(Re)thinking the city of proximity for Salutogenic purposes

As centres of population and human activities, nowadays urban environments are simultaneously the main cause of and solution to a growing number of health-related challenges. In this setting, COVID-19 pandemic has helped reiterate this and serves as a wake-up call and an opportunity to rethink the way we approach cities. Aim of this paper is to research what today seems the most promising urban model for long-term individual and global resilience: the “city of proximity”, namely about inclusive walkable and cycling environments where people can access all basic destinations within reasonable times and distances from home. Therefore, urban proximity dimension, methodological approach and urban features and functions become the main subject of a quanti-qualitative matrix of comparison of five international case studies centred on the topic, by which it is possible to set out general criteria for such model, along with a methodology to measure all cities in its respect. As a result, residential density, functional mix, pedestrian surface, cycle routes, public transport stops, green areas, schools, cultural facilities, sport facilities, retail services and urban gardens make up the fix components of a comprehensive set of 11+n urban features, whose occurrence is investigated through GIS-based analysis within designated distance ranges, creating a comprehensive assessment framework that is adjustable to all urban contexts worldwide. In the end, the application of such framework to the city of Milan finally helps to validate its effectiveness in providing a picture of city-wide accessibility to proximity services, and in highlighting the value of integrated analysis in view of shaping public policies and informed planning choices which put health and sustainability at the centre.

Lifetime measurements of the neutron-rich N = 30 isotones 50Ca and 51Sc: orbital dependence of effective charges in the fp shell

The lifetimes of the first excited states of the N = 30 isotones (50)Ca and (51)Sc have been determined using the Recoil Distance Doppler Shift method in combination with the CLARA-PRISMA spectrometers. This is the first time such a method is applied to measure lifetimes of neutron-rich nuclei populated via a multinucleon transfer reaction. This extends the lifetime knowledge beyond the f_{7/2} shell closure and allows us to derive the effective proton and neutron charges in the fp shell near the doubly magic nucleus (48)Ca, using large-scale, shell-model calculations. These results indicate an orbital dependence of the core polarization along the fp shell.

Giant dipole resonance in the hot and thermalized 132Ce nucleus: damping of collective modes at finite temperature

The gamma decay of the giant dipole resonance (GDR) in the 132Ce compound nucleus with temperature up to approximately 4 MeV has been measured, using the reaction 64Ni + 68Zn at E(beam) = 300, 400, and 500 MeV. The gamma and charged particles measured in coincidence with recoils are consistent with a fully equilibrated compound nucleus emission. The GDR width, obtained with the statistical model analysis, is found to increase almost linearly with temperature. This increase is rather well reproduced within a model including thermal shape fluctuations and the lifetime of the compound nucleus.

Forced swimming test and fluoxetine treatment: in vivo evidence that peripheral 5-HT in rat platelet-rich plasma mirrors cerebral extracellular 5-HT levels, whilst 5-HT in isolated platelets mirrors neuronal 5-HT changes

Low levels of central serotonin (5-HT) have been related to the state of depression, and 5-HT is the major target of the newer antidepressant drugs such as selective serotonin reuptake inhibitors (SSRIs). Neurons and platelets display structural and functional similarities, so that the latter have been proposed as a peripheral model of central functions. In particular, in blood more than 99% of 5-HT is contained in platelets, so that one could consider changes in 5-HT levels in platelets as a mirror of changes in central 5-HT. Here, this hypothesis has been studied via the analysis of the influence of: (1) the forced swimming test (FST, which has been proved to be of utility to predict the clinical efficacy of antidepressants in rodents) and (2) treatment with the SSRI fluoxetine upon 5-HT levels monitored in brain regions and in peripheral platelets by means of electrochemical in vivo and ex vivo measurements. The results obtained confirm that the FST increases immobility; furthermore they show a parallel and significant decrease in cerebral (brain homogenate) and peripheral (in platelet-rich plasma, PRP) voltammetric 5-HT levels following the FST in naive rats. In addition, subchronic treatment with fluoxetine was followed by a significant increase in 5-HT levels in PRP, while the same SSRI treatment performed within the FST resulted in a decrease in the 5-HT levels in PRP. However, this decrease was inferior to that observed without SSRI treatment. These data suggest that there is an inverse relationship between immobility and the levels of 5-HT in PRP and that these peripheral 5-HT levels are sensitive to: (1) the FST, (2) the treatment with fluoxetine and (3) the combination of both treatments, i.e. SSRI + FST. It has been reported that SSRI treatment at first inhibits the 5-HT transporter in brain, resulting in increased extracellular 5-HT, while following sustained SSRI treatments decreased intracellular levels of central 5-HT were observed. Accordingly, the present data show that the initial block of 5-HT reuptake is revealed by the selective increase in 5-HT levels (extracellular content) measured in PRP (not in insulated platelets, IPs) the 1st day of fluoxetine treatment. The initial action of this SSRI upon the 5-HT transporter in brain has also been confirmed by in vivo voltammetric data showing selective increase in the serotonergic signal following local injection of fluoxetine into the brain region studied. Successively, the major effect monitored is a decrease in 5-HT levels, which is more evident in IPs than in PRP. However, it is known that following 2 weeks treatment with an SSRI, 5-HT autoreceptors are desensitized and the serotonin synthesis is restored, together with the intracellular 5-HT levels. The present data showing that the levels of 5-HT in IPs tend to return to control values 12 days after the beginning of chronic fluoxetine treatment suggest that 5-HT levels in IPs (intracellular environment) mirror the influence of SSRI treatment upon the central 5-HT system. On the other hand, at day 12 of the chronic fluoxetine treatment, 5-HT content remains low in PRP. Similarly, low levels of 5-HT have been monitored in brain homogenate of rats chronically treated with fluoxetine. This would support the similarity between PRP preparation and brain homogenate as in both cases cells are disrupted by sample preparation. In conclusion this work supports the literature in proposing platelets as a peripheral model of central functions. In particular, the present data support the idea that peripheral 5-HT platelet levels can reflect the state of the central 5-HT system in conditions of depression. Furthermore, the main outcome of this study is that PRP may mirror central extracellular 5-HT levels, whilst IPs mirror neuronal 5-HT changes.

Can voltammetry measure nitrogen monoxide (NO) and/or nitrites?

