The role of NMDA receptors in in vitro epileptogenesis.
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Animals↗
Biomedical subjects
W W Anderson
Publications and source records attributed to W W Anderson.
Four decades of inversion polymorphism in Drosophila pseudoobscura.
We report data that continue the studies of Dobzhansky and others on the frequencies of third-chromosome inversions in natural populations of Drosophila pseudoobscura in North America. The common gene arrangements continue to be present in frequencies similar to those described four decades ago, and the broad geographic patterns also remain unchanged. There is only one pronounced trend over time: the increase in frequency of the Tree Line inversion in Pacific coast populations.
Animals↗
Molecular evolution of inversions in Drosophila pseudoobscura: the amylase gene region.
The amylase region of the third chromosome of Drosophila pseudoobscura has been cloned and localized to cytological band 73A. It is contained within a series of highly polymorphic inversions and serves as a convenient tool for a molecular evolutionary analysis of the inverted gene arrangements. Amylase in D. pseudoobscura is a family of three genes, and some chromosomes have deletions for one or two of them. Two overlapping clones covering 26 kilobases were isolated and used as probes to survey DNA restriction map polymorphism among 28 lines, representing five of the major inversion types found in natural populations, as well as single chromosomes from the closely related species Drosophila persimilis and Drosophila miranda. Restriction-site differences are considerably greater among the various gene arrangements than among chromosomes with the same gene arrangement. Clustering the restriction map haplotypes yielded a dendrogram concordant with the phylogeny generated independently from cytogenetic considerations. The inversion polymorphism is estimated to be about 2 million years old.
Amylases↗
Exposure of hippocampal slices to magnesium-free medium produces epileptiform activity and simultaneously decreases calcium and calmodulin-dependent protein kinase II activity.
The effect of magnesium-free medium on electrical and CaM kinase II activity in the rat hippocampal slice was examined. Experimental slices were incubated in 2 mM Mg, then exposed to magnesium-free medium for 1 h. Control slices were concurrently run in 2 mM Mg. