ethanol) on neurochemical systems.

Simultaneous telemetric monitoring of brain glucose and lactate and motion in freely moving rats

A new telemetry system for simultaneous detection of extracellular brain glucose and lactate and motion is presented. The device consists of dual-channel, single-supply miniature potentiostat-I/V converter, a microcontroller unit, a signal transmitter, and a miniaturized microvibration sensor. Although based on simple and inexpensive components, the biotelemetry device has been used for accurate transduction of the anodic oxidation currents generated on the surface of implanted glucose and lactate biosensors and animal microvibrations. The device was characterized and validated in vitro before in vivo experiments. The biosensors were implanted in the striatum of freely moving animals and the biotelemetric device was fixed to the animal's head. Physiological and pharmacological stimulations were given in order to induce striatal neural activation and to modify the motor behavior in awake, untethered animals.

Further in-vitro characterization of an implantable biosensor for ethanol monitoring in the brain

Ethyl alcohol may be considered one of the most widespread central nervous system (CNS) depressants in Western countries. Because of its toxicological and neurobiological implications, the detection of ethanol in brain extracellular fluid (ECF) is of great importance. In a previous study, we described the development and characterization of an implantable biosensor successfully used for the real-time detection of ethanol in the brain of freely-moving rats. The implanted biosensor, integrated in a low-cost telemetry system, was demonstrated to be a reliable device for the short-time monitoring of exogenous ethanol in brain ECF. In this paper we describe a further in-vitro characterization of the above-mentioned biosensor in terms of oxygen, pH and temperature dependence in order to complete its validation. With the aim of enhancing ethanol biosensor performance, different enzyme loadings were investigated in terms of apparent ethanol Michaelis-Menten kinetic parameters, viz. I_MAX, K_M and linear region slope, as well as ascorbic acid interference shielding. The responses of biosensors were studied over a period of 28 days. The overall findings of the present study confirm the original biosensor configuration to be the best of those investigated for in-vivo applications up to one week after implantation.

Development and characterization of an implantable biosensor for telemetric monitoring of ethanol in the brain of freely moving rats

Ethanol is one of the most widespread psychotropic agents in western society. While its psychoactive effects are mainly associated with GABAergic and glutamatergic systems, the positive reinforcing properties of ethanol are related to activation of mesolimbic dopaminergic pathways resulting in a release of dopamine in the nucleus accumbens. Given these neurobiological implications, the detection of ethanol in brain extracellular fluid (ECF) is of great importance. In this study, we describe the development and characterization of an implantable biosensor for the amperometric detection of brain ethanol in real time. Ten different designs were characterized in vitro in terms of Michaelis-Menten kinetics (V(MAX) and K(M)), sensitivity (linear region slope, limit of detection (LOD), and limit of quantification (LOQ)), and electroactive interference blocking. The same parameters were monitored in selected designs up to 28 days after fabrication in order to quantify their stability. Finally, the best performing biosensor design was selected for implantation in the nucleus accumbens and coupled with a previously developed telemetric device for the real-time monitoring of ethanol in freely moving, untethered rats. Ethanol was then administered systemically to animals, either alone or in combination with ranitidine (an alcohol dehydrogenase inhibitor) while the biosensor signal was continuously recorded. The implanted biosensor, integrated in the low-cost telemetry system, was demonstrated to be a reliable device for the short-time monitoring of exogenous ethanol in brain ECF and represents a new generation of analytical tools for studying ethanol toxicokinetics and the effect of drugs on brain ethanol levels.

Do on- and off-pump coronary bypass surgery differently affect perioperative peripheral tissue metabolism?

BACKGROUND

Microdialysis allows the in-vivo assessment of interstitial fluids. We studied the metabolic status of peripheral tissues (skeletal muscle) in patients undergoing coronary artery bypass surgery on- (CABG) or off-pump (OPCAB).

METHODS

Twenty patients candidates to elective coronary bypass surgery were randomly assigned to undergo CABG or OPCAB. A microdialysis catheter was inserted in the left deltoid muscle before surgery and left in place for 24 hours, and metabolic markers of peripheral tissue perfusion (glucose, lactate, pyruvate, glycerol and lactate/pyruvate (L/P) ratio) were assessed before, at the end, and 24 hours after surgery.

