Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0040822 (tremor)
 18,428 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The neurotoxic pyrethroid, deltamethrin, induces a severe motor syndrome characterised by tremor and choreoathetosis when injected systemically to rats. The interaction between deltamethrin and the two major dopaminergic pathways - the nigrostriatal and mesolimbic pathways - was investigated in rats. Striatal catecholamines, indoleamines and metabolites were measured by HPLC with electrochemical detection. Unilateral injection of deltamethrin (1.0 microgram) into the ventral tegmental nucleus or substantia nigra induced rapid ipsilateral or contralateral circling respectively but was ineffective at other basal ganglia sites. Both the sham and vehicle injections at either site, resulted in a marked increase above normal in DA turnover in the ipsilateral striatum without inducing circling behaviour. DA turnover was increased to the same extent in the ipsilateral stratum of deltamethrin-treated rats where rapid circling was present. Therefore the neurochemical findings were not consistent with the rotation theories based on striatal DA asymmetry but rather followed alternative mechanisms previously proposed, where circling behaviour can occur by mechanisms not causally related to striatal DA. These findings also indicate that a degree of selectivity exists in the action of deltamethrin, a sodium channel toxin that might be expected to act on all neuronal systems within the SN or VTN or equally at other sites within the basal ganglia associated with circling behaviour.
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PMID:Dissociation between circling behaviour and striatal dopamine activity following unilateral deltamethrin administration to rats. 241 69

p,p'-DDT and related agents act to hold the sodium channel open once opened and this effect is believed to be responsible for neurological effects of tremor and hyperexcitability in vivo. There is a good correlation between DDT-induced tremor and an increase in the levels of the metabolites of norepinephrine (NE), serotonin (5HT) and, to a lesser extent, dopamine (DA) in the brain stem (BS), hypothalamus (HYP), striatum (STR), or hippocampus (HPC). DDT also increases levels of excitatory amino acids glutamate (GLU) and aspartate (ASP), but the effect occurs only in the brain stem. These effects are dose- and time-related. Pharmacological studies found that blockade of alpha 1-adrenergic receptors attenuate DDT-induced tremor, while blockade of serotonergic, cholinergic muscarinic, and dopaminergic receptors augment the toxicity of DDT. Tremor was almost completely blocked in rats pretreated with hydantoin, an anticonvulsant believed to block repetitive firing of nerves by interfering with the inactivation gate of the sodium channel. A similar antagonism was observed for permethrin, a Type I pyrethroid believed to have a mechanism of action very similar to that of DDT. However, hydantoin increased the tremorigenic effects of chlordecone, an organochlorine whose mechanism has not been linked to the sodium channel. These data are consistent with the hypothesis that the in vivo neurotoxicity of some organochlorine insecticides is related to their effects on the sodium channel.
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PMID:Neurochemical effects of DDT in rat brain in vivo. 243 59

The extensive worldwide efforts of structural modification of natural pyrethrins for better performances have resulted in successful development of a wide variety of synthetic pyrethroids with tremendously high efficacy, knock-down activity or vapor action, and/or with acceptable environmental stability and safety. Currently these pyrethroids including their preferentially manufactured stereoisomers are widely used in agriculture, and for public health as well as household insect control. The detailed toxicology and metabolism studies intended to attain human risk assessment have revealed that with voltage-dependent sodium channel as target site pyrethroids induce pronounced repetitive activity characterized grossly by tremor, hypersensitivity, choleoathetosis, and salivation. In addition, so-called cyano-pyrethroids cause transient skin paresthesia in workers. With regard to tumorigenicity, mutagenicity, teratogenicity and developmental toxicity, no significant findings have been reported. Pyrethroids are eliminated from the animals quite rapidly and completely, undergoing oxidation and ester hydrolysis followed by various conjugations, with low tissue residues. Thus, overall, sound scientific bases exist for human risk assessment under the present usage conditions.
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PMID:Pyrethroids, nerve poisons: how their risks to human health should be assessed. 859 64

