Formation of dopamine from 3-methoxytyrosine

Summary l-3-Methoxytyrosine-¹⁴C was given intravenously to mice, alone or following inhibitors of monoamine oxidase, catechol-O-methyl transferase or dopa decarboxylase. ¹⁴C-noradrenaline and ¹⁴C-dopamine in brain and heart were determined 2 h after the administration of the labelled compound. The results were very similar to those obtained in previous studies after a small dose of labelled dopa. Therefore, a careful paperchromatographic analysis of the l-3-methoxytyrosine-¹⁴C was made. It was found that 1.5% of the total radioactivity corresponded to dopa. Attempts to make a preparative separation of ¹⁴C-dopa from ¹⁴C-3-methoxytyrosine failed due to the appearance of another labelled impurity interfering with the determination of dopamine. Thus, the question whether dopamine can be formed from 4-methoxytyrosine in vivo could not be definitely answered. However, the serious interference of small amounts of radioactive impurities when working with labelled material in biological systems has been demonstrated once more.     

Characterization of nicotinic acetylcholine receptors on cultured bovine adrenal chromaffin cells using modified l-[3H]nicotine binding assay

Summary To characterize the properties of nicotinic acetylcholine receptors (nAChRs) in autonomic ganglia, we examined l-[³H]nicotine binding to membrane fraction prepared from cultured bovine adrenal chromaffin cells, using a modified filtration method. Binding of l-[³H]nicotine to non-treated glass fiber filters interfered with the detection of specific binding to the membrane fraction. Presoaking glass fiber filters in 3% or higher concentrations of polyethyleneimine (PEI) solution (sixty times higher than earlier used concentration) for at least 5 h could reduce the binding of l-[³H]nicotine to the filters to the background level. Specific l-[³H]nicotine binding to the membrane fraction was detected only when the membrane fraction was prepared in Ca²⁺- and Mg²⁺ (EDTA, EGTA and protease inhibitors were added)-free buffer. Specific binding of l-[³H]nicotine was saturable and reversible. Both computer program and Scatchard analysis revealed a single class of high affinity binding sites with an average K_d of 8.9 nM and a B_max of 42.5 fmol/mg protein. The Hill coefficient was 0.98. In inhibition studies, both cholinergic agonists (carbachol and l-nicotine) and ganglionic agonists (lobeline and 1,1-dimethyl-4-phenylpiperazinium iodide) were much effective in inhibiting l-[³H]nicotine binding, whereas both neuromuscular blocking (-bungarotoxin and d-tubocurarine) and ganglionic blocking agents were less effective. These results suggest that high affinity nicotinic binding sites on adrenal chromaffin cells are nAChRs of the ganglion-type, which have properties different from nAChRs on the neuromuscular junction but similar to nAChRs in the brain. Send offprint requests to K. Lee at his present address     

Striatal dopamine turnover and l-dopa treatment after short-term exposure of rats to manganese

The turnover rate of striatal dopamine (DA) and the effect of l-dopa treatment was investigated in rats after the daily oral administration of MnCl₂ · 4H₂O for a period of 30 days. The turnover rate of striatal DA, as determined by the administration of -methyl-p-tyrosine, increased significantly in manganese-exposed rats. l-Dopa administration resulted in a significant elevation in the levels of DA and its metabolite, homovanillic acid, in manganese-exposed rats, but these neurochemical changes could not be correlated with the concentration of manganese in the striatum. We therefore advise that l-dopa therapy should not be tried in early manganese intoxication, as it may aggravate manic symptoms due to marked increase in brain DA.     

Possible involvement of l-arginine-nitric oxide pathway in modulating regional blood flow to brown adipose tissue of rats

