The effects of dl-p-chlorophenylalanine and dl-α-methyl-p-tyrosine on the brain catecholamine,serotonin and free amino acid contents in rat

The changes in the brain levels of catecholamines, serotonin and free amino acids have been considered as a factor in the development of the physical dependence on and tolerance to some drugs. In order to show the relationships among the brain levels of these substances, three groups of rats were given i.p. dl-MpT alone, dl-pCPA alone, or dl-MpT and dl-pCPA together, twice a day for three days. Another group was kept as control. The brain levels of catecholamines, serotonin and free amino acids were determined. Although dl-MpT and dl-pCPA alone caused a decrease in the levels of catecholamines and serotonin respectively, the administration of dl-MpT and dl-pCPA together did not. The changes in the levels of free amino acids which were found were related to the metabolism of catecholamines and serotonin.     

Inhibition of the in vivo biosynthesis and changes of catecholamine levels in rat brain after α-methyl-p-tyrosine; time- and dose-response relationships

Summary Male Sprague-Dawley rats were given 0.407 mmoles/kg of D,l--methyl-p-tyrosine methylester HCl (H44/68; -MT) at eleven time-points between 0–24h, or 8 doses between 0.013–1.628 mmoles/kg of the drug at 1 h before i. v. injection of 160 Ci tyrosine-2,6-³H. The rats were killed 15 min after tyrosine-³H and brain -MT, tyrosine and catecholamines (endogenous and labelled), and plasma -MT and tyrosine (-³H) were chromatographically isolated before being assayed spectrophotofluorimetrically (endogenous) or by liquid scintillation methods (labelled compounds).A delayed penetration of -MT from plasma into brain, different elimination rates of -MT in plasma and brain, and decreasing brain/plasma drug concentration on increasing -MT dosages indicated, that -MT in brain and plasma belong to different pharmacokinetic compartments.The endogenous levels of catecholamines in the time-response experiment, declined to a minimum 4 h after -MT administration, where the dopamine level was 38% and the noradrenaline level 51% of the saline controls. Kinetic data of the catecholamine elimination is given. In the dose-response experiment the decrease in the endogenous catecholamine levels was doserelated up to 0.407 mmoles/kg of -MT, with no further decline on higher doses.The maximal inhibition of brain catecholamine synthesis occurred within 30 min after -MT administration and the inhibition correlated better with the brain than with plasma -MT content. The inhibition was dose-related with a maximal synthesis inhibition of 95% for dopamine and 80% for noradrenaline at the highest dose of -MT. The duration of synthesis inhibition and storage depletion were shorter for noradrenaline (12 h) than for dopamine (16 h). Further, the ED₅₀ for synthesis inhibition of dopamine (0.057 mmoles/kg) was half of the ED₅₀ for synthesis inhibition of noradrenaline (0.117 mmoles/kg). This might suggest different sensitivities towards -MT or different availabilities of -MT in the two neuron populations.At the three highest doses of -MT there were signs of interference with the uptake process for tyrosine from plasma into the brain. This was indicated by increased plasma levels and decreased brain levels of tyrosine (-³H).     

Isoprenaline increases brain concentrations of administered l-dopa and l-tryptophan in the rat

A small dose of isoprenaline or saline was administered intraperitoneally to rats 20 min before the administration of one of the amino acids l-dopa or l-tryptophan. Isoprenaline caused a marked increase in the brain concentration of the administered amino acid. Isoprenaline has previously been shown to cause a decrease in at least some of those plasma amino acids which compete with l-dopa and tryptophan for carrier-mediated transport into the brain. The effect of isoprenaline on the concentrations of dopa and tryptophan in the brain is suggested to be at least partly caused by a change in the relationship between endogeneous and administered amino acids. It is also possible that a direct effect of isoprenaline on the blood-brain barrier transport system contributes to the effect.The reported finding might be of clinical interest in view of the therapeutic importance of aromatic amino acids with a central site of action.     

