A selected ion monitoring assay for dopamine and its metabolites using negative chemical ionization

"Lipidomics": Mass spectrometric and chemometric analyses of lipids

Lipids are ubiquitous in the human organism and play essential roles as components of cell membranes and hormones, for energy storage or as mediators of cell signaling pathways. As crucial mediators of the human metabolism, lipids are also involved in metabolic diseases, cardiovascular and renal diseases, cancer and/or hepatological and neurological disorders. With rapidly growing evidence supporting the impact of lipids on both the genesis and progression of these diseases as well as patient wellbeing, the characterization of the human lipidome has gained high interest and importance in life sciences and clinical diagnostics within the last 15 years. This is mostly due to technically advanced molecular identification and quantification methods, mainly based on mass spectrometry. Mass spectrometry has become one of the most powerful tools for the identification of lipids. New lipidic mediators or biomarkers of diseases can be analysed by state-of-the art mass spectrometry techniques supported by sophisticated bioinformatics and biostatistics. The lipidomic approach has developed dramatically in the realm of life sciences and clinical diagnostics due to the available mass spectrometric methods and in particular due to the adaptation of biostatistical methods in recent years. Therefore, the current knowledge of lipid extraction methods, mass-spectrometric approaches, biostatistical data analysis, including workflows for the interpretation of lipidomic high-throughput data, are reviewed in this manuscript.

Mass spectrometry strategies for clinical metabolomics and lipidomics in psychiatry, neurology, and neuro-oncology

Metabolomics research has the potential to provide biomarkers for the detection of disease, for subtyping complex disease populations, for monitoring disease progression and therapy, and for defining new molecular targets for therapeutic intervention. These potentials are far from being realized because of a number of technical, conceptual, financial, and bioinformatics issues. Mass spectrometry provides analytical platforms that address the technical barriers to success in metabolomics research; however, the limited commercial availability of analytical and stable isotope standards has created a bottleneck for the absolute quantitation of a number of metabolites. Conceptual and financial factors contribute to the generation of statistically under-powered clinical studies, whereas bioinformatics issues result in the publication of a large number of unidentified metabolites. The path forward in this field involves targeted metabolomics analyses of large control and patient populations to define both the normal range of a defined metabolite and the potential heterogeneity (eg, bimodal) in complex patient populations. This approach requires that metabolomics research groups, in addition to developing a number of analytical platforms, build sufficient chemistry resources to supply the analytical standards required for absolute metabolite quantitation. Examples of metabolomics evaluations of sulfur amino-acid metabolism in psychiatry, neurology, and neuro-oncology and of lipidomics in neurology will be reviewed.

WIN 44,441: A Stereospecific and Long-Acting Narcotic Antagonist

The opiate antagonist WIN 44,441-3 is a potent, stereospecific antagonist of mu, delta, and kappa opiate receptors. This antagonist activity is of long duration (> 4 h) with no agonist activity being observed. It therefore appears that WIN 44,441-3 will be a useful long-acting opiate antagonist for in vivo studies.

Neurobiology of 50-kHz ultrasonic vocalizations in rats: Electrode mapping, lesion, and pharmacology studies

Fifty-kHz ultrasonic vocalizations have been proposed to reflect a positive appetitive affective state in rats, being consistently linked to the positive appetitive behavior. In the first study, we examined the brain substrates of 50-kHz ultrasonic vocalizations (USVs) by using localized electrical stimulation of the brain (ESB) at various sites that are known to mediate reward. We found that the brain areas that produced ESB-induced 50-kHz calls are the areas that have previously been shown to support the most vigorous self-stimulation behavior (prefrontal cortex, nucleus accumbens, ventral pallidum, lateral preoptic area, lateral hypothalamus, ventral tegmental area, and raphe). Importantly, all animals that showed repeatable ESB-induced 50-kHz USVs demonstrated self-stimulation behavior. In the second study, conditioned place preference was assessed following microinjection of the mu-opiate agonist Tyr-D-Ala-Gly-N-methyl-Phe-Gly-ol (DAMGO) directly into the ventral tegmental area (VTA) at a dose previously found to be rewarding. Animals that showed more 50-kHz USVs in response to drug injections compared to vehicle injections showed significant place preferences, whereas animals that did not show elevated vocalization to DAMGO did not show place preference. In experiment 3, we examined the effect of VTA electrolytic lesions, 6-OHDA lesions, and the effect of the D1/D2 dopamine antagonist flupenthixol (0 and 0.8 mg/kg, i.p.) on 50-kHz ultrasonic vocalizations. We found that these manipulations all selectively reduced 50-kHz ultrasonic vocalizations, and that these effects could be disassociated from any side effects. These data are consistent with the proposition that 50-kHz calls are tightly linked to reward in rats and that the neural circuit of 50-kHz calls closely overlaps that of ESB self-stimulation reward, drug reward, and the mesolimbic dopamine system.

Bilateral changes in striatal dopamine metabolism after unilateral intracarotid and intrastriatal administration of apomorphine

Following cannulation of the common carotid artery of female Sprague-Dawley rats, 3 microCi (10 micrograms) of [3H]apomorphine were infused. At various time intervals, drug concentrations were determined in the right and left striata, anterior forebrains, posterior forebrains and cerebella. One minute following intracarotid infusion of apomorphine, approximately a 65-fold right/left difference in apomorphine concentrations was attained in all forebrain structures, and this difference steadily diminished with time as a result of declining drug levels in the infused hemisphere. The concentrations of dopamine and its metabolites (DOPAC, HVA and 3-MT) were quantified by gas chromatography-mass spectrometry in the right and left striata at 5 and 15 min after unilateral intracarotid infusion of 1 microgram apomorphine. At both time intervals and regardless of the side infused, the metabolites of dopamine increased ipsilateral to the side of infusion. Moreover, 3-MT levels were significantly decreased in the contralateral striatum. After direct intrastriatal injection of either 0.1 or 1.0 microgram apomorphine into the right striatum, the levels of dopamine metabolites were again increased in the ipsilateral striatum. 3-MT levels were also decreased significantly in the left striatum. In contrast to the effects observed after systemic administration of apomorphine, these results demonstrate that dopamine release in the striatum is increased by selectively delivering higher concentrations of apomorphine to the nerve terminals of the nigrostriatal neurons. The effects of unilateral apomorphine on dopamine metabolism in the contralateral striatum are most likely the effect of interhemispheric communication.