To evaluate whether the l-arginine-nitric oxide (NO) pathway is involved in the regulation of regional blood flow to brown adipose tissue (BAT), the effects of two specific NO synthase inhibitors, N^G-nitro-l-arginine methyl ester (l-NAME) and N^G-monomethyl-l-arginine (l-NMMA), on the blood flow to interscapular brown adipose tissue (IBAT) were studied in urethane-anesthetized rats. Regional blood flow in MAT was measured with laser-Doppler flowmetry.An intravenous injection of l-NAME and l-NMMA, but not of either d-enantiomer, caused a transient and dose-dependent increase in IBAT blood flow. Dose-response curves for these NO synthase inhibitors showed that l-NAME was more potent than l-NMMA in increasing IBAT blood flow. We also observed a concomitant pressor effect accompanied by a slight decrease in heart rate following intravenous injection of l-NAME and l-NMMA. An elevation of IBAT blood flow and blood pressure induced by both l-NAME and l-NMMA was reversed by l-arginine in an enantiomerically specific manner. The increase in IBAT blood flow induced by NO synthase inhibitors was of shorter duration and less sensitive to l-arginine than the increase in blood pressure.Our results show that the WAY blood flow is increased by inhibition of NO synthase and that the response of IBAT vasculature to NO synthase inhibitors is different from that of the resistance vessels which regulate blood pressure. The involvement of l-arginine-NO pathways in modulating microcirculation in IBAT is suggested. Correspondence to: Y. Uchida at the above address     

Protriptyline induced inhibition of the in vivo 3H-noradrenaline synthesis from 3H-l-Dopa in the rat brain

Summary ³H-l-Dopa was given intraperitoneally, after a peripheral decarboxylase inhibitor Ro 4-4602 (50 mg/kg), to male Wistar rats and the effect of protriptyline pretreatment (10 mg/kg, 30 min) on the formation and metabolism of the brain ³H-catecholamines, dopamine and noradrenaline and all their metabolites was investigated.Protriptyline produced a strong decrease of labelled noradrenaline and its metabolites normetanephrine, free and conjugated 3-methoxy-4-hydroxyphenyl-eneglycol and 3,4-dihydroxyphenyleneglycol 60 and 120 min after ³H-l-Dopa. ³H-noradrenaline was also decreased 30 and 45 min after ³H-l-Dopa. In rats and mice the pretreatment with protriptyline (10 mg/kg, 30 min) induced also a significant decrease in brain ³H-noradrenaline but not ³H-dopamine synthesized from ³H-l-tyrosine. Protriptyline (10 mg/kg) produced no effect on endogenous dopamine and noradrenaline in the rat or mouse brain.The present findings strongly indicate that the acute treatment with protriptyline inhibits the ³H-noradrenaline formation from ³H-l-Dopa. This effect seems most likely to be related to an interaction of protriptyline with the precursor(s) ³H-l-Dopa or ³H-dopamine at sites of ³H-noradrenaline biosynthesis.A preliminary report of the present study was presented at the Scandinavian Pharmacological Society, June 1972, Uppsala, Sweden and the VIII C.I.N.P. Congress, August 1972, Copenhagen, Denmark.     

Studies on some metabolic effects of dopa and dopamine in the rat

Summary In male rats some metabolic effects of l-dopa and dopamine were compared with those of noradrenaline, adrenaline and tyramine by measuring the changes of plasma free fatty acids (FFA), plasma glycerol and plasma glucose as well as those of blood lactate and blood pyruvate. After intravenous injection of dopamine lactate and pyruvate concentrations were elevated maximally already within 5 min and returned to control levels after 10–20 min, i.e. at a time, when the levels of FFA, glycerol and glucose were maximally elevated in plasma. l-dopa had about 1/8 to 1/6 the potency of dopamine in producing these metabolic effects. The effects of dopamine were similar to those obtained with 1/20 the dose of noradrenaline, while adrenaline produced a more pronounced hyperglycaemic response than dopamine did when given in lipolytically equieffective doses.Pretreatment of the animals with phentolamine completely prevented the hyperglycaemic response to dopamine or noradrenaline without clearcut effects on the lipolytic effect of these catecholamines. Also, pretreatment with dihydroergotamine antagonized the hyperglycaemic effect of adrenaline and prevented that of dopamine and noradrenaline, while the effect of catecholamines on plasma glycerol concentration was not affected. However, the elevation in plasma FFA level induced by catecholamines was clearly antagonized by dihydroergotamine. The -adrenolytic drug Kö 592 had no effect on the hyperglycaemic effect of dopamine or noradrenaline, but antagonized the lipolytic effect of these amines. Pargyline enhanced the elevation of FFA and glycerol induced by dopamine or noradrenaline but reduced their hyperglycaemic effect. Chemical sympathectomy induced by pretreatment with 6-hydroxydopamine prevented the hyperglycaemic and lipolytic effects of tyramine, antagonized those of dopamine and potentiated the lipolytic response to noradrenaline. The effect of syrosingopine on the metabolic responses to the catecholamines was similar to that of 6-hydroxydopamine.Since the metabolic effects of dopamine were clearly antagonized by various - and -receptor-blocking agents and by chemical sympathectomy, we conclude that dopamine exerts its metabolic effects through a stimulation of - and -adrenoceptors and that part of this effect is mediated by a tyramine-like action of dopamine.     