RESULTS

Preoperative clinical features were similar in both groups. Interstitial levels of glucose and lactate increased over time, being in both groups significantly higher than baseline 24 hours after surgery, whereas glycerol levels did not change over time and between groups. In addition, there was an increase over time of pyruvate levels which were significantly higher in CABG after surgery, whereas L/P ratio was significantly higher in OPCAB 24 hours after surgery.

CONCLUSION

Metabolic changes after coronary bypass surgery occur with some differences related to CPB use. Overall, these changes suggest that, after coronary surgery, a certain degree of hypermetabolic state ensues, lasting up to 24 hours after surgery; the postoperative increase in pyruvate levels in CABG patients, together with the changes in L/P ratio occurring only in OPCAB patients implies an higher risk of tissue hypoperfusion/ischemia for patients submitted to OPCAB, although this does not lead to permanent cellular damage, as the markers of this complication (e.g., glycerol) do not change over time.

Brain microdialysis in freely moving animals

Brain microdialysis is an analytical technique used for the dynamic monitoring of brain neurochemistry in awake, freely moving animals. This technique requires the insertion of a small dialysis catheter, called a microdialysis probe, into a specific brain region, and its perfusion with an artificial extracellular fluid. The microdialysate samples, obtained from the probe outlet, can be analysed using high-performance liquid chromatography with electrochemical detection for the quantification of oxidizable molecules recovered from the extracellular space. In this chapter, we describe a protocol for performing a microdialysis setup and experiment in freely moving rats and mice. Furthermore, the high-performance liquid chromatographic determination of ascorbic acid, uric acid, catecholamines, indolamines and derivatives is described in detail.

A 6-hydroxydopamine in vivo model of Parkinson's disease

Animal models of Parkinson's disease are essential to explore pathophysiological hypotheses and to test new treatment options, including neurotrophic factors. Catecholaminergic neurotoxins used to generate such models are 6-hydroxydopamine and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. These neurotoxins predominantly kill dopaminergic neurons through oxidative damage and mitochondrial failure, although 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine fails to induce a significant dopaminergic neurodegeneration in rats. The present chapter describes a protocol for the 6-hydroxydopamine rat model based on stereotaxic injection performed only unilaterally, which mimics an early-to-mid stage of the disease.

Dual asymmetric-flow microdialysis for in vivo monitoring of brain neurochemicals

Microdialysis is an extensively used technique for both in vivo and in vitro experiments, applicable to animal and human studies. In neurosciences, the in vivo microdialysis is usually performed to follow changes in the extracellular levels of substances and to monitor neurotransmitters release in the brain of freely moving animals. Catecholamines, such as dopamine and their related compounds, are involved in the neurochemistry and in the physiology of mental diseases and neurological disorders. It is generally supposed that the brain's energy requirement is supplied by glucose oxidation. More recently, lactate was proposed to be the metabolic substrate used by neurons during synaptic activity. In our study, an innovative microdialysis approach for simultaneous monitoring of catecholamines, indolamines, glutamate and energy substrates in the striatum of freely moving rats, using an asymmetric perfusion flow rate on microdialysis probe, is described. As a result of this asymmetric perfusion, two samples are available from the same brain region, having the same analytes composition but different concentrations. The asymmetric flow perfusion could be a useful tool in neurosciences studies related to brain's energy requirement, such as toxin-induced models of Parkinson's disease.

alpha-Synuclein- and MPTP-generated rodent models of Parkinson's disease and the study of extracellular striatal dopamine dynamics: a microdialysis approach

The classical animal models of Parkinson's disease (PD) rely on the use of neurotoxins, including 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 6-hydroxydopamine and, more recently, the agricultural chemicals paraquat and rotenone, to deplete dopamine (DA). These neurotoxins elicit motor deficits in different animal species although MPTP fails to induce a significant dopaminergic neurodegeneration in rats. In the attempt to better reproduce the key features of PD, in particular the progressive nature of neurodegeneration, alternative PD models have been developed, based on the genetic and neuropathological links between -synuclein ( -syn) and PD. In vivo microdialysis was used to investigate extracellular striatal DA dynamics in MPTP- and -syn-generated rodent models of PD. Acute and sub-acute MPTP intoxication of mice both induce prolonged release of striatal DA. Such DA release may be considered the first step in MPTP-induced striatal DA depletion and nigral neuron death, mainly through reactive oxygen species generation. Although MPTP induces DA reduction, neurochemical and motor recovery starts immediately after the end of treatment, suggesting that compensatory mechanisms are activated. Thus, the MPTP mouse model of PD may be unsuitable for closely reproducing the features of the human disease and predicting potential long-term therapeutic effects, in terms of both striatal extracellular DA and behavioral outcome. In contrast, the -syn-generated rat model of PD does not suffer from a massive release of striatal DA during induction of the nigral lesion, but rather is characterized by a prolonged reduction in baseline DA and nicotine-induced increases in dialysate DA levels. These results are suggestive of a stable nigrostriatal lesion with a lack of dopaminergic neurochemical recovery. The -syn rat model thus reproduces the initial stage and slow development of PD, with a time-dependent impairment in motor function. This article will describe the above experimental PD models and demonstrate the utility of microdialysis for their characterization.

