In vivo temporal sequence of rat striatal glutamate, aspartate and dopamine efflux during apomorphine, nomifensine, NMDA and PDC in situ administration

Droplets for Sampling and Transport of Chemical Signals in Biosensing: A Review

The chemical, temporal, and spatial resolution of chemical signals that are sampled and transported with continuous flow is limited because of Taylor dispersion. Droplets have been used to solve this problem by digitizing chemical signals into discrete segments that can be transported for a long distance or a long time without loss of chemical, temporal or spatial precision. In this review, we describe Taylor dispersion, sampling theory, and Laplace pressure, and give examples of sampling probes that have used droplets to sample or/and transport fluid from a continuous medium, such as cell culture or nerve tissue, for external analysis. The examples are categorized, as follows: (1) Aqueous-phase sampling with downstream droplet formation; (2) preformed droplets for sampling; and (3) droplets formed near the analyte source. Finally, strategies for downstream sample recovery for conventional analysis are described.

In Vivo Monitoring of Dopamine by Microdialysis with 1 min Temporal Resolution Using Online Capillary Liquid Chromatography with Electrochemical Detection

Microdialysis is often applied to understanding brain function. Because neurotransmission involves rapid events, increasing the temporal resolution of in vivo measurements is desirable. Here, we demonstrate microdialysis with online capillary liquid chromatography for the analysis of 1 min rat brain dialysate samples at 1 min intervals. Mobile phase optimization involved adjusting the pH, buffer composition, and surfactant concentration to eliminate interferences with the dopamine peak. By analyzing electrically evoked dopamine transients carefully synchronized with the switching of the online LC sample valve, we demonstrate that our system has both 1 min sampling capabilities and bona fide 1 min temporal resolution. Evoked DA transients were confined to single, 1 min brain dialysate samples. After uptake inhibition with nomifensine (20 mg/kg i.p.), responses to electrical stimuli of 1 s duration were detected.

Dopamine physiology in the basal ganglia of male zebra finches during social stimulation

Accumulating evidence suggests that dopamine (DA) is involved in altering neural activity and gene expression in a zebra finch cortical–basal ganglia circuit specialized for singing, upon the shift between solitary singing and singing as a part of courtship. Our objective here was to sample changes in the extracellular concentrations of DA in Area X of adult and juvenile birds, to test the hypothesis that DA levels would change similarly during presentation of a socially salient stimulus in both age groups. We used microdialysis to sample the extracellular milieu of Area X in awake, behaving adult and juvenile male zebra finches, and analysed the dialysate using high-performance liquid chromatography coupled with electrochemical detection. The extracellular levels of DA in Area X increased significantly during both female presentation to adult males and tutor presentation to juvenile males. DA levels were not correlated with the time spent singing. We also reverse-dialysed Area X with pharmacologic agents that act either on DA systems directly or on norepinephrine, and found that all of these agents significantly increased DA levels (3- to 10-fold) in Area X. These findings suggest that changes in extracellular DA levels can be stimulated similarly by very different social contexts (courtship and interaction with tutor), and influenced potently by dopaminergic and noradrenergic drugs. These results raise the possibility that the arousal level or attentional state of the subject (rather than singing behavior) is the common feature eliciting changes in extracellular DA concentration.

Microdialysis in the rat striatum: effects of 24 h dexamethasone retrodialysis on evoked dopamine release and penetration injury

The power of microdialysis for in vivo neurochemical monitoring is a result of intense efforts to enhance microdialysis procedures, the probes themselves, and the analytical systems used for the analysis of dialysate samples. Our goal is to refine microdialysis further by focusing attention on what happens when the probes are implanted into brain tissue. It is broadly acknowledged that some tissue damage occurs, such that the tissue nearest the probes is disrupted from its normal state. We hypothesize that mitigating such disruption would refine microdialysis. Herein, we show that the addition of dexamethasone, an anti-inflammatory drug, to the perfusion fluid protects evoked dopamine responses as measured by fast-scan cyclic voltammetry next to the probes after 24 h. We also show that dexamethasone stabilizes evoked dopamine responses measured at the probe outlet over a 4-24 h postimplantation interval. The effects of dexamethasone are attributable to its anti-inflammatory actions, as dexamethasone had no significant effect on two histochemical markers for dopamine terminals, tyrosine hydroxylase and the dopamine transporter. Using histochemical assays, we confirmed that the actions of dexamethasone are tightly confined to the immediate, local vicinity of the probe.

