The effects of methaqualone on the seizure susceptibility of mice

Methaqualone produces dose-and time-dependent decreases in susceptibility to electrically, chemically, and sound-induced seizures. The antagonism of methaqualone to electroconvulsive shock can be dissociated from its effects on temperature regulation and plasma corticosterone. Studies with SKF 525 A, a drug known to block enzymes in the liver that metabolize drugs, suggest that methaqualone, rather than a metabolite produced in the liver, is responsible for its anticonvulsant effects. Tolerance to the anticonvulsant effects of methaqualone is also demonstrated.     

Acute and chronic effects of d- and 1-amphetamine on seizure susceptibility in mice

The effects of d- and 1-amphetamine were studied on different patterns of seizure activity in male mice, e.g., pentylenetetrazol-induced minimal (clonic) and maximal (tonic) seizures and low-frequency electroshock seizure threshold (1.f. EST). Acute administration of d- and 1-amphetamine increased susceptibility to minimal and 1.f. EST. Whereas 1-amphetamine increased maximal seizure susceptibility, the d-isomer decreased susceptibility to this seizure pattern. Daily injections of the amphetamine isomers for 7 consecutive days produced tolerance to all these changes in seizure threshold. d-Amphetamine was approximately twice as active as 1-amphetamine in altering seizure threshold. These studies are in agreement with the concept that amphetamine-enhanced pentylenetetrazol-induced seizures are mediated by dopamine. Chronic administration of saline for 7 days reduced susceptibility to maximal seizures and 1.f. EST 35 and 72%, respectively, but had little effect on minimal seizure threshold.     

Effect of antidepressant drugs in mice lacking the norepinephrine transporter.

One of the main theories concerning the mechanism of action of antidepressant drugs (ADs) is based on the notion that the neurochemical background of depression involves an impairment of central noradrenergic transmission with a concomitant decrease of the norepinephrine (NE) in the synaptic gap. Many ADs increase synaptic NE availability by inhibition of the reuptake of NE. Using mice lacking NE transporter (NET-/-) we examined their baseline phenotype as well as the response in the forced swim test (FST) and in the tail suspension test (TST) upon treatment with ADs that display different pharmacological profiles. In both tests, the NET-/- mice behaved like wild-type (WT) mice acutely treated with ADs. Autoradiographic studies showed decreased binding of the beta-adrenergic ligand [3H]CGP12177 in the cerebral cortex of NET-/- mice, indicating the changes at the level of beta-adrenergic receptors similar to those obtained with ADs treatment. The binding of [3H]prazosin to alpha1-adrenergic receptors in the cerebral cortex of NET-/- mice was also decreased, most probably as an adaptive response to the sustained elevation of extracellular NE levels observed in these mice. A pronounced NET knockout-induced shortening of the immobility time in the TST (by ca 50%) compared to WT mice was not reduced any further by NET-inhibiting ADs such as reboxetine, desipramine, and imipramine. Citalopram, which is devoid of affinity for the NET, exerted a significant reduction of immobility time in the NET-/- mice. In the FST, reboxetine, desipramine, imipramine, and citalopram administered acutely did not reduce any further the immobility time shortened by NET knockout itself (ca 25%); however, antidepressant-like action of repeatedly (7 days) administered desipramine was observed in NET-/- mice, indicating that the chronic presence of this drug may also affect other neurochemical targets involved in the behavioral reactions monitored by this test. From the present study, it may be concluded that mice lacking the NET may represent a good model of some aspects of depression-resistant behavior, paralleled with alterations in the expression of adrenergic receptors, which result as an adaptation to elevated levels of extracellular NE.     

Toluene exposure increases aminophylline-induced seizure susceptibility in mice

The effects of toluene on the sensitivity to seizures induced by aminophylline were investigated. Mice were pretreated with an ip injection of corn oil or toluene (100-500 mg/kg) followed by a timed intravenous infusion of aminophylline at various time intervals to assess the seizure thresholds and lethal doses. Toluene increased seizure susceptibility to aminophylline in a dose- and time-dependent manner. Toluene-induced enhancement of seizure susceptibility to aminophylline occurred as early as 30 min and persisted for at least 3 days after a single administration of toluene (500 mg/kg). Treatment of benzaldehyde, one of toluene's metabolites, also showed an increase in the susceptibility to aminophylline. The enhancing effect was also observed in caffeine-induced seizures 1 h, but not 1 day after toluene treatment. These results suggest that individuals with toluene exposure may increase the risk for convulsive and even lethal complications associated with the therapeutic use of aminophylline.     