Dopamine release and metabolism in the rat frontal cortex, nucleus accumbens, and striatum: a comparison of acute clozapine and haloperidol

1. The effects of the typical and typical neuroleptic agents clozapine (CLZ) (2.5-20 mg kg-1, i.p.) and haloperidol (Hal) (0.05-1.0 mg kg-1), were compared on dopamine release and metabolism in the rat prefrontal cortex (PFC), nucleus accumbens (ACC) and striatum (ST). Dopamine release was estimated by measuring the steady-state concentration of 3-methoxytyramine (3-MT) and the level of 3-MT 10 min after pargyline (3-MT accumulation); dopamine metabolism was evaluated from the steady-state concentrations of its acidic metabolites. 2. Both drugs increased 3-MT accumulation in the PFC in a dose-dependent manner. In contrast to Hal, CLZ failed to increase 3-MT accumulation in the ACC or ST. The ST was the region most sensitive to Hal in terms of 3-MT accumulation and, by inference, dopamine release. 3. Both CLZ and Hal dose-dependently elevated the concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in all 3 brain regions studied. The ACC appears to be the region most sensitive to these drugs in terms of changes in the levels of HVA. 4. The result of the present investigations suggest measurements of 3-MT production in the 3 brain regions analysed might be a useful and simple pharmacological tool in the search for atypical neuroleptic drugs with a selectivity of action for the cortical systems.

(+) 3-[3-hydroxyphenyl-N-(1-propyl) piperidine] selectively differentiates effects of sigma ligands on neurochemical pathways modulated by sigma receptors: evidence for subtypes, in vivo

The effects of sigma ligands, (+)3PPP 3-[3-hydroxyphenyl-N(1-propyl) piperidine] and (-)butaclamol, were evaluated in vivo on the metabolism of dopamine (DA) and in the striatum release of adrenocorticotrophic hormone (ACTH) and prolactin in the rat and changes in levels of cyclic guanosine monophosphate (cGMP) in the cerebellum of the mouse and compared with the effects of (+)NANM (N-allyl-normetazocine, SKF 10,047) and (+)pentazocine. Both (+)3PPP and (-) butaclamol decreased the release of prolactin and did not affect the metabolism of DA. N-Allyl-normetazocine and (+)pentazocine increased release of prolactin and have been shown previously to increase the metabolism of DA. All four ligands increased release of ACTH; however, only the increases caused by (+)NANM and (+)pentazocine were reversed by pretreatment with CPP, a N-methyl-D-aspartate (NMDA) receptor antagonist. (+)Pentazocine and (+)NANM inhibited the NMDA receptor-mediated changes in levels of cGMP in the cerebellum of the mouse, while (+)3PPP and (-)butaclamol did not attenuate the response to NMDA. In addition to further confirming a functional interaction between sigma receptors and NMDA receptors, these studies divide the observed effects of putative sigma ligands into two groups, characterized by benzomorphan compounds and non-benzomorphan compounds, suggesting the possibility of subtypes at sigma receptor in vivo.

Contrasting neurochemical interactions of tiletamine, a potent phencyclidine (PCP) receptor ligand, with the N-methyl-D-aspartate-coupled and -uncoupled PCP recognition sites

Neurochemical interactions of tiletamine, a potent phencyclidine (PCP) receptor ligand, with the N-methyl-D-aspartate (NMDA)-coupled and -uncoupled PCP recognition sites were examined. Tiletamine potently displaced the binding of [3H]1-(2-thienyl)cyclohexylpiperidine with an IC50 of 79 nM without affecting sigma-, glycine, glutamate, kainate, quisqualate, or dopamine (DA) receptors. Like other PCP ligands acting via the NMDA-coupled PCP recognition sites, tiletamine decreased basal, harmaline-, and D-serine-mediated increases in cyclic cGMP levels and induced stereotypy and ataxia. Tiletamine was nearly five times more potent than PCP at inhibiting the binding of 3-hydroxy[3H]PCP to its high-affinity NMDA-uncoupled PCP recognition sites. However, following parenteral administration, dizocilpine maleate (MK-801), ketamine, PCP, dexoxadrol, and 1-(2-thienyl)cyclohexylpiperidine HCl, but not tiletamine, increased rat pyriform cortical DA metabolism and/or release, a response modulated by the NMDA-uncoupled PCP recognition sites. Pretreatment with tiletamine did not attenuate the MK-801-induced increases in rat pyriform cortical DA metabolism, a result suggesting that tiletamine is not a partial agonist of the NMDA-uncoupled PCP recognition sites in this region. However, following intracerebroventricular administration (100-500 micrograms/rat), tiletamine increased pyriform cortical DA metabolism with a bell-shaped dose-response curve. These data indicate a differential interaction of tiletamine with the NMDA-coupled and -uncoupled PCP recognition sites. The paradoxical effects of tiletamine suggest that tiletamine might activate receptor(s) or neuronal pathways of unknown pharmacology.