Differential involvement of amygdala and cortical NMDA receptors activation upon encoding in odor fear memory

Although the basolateral amygdala (BLA) plays a crucial role for the acquisition of fear memories, sensory cortices are involved in their long-term storage in rats. However, the time course of their respective involvement has received little investigation. Here we assessed the role of the glutamatergic N-methyl-d-aspartate (NMDA) receptors in the BLA and olfactory cortex at discrete moments of an odor fear conditioning session. We showed that NMDA receptors in BLA are critically involved in odor fear acquisition during the first association but not during the next ones. In the cortex, NMDA receptor activation at encoding is not necessary for recent odor fear memory while its role in remote memory storage needs further investigation.

Correlation of 3-mercaptopropionic acid induced seizures and changes in striatal neurotransmitters monitored by microdialysis

OBJECTIVES

The goal of this study was to use a status epilepticus steady-state chemical model in rats using the convulsant, 3-mercaptopropionic acid (3-MPA), and to compare the changes in striatal neurotransmission on a slow (5min) and fast (60s) timescale. In vivo microdialysis was combined with electrophysiological methods in order to provide a complete evaluation of the dynamics of the results obtained.

OBJECTIVE

To compare the effects of a steady-state chemical model pof status epilepticus on striatal amino-acid and amine neurotransmitters contents, as measured via in vivo microdialysis combined with electrophysiological methods. Measurements were performed on samples collected every 60s and every 5min. "Fast" (60s) and "slow" (5min) sampling timescales were selected, to gain more insight into the dynamics of GABA synthesis inhibition and of its effects on other neurotransmitters and on cortical electrical activity.

METHODS

3-MPA was administered in the form of an intra-venous load (60mg/kg) followed by a constant infusion (50mg/kg/min) for min. Microdialysis samples were collected from the striatum at intervals of 5min and 60s and analyzed for biogenic amine and amino acid neurotransmitters. ECoG activity was monitored via screws placed over the cortex.

RESULTS

In the 5min samples, glutamate (Glu) increased and γ-aminobutyric acid (GABA) decreased monotonically while changes in dopamine (DA) concentration were bimodal. In the sixty second samples, Glu changes were bimodal, a feature that was not apparent with the 5min samples. ECoG activity was indicative of status epilepticus.

CONCLUSIONS

This study describes the combination of in vivo microdialysis with electrophysiology to monitor the effect of 3-MPA on neurotransmission in the brain. This led to a better understanding of the chemical changes in the striatum due to the applied 3-MPA chemical model of status epilepticus.

Ethanol-induced alterations of amino acids measured by in vivo microdialysis in rats: a meta-analysis

PURPOSE

In recent years in vivo microdialysis has become an important method in research studies investigating the alterations of neurotransmitters in the extracellular fluid of the brain. Based on the major involvement of glutamate and γ-aminobutyric acid (GABA) in mediating a variety of alcohol effects in the mammalian brain, numerous microdialysis studies have focused on the dynamical behavior of these systems in response to alcohol.

METHODS

Here we performed multiple meta-analyses on published datasets from the rat brain: (i) we studied basal extracellular concentrations of glutamate and GABA in brain regions that belong to a neurocircuitry involved in neuropsychiatric diseases, especially in alcoholism (Noori et al., Addict Biol 17:827-864, 2012); (ii) we examined the effect of acute ethanol administration on glutamate and GABA levels within this network and (iii) we studied alcohol withdrawal-induced alterations in glutamate and GABA levels within this neurocircuitry.

RESULTS

For extraction of basal concentrations of these neurotransmitters, datasets of 6932 rats were analyzed and the absolute basal glutamate and GABA levels were estimated for 18 different brain sites. In response to different doses of acute ethanol administration, datasets of 529 rats were analyzed and a non-linear dose response (glutamate and GABA release) relationship was observed in several brain sites. Specifically, glutamate in the nucleus accumbens shows a decreasing logarithmic dose response curve. Finally, regression analysis of 11 published reports employing brain microdialysis experiments in 104 alcohol-dependent rats reveals very consistent augmented extracellular glutamate and GABA levels in various brain sites that correlate with the intensity of the withdrawal response were identified.