Lamotrigine (LTG) inhibits repetitive high frequency firing in depolarised neurones by selectively prolonging slow inactivation of the sodium channel, thereby suppressing the release of excitatory amino acids. It has been shown to be effective in 11 pivotal double-blind add-on trials in patients with refractory partial seizures with or without secondary generalisation. Subsequent anecdotal data support its efficacy for typical and atypical absences, myoclonic jerks, tonic or clonic seizures, Lennox-Gastaut syndrome and infantile spasms. Most recently LTG has been compared with carbamazepine and phenytoin in double-blind trials in patients with newly diagnosed partial and primary and secondary generalised tonic-clonic seizures. At the doses used, its efficacy was similar to the older agents for all seizure types, but LTG was better tolerated than both of the older agents. The commonest side-effects with LTG include headache, nausea, diplopia, dizziness, ataxia and tremor. Rash occurs in fewer than 5% patients. Its incidence can be reduced by starting treatment with a low dose, particularly in patients receiving concomitant sodium valproate which inhibits LTG metabolism. Enzyme inducers, such as carbamazepine, phenytoin and phenobarbital, accelerate its elimination, but LTG itself has no effect on hepatic metabolic processes. A pharmacodynamic interaction with carbamazepine necessitates a dosage reduction in some patients when LTG is introduced. LTG is a new antiepileptic agent with a long elimination half-life, a broad spectrum of activity, and a wide therapeutic ratio.
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PMID:Lamotrigine--an update. 895 Dec 13

The human genome contains 10 voltage-gated sodium channel genes, 7 of which are expressed in neurons of the CNS and PNS. The availability of human genome sequences and high-throughput mutation screening methods make it likely that many human disease mutations will be identified in these genes in the near future. Mutations of Scn8a in the mouse demonstrate the broad spectrum of neurological disease that can result from different alleles of the same sodium channel gene. Null mutations of Scn8a produce motor neuron failure, loss of neuromuscular transmission, and lethal paralysis. Less severe mutations result in ataxia, tremor, muscle weakness, and dystonia. The effects of Scn8a mutations on channel properties have been studied in the Xenopus oocyte expression system and in neurons isolated from the mutant mice. The Scn8a mutations provide insight into the mode of inheritance, effect on neuronal sodium currents, and role of modifier genes in sodium channel disease, highlighting the ways in which mouse models of human mutations can be used in the future to understand the pathophysiology of human disease.
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PMID:Sodium channels and neurological disease: insights from Scn8a mutations in the mouse. 1149 24

The Food Quality Protection Act (FQPA) of 1996 requires the United States Environmental Protection Agency to consider the cumulative effects of exposure to pesticides having a 'common mechanism of toxicity.' This paper reviews the information available on the acute neurotoxicity and mechanisms of toxic action of pyrethroid insecticides in mammals from the perspective of the 'common mechanism' statute of the FQPA. The principal effects of pyrethroids as a class are various signs of excitatory neurotoxicity. Historically, pyrethroids were grouped into two subclasses (Types I and II) based on chemical structure and the production of either the T (tremor) or CS (choreoathetosis with salivation) intoxication syndrome following intravenous or intracerebral administration to rodents. Although this classification system is widely employed, it has several shortcomings for the identification of common toxic effects. In particular, it does not reflect the diversity of intoxication signs found following oral administration of various pyrethroids. Pyrethroids act in vitro on a variety of putative biochemical and physiological target sites, four of which merit consideration as sites of toxic action. Voltage-sensitive sodium channels, the sites of insecticidal action, are also important target sites in mammals. Unlike insects, mammals have multiple sodium channel isoforms that vary in their biophysical and pharmacological properties, including their differential sensitivity to pyrethroids. Pyrethroids also act on some isoforms of voltage-sensitive calcium and chloride channels, and these effects may contribute to the toxicity of some compounds. Effects on peripheral-type benzodiazepine receptors are unlikely to be a principal cause of pyrethroid intoxication but may contribute to or enhance convulsions caused by actions at other target sites. In contrast, other putative target sites that have been identified in vitro do not appear to play a major role in pyrethroid intoxication. The diverse toxic actions and pharmacological effects of pyrethroids suggest that simple additivity models based on combined actions at a single target are not appropriate to assess the risks of cumulative exposure to multiple pyrethroids.
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PMID:Mechanisms of pyrethroid neurotoxicity: implications for cumulative risk assessment. 1181 16

