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

Short-term development of behavioral sensitization to amphetamine requires N-methyl-D-aspartate- and nicotinic-dependent mechanisms in the nucleus accumbens

Repeated administration of psychostimulant drugs, such as amphetamine, induces an enhanced behavioral response to subsequent drug challenge. This behavioral sensitization is proposed to model the increased drug craving observed in human psychostimulant abusers. Current thinking is that the ventral tegmental area, but not the nucleus accumbens, plays a critical role in the development of behavioral sensitization. Here, we report that the concomitant blockade of glutamatergic and nicotinic ionotropic receptors in the core of the nucleus accumbens blocks the development of behavioral sensitization to amphetamine and further abolishes the increase in extracellular dopamine release induced by amphetamine in the nucleus accumbens. These findings demonstrate that the development of behavioral sensitization to amphetamine depends, in addition to the well-known role of the ventral tegmental area, on glutamatergic and nicotinic-dependent mechanisms in the core of the nucleus accumbens and further indicate that the dopaminergic mesolimbic pathway must be viewed as a single coordinated system of critical importance in the development of behavioral sensitization to psychostimulant drugs.

Nitrous oxide and xenon prevent amphetamine-induced carrier-mediated dopamine release in a memantine-like fashion and protect against behavioral sensitization

BACKGROUND

Amphetamine administration induces stimulation-independent dopamine release in the nucleus accumbens (NAcc) through reverse dopamine transport, a critical neurochemical event involved in its psychostimulant action, and furthermore decreases stimulation-dependent vesicular dopamine release. These effects may involve possible indirect glutamatergic mechanisms.

METHODS

We investigated the effects of nitrous oxide and xenon, which possess antagonistic action at the N-methyl-D-aspartate (NMDA) receptor, on brain slices ex vivo on amphetamine-induced changes in carrier-mediated and KCl-evoked dopamine release in the NAcc, and in vivo on amphetamine-induced locomotor sensitization.

RESULTS

Like the low-affinity NMDA receptor antagonist memantine, but not the prototypical compound MK-801, nitrous oxide and xenon at appropriate concentrations blocked both the increase in carrier-mediated dopamine release and locomotor sensitization produced by amphetamine.

CONCLUSIONS

In contrast to what has generally been found using prototypical NMDA receptor antagonists, these data regarding the effect of memantine, nitrous oxide, and xenon support the hypothesis that activation of certain NMDA receptors (possibly those containing the NR1a/NR2D subunit) in the NAcc is involved in the amphetamine-induced increase in carrier-mediated dopamine release and the development of behavioral sensitization to amphetamine. Nitrous oxide, xenon, and memantine may be of therapeutic interest for treating drug dependence.

On the significance of brain extracellular uric acid detected with in-vivo monitoring techniques: a review

The concentration of uric acid [UA] in the extracellular fluid (ECF) estimated with in-vivo voltammetry and microdialysis data is compared for probes of different diameters from the day of implantation (acute) to several days (chronic) or even months after surgery. For small probes (diameter < 160 microns) the acute [UA] of ca. 5 microM decreased significantly to ca. 1 microM under chronic conditions. For larger probes (e.g., 320-microns diameter) the acute [UA] was also ca. 5 microM, but this value significantly increased to ca. 50 microM under chronic conditions. Associated with this difference in [UA], there were parallel differences in the extent of gliosis around the probes. These findings are discussed in terms of possible sources of extracellular UA and their implications for in-vivo monitoring techniques in behaving animals.

Extrapyramidal symptoms with selective serotonin reuptake inhibitors

BACKGROUND

Several case reports in the literature suggest that selective serotonin reuptake inhibitors can produce extrapyramidal symptoms.

METHODS

Computerised literature searches were used to identify reports on extrapyramidal symptoms and serotonin reuptake inhibitors. Subsequently, manual searches were made for articles in which there was any indication of the mechanisms responsible for these extrapyramidal symptoms.

RESULTS

Only a few reports could be identified in which serotonin reuptake inhibitors were implicated in extrapyramidal symptoms in some patients.

CONCLUSIONS

Evidence is discussed from preclinical and clinical studies suggesting the interaction between serotoninergic and dopaminergic neurotransmitter system, as a possible mechanism for production of extrapyramidal symptoms.