Demethylation of l-3-methoxytyrosine in vivo

Summary After administration of purified l-¹⁴C-3-methoxytyrosine (l-¹⁴C-3-MTO) to rats, the fractions of labelled amino acids, catecholamines and phenolcarboxylic acids of urine and brain have been separated by column chromatography. Prior to performing the quantitative determinations, the individual metabolites of each urinary fraction and of the cerebral catecholamine fraction were isolated by paper chromatography using different systems. Susbtantial amounts of ¹⁴C-3,4-dihydroxyphenylacetic acid (¹⁴C-DOPAC) as well as some ¹⁴C-3,4-dihydroxyphenylalanine (¹⁴C-DOPA) and traces of dopamine (DA) appeared in the urine. Furthermore, small amounts of ¹⁴C-DA and ¹⁴C-norepinephrine were found in the brain with two different chromatographic systems. The urinary excretion of ¹⁴C-DOPAC and ¹⁴C-DA was increased by pretreatment with dopacetamide, an inhibitor of catechol-3-O-methyl-transferase. A possible contamination of the l-¹⁴C-3-MTO with traces of l-¹⁴C-DOPA as a major source of the dihydroxylated metabolites has been ruled out. It is concluded that part of l-3-MTO undergoes demethylation in vivo and that the finding of DA in brain and urine after administration of l-3-MTO is not an artifact.     

Evidence for the role of nitric oxide in nicotine-induced locomotor sensitization in mice

Rationale Nitric oxide (NO) is implicated in both acute effects of addictive drugs and development of dependence to them. We investigated the role of NO in nicotine-induced locomotor sensitization.Objectives The effects of N-nitro-l-arginine methyl ester (l-NAME), a NO synthase inhibitor, and a combination of a NO precursor l-arginine and l-NAME on nicotine-induced locomotor sensitization were investigated in Swiss Webster mice.Methods Sensitization to psychomotor stimulating effect of nicotine was rendered by seven injections of nicotine (1 mg/kg) on every other day. To investigate their effect on the development of sensitization to nicotine, l-NAME (15–60 mg/kg) and l-arginine (1 g/kg) were given before nicotine administration during the first seven sessions. To investigate the effect of these compounds on the expression of nicotine sensitization, after a 4-day drug-free period another group of mice received a challenge injection of nicotine on day 18.Results Nicotine (1 mg/kg) produced a robust locomotor sensitization in mice. The doses of 30 mg/kg and 60 mg/kg of l-NAME blocked the development of sensitization to nicotine; and, l-arginine (1 g/kg) pretreatment reversed this effect of l-NAME. Likewise, the doses of 30 mg/kg and 60 mg/kg of l-NAME inhibited the expression of sensitization to nicotine on day 18; and, l-arginine (1 g/kg) pretreatment reversed this inhibitory effect of l-NAME.Conclusions Our results suggest that NO is implicated in the development and expression of nicotine-induced locomotor sensitization in mice.     

The effect of l-dopa on young patients with simple schizophrenia,treated with neuroleptic drugs

Thirteen out of 18 young out-patients with simple schizophrenia under neuroleptic treatment completed a double-blind cross-over trial with Madopar® [l-Dopa + benserazid (a peripheral decarboxylase inhibitor)] and placebo. Nine patients were given 900 mg l-Dopa + 225 mg benserazid daily, 1 patient received 600 mg l-Dopa + 150 mg benserazid, and 3 patients, 300 mg l-Dopa + 75 mg benserazid. In these doses, l-Dopa was effective against emotional withdrawal, blunted affect, tendency to isolation and apathy, without inducing or aggravating productive, accessory symptoms. The activity score, according to the specific activity-withdrawal scale, was significantly increased (P<0.05), whereas the total BPRS score (Brief Psychiatric Rating Scale) was slightly, but significantly reduced (P<0.05). In cases where l-Dopa had to be limited to 600 and 300 mg daily, a tendency to anxiety, distortion of thinking, and a sense of unreality were observed, depending on the dose of l-Dopa. In no case were gastrointestinal, cardiovascular or neurological sideeffects observed.     