Recently, voltammetry with carbon fibre electrodes (CFE) has been implemented for real time measurement of nitrogen monoxide (NO) indicating that it is oxidised at the potential value of nitrites, approximately +700 mV. In contrast, here we show that modified CFE can monitor NO at oxidation potentials different than that of nitrites, i.e. +550 mV. Indeed, at +550 mV a significant increase of amperometric current levels was obtained when NO but not nitrites, were added to a phosphate buffer saline solution (PBS). Differential pulse voltammetry (DPV) supports these findings as two oxidation peaks were obtained when examining air preserved NO; peak 1 at +550 mV and peak 2 at +700 mV, respectively. In contrast, only peak 2 was monitored when nitrites or a solution of NO oxidised in air was added to PBS. Biological support to these in vitro data comes from the observation that the relaxation of an adrenaline-contracted aortic ring produced via addition of NO is concomitant with peak 1 at +550 mV. The relaxation is almost completed before the appearance of peak 2 at +700 mV. Furthermore, in vivo experiments performed in the striatum of rats show that the amperometric signal monitored at +550 mV is responsive to glutamatergic stimulation or inhibition of NO synthase.

Electrochemical evidence that lacidipine stimulates release of nitrogen monoxide in rat aorta

Dihidropyridines (DHPs) such as amlodipine, lercanidipine and lacidipine, are compounds capable of vascular protection via their calcium antagonist activity. In addition, they present vascular dilatation function, which has been related to an anti endothelin efficacy, particularly for lacidipine. Recent works have suggested that DHPs modulate vascular relaxation via increase in the release of nitrogen monoxide (NO). Using voltammetry with selective biosensors the present experiments performed in rat aortic rings demonstrate the capability of DHPs to implement endothelial NO at 'useful' and not toxic nanomolar levels, with a maximum efficacy for lacidipine. This activity joins the already described positive effects of these compounds upon vascular functions.

Involvement of cholecystokinin within craving for cocaine: role of cholecystokinin receptor ligands

In the brain, cholecystokinin (CCK) has been described to act as a central neurotransmitter or neuromodulator involved in functions such as food consumption, stress and anxiety. Recently, the CCK system has been involved in drug dependence phenomena and proposed to be correlated to a putative state of 'drug preferring' phenotype within free choice tests. CCK exerts its action in the CNS through at least two different G-protein coupled high affinity receptors, CCK1 and CCK2. Various selective CCK receptor agonists and antagonists have been synthesised. In particular, L-364,718 has been demonstrated to be a potent and selective CCK1 receptor antagonist, whereas L-365,260 is a potent and selective CCK2 receptor antagonist. More recently, GV150013 has been reported to be a highly selective CCK2 receptor antagonist. This paper reviews the putative role of the CCK system within drug dependence phenomena. In particular, it analyses the relationship between central CCK activity and the exhibition of spontaneous preference for drugs of abuse, such as cocaine or alcohol. The potential therapeutic role for CCK receptor antagonists is also discussed.

Voltammetric and functional evidence that N-methyl-D-aspartate and substance P mediate rat vascular relaxation via nitrogen monoxide release

It is known that substance P acts as a vasodilator via activation of the enzyme nitrogen monoxide synthase (NOS) in endothelial tissue and it is suggested that N-methyl-D-aspartate (NMDA) could stimulate nitrogen monoxide (NO) release within nervous tissue. However, the data reported concern NO metabolites (nitrites, nitrates), while there is no clear evidence to date of the action of the latter compound within the aortic tissue. In this study, amperometry with specifically prepared carbon fiber electrodes has been applied to examine the effect of NMDA or substance P upon NO release. In particular, the data obtained confirm that NMDA can stimulate NO release in vivo, in the striatum of anaesthetized rats, and that substance P can stimulate NO release in rat aortic rings (ex vivo experiments). In addition, they indicate that NMDA also stimulates NO release in rat aortic rings. This original data has been confirmed by the observation of a vasorelaxant action of NMDA within noradrenaline precontracted aortic rings. Thus, these experiments provide the first direct evidence that NMDA can mediate vascular relaxation via NO release.

Proinflammatory and regulatory cytokine levels in AIDS cachexia

The serum concentrations of inflammatory (Interleukin-1 beta, Tumor necrosis alpha, Interleukin-6) and regulatory cytokines (Interleukin twelve) have been studied in ten AIDS cachectic patients and compared to a control group. A cytokine imbalance, and peculiarly a significant increase in proinflammatory cytokines (Interleukin-1, Interleukin-6, Tumor necrosis Factor alpha) and a decrease in regulatory cytokines such as Interleukin-12 were found. A significant correlation resulted between weight loss and Interleukin-1 beta and 6. A negative correlation between Interleukin-1 and 12 was noted, indicating that this last cytokine has an important regulatory role also in advanced state of the disease.

Cholecystokinin-B (CCK-B) receptor antagonists improve "aged" sleep: a new class of sleep modulators?

Sleep disorders are a major, although often minimized and underdiagnosed, medical problem. Current therapy is based on the use of hypnotics, mainly benzodiazepines, which disrupt the sleep pattern often suppressing rapid-eye-movement (REM) sleep. Here, new types of pharmacological tools such as cholecystokinin (CCK) receptor antagonists are examined. In particular, since the awake-sleep rhythm is mainly altered in old age in humans, the influence of these compounds over REM and non-REM sleep has been studied in aged rats (21 months) vs. young rats (5 months) prepared for electroencephalographic (EEG) recordings. Basal EEG data indicated that REM and non-REM sleep was reduced in aged rats vs. young rats. GV-150013, a selective CCK-B receptor antagonist, was found to increase REM sleep, as well as non-REM sleep, and therefore total sleep (non-REM + REM) mainly in aged rats. The dose-range of activity (0.5-60 micrograms/kg) together with the evidence that another CCK-B receptor antagonist, L-365,260 (5 micrograms/kg) increased, while devazepide (a CCK-A receptor antagonist; 20 micrograms/kg) decreased non-REM sleep and total sleep time, support the original hypothesis that the activity of GV-150013 on sleep progress through CCK-B receptors. Furthermore, no tolerance was detected after chronic treatments with GV-150013. In contrast, typical EEG modifications (decrease of REM) and the development of tolerance towards benzodiazepines were monitored following chronic treatment with triazolam (400 micrograms/kg). These results suggest that the CCKergic compounds studied are involved via a different mechanism of action than benzodiazepines in the modulation of the awake-sleep rhythm. A further observation is that the total sleep time recorded in aged rats after treatment with GV-150013 reached the value of the total sleep time of young untreated rats also prepared for EEG. Finally, this work suggests that CCK receptor antagonists, GV-150013 in particular, are more effective in aged resulting in an improvement of sleep quality towards that of young rats.