Neurochemical interactions of competitive N-methyl-D-aspartate antagonists with dopaminergic neurotransmission and the cerebellar cyclic GMP system: functional evidence for a phasic glutamatergic control of the nigrostriatal dopaminergic pathway

Direct intrastriatal injection of N-methyl-D-aspartate (NMDA; 100 micrograms/rat) increased striatal dopamine (DA) release in vivo. However, parenteral administration of (+/-)-3-(2-carboxypiperizin-4-yl)propyl-1-phosphonic acid (CPP) and cis-4-phosphonomethyl-2-piperidine carboxylic acid (CGS-19755) did not alter DA metabolism and release in several brain regions in the rat and mouse. Intracerebroventricular administration of the competitive NMDA antagonists CPP, CGS-19755, 2-amino-5-phosphonopentanoate, and 2-amino-7-phosphonoheptanoate did not alter rat striatal DA metabolism and release but profoundly reduced cerebellar cyclic GMP (cGMP) levels in the same animals. CPP and CGS-19755 decreased basal cerebellar cGMP levels in the mouse with ED50 values of 6 and 1 mg/kg, i.p., respectively. CPP antagonized the harmaline-induced increases in cGMP levels with an ED50 value of 5.0 mg/kg, i.p. CPP (25 mg/kg, i.p.) also decreased basal cGMP levels in mouse cerebellum for up to 3 h, a result suggesting brain bioavailability and a long duration of NMDA receptor antagonism in vivo. These contrasting patterns suggest that NMDA receptors exert a tonic excitatory tone on the guanine nucleotide signal transduction pathway in the cerebellum while exerting a phasic control over nigrostriatal dopaminergic neurotransmission. These results also indicate that competitive NMDA antagonists, unlike phencyclidine receptor agonists, may not mediate biochemical and behavioral effects via dopaminergic mechanisms.

Analysis of rat brain microdialysate by gas chromatography-high-resolution selected-ion monitoring mass spectrometry

Gas chromatography-high-resolution selected-ion monitoring mass spectrometry was used to analyze catecholamine metabolites in rat brain microdialysate. Dialysate samples were collected in vials containing stable isotope analogues of homovanillic acid (HVA), 3-methoxy-4-hydroxyphenylglycol (MHPG) and 5-hydroxyindoleacetic acid (5HIAA) and analyzed as their trimethylsilyl derivatives. The metabolite levels were monitored at 20-min intervals throughout the time course of the experiment, beginning immediately after surgery and implantation of the dialysis probe and ending 4 h after amphetamine treatment. The levels of HVA were observed to decrease after amphetamine treatment, while those of MHPG and 5HIAA did not change significantly.

Sigma receptors modulate both A9 and A10 dopaminergic neurons in the rat brain: functional interaction with NMDA receptors

The sigma receptor ligands, (+)-pentazocine and (+)-SKF 10,047, were found to increase dopamine metabolism (DOPAC, HVA) and release (3-MT) in both the striatum and olfactory tubercle of the rat, in a dose-dependent manner, after central as well as peripheral administration. The effect of (+)-SKF 10,047 was stereospecific. The increase in dopamine metabolism was not blocked by naloxone pretreatment, excluding an action via opioid receptors. More interestingly, this modulation was blocked by pretreatment with the NMDA receptor antagonist, CPP. Neither sigma ligand exhibited any affinity for D1 or D2 dopamine receptors or for NMDA, PCP or NMDA-associated glycine receptors. Sigma receptors thus appear to modulate dopaminergic function in both A9 and A10 projections. This modulation appears to involve a functional interaction with NMDA receptors or an NMDA-utilizing synapse downstream to neurons modulated by sigma receptors.

Increased release of dopamine in vivo by BMY-14802: contrasting pattern to clozapine

In preclinical studies, BMY-14802 [alpha-(fluorophenyl)-4-(5-fluoro-2-pyramidinyl)-l-piperazine-buta nol], a potent sigma ligand, exhibited a profile similar to clozapine, an atypical antipsychotic agent. Several atypical antipsychotics have previously been demonstrated to increase dopamine (DA) metabolism without altering DA release in vivo, suggesting a potential mechanism for their lack of extrapyramidal side effects. BMY-14802 increased DA metabolism and release while clozapine increased DA metabolism but decreased DA release in the mouse. This is the first demonstration of a sigma ligand mediated DA release in vivo. The lack of extrapyramidal side effects, despite the enhanced DA release in vivo after BMY-14802 suggests that the atypical profile of clozapine can not be explained by its depressant actions on DA release alone.

Interactions of phencyclidine receptor agonist MK-801 with dopaminergic system: regional studies in the rat

Interactions of the potent phencyclidine receptor agonist MK-801 with the dopaminergic system were examined in various brain regions in the rat. MK-801 increased dopamine (DA) metabolism in the pyriform cortex, entorhinal cortex, prefrontal cortex, striatum, olfactory tubercle, amygdala, and septum without affecting DA metabolism in the cingulate cortex and nucleus accumbens. In pyriform cortex and amygdala, MK-801 was more potent than phencyclidine at increasing DA metabolism. Local injections of MK-801 into ventral tegmental area and into the amygdala/pyriform cortex interface indicated that MK-801 may act at the cell body as well as the nerve terminal level to increase DA metabolism and that ongoing dopaminergic neuronal activity is a prerequisite for full drug action.

Selective activation of dopaminergic pathways in the mesocortex by compounds that act at the phencyclidine (PCP) binding site: tentative evidence for PCP recognition sites not coupled to N-methyl-D-aspartate (NMDA) receptors

Several lines of evidence suggest a tight functional coupling between N-methyl-D-aspartate (NMDA) and phencyclidine (PCP) receptors. The effects of PCP receptor agonists (PCP, dexoxadrol, ketamine and MK-801) and NMDA receptor antagonists, cis-4-phosphonomethyl-2-piperidine carboxylic acid (CGS-19755) and 3-(2-carboxypiperizin-4-yl)-propyl-1-phosphonic acid (CPP), have been examined on the metabolism of dopamine in the mesocortex, with a view of studying the coupling between these two receptor systems. Phencyclidine receptor agonists selectively increased the metabolism of dopamine in the mesocortex without affecting the metabolism of dopamine in the striatum. N-Methyl-D-aspartate and the competitive antagonists of NMDA receptors did not effect the metabolism of dopamine, neither did the sigma receptor ligands, 1,3-di-(2-tolyl)guanidine (DTG) and rimcazole. Rimcazole also did not affect the increases in the metabolism of dopamine in the mesocortex, seen after MK-801. These data indicate that dopaminergic neurons in the mesocortex are positively modulated by PCP receptors but tentatively suggest that those recognition sites for PCP are not coupled to NMDA receptors.

