Investigations of Amitraz Neurotoxicity in Rats: I. Effects on Operant Performance

Investigations of Amitraz Neurotoxicity in Rats. I. Effectson Operant Performance. MOSER, V. C., BOYES, W. K., AND MACPHAIL,R. C. (1987). Fundam. Appl. Toxicol. 9, 131–139. Amitraz(AMZ) is a formamidine pesticide which is often compared tochiordimeform (CDM). The effects of AMZ (6.25–75 mg/kg)and CDM (5–20 mg/kg) on the schedule-controlled performanceof rats were examined using a multiple flxed-ratio (FR) 10 fixed-interval(FI) 300-sec schedule of milk reinforcement. Following dose-effectdeterminations, rats received three daily doses of AMZ (50 mg/kg).Low to intermediate doses of AMZ (6.25–25 mg/kg), administered20 min presession, significantly decreased FI responding butnot FR responding. In contrast, CDM appeared to decrease respondingsimilarly under both components. Both compounds disrupted thetemporal pattern of responding within the interval; AMZ hadonly a moderate influence at all effective doses but CDM produceda marked dose-dependent disruption of temporal response patterning.The effects of the high doses of AMZ (50–75 mg/kg) weremore pronounced 24 hr after dosing, whereas the rats had recoveredfrom lower doses at this time. Performance was progressivelydisrupted and the rats' health rapidly deteriorated during thecourse of three daily injections of AMZ (50 mg/kg). Operantperformance recovered more quickly than did the general healthof the rats. Thus AMZ produced effects on multiple-scheduleperformance that were distinct from the effects of CDM. Moreover,the signs of intoxication and the effects on schedule-controlledbehavior following a high dose (50 mg/kg) were augmented andpersistent with short-term repeated administration.     

Investigations of Amitraz Neurotoxicity in Rats: II Effects on Visual Evoked Potentials

Investigations of Amitraz Neurotoxicity in Rats. II. Effectson Visual Evoked Potentials. BOYES W. K., AND MOSER, V. C. (1987).Fundam. Appl. Toxicol 9, 140–153. As a part of a seriesof studies investigating the possible neurotoxicity of amitraz(AMZ), a formamidine pesticide, visual evoked potentials wererecorded from Long-Evans rats following acute and shorttermrepeated exposures to AMZ. The first of three experiments examinedthe relationship between a single ip injection of AMZ (0, 50,and 100 mg/kg) and the latency and peak-to-peak amplitude ofpattern-reversal (PREP) and flash-evoked potentials (FEP). Theeffects of another formamidine, chlordimeform (CDM; 40 mg/kg),were also studied for comparison purposes. Two hours after treatment,AMZ exposure produced large, dose-related increases in PREPamplitudes. Exposure to CDM produced similar changes. Neithercompound changed FEP amplitudes. Body temperatures were reducedand evoked potential peak latencies were increased by both compounds.The latency increases were probably a secondary consequenceof hypothermia. In the second experiment, PREPs were recordedbefore and 2, 24, 48, and 72 hr after treatment with AMZ (100mg/kg). The time course of changes was biphasic in nature, withincreases in amplitudes (N1P1, P1N2, and N2P3) 2 hr after treatmentfollowed by subsequent depression in amplitude (P2N3) at 48hr. Recovery occurred by 72 hr after treatment. The third experimentexamined the effects of three daily treatments with either vehicleor 50 or 100 mg/ kg AMZ. Body weights and body temperaturesshowed dose-related reductions which progressed with each additionaltreatment and recovered partially by 6 days after cessationof treatment. The PREPs of AMZ-treated rats again showed biphasicchanges, with N1P1 and P1N2 amplitudes significantly increasedon each day of treatment and 1–2 days following the thirdtreatment. Amplitude P2N3 showed an initial increase on thefirst 2 days of treatment, followed by subsequent, progressiveamplitude reductions. In summary, AMZ produced two phases ofchange in visual evoked potentials. The first phase was characterizedby large increases in PREP amplitudes without increasing FEPamplitudes in the same rats. The second phase was characterizedby suppression of PREP P2N3 amplitude. Short-term repeated exposureproduced signs of accumulating intoxication including progressiveloss of body weight, lowered body temperature, and prolongedduration of evoked potential changes.     