CONCLUSIONS

In summary, our results provide standardized basal values for future experimental and in silico studies on neurotransmitter release in the rat brain and may be helpful to understand the effect of ethanol on neurotransmitter release. Furthermore, this study illustrates the benefit of meta-analyses using the generalization of a wide range of preclinical data.

Microfabricated sampling probes for in vivo monitoring of neurotransmitters

Microfabricated fluidic systems have emerged as a powerful approach for chemical analysis. Relatively unexplored is the use of microfabrication to create sampling probes. We have developed a sampling probe microfabricated in Si by bulk micromachining and lithography. The probe is 70 μm wide by 85 μm thick by 11 mm long and incorporates two buried channels that are 20 μm in diameter. The tip of the probe has two 20 μm holes where fluid is ejected or collected for sampling. Utility of the probe was demonstrated by sampling from the brain of live rats. For sampling, artificial cerebral spinal fluid was infused in through one channel at 50 nL/min while sample was withdrawn at the same flow rate from the other channel. Analysis of resulting fractions collected every 20 min from the striatum of rats by liquid chromatography with mass spectrometry demonstrated reliable detection of 17 neurotransmitters and metabolites. The small probe dimensions suggest it is less perturbing to tissue and can be used to sample smaller brain nuclei than larger sampling devices, such as microdialysis probes. This sampling probe may have other applications such as sampling from cells in culture. The use of microfabrication may also enable incorporation of electrodes for electrochemical or electrophysiological recording and other channels that enable more complex sample preparation on the device.

Amygdalofugal axon terminals immunoreactive for L-aspartate or L-glutamate in the nucleus accumbens of rats and domestic chickens: a comparative electron microscopic immunocytochemical study combined with anterograde pathway tracing

Several studies have shown that L-aspartate (Asp) is present in synaptic vesicles and released exocytotically from presynaptic terminals, possibly by Ca(2+)-dependent corelease of Asp and L-glutamate (Glu). It has been demonstrated that both excitatory amino acids (EAAs) are released from the rat striatum as part of corticostriatal neurotransmission. The single or colocalized occurrence of Asp and Glu in specific synaptic boutons of the chicken medial striatum/nucl. accumbens has been demonstrated by our group using ultrastructural immunocytochemistry. However, evidence for the presence of EAAs in any specific striatal pathway was only circumstantial. Here, we report on the distribution of Asp and Glu in specific synaptic terminals of the amygdalostriatal pathway, both in rat and chicken brains, combining anterograde tracing with postembedding immunogold labeling of Asp or Glu. Immunoreactivity for Asp and Glu was observed in amygdalofugal terminals with asymmetrical synaptic junctions (morphologically representing excitatory synapses) in both species. The postsynaptic targets were either dendritic spines or small dendrites, whereas axosomatic or axo-axonic connections were not observed. Ultrastructurally, the synaptic terminals immunoreactive for Asp were indistinguishable from those immunoreactive for Glu. The findigs are consistent with an Asp-Glu corelease mechanism, with a distinct synaptic contingent, evolutionarily conserved in the amygdalostriatal pathway.

Microdialysis probes alter presynaptic regulation of dopamine terminals in rat striatum

The insertion of microdialysis probes into the rat striatum disrupts dopaminergic activity near the probe track. The present study suggests that a substantial fraction of DA terminals near the probe track (200 μm) survive the probe implantation itself but that the surviving terminals experience altered presynaptic inhibition. We found that probe implantation did not just alter the amplitude of evoked dopamine responses recorded by voltammetry, but also changed their temporal profile in a fashion similar to that previously observed by quinpirole, an agonist of dopamine D2 autoreceptors. Altered presynaptic inhibition is supported by a hypersensitivity of evoked dopamine responses recorded near to microdialysis probes to raclopride, a D2 antagonist. Further, we found that evoked dopamine release was also hypersensitive to a final dose of the dopamine transporter inhibitor, nomifensine.

