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Biomedical subjects

A Saria

Publications and source records attributed to A Saria.

At least 19 recordsLinked to original sources
PubMed2003

Secretoneurin promotes pertussis toxin-sensitive neurite outgrowth in cerebellar granule cells.

The neuropeptide secretoneurin (SN) is an endoproteolytic product of the chromogranin secretogranin II. We investigated the effects of SN on the differentiation of immature cerebellar granule cells derived from the external granular layer (EGL). Secretoneurin caused concentration-dependent increases in neurite outgrowth, reflecting differentiation. The maximum effect was reached at a concentration of 100 nm SN. Secretoneurin immunoneutralization using specific antiserum significantly decreased neurite outgrowth; however, neurite morphology was altered. An affinity chromatography-purified antibody significantly inhibited the outgrowth response to SN (p < 0.001) without altering the morphology. Binding studies suggest the existence of specific G-protein-coupled receptors on the surface of monocytes that recognize SN. Assuming that SN promotes neurite outgrowth in EGL cells by acting through a similar G-protein-coupled mechanism, we treated SN-stimulated EGL cultures with pertussis toxin. Exposure to pertussis toxin (0.1 micro g/mL) showed a significant inhibition of the SN-induced outgrowth. To establish a second messenger pathway we used the protein kinase C inhibitor staurosporine. We found that EGL cell viability was not enhanced following chronic SN treatment for 24 h. These data indicate that SN is a novel trophic substance that can affect cerebellar maturation, primarily by accelerating granule cell differentiation through a signalling mechanism that is coupled to pertussis toxin-sensitive G-proteins.

Animals↗
PubMed2003

Intravenous drug injection habits: drug users' self-reports versus researchers' perception.

The present study was designed to obtain human data on the speed of intravenous (i.v.) injection of cocaine, heroin, and morphine as well as on the rate of onset of their subjective effects and their duration in order to improve the accuracy of animal and human experimental models of i.v. drug abuse. To that end, a questionnaire was submitted both to clients of a substitution therapy outpatient clinic and to members of the drug abuse research community. It was found that i.v. drug abusers injected cocaine, heroin, or morphine much faster and also experienced the drug effects much faster than assumed by the drug abuse researchers. The time course of the reemergence of craving was also greatly misjudged by the researchers. On the other hand, the i.v. drug users' self-reports were internally consistent and corresponded well to data obtained in several different human behavioral laboratories. Interestingly, more than half of the i.v. drug users reported that injection speed was not important when injecting cocaine (57%), heroin (72%) or morphine (73%) under conditions that guarantee a maximum effect, suggesting that the rate of the rise in the brain concentration of a drug of abuse is less important for its reinforcing effect and, thus, for its abuse liability, than previously assumed, at least within the time frame of an i.v. drug injection.

Adult↗
PubMed2001

Intravenous administration of ecstasy (3,4-methylendioxymethamphetamine) enhances cortical and striatal acetylcholine release in vivo.

The effect of intravenous administration of 3,4-methylendioxymethamphetamine (MDMA), in a range of doses (0.32-3.2 mg/kg) that have been shown to maintain self-administration behaviour in rats, on in vivo acetylcholine release from rat prefrontal cortex and dorsal striatum was studied by means of microdialysis with vertical concentric probes. Intravenous administration of MDMA dose-dependently increased basal acetylcholine release from the prefrontal cortex to 57+/-21%, 98+/-20%, 102+/-7% and 141+/-14% above baseline, at doses of 0.32, 0.64, 1.0 and 3.2 mg/kg, respectively. MDMA also stimulated striatal acetylcholine release at the dose of 3.2 mg/kg i.v. (the maximal increase being 32+/-3% above baseline) while at the dose of 1 mg/kg i.v., MDMA failed to affect basal acetylcholine output. Administration of MDMA also dose-dependently stimulated behaviour. The results of the present study show that MDMA affects measures of central cholinergic neurotransmission in vivo and suggest that at least some of the psychomotor stimulant actions of MDMA might be positively coupled with an increase in prefrontal cortical and striatal acetylcholine release.

Acetylcholine↗
PubMed2001

Lack of reinforcing effect of the benzodiazepine and tricyclic antidepressant combination of diazepam and dothiepin.

