Is it possible to measure hemodynamic changes in the prefrontal cortex through the frontal sinus using continuous wave DOT systems?

The present work shows the capability of near infrared (NIR) light to reach the cerebral cortex through the frontal sinus using continuous-wave techniques (CW-DOT) in a dual study. On the one hand, changes in time during the tracking of a blood dye in the prefrontal cortex were monitored. On the other hand, hemodynamic changes induced by low frequency of transcranial magnetic stimulation applied on the prefrontal cortex were recorded. The results show how NIR light projected through the frontal sinus reaches the cerebral cortex target, providing enough information to have a reliable measurement of cortical hemodynamic changes using CW-DOT.

The mirror neuron system and motor dexterity: what happens?

The mirror neuron system (MNS) is currently one of the most prominent areas of research in neuroscience. Some of the work has focused on the identification of factors that modulate its activity, but until now, no one has tried to identify the effect of motor ability on the MNS regions. The aim of the present work is to study a possible modulation of hand dexterity on the MNS activity. A blocked fMRI experiment has been designed, consisting of an execution condition, where participants must repeatedly perform a precision grasping pantomime, and an observation condition, where the same motor action is passively observed. A conjunction analysis was performed in order to confirm the existence of mirror activity. Moreover, participants were classified depending on their hand dexterity (measured with the Purdue Pegboard Test) as "High dexterity" or "Low dexterity" and a regression analysis was performed to investigate a possible linear relationship between the degree of dexterity and brain activity in the MNS. The conjunction analysis revealed, as expected, activity in the inferior parietal lobule, a region that constitutes one of the nuclei of the putative MNS and which is consistently activated by intransitive actions. The degree of dexterity only seems to modulate MNS regions during action execution. However, under the observation condition, no linear relationship of hand dexterity in MNS regions was registered in either the comparison between groups, or in the regression analysis. Therefore, the MNS network does not seem to be linearly modulated by the degree of motor dexterity, as occurs with other action-related factors like familiarity.

Surfactant-promoted Prussian Blue-modified carbon electrodes: enhancement of electro-deposition step, stabilization, electrochemical properties and application to lactate microbiosensors for the neurosciences.

We report here for the first time a comparison of the beneficial effects of different cationic surfactants - cetyl trimethyl ammonium bromide (CTAB), benzethonium chloride (BZT) and cetylpyridinium chloride (CPC) - for the electrochemical synthesis of Prussian Blue (PB) films, using cyclic voltammetry (CV), on screen-printed carbon electrodes (SPCEs). Their electrochemical properties were investigated, paying special attention to parameters such as the amount of PB deposited, film thickness, charge transfer rate, permeability, reversibility, stability and sensitivity to hydrogen peroxide detection. All surfactant-enhanced PB-modified SPCEs displayed a significant improvement in their electrochemical properties compared with PB-modified SPCEs formed in the absence of surfactants. Surfactant-modified electrodes displayed a consistently higher PB surface concentration value of 2.1±0.4×10(-8) mol cm(-2) (mean±SD, n=3) indicating that PB deposition efficiency was improved 2-3 fold. K(+) and Na(+) permeability properties of the films were also studied, as were kinetic parameters, such as the surface electron transfer rate constant (k(s)) and the transfer coefficient (α). The hydrogen peroxide sensitivity of surfactant-modified PB films generated by 10 electro-deposition CV cycles gave values of 0.63 A M(-1) cm(-2), which is higher than those reported previously for SPCEs by other authors. Finally, the first lactate microbiosensor described in the literature based on BZT-modified PB-coated carbon fiber electrodes is presented. Its very small cross-section (~10 µm diameter) makes it particularly suitable for neuroscience studies in vivo.

Simultaneous measurements of glucose, oxyhemoglobin and deoxyhemoglobin in exposed rat cortex.