Habituation of acoustic startle is disrupted by psychotomimetic drugs: differential dependence on dopaminergic and nitric oxide modulatory mechanisms

Rationale A deficit in attention and information processing has been considered a central feature in schizophrenia, which might lead to stimulus overload and cognitive fragmentation. It has been shown that patients with schizophrenia display a relative inability to gate incoming stimuli. Thus, patients repeatedly subjected to acoustic startle-eliciting stimuli habituate less to these stimuli than controls. Furthermore, schizophrenia-like symptoms can be induced by pharmacological manipulations in humans by psychotomimetic drugs, e.g. phencyclidine (PCP) and d-amphetamine (d-AMP). Recent studies show that the behavioural and biochemical effects of PCP in rodents are blocked by nitric oxide synthase (NOS) inhibitors, suggesting that NO plays an important role in at least the pharmacological effects of PCP.Objectives The first aim of the present study was to investigate if PCP, MK-801 and d-AMP impair habituation of acoustic startle in mice. Secondly, we examine the effect of the NOS inhibitor, l-NAME, and the dopamine receptor antagonist, haloperidol, on drug-induced deficit in habituation.Results PCP (4 mg/kg), MK-801 (0.4 mg/kg) and d-AMP (5.0 mg/kg), impaired habituation of the acoustic startle response in mice. This effect was reversed by the NOS inhibitor, l-NAME. The typical antipsychotic, haloperidol, reversed the effects of PCP and d-AMP, but not that of MK-801.Conclusions The finding that PCP, MK-801 and d-AMP impair habituation in mice is consistent with the idea that these treatments model certain filter deficits seen in schizophrenic patients. Furthermore, the present results suggest that NO is critically involved in these effects on habituation, whereas that of dopamine is less clear.     

Ionically Fixed Polymeric Nanoparticles as a Novel Drug Carrier

Purpose

In this study, we have prepared a novel polymeric drug delivery system comprised of ionically fixed polymeric nanoparticles (IFPN) and investigated their potential as a drug carrier for the passive targeting of water-insoluble anticancer drugs.

Materials and Methods

For this purpose, the physicochemical characteristics of the IFPN were investigated by comparing them with conventional polymeric micelles. IFPN containing paclitaxel were prepared and evaluated for in vitro stability and in vivo pharmacokinetics.

Results

The IFPN were successfully fabricated using a monomethoxypolyethylene glycol-polylactide (mPEG-PLA) diblock copolymer and a sodium salt of d,l-poly(lactic acid) (d,l-PLACOONa) upon the addition of CaCl₂. The transmittance of the IFPN solution was much lower than that of a polymeric micelle solution at the same polymer concentration implicating an increase in the number of appreciable particles. The particle size of the IFPN was approximately 20～30 nm which is in the range of particle sizes that facilitate sterile filtration using a membrane filter. The IFPN also have a regular spherical shape with a narrow size distribution. The zeta potential of the IFPN was almost neutral, similar to that of the polymeric micelles. In contrast, mixed micelles with a combination of mPEG-PLA and d,l-PLACOONa prior to the addition of Ca²⁺ showed a negative charge (?17 mV), possibly due to the carboxyl anion of polylactic acid exposed on the surface of the micelles. The IFPN formulation was highly kinetically stable in aqueous medium compared to the polymeric micelle formulation. The molecular weight of d,l-PLACOONa in the IFPN and the mPEG-PLA/d,l-PLACOONa molar ratio had a great influence upon the kinetic stability of the IFPN. Pharmacokinetic studies showed that the area under the concentration vs time curve (AUC) of IFPN in blood was statistically higher (about two times) when compared with that of Cremophor EL-based formulation (Taxol^® equivalent) or polymeric micelle formulation.

