Functional aspects of 5-hydroxytryptamine neurones — Application of electrochemical monitoring in vivo

Long-term depression in striatal dopamine release monitored by in vivo voltammetry in free moving rats

It was proposed to monitor in free moving rats, by in vivo voltammetry, the effects of intracerebroventricular (i.c.v.) administration of drugs known to act on the synthesis of dopamine (DA), using an original multifiber carbon electrode which enables without-discontinuity long-term recordings in extracellular DA release. Results show that i.c.v. administration of alpha-methyl-p-tyrosine, gamma-butyrolactone, and apomorphine induced long-term depression in striatal DA release, over periods of time of more than 24 h. These results are in agreement with the dopaminergic hypothesis; and we conclude that i.c.v. administration of drugs and the use of the multifiber carbon electrode constitutes a valuable tool to monitor DA metabolism in chronically implanted animals.

Differential pulse voltammetric determination of 5-hydroxyindoles in four raphe nuclei of chronic freely moving rats simultaneously recorded by polygraphic technique: physiological changes with vigilance states

Nuclei raphe dorsalis ( RDN ), centralis (RCN), pontis (RPN) and magnus ( RMN ) were separately studied using differential pulse voltammetry ( DPV ) in chronic freely moving rats during the recording of their sleep-waking cycle by polygraphic technique. In each of these nuclei the height of the electrochemical signal appearing at +300 mV (peak 3) was maximum during waking (W), lower during slow-wave sleep (SWS) and minimum during paradoxical sleep (PS). Some pharmacological treatments indicated that in each of these nuclei the peak 3 represents the oxidation of the 5-hydroxyindoles. DPV measurements performed during specific behavioral states (eating, grooming, washing, drinking) called active waking (AW) or manipulations (handling, tail-pinch) demonstrated that this technique enables detection of changes occurring in animals under physiological conditions.

Differential pulse voltammetry in the dorsal horn of the spinal cord of the anesthetized rat: are the voltammograms related to 5-HT and/or to 5-HIAA?

Treated carbon fiber microelectrodes were used with the differential pulse voltammetry method for in vitro and in vivo determination of indoleamines. Under these conditions a peak of oxidation current which is characteristic of 5-hydroxyindoles is recorded at 280-300 mV. Treated carbon fiber microelectrodes respond in vitro linearly over a large range of concentrations of 5-hydroxytryptamine (5-HT) and of 5-hydroxyindoleacetic acid (5-HIAA), but are 5-8 times more sensitive to 5-HT than to 5-HIAA. In vivo, the question remains as to the exact nature of the peak because the oxidation potentials of 5-HT and 5-HIAA are close together and cannot be monitored separately. Pharmacological investigations were hence carried out in order to characterize the electrochemical signal detected at 300 mV in the dorsal horn of the lumbar spinal cord of chloral hydrate-anesthetized rats. Using 250 micron long carbon fiber microelectrodes, the electrochemical signal stabilizes at 30-90 min and the peak remains constant for up to 210 min. Administration of the monoamine oxidase inhibitor (MAOI) clorgyline produced a progressive decrease of the signal which reached a decrease of 33% of control at 180 min after injection. At this time biochemical measures demonstrated a 117% increase in 5-HT and a 32% decrease in 5-HIAA in the dorsal half of the spinal cord. Reserpine provoked an increase of 20% in the electrochemical peak and the 5-HIAA outflow blocker probenecid gave rise to a sustained plateau of about 60% above control values.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential pulse voltammetry in brain tissue: III. Mapping of the rat serotoninergic raphe nuclei by electrochemical detection of 5-HIAA

Differential pulse voltammetry using a new type of carbon fiber electrode, electrochemically treated, is described. The working electrode contains 3 pyrolytic carbon fibers, and passes more current, thus giving a greater sensitivity (with the PRG5 Tacussel polarographic system) than the original monofiber electrodes. It is now possible to investigate brain areas where the monofiber electrodes, working near the limit of PRG5 sensitivity, showed too small a signal. These electrodes have, in addition, better mechanical resistance and can be used (after trypsin cleaning and further electrochemical treatment) for several experiments. Electrochemical measurements made in the nucleus raphe dorsalis before and after treatment with p-chlorophenylalanine, reserpine, clorgyline and clorgyline followed by reserpine, suggest that as in the striatum 5-hydroxyindoleacetic acid (5-HIAA) is mainly responsible for peak 3. The map of the raphe system made with this technique is well correlated with the serotoninergic system of the raphe: the highest peak heights are recorded in the raphe dorsalis.