Fixed combinations of a tricyclic antidepressant (TCA) with a benzodiazepine (BZD) for the treatment of depressive syndromes enjoy remarkable acceptance among patients and prescribing physicians. In order to investigate if the widespread use of one such fixed TCA-BZD combination might be due to its high positive reinforcing effect, we tested each drug alone and in combination in an operant conditioning paradigm (fixed ratio 1 time-out 150 s) of intravenous self-administration in rats and compared their reinforcing effects to that of cocaine. Diazepam proved to be of only moderate reinforcing strength. Dothiepin alone was ineffective as a reinforcer but essentially abolished the reinforcing effect of diazepam when given in combination with it. These data indicate that the widespread acceptance of the fixed diazepam-dothiepin combination by the therapeutic community is not due to an increase in the positive reinforcing effect of diazepam by dothiepin but that, in contrast, addition of dothiepin might even decrease diazepam's moderately positive reinforcing effect.

Animals↗
PubMed2001

Reinforcing effects of MDMA ("ecstasy") in drug-naive and cocaine-trained rats.

3,4-Methylenedioxymethamphetamine (MDMA; "ecstasy") is one of the most prevalent illegal drugs of abuse among European adolescents, a population not generally experienced with respect to "hard" drugs such as cocaine. We, therefore, determined the reinforcing effect of intravenously self-administered MDMA in a fixed ratio 1 time-out 150 s schedule of reinforcement in rats that were truly drug naive and compared it to cocaine-trained rats. The reinforcing effect of MDMA [0.032-10 mg/(kg.injection)] did not differ between drug-naive rats and cocaine-trained ones. MDMA sensitized the animals to its own rate-increasing effect but not to that of cocaine. When MDMA was tested after cocaine, there was no carryover of cocaine's reinforcing effect to that of MDMA, suggesting that MDMA and cocaine produce distinct interoceptive stimuli in rats.

Animals↗
PubMed2000

Alterations within the endogenous opioid system in mice with targeted deletion of the neutral endopeptidase ('enkephalinase') gene.

The biological inactivation of enkephalins by neutral endopeptidase (enkephalinase, NEP, EC3.4.24.11) represents a major mechanism for the termination of enkephalinergic signalling in brain. A pharmacological blockade of NEP-activity enhances extracellular enkephalin concentrations and induces opioid-dependent analgesia. Recently, knockout mice lacking the enzyme NEP have been developed [Lu et al., J. Exp. Med. 1995;181:2271-2275]. The present study investigates the functional consequences and biochemical compensatory strategies of a systemic elimination of NEP activity in these knockout mice. Using biochemical and behavioural tests we found that the lack of NEP activity in brain is not compensated by enhanced activities of alternative enkephalin-degrading enzymes. Also no change in enkephalin biosynthesis was detectable by in situ methods quantifying striatal proenkephalin-mRNA levels in NEP-deficient mice compared with wildtype. Only a 21% reduction of mu receptor density in crude brain homogenates of NEP knockout mice was observed, while delta- and kappa-opioid receptor densities were unchanged. This receptor downregulation was also confirmed functionally in the hot-plate paradigm. NEP knockouts developed normally, but showed enhanced aggressive behaviour in the resident-intruder paradigm, and altered locomotor activity as assessed in the photobeam system. Thus, although NEP plays a substantial role in enkephalinergic neurotransmission, the biochemical adaptations within the opioid system of NEP-deficient mice are of only modest nature.

Aggression↗
PubMed2000

Retinoic acid treatment enhances the acetylcholine contents in the human teratocarcinoma cell line NTera-2.

Human NTera-2/clone D1 teratocarcinoma cells are induced by retinoic acid (RA) to differentiate into postmitotic cells with morphological and biochemical characteristics of embryonic human neurones. Currently only limited information concerning peptide-contents and neurotransmitter pools of these cells is available. Zeller and Strauss [Int. J. Dev. Neurosci. 1995;13(5):437] described an increase in choline acetyltransferase (ChAT) activity in RA-treated, but not in untreated NTera-2 cells, suggesting the induction of a cholinergic phenotype during treatment with RA. In the present study we investigated the effect of RA-differentiation on the amount of the neurotransmitters acetylcholine (ACh), and dopamine in NTera-2 in order to specify the transmitter phenotype induced by RA-differentiation. We found that a 4-week treatment of NTera-2 cells with 10 microM RA markedly increased the ACh-content of these cells, while dopamine levels were unchanged. Depolarisation with potassium (60 mM) enhanced ACh-outflow in the differentiated cells in a Ca(++) dependent way. Also neuropeptides like substance P and NPY were detectable in the undifferentiated NTera-2 cells, while vasointestinal peptide (VIP) could not be found in either precursor or RA-differentiated cells. Differentiation was accompanied by a marked reduction of neutral endopeptidase enzyme activity and aminopeptidase activity. From these observations it was concluded that RA induces a cholinergic neurochemical differentiation of this human teratocarcinoma cell line, and that these cells might provide a model system to investigate cholinergic properties of human origin.