Comparison of stress-induced changes in noradrenergic and serotonergic neurons in the rat hippocampus using microdialysis

The effects of stress on the serotonergic and noradrenergic projection to the hippocampus were compared in freely moving rats using microdialysis. Stress-induced changes in 5-hydroxytryptamine (5-HT), noradrenaline and their metabolites 5-hydroxyindoleacetic acid (5-HIAA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were measured in the presence of their respective uptake blockers. Local infusion of tetrodotoxin and replacement of Ca2+ with Cd2+ were used to test dependence on impulse traffic. A 5 min tail pinch or 10 min restraint stress increased 5-HT, 5-HIAA, noradrenaline and DOPAC levels. A subcutaneous saline injection produced an increase in 5-HT and DOPAC but not noradrenaline or 5-HIAA. Although alpha 2 adrenoceptor agonists and antagonists produced changes in the baseline values of noradrenaline and DOPAC, they had little or no effect on stress-induced changes. Both the abolition of impulse traffic and its enhancement by stress had a greater effect on transmitter than on metabolite levels. Although the responses to stress of the noradrenergic and serotonergic pathway showed many similarities, there was evidence for their activation by separate pathways.

Evidence that corticotropin-releasing factor within the extended amygdala mediates the activation of tryptophan hydroxylase produced by sound stress in the rat

Non-endocrine corticotropin-releasing factor (CRF) is believed to be involved in mediating stress behaviors in rats. The present study investigated the role of CRF in mediating the activation of tryptophan hydroxylase, the rate-limiting enzyme in serotonin synthesis, produced in response to sound stress. Bilateral injections of 0.5-3.0 micrograms of CRF directed towards the central nucleus of the amygdala increased tryptophan hydroxylase activity measured ex vivo when compared to vehicle-injected controls. This increase in enzyme activity, like that due to sound stress, was reversed in vitro by alkaline phosphatase. Intra-amygdala CRF (0.5 microgram) also enhanced the in vivo accumulation of 5-hydroxytryptophan (5-HTP) following the administration of m-hydroxylbenzylamine (NSD-1015, 200 mg/kg). The activation of tryptophan hydroxylase, produced by intra-amygdala CRF, was blocked by the CRF receptor antagonist alpha-helical CRF9-41 (10 micrograms). Additionally, the 5-HT1A agonist, gepirone, given either systemically (10 mg/kg) or intracerebrally into the region of the dorsal raphe (14 micrograms), blocked the tryptophan hydroxylase response to CRF. CRF did not increase tissue levels of 5-hydroxyindole acetic acid (5-HIAA) or the ratio of 5-HIAA to serotonin (5-HT) within the striatum of the same animals in which tryptophan hydroxylase activity was quantified, an effect produced by sound stress. Thus, while intra-amygdala CRF failed to mimic the sound stress response in its entirety, these data suggest that CRF is involved in mediating the activation of tryptophan hydroxylase produced by sound stress within the midbrain serotonin neurons.

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.

Principles of voltammetry and microelectrode surface states

In vivo voltammetry is approaching the end of its second decade as a technique to explore extracellular concentrations in the brain. The issues of selectivity and sensitivity, which caused considerable discussion and confusion in the early 1980s, are now resolved. It is clear that in vivo voltammetry and dialysis are complimentary tools to understand neurotransmitter dynamics. The two chief advantages of voltammetry compared to dialysis, improved temporal resolution and reduced tissue damage, make this technique exceptionally well suited for providing information which is complementary to that obtained by single-unit recording and is uniquely capable of providing information on the short-term regulation of extracellular levels of biogenic amines.

Nonserotonergic control of nucleus accumbens dopamine metabolism by the median raphe nucleus

Injections of the GABA agonist muscimol into the median raphe nucleus (MR) have been shown to result in an acceleration of dopamine metabolism within the nucleus accumbens. To examine whether serotonergic mechanisms play a role in this effect, muscimol or its vehicle was injected into the MR of either control subjects or of rats that had received prior injections of the serotonin-depleting agent p-chlorophenylalanine (PCPA). Although PCPA treatments produced massive depletions of forebrain serotonin, they failed to alter the effect of muscimol infusions on dopamine metabolism. This finding suggests that the effects of intra-MR injections of muscimol on accumbens dopamine turnover do not result entirely from an interaction between serotonergic and dopaminergic systems.