Central and peripheral effects of 5-hydroxytryptophan on motor activity in mice

Spontaneous motor activity was studied in mice given dl-5-hydroxytryptophan (5-HTP) i.p. in doses ranging from 6.25 to 800 mg/kg with and without previous administration of l--hydrazino--methyl--(3,4-dihydroxyphenyl)-propionic acid (MK-486), an inhibitor of peripheral amino acid decarboxylase. Some mice were also given repeated injections of dl--methyl-metatyrosine (-MMT) prior to MK-486 and 5-HTP. The brain levels of noradrenaline (NA), dopamine (DA) and 5-hydroxytryptamine (5-HT) were also determined in these animals.5-HTP in doses between 100 and 800 mg/kg caused a decrease in motor activity when given alone, whereas after pretreatment with MK-486 it increased motor activity. Lower doses of 5-HTP, alone or in combination with MK-486, had no significant effect on motor activity. Pretreatment with -MMT caused a marked depletion of NA and DA without counteracting the increase in motor activity induced by MK-486 and 5-HTP.It is concluded that the central effects of large doses of 5-HTP are excitatory whilst the effects outside the blood-brain barrier have an inhibitory influence on the motor activity in mice. The mechanisms for the central excitatory effects are discussed.     

The effects of Δ9-tetrahydrocannabinol on the metabolism of norepinephrine in rat brain

⁹-THC (approximately 80 mg/kg) was administered to rats by intraperitoneal injection. This dose was found to cause an accelerated rate of disappearance of intracisternally administered norepinephrine-H³ from the brain and a small increase in the uptake of norepinephrine-H³ in the brain. In contrast to most stimulants, euphoriants, or antidepressants (e.g., cocaine or amphetamine, monoamine oxidase inhibitors and tricyclic antidepressants), ⁹-THC appeared to cause no decrease in the deamination of norepinephrine-H³ in brain. Levels of endogenous norepinephrine in brain tended to be slightly lower, whereas levels of endogenous serotonin were slightly higher in animals treated with ⁹-THC than in matched control animals. Behavioral effects were observed and are described in the text.     

The metabolic fate of infusedl-tryptophan in men: possible clinical implications of the accumulation of circulating tryptophan and tryptophan metabolites

l-Tryptophan (Trp) was widely used as a natural tool for the support of serotonin-mediated brain functions and as a challenge probe for the assessment of serotonin-mediated neuroendocrine responses. The metabolic fate of the administered Trp and the kinetics of the accumulation of Trp metabolites in the circulation, however, have never thoroughly been investigated.This study describes the time- and dose-dependent alterations in the plasma levels of various Trp metabolites and large neutral amino acids after the infusion of Trp to healthy young men (1, 3 and 5 g; placebo-controlled, double-blind, cross-over study during day- and night-time).The major Trp metabolites (kynurenine, indole acetic acid and indole lactic acid) in plasma increased dose-dependently but rather slowly after Trp administration to reach their maximal plasma levels (up to 10-fold after the 5 g dose) at about 3 h p.i., and remained at an elevated level (about 5-fold) for up to 8 h. N-acetyl-Trp and 5-hydroxy-Trp rose rapidly and massively after Trp infusions, at the 5 g dose more than 200- and 20-fold, respectively, and declined rapidly to about 5-fold baseline levels within 2 h. Whole blood serotonin levels were almost unaffected by the Trp infusions. A rather slow increase of 5-hydroxyindole acetic acid was seen, reaching maximum values (3-fold at the 5 g dose) at about 2 h after the infusion of Trp. Additionally, a dose-dependent rise of circulating melatonin was observed afterl-Trp infusions. The administration ofl-Trp caused a depletion of the concentrations of the other large neutral amino acids and a dose dependent decrease of the ratio between plasma tyrosine and the sum of the plasma concentrations of the other large neutral amino acids. Apparently, none of the existing pathways of peripheral Trp metabolism is saturated by its substrate, Trp in men. At least some of the central effects reported afterl-Trp administration may be mediated by the Trp-stimulated formation of neuroactive metabolites or by the decreased availability of tyrosine for catecholamine synthesis.Part of this work was presented at the International Symposium on Future Prospects ofl-Tryptophan in Medicine, Heidelberg, Germany, November 22–23, 1991     