Effect of sodium cyanate on the seizure susceptibility of mice

The LD50 and median neurotoxic dose (as determined by impairment of rotarod performance) of sodium cyanate (NaOCN) were determined to be 278 and 155 mg/kg, ip, respectively. At doses of 38.75–155 mg/kg, NaOCN increased the susceptibility of mice to iv pentylenetetrazol-induced maximal seizures; the magnitude of this enhanced seizure susceptibility (15–47%) and its duration (5–60 min) were dose-dependent. Similarly, the two higher doses of NaOCN decreased the maximal electroshock seizure threshold 21–38%. Meclofenoxate pretreatment conferred a slight protection (12–14%) against cyanate potentiation of pentylenetetrazol-induced seizures. The oxygen affinity of hemoglobin was increased 6–10% by NaOCN, and P_CO2 values were elevated by 31–68%. The results of this study suggest that hypoxia may play a contributory role in cyanate-induced and potentiated seizure susceptibility in mice.     

Animal models of depression in dopamine, serotonin, and norepinephrine transporter knockout mice: prominent effects of dopamine transporter deletions

Antidepressant drugs produce therapeutic actions and many of their side effects via blockade of the plasma membrane transporters for serotonin (SERT/SLC6A2), norepinephrine (NET/SLC6A1), and dopamine (DAT/SLC6A3). Many antidepressants block several of these transporters; some are more selective. Mouse gene knockouts of these transporters provide interesting models for possible effects of chronic antidepressant treatments. To examine the role of monoamine transporters in models of depression DAT, NET, and SERT knockout (KO) mice and wild-type littermates were studied in the forced swim test (FST), the tail suspension test, and for sucrose consumption. To dissociate general activity from potential antidepressant effects three types of behavior were assessed in the FST: immobility, climbing, and swimming. In confirmation of earlier reports, both DAT KO and NET KO mice exhibited less immobility than wild-type littermates whereas SERT KO mice did not. Effects of DAT deletion were not simply because of hyperactivity, as decreased immobility was observed in DAT+/- mice that were not hyperactive as well as in DAT-/- mice that displayed profound hyperactivity. Climbing was increased, whereas swimming was almost eliminated in DAT-/- mice, and a modest but similar effect was seen in NET KO mice, which showed a modest decrease in locomotor activity. Combined increases in climbing and decreases in immobility are characteristic of FST results in antidepressant animal models, whereas selective effects on swimming are associated with the effects of stimulant drugs. Therefore, an effect on climbing is thought to more specifically reflect antidepressant effects, as has been observed in several other proposed animal models of reduced depressive phenotypes. A similar profile was observed in the tail suspension test, where DAT, NET, and SERT knockouts were all found to reduce immobility, but much greater effects were observed in DAT KO mice. However, to further determine whether these effects of DAT KO in animal models of depression may be because of the confounding effects of hyperactivity, mice were also assessed in a sucrose consumption test. Sucrose consumption was increased in DAT KO mice consistent with reduced anhedonia, and inconsistent with competitive hyperactivity; no increases were observed in SERT KO or NET KO mice. In summary, the effects of DAT KO in animal models of depression are larger than those produced by NET or SERT KO, and unlikely to be simply the result of the confounding effects of locomotor hyperactivity; thus, these data support reevaluation of the role that DAT expression could play in depression and the potential antidepressant effects of DAT blockade.     

Catecholaminergic involvement in the effects of amphetamine isomers on seizure susceptibility

The (+)-amphetamine (2.5 mg/kg) increase in pentylenetetrazol seizure was abolished by pretreatment with reserpine, α-methyltyrosine methyl ester (α-MT), FLA-63 or 6-hydroxydopa. All treatments except reserpine antagonized the increase in seizure threshold produced by (-)-amphetamine (4 mg/kg). Only reserpine +α-MT antagonized the decrease in seizure threshold produced by (+)-amphetamine (15 mg/kg). These results indicate that amphetamine alterations in PLZ seizure susceptibility are mediated indirectly via the release of newly synthetized and/or granular stores of catecholamines.     