Conclusions

The results suggests that the IFPN were retained in the circulation long enough to play a significant role as a drug carrier in the bloodstream, possibly resulting in improved therapeutic efficiency. Therefore, the IFPN are expected to be a promising novel polymeric nanoparticulate system for passive tumor targeting of water-insoluble anticancer drugs including paclitaxel.     

Normalization by antipsychotic drugs of biochemically induced abnormal behavior in rats

Male rats were trained to perform a conditioned avoidance response combined with a successive discrimination in a modified shuttle box. The administration of l-Dopa, 100 mg/kg i.p., after inhibition of peripheral aromatic amino acid decarboxylase, or apomorphine, 2 mg/kg i.p., was found to disrupt the discriminative but not the avoidance behavior. The dopamine receptor antagonist pimozide (0.5 mg/kg i.p.), but not the noradrenaline receptor antagonist phenoxybenzamine (10 or 20 mg/kg i.p.) completely antagonized the l-Dopa-induced abnormal behavior, indicating an involvement of central dopamine mechanisms. The present data show that antipsychotic drugs not only inhibit behavior but can also improve behavior in animals with a disturbed function.     

N-ccetyl-S-(1-cyano-2-hydroxyethyl)-l-cysteine,a new urinary metabolite of acrylonitrile and oxiranecarbonitrile

Two mercapturic acids, i. e., N-acetyl-S-(1-cyano-2-hydroxyethyl)-l-cysteine (CHEMA) and N-acetyl-S(2-hydroxyethyl)-l-cysteine (HEMA), were isolated from the urine of rats dosed with four successive doses of oxiranecarbonitrile (glycidonitrile, GN), 5 mg/kg, a reactive metabolic intermediate of acrylonitrile (AN). GC-MS analysis of methylated urine extracts from both AN- and GN-dosed rats showed another mercapturate which was identified as N-acetyl-S-(1-cyanoethenyl)-l-cysteine (1-CEMA) methyl ester using an authentic reference sample. The mass spectrum of this compound was very similar to that of a methylated metabolite of AN tentatively identified by Langvardt et al. (1980) as N-acetyl-3-carboxy-5-cyanothiazane (ACCT). In contrast, no ACCT was found in rats dosed with either GN or AN. Hence, there is no evidence for the formation of ACCT or its isomers in rats dosed with AN or GN. The methyl ester of 1-CEMA is formed artificially by dehydration of CHEMA methyl ester in the injector of the gas chromatograph.Details of the synthetic procedures and NMR-spectra are available from the authors on request     

Dopamine receptor sensitivity after chronic dopamine agonists

Several previous reports have demonstrated that chronic administration of both directly and indirectly acting dopamine agonists produces a supersensitive behavioral response to challenge doses of dopamine agonists when compared to the responses induced by acute administration of these drugs. That is, a given dose of a dopamine agonist will produce a greater response after chronic dopamine agonist treatment than is observed upon acute administration of that dose. A similar behavioral phenomenon resulting from chronic administration of dopamine antagonists has been suggested to be due to an increase in the number of dopamine receptors present in relevant brain areas. The same hypothesis has been put forward for the hypersensitivity induced by chronic dopamine agonist administration. The present study was designed to investigate the effect of chronic administration of high doses of both direct and indirect dopamine agonists on the dopamine receptors labeled by ³H-spiroperidol. Groups of animals (CD-1 mice) were sacrificed 1, 3 and 5 days following the last chronic injection. Striatal tissue from these mice was incubated with ³H-spiroperidol and dopamine receptor binding evaluated. Affinity of the receptors for the ligand was unaltered by treatments. The receptors labeled by ³H-spiroperidol showed no significant differences in number following the chronic administration of high doses of apomorphine (30 mg/kg). The B _max was significantly decreased at only one time period following chronic administration of dextroamphetamine (4 mg/kg); however, these was a dramatic 30% reduction in the B _max in striatal tissue from those mice treated with N-n-propylnorapomorphine. These results suggest that the hypersensitive behavioral response in mice following chronic administration of direct and indirect acting dopamine agonists is not due to an increase in the number of dopamine receptors in the striatum which are labeled by ³H-spiroperidol.     