The present work addresses the simultaneous monitoring of hemoglobin and glucose consumption in rat somatosensory cortex in vivo. We propose a method which combines two techniques: 2-dimensional optical imaging and an amperometric microbiosensor. The mounted setup optimizes the space in the cranial window so that three micro-electrodes can be inserted: glucose microbiosensor, sentinel and stimulating electrode as well as the holder to manipulate the optical fiber. Additionally, a tool based on graphical user interface programming has been developed to visualize a two-dimension spectral map of oxy-, deoxy- and total hemoglobin, HbO2, HbR and HbT respectively, in the cortex. Our results showed a good sensitivity, selectivity and spatial resolution for both methods. Relevant hemodynamic responses had a common central focus (at the site of the stimulus) which later segregated to other vascular compartments. A good linear relationship between extracellular glucose concentration and HbO2 values during brain activation after local electrical stimulation was observed for electrochemical and optical recordings (R² values were over 0.94). Time courses between glucose and HbO2 signals showed a temporal delay ranging from 1 s to 2 s, suggesting that both variables are not always coupled. The temporal mismatching reported here, provides in vivo evidence that supports a neuronal hypothesis: cerebral blow flow and oxidative metabolism are driven in parallel by neural activity--rather than a concatenation of events ('in-series' events) occurring at sites of neuronal activation.

Microbiosensors for glucose based on Prussian Blue modified carbon fiber electrodes for in vivo monitoring in the central nervous system.

Carbon fiber electrodes (CFEs) were used to develop microbiosensors for glucose as an alternative to the classical Pt and Pt-Ir transducers. Their low dimensions (∼250 µm CFE length and ∼10 µm diameter) are important factors for measurements in physiological environments. An electrocatalytic Prussian Blue (PB) film facilitated detection of enzyme-generated hydrogen peroxide at a low applied potential (∼0.0 V against SCE), contrasting the high potential used in many previous designs (∼0.7 V). The electrosynthesized polymer, poly-o-phenylenediamine (PoPD), was used to improve biosensor stability and selectivity against endogenous interference species, such as ascorbic and uric acids. Optimization of the fabrication procedure is described, including activation of CFE/PB, enzyme immobilization and stabilization, anti-interference films, optimizing applied potential, and pH effects. Analytical properties were also characterized such as sensitivity, LOD, linear range, and enzyme loading. Finally, an optimized biosensor displaying a linear sensitivity of 9.3±0.1 µA mM(-1) cm(-2) (n=3), a 2% RSD and free of interference, is proposed as a suitable candidate for in vivo glucose monitoring in the CNS.

Different levodopa actions on the extracellular dopamine pools in the rat striatum.

Levodopa has been the mainstay treatment for Parkinson's disease for several decades, but the precise mechanism for its therapeutic action is still not well understood. To date, little distinction has been made between the effects of levodopa on the different brain DA pools. We studied the levodopa action on two extracellular DA pools: one was analyzed by microdialysis (often considered as indicative of volume transmission) and the other by in vivo amperometry during nigrostriatal cell stimulation (more indicative of neurotransmission). Levodopa administration induced a moderate (increased 200%) and tardy (began at 60 min) increase in the DA-pool measured by microdialysis, an effect that increased (increased 500%) and accelerated (began at 10 min) after DA-cell degeneration. Levodopa action on the DA-pool measured by amperometry was very fast (10 min) and prominent (increased 600%) in normal rats. The DA-denervated striatum showed a fast exhaustion during cell stimulation, which prevented further study of the levodopa effect on the DA amperometry-pool under this condition. This study suggests a different kinetic for levodopa action on the volume transmitter and neurotransmitter DA-pool, showing marked changes in levodopa action in the denervated striatum.

Opposite effects of low and high doses of arginine on glutamate-induced nitric oxide formation in rat substantia nigra.