Role of Monoamine Oxidase Inhibition and Monoamine Depletion in Fenfluramine‐Induced Neurotoxicity and Serotonin Release

Abstract: The role of both monoamine synthesis and monoamine oxidase inhibition in mediating the fenfluramine‐induced damage to serotonin neurones was examined; as pretreatment agents, both alpha‐methyl‐para‐tyrosine (AMPT) and para‐chlorophenylalanine (PCPA) were used to deplete dopamine and serotonin, respectively, while clorgyline and deprenyl were used to inhibit monoamine oxidase types A and B. While both AMPT and deprenyl did not alter fenfluramine‐induced serotonin or 5‐hydroxyindoleacetic acid (5‐HIAA) depletion in any area, PCPA did partially reduce the serotonin depletion in the hippocampus and hypothalamus. Although pretreatment with clorgyline did not significantly alter fenfluramine‐induced serotonin depletion, it did produce a 65% mortality rate in animals treated with both drugs. Both PCPA and clorgyline significantly increased the depletion of striatal 5‐HIAA concentration consequent to fenfluramine; however, these drugs also produced a long‐term depletion of striatal 5‐HIAA when administered alone, therefore, the changes seen after the coadministration with fenfluramine may be viewed as additive. Finally, acute PCPA pretreatment attenuated the rapid rise in 3,4‐dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (homovanillic acid) induced by fenfluramine, and acute clorgyline reversed the drop in serotonin and rise in 5‐HIAA induced by fenfluramine. These results indicate that the rapid increase in dopamine activity induced by fenfluramine is partially dependent on serotonin concentration and release and that the mechanism of fenfluramine‐induced toxicity is unlike that of the other substituted amphetamines.     

Effects of Different Monoamine Oxidase Inhibitors on Respiratory Activity in Rats with Chronically Impaired Central Serotonergic Function

Abstract: Resting and CO₂ stimulated respiration were measured by means of a whole-body plethysmograph in rats lightly anaesthetized with halothane. Rats pretreated neonatally with intracisternal 5,7-dihydroxytryptamine (5,7-DHT) to destruct permanently central serotonergic neurones had significantly lower resting and CO₂ stimulated respiratory frequency (RF) and minute volume (V_M) than naive rats. In the 5,7-DHT pretreated rats, but not in naive rats, the monoamine oxidase inhibitors clorgyline and pargyline further reduced both resting and CO₂ stimulated RF and Vm, whereas 1-deprenyl stimulated respiration. The results provide additional evidence that monoaminergic mechanisms are involved in central modulation of respiration in which activation of a serotonergic neuronal system depresses, and dopaminergic activation stimulates respiration.     

Effects of Amitraz on Motor Function *

The effects of amitraz, a formamidine derivative, on motor function were studied in rats. Behavioural and neurochemical studies were performed. Results show that amitraz was able: 1) to decrease locomotion and rearing frequencies of rats and to increase their immobility time in an open-field; 2) to displace to the left the control dose-response curve constructed to apomorphine-induced stereotyped behavior; 3) to potentiate both pentobarbital sleeping time and amphetamine effects on open-field behaviour of rats and 4) to increase not only the whole brain levels of noradrenaline but also the striatal levels of dopamine. In relation to control animals, the pesticide also induced 5) a decrease in the striatal levels of homovanillic acid, 6) pesticide effects on open-field behaviour of rats were not antagonized by yohimbine administration, and 7) metoclopramide administration on amitraz pretreated rats antagonized not only amphetamine effects on open-field behaviour, but also apomorphine-induced stereotypy. These results are discussed in the light of the actions of amitraz on biogenic amines. It is suggested that the pesticide effects on motor function are consequences of the inhibitory effects on MAO activity, most probably through the increases produced on catecholamine levels within the central nervous system.     

酶标仪比色法测定单胺氧化酶活性

目的 建立用酶标仪比色测定单胺氧化酶A(monoamine oxidase A,MA0 A)和MA0 B活性的方法。方法以大鼠肝组织匀浆作酶原,分别以血清素(5-HT)和苄胺作为MAO A和MA0 B底物,以2,4-二硝基苯肼(DNPH)和氢氧化钠为显色剂,在450 nm处用酶标仪比色测定。结果该方法能快速、灵敏、稳定...     