Titration of human brain monoamine oxidase-A and-B by clorgyline andl-deprenil

Summary The interaction of clorgyline andl-deprenil with the-A and-B forms of human brain monoamine oxidase (MAO) has been studied. Both compounds inhibit cerebrocortical MAO in a manner consistent with a suicide inactivation of the enzyme. The interaction of clorgyline with the-A form of the enzyme appears to take place almost entirely at specific binding sites, and the conditions required for this inhibitor to titrate the concentrations of MAO-A have been elucidated.l-Deprenil has also been used to titrate the concentration of the-B form of MAO in cerebrocortical homogenates, but there is a considerable degree of non-specific binding of this compound. The two inhibitors have been used to titrate the concentrations of the two enzyme forms in frontal cortex homogenates from different age groups. There was a significantly higher MAO-B activity for the age range 73–95 years than for the age range 2–63 years. No significant differences between the two age groups were found for MAO-A. The activity of MAO-A in the samples correlated very well with the concentration of this enzyme form. Titration of the B-form of the enzyme withl-deprenil indicated an increased enzyme concentration with age, although other factors, such as the non-specific binding of this compound, could contribute to this effect.     

Biotransformation of l-DOPA in striatum and substantia nigra of rats with a unilateral,nigrostriatal lesion: a microdialysis study

Summary Microdialysis was used to study the biotransformation of l-DOPA in the striatum and substantia nigra of rats with a unilateral 6-hydroxydopamine (6-OHDA) lesion of the substantia nigra. The animals were pretreated with carbidopa (50 mg/kg p.o.) for 5 days. They were anaesthetized, and microdialysis probes were implanted into the intact and denervated striatum and into the intact and lesioned substantia nigra. The biotransformation of l-DOPA (5 mg/kg i.p.) in these regions was investigated. These results were compared with those obtained after administration of a much higher dose of l-DOPA (100 mg/kg i.p.). Changes in extracellular l-DOPA, 3-O-methyldopa (3-OMD), dopamine, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were determined by HPLC with electrochemical detection.Although rats with a unilateral nigrostriatal lesion did not show rotational behaviour after 5 mg/kg l-DOPA, DA levels were increased significantly both in the intact and the denervated striatum and in the intact and the lesioned substantia nigra. This increase was most pronounced in the denervated striatum. At 100 mg/kg l-DOPA, the increases in extracellular dopamine in intact and denervated striatum were about twice as high as the increases observed at the lower dose. A similar increase was observed in the intact substantia nigra. However, in the lesioned substantia nigra there was a fourfold increase. l-DOPA, at both doses, was evenly distributed between the brain areas studied and the lesion had no effect on the uptake of the drug at the blood-brain barrier.Our data suggest that l-DOPA in the substantia nigra might play a role additional to that in the striatum in relieving symptoms of Parkinson's disease. Even at a low dose (5 mg/kg i.p.), the drug had an effect on extracellular dopamine in all the brain regions studied. Correspondence to S. Sarre     

Effects on self-stimulation behavior of drugs influencing dopaminergic neurotransmission mechanisms

Summary Drugs preferentially influencing dopaminergic neurotransmission mechanisms were administered to rats which lever-pressed to receive electrical stimulation in either the lateral hypothalamus or periaqueductal mesencephalon. The same drug effects were observed regardless of the site of electrical stimulation. Blockade of dopamine receptors by 0.35 or 0.5 mg/kg pimozide reduced self-stimulation rates. Increasing the reward value of the stimulation by doubling of self-stimulation current induced control rates of lever-pressing in animals given 0.35 mg/kg pimozide but not in those receiving 0.5 mg/kg. At doses of 0.75 and 1.5 mg/kg, apomorphine, a putative dopamine receptor stimulator, reduced self-stimulation rates at normal current. Doubling of the stimulation current produced greater than normal rates of lever-pressing at 0.75 mg/kg apomorphine, but at 1.5 mg/kg no such increase in rate was observed. l-DOPA, 75 and 150 mg/kg, also reduced self-stimulation, but doubled current restored rates to control levels at both doses. For comparison purposes, pharmacological effects on predominantly noradrenergic mechanisms were also studied. Inhibition of dopamine--hydroxylase by 150 mg/kg disulfiram reduced self-stimulation under normal current, but rates were increased to above control levels with doubled current. That self-stimulation behavior could be reinstated by doubling of current suggests that motor incapacity is not a sufficient explanation for most of the observed reductions in lever-pressing rate. These results further suggest that, in addition to noradrenaline, the integrity of central dopaminergic systems may be essential for the behavioral expression of certain motivational processes.     