Effect of cholecystokinin on acetylcholine turnover and dopamine release in the rat striatum and cortex

The effect of sulfated cholecystokinin (CCK-8S) on acetylcholine turnover (TRACh) and dopamine (DA) release in the rat cerebral cortex and striatum was studied in unanaesthetized animals in vivo. CCK-8S (1 mg/kg s.c.) decreased TRACh in the fronto-parietal cortex but not in the striatum. This effect was prevented by peripheral (10 mg/kg i.p.) but not central (1 microgram i.v.t.) administration of the peripheral CCK receptor antagonist CR 1409. In a separate study, CCK-8S decreased 3-methoxytyramine (3-MT) levels (an index of DA release) in the fronto-parietal cortex and in the striatum. CR 1409 appeared to have a partial agonist action, reducing cortical and striatal 3-MT levels, and only partially reversing the effect of CCK-8S in the striatum. These data indicate that peripheral administration of CCK-8S decrease TRACh in the cortex but not in the striatum and that this action is mediated by peripheral-type CCK receptors possibly located outside the CNS. CCK-8S also reduces DA release in the cortex and in the striatum, and this effect appears to be mediated by a mechanism of action different from that modulating cortical TRACh.

Brain CCK-B receptors mediate the suppression of dopamine release by cholecystokinin

The sulfated octapeptide of cholecystokinin (CCK-8S) and CCK fragments were administered to mice to determine the subtype and central versus peripheral location of the CCK receptor that modulates dopamine release in the neostriatum. Dopamine release was decreased when unsulfated CCK (CCK-8U) or the butoxycarbonyl tetrapeptide of CCK (t-boc-CCK-4) was infused into the brain ventricles but not when injected subcutaneously. These CCK fragments bind to the brain-type (CCK-B) but not alimentary-type (CCK-A) receptor. Centrally or peripherally administered CCK-8S also lowered dopamine release and this action was not blocked by the selective CCK-A receptor antagonist, L 364,718. The increase in dopamine release following amphetamine administration was attenuated by central injections of t-boc-CCK-4, CCK-8U, or CCK-8S, and this action of CCK-8S was not prevented by L 364,718. These data are the first to demonstrate that CCK-B receptors in brain mediate the suppression of dopamine release by cholecystokinin, especially when release is augmented. CCK-B receptor agonists should be useful for the treatment of psychiatric conditions that result from hyperactive dopamine neurons.

Modulation of mesolimbic dopaminergic projections by beta-endorphin in the rat

Intracerebroventricular injection of beta-endorphin stimulated the metabolism of dopamine in a dose-dependent, opiate antagonist-reversible manner. Local injections into the nucleus accumbens also caused similar increases, indicating that the actions of this peptide on mesolimbic dopaminergic projections were occurring at opioid receptor sites within the nucleus accumbens. Tolerance experiments suggested that epsilon opioid receptors may be involved in mediating these effects in the n. accumbens, unlike in the striatum.

Preservation of dopamine release in the denervated striatum

Dopamine metabolism and release were determined in the striata of rats sustaining varying damage to the nigrostriatal dopamine (DA) projection. DA metabolism, inferred from concentrations of dihydroxy-phenylacetic acid (DOPAC) or homovanillic acid (HVA), decreased with DA denervation of more than 20%. Dopamine release, inferred from the concentration of 3-methoxytyramine (3-MT), did not decrease unless the denervation was at least 80%. The amount of 3-MT per surviving neuron exceeded that for DOPAC over most of the denervation range. Thus, striatal DA release is preserved at normal levels with the survival of only 20% of the striatal DA innervation. Decreases in DA release, rather than decreases in DA metabolism or the density of dopamine innervation, coincide with the appearance of behavioral impairments.

NMDA-coupled and uncoupled forms of the PCP receptor: preliminary in vivo evidence for PCP receptor subtypes

1. As reported for many other PCP receptor actions, the pharmacological profile of PCP receptor agonists and NMDA receptor antagonists were similar with regard to their effects on cerebellar cGMP levels in vivo. 2. PCP receptor agonists act to increase mesocortical dopamine (DA) metabolism and release. 3. This receptor action is stereospecific and is both dose- and time-dependent. 4. The actions of PCP on DA metabolism appear to involve PCP receptors both in the ventral tegmental area (VTA) and the cortical nerve terminal regions. 5. In contrast to many other systems which have been studied, competitive NMDA antagonists do not act in a manner similar to PCP agonists, with regard to mesocortical DA metabolism. 6. Sigma receptor ligands and NMDA agonists also do not alter mesocortical DA metabolism. 7. These data suggest that the PCP receptor population which modulates mesocortical dopaminergic neurons is not coupled to NMDA receptors.

Cholecystokinin receptor subtypes and neuromodulation

The sulfated octapeptide of cholecystokinin (CCK-8S) and CCK fragments have been administered to mice to determine the subtype and location of the CCK receptor that modulates the release of dopamine (DA) in brain. 1. Centrally (i.c.v.) or peripherally (s.c.) administered CCK-8S lowers DA release, and to a lesser extent, metabolism, in the neostriatum and olfactory tubercle. 2. DA release is decreased when the CCK-B selective compounds, unsulfated CCK-8 (CCK-8U) or the butoxycarbonyl tetrapeptide of CCK (t-boc-CCK-4), are given i.c.v. but not when injected s.c. 3. The increase in DA release following amphetamine administration is attenuated by i.c.v. but not s.c. injections of t-boc-CCK-4 or CCK-8U and by CCK-8S given via either route. 4. None of the s.c. actions of CCK-8S are prevented by the CCK-A receptor antagonist, L 364,718. CCK-B receptors in brain mediate the suppression by CCK of basal and augmented DA release. CCK-B receptor agonists may be useful for the treatment of psychiatric conditions that result from excessive DA release.

Differential effects of phencyclidine (PCP) and ketamine on mesocortical and mesostriatal dopamine release in vivo

The interactions of phencyclidine (PCP) with the mesocortical dopaminergic system were of interest because of the putative role of this pathway in the etiology of schizophrenia. In the present investigation we examined the effects of PCP, and PCP-receptor agonist, ketamine, on dopamine (DA) release by measuring the levels of 3-methoxytyramine (3-MT), the only DA metabolite which is a reliable indicator of DA release in vivo. PCP increased DA release in the amygdala, pyriform and prefrontal cortices, while ketamine was less potent than PCP in this respect. In contrast to the changes in DA release in the cortical regions, ketamine decreased DA release in striatum, while PCP did not change DA release.