Improved temporal resolution for in vivo microdialysis by using segmented flow

Microdialysis sampling probes were interfaced to a segmented flow system to improve temporal resolution for monitoring concentration dynamics. Aqueous dialysate was segmented into nanoliter plugs by pumping sample stream into the base of a tee channel structure microfabricated on a PDMS chip that had an immiscible carrier phase (perfluorodecalin) pumped into the cross arm of the tee. Varying the oil flow rate from 0.22 to 6.3 microL/min and sample flow rate from 42 to 328 nL/min allowed control of plug volume, interval between plugs, and frequency of plug generation between 6 and 28 nL, 0.6 and 10 s, and 0.1 and 1.7 Hz, respectively. Temporal resolution of the system, determined by measuring fluorescence in individual sample plugs following step changes of fluorescein concentration at the sampling probe surface, was as good as 15 s. Temporal resolution was independent of both sampling flow rate and distance that samples were pumped from the sampling probe. This effect is due to the prevention of Taylor dispersion of the sample as it was transported by segmented flow. In contrast, without flow segmentation, temporal resolution was worsened from 25 to 160 s as the detection point was moved from the sampling probe to 40 cm downstream. Glucose was detected by modifying the chip to allow enzyme assay reagents to be mixed with dialysate as sample plugs formed. The resulting assay had a detection limit of 50 microM and a linear range of 0.2-2 mM. This system was used to measure glucose in the brain of anesthetized rats. Basal concentration was 1.5 +/- 0.1 mM (n = 3) and was decreased 60% by infusion of high-K(+) solution through the probe. These results demonstrate the potential of microdialysis with segmented flow to be used for in vivo monitoring experiments with high temporal resolution.

Time-resolved microdialysis for in vivo neurochemical measurements and other applications

Monitoring changes in chemical concentrations over time in complex environments is typically performed using sensors and spectroscopic techniques. Another approach is to couple sampling methods, such as microdialysis, with chromatographic, electrophoretic, or enzymatic assays. Recent advances of such coupling have enabled improvements in temporal resolution, multianalyte capability, and automation. In a sampling and analysis method, the temporal resolution is set by the mass sensitivity of the analytical method, analysis time, and zone dispersion during sampling. Coupling methods with high speed and mass sensitivity to microdialysis sampling help to reduce some of these contributions to yield methods with temporal resolution of seconds. These advances have been primarily used in monitoring neurotransmitters in vivo. This review covers the problems associated with chemical monitoring in the brain, recent advances in using microdialysis for time-resolved in vivo measurements, sample applications, and other potential applications of the technology such as determining reaction kinetics and process monitoring.

Contributions of capillary electrophoresis to neuroscience

Capillary electrophoresis (CE) is a small-volume separation approach amenable to the analysis of complex samples for their small molecule, peptide and protein content. A number of the features of CE make it a method of choice for addressing questions related to neurochemistry. The figures of merit inherent to CE that make it well suited for studying cell-to-cell and intracellular signaling include small sample volumes, high separation efficiency, the ability for online analyte concentration, and compatibility with sensitive and high-information content detection methods. A variety of instrumental aspects are detailed, including detection methods and sampling techniques that are particularly useful for the analysis of signaling molecules. Studies that have used these techniques to increase our understanding of neurobiology are emphasized throughout. One notable application is single neuron chemical analysis, a research area that has been greatly advanced by CE.

Separation and determination of amino acids by micellar electrokinetic chromatography coupling with novel multiphoton excited fluorescence detection

In this article, it was demonstrated that separation and determination of 20 amino acids were accomplished by micellar electrokinetic chromatography (MEKC) coupling with novel multiphoton excited fluorescence (MPEF) detection method. Different from MPEF achieved by expensive fs laser, continuous wave (CW) diode laser of ultra-low cost was uniquely employed in our MPEF system. Amino acids were fluorescently labeled with fluorescein isothiocyanate (FITC), and were subjected to sodium dodecyl sulfate (SDS)-based MEKC separation and CW-based MPEF detection. The result was compared with that by single photon excited fluorescence (SPEF), which indicated that MPEF had the advantages of better mass detectability and higher separation selectivity over SPEF. Quantitative analysis was performed and revealed linear dynamic range of over 2 orders of magnitude, with mass detection limit down to ymole level. To evaluate the reliability, this method was successfully applied for analyzing a commercial nutrition supplement liquid.