L-arginine is a very versatile amino acid that is involved in many important physiological processes such as protein, nitric oxide (NO), agmatine, putrescine, urea, L-ornithine or creatine synthesis and is essential for posttranslational arginylation of protein. The present study was designed to evaluate in vivo the effect of L-arginine on NO production in substantia nigra. In vivo spectroscopic and voltammetric studies were addressed in rats to record modifications in methemoglobin and NO levels under glutamate stimulation. Results showed that, under physiological L-arginine extracellular concentration, the intranigral infusion of glutamate produced an increase in NO levels. When a low dose of L-arginine was co-infused with glutamate, a persistent and higher increase in NO levels was observed. The co-infusion of glutamate with a moderate dose of L-arginine induced drastic and persistent NO production. It was also observed that high doses of either L-arginine or D-arginine inhibit NO production. Subsequently, these data show that L-arginine and D-arginine are involved in a mechanism that inhibits NO production.

Amphetamine increases the extracellular concentration of glutamate in striatum of the awake rat: involvement of high affinity transporter mechanisms.

Using microdialysis it was found that intracerebral infusions of amphetamine increase the extracellular concentration of glutamate, and also of dopamine, aspartate, GABA, and taurine. The increases in glutamate produced by amphetamine was independent of calcium in the perfusion medium but was significantly attenuated by specific blockers of the high affinity transporters of this neurotransmitter. Amphetamine infusions also produced a decrease in the extracellular concentration of Na+, an increase in the extracellular concentration of lactate, and a decrease in haemoglobin in the area of perfusion. All these data suggest that amphetamine increases the extracellular concentration of glutamate and other neurotransmitters through a hypoxic mediated process. This study also shows that an alpha-noradrenergic receptor antagonist is able to attenuate the effects of amphetamine on the release of glutamate, dopamine, GABA and taurine, which further suggests a vasoconstrictor effect of amphetamine as a result of which hypoxia could develop.

Nitric oxide release in penile corpora cavernosa in a rat model of erection.

1. Nitric oxide (NO) levels were measured in the corpus cavernosum of urethane-anaesthetized rats by using differential normal pulse voltammetry with carbon fibre microelectrodes coated with a polymeric porphyrin and a cation exchanger (Nafion). A NO oxidation peak could be recorded at 650 mV vs. a Ag-AgCl reference electrode every 100 s. 2. This NO signal was greatly decreased by the NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME), given by local and systemic routes, and enhanced by the NO precursor L-arginine. Treatment with L-arginine reversed the effect of L-NAME on the NO peak. 3. Both the NO signal and the intracavernosal pressure (ICP) were increased by electrical stimulation of cavernosal nerves (ESCN). However, the rise in the NO levels long outlived the rapid return to baseline of the ICP values at the end of nerve stimulation. 4. The ICP and the NO responses to ESCN were suppressed by local and systemic injections of L-NAME. Subsequent treatment with L-arginine of L-NAME-treated animals restored the NO signal to basal levels and the NO response to ESCN. The ICP response to ESCN was restored only in part by L-arginine. 5. The observed temporal dissociation between the NO and ICP responses could be accounted for by several factors, including the buffering of NO by the blood filling the cavernosal spaces during erection. 6. These findings indicate that an increased production of NO in the corpora cavernosa is necessary but not sufficient for maintaining penile erection and suggest a complex modulation of the NO-cGMP-cavernosal smooth muscle relaxation cascade.

Autotomy in rats following peripheral nerve transection is attenuated by preceding formalin injections into the same limb.

The influence of an evolving painful inflammatory lesion on the development of autotomy, a behavioural model of denervation pain, was studied in rats suffering sciatic and saphenous nerves transection 30 or 60 min, and 1, 3, 7 or 14 days after being injected with formalin (50 microl, 5%, s.c). Hindpaws pressure and heat nociceptive thresholds and volume of the injected paw were assessed, in non-operated rats, at the above time-points. The main effects on autotomy were: (1) a significant attenuation when formalin injection preceded the neurectomies by 1 day or more, a period characterized by hypalgesia of the injected paw to both mechanical (during the first week) and thermal (spanning up to the third day after formalin) stimuli and inflammation (lasting for 14 days); (2) a significantly earlier onset when formalin was injected 30 min before neurectomies. Possible mechanisms linking nociceptive responsiveness and inflammation to the development of autotomy are discussed.

Constitutive NOS isoforms account for gastric mucosal NO overproduction in uremic rats.

