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F Crespi

Publications and source records attributed to F Crespi.

At least 37 records · Page 2Linked to original sources
PubMed1990

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.

Animals↗
PubMed1990

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.

Action Potentials↗
PubMed1990

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.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1989

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.

Animals↗
PubMed1988

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.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1988

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).

Animals↗
PubMed1987

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.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1987

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.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1986

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.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1986

In vivo evaluation by differential pulse voltammetry of the effect of thyrotropin-releasing hormone (TRH) on dopaminergic and serotoninergic synaptic activity in the striatum and nucleus accumbens of the rat.

In vivo differential pulse voltammetry was used to determine the effect of thyrotropin-releasing hormone (TRH) on dopaminergic and serotoninergic synaptic activity in the striatum and nucleus accumbens of the rat. Thyrotropin releasing hormone (TRH) produces marked stimulatory effects on behaviour, which have been attributed to the release of dopamine in the nucleus accumbens. Other studies indicate a close relationship between the peptide and serotonin in the brain. We have thus used an improved differential pulse voltammetry technique to evaluate the effects of TRH on the extracellular content of the dopamine and serotonin metabolites. Dihydroxyphenylacetic acid (DOPAC) and 5-Hydroxy-indoleacetic acid (5HIAA) in the nucleus accumbens and striatum of the rat in vivo. TRH rapidly increased extracellular DOPAC, reaching a maximum after 60 min in the nucleus accumbens, and after 40 min in the striatum. There was also a slower increase in extracellular 5-HIAA content in both areas, reaching a plateau after 100 min. The delayed time course of the increase in 5-HIAA suggested that the increase in 5-HIAA content might be secondary to the increase in dopamine turnover produced by TRH. These results suggest that doses of TRH which produce behavioural stimulation increase the release of both dopamine and serotonin in the nucleus accumbens and striatum.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1986

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.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1985

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.

Animals↗
PubMed1984

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.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1984

Differential pulse voltammetry: simultaneous in vivo measurement of ascorbic acid, catechols and 5-hydroxyindoles in the rat striatum.

This paper describes carbon fibre electrodes that can simultaneously monitor changes in ascorbic acid, dihydroxyphenylacetic acid (DOPAC), 5-hydroxyindoleacetic acid (5HIAA) and homovanillic acid (HVA) in vivo in the rat striatum using differential pulse voltammetry. The separation between DOPAC and 5HIAA oxidation is improved and the size of the 5HIAA peak decreased by the removal of uric acid using the enzyme uricase indicating that uric acid oxidation may contribute to the oxidation peak at + 300 mV. Haloperidol (0.5 mg/kg) decreased ascorbic acid and 5HIAA but increased DOPAC and HVA while D-amphetamine (3 mg/kg) increased ascorbic acid, decreased DOPAC and HVA but had no effect on 5HIAA. These electrodes should be a useful means of investigating interactions between dopamine and serotoninergic systems in vivo.

3,4-Dihydroxyphenylacetic Acid↗