Real-time monitoring of brain tissue oxygen using a miniaturized biotelemetric device implanted in freely moving rats

A miniaturized biotelemetric device for the amperometric detection of brain tissue oxygen is presented. The new system, derived from a previous design, has been coupled with a carbon microsensor for the real-time detection of dissolved O(2) in the striatum of freely moving rats. The implantable device consists of a single-supply sensor driver, a current-to-voltage converter, a microcontroller, and a miniaturized data transmitter. The oxygen current is converted to a digital value by means of an analog-to-digital converter integrated in a peripheral interface controller (PIC). The digital data is sent to a personal computer using a six-byte packet protocol by means of a miniaturized 434 MHz amplitude modulation (AM) transmitter. The receiver unit is connected to a personal computer (PC) via a universal serial bus. Custom developed software allows the PC to store and plot received data. The electronics were calibrated and tested in vitro under different experimental conditions and exhibited high stability, low power consumption, and good linear response in the nanoampere current range. The in vivo results confirmed previously published observations on oxygen dynamics in the striatum of freely moving rats. The system serves as a rapid and reliable model for studying the effects of different drugs on brain oxygen and brain blood flow and it is suited to work with direct-reduction sensors or O(2)-consuming biosensors.

Biotelemetric monitoring of brain neurochemistry in conscious rats using microsensors and biosensors

In this study we present the real-time monitoring of three key brain neurochemical species in conscious rats using implantable amperometric electrodes interfaced to a biotelemetric device. The new system, derived from a previous design, was coupled with carbon-based microsensors and a platinum-based biosensor for the detection of ascorbic acid (AA), O₂ and glucose in the striatum of untethered, freely-moving rats. The miniaturized device consisted of a single-supply sensor driver, a current-to-voltage converter, a microcontroller and a miniaturized data transmitter. The redox currents were digitized to digital values by means of an analog-to-digital converter integrated in a peripheral interface controller (PIC), and sent to a personal computer by means of a miniaturized AM transmitter. The electronics were calibrated and tested in vitro under different experimental conditions and exhibited high stability, low power consumption and good linear response in the nanoampere current range. The in-vivo results confirmed previously published observations on striatal AA, oxygen and glucose dynamics recorded in tethered rats. This approach, based on simple and inexpensive components, could be used as a rapid and reliable model for studying the effects of different drugs on brain neurochemical systems.

Novel integrated microdialysis-amperometric system for in vitro detection of dopamine secreted from PC12 cells: design, construction, and validation

A novel dual channel in vitro apparatus, derived from a previously described design, has been coupled with dopamine (DA) microsensors for the flow-through detection of DA secreted from PC12 cells. The device, including two independent microdialysis capillaries, was loaded with a solution containing PC12 cells while a constant phosphate-buffered saline (PBS) medium perfusion was carried out using a dual channel miniaturized peristaltic pump. One capillary was perfused with normal PBS, whereas extracellular calcium was removed from extracellular fluid of the second capillary. After a first period of stabilization and DA baseline recording, KCl (75 mM) was added to the perfusion fluid of both capillaries. In this manner, a simultaneous "treatment-control" experimental design was performed to detect K+-evoked calcium-dependent DA secretion. For this purpose, self-referencing DA microsensors were developed, and procedures for making, testing, and calibrating them are described in detail. The electronic circuitry was derived from previously published schematics and optimized for dual sensor constant potential amperometry applications. The microdialysis system was tested and validated in vitro under different experimental conditions, and DA secretion was confirmed by high-performance liquid chromatography with electrochemical detection (HPLC-EC). PC12 cell viability was quantified before and after each experiment. The proposed apparatus serves as a reliable model for studying the effects of different drugs on DA secretion through the direct comparison of extracellular DA increase in treatment-control experiments performed on the same initial PC12 cell population.