To study whether renal failure enhances gastric mucosal nitric oxide (NO) formation in the rat, we measured 1) in vivo NO concentration and 2) NO synthase (NOS) activity, content, and mRNA expression in gastric mucosal homogenates of uremic and sham-operated anesthetized rats. Gastric mucosal NO release was measured by an electrochemical technique. NOS content was analyzed by Western immunoblots, using specific monoclonal antibodies. Constitutive (Ca2+ dependent; cNOS) and inducible (Ca2+ independent; iNOS) NOS activities were assayed by following the conversion of L-[U-14C]arginine to [U-14C]citrulline. mRNA expression for the constitutive neuronal (ncNOS), endothelial (ecNOS), and iNOS isoforms was determined by reverse transcription-polymerase chain reaction. Under basal conditions, gastric mucosal NO concentration was significantly greater in uremic compared with control rats. This was accompanied by significantly greater gastric mucosal cNOS activity in uremic rats than in control rats, whereas no differences were observed in iNOS activity between both groups of animals. Moreover, total enzyme content and the levels of gastric mucosal mRNA expression for ncNOS, ecNOS, and iNOS showed no significant differences between uremic and sham-operated rats. These data confirm that, in uremic rats, enhanced Ca2+-dependent NOS activity is responsible for gastric mucosal NO overproduction and suggest that the main regulatory mechanism is not transcriptional but translational and/or posttranslational in nature.

In vivo monitoring of brain neurotransmitter release for the assessment of neuroendocrine interactions.

1. The neurotransmitter mechanisms regulating neuroendocrine processes have been traditionally inferred from the effects of drugs purportedly acting through specific transmitter systems. The direct appraisal of changes in endogenous neuromediators had to rely initially on analyses of brain samples obtained post-morten. 2. Currently, a more physiological assessment is available through the monitoring ot the extracellular levels of neurotransmitters and their metabolites in discrete brain areas of living animals. Two methodologies, namely in vivo voltammetry and microdialysis, are being increasingly used for this purpose. This article summarizes their principles, relative merits, and limitations and presents some relevant applications. 3. Thus, microdialysis data show a differential response in the amphetamine-induced dopamine release in the nucleus accumbens in adult male and female rats castrated prepuberally. Given their high time-resolution, in vivo electrochemistry techniques seem especially suited for studying the fast, non-genomic effects of steroid hormones. This is illustrated by the voltammetric detection of a rapid release of dopamine in the corpus striatum induced by progesterone in males. 4. These methodologies should be regarded as complementary tools for the assessment of the neurochemical correlates of neuroendocrine interactions.

Voltammetric and microdialysis monitoring of brain monoamine neurotransmitter release during sociosexual interactions.

The monoamine neurotransmitters have long been ascribed important modulatory actions on male sexual behavior by a wealth of pharmacological studies. Methodological developments have now made possible the assessment of the extracellular levels of amine transmitters and their metabolites in discrete brain areas of sexually behaving animals using in vivo voltammetry and microdialysis. Studies in our and other laboratories consistently show increased dopamine release in forebrain structures known to be involved in mating activity, including the nucleus accumbens and the medial preoptic area, during both the appetitive (i.e., non-contact exposure to sexual stimuli) and consummatory phases of this behavior. Serotonin utilization seems to be mainly related to consummatory events. These findings are consistent with the pharmacological evidence as well as previous ex vivo work. The state of sexual inactivity that follows unrestricted mating associates with increased dopamine turnover in the preoptic area. According to the available information, it could reflect some blockade of dopaminergic receptors, possibly involving prolactin. No disturbance of ongoing sexual behavior was observed during the neurochemical monitoring sessions with either methodology. These studies show voltammetry and microdialysis as powerful complementary tools for the assessment of sociosexual interactions.

Neurochemical correlates of sexual exhaustion and recovery as assessed by in vivo microdialysis.