The role of cholecystokinin (CCK), CCK-A or CCK-B receptor antagonists in the spontaneous preference for drugs of abuse (alcohol or cocaine) in naive rats

A "free choice" two-bottle drinking test paradigm was implemented in naive adult male Wistar rats, resulting in a clear identification of rats drinking mainly water (water-preferring, WP rats) and rats spontaneously drinking also a consistent amount of a solution of cocaine (0.5 mg/ml water, cocaine-drinking, CD rats) or ethanol 10% v/v (ethanol-drinking, ED rats). Low, selective doses (5 micrograms/kg) of the specific cholecystokinin (CCK)-A receptor antagonist L-364,718 largely reduced the intake of ethanol 10% of ED rats only. In contrast, low, selective doses of GV-150013 (5 micrograms/kg) reduced significantly the consumption of cocaine of CD rats only. These results indicate that the CCK-A or B receptors are selectively involved in the modulation of alcohol or cocaine intake, respectively, and suggest an involvement of the CCKergic system in the drug-seeking behavior. WP rats and CD rats were then prepared for ex vivo electro-neurochemical analysis by means of differential pulse voltammetry (DPV) with micro-biosensors to monitor catechol, 5-hydroxyindole and peptidergic oxidation signals in the nucleus accumbens (nAcc). In this area, the peptidergic signal appeared to be related to the oxidation of endogenous CCK, which basal levels resulted higher in ED and CD rats than WP rats. Thus, the hypothesis that the endogenous tone of the CCK system is higher in the ED and CD rats than in the WP rats is proposed, and is supported by the observation that treatment with CCK-5 (CCK receptor agonist) selectively induced the WP rats to drink alcohol or cocaine. The selective effect of the CCK-antagonists on reducing the drug intake of ED or CD rats further supports this view, as it suggests that CCK antagonists may modify the individual sensitivity towards drugs of abuse set by the stimulating effect of high endogenous CCKergic tone over CCK-B or CCK-A receptors in spontaneous ED or CD rats, respectively. Therefore, the present data indicate that: i) Free-choice models may reveal the presence of individual sensitivity to alcohol or cocaine in naive rats; ii) the dopaminergic system is involved within the reward state, while peptidergic (CCKergic) activities modulate the drug-seeking state (craving state); iii) the CCK system could be a new target in the study of the drug dependency phenomenon. In particular, the data imply a CCK-A receptor mechanism in the regulation of individual sensitivity towards ethanol and a CCK-B receptor mechanism in the regulation of individual sensitivity towards cocaine. Thus, a potential therapeutic role for CCK-A antagonists in the treatment of ethanol abuse and for CCK-B antagonists in the treatment of cocaine abuse is proposed.

SB-204269 SmithKline Beecham

SB-204269 is an anticonvulsant agent under development by SmithKline Beecham, It is in phase II clinical trials as a potential treatment for epilepsy [243338]. The compound is structurally-related to the benzopyran ATP-sensitive potassium channel (KATP) opener, cromakalim, but has opposite stereochemistry. No KATP activators, however, show significant affinity for the binding site of SB-204269 and the mechanism of action of the latter is not thought to involve KATP. SB-204268, the opposite enantiomer, shows no anticonvulsant activity [226615]. SB concludes that SB-204269 represents a mechanistically novel anticonvulsant agent.

Middle cerebral artery occlusion alters neurotransmitter activities in ipsilateral and contralateral rat brain regions: an ex vivo voltammetric study

Differential pulse voltammetry with treated carbon fibre micro-electrodes has been successfully employed in in vivo analysis of neurotransmitter release and metabolism. This methodology has been now applied to ex vivo preparations (brain slices) in order to study diverse neurotransmitter activities in various brain regions ipsilateral and controlateral to a middle cerebral artery (MCA) occlusion performed in anaesthetised adult male rats. Data demonstrated that significant changes of voltammetric ascorbic acid levels related to the ischaemic state were monitored within the ipsilateral to MCA occlusion frontal cortex, striatum, nucleus accumbens and hippocampus which were the brain area studied. Furthermore, it appeared that voltammetric catecholaminergic and 5-hydroxy indolaminergic values measured within the nucleus accumbens controlateral to MCA occlusion differ significantly from the results monitored with the same technique in brain slices obtained from sham rats. In various studies, the brain regions contralateral to MCA occlusion are generally considered as control areas, however, the present data suggest that the nucleus accumbens contralateral to the MCA occlusion side is specifically affected by the ischaemic state.

Spontaneous preference for ethanol in naive rats is influenced by cholecystokinin A receptor antagonism

Naive adult male Wistar rats free to choose between water or 10% ethanol (v/v) spontaneously became water-preferring (WP) rats, as they drank mainly water (approximately 35 ml per day), or alcohol-drinking (ED) rats, as they also drank a significant amount of ethanol (approximately 14 ml per day). The selective CCKA receptor antagonist L-364,718 at doses selective for the CCKA receptor (5 micrograms/kg, IP) halved the consumption of alcohol of the ED rats without modifying their total liquid in-take. In contrast, the CCKB antagonists L-365,260 or GV150013 were without effect when used at doses selective for the CCKB receptor. These data indicate that the CCK system could be involved in the modulation of alcohol intake. In particular, they suggest that CCKA receptors could play a role in the ethanol preference.

Concomitant in vivo electrophysiological and voltammetric analysis indicate that ascorbic acid is a biochemical index of early ischaemia

A number of in vitro studies or in vivo cortical microdialysis measurements have observed that changes in the levels of ascorbic acid (AA), uric acid (UA), tryptophan (TRY), indoles and other compounds may be biochemical markers of cerebral ischaemic damages following occlusion of the rat middle cerebral artery (MCAO). The aim of the present work was to study the influence of early ischaemia upon presynaptic and postsynaptic activities in the cerebral cortex of rats. These activities have been studied by means of electrophysiological and electro-biochemical (voltammetric) measurements performed concomitantly every 5 min and applied with the same biosensor. The biosensor was inserted in the cerebral cortex of anaesthetised adult male rats which were then submitted to focal ischaemia via MCAO. Since changes in electrophysiological activity are considered marker of rise of ischaemia, the choice of simultaneous electrophysiological and electrochemical (voltammetric) analysis could allow the observation of specific biochemical(s) correlation(s) with the initial phase of ischaemia. The data obtained indicated that electrophysiological and voltammetric changes can be monitored simultaneously in the same brain region (i.e. effected by MCAO) by means of a single biosensor with an improved time resolution when compared with previous biochemical in vivo studies. In addition, a high correlation was observed between MCAO reduced functional responses of the neurons monitored by electrophysiology and increased levels of AA measured by voltammetry. This original observation suggests that AA is a biochemical marker of the very early stages of focal ischaemia and could be a useful tool for the evaluation of initial ischaemic damage.