酶标仪比色法测定单胺氧化酶活性

目的建立用酶标仪比色测定单胺氧化酶A(monoamine oxidase A,MAO A)和MAO B活性的方法。方法以大鼠肝组织匀浆作酶原,分别以血清素(5-HT)和苄胺作为MAO A和MAO B底物,以2,4-二硝基苯肼(DNPH)和氢氧化钠为显色剂,在450 nm处用酶标仪比色测定。结果该方法能快速、灵敏、稳定、选择性地测定MAO活性。结论建立了以酶标仪比色法测定MAO活性的方法用于筛选药物。     

Further Studies on the Ex-vivo Effects of Procarbazine and Monomethylhydrazine on Rat Semicarbazide-sensitive Amine Oxidase and Monoamine Oxidase Activities

Following administration of the anticancer agent, procarbazine, or one of its metabolites, monomethylhydrazine, to rats, activities of monoamine oxidases A and B (MAO A and MAO B) and of semicarbazidesensitive amine oxidase (SSAO) were measured ex-vivo. Both compounds were found to be potent inhibitors of SSAO in tissue homogenates, exhibiting ID50 values in most tissues of approximately 8 mgkg^?1 (procarbazine) and 0.08 mg kg^?1 (monomethylhydrazine). Concurrent dose-dependent inhibition of MAO activities did not occur. However, in liver, potentiation of MAO B activity, to 140% of that in controls, was apparent following monomethyl-hydrazine and this effect was independent of the drug dose. Both compounds produced a dose-dependent potentiation of MAO A in brown adipose tissue, the elevation being more pronounced following monomethylhydrazine, with activity rising to 350% of that in control homogenates. In a parallel in-vitro study, monomethylhydrazine was without effect on MAO A in brown adipose tissue homogenates. By perfusing the SSAO substrate, benzylamine, through the isolated mesenteric arterial bed of the rat, it was found that pretreatment of animals with procarbazine or monomethylhydrazine reduced metabolism of this amine by a similar degree as had been determined ex-vivo in blood vessel homogenates. The results presented suggest that these compounds would be suitable for use as selective inhibitors in pharmacological examinations of SSAO function in isolated tissues and organs.     

Monoamine Oxidase Inhibitory Activity of Novel Pyrazoline Analogues: Curcumin Based Design and Synthesis

相似文献   

Neuroprotective Activity of Pongamia pinnata in Monosodium Glutamate-induced Neurotoxicity in Rats

This study was designed to evaluate the neuroprotective activity of ethanol extract of Pongamia pinnata stem bark in monosodium glutamate-induced neurotoxicity in rats. Neurotoxicity was induced by intraperitoneal injection of monosodium glutamate 2 g per kg body weight daily for 7 days. Ethanol extract of Pongamia pinnata stem bark (200 and 400 mg/kg) was administered orally after 1 h of monosodium glutamate treatment. Dextromethorphan (30 mg/kg, p.o.) was used as standard drug for the comparison. The degree of protection was determined by various behavioural, locomotor, muscle grip activity, lipid peroxidation and measurement of antioxidant status of glutathione, catalase and superoxide dismutase. Estimation of calcium, sodium and potassium ions in brain tissue and gamma aminobutyric acid level in serum was carried out. The histopathological study of brain tissue was also carried out. Treatment with Pongamia pinnata significantly improved monosodium glutamate-induced alteration in behavioural and locomotor activity and muscle strength. Significant decrease in lipid peroxidation and increase in glutathione, superoxide dismutase and catalase was observed in Pongamia pinnata treated group. Further, Pongamia pinnata also significantly reduced the monosodium glutamate-induced excitotoxicity by decreasing the level of Ca⁺² and Na⁺ with concomitant increase in the level of K⁺. Serum gamma aminobutyric acid level was also increased in Pongamia pinnata treated animals. Further, the histopathological evidence supports the neuroprotective activity of Pongamia pinnata. In conclusion, the present study suggests that the ethanol extract of stem bark of Pongamia pinnata possesses significant neuroprotective activity in albino rats.     