Selected-ion monitoring gas chromatographic-mass spectrometric analysis of catecholamines: enhancement of sensitivity by a simple clean-up step on Sephadex G-10

The sensitivity of catecholamines using selected-ion monitoring gas chromatography-mass spectrometry (SIM GC-MS) has been enhanced by employing a simple clean-up step using Sephadex G-10 columns. This procedure allows for the detection of extremely small amounts (1-10 pg) of biogenic amines (e.g., epinine) which corresponds to a 25-fold increase in detection limits compared to electron ionization GC-MS or high-performance liquid chromatography with electrochemical detection (HPLC-ED). The SIM GC-MS assay was used to monitor the dopamine-beta-hydroxylase-mediated conversion of epinine d6 to epinephrine d6 in rat hypothalamus and brainstem in vitro and the results were compared to those obtained by HPLC-ED.

Cholecystokinin attenuates basal and drug-induced increases of limbic and striatal dopamine release

Subcutaneous administration to mice of the sulfated octapeptide of cholecystokinin (CCK; 0.2-1 mg/kg) lowered dopamine release and metabolism in the caudate-putamen and frontal cortex in a dose- and time-related manner. Twelve-fold higher doses of CCK were required to lower dopamine release and metabolism in the olfactory tubercle. Amphetamine-induced increases in dopamine release but not metabolism in the caudate-putamen and olfactory tubercle were attenuated in a dose-related manner by CCK. Increases in dopamine release and metabolism following haloperidol were also attenuated by CCK. These data are consistent with the potential antipsychotic action of CCK receptor agonists. CCK appears to be a suppressor of striatal, limbic and cortical dopamine release, especially when release is augmented.

Catecholamines and their metabolites

The research on biosynthesis, physiology, pharmacology, regulation and degradation of catecholamines has continuously increased for more than 50 years. This is not unexpected because of the fact that catecholamines are involved in so many life processes such as nerve conduction, blood circulation and hormone regulations in health and disease. This demands that methods for their determination should be improved, and in fact during the years a number of analytical methods have been published. About 20 years ago radioenzyme techniques with thin-layer chromatographic (TLC) separation of radiolabelled catecholamine derivatives were developed which greatly contributed to our knowledge of physiological concentrations of catecholamines in biological media, particularly in plasma and brain. Radioimmune methods were successful for analysis of a number of analytes, but for catecholamines radioimmunoassays developed slowly. We believe that the greatest potential for radioimmunochemical methods lies in their ability to localize catecholamines and metabolites at the cellular and subcellular levels. With the advent of gas chromatographic-mass spectrometric (GC-MS) and high-performance liquid chromatographic (HPLC) procedures analysis of catecholamines improved greatly., The equipment for GC-MS is expensive and requires technical skillfulness, but in experienced hands a lot of new biological data have emerged. An outstanding quality with GC-MS is that the method offers the ability to identify unknown compounds and is relatively free from interferences from extraneous compounds. In comparison with GC-MS, HPLC is versatile and has gained a widespread use. Applications for research in the catecholamine field are numerous. In general, the sensitivity and specificity are satisfactory with HPLC, but it should be borne in mind that a number of pitfalls can obscure the results. This involves both sample handling, clean-up and chromatographic procedures. At present, HPLC is the most expanding field in chromatographic determination of catecholamines and their metabolites. This is particularly the case for HPLC with electrochemical detection which has revolutionized our analytical potential in this field. These chromatographic procedures continue to develop. The prerequisites for further improved methods such as capillary zone electrophoresis and combined HPLC-MS are at hand and hopefully will soon come into more general use for analysis of catecholamines in biological samples.

Presynaptic inhibition of nigrostriatal dopamine release in the mouse: lack of cross tolerance between apomorphine, GBL and CGS 10746B

Acute parenteral injections of apomorphine, gamma-butyrolactone (GBL) and CGS 10746B decreased dopamine release in the mouse nigrostriatal pathway as evidenced by decreases in striatal 3-methoxytyramine levels. In a 7 day treatment paradigm, the effects of acute apomorphine, GBL and CGS 10746B were unaltered in animals treated b.i.d. with GBL (500 mg/kg, i.p.). In contrast, the actions of acute CGS 10746B expressed a complete tolerance in mice treated b.i.d. with CGS 10746B (20 mg/kg, i.p.), while the actions of acute apomorphine or GBL were similar in the chronic saline and chronic CGS 10746 groups. These data show that the inhibition of striatal dopamine release by CGS 10746B is susceptible to tolerance. In addition, the lack of cross tolerance between GBL, apomorphine and CGS 10746B suggests independent sites of action for these agents in inhibiting dopamine release.

Heterogeneous rotational responsiveness in 6-hydroxydopamine-denervated rats: pharmacological and neurochemical characterization

Qualitative differences in pharmacological responsiveness to various types of dopamine agonists have been reported in rats that have undergone unilateral 6-hydroxydopamine (6-OHDA)-induced denervation of the nigro-striatal pathway. The present experiments further characterize these differences, pharmacologically and neurochemically. Rats were classified as having high rotational sensitivity (0.03 mg/kg SC apomorphine sufficient to induce more than 100 rotations/20 min) or low sensitivity (0.3 mg/kg SC apomorphine required to meet this criterion). High sensitivity rats showed marked contralateral rotational behavior (approximately 150 rotations/20 min) in response to apomorphine (ED50 = 0.08 mg/kg IP), CGS 15855A (ED50 = 0.07 mg/kg), CGS 15873A (ED50 = 0.43 mg/kg), (+)-3-PPP (ED50 = 2.3 mg/kg), (-)-3-PPP (ED50 = 0.87 mg/kg) and quinpirole (peak effective dose, 0.03 mg/kg). In low sensitivity rats, 3- to 10-fold higher doses of apomorphine induced a maximal rate of rotational behavior, but only partial effects were produced by quinpirole, CGS 15855A, CGS 15873A, (+)-3-PPP, and (-)-3-PPP (40-80 rotations/20 min). Because apomorphine is a nonselective D1 and D2 agonist, it is proposed that activation of either D1 or D2 receptors suffices to induce high rates of rotation in high sensitivity rats, whereas in low sensitivity rats, D1 or D2 agonism alone induces submaximal rotation rates. The ipsilateral rotational behavior induced by d-amphetamine was more pronounced and occurred at lower doses in the high-sensitivity rats. Striatal dopamine depletion on the lesioned side did not differ between the groups, but low sensitivity rats showed two-fold higher DOPAC/DA ratios on the lesioned side than did high-sensitivity rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynamics of the striatal 3-MT pool in rat and mouse: species differences as assessed by steady-state measurements and intracerebral dialysis