Behavioral observation and intracerebral electrochemical recording following administration of amphetamine in rats

Intracerebral electrochemistry (chronoamperometry) was performed on rats that were administered 1, 4, and 8 mg/kg doses of amphetamine. Graphpoxy working electrodes were implanted bilaterally in nucleus accumbens (ACC) and ventral anterior stratum (VAS). Following drug injection, locomotor and stereotyped behaviors were observed. Intracerebral electrochemical signals reliably increased following injection of amphetamine. The magnitude of these increases did not change significantly across the dose range tested for VAS electrodes. ACC electrodes had increases similar in magnitude to VAS electrodes at 1 and 4 mg/kg. At 8 mg/kg increases obtained from ACC electrodes were significantly lower than those recorded from VAS. Onset of the change in electrochemical signal paralleled the onset of activity or stereotypy but the subsequent declines in signal and behavior were only loosely correlated. At the 4 mg/kg dose, the magnitude of signal increase from striatum was negatively correlated with indices of stereotypy and positively correlated with locomotor counts.

Linear sweep voltammetry with carbon paste electrodes in the rat striatum

Voltammetry has been widely used in attempts to measure catecholamine release in vivo. The voltammogram recorded in the rat striatum using carbon paste electrodes and linear sweep voltammetry with semidifferentiation consists of a number of separate peaks; changes in the height of the first of these peaks have been attributed to changes in catecholamine release. We have found that ascorbate, either microinjected into the striatum or injected intraperitoneally, increases the height of the first peak without changing its potential. Microinjection of dopamine or 3,4-dihydroxyphenylacetic acid, or intraperitoneal injection of 3,4-dihydroxyphenylalanine, caused a shift in the potential of peak 1 of 25-50 mV in a positive direction. Amphetamine, administered intraperitoneally to freely moving animals, caused an increase in the height of the first peak but did not change its potential. Oxidation potentials in vitro and the effect of other drugs on the voltammogram obtained in vivo were also measured. Peak 1 is caused by the oxidation of both ascorbate and catechols whose oxidation potentials differ by only 50 mV in vivo; the contribution of catechols in control animals is negligible. Shifts in the potential of peak 1 caused by drugs are not due to changes in the oxidation potentials of the components but to a change in their relative contributions. Therefore changes in the height of peak 1 with no change in position do not represent changes in the extracellular concentration of catechols but are due to changes in ascorbate concentration. Changes in the concentration of catecholamine-related compounds can be detected at potentials some 50 mV greater than that of the first peak.

Increase of serotonin metabolism within the dorsal horn of the spinal cord during nucleus raphe magnus stimulation, as revealed by in vivo electrochemical detection

Carbon fiber microelectrodes were used with the differential pulse voltammetry method for in vivo determination of indolamines within the extracellular space of the dorsal horn of the spinal cord or chloral hydrate-anesthetized rats. Under these conditions a peak of oxidation current which is characteristic of 5-hydroxyindoles is recorded at 280-300 mV. Stimulation of the nucleus raphé magnus (NRM) with stimulation parameters comparable to those used to elicit analgesia in freely moving animals produced marked alterations in the voltammograms: (1) stimulation of the NRM for 10 min induced an immediate and sustained increase in the peak amplitude; (2) post-effects of variable duration were observed; (3) the increase in the 5-hydroxyindolaminergic signal was significantly reduced during a second series of NRM stimulations indicating some degree of tolerance to central stimulation. The accuracy of these observations is strengthened by the fact that the basal 5 hydroxyindolaminergic signal is strongly depressed after pretreatment of the animal with p-chlorophenylalanine; in addition, under these conditions, NRM stimulation is totally inefficient. We suggest that these results reflect the in vivo modification of 5-HT metabolism. This represents the first evidence for an in vivo release of 5-HT during stimulation of brain stem areas which induces powerful analgesia in freely moving animals.