Acetylcholine↗
PubMed2000

Neutral endopeptidase and alcohol consumption, experiments in neutral endopeptidase-deficient mice.

Alcohol consumption was investigated in mice which were rendered deficient in the peptide-degrading enzyme neutral endopeptidase (EC 3.4.24.11) (NEP-/-) by gene targeting and compared to alcohol consumption in corresponding wild type mice (NEP+/+). Mice were offered a free choice to drink tap water or 10% alcohol. The NEP-/- mice consumed significantly more alcohol ( approximately 42%) than the NEP+/+ mice, whereas no significant differences were observed in the total fluid consumption. The daily food consumption of alcohol naive NEP-/- animals was elevated ( approximately 29%). Furthermore, the activities of peptidases closely related to neutral endopeptidase were analysed ex vivo in several brain regions from NEP-/- and NEP+/+ mice not treated with alcohol. There was no obvious compensation for the total loss of neutral endopeptidase by the functionally related peptidases angiotensin-converting enzyme and aminopeptidase N. In vitro, the degradation of exogenously applied [Leu(5)]enkephalin was not reduced in membrane preparations of those brain regions assayed in NEP-/- mice. A small reduction in [Leu(5)]enkephalin degradation was detected in striatal membrane preparations of NEP-/- mice, if aminopeptidase N was additionally blocked by bestatin or amastatin.

Alcohol Drinking↗
PubMed2000

Signal transduction efficacy of the highly potent mu opioid agonist 14-methoxymetopon.

In search of a truly high-efficacy (i.e., tau > 100) mu opioid analgesic, we determined the efficacy (tau) and apparent in vivo affinity (KA) of the high-potency alkoxymorphinan 14-methoxymetopon. However, in the present study, 14-methoxymetopon's efficacy proved to be only 1.5-fold higher than that of morphine (tau, 19 vs. 12). KA values were 2,900 nmol/kg for 14-methoxymetopon and 46,000 nmol/kg for morphine (Ki for [3H]DAMGO binding, 0.33 vs 3.4 nmol/l). Thus, the 24-fold higher potency of methoxymetopon could be fully accounted for by its 16-fold higher apparent in vivo affinity and its only 1.5-fold higher efficacy. Furthermore, the 10-fold higher affinity of 14-methoxymetopon for the mu opioid receptor - as previously determined in radioligand binding assays - was confirmed in the present behavioral tests of thermal antinociception.

Analgesics, Opioid↗
PubMed2000

3,4-Methylenedioxymetamphetamine (ecstasy) induces c-fos-like protein and mRNA in rat organotypic dorsal striatal slices.

3,4-Methylenedioxymetamphetamine (MDMA, "ecstasy") is an increasingly abused drug, which has significant effects on the dopamine system in the striatum. The isolated single organotypic slice model allows investigation of the effects of drugs of abuse on the expression of transcription factors in the striatum without dopaminergic and glutamatergic interactions. In this study the effects of MDMA on the expression of c-fos mRNA by in situ hybridization as well as the c-fos-like protein by immunohistochemistry in isolated dorsal striatum was investigated. It was shown that 100 microM MDMA induced c-fos mRNA expression 30 min after treatment. Expression of c-fos-like protein was transiently detected 3 h afterwards. The c-fos expression was inhibited by MK 801 and metoclopramide, indicating the involvement of dopaminergic D2 receptors and glutamatergic NMDA receptors. The dopaminergic D1 receptor antagonist SCH 23390 did not affect c-fos expression. We conclude that MDMA treatment leads to the induction of c-fos expression in isolated rat striatal slices. This effect is independent of extrinsic neuronal circuitry and seems to be associated with direct interactions between MDMA and the dopamine/glutamate receptor system.

Animals↗
PubMed2000

Margatoxin and iberiotoxin, two selective potassium channel inhibitors, induce c-fos like protein and mRNA in rat organotypic dorsal striatal slices.

The isolated single organotypic slice model allows to investigate the effects of drugs and toxins on the expression of transcription factors in the striatum without dopaminergic and glutamatergic interactions. In this study the effects of margatoxin and iberiotoxin on the expression of c-fos mRNA by in situ hybridization as well as on c-fos like protein by immunohistochemistry in isolated dorsal striatum after 10 days in culture were investigated. C-fos mRNA dose-dependently increased 30 min after incubation with margatoxin and iberiotoxin. Expression of c-fos like protein was transiently detected 3h afterwards. This effect is independent from extrinsic neuronal circuitry as dopamine neurons were found to be absent in the cultured slices. It is concluded that inhibition of voltage-gated as well as calcium-activated (Slo) potassium channels leads to activation of gene transcription in striatal neurons which may trigger long-term changes in transmitter plasticity.