Catecholamines and memory: Enhanced verbal learning during l-DOPA administration

Verbal learning was measured during the administration of l-DOPA in large oral doses to depressed patients. Longer-term memory on two different tasks improved during treatment, while short-term memory (immediate recall) was unaffected. In contrast, the catecholamine synthesis inhibitor -methyl-p-tyrosine did not alter either memory process.The effects of l-DOPA on learning may be related to increased arousal produced by this drug.     

The effect of tryptophan and a tryptophan/5-hydroxytryptophan combination on indoles in the brains of rats fed a tryptophan deficient diet

Rats maintained on a tryptophan deficient diet had reduced brain and serum tryptophan and brain 5-hydroxy-indolacetic acid levels compared to controls. 5-Hydroxytryptophan and l-tryptophan administered to these deficient rats in a combination (595) produced a greater elevation of indolamines and tryptophan in the brain than either amino acid alone. In rats maintained on a normal diet the urinary output of 3-hydroxykynurenine was considerably reduced by treatment with the combination of amino acids as com pared to tryptophan treatment. 5-Hydroxytryptophan reduced the induction of kynurenine synthesis in the liver produced by tryptophan, implying that it is capable of inhibiting the enzyme tryptophan pyrrolase in vivo. It is suggested that the possession by 5-hydroxytryptophan of tryptophan pyrrolase inhibitory properties may make the administration of the combination a better treatment of depressed patients exhibiting an indolamine deficit than either amino acid alone.     

Enhancement of blood-brain barrier permeability to sodium fluorescein by stimulation of µ opioid receptors in mice

Summary The effects of opioids on the permeability of the blood-brain barrier (BBB) were examined in mice with sodium fluorescein as an indicator of the permeability. The brain was perfused with saline 30 min after injection of sodium fluorescein (40 mg/kg, i. v.) and examined by fluorometry. Morphine hydrochloride (0.3–10 mg/kg, s. c.) markedly increased the brain level of sodium fluorescein dose-dependently without influencing the plasma level, when administered 20 min before sodium fluorescein injection. Intracerebroventricularly (i. c. v.) injected morphine hydrochloride (0.5 and 1.0 Erg) increased the brain sodium fluorescein level. Buprenorphine (0.1 and 0.5 mg/kg, s. c.) was also effective. However, pentazocine, ethylketazocine, U-50488H and SKF-10047 had no significant influence. The i.c.v. administration of [D-Ala², McPhe⁴, Gly(ol)⁵]enkephalin (0.1 g) and [D-Ala², D-Leu⁵]enkephalin (0.5 g) but not of [D-Thr², Leu⁵]enkephalin-Thr increased the brain level of sodium fluorescein significantly. A small dose of naloxone (i. p.) significantly inhibited the effects of morphine, buprenorphine, [D-Ala², McPhe⁴, Gly(ol)⁵]enkephalin and [D-Ala³, D-Leu⁵]enkephalin. ICI-174864 co-administered i. c. v. with [D-Ala², D-Leu⁵]enkephalin was ineffective in antagonizing the effect of the latter. These findings suggest that the stimulation of µ opioid receptors results in an increase in BBB permeability to sodium fluorescein. Send offprint requests to K. Saeki     

Effect of inhibition of γ-glutamyltranspeptidase by AT-125 (Acivicin) on glutathione and cysteine levels in rat brain and plasma