Sleep suppressant action of quipazine: relation to central serotonergic stimulation

Administration of quipazine maleate (1-10 mg/kg, IP), a proposed 5-hydroxytryptamine (5-HT) receptor stimulant to rats produced a dose-related suppression of both slow-wave sleep (SWS) and rapid-eye-movement sleep (REMS) accompanied by an increase in head-shaking behavior. These effects were observed during the first 6 hr of a 12-hr EEG recording session. The latencies to the sleep states were markedly prolonged and correlated with the duration of head-shaking behavior induced by the drug. A significant inverse relationship was found between the amount of SWS or REMS and the number of head-shakes occurring during the first 6-hr period. Since head-shaking behavior in rodents has been proposed as a quantitative, behavioral model of central 5-HT activation, the data suggest a causal relationship between enhanced 5-HT activity and sleep suppression. This assumption is further supported by the observation that pretreatment with metergoline (2.5 mg/kg, IP) a 5-HT receptor blocker, reduced quipazine's effects on both SWS and head-shaking behavior.

Differential pulse voltammetry in brain tissue. II. Detection of 5-hydroxyindoleacetic acid in the rat striatum

Differential pulse voltammetry with electrochemically treated carbon fiber electrodes was used to study, in anesthetized rats, the alterations of the striatal electrochemical signal appearing at +300 mV (peak 3), following pharmacological manipulation of the animals. Decreases in peak 3 were obtained after injections of NSD 1015, Ro 4-4602 and Clorgyline. This, in conjunction with biochemical measurements, suggested that 5-hydroxyindoleacetic acid (5-HIAA) is, to a considerable extent, responsible for this electrochemical signal. Increases in peak 3 obtained after reserpine, L-tryptophan and D,L-5-HTP, as well as biochemical data reinforced this hypothesis, as did the detection of peak 3 in cerebrospinal fluid and its increase after probenecid injection. The occurrence of a feed-back mechanism is discussed following injection of D,L-5-HTP.

Differential pulse voltammetry in brain tissue. I. Detection of 5-hydroxyindoles in the rat striatum

In vitro, differential pulse voltammetry combined with electrochemically treated carbon fiber electrodes enabled detection, in different solution of 5-hydroxyindole compounds, of an oxidation peak 3 at +300 mV. In vivo, a striatal peak 3 was also recorded at this potential. Electrolytic or 5,7-dihydroxytryptamine lesions interrupting the medial forebrain bundle (MFB) were followed by a decrease of 65% and 64% in peak height, but not elimination of the peak. Biochemical determinations were significantly correlated to the peak 3 measurements. The existence of peak 3 as well as hydroxyindole compounds in blood suggested a blood contamination under the experimental conditions employed. This possibility is confirmed both by the complete disappearance of striatal peak 3 in animals with the MFB lesioned and surgically prepared a week before recordings, and by biochemical measurements in parachlorophenylalanine-treated or perfused (phosphate-buffered saline solution) animals.

An automated electrochemical method for in vivo monitoring of catecholamine release

A computer-controlled electrochemical system for the in vivo monitoring of catecholamines and their metabolites is described. The system is composed of a microcomputer, real time interface board, and a commercial electrochemical instrument. The method and theory of the electrochemical technique are explained and details concerning the construction of the electrodes are given. Descriptions of the hardware and software are also provided. Experimental results are presented to demonstrate the use of the system for long-term in vivo monitoring and for detecting the change in the level of oxidizable species after amphetamine administration.