Carbon fibre micro-electrode and in vitro or in brain slices voltammetric measurement of ascorbate, catechol and indole oxidation signals: influence of temperature and physiological media

Carbon fibre micro-electrodes have been used to determine the influence of temperature and physiological media on the oxidation potential value of three carboxylic acids of physiological interest such as ascorbate (AA), 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindolacetic acid (5HIAA). Standard calibrations at room temperature (18-20 degrees C) in phosphate buffered saline (PBS, pH 7.4), in Krebs (pH 7.4) or in artificial cerebral spinal fluid (ACSF, pH 7.4) have been compared with calibrations performed at 37 degrees C under 95% oxygen, 5% carbon dioxide. Ex vivo experiments were then performed with the electrode inserted in the striatum of rat brain slices maintained in ACSF at 37 degrees C under 95% oxygen, 5% carbon dioxide. The results obtained from both in vitro and ex vivo experimentation indicate that the oxidation potential of peak 2 (DOPAC) is highly sensitive to changes in temperature and medium. Therefore the extrapolation from in vitro electrode calibrations performed in PBS at room temperature to ex vivo (brain slices) and possibly in vivo measurements of DOPAC oxidation should be reconsidered.

Simultaneous, selective detection of catecholaminergic and indolaminergic signals using cyclic voltammetry with treated micro-sensor

Selective and simultaneous voltammetric analysis of catechols and indoles in vivo and in vitro has until now been feasible only by means of 'slow' scanning methods (scan speed in tens of seconds) such as differential pulse (DPV) and differential normal pulse voltammetry in conjunction with electrically and/or chemically treated carbon-fiber micro-electrodes (mCFE). Faster electrochemical techniques, such as chronoamperometry and cyclic voltammetry (CV), allow more rapid (seconds or fractions of a second) and frequent measurements of these chemicals. However, these methods show poor sensitivity and selectivity in the presence of different electroactive compounds with similar oxidation potentials. In order to analyze whether the lack of sensitivity and selectivity of the fast voltammetric methods results from the rapidity of the measurement or from the use of untreated sensors, the methods of CV (scan speed: 1000 mV/s) and DPV (scan speed: 10 mV/s) have been applied with either untreated or electrically treated mCFE to analyze the in vitro oxidation potential and current values of DA and 5-HT. When associated with untreated mCFE, neither method was able to separate and selectively detect the two compounds dissolved together in an inert vehicle; the voltammogram recorded resulted in a single broad oxidation signal. In contrast, when these techniques were performed with electrically treated mCFE, oxidation signals for DA (peak A) and 5-HT (peak B) were monitored simultaneously at approximately + 65 mV and + 240 mV, with DPV respectively, and at + 120 mV and + 300 mV with CV, respectively. Additionally, CV with treated mCFE on anesthetized rats, simultaneously monitored two striatal signals at approximately + 100 mV and + 300 mV. The oxidation values (Em) and current levels (nA) of these peaks remained stable during control recordings. The current levels were selectively increased by peripheral injection of fluphenazine (DA antagonist) or of 5-hydroxytryptophan (precursor of serotonin). The chemical nature of these two peaks may therefore be considered catecholaminergic and indolaminergic, respectively. Hence, this report provides the first evidence for the feasibility of concomitant in vitro analysis of DA and 5-HT using a rapid scanning method such as CV. In addition, the values of current level (nA) obtained with CV-mCFE for DA and 5-HT are comparable to those monitored with DPV-mCFE, supporting the view that treatment of the sensor is a key point for increasing the selectivity and the sensitivity of these voltammetric techniques. The feasibility of using CV with electrically treated mCFE for fast in vivo analysis of catechol and indole activities is also demonstrated.

Carbon fibre micro-electrodes for concomitant in vivo electrophysiological and voltammetric measurements: no reciprocal influences

Differential pulse voltammetry and more recently cyclic voltammetry have been successfully used to monitor basal levels of endogenous chemicals by means of treated carbon fibre microbiosensors inserted in specific brain regions. In this study, feasibility of concomitant in vivo recordings of stable electrophysiological signals and basal ascorbate, catecholaminergic and indolaminergic voltammetric peaks at the same cerebral site by means of a single electrically treated carbon fibre micro electrode (microbiosensor) is presented. The results indicate that these two independent techniques can be combined in vivo at a single electrode, and that voltammetric measurements of unstimulated levels of extracellular compounds do not alter concomitant basal cell firing for a period long enough (more than 6 h) to allow pharmacological manipulations.

Melatonin, a hormone monitorable in vivo by voltammetry?

Melatonin, an indoleamine hormone synthesized in the pinealocytes, is electroactive at the surface of pre-treated carbon fibre microelectrodes (mCFE) in vitro when using differential-pulse voltammetry (DPV), at the specific oxidation potential of approximately +570 mV. In vivo DPV experiments have then been performed in melatonergic regions such as the pineal gland or the suprachiasmatic nucleus (SCH) of anaesthetized adult male rats. These experiments indicated the feasibility of simultaneous measurements of the indolaminergic peak 3, which occurred at approximately +280 mV, due mainly to the oxidation of extracellular 5-hydroxyindoleacetic acid (5HIAA), and a signal at approximately +580 mV which we called peak M. Pharmacological in vivo experiments performed in anaesthetized rats prepared for DPV analysis with the mCFE implanted into the pineal gland or the SCH indicated that intravenous or intra-cerebral injections of exogenous melatonin (5 mg kg-1 or 2 micrograms microliter-1, n = 3, respectively) were followed by a selective and significant increase of in vivo peak M. Other in vivo experiments with anaesthetized rats prepared for DPV analysis with the mCFE into the SCH showed that tryptophan [TRY, 30 mg kg-1 intravenous (i.v.), n = 3] and n-acetyl serotonin (nA-5HT, 5 mg kg-1 i.v., n = 3), both precursors of melatonin, were responsible for a transient but significant increase in the size of peak M (approximately 320% or 126% of control levels within 10 min or 20 min, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Short-range differential pulse voltammetry for fast, selective analysis of basal levels of cerebral compounds in vivo