Synthesis and Selective Human Monoamine Oxidase B Inhibition of Heterocyclic Hybrids Based on Hydrazine and Thiazole Scaffolds

A new scaffold of hydrazothiazoles has been designed as monoamine oxidase (MAO) inhibitors combining the hydrazine moiety of iproniazid and the thiazole nucleus of glitazones, a class of peroxisome proliferator‐activated receptor (PPAR)γ agonists recently co‐crystallized with human MAO‐B. The resulting derivatives were synthesized and assayed to evaluate their in vitro activity against both the A and B isoforms of hMAO. All compounds were shown to be selective hMAO‐B inhibitors with IC₅₀ values in the low micromolar/high nanomolar range. Such results suggest that the hydrazothiazole scaffold could be considered as an interesting pharmacophore for the future design of new lead compounds as coadjuvants for the treatment of neurodegenerative diseases.     

Effects of 5-HT1A Receptor Agonists on Patterns of Rat Motor Activity in Relation to Effects on Forebrain Monoamine Synthesis

Abstract: The effects of the 5-HT_1A receptor agonists 8-OH-DPAT (0.15–2.5 μmol kg^?1 subcutaneously), flesinoxan (0.6–10.0 μmol kg^?1 subcutaneously) and buspirone (1.9–30.0 μmol kg^?1 subcutaneously) on spontaneous motor activity in male Sprague-Dawley rats was examined in a photocell-equipped open-field arena. Following motor activity observations, the cerebral aromatic L-amino acid decarboxylase inhibitor NSD-1015 (100 mg kg^?1 intraperitoneally) was administered and 30 min. later the animals were decapitated for subsequent analysis of the accumulated forebrain DOPA and 5-HTP levels, as an estimate of the rate of monoamine synthesis. 8-OH-DPAT and flesinoxan produced a similar and characteristic pattern of changes of the spontaneous motor activity in normal animals i.e. a moderate decrease in locomotor activity, a marked suppression of rearing and an increase in the relative amount of forward locomotion and of activity in the periphery of the open-field arena. This behavioural profile was closely related to a decrease in forebrain 5-HTP accumulation, indicating 5-HT receptor stimulation. In agreement with these observations buspirone also produced an increase in peripheral activity and a suppression of rearing. In contrast to effects by 8-OH-DPAT and flesinoxan, however, buspirone produced a further reduction of locomotor activity and reduced the forward locomotion. This difference in behavioural profile between buspirone and the other two compounds is probably explained by its DA receptor blocking properties, as indicated by an increased DOPA accumulation in the neostriatum. At least partially, 8-OH-DPAT, flesinoxan and buspirone, all antagonized reserpine-induced (5 mg kg^?1 subcutaneously – 16 hr) suppression of locomotor activity. This stimulation of locomotor activity in reserpine-treated rats is in all probability related to 5-HT_1A receptor stimulation since concomitant DA D₂ receptor blockade, in the case of buspirone, did not markedly affect this behavioural response.     

Inhibition of Monoamine Oxidase from Bovine Retina by β-Carbolines

Abstract— The behaviour of some β-carboline derivatives as inhibitors of monoamine oxidase has been studied in bovine retina. Inhibition was found not to show any significant time dependence. Di- and tetrahydro-β-carbolines were shown to behave as reversible and competitive inhibitors. In contrast, the fully unsaturated β-carbolines harmane, harmine and harmaline, which showed deviation from linearity at high substrate concentrations, behaved as tight-binding inhibitors. In these cases, the concentration of the enzyme and the inhibitor were of the same order. This was confirmed by the K_i values for these compounds in the nanomolar concentration range. Consistent with this was that inhibition was only partly reversed by dialysis for 18 h at 4°C, although complete reversal was observed after dialysis for the same period at 37°C. Structure-activity relationships indicated that substitution of a methoxy group at the C7 position of the aromatic ring is determinant for this tight-binding behaviour; a substitution of this group at the C6 position greatly reduced inhibition. Since β-carbolines have been reported to be formed endogenously, this suggests that they might have important physiological actions on monoamine oxidase activity in-vivo. In contrast, all the β-carbolines investigated in this study had low potencies as inhibitors of monoamine oxidase B.     