Analysis of dopamine and 3-MT dynamics in the striatum and in striatal dialysates, after pargyline treatment, indicates that the 3-MT pool in the rat is smaller but more dynamic than that in the mouse. The fractional rate constants calculated for the extracellular 3-MT and dopamine pools also indicate that a larger proportion of released dopamine is metabolized to 3-MT in the rat, or alternatively, 3-MT is cleared more slowly from the mouse striatum. Our striatal dialysis data also support previous in vivo voltammetry studies which have demonstrated that the fractional rate constant of the extracellular dopamine pool is at least 10-fold greater than that of the total striatal dopamine pool. These data suggest that multiple striatal dopamine pools exist and that a minimum of 20 to 30% of the extracellular DA pool is metabolized to 3-MT.

Reversal of the actions of morphine on mesocortical dopamine metabolism in the rat by the kappa agonist MR-2034: tentative mu-2 opioid control of mesocortical dopaminergic projections

Morphine was shown to enhance dopamine metabolism, as assessed by increased dihydroxyphenylacetic acid measurements, in the mesocortical dopaminergic projections of the rat (cingulate, pyriform and prefrontal cortices). In contrast, the kappa agonist MR-2034 did not alter dopamine metabolism but did antagonize the actions of morphine. Similar antagonism of the actions of morphine were noted in the striatum and olfactory tubercle. These data suggest that the mesolimbic and mesocortical dopaminergic projections may possess a mu-2 opioid receptor regulation as previously defined for the nigrostriatal pathway.

Injections of deuterated tryptamine into the nucleus accumbens of the rat: effects on locomotor activity and monoamine metabolism

Previous studies have shown that the systemic injection of tryptamine stimulates locomotion in rats and that the nucleus accumbens, a region involved in locomotion, contains the largest concentrations of binding sites for tryptamine in the brain of the rat. The present study examined the behavioral and neurochemical effects of bilateral injections into the accumbens of a deuterated analog of tryptamine, a,a-[2H]tryptamine. Injections of 25 micrograms a,a-[2H]tryptamine increased movements in rats at 25-70 min after injection and increased vertical (rearing) activity at 25-40 min. Injections of 50 micrograms of a,a-[2H]tryptamine produced a transient suppression of movement and vertical activity at 5-15 min, followed by increases in these activities at 40-65 min after injection that were comparable to the increases elicited by 10 micrograms of d-amphetamine. At 30 min after the injection of 50 micrograms a,a-[2H]tryptamine the concentration of dopamine in the nucleus accumbens was increased by 87%, and was preceded by a transient decrease in the level of the metabolite of dopamine homovanillic acid. The levels of 5-hydroxytryptamine and its major metabolite, 5-hydroxyindoleacetic acid in the nucleus accumbens were not changed. Thus, a,a-[2H]tryptamine may interact with tryptamine receptors in the nucleus accumbens to modulate locomotor behavior through mesolimbic dopamine neurons.

Intracerebral dialysis: direct evidence for the utility of 3-MT measurements as an index of dopamine release

Intracerebral dialysis was used to monitor the in vivo efflux of striatal dopamine (DA), homovanillic acid (HVA), dihydroxyphenylacetic acid (DOPAC) and 3-methoxytyramine (3-MT) in the pentobarbital anesthetized rat. In untreated rats, there were low levels of extra-cellular DA and 3-MT which were increased 15-fold by treatment with amphetamine. Under basal and drug-stimulated conditions, 3-MT concentrations were maintained at approximately 30% of the extracellular DA levels. These data agree with in vivo turnover estimates which indicate that 20 to 30% of DA turnover is through the 3-MT pool in the striatum. In contrast, extracellular DOPAC and HVA levels were reduced only slightly by amphetamine and with a delayed onset. Our data support the hypothesis that striatal DOPAC is an accurate index of intraneuronal DA metabolism and that 3-MT is an index of the extracellular concentration of DA.

Agonist action of the agonist/antagonist analgesic butorphanol on dopamine metabolism in the nucleus accumbens of the rat

The action of butorphanol, an opiate agonist/antagonist, was studied on dopamine (DA) metabolism in several mesocortical and mesolimbic areas and compared with its effects on the nigrostriatal DA pathway. While butorphanol had a bell-shaped dose-response relationship for elevation of DA metabolites in the striatum, it had no action on DA metabolites in the entorhinal, prefrontal, pyriform and cingulate cortices and in the olfactory tubercle. In all of these areas morphine stimulated dopamine metabolism (except for the entorhinal cortex). In contrast, in the nucleus accumbens, butorphanol increased the levels of dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 3-methoxytyramine (3-MT) with no increase in DA steady state levels. This effect was reversible by both opiate antagonists, naloxone and WIN 44441-3 and appears to be mu-opioid receptor-mediated.

Modulation of in vivo dopamine release by D2 but not D1 receptor agonists and antagonists

The capacity of D1 and D2 agonists and antagonists to regulate the in vivo release and metabolism of dopamine (DA) in mesolimbic and nigrostriatal DA neurons of the mouse was determined using gas chromatographic and mass fragmentographic (GC-MF) analysis. DA release was inferred from levels of 3-methoxytyramine (3-MT) and DA metabolism was inferred from levels of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). DA release was increased by the D2 antagonists haloperidol and metoclopramide but not by the D1 antagonists SCH 23390 and SKF 83566. DA metabolism was increased by each of the four antagonists but to a greater extent with the D2 antagonists. The D2 agonists CGS 15855A and LY 171555 decreased DA release whereas the D1 agonist SKF 38393, at relatively high doses, only slightly affected DA release. Each of the three agonists decreased DA metabolism but again metabolism was more affected by the D2-selective drugs. The in vivo release of DA from mesolimbic and neostriatal DA neurons appears to be modulated by D2 but not by D1 receptors, whereas both receptor types can modulate DA metabolism.