Differential pulse voltammetry (DPV) with pretreated biosensors (carbon fibre microelectrodes (mCFE), 10-30 microns diameter) allows selective in vivo measurement of basal endogenous levels of dopamine (DA), serotonin (5-HT), their metabolites (dihydroxyphenylacetic acid, DOPAC; 5-hydroxyindoleacetic acid, 5-HIAA), and neuropeptides. We have now modified DPV in order to reduce the time of analysis from tens of seconds to 1-2 s without losing selectivity. We call this newly reported method short-range differential pulse voltammetry (SRDPV). Simply, while in DPV the complete oxidation peak is recorded, SRDPV measures only the top of each oxidation peak. For example, to monitor peak 2 which corresponds to the in vivo oxidation of extracellular DOPAC and occurs at approximately +85 +/- 10 mV, the initial (Ei) and final (Ef) potentials applied with DPV were -100 mV and +200 mV, respectively, while they were +75 mV (Ei) and +95 mV (Ef) with SRDPV. At the typical scan range of 10 mV.s-1, the effective time of measurement was 30 s for DPV and 2 s for SRDPV. A similar procedure was performed to analyze peak 3 (5-HIAA, occurring at +230 +/- 11 mV) with Ei + 50 mV and Ef + 350 mV for DPV, or +220 mV and +240 mV for SRDPV. DPV and SRDPV were compared in vitro by quantitating DOPAC and 5-HIAA in solutions of increasing concentrations (chosen on the basis of the suggested in vivo content of these two compounds). Data indicated that similar sensitivity and selectivity were obtained with both methods at all concentrations, supporting the applicability of SRDPV for in vitro studies. In vivo experiments were performed in anesthetized adult male rats prepared for voltammetry by inserting the electrically pretreated biosensor (mCFE) into the striatum. DPV measurements were performed automatically every 3-5 min and were alternated every 10-20 min with a sequence of 5-10 SRDPV scans performed every 10-30 s. Subsequent pharmacological or electrical manipulations of the two biogenic amine systems studied were monitored by alternate use of DPV and SRDPV. The data presented support the capability of SRDPV with pretreated biosensors to measure in vivo electroactive compounds with selectivity and sensitivity comparable to that of DPV, but with improved time resolution.

Functional in vivo interaction between growth hormone and dopamine systems are correlated to changes in striatal somatostatin levels as detected by voltammetry

The effects of growth hormone (GH) and somatomedin C (SmC), as well as those of apomorphine, dopamine (DA) agonist, or haloperidol (DA antagonist), upon the size of striatal voltammetric peaks 2 and 5 were investigated. Local intrastriatal injections of GH or SmC were followed by an increase in the height of both peak 2 (corresponding to the oxidation of extracellular dihydrophenylacetic acid, DOPAC, a metabolite of DA) and peak 5 (which may represent the oxidation of striatal extracellular somatostatin, SRIF). Treatment with haloperidol also increased the size of the striatal catechol peak but was responsible for a reduction of the neuropeptidergic signal. By contrast, apomorphine determined a decrease in striatal peak 2 (DOPAC) while increasing the levels of peak 5 (SRIF). The data further support the chemical identification of peak 5 at +800 mV as related to the in vivo oxidation of SRIF; in addition they indicate the presence of a functional relationship between this neuropeptide and the GH and DA systems in the striatum of anaesthetised rats.

Evidence for a relationship between recovery from anaesthesia, modified state of consciousness and striatal voltammetric levels of ascorbic acid

The effects of various procedures which modify consciousness were studied on the extracellular concentration of ascorbic acid (AA), 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindolacetic acid (5HIAA) in rat striatum, as measured by differential pulse voltammetry (DPV) with electrically pretreated carbon fibre micro-electrodes (CFE). Recovery from anaesthesia (produced by 500 mg/kg i.p. chloral hydrate) was accompanied by a six-fold increase in extracellular striatal AA levels, while negligible changes in DOPAC and 5HIAA occurred. Following complete recovery from anaesthesia, the animals were re-injected with the same dose of anaesthetic which specifically reduced AA levels by 90% (DOPAC levels were unchanged and 5HIAA concentrations slightly reduced). In conscious rats, the neuroleptic haloperidol (1 mg/kg i.p., n = 5) and the minor tranquillizer diazepam (10 mg/kg i.p., n = 5), both considered as behaviourally depressant drugs, reduced extracellular AA levels to 50% of controls. The psychomotor stimulant D-amphetamine (1 mg/kg i.p., n = 5) increased AA levels by 90% over controls. Stress activation of animals (handling for 10 min, n = 10) also produced a transient, significant increase (180% of control values) in this striatal parameter. Taken together with previous reports, our results suggest a close relationship between the state of consciousness and extracellular AA levels in the rat striatum and that this relationship appears to be more correlated to AA as no such clear interdependence was noted between the levels of consciousness and extracellular striatal DOPAC or 5HIAA.

In vivo selective monitoring of basal levels of cerebral dopamine using voltammetry with Nafion modified (NA-CRO) carbon fibre micro-electrodes

The electrochemical technique of differential pulse voltammetry (DPV) with micro-biosensors has been used for a number of years to monitor in vivo and in situ changes in the extracellular concentration of cerebral ascorbic acid, as well as that of the metabolites of dopamine (DA) and serotonin (5-HT). We have recently prepared a carbon fibre micro-electrode (mCFE) which specifically pretreated and coated with Nafion (a negatively charged polymer which repels acids such as 3,4-dihydroxyphenylacetic acid (DOPAC)) allows the direct selective detection of the oxidation of DA and 5-HT in nanomolar concentration in vitro and that of extracellular basal levels of cerebral 5-HT in vivo (peak B at +240 mV). We describe here a modified version of this micro-biosensor now called NA-CRO mCFE as its active tip (30 microns in diameter) is coated with a 50/50 (v:v) mixture of Nafion and dibenzo-18-crown-6 (Aldrich). In vitro this newly reported electrode shows insensitivity to acids (e.g., DOPAC) up to 100 microns and sensitivity to 0.5-1 nM DA. In vivo, in the striatum of anaesthetised rats, a basal oxidation peak at +80 mV (peak A, on average 0.6 nA in height), which corresponds to the oxidation potential of DA in vitro, is consistently detectable with the NA-CRO mCFE (corresponding to an estimated concentration of 1.5 nM). Experiments performed in vivo in anaesthetised rats implanted in the striatum with uncoated (normal) mCFE to measure extracellular DOPAC or with NA-CRO mCFE have been performed in order to analyse the chemical nature of peak A in vivo. It is concluded that the addition of the crown-ether compound to the Nafion coat improves the sensitivity of the micro-biosensor for DA in vitro and allows the detection of its basal extracellular levels in vivo.