Beyond Topoisomerase Inhibition: Antitumor 1,4‐Naphthoquinones as Potential Inhibitors of Human Monoamine Oxidase

Monoamine oxidase (MAO) action has been involved in the regulation of neurotransmitters levels, cell signaling, cellular growth, and differentiation as well as in the balance of the intracellular polyamine levels. Although so far obscure, MAO inhibitors are believed to have some effect on tumors progression. 1,4‐naphthoquinone (1,4‐NQ) has been pointed out as a potential pharmacophore for inhibition of both MAO and DNA topoisomerase activities, this latter associated with antitumor activity. Herein, we demonstrated that certain antitumor 1,4‐NQs, including spermidine‐1,4‐NQ, lapachol, and nor‐lapachol display inhibitory activity on human MAO‐A and MAO‐B. Kinetic studies indicated that these compounds are reversible and competitive MAO inhibitors, being the enzyme selectivity greatly affected by substitutions on 1,4‐NQ ring. Molecular docking studies suggested that the most potent MAO inhibitors are capable to bind to the MAO active site in close proximity of flavin moiety. Furthermore, ability to inhibit both MAO‐A and MAO‐B can be potentialized by the formation of hydrogen bonds between these compounds and FAD and/or the residues in the active site. Although spermidine‐1,4‐NQs exhibit antitumor action primarily by inhibiting topoisomerase via DNA intercalation, our findings suggest that their effect on MAO activity should be taken into account when their application in cancer therapy is considered.     

Effects of Anticonvulsants on Local Anaesthetic‐Induced Neurotoxicity in Rats

Abstract: The effects of various anticonvulsants on local anaesthetics procaine‐ and lidocaine‐induced convulsions were investigated in rats. Pretreatment with diazepam (2.5–5 mg/kg, intraperitoneally) and clonazepam (5–10 mg/kg, intraperitoneally) completely protected the rats against both local anaesthetic‐induced convulsions. Phenobarbital (12.5–50 mg/kg, subcutaneously) also significantly decreased the incidence of both convulsions and prolonged their latencies. Carbabazepine (10–40 mg/kg, intraperitoneally) did not completely repress both convulsions, but it prolonged their latencies. Phenytoin (5–20 mg/kg, intraperitoneally) and primidone (30–60 mg/kg, intraperitoneally) markedly enhanced both local anaesthetic‐induced convulsions, as shown by shortening of latency and increase in mortality. Valproate (100–200 mg/kg, intraperitoneally) produced a protective effect against procaine‐induced convulsions, while it strongly enhanced lidocaine‐induced convulsions. These results suggest that the benzodiazepines are effective drugs to prevent neurotoxicity induced by local anaesthetics, while phenytoin and primidone potentiate them.     

Determination of Isatin,an Endogenous Monoamine Oxidase Inhibitor,in Urine and Tissues of Rats by HPLC

• 1.We have previously identified isatin as one of the endogenous monoamine oxidase (MAO) inhibitors in the urine and the brain of stroke-prone spontaneously hypertensive rats (SHRSP), using gas chromatography-mass spectrometry (GC-MS).
• 2.In this study, we attempted to develop a convenient assay to determine isatin using high performance liquid chromatography with an ultraviolet detector (HPLC-UV). The standard curve for authentic isatin was linear at a range from 2 to 20 nmol per ml. The coefficient of variance was within 3% for both intra-assay and inter-assay. The sensitivity was 20 pmol per 10 μl of urine sample.
• 3.Isatin concentration correlated significantly and positively with endogenous MAO activity (tribulin-like activity) in both urine (r=0.924, P<0.001) and kidney extracts (r=0.862, P<0.01). There was a significant difference in urinary isatin between Wistar Kyoto rats (WKY) and SHRSP. Oral administration of isatin increased urinary isatin concentration and systolic blood pressure in WKY.
• 4.Determination of isatin using HPLC-UV may be useful for elucidating role of isatin in various conditions of stress and disease.