Dopamine autoreceptor agonists including CGS 15855A decrease dopamine release and metabolism in mouse brain

The ability of dopamine autoreceptor agonists to suppress the in vivo release or metabolism of dopamine in mouse brain was determined by measuring steady state levels of 3-methoxytyramine (3-MT) or dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), respectively. These experiments provide the first neurochemical evidence for dopamine autoreceptors in the mouse. (-)N-n-propylnorapomorphine, apomorphine, (+)-3-PPP, TL-99, and the novel dopamine autoreceptor agonist CGS 15855A each decreased 3-MT levels at doses that approximated their potency in the gamma-butyrolactone model. CGS 15855A suppressed dopamine release and metabolism to the same extent in the rat and mouse neostriatum. Generally, agonist-induced decreases in 3-MT levels were obtained to a greater extent or with lower doses than were changes in DOPAC or HVA. The autoreceptor efficacy of CGS 15855A was confined to the (+) and not the (-) optical isomer. Consecutive injections of CGS 15855A did not induce an acute tolerance to its actions but instead prolonged for at least 3.5 h the suppression of dopamine metabolism and release. The release and metabolism of dopamine in mouse limbic and striatal regions is regulated by autoreceptors with a pharmacological specificity that is similar to autoreceptors of the rat.

In vivo assessment of dopamine and norepinephrine release in rat neocortex: gas chromatography-mass spectrometry measurement of 3-methoxytyramine and normetanephrine

A new method with the sensitivity and specificity required to measure regional levels of 3-methoxytyramine (3-MT) and normetanephrine (NMN) in the rat cortex is described. The method utilizes a liquid ion exchanger to isolate the parent amines, dopamine (DA) and norepinephrine (NE), along with their methylated metabolites. These samples are derivatized and analyzed by negative ion gas chromatography-mass spectrometry. Using this method, we examined a number of drug actions on steady-state levels as well as pargyline-induced increases in 3-MT and NMN. In the prefrontal cortex, cingulate cortex, striatum, and olfactory tubercle, nomifensine was found to increase 3-MT steady-state levels and accumulation rates. Similar actions of this drug were observed in the cingulate and prefrontal cortices with NMN. In contrast, clonidine decreased cortical NMN levels and accumulation. A unique action was observed with haloperidol, in that both 3-MT levels and accumulation after pargyline were increased in the nigrostriatal and mesolimbic dopaminergic projections, whereas only the accumulation rates were accelerated in the mesocortical projections. In summary, our data indicate that this new assay is a useful approach for the in vivo evaluation of DA and NE release in cortical regions of the rat. This approach is unique in that no surgery, restraint, or anesthetic is required, thereby permitting more complicated experimental paradigms to be utilized.

Time course of adaptations in dopamine biosynthesis, metabolism, and release following nigrostriatal lesions: implications for behavioral recovery from brain injury

Alterations in neostriatal dopamine metabolism, release, and biosynthesis were determined 3, 5, or 18 days following partial, unilateral destruction of the rat nigrostriatal dopamine projection. Concentrations of dopamine and each of its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 3-methoxytyramine (3-MT) were markedly decreased in the lesioned striata at 3, 5, or 18 days postoperation. The decline in striatal high-affinity [3H]dopamine uptake closely matched the depletion of dopamine at 3 and 18 days postoperation. However, neither DOPAC, HVA, nor 3-MT concentrations were decreased to as great an extent as dopamine at any time following lesions that depleted the dopamine innervation of the striatum by greater than 80%. In these more severely lesioned animals, dopamine metabolism, estimated from the ratio of DOPAC or HVA to dopamine, was increased two- to four-fold in the injured hemisphere compared with the intact hemisphere. Dopamine release, estimated by the ratio of 3-MT to dopamine, was more increased, by five- to sixfold. Importantly, the HVA/dopamine, DOPAC/dopamine, and 3-MT/dopamine ratios did not differ between 3 and 18 days postlesioning. The rate of in vivo dopamine biosynthesis, as estimated by striatal DOPA accumulation following 3,4-dihydroxyphenylalanine (DOPA) decarboxylase inhibition with NSD 1015, was increased by 2.6- to 2.7-fold in the surviving dopamine terminals but again equally at 3 and 18 days postoperation. Thus, maximal increases in dopamine metabolism, release, and biosynthesis occur rapidly within neostriatal terminals that survive a lesion. This mobilization of dopaminergic function could contribute to the recovery from the behavioral deficits of partial denervation by increasing the availability of dopamine to neostriatal dopamine receptors. However, these presynaptic compensations are not sufficient to account for the protracted (at least 3-week) time course of sensorimotor recovery that has been observed following partial nigrostriatal lesion.

Opiate actions on mesocortical dopamine metabolism in the rat

The actions of parenteral morphine were examined with regard to dopamine metabolism in the mesocortical dopaminergic pathways of the rat. The effects of morphine on dopamine metabolism in the prefrontal, cingulate, pyriform and entorhinal cortices were compared with the actions of morphine on the metabolism of dopamine in the striatum and olfactory tubercle. In all tissues, except the entorhinal cortex, morphine significantly elevated the dopamine metabolites dihydroxphenylacetic acid and homovanillic acid. These data, along with previous studies of various pharmacological agents, clearly indicate that the mesocortical dopaminergic projections possess unique opioid and non-opioid regulatory inputs.