Isolation rearing of rats alters release of 5-hydroxytryptamine and dopamine in the frontal cortex: an in vivo electrochemical study

The effects of rearing hooded Lister rats either in groups of seven or singly on 5-hydroxytryptamine (5-HT) and dopamine (DA) release in the frontal cortex were investigated using in vivo voltammetry together with Nafion coated carbon fibre micro-electrodes. The selective detection of basal extracellular levels of 5-HT with this technique (Peak B) was confirmed with parallel experiments using intracranial microdialysis to measure 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) levels in vivo. The DA voltammetric signal (Peak A) was observed in vivo only following pharmacological or electrical stimulation of DA release. Enhanced efflux of cortical DA and 5-HT in response to local application of KCl and that of 5-HT following parentelar fenfluramine were selectively detected by the association: differential pulse voltammetry (DPV)-Nafion coated microbiosensors, supporting the capability of this electrochemical method to selectively monitor release of these amine neurotransmitters in vivo and in situ. The locomotor behaviour data indicated that isolation rearing resulted in augmented locomotor activity in a novel environment. In addition, the in vivo voltammetric results showed that following KCl or fenfluramine treatment cortical 5-HT release is prolonged while that of DA is increased in rats reared in isolation when compared with socially reared rats. This imbalance between extracellular levels of DA and 5-HT recorded in the frontal cortex of rats exposed to isolated housing conditions may contribute to the behavioural differences reported between isolation and group reared rats.

In vivo voltammetric detection of neuropeptides with micro carbon fiber biosensors: possible selective detection of somatostatin

The electrochemical activity of catechol- and indoleamines, measured by differential pulse voltammetry (DPV) with specifically electrically pretreated carbon fiber microelectrodes, has been utilized to develop sensitive assays for amine neurotransmitters and metabolites. So far, four oxidation peaks have been recorded in vivo between -200 and +500 mV and are well identified. We now report that by increasing the potential sweep range to +950 mV, a further peak, called Peak 5, was detected at +800 mV in vivo in the striatum of anesthetized rats. Neuropeptides containing tyrosine, tryptophan and/or cysteine appear to be electrochemically active between +600 and +900 mV in vitro in a buffered solution at pH 7.4. The present study investigates the chemical nature of Peak 5 and the possible contribution of electroactive neuropeptides to this in vivo voltammetric signal. Experiments performed in vitro and in vivo with amino acids, neuropeptides, or bacitracin (a potent peptidase inhibitor) support the view that Peak 5 is peptidergic. Furthermore, peripheral administration of cysteamine and intrastriatal injection of specific somatostatin antisera both cause the eventual disappearance of Peak 5, suggesting that somatostatin (which oxidases in vitro at approx +800 mV), or a structurally related peptide, could be the principal component of striatal Peak 5.

Effects of idazoxan on dorsal raphe 5-hydroxytryptamine neuronal function

The effects of the alpha 2-adrenoceptor antagonist idazoxan on 5-hydroxytryptamine (5-HT) neuronal firing and release have been investigated. Idazoxan, administered i.v. (10 micrograms/kg and 0.5 mg/kg) increased dorsal raphe nucleus (DRN)-5-HT neuronal firing rate in a dose-dependent fashion. At the higher dose, a voltammetric study revealed increases in extracellular 5-HT and 5-hydroxyindole acetic acid (5-HIAA) levels, there was no effect with the lower dose. Intra-raphe administration of idazoxan (1 ng) also elevated the firing rate of 5-HT neurones in the dorsal raphe, suggesting that idazoxan may produce the increase in firing by a direct effect in the DRN. However, microiontophoretic application of idazoxan did not increase the firing rate of 5-HT neurones in the DRN. Thus the increase in the firing rate of 5-HT neurones in the DRN observed with systemic and local administration of idazoxan is probably not due to a direct action of idazoxan on the 5-HT neurone. Possibly the idazoxan acted at alpha 2-adrenoceptors located on noradrenergic terminals thus stimulating noradrenaline release and consequently increased 5-HT activity. Chronic administration of idazoxan (0.8 mg/kg per h for 14 days), using osmotic mini-pumps, caused an elevation in basal firing rate and an attenuation of the inhibitory response of DRN 5-HT neurones to the 5-HT1A agonist, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OHDPAT) (10 micrograms/kg i.v.). This finding suggests that chronic infusion with idazoxan leads to desensitisation of the 5-HT1A somatodendritic autoreceptor.

In vivo voltammetry with micro-biosensors for analysis of neurotransmitter release and metabolism

In vivo voltammetry involves the electrochemical detection of central oxidisable substances in situ. In association with this technique micro carbon fibre electrodes (CFE) are able to separate ascorbic acid (Peak 1) from 3,4-dihydroxyphenylacetic acid (DOPAC) plus dopamine (DA) (Peak 2) and 5-hydroxyindoleacetic acid (5-HIAAA) plus serotonin (5-HT) (Peak 3) in vitro. In vivo these biosensors detect the amine metabolites, due to their high extracellular concentration (microM) compared to the amines (nM). In addition homovanillic acid (HVA) (or 3-methoxytyramine (3-MT) in pargyline-pretreated mice) (Peak 4) and somatostatin (Peak 5) were also measured in vivo. However, potassium-stimulated release of DA has been directly monitored in pargyline pretreated mice. In addition, low concentrations (nM) of DA and 5-HT can now be selectively monitored in vitro with new biosensors coated with Nafion which repels negatively charged species including acid metabolites. In vivo, the combination of the Nafion-CFE and normal CFE allowed simultaneous measurements of release and metabolism of 5-HT, respectively. This permitted the observation that changes in 5-HT release are not necessarily reflected by changes in 5-HIAA levels. At present we are developing a Nafion biosensor to monitor basal extracellular DA. Electron microscope studies have shown radical modifications in the surface and structure of carbon fibres following chemical and electrical pretreatments, which may be involved in the development of sensitivity and selectivity displayed by the pretreated CFE towards electroactive compounds. A new approach for selective detection of neuroamines is the analysis of their stimulated fluorescence using LASER. In vitro, the fluorescence of 5-HT is in fact clearly distinguishable from that of 5-HIAA. The feasibility of this methodology in vivo using fiber optic probes will be explored.