Summary AT-125 (Acivicin) is an inhibitor of -glutamyltranspeptidase (-GTP) which initiates glutathione catabolism to cysteine. We measured plasma and brain glutathione and cysteine in rats treated with AT-125. Six h after AT-125 treatment, plasma glutathione had increased 6-fold and plasma cysteine had fallen significantly. Brain cysteine fell after 24 h of AT-125 treatment, and brain glutathione had also decreased 18%. AT-125 pretreatment inhibited brain uptake of ³⁵S when it was given as ³⁵S-GSH but had no effect when it was given as ³⁵S-cysteine. These results suggest that plasma glutathione is catabolized by -GTP, and cysteine derived from it is taken up by the brain. N-acetylcysteine was administered to AT-125 treated rats in an attempt to supply cysteine to the brain in the face of -GTP inhibition. N-acetylcysteine supported brain glutathione levels, suggesting that it can serve as a source of cysteine under these conditions.Abbreviations -GTP -glutamyltranspeptidase - GSH reduced glutathione - TCA trichloroacetic acid     

Effects of low and high doses of l-Dopa on the tetrabenazine or α-methyltyrosine-induced suppression of behaviour in a successive discrimination task

The effect of the administration of l-Dopa, 10 or 100 mg/kg i.p., on the -methyltyrosine methylester HCl (-MT; 250+50 mg/kg i. p.) or tetrabenazine (TBZ; 2 mg/kg i.p.)-induced suppression of a successive discrimination-conditioned avoidance task has been studied. It was found that administration of the high l-Dopa dose resulted in a reversal of the -MT- or TBZ-induced suppression of the avoidance behaviour, although the discrimination was lost. Restoration of the avoidance behaviour and the correct discrimination was obtained with the low l-Dopa dose after -MT but not after TBZ. The difference in the behavioural response to l-Dopa after -MT as compared to the response obtained after TBZ is discussed in terms of the availability of the catecholamines formed from l-Dopa for release by the nerve impulses. Biochemical determinations of brain noradrenaline and dopamine were made in parallel. Further, a simple and reliable method for the aquisition of a successive discrimination in the rat is described.     

Morphine-like discriminative stimulus effects of opioid peptides: possible modulatory role ofd-Ala2-d-Leu5-enkephalin (DADL) and dynorphin A(1-13)

The role of the different opioid receptors was studied in rats trained to discriminate SC injections of 3.0 mg/kg morphine from saline by tests for generalization to graded doses of morphine and receptor-selective peptides administered into the lateral cerebral ventricle. Dose-dependent morphine-like stimulus effects were produced over a wide range of doses (0.001–30 g), depending upon ligand and animal, by morphine, by themu-selective peptides DAGO[d-Ala²-NMePhe⁴-Gly(ol)-enkephalin] and FK33824[d-Ala²,NMePhe⁴-Met(O)⁵-(ol)-enkephalin], and by thedelta-selective peptide, DADL[d-Ala²,d-Leu⁵enkephalin]. The order of relative potency of these substances was: FK33824>DAGO>morphine>DADL. In contrast, DPLPE[d-Pen²,l-Pen⁵)enkephalin], which has much greaterdelta receptor selectivity than does DADL, and dynorphin A(1-13) (0.1–10 g), akappa-receptor agonist, engendered choice responding appropriate for saline. When 1.0 g DADL, a dose lacking morphine-like discriminative effects, was administered concurrently with SC morphine, the stimulus effects of morphine were potentiated. Concurrent administration of 10 g dynorphin A(1-13) and morphine attenuated the stimulus effects of morphine inconsistently. These results support previous findings thatmu-opioid receptors are of primary importance in mediating the morphine-like discriminative effects of opioid peptides. They also suggest that morphine-like discriminative effects can be modulated by other types of opioid receptors.     