Determination of acidic catecholamine metabolites in plasma and cerebrospinal fluid using gas chromatography-negative-ion mass spectrometry

A method for the assay of acidic catecholamine metabolites in biological fluids using capillary gas chromatography--electron-capture negative-ion mass spectrometry is described. The method combines acetylation of phenolic hydroxy groups in buffered aqueous solution followed by pentafluorobenzyl ester formation and acetylation of aliphatic hydroxy groups under anhydrous conditions. The resulting per-O-acetyl carboxypentafluorobenzyl esters provided excellent negative-ion mass spectra with intense and diagnostic anions. The sensitivity of the analysis using electron-capture negative-ion mass spectrometry exceeds that using electron-impact mass spectrometry by two to three orders of magnitude. Analysis of acidic catecholamine metabolites in human lumbar cerebrospinal fluid and plasma were performed with good precision (sigma rel less than 5%) at the low nanomoles per litre level.

CGS 10746B: an atypical antipsychotic candidate that selectively decreases dopamine release at behaviorally effective doses

CGS 10746B, a benzothiadiazepine, has a behavioral profile in mice and monkeys similar to the atypical antipsychotic clozapine. Unlike clozapine, CGS 10746B suppresses dopamine neuron firing rates and, when administered at behaviorally effective doses by the oral or intraperitoneal route, decreases neostriatal dopamine release without changing dopamine metabolism or occupying D2 receptors. CGS 10746B is the first atypical antipsychotic candidate that selectively decreases dopamine release.

Effects of kappa opiate agonists on neurochemical and neuroendocrine indices: evidence for kappa receptor subtypes

Four kappa opiate agonists, U-50488H, MR-2034, EKC and tifluadom, elevated plasma corticosterone and decreased plasma TSH in a dose-dependent manner. These effects were naloxone-reversible. However, WIN 44441-3, a long acting narcotic antagonist, was unable to reverse the effects of U-50488H and MR-2034 upto doses of 5 mg/kg. U-50488H and MR-2034 but not tifluadom or EKC, also increased levels of DOPAC and HVA in the olfactory tubercle. This effect was also naloxone-reversible but not WIN 44441-3 reversible. Tifluadom and EKC did not increase DOPAC and HVA. The differential responses of the tested kappa agonists to WIN 44441-3 antagonism and dopamine metabolism in A10 neurons suggest that the kappa agonists can be separated into two groups. This is the first physiological evidence suggestive of kappa opioid receptor subtypes.

Metabolism of catecholamines in the developing spinal cord of the rat

The metabolism of 3,4-dihydroxyphenylethylamine (DA, dopamine) and norepinephrine (NE) both normally, and after the administration of levo-3,4-dihydroxyphenylalanine (L-DOPA), has been studied in several regions of the developing spinal cord of the rat from fetal day (FD) 16 to the young adult stage. During late fetal (from FD 16) and most of neonatal life [to neonatal day (ND) 20], dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were either just detectable or present in very low concentration in all regions in the untreated developing rat. However, the developing spinal cord possesses an enormous capacity to metabolize the large amounts of DA synthesized from injected L-DOPA. At the end of 1 h after 100 mg/kg i.p. of L-DOPA, DOPAC and HVA are 54 +/- 14 (n = 5) and 16 +/- 5 (n = 5) nmol/g, respectively, in the thoracic zona intermedia in the 12-h-old (ND 0.5) rat. This metabolic capability is already highly developed as early as FD 16, peaks during the first half of neonatal life (ND 4 for DOPAC, and ND 15 for HVA), and is considerably reduced toward the end of neonatal life (approximately ND 28) and in the young adult. Control experiments suggest that a substantial part of this synthesis (from L-DOPA) and metabolism of DA occurs in elements other than the descending monoaminergic nerve fibers. By comparison, the synthesis and metabolism of NE develop more slowly, peak in the latter half of neonatal life, and then decline to the level found in the young adult.(ABSTRACT TRUNCATED AT 250 WORDS)

Some factors affecting striatal 3-methoxytyramine concentrations in the mouse and rat

Apomorphine, a DA agonist, at a dose of 2 mg/kg, produced a rapid decline in 3-MT concentrations in the rat striatum; this is consistent with a reduction in the firing rate of nigrostriatal neurons. The injection of a 12.5 mg/kg dose of phenylethylamine transiently increased 3-MT concentrations in the mouse striatum. A more profound increase was produced by this dose in the rat striatum. Cocaine (5 mg/kg) produced a decrease in DOPAC concentrations in both species thus suggesting that the re-uptake of DA from the synaptic cleft in both species was very similar. Amfonelic acid, however, produced a different profile in each species. The concentration of 3-MT is larger in the mouse striatum as a result of several possible mechanisms: the higher percentage of MAO isoenzyme B in the mouse brain (3-MT is a preferred substrate of MAO isoenzyme A) and/or due to differences in the clearance mechanisms for 3-MT produced extraneuronally - with the mouse having a less avid clearance system either for DA or for 3-MT.

Benzodiazepines and GABAergic regulation of nigrostriatal neurons: lack of tolerance

Decreases of 40 to 50% in striatal dopamine release by diazepam in doses above 5 mg/kg were elicited. Similar actions were observed with clonazepam and nitrazepam. No tolerance to these actions was evident after 3 weeks of chronic treatment. These data are consistent with a potent inhibitory GABAergic regulation of nigrostriatal dopaminergic neurons.

The effects of administration of meta-tyramine and para-tyramine on dopamine and its metabolites in the rat striatum

Para-tyramine administration decreased the release of dopamine as indicated by the decline in 3-MT concentrations, increased HVA concentrations at 30 and 60 min and decreased DA concentrations at the same times. DOPAC concentrations declined after 60 min. Meta-tyramine reduced the synthesis of dopamine thus causing a decrease in the concentrations of all its metabolites by 60 min post injection. The failure of the deaminated products of the tyramines to affect the concentrations of dopamine and its metabolites suggested that the effects produced by either meta or para-tyramine were due to the amines and not due to interference with various transport mechanisms. Para-tyramine and meta-tyramine may achieve their actions on dopamine neurotransmission by different mechanisms. Para-tyramine may act as a partial agonist reducing DA release extraneuronally (the decrease in 3-MT levels) or by displacing DA intraneuronally as evidenced by the decline in DA concentrations or increase in HVA concentrations. Meta-tyramine appears to inhibit the synthesis of dopamine.