In vivo evidence that 5-hydroxytryptamine (5-HT) neuronal firing and release are not necessarily correlated with 5-HT metabolism

The relationship between 5-hydroxytryptamine release, metabolism and unit activity has been investigated in the anaesthetized rat. 5-Hydroxytryptamine release and metabolism were monitored in vivo by the measurement of extracellular 5-hydroxytryptamine and 5-hydroxyindoleacetic acid in the frontal cortex using in vivo voltammetry combined with nafion-coated and uncoated electrically pretreated carbon fibre electrodes. The monoamine oxidase inhibitor pargyline (100 mg/kg) increased extracellular 5-hydroxytryptamine and decreased 5-hydroxyindoleacetic acid. The 5-hydroxytryptamine releaser fenfluramine (10 mg/kg i.p.) acutely increased extracellular 5-hydroxytryptamine while having no effect on 5-hydroxyindoleacetic acid and the effect on extracellular 5-hydroxytryptamine was markedly reduced in rats pretreated (four weeks) with 5,7-dihydroxytryptamine. 8-Hydroxy-2-(di-n-propyl-amino) tetralin (10 micrograms/kg i.v.), an agonist at the 5-hydroxytryptamine1A somatodendritic autoreceptor, inhibited 5-hydroxytryptamine neuronal firing in the dorsal raphe nucleus and decreased extracellular 5-hydroxytryptamine during the period when firing was inhibited but did not alter extracellular 5-hydroxyindoleacetic acid. In contrast 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridin-4-yl) (RU 24969), which is an agonist at the terminal autoreceptor in the rat, had no effect on 5-hydroxytryptamine neuronal firing but decreased 5-hydroxytryptamine and 5-hydroxyindoleacetic acid. The results support the view that extracellular 5-hydroxyindoleacetic acid is not a good index of 5-hydroxytryptamine release and that under specific circumstances 5-hydroxytryptamine neuronal firing, release and metabolism are independent of one another.

Biochemical and in vivo voltammetric evidence for differences in striatal dopamine levels in inbred strains of mice

High performance liquid chromatography with electrochemical detection and differential pulse voltammetry were used to provide a direct measurement of tissue content of dopamine and its metabolites and extracellular dopamine levels, respectively, in the striata of BALB/c and CBA inbred strains of mice. We found that levels of striatal dopamine and its metabolite, dihydroxyphenylacetic acid, were significantly higher in the CBA strain than in the BALB/c strain, whereas levels of homovanillic acid were not significantly different between the strains. Levels of the dopamine metabolite 3-methoxytyramine, on the other hand, were higher in the BALB/c mice. Dopamine turnover rates were significantly higher in the CBA strain when the homovanillic acid/dopamine ratio was used as an index of dopamine activity. Voltammetric recording showed that the local infusion of K+ in pargyline-treated mice resulted in the immediate appearance of a peak at +85 mV, which has been shown to correspond to extracellular dopamine in the rat. The mean height of this peak detected in vivo following K+ stimulation corresponds to in vitro dopamine concentrations of 25 +/- 8 microM for BALB/c mice and 7 +/- 2 microM for CBA mice. K(+)-stimulated dopamine release in the BALB/c mice could be evoked every 10-15 min with similar magnitude. In contrast, very little dopamine release in CBA mice could be evoked after the first stimulation. Since striatal dopamine levels are higher in CBA mice, these data suggest that (a) BALB/c strain may have more dopamine in the readily releasable pool, whereas the CBA mice have a larger storage pool of dopamine, and/or (b) that dopamine uptake in the CBA mice is much more avid than in BALB/c.

Measurement of 3-methoxytyramine by in vivo voltammetry: evidence for differences in central dopamine function in BALB/c and CBA mice

Differential pulse voltammetry (DPV) combined with carbon fibre electrodes allows selective detection of electroactive dopamine and serotonin metabolites in vivo. While usually employed in rats, we have now applied this in vivo technique in two inbred strains of mice: BALB/c and CBA. Three distinct oxidation peaks were recorded in vivo in the striatum of either BALB/c or CBA mice with a small shoulder occurring after the third peak at approximately +400 mV. Pargyline (150 mg/kg i.p.) potentiated this voltammetric shoulder into an easily measurable peak (Peak 4). In addition, Peak 4 was 2-3 times larger in BALB/c than in CBA mice. Homovanillic acid (HVA) and 3-methoxytyramine (3-MT), both catabolites of dopamine, oxidised at approximately +400 mV in vitro. Brain tissue levels of HVA and 3-MT, measured by high-performance liquid chromatography (HPLC) with electrochemical detection, demonstrated that pargyline treatment reduced striatal HVA, but increased 3-MT. These results support the view that Peak 4 recorded in the striatum of pargyline-treated mice in vivo is due to the oxidation of extracellular 3-MT. Thus, Peak 4 may be a useful index of dopamine release in situations where dopamine itself cannot be detected. Local infusion of KCl (2 microliters, 0.1 M) further increased the size of Peak 4 in the striatum of both BALB/c and CBA mice. However, the increase was approx. 3 times greater in BALB/c mice, supporting previous evidence of greater dopaminergic function of BALB/c compared with CBA mice. In addition these two inbred strains of mice provide model systems for investigating the comparative functional roles of nigrostriatal pathways.

Measurement of extracellular basal levels of serotonin in vivo using nafion-coated carbon fibre electrodes combined with differential pulse voltammetry

Carbon fibre electrodes combined with differential pulse voltammetry have been used for a number of years to monitor changes in the extracellular concentrations of ascorbic acid, dihydroxyphenylacetic acid, and 5-hydroxyindoleacetic acid. However, the primary objective of in vivo electrochemists has been to monitor changes in the extracellular concentrations of the neurotransmitter amines; dopamine and serotonin rather than their metabolites. In this paper we describe a new chemically- and electrically-pretreated Nafion-coated carbon fibre electrode which can be used to monitor basal levels of serotonin in the extracellular fluid in the frontal cortex and the dorsal raphe nucleus of rat. These electrodes combined with differential pulse voltammetry detect dopamine (Peak A at -70 mV) and serotonin (Peak B at +240 V) oxidation peaks in vitro but not the oxidation of ascorbic acid, dihydroxyphenylacetic acid, 5-hydroxyindoleacetic acid or uric acid, at concentrations up to 10 microM. These electrodes were able to detect serotonin concentration as large as 1 nM in vitro. When used in vivo the oxidation peaks obtained in the frontal cortex and dorsal raphe indicate the basal concentrations of serotonin to be 5 nM and 10 nM respectively. Pharmacological interventions in rats implanted with normal carbon fibre electrodes or with Nafion carbon fibre electrodes further demonstrate that the new Nafion electrodes measure serotonin in vivo. The Nafion-coated electrodes therefore may be a useful tool for the study of serotoninergic systems in vivo with the added advantage that they cause minimal damage due to their small tip size (30 micron).