The extracellular levels of the dopamine (DA) metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) and the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the medial preoptic area (MPOA) of male rats were monitored during unrestricted copulation, the ensuing state of sexual refractoriness and the resumption of mating activity. MPOA dialysates were collected from the same animal during four consecutive days. In the first day the subjects were allowed to copulate until reaching a satiation criterion. That was associated with a marked increase in the dialysate levels of the three metabolites assessed. During the next two days the animals remained sexually inactive when exposed to receptive females. Their basal levels of DOPAC and HVA were elevated, whereas those of 5-HIAA remained as low as in the first session. During the non-mating exposure to receptive females there were only minor changes in the three metabolites. By the fourth day, just before the animals resumed copulation, the basal levels of the DA metabolites, especially HVA, had decreased to values closer to those found in the first day. When they mated again to exhaustion the levels of DOPAC, HVA, and 5-HIAA increased as in the first session. The neurochemical changes found during the intervening state of sexual inactivity (i.e. increased levels of DA metabolites) are reminiscent of the effects of DA receptor blockers, which suggests a possible neurochemical mechanism for sexual refractoriness.

Changes in monoamine turnover in forebrain areas associated with masculine sexual behavior: a microdialysis study.

This report compares the changes in the main dopamine (DA) and serotonin (5-HT) metabolites, respectively dihydroxyphenylacetic acid (DOPAC) and 5-hydroxy indoleacetic acid (5-HIAA) in three relatively close brain regions, namely the nucleus accumbens (ACB), the medial preoptic area, and the medial basal hypothalamus (MBH), as well as DA in the ACB, of copulating male rats. All these neurochemicals remained fairly stable when the animals were exposed to non sexual social stimuli (castrated females), and they increased during mating with receptive females. There were regional differences in these copulation-related changes, however, with those in the MBH being shorter-lived. There were also differences in the time-course of the changes in DOPAC and 5-HIAA the latter being slower. It is suggested that they reflect the involvement of the DA and 5-HT innervation of diencephalic structures in, respectively the appetitive and consummatory/satiation mechanisms of sexual behavior. The physiological relevance of these neurochemical changes is supported by the lack of differences between the standard measures for sexual behavior recorded before surgery and during the dialysis session.

Fixed versus removable microdialysis probes for in vivo neurochemical analysis: implications for behavioral studies.

The levels of several neurochemicals, i.e., uric acid (UA), dopamine (DA), dihydroxyphenylacetic acid, and 5-hydroxyindoleacetic acid, collected daily from the rat striatum with either fixed or removable microdialysis probes for 7 days after surgery were compared. The implantation of the fixed cannula was followed by a 10-fold increase in the UA content in the dialysates collected from the first day after surgery onward and by a steady decrease in dihydroxyphenylacetic acid levels, whereas those of DA remained fairly stable. With the removable cannula system, only a smaller, transient increase in UA during the first 3 days after surgery was observed, with no change in DA or monoamine metabolites. The glial reaction around the cannula tracks was assessed by both quantitative histological techniques and measuring the glutamine levels in the dialysates collected at the time of surgery and 7 days later. Both the glial cell number and nuclear size, as well as the glutamine outflow, were considerably larger in the animals implanted with the fixed probes. It is, therefore, likely that the UA levels in the dialysate reflect the glial reaction to the probe. The suitability of the removable probe system for behavioral experiments involving repeated microdialysis sampling was illustrated in an experiment showing that the DA release in the nucleus accumbens of male rats assessed daily at postsurgery days 5-10 was virtually identical in three alternating sessions of sexual behavior as was the smaller release of this neurotransmitter detected during intervening nonsexual social interactions.

Voltammetric monitoring of brain extracellular levels of serotonin, 5-hydroxyindoleacetic acid and uric acid as assessed by simultaneous microdialysis.

We have previously developed a microcomputer-assisted curve-fitting method for measuring the components of the mixed electrochemical signals recorded by differential normal pulse voltammetry in the living brain. It was initially used for resolution of the dopamine and dihydroxyphenylacetic acid components of the catechol signal (peak 2). This report shows how it can be applied to analysis of the indoleamine/uric acid (UA) components of the more complex peak 3. The voltammogram is modeled as a mixture of 3 normal curves of known parameters corresponding to the oxidation of UA, 5-hydroxyindoleacetic acid and serotonin, which is solved by non-linear iterative procedures. Performance was assessed by treatments with drugs having well-known effects on the substances monitored, pargyline and allopurinol, and by the chromatographic analysis of microdialysates collected simultaneously from the contralateral side.