Pharmacokinetics of 2′,3′-dideoxyadenosine in dogs

The pharmacokinetics of 2,3-dideoxyadenosine (ddAdo) and 2-3-dideoxyinosine (ddIno) were determined after intravenous bolus administration and long-term intravenous infusion of ddAdo in dogs. ddAdo was rapidly deaminated to ddIno and ddAdo plasma concentrations were only a fraction of ddIno concentrations. The total body clearance of ddAdo exceeded the literature value for the cardiac output of the dog, indicating an extremely rapid metabolism, and the existence of extrahepatic metabolism. Urinary excretion of unchanged ddAdo was a minor route of elimination ( 1%). The pharmacokinetics of ddIno was determined assuming complete conversions of ddAdo to ddIno. ddIno elimination was dose-dependent with total body clearance ranging from 4 to 55 ml/min/kg in individual animals. The plasma half-life was approximately 30 min after most routes of administration, but increased to approximately 60 min in two animals receiving a large intravenous dose of 500 mg/kg. ddIno penetrated into the cerebrospinal fluid to a limited extent, reaching concentrations of 3–11% of those in plasma. Urinary excretion of unchanged ddIno accounted for approximately 20% of the administered dose of ddAdo, while uric acid and hypoxanthine were minor urinary metabolites.Concentrations exceeding the in vitro minimal viral inhibitory concentration (2.4 g/mL) could be safely maintained in plasma for a 10-day period. Infusions which gave cerebrospinal fluid concentrations of 12 to 17 Lg/mL resulted in dose limiting myelosuppression and intestinal toxicity, after less than 10 days of infusion. Orally administered ddAdo was absorbed as ddIno, with bioavailabilities ranging from 28 to 93% in experiments where no emesis occurred. These studies indicate the rapid in vivo conversion of ddAdo to ddIno, and support the selection of ddIno over ddAdo for further drug development.     

Cannabinols and feeding in sheep

Marijuana, long used for the euphoria which results, recently has been found to stimulate hunger in humans but in several laboratory animals cannabinoids decrease food intake. Sheep, relatively more sensitive to chemicals that affect food intake, were injected IV with the d-and l-isomers of tetrahydrocannabinol and with a 9-aza-cannabinol) 9-AC) (8-(1,2-dimethylheptyl)-5,5-dimethyl-5H-[1]benzopyranol[3,4]pyridin-10-01, HCl) and feeding behavior was monitored. In the first 30 min, food intake was increased by the l-isomer and by 9-AC but not affected by d- ⁹-THC. After 24h, feed intake was decreased by at least one dose of d-and l- ⁹-THC and 9-AC. The l- but not d-isomer was active at very low doses compared with doses used in many laboratory animals.     

Myeloid hyperplasia in growing rats after chronic treatment with Δ9-THC at behavioral doses

Summary ⁹-THC at the dose of 1 mg/kg/die was administered subcutaneously in growing rats, from the second to the 30th day of life. A statistically significant myeloid hyperplasia was demonstrated, which persisted up to 4 months after the end of the treatment, together with significant blood granulocytosis.     

Behavioral and biochemical effects of α-methyltyrosine in cats

A single dose of orally administered DL--methyltyrosine methylester hydrochloride (AMT) significantly increased the number of errors made by cats performing a spatial delayed response (DR) task. The same doses of AMT had no such effect on simultaneous visual discrimination (VD) performance. Response latencies were increased in all cats, whichever task performed. In an attempt to correlate the behavioral and biochemical effects of AMT, dopamine (DA), noradrenaline (NA) and serotonin (5-HT) were assayed in 5 brain structures, 4 to 48 h after 100 to 175 mg/kg. DA was reduced significantly with all doses of AMT used, NA with doses of 125 mg/kg and more. 5-HT increased significantly after 100 and 125 mg/kg but remained unchanged after higher doses. Due to the simultaneous action of AMT on DA, NA and 5-HT, the respective roles of these amines are difficult to dissociate. In contradistinction, previous findings suggest that brain DA be responsible for the impairment of DR performance.Preliminary report of this research was presented at the meeting of the Canadian Federation of Biological Sciences, June 1972.Andrée G. Roberge was responsible for the biochemical part of this work and Anne Kitsikis for the neuropsychopharmacological part.     