Simultaneous in vivo voltammetric measurement of striatal extracellular DOPAC and 5-HIAA levels: effect of electrical stimulation of DA and 5-HT neuronal pathways

Differential pulse voltammetry (DPV) combined with electrically pretreated carbon fibre electrodes has been used to study dopamine (DA)-5-hydroxytryptamine (5-HT) interactions in the striatum of anaesthetised rats. Electrical stimulation of the dorsal raphe (DRN) increased 5HT and decreased DA metabolism in the striatum. Conversely, stimulation of the DA pathway to the striatum was associated with increased DA and decreased 5-HT metabolism. These data support previous studies and demonstrate that there is a functional interaction between DA and 5-HT systems in the striatum. The receptors and other transmitters (if any) involved in this interaction remain to be determined.

Analysis of extracellular DOPAC, HVA and 5-HIAA in rat striatum in vivo by differential pulse voltammetry: effect of phencyclidine, haloperidol and their coadministration

Phencyclidine (PCP, 10 mg/kg s.c.) produced a marked reduction in the extracellular concentrations of DOPAC and HVA in the rat striatum in vivo, as measured by differential pulse voltammetry. In contrast, extracellular 5-HIAA levels were significantly elevated. Haloperidol (1 mg/kg i.p.) increased DOPAC and HVA, and reduced 5-HIAA, in agreement with previous studies. When PCP and haloperidol were injected together, the effects of PCP were abolished. These results suggest that PCP administration leads to increased activation of dopamine receptors, which results in a decrease in striatal dopamine turnover and an increase in striatal serotonin turnover.

The effect of diazepam and Ro 15-1788 on extracellular ascorbic acid, DOPAC and 5-HIAA in the striatum of anaesthetized and conscious freely moving rats, as measured by differential pulse voltammetry

The effects of diazepam (10 mg/kg i.p.) and the central benzodiazepine receptor antagonist, Ro 15-1788 (30 mg/kg i.p.), on extracellular ascorbate, 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) were examined using differential pulse voltammetry in anaesthetized and freely moving rats. In anaesthetized animals, diazepam did not significantly alter the heights of peak 1 (ascorbate) or peak 3 (5-HIAA), but significantly reduced that of peak 2 (DOPAC). In freely moving rats, diazepam greatly reduced the heights of all 3 peaks. Ro 15-1788, injected 2 h after diazepam, reversed the effect of diazepam on peak 3, but not on peaks 1 and 2.

Voltammetry in vivo with a single working electrode may permit detection of striatal dopamine-serotonin interactions in anesthetized and freely moving rats

We have recently improved the technique of differential pulse voltammetry to detect extracellular 3,4-dihydroxyphenylacetic and 5-hydroxyindoleacetic acid concentrations in vivo with a single monopyrolytic carbon fibre electrode (working electrode). Thus it is now possible to perform a simultaneous evaluation of the turnover of dopamine (DA) and serotonin (5-HT) in a specific brain area of anaesthetized or conscious freely moving rats. We have attempted to determine whether there is an interaction between the two neuronal systems in the striatum. Our results show that various pharmacological manipulations in anaesthetized or conscious freely moving rats alter the activity of both systems suggesting the presence of interactions between 5-HT and DA systems in brain.

Anaesthesia abolishes the effect of valproate on extracellular 5-HIAA, DOPAC and ascorbate as measured in rat striatum by differential pulse voltammetry

The effect of sodium valproate (VPA, 400 mg kg-1, i.p.) on extracellular ascorbate, 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) in the striatum was examined by differential pulse voltammetry in anaesthetized and freely-moving rats. In rats anaesthetized with chloral hydrate (400 mg kg-1, i.p.) pentobarbitone (50 mg kg-1, i.p.) or phenobarbitone (60 mg kg-1, i.p.), VPA produced no significant changes in peak 1 (extracellular ascorbate) or peak 2 (extracellular DOPAC), but produced a slight but statistically significant reduction in the height of peak 3 (extracellular 5-HIAA). In contrast, in freely-moving rats the same dose of VPA greatly reduced extracellular ascorbate and DOPAC concentrations, and increased that of 5-HIAA. These results suggest that VPA may reduce the release or turnover of dopamine, and increase that of 5-hydroxytryptamine in conscious rats. Our data also suggest that caution may be required in the interpretation of the effects of VPA in anaesthetized animals, as the results obtained may not always reflect the situation in the absence of anaesthesia.

Growth hormone-releasing factor modifies dopaminergic but not serotonergic activity in the arcuate nucleus of hypothalamus in the rat, as recorded in vivo by differential pulse voltammetry

Parenteral (i.v.) injection of growth hormone-releasing factor (GRF) increases the height of the 3,4-dihydroxyphenylacetic acid oxidation peak (peak 2) but does not change 5-hydroxyindole extracellular content (peak 3) in the arcuate nucleus of the hypothalamus, both peaks being recorded by the differential pulse voltammetry technique using a single specifically pretreated monopyrolytic carbon fibre electrode. Conversely, no significant changes are observed in the peak 2 and peak 3 heights recorded in the medial or in the lateral nucleus of the hypothalamus. These data suggest a specific interaction between GRF and the dopaminergic system.

An improved differential pulse voltammetry technique allows the simultaneous analysis of dopaminergic and serotonergic activities in vivo with a single carbon-fibre electrode

Differential pulse voltammetry has successfully been employed to study either 5-hydroxyindoles, or ascorbic acid and catechols in the brain of anaesthetised or freely moving rats. A new electrochemical pretreatment of pyrolytic carbon-fibre electrodes has been developed, enabling the simultaneous recording of all three compounds in the striatum of anaesthetised rats, using a Tacussel polarography. Furthermore, a fourth peak was recorded at +450 mV. Pharmacological treatments performed to define the nature of the four peaks recorded in the striatum confirmed that peak 1 corresponds to ascorbic acid, peak 2 to dihydroxyphenylacetic acid, peak 3 to 5-hydroxyindoleacetic acid and peak 4 to homovanillic acid.