Monitoring dopamine in vivo by microdialysis sampling and on-line CE-laser-induced fluorescence

Microdialysis sampling was coupled on-line to micellar electrokinetic chromatography (MEKC) to monitor extracellular dopamine concentration in the brains of rats. Microdialysis probes were perfused at 0.3 microL/min and the dialysate mixed on-line with 6 mM naphthalene-2,3-dicarboxaldehye and 10 mM potassium cyanide pumped at 0.12 microL/min each into a reaction capillary. The reaction mixture was delivered into a flow-gated interface and separated at 90-s intervals. The MEKC separation buffer consisted of 30 mM phosphate, 6.5 mM SDS, and 2 mM HP-beta-CD at pH 7.4, and the electric field was 850 V/cm applied across a 14-cm separation distance. Analytes were detected by laser-induced fluorescence excited using the 413-nm line of a 14-mW diode-pumped laser. The detection limit for dopamine was 2 nM when sampling by dialysis. The basal dopamine concentration in dialysates collected from the striatum of anesthetized rats was 18 +/- 3 nM (n = 12). The identity of the putative dopamine peak was confirmed by showing that dopamine uptake inhibitors increased the peak and dopamine synthesis inhibitors eliminated the peak. The utility of this method for behavioral studies was demonstrated by correlating dopamine concentrations in vivo and with psychomotor behavior in freely moving rats following the intravenous administration of cocaine. Over 60 additional peaks were detected in the electropherograms, suggesting the potential for monitoring many other substances in vivo by this method.

Monitoring neurotransmitter release from isolated retinas using online microdialysis-capillary electrophoresis

Release of neurotransmitters and other primary amine-containing analytes from intact, isolated larval salamander (Ambystoma tigrinum) retinas maintained in a 6.5-microL perfusion chamber was monitored using online microdialysis-capillary electrophoresis with laser-induced fluorescence detection (CE-LIF). Primary amines were derivatized online with o-phthaldialdehyde (OPA) and beta-mercaptoethanol. With the use of overlapping injections, the perfusate was sampled every approximately 10 s. Although separation conditions were optimized using 20 mM hydroxypropyl-gamma-cyclodextrin (HP-gamma-CD) for a number of important neuromessengers including D- and L-serine, D- and L-asparate, glutamate, GABA, serotonin, dopamine, norepinephrine, and taurine, only glutamate (0.48 +/- 0.27 microM), GABA (0.25 +/- 0.12 microM), taurine (5.5 +/- 2.1 microM), and l-serine (2.8 +/- 1.0 microM) were identified in the perfusate. Elevated levels of glutamate, GABA, and taurine were detected during stimulation with 60 mM K+. This method is the first to directly sample multiple neurotransmitters from perfused, isolated retinas and to observe changes in efflux of these neurotransmitters as a result of pharmacological stimulation.

Striatal glutamate release evoked in vivo by NMDA is dependent upon ongoing neuronal activity in the substantia nigra, endogenous striatal substance P and dopamine

The aim of the present microdialysis study was to investigate whether the increase in striatal glutamate levels induced by intrastriatal perfusion with NMDA was dependent on the activation of extrastriatal loops and/or endogenous striatal substance P and dopamine. The NMDA-evoked striatal glutamate release was mediated by selective activation of the NMDA receptor-channel complex and action potential propagation, as it was prevented by local perfusion with dizocilpine and tetrodotoxin, respectively. Tetrodotoxin and bicuculline, perfused distally in the substantia nigra reticulata, prevented the NMDA-evoked striatal glutamate release, suggesting its dependence on ongoing neuronal activity and GABA(A) receptor activation, respectively, in the substantia nigra. The NMDA-evoked glutamate release was also dependent on striatal substance P and dopamine, as it was antagonized by intrastriatal perfusion with selective NK(1) (SR140333), D(1)-like (SCH23390) and D(2)-like (raclopride) receptor antagonists, as well as by striatal dopamine depletion. Furthermore, impairment of dopaminergic transmission unmasked a glutamatergic stimulation by submicromolar NMDA concentrations. We conclude that in vivo the NMDA-evoked striatal glutamate release is mediated by activation of striatofugal GABAergic neurons and requires activation of striatal NK(1) and dopamine receptors. Endogenous striatal dopamine inhibits or potentiates the NMDA action depending on the strength of the excitatory stimulus (i.e. the NMDA concentration).