Animals↗
PubMed2000

MDMA ('ecstasy') enhances basal acetylcholine release in brain slices of the rat striatum.

The pharmacological basis of acute (+/-)-MDMA (3, 4-methylenedioxymethamphetamine) intoxication still awaits full characterization. According to present knowledge, MDMA enhances the release of serotonin and dopamine in striatal slices and interacts with different types of receptors such as 5-HT2 (5-hydroxytryptamine or serotonin), M1 and M2 muscarinic acetylcholine (ACh), and histamine H1 receptors. Currently, no information is available about the influence of (+/-)-MDMA on striatal cholinergic neurotransmission. In the present study, we used the in vitro perfusion technique to investigate the effect of (+/-)-MDMA on ACh release in rat striatal slices. Perfusions with (+/-)-MDMA (10-300 microM) resulted in a dose-dependent increase of spontaneous ACh release (EC50 approximately 30 microM). The effect was reversible and Ca++- and tetrodotoxin-sensitive. To determine the neurochemical pathways underlying this response, we perfused with (+/-)-MDMA in the presence of various inhibitors of neurotransmitter receptors. Blockade of glutamate or muscarinic ACh receptors as well as 5-HT1, 5-HT2, 5-HT3C or dopamine D2 receptors did not modulate (+/-)-MDMA-induced ACh release. However, the presence of histamine H1 receptor antagonists in the perfusion medium abolished (+/-)-MDMA-induced ACh release. The present data clearly demonstrate that (+/-)-MDMA enhances the activity of striatal cholinergic neurons and suggest an involvement of histamine H1 receptors. The effect is not mediated by glutamate and does not involve the activation of receptors of dopamine D2, 5-HT1, 5-HT2, 5-HT3C or muscarinic ACh. Considering the relatively high affinity of (+/-)-MDMA for the H1 histamine receptor (Ki 6 microM), a direct activation of this type of receptor might represent a plausible mechanism for (+/-)-MDMA-induced ACh release.

Acetylcholine↗
PubMed2000

Simultaneous determination of paroxetine, risperidone and 9-hydroxyrisperidone in human plasma by high-performance liquid chromatography with coulometric detection.

A method for the simultaneous determination of paroxetine, risperidone and its main metabolite 9-hydroxyrisperidone in human plasma has been developed. The procedure involved a multistep solid-phase liquid extraction with an internal standard. The drugs were separated on a cyano column followed by coulometric detection. This method described here has sufficient sensitivity to quantitate paroxetine accurately in the range 5-500 ng/ml with a lower limit of detection of 1 ng/ml and risperidone and its main metabolite 9-hydroxyrisperidone in the range 2-100 ng/ml with a lower limit of detection of 1 ng/ml when 1 ml of plasma was used for the analysis. The precision, accuracy and specificity have been proven, and show that the method is reliable for clinical studies and routine drug monitoring.

Chromatography, High Pressure Liquid↗
PubMed1999

The tachykinin NK1 receptor in the brain: pharmacology and putative functions.

After its discovery in 1931, substance P (SP) remained the only mammalian member of the family of tachykinin peptides for several decades. Tachykinins thus refer to peptides sharing the common C-terminal amino acid sequence Phe-X-Gly-Leu-Met x NH2. In recent years the family of mammalian tachykinins has grown with the isolation of two novel peptides from bovine and porcine central nervous system (CNS), neurokinin A and neurokinin B. In parallel with the identification of multiple endogenous tachykinins several classes of tachykinin receptors were discovered. The receptors described so far are named tachykinin NK1 receptor, tachykinin NK2 receptor and tachykinin NK1 receptor, respectively. The present review focuses on the pharmacology and putative function of tachykinin NK1 receptors in brain. The natural ligand with the highest affinity for the tachykinin NK1 receptor is SP itself. The C-terminal sequence is essential for activity, the minimum length of a fragment with reasonable affinity for the tachykinin NK1 receptor is the C-terminal hexapeptide. A rapid advance of knowledge was caused by development of non-peptidic tachykinin NK1 receptor antagonists. This area is under rapid development and a variety of different chemical classes of compounds are involved. Species-dependent affinities of tachykinin NK1 receptor antagonists reveal two clusters of compounds, targeting the tachykinin NK1 receptor subtype found in guinea pig, human or ferret or the one in rat or mouse, respectively. The most recently developed compounds are highly selective, enter the brain and are orally bioavailable. Distinct behavioural effects in experimental animals suggest the involvement of tachykinin NK1 receptors in nociceptive transmission, basal ganglia function or anxiety and depression. Recent clinical trials in man showed that tachykinin NK1 receptor antagonists are effective in treating depression and chemotherapy-induced emesis. Therefore, it is well possible that tachykinin NK1 receptor antagonists will be clinically used for treatment of specific CNS disorders within a short period of time.