The norepinephrine transporter in physiology and disease

The norepinephrine transporter (NET) terminates noradrenergic signalling by rapid re-uptake of neuronally released norepinephrine (NE) into presynaptic terminals. NET exerts a fine regulated control over NE-mediated behavioural and physiological effects including mood, depression, feeding behaviour, cognition, regulation of blood pressure and heart rate. NET is a target of several drugs which are therapeutically used in the treatment or diagnosis of disorders among which depression, attention-deficit hyperactivity disorder and feeding disturbances are the most common. Individual genetic variations in the gene encoding the human NET (hNET), located at chromosome 16q12.2, may contribute to the pathogenesis of those diseases. An increasing number of studies concerning the identification of single nucleotide polymorphisms in the hNET gene and their potential association with disease as well as the functional investigation of naturally occurring or induced amino acid variations in hNET have contributed to a better understanding of NET function, regulation and genetic contribution to disorders. This review will reflect the current knowledge in the field of NET from its initial discovery until now.     

Involvement of corticosteroids in acoustic induction of audiogenic seizure susceptibility in mice

Genetically seizure-resistant C57BL/6 mice were induced to develop high susceptibility (90%) to audiogenic seizures by prior exposure to auditory stimulation (acoustic priming) on day 19 of age. The administration of metopyrone (MP) or aminoglutethimide (AG), two inhibitors of adrenal corticosteroid synthesis, at 5 hrs before acoustic priming, prevented the induction of seizure susceptibility. 11-Deoxy-17-hydroxycorticosterone, an antagonist of glucocorticoid action by blocking glucocorticoid receptors, was also effective in completely preventing the priming effect. Similarly, acoustic priming failed to induce audiogenic seizure susceptibility in adrenalectomized mice. When MP or AG was administered to primed mice at 5 hrs before testing for audiogenic seizures on day 28 of age, they did not affect the elicitation of seizures by sound stimulus in the already susceptible mice. These results indicate that corticosteroids are required in order for the acoustic induction of audiogenic seizure susceptibility to occur.     

过量表达GABA转运蛋白-1的转基因小鼠对药物诱发癫痫易感

目的：应用过量表达GABA转运蛋白Ⅰ(GAT-1)的转基因小鼠研究GAT-1在癫痫发生中的作用。方法：采用腹腔注射戊四唑(PTZ),印防己毒素(PIC)或红藻氨酸(KA)诱导的癫痫发作为模型,比较GAT-1转基因小鼠和C57BL／6J对照小鼠阵挛性发作和强直性痉挛发生的百分率及潜伏期．结果：GAT-1转基因小鼠不但对不同剂量GABAA受体抑制剂PTZ,PIC,也对谷氨酸受体激动剂KA诱导的癫痫易感．GAT-1抑制剂ethyl nipecotate可明显减轻PTZ诱导的癫痫发作。结论：GAT-1转基因小鼠对癫痫易感证明GABA系统参与了癫痫发生,并且该转基因小鼠模型可作为研究癫痫发生的有用动物模型。     

Catechol-O-methyltransferase activity in CHO cells expressing norepinephrine transporter.

1. We examined the existence of catecholamine metabolizing enzymes (catechol-O-methyltransferase, COMT, and monoamine oxidase, MAO) in CHO cells transfected with norepinephrine (NE) transporter (NET) cDNA. 2. NET activity was studied by incubating cells with [3H]-NE (0. 5 microCi ml-1, 20 min) in a Na+ containing medium. Incubation with [3H]-NE lead to [3H] accumulation at 47797+/-4864 d.p.m. per well. Specific inhibitors of NET abolished this uptake. 3. During post-uptake incubation, [3H] leaked rapidly from cells and the extracellular phase comprised 89% of total radioactivity within 40 min. Both [3H] retention and [3H] 'leakage' were largely unaffected by inhibitors for MAO. In contrast, COMT inhibitors, U-0521 and Ro 41-0960, dose-dependently increased intracellular [3H]-NE retention with a maximal increase of 4.5 fold. The EC50 for Ro 41-0960 was 139-times lower than that of U-0521. U-0521 largely inhibited [3H] 'leakage' and doubled the apparent Vmax for [3H]-NE uptake. 4. Addition of U-0521 during uptake incubation increased intracellular NE content by 8 fold. Normetanephrine, the COMT-dependent metabolite of NE, was formed in large quantities during post-uptake incubation. U-0521 significantly inhibited the formation of NMN with an equal preservation of intracellular NE. 5. CHO cells expressing NET possess COMT activity, which is responsible for the metabolism of NE to form lipophilic metabolite normetanephrine. The apparent 'properties' of the NET function expressed in CHO cells changed, after inhibition of COMT, in such a way closer to that described in the native neuronal preparations.     