High temporal resolution for in vivo monitoring of neurotransmitters in awake epileptic rats using brain microdialysis and capillary electrophoresis with laser-induced fluorescence detection

A method for high temporal resolution monitoring of five neurotransmitters, dopamine (DA), noradrenaline (NA), gamma-aminobutyric acid (GABA), glutamate (Glu), l-aspartate (L-Asp), in freely-moving rats using microdialysis and capillary electrophoresis with laser-induced fluorescence detection (CE-LIFD) was developed. An on-line device, including microdialysis and derivatization with naphthalene-2,3-dicarboxaldehyde, mixes the dialysate with derivatization reagents directly in the collection tube, i.e. with no reactor. Thereafter, collected derivatized samples are analyzed off-line with an automated CE system coupled to a LIFD using a 442 nm excitation. The sampling time was limited by the minimal volume required for the analysis by the automated CE system used: neurotransmitters could be determined in 667 nl dialysates (940 nl after derivatization), i.e. in samples collected every 20 s with a flow rate of 2 microl/min. The detection limits at the dialysis probe were 3 x 10(-9), 1 x 10(-9), 1.9 x 10(-8), 4.2 x 10(-7), 2.1 x 10(-7) mol/l for DA, NA, GABA, Glu and L-Asp, respectively. The protocol was validated using in vitro/in vivo tests and the performances--repeatability, linearity, characteristics of the probes--were determined. Finally, the high temporal resolution allowed the simultaneous monitoring of these neurotransmitters in rats with genetic absence epilepsy and revealed, for the first time, increases in GABA concentrations concomitantly with the seizures, detected when our new microdialysis method was combined to electroencephalographic recordings.

In vivo monitoring of amino acids by microdialysis sampling with on-line derivatization by naphthalene-2,3-dicarboxyaldehyde and rapid micellar electrokinetic capillary chromatography

An analytical method was developed to monitor amino acids collected by in vivo microdialysis. Microdialysate was continuously derivatized on-line by mixing 6 mM naphthalene-2,3-dicarboxyaldehyde (NDA) and 10 mM potassium cyanide with the dialysate stream in a fused silica capillary to form fluorescent products. Reaction time, determined by the flow rate and volume of reaction capillary, was 3 min. Derivatized amino acids were continuously delivered into a flow-gated interface and periodically injected onto a capillary electrophoresis unit equipped with a laser-induced fluorescence detection based on a commercial microscope. Separation was performed in the micellar electrokinetic chromatography mode using 30 mM sodium dodecyl sulfate in 15 mM phosphate buffer at pH 8.0 as the separation media. An electric field of 1.3 kV/cm was applied across a 10 cm long, 10 microm internal diameter separation capillary. These conditions allowed 17 amino acid derivatives to be resolved in less than 30 s. On-line injections could be performed at 30 s intervals for in vivo samples. Detection limits were from 10 to 30 nM for the amino acids. The method was applied to monitor the acute ethanol-induced amino acid level changes in freely moving rats. The results demonstrate the utility of the method to reveal dynamics of amino acid concentration in vivo.

Discovery and Neurochemical Screening of Peptides in Brain Extracellular Fluid by Chemical Analysis of in Vivo Microdialysis Samples