N2-Acetylphenelzine : effects on rat brain GABA,alanine and biogenic amines

Summary The neurochemical properties of N ²-acetyl-phenelzine were compared with those of phenelzine in a rat model. N ²-Acetylphenelzine is a relatively potent inhibitor of monoamine oxidase-A and -B and causes increases in whole-brain levels of noradrenaline and 5-hydroxytryptamine, and decreases in homovanillic acid, 5-hydroxyindole-3-acetic acid, and 3,4-dihydroxyphenylacetic acid after acute i.p. administration of the drug. Phenelzine is a more potent monoamine oxidase inhibitor than is N ²-acetylphenelzine. The most marked difference in the profile was that N ²-acetylphenelzine had no effect on whole brain levels of the amino acid neurotransmitters alanine and -aminobutyric acid, whereas phenelzine caused dramatic increases. Acetylation of phenelzine at the N² position presumably interferes with the inhibition of the transaminase enzymes for -aminobutyric acid and alanine.     

Differences in presynaptic α-blockade,noradrenaline uptake inhibition,and potential antidepressant activity between (+)- and (-)mianserin

The effect of racemic mianserin on K⁺-evoked tritium release from rat brain cortex slices previously incubated with ³H-l-noradrenaline was studied. Racemic mianserin (10^-9-10^-5 M) increased stimulation-induced release dose-dependently. As methysergide, metiamide, and cyproheptadine failed to do so, it was concluded that this effect was probably not caused by the antihistamine or antiserotonin activity of racemic mianserin, but due to its -adrenolytic effect. Evaluation of the effects of the enantiomers (+)(S)mianserin and (-)(R)mianserin showed that the -adrenolytic effect resided in the (+)isomer, whereas the (-)isomer was inactive at a concentration of 10^-6 M. Inhibition of noradrenaline into rat hypothalamic synaptosomes also showed stereospecificity in that (+)mianserin was about 300-times more active than (-)mianserin. Inhibition of rat muricidal behavior, a test for potential antidepressant activity, showed a similar dissociation in the effects of the two enantiomers, in that (+)mianserin was active, whereas (-)mianserin was not.     

The effects of chronic treatment with δ9-tetrahydrocannabinol on catecholamine synthesis in the rat

Chronic administration of ⁹-tetrahydrocannabinol (2 mg/kg intravenously daily, for one week) to rats resulted in a significant increase in the synthesis of H³-catecholamines in the brain and adrenals. Endogenous noradrenaline and dopamine concentration in the brain, adrenaline and noradrenaline level in adrenals and cardiac noradrenaline content of experimental rats did not differ from those of control animals injected with the solvent alone.WHO Fellow     

Developmental Responses of a Terrestrial Insect Detritivore, <Emphasis Type="BoldItalic">Megaselia scalaris</Emphasis> (Loew) to Four Selenium Species

Megaselia scalaris (Loew) (Diptera: Phoridae) is an important and ubiquitous terrestrial detritivore that consumes both animal and plant material. Because both plants and animals convert selenium pollutants into various forms, the relative toxicities of ecologically relevant concentrations of sodium selenate, sodium selenite, seleno-L-methionine, and Se-(methyl) selenocysteine hydrochloride to larvae were assessed in diet bioassays. In addition, ovipositional preferences of adults and developmental effects on the eggs and larvae were measured. With chronic exposure selenocysteine was the most toxic of the selenium species to the larvae (LC₅₀: 83 g/g wet weight), followed by seleno-L-methionine (LC₅₀: 130 g/g), selenate (LC₅₀: 258 g/g), and selenite (LC₅₀: 392 g/g). Ovipositing females did not discriminate between the highest treatment concentrations of any of the pollutants as compared to the controls, indicating a lack of avoidance behavior. Larval development time was significantly increased with exposure to selenate at 100 g/g wet weight and above, selenite at 300 g/g and above, and at 50 g/g and 25 g/g and above for seleno-L-methionine and selenocysteine respectively. Pupal development was not affected by any of the selenium treatments. Significant differences between male and female adult eclosion times were observed, with females eclosing later than males as selenium concentrations increased. Significant decreases in larval survival relative to controls occurred at the lowest treatment tested (100 g/g) for both selenate and selenite and at 100 g/g for seleno-L-methionine, and 50 g/g for selenocysteine. The population level implications of lack of avoidance of contaminated food, and the effects of increased development times, reduced survivorship, and non-synchronized male and female emergence are discussed.