Altering neurotransmitter levels within the nervous system can cause profound changes in behavior and neuronal function. Neurotransmitter transporters play important roles in regulating neurotransmitter levels by performing neurotransmitter reuptake. It was previously shown that mutations in the Drosophila inebriated (ine)-encoded neurotransmitter transporter cause increased neuronal excitability. Here we report a further functional characterization of Ine. First we show that Ine functions in the short-term (time scale of minutes to a few hours) to regulate neuronal excitability. Second, we show that Ine is able to control excitability from either neurons or glia cells. Third, we show that overexpression of Ine reduces neuronal excitability. Overexpression phenotypes of ine include: delayed onset of long-term facilitation and increased failure rate of transmitter release at the larval neuromuscular junction, reduced amplitude of larval nerve compound action potentials, suppression of the leg-shaking behavior of mutants defective in the Shaker-encoded potassium channel, and temperature-sensitive paralysis. Each of these overexpression phenotypes closely resembles those of loss of function mutants in the para-encoded sodium channel. These data raise the possibility that Ine negatively regulates neuronal sodium channels, and thus that the substrate neurotransmitter of Ine positively regulates sodium channels.
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PMID:In vivo properties of the Drosophila inebriated-encoded neurotransmitter transporter. 1188 Apr 99

Scn8a encodes an abundant, widely distributed voltage-gated sodium channel found throughout the central and peripheral nervous systems. Mice with different mutant alleles of Scn8a provide models of the movement disorders ataxia, dystonia, tremor and progressive paralysis. We previously reported that the phenotype of the hypomorphic allele of Scn8a, medJ, is dependent upon an unlinked modifier locus, Scnm1. Strain C57BL/6J carries a sensitive allele of the modifier locus that results in juvenile lethality. We now provide evidence that the modifier acts on the splicing efficiency of the mutant splice donor site. Mutant mice display either 90% or 95% reduction in the proportion of correctly spliced mRNA, depending on modifier genotype. The abundance of the channel protein, Na(v)1.6, is also reduced by an order of magnitude in medJ mice, resulting in delayed maturation of nodes of Ranvier, slowed nerve conduction velocity, reduced muscle mass and reduction of brain metabolic activity. medJ mice provide a model for the physiological effects of sodium channel deficiency and the molecular mechanism of bigenic disease.
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PMID:Molecular and pathological effects of a modifier gene on deficiency of the sodium channel Scn8a (Na(v)1.6). 1237 66

The med(J) mouse with twisting movements related to deficiency of the sodium channel Scn8a has been proposed as a model of kinesiogenic dystonia. This prompted us to examine the phenotype of these mice in more detail. By cortical electroencephalographic (EEG) recordings, we could not detect any changes, demonstrating that the motor disturbances are not epileptic in nature, an important similarity to human dystonia. The significantly decreased body weight of med(J) mice was related to reduced food intake. Observations in the open field and by video recordings revealed that the mice exhibit sustained abnormal postures and movements of limbs, trunk and tail not only during locomotor activity but also at rest. With the exception of the head tremor, the other motor impairments were persistent rather than paroxysmal. When several neurological reflexes were tested, alterations were restricted to the posture and righting reflexes. Results of the wire hang test confirmed the greatly reduced muscle strength in the med(J) mouse. In agreement with different types of human dystonia, biperiden, haloperidol and diazepam moderately reduced the severity of motor disturbances in med(J) mice. In view of the sodium channel deficiency in med(J) mice, the beneficial effects of the sodium channel blocker phenytoin was an unexpected finding. By immunohistochemical examinations, the density of nigral dopaminergic neurons was found to be unaltered, substantiating the absence of pathomorphological abnormalities within the brain of med(J) mice shown by previous studies. With the exception of muscle weakness, many of the features of the med(J) mouse are similar to human idiopathic dystonia.
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PMID:Motor disturbances in mice with deficiency of the sodium channel gene Scn8a show features of human dystonia. 1476 75

The sodium channel gene Scn8a encodes the channel NaV1.6, which is widely distributed in the central and peripheral nervous system. NaV1.6 is the major channel at the nodes of Ranvier in myelinated axons. Mutant alleles of mouse Scn8a result in neurological disorders including ataxia, tremor, paralysis, and dystonia. We generated a floxed allele of Scn8a by inserting loxP sites around the first coding exon. The initial targeted allele containing the neo-cassette was a severe hypomorph. In vivo deletion of the neo-cassette by Flp recombinase produced a floxed allele that generates normal expression of NaV1.6 protein. Ubiquitous deletion of the floxed exon by Cre recombinase in ZP3-Cre transgenic mice produced the Scn8a(del) allele. The null phenotype of Scn8a(del) homozygotes confirms the in vivo inactivation of Scn8a. Conditional inactivation of the floxed allele will make it possible to circumvent the lethality that results from complete loss of Scn8a in order to investigate the physiologic role of NaV1.6 in subpopulations of neurons.
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PMID:Floxed allele for conditional inactivation of the voltage-gated sodium channel Scn8a (NaV1.6). 1528 95


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