贝那替秦对最大电休克发作模型和戊四氮惊厥发作阈模型小鼠的抗惊厥作用

目的评价贝那替秦等抗胆碱药在不同惊厥模型的抗惊厥疗效,探讨其可能的作用机制。方法通过ig给予贝那替秦2~40 mg·kg-1记录最大电休克发作模型(MES)及戊四氮惊厥发作阈模型(MST)模型小鼠的未出现惊厥数。制备新生Wistar小鼠海马神经元细胞,加入贝那替秦1~100μmol·L-1,MTT检测细胞存活率。结果贝那替秦2~40 mg·kg-1在MES模型未出现惊厥数为2/10~7/10,在MST模型上未出现惊厥数为1/10~9/10均明显高于模型组(P<0.05,P<0.01),2个模型的ED50分别为12.2(4.7~53.6)mg·kg-1和12.5(7.0~25.9)mg·kg-1。贝那替秦1~100μmol·L-1能明显对抗N-甲基-D-天冬氨酸(NMDA)对海马神经元的损伤作用,细胞存活率明显增加(P<0.05)。结论贝那替秦在MES及MST惊厥模型均具明显抗惊厥作用,其作用机制可能与其对NMDA受体的拮抗作用有关。     

Changes in seizure susceptibility after successive treatments of mice with tryptophol and ethanol

Changes in leptazol (pentetrazol) seizure susceptibility after successive treatments of mice with tryptophol, a neutral metabolite of indoleamine, in combination with ethanol have been examined. Mice treated with tryptophol plus ethanol became highly susceptible to convulsions. There was little or no difference in seizure susceptibility in mice treated with tryptophol or ethanol alone, compared with the corresponding controls. In the mice treated with tryptophol plus ethanol, a much higher brain tryptophol level was observed, compared with that in mice treated with tryptophol alone. There appeared to be a good correlation between the reduction of the length of the seizure latency time and the time for which the brains were exposed to high levels of tryptophol. These results suggest that elevation of the levels of neutral indoleamine metabolites in the brain may have resulted in the increase in the seizure susceptibility.     

Changes in seizure susceptibility after successive treatments of mice with tryptophol and ethanol

Changes in leptazol (pentetrazol) seizure susceptibility after successive treatments of mice with tryptophol, a neutral metabolite of indoleamine, in combination with ethanol have been examined. Mice treated with tryptophol plus ethanol became highly susceptible to convulsion. There was little or no difference in seizure susceptibility in mice treated with tryptophol or ethanol alone, compared with the corresponding controls. In the mice treated with tryptophol plus ethanol, a much higher brain tryptophol level was observed, compared with that in mice treated with tryptophol alone. There appeared to be a good correlation between the reduction of the length of the seizure latency time and the time for which the brains were exposed to high levels of tryptophol. These results suggest that elevation of the levels of neutral indoleamine metabolites in the brain may have resulted in the increase in the seizure susceptibility.     

Studies in audiogenic seizure susceptibility

A genetically heterogeneous (HS) group of mice and a highly inbred strain of mice (C57BL/6) were both shown to become highly susceptible to audiogenic seizures after exposure to acoustic stimulation (priming). In heterogeneous mice the optimal age for priming was 18 days with a test-retest interval of 48 hours. The optimal test-retest interval in C57BL/6 mice primed at 20 days of age was 8 days. One second of priming was found effective in enhancing seizure susceptibility. Drugs known to alter steady state levels of biogenic amines and to change responses of mice genetically predisposed to audiogenic seizures were found to be effective in altering seizure susceptibility from priming, but not effective in altering the priming itself.This research was supported by research grants State of Illinois Public Welfare 17-302, National Institute of Mental Health MH 13026, USPHS MH No. 07083-08 and 09, and by a research fellowship (to R.A.L.) from the Schweppe Foundation.