Animals↗
PubMed1999

Voltage-gated, margatoxin-sensitive potassium channels, but not calcium-gated, iberiotoxin-sensitive potassium channels modulate acetylcholine release in rat striatal slices.

We evaluated the effects of iberiotoxin, an inhibitor of Slo-type Ca2+-activated potassium channels and two inhibitors of Shaker-type voltage-gated potassium channels margatoxin and dendrotoxin on acetylcholine outflow in rat striatal slices. An in vitro perfusion with 100 nM margatoxin or dendrotoxin induced a concentration-dependent and tetrodotoxin-sensitive enhancement in spontaneous acetylcholine release. In contrast, a perfusion with iberiotoxin did neither modulate basal, nor electrically- or N-methyl-d-aspartate-induced transmitter release. Therefore, Slo-type Ca2+-activated K+-channels do not seem to contribute significantly to cholinergic neurotransmission within rat striatal slices. As the Kv1.2 subtype represents the only common high affinity binding site of margatoxin and dendrotoxin and the effects of these toxins are not additive, this subtype is suggested to be the channel utilized by margatoxin and dendrotoxin to release acetylcholine in this model.

Acetylcholine↗
PubMed1999

Dopamine neurons in a simple GDNF-treated meso-striatal organotypic co-culture model.

Neurodegeneration of dopamine neurons in the ventral mesencephalon projecting to the dorsal striatum (meso-striatal system) plays a major role in Parkinson's disease. The aim of this study was to establish a simple organotypic, in vitro co-culture model for investigating the survival of dopamine neurons stimulated by the novel growth factor, glial-cell-line-derived neurotrophic factor. This model should allow investigation of the effects of the dopaminergic neurotoxin, 6-hydroxydopamine, on the expression of the transcription factor c-fos and on TUNEL staining in vitro. The dopaminotrophic factor, glial-cell-line-derived neurotrophic factor, markedly enhanced dopamine tissue levels and dopamine neuron number. Nerve-fiber ingrowth of dopamine neurons into its striatal target was found to be enhanced with glial-cell-line-derived neurotrophic factor. Using an optimized protocol, it was shown that the neurotoxin 6-hydroxydopamine selectively destructed dopamine neurons. C-fos-like immunoreactivity was enhanced in the mesencephalic part of the co-slices 3 h after application of the neurotoxin. The TUNEL staining occurred 2-5 days after the application of the neurotoxin, but did not seem to be related to dopamine neurons. In conclusion, the organotypic co-culture model provides a simple model for studying survival of dopamine neurons and for observing expression of genes and proteins that could be related to Parkinson's disease. This simple model is useful for screening novel drugs and growth factors and may markedly reduce severe animal experiments.

Animals↗
PubMed1998

Margatoxin increases dopamine release in rat striatum via voltage-gated K+ channels.

The distribution of iodinated margatoxin ([125I]margatoxin) binding sites in rat was investigated by autoradiography. Rat striatum expresses a high density of margatoxin binding sites and, therefore, the effects of margatoxin, charybdotoxin and iberiotoxin have been studied on [3H]dopamine release from rat striatal slices in vitro. Margatoxin (0.1-100 nM) and charybdotoxin (10-1000 nM), but not iberiotoxin increased the spontaneous and the electrically evoked [3H]dopamine release. [3H]dopamine release by margatoxin was inhibited by tetrodotoxin and omega-conotoxin GVIA, but not by atropine, naloxone, N(omega)-nitro-L-arginine and neurokinin or neurotensin receptor antagonists. In the buffer solution used for release experiments, [125I]margatoxin labels a maximum of 0.12 pmol of sites/mg protein in rat striatal membranes with a Kd of 5 pM. [125I]margatoxin binding was inhibited by margatoxin (Ki of 4 pM), charybdotoxin (Ki of 162 pM) but not by iberiotoxin. We conclude that inhibition of margatoxin-sensitive voltage-gated K+ channels increases [3H]dopamine release demonstrating their role in repolarization of nigrostriatal projections. In contrast, iberiotoxin-sensitive, high-conductance Ca2+-activated K+ channels are not involved in release of [3H]dopamine.

Animals↗