Reversal of the increase in apomorphine-induced stereotypy and aggression in REM sleep deprived rats by dopamine agonist pretreatments

REM sleep deprivation (REMSD) induces augmented responses to dopaminergic agonists. Prolonged administration of neuroleptics induces a similar state, probably by the production of supersensitivity of dopaminergic receptors. Such a supersensitive state could be induced by REMSD as a result of impairment of dopamine neurotransmission. In order to test this hypothesis, bromocriptine, nomifensine, amphetamine,l-dopa, imipramine and electroconvulsive shock (ECS) were administered to rats during REMSD, and aggressive and stereotyped behaviors were measured. Amphetamine andl-dopa pretreatment attenuated the increases in apomorphine-induced stereotypy and aggression in REMSD rats, but ECS selectively reduced apomorphine-induced aggression. The other drugs tested were ineffective on both behavioral tests. Such a selective action may reflect different effects of ECS on different dopaminergic systems such as those involved with stereotypy and aggression. The results suggest that REMSD induces an increase in dopaminergic sensitivity which may be reversed by pretreatment with some dopaminergic agonists.1 Fellowship from Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)2 Universidade Federal de Goiás3 Fellowship from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)     

Nitric oxide synthesis in endothelial cytosol: Evidence for a calcium-dependent and a calcium-independent mechanism

Summary Release of nitric oxide (NO) from endothelial cells critically depends on a sustained increase in intracellular free calcium maintained by a transmembrane calcium influx into the cells. Therefore, we studied whether the free cytosolic calcium concentration directly affects the activity of the NO-forming enzyme(s) present in the cytosol from freshly harvested porcine aortic endothelial cells. NO was quantified by activation of a purified soluble guanylate cyclase coincubated with the cytosol. In the presence of 1 mM L-arginine, 0.1 mM NADPH and 0.1 mM EGTA, endothelial cytosol (0.2 mg of cytosolic protein per ml) stimulated the activity of guanylate cyclase 5.0 + 0.5-fold (from 31 + 9 to 153 + 15 nmol cyclic GMP formed per min per mg guanylate cyclase). Calcium chloride increased this stimulation further in a concentration-dependent fashion by up to 136 + 15% (with 2 M free calcium; EC₅₀ 0.3 M). The calcium-dependent and -independent activation of guanylate cyclase was enhanced by superoxide dismutase (0.3 M) and was inhibited by the stereospecifically acting inhibitor of L-arginine-dependent NO formation N^G-nitro-L-arginine (1 mM) and by LY 83583 (1 M), a generator of superoxide anions. Our findings suggest a calcium-dependent and -independent synthesis of NO from L-arginine by native porcine aortic endothelial cells. Send of fprint requests to A. Mülsch, at the above address     

The effects of l-Dopa,clonidine, and apomorphine on the acoustic startle reaction in rats

The present investigation provides evidence for noradrenergic involvement in the elaboration of the acoustic startle reaction.Within-subject experiments demonstrated that an amine-depleting dose of reserpine enhanced the level of the startle reaction and that this effect was reversed by the catecholamine precursor, l-Dopa. Chemical assays suggested a correlation between the accumulation of noradrenaline and reversal of reserpine effects. Administration of the noradrenaline receptor-stimulating agent, clonidine (0.125 or 0.250 mg/kg) produced marked reductions in startle amplitude reducing the response far below normal values in reserpinized subjects. By contrast, the dopamine receptor-stimulating agent, apomorphine (1.0 mg/kg) did not alter the response. None of the pharmacological agents used was found to alter the inhibition of the startle reaction which results from the presentation of neutral stimuli (prepulses) shortly before reflex elicitation.Taken together with an earlier report, the present data suggest that noradrenaline and serotonin have partially antagonistic control over the startle reaction.Submitted in partial fulfillment of the requirements for the Ph. D. degree from the University of Rochester. The thesis advisors, Dr. Carol Kellogg and Dr. James Ison, are warmly thanked for their advice, encouragement, guidance, and continuing support. The research was supported in part by NSF grant GB-14814, NIMH grant MH-10825, and ONR contact N00014-68-0091.