Mathematical resolution of mixed in vivo voltammetry signals. Models, equipment, assessment by simultaneous microdialysis sampling.

A microcomputer-assisted curve-fitting procedure was developed for the quantitative estimation of the components of the mixed "catechol peak" recorded with differential normal pulse voltammetry (DNPV) at electrochemically pretreated carbon fiber microelectrodes in the living brain. The contribution of each of the relevant electroactive species is fitted by a normal probability function, the parameters of which are previously determined in vitro for each electrode and substance. The voltammogram is thus modeled as a mixture of normal curves corresponding to the individual oxidizable substances plus a low order polynomial approximating the baseline. In a former approach the function was solved by linear least squares techniques. As a further improvement, we now propose a non-linear model of the voltammogram and a Gauss-Newton iterative algorithm with stepwise regression for parameter estimation. This report shows the application of the method for the resolution of the dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) components of the DNPV signal recorded from the striatum of freely moving animals in response to amphetamine and pargyline. The method was validated by the chemical assay of contralateral microdialysates collected simultaneously. The changes detected by both methodologies were closely parallel, with highly significant correlation coefficients (0.87 and 0.99 for DA and DOPAC, respectively, P less than 0.001). This study further illustrates that the in vivo voltammetry methodology can be improved substantially by incorporating a suitable mathematical treatment of the electrochemical signals.

Anomalously high concentrations of brain extracellular uric acid detected with chronically implanted probes: implications for in vivo sampling techniques.

The height of peak 2, h2, recorded using linear sweep voltammetry with 350-micron-diameter carbon paste electrodes in rat striatum was measured from the day of implantation (day 0) to 4 months after surgery. The value of h2 was at a minimum on day 0 (0.6 +/- 0.2 nA; n = 20), rose sharply to a maximum on day 2 (6.3 +/- 0.9 nA; n = 12), and decreased to a stable level by day 7 (3.3 +/- 0.7 nA; n = 16), which lasted for 4 months (3.2 +/- 0.6 nA; n = 9). These changes were shown by microinfusion of uricase to be due to variations in the concentrations of extracellular uric acid, although h2 appears to have a small baseline contribution of approximately 0.3 nA from 5-hydroxyindoleacetic acid. The stable value of h2 recorded under chronic conditions was estimated to correspond to a minimal uric acid concentration of 50 mumol/L, which represents a 10-fold increase in the extracellular level of this purine metabolite compared with the initial (acute) value. Very similar results were obtained using a microdialysis technique that detected uric acid directly. These estimates of striatal uric acid concentration are in marked contrast to those obtained using 40-micron diameter carbon fiber electrodes, which showed a decrease from the acute preparation to less than 1 mumol/L under chronic conditions. Large values of h2 were also recorded with chronically implanted paste electrodes in the hippocampus and frontal cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Sex-related olfactory stimuli induce a selective increase in dopamine release in the nucleus accumbens of male rats. A voltammetric study.

Changes in the dopaminergic (DA) transmission in the nucleus accumbens were investigated in male rats exposed to sociosexual olfactory stimuli from different conspecifics: receptive female, non-receptive female and intact male. DAergic transmission was assessed by measurement of extracellular levels of DA and dihydroxyphenylacetic acid (DOPAC). Both compounds were recorded by using differential normal pulse voltammetry (DNPV) with electrochemically pretreated carbon fiber electrodes and numerical analysis of the catechol peak. Exposition to receptive female odors induced a marked and selective increase in DA release compared to control values. Exposition to non-receptive female odors and male odors induced an increase in DA release not significantly different from that following the change of environment. In conclusion, mesencephalic DAergic neurons reaching the nucleus accumbens appear to be involved in the perception of behaviorally significant olfactory cues.