Effect of cocaine and 5-HT3 receptor antagonists on 5-HT-induced [3H]dopamine release from rat striatal synaptosomes

The effect of serotonin (5-HT) on the release of tritium from striatal synaptosomes previously loaded with [3H]dopamine ([3H]DA) was studied. 5-HT stimulated both the spontaneous and Ca(2+)-evoked efflux of tritium in a concentration-dependent manner. This effect was not mimicked by the non-selective 5-HT agonist, d-lysergic acid diethylamide. Further, the stimulatory effects of 5 muM 5-HT were unaffected by the selective 5-HT3 receptor antagonists, MDL-72222 and GR-38032F. On the other hand, cocaine and the selective DA uptake inhibitor, nomifensine completely antagonized the effect of 5 muM 5-HT on spontaneous tritium efflux with IC50 values of 0.2 and 0.09 muM, respectively. The effect of 5-HT on Ca(2+)-evoked tritium efflux was also blocked by these DA uptake inhibitors, albeit at somewhat higher concentrations. These data support the hypothesis that 5-HT induces the release of DA from striatal nerve terminals via a mechanism involving the transport of 5-HT into the dopaminergic terminal, rather than by activating 5-HT3 receptors as has been proposed to account for the effect of 5-HT observed in striatal slices.

Local depletion of monoamines induced with in vivo voltammetry in the cat brain

A significant depletion of the electroactive monoamines and their metabolites in the vicinity of a carbon fiber microelectrode may be induced by in vivo staircase voltammetry in the brain, even if the duration of the voltammetric scans is relatively short (approximately 5 s). The variation of this depletion was determined in the extracellular fluid of the cat thalamus at different durations of the pauses separating consecutive measurements. Pauses not shorter than 5 min ensured a nearly full relaxation, so that at the beginning of each subsequent scan a virtually undisturbed environment surrounded the electrode. With pauses shorter than 5 min, it is still possible to monitor major changes in the monoamine concentration. Staircase scans separated with 45 s pauses, for example, were suitable to study the increase in monoamine levels after administration of reserpine, and release phenomena stimulated with KCl were monitored with frequently repeated voltammetric pulses. The electrochemically induced depletion, on the other hand, can be used for characterizing the dynamics of mass transport in the studied brain structure. This was demonstrated with staircase voltammetry alternated with pauses of 1-100 s, and with quasi-chronoamperometry. In vivo brain voltammetry is generally used for monitoring extracellular monoamine (including dopamine) levels. These may be significantly altered by the voltammetric measurement itself through depletion in the vicinity of the electrode. This effect can be minimized with appropriate selection of sampling intervals and other parameters of staircase voltammetry. Conversely, depletion and the following relaxation can be used for determining dynamic characteristics of the studied brain structure which would be difficult to obtain otherwise.

Application of in vivo electrochemistry to the measurement of changes in dopamine release during intracranial self-stimulation

Stearate-modified graphite paste recording electrodes were acutely or chronically implanted into the nucleus accumbens along with bipolar stimulating electrodes in the ipsilateral ventral tegmental area (VTA). Chronoamperometry was used to monitor changes in electrochemical signals that may correspond to the oxidation of dopamine (DA) during experimenter-administered stimulation (EAS) and intracranial self-stimulation (ICS). Application of EAS to stimulating electrodes in the VTA produced increases in the electrochemical signal in both the anesthetized and conscious preparation. The magnitude of both effects increased as a function of current intensity. Initiation of ICS was also accompanied by an immediate increase in the electrochemical signal. Rate-intensity experiments revealed a corresponding increase in both the ICS rates and the electrochemical signal with successive increases or decreases in current intensity. In subsequent experiments, intraperitoneal injections of DA uptake blockers nomifensine and GBR-12909 produced significant increases in the amplitude of the chronoamperometric signal which corresponded to drug-induced increases in bar press rates. The noradrenergic uptake blocker desipramine had no significant effect on either ICS rates or oxidation current. These data indicate that ICS of the VTA may produce concurrent increases in DA neurotransmission in the nucleus accumbens. The pharmacological studies are consistent with a dopaminergic substrate of brain stimulation reward at electrode sites in the VTA.

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.