Endogenous peptides from brain extracellular fluid of live rats were analyzed using capillary liquid chromatography (LC)-tandem mass spectrometry (MS2). A 4-mm-long microdialysis probe perfused at 0.6 microL/min implanted into the striatum of anesthetized male rats was used to collect 3.6 microL dialysate fractions that were injected on-line into the capillary LC-MS2 system for analysis. A total of 3349 MS2 spectra were collected from 13 different animals under basal conditions and during localized depolarization evoked by infusion of a high-K+ solution through the microdialysis probe. Subtractive analysis revealed a total of 859 MS2 spectra that were observed only during depolarization. From these spectra, 29 peptide sequences (25 were peptides not previously observed) from 6 different protein precursors were identified using database searching software. Proteins identified include precursors to neuropeptides, synaptic proteins, blood proteins, and transporters. The identified peptides represent candidates for neurotransmitters, neuromodulators, and markers of synaptic activity or brain tissue damage. A screen for neuroactivity of novel proenkephalin fragments that were found was performed by infusing the peptides into the brain while monitoring amino acid neurotransmitters by microdialysis sampling combined with capillary electrophoresis. Three of the six tested peptides evoked significant increases in various neuroactive amino acids. These results demonstrate that this combination of methods can identify novel neurotransmitter candidates and screen for potential neuroactivity.

β-Phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids derived from them, including further products of oxidation. condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2002 to June 2003 is reviewed, with 568 references cited.

Neurochemical Mechanisms Induced by High Frequency Stimulation of the Subthalamic Nucleus: Increase of Extracellular Striatal Glutamate and GABA in Normal and Hemiparkinsonian Rats

High frequency stimulation (HFS) (130 Hz) of the subthalamic nucleus (STN) provides beneficial effects in patients suffering from severe parkinsonism, but the mechanisms underlying these clinical results remain to be clarified. To date, very little is known concerning the effects of STN-HFS on neurochemical transmission in the different basal ganglia nuclei and in particular the striatum. This study examines the effects of STN-HFS in intact and hemiparkinsonian rats on extracellular striatal glutamate (Glu) and GABA levels by means of intracerebral microdialysis. Unilateral STN-HFS was found to induce a significant bilateral increase of striatal Glu and GABA both in intact and in dopamine-lesioned animals. In intact rats, these increases were reversed by local administration of the D1 antagonist SCH 23390, but were potentiated by the D2 antagonist sulpiride. Potentiation was also observed after local administration of both D1 and D2 antagonists whose amplitude was similar to that measured in hemiparkinsonian rats. These data furnish the first evidence that STN-HFS influences striatal amino-acid transmission and that this influence is modulated by dopamine. They provide evidence that the effects of STN-HFS are not only restricted to the direct STN targets, but also involve adaptive changes within other structures of the basal ganglia circuitry.

Electrophysiological Interactions between Striatal Glutamatergic and Dopaminergic Systems

Glutamatergic and dopaminergic systems play a primary role in frontal-subcortical circuits involved in motor and cognitive functions. Considerable evidence has emerged indicating that the complex interaction between these neurotransmitter systems within the dorsal striatum and nucleus accumbens is critically involved in the gating of information flow in these highly integrative brain regions. As a result, disruptions of the interaction between glutamate and dopamine has been proposed as a pathological basis for a number of disorders, including the pathophysiology of schizophrenia. In this chapter, we discuss recent studies that have significantly advanced our understanding of the reciprocal interactions between glutamatergic and dopaminergic systems within the striatal complex in the normal brain and in pathological states.

Oral dyskinesias and histopathological alterations in substantia nigra after long-term haloperidol treatment of old rats

The pathophysiologic basis of tardive dyskinesia remains unclear, but several lines of evidence suggest that persistent neuronal changes in the basal ganglia produced by oxidative stress or glutamate toxicity may play a role, especially in the elderly. In the present study we examined whether histopathological alterations in substantia nigra are related to oral dyskinesia in a rodent model of tardive dyskinesia. Haloperidol decanoate (38 mg/kg/4 weeks) was administered to young (8 weeks) and old (38 weeks) rats for a total period of 28 weeks, and the development of vacuous chewing movements (VCM) was observed. Rats with high and low levels of VCM and saline-treated controls were analyzed for histopathological alterations. Reduced nerve cell number and atrophic neurons were prominent features in the substantia nigra of old rats with high levels of VCM. Some alterations were also present in the substantia nigra of the old rats with low levels of VCM and young rats with high VCM levels, but these were significantly less affected than the high VCM rats. These results show that the development of haloperidol-induced oral dyskinesias in old rats is associated with histopathological alterations in the substantia nigra. This suggests that nigral degeneration induced by neuroleptics may contribute to the development of persistent VCM in rats and possibly irreversible tardive dyskinesia in humans.