     

Effects of Acute and Repeated Exposures to Aroclor 1254 in Adult Rats: Motor Activity and Flavor Aversion Conditioning

While considerable research has focused on the neurotoxicityof developmental exposures to polychlorinated biphenyls, includingAroclor 1254, relatively little is known about exposures inadult animals. This study investigated the behavioral effectsof acute and repeated Aroclor 1254 exposures to adult rats onmotor activity and flavor aversion conditioning. Male Long-Evansrats (60 days old) were tested for motor activity in a photocelldevice after acute (0, 100, 300, or 1000 mg/kg, po) or repeated(0, 1, 3, 10, 30 or 100 mg/kg/day, po, 5 days/week for 4 to6 weeks) exposure to Aroclor 1254. Motor activity was decreaseddose-dependently at doses of 300 mg/kg or more after acute exposure.Severe body weight loss and deaths occurred at 1000 mg/kg. Recoveryof activity occurred over 9 weeks but was incomplete. Afterrepeated exposure, motor activity was decreased dose-dependentlyat doses of 30 mg/kg or more, and severe weight loss and deathsoccurred at 100 mg/kg. In contrast to acute exposure, completerecovery of activity occurred 3 weeks after exposure. Additionalrats were water deprived (30 mm/day) and received acute po administrationof Aroclor 1254 (0, 10, 15, 25, 30, 100, or 300 mg/kg) shortlyafter consuming a saccharin solution. Three days later theywere given the choice between consuming saccharin or water,and saccharin preferences were recorded. Saccharin preferencewas decreased at doses of 25 mg/kg or more. Additional experimentsdetermined the effect of repeated saccharin-Aroclor 1254 pairings(0, 3.75, 7.5, or 15 mg/kg/day, 14 days) followed by a choicetest 1 day after the last dose. Repeated exposure to 15 mg/kgproduced robust flavor aversion conditioning. Repeated exposureto 7.5 mg/kg produced flavor aversion conditioning in four of12 rats. These results demonstrate that Aroclor 1254 causeshypoactivlty and flavor aversions in adult rats; the no observableeffect level (NOEL) for motor activity was 100 mg/kg for acuteexposure and 10 mg/kg for repeated exposure for a period ofup to 6 weeks. The acute NOEL for flavor aversion conditioningwas 15 mg/kg while the repeated NOEL was 7.5 mg/kg.     

Effects of Salicylate on 3,4-Methylenedioxymethamphetamine (MDMA)-Induced Neurotoxicity in Rats

The drug 3,4-methylenedioxymethamphetamine (MDMA) is a serotonergic neurotoxicant that causes hyperthermia and depletion of serotonin (5-HT) and 5-hydroxy-indole-3-acetic acid (5-HIAA) in the central nervous system. Formation of neurotoxic metabolites of MDMA, e.g., 2,4,5-trihydroxy-methamphetamine and 2,4,5-trihydroxyamphetamine, involves hydroxyl and/or superoxide free radicals. The present study was designed to determine whether the hydroxyl free-radical-trapping agent salicylate could provide protection against MDMA neurotoxicity in rats. In the acute studies, sodium salicylate (12.5–400 mg/kg, calculated as free acid) was injected interperitoneally (IP) 1 h before subscutaneous (SC) injections of MDMA (20 mg/kg as base). In the chronic studies, sodium salicylate (3.1–100 mg/kg) was injected IP 1 h before repeated SC injections of MDMA (10 mg/kg as base, twice daily, at 0830 and 1730 h for 4 consecutive days). Repeated MDMA administration depleted contents of 5-HT and 5-HIAA in the frontal cortex, hippocampus and striatum. Coadministration of salicylate plus MDMA did not significantly alter MDMA-induced depletion of 5-HT and 5-HIAA in these tissues. Thus, salicylate, a hydroxyl free-radical-trapping agent, does not protect against MDMA-induced hyperthermia and depletion of 5-HT and 5-HIAA. These observations suggest that MDMA-induced neurotoxicity may occur mainly through the production of superoxide or other radicals rather than hydroxyl free radicals. Salicylate actually potentiated MDMA-induced hyperthermia and lethality, findings that might be of clinical relevance. Published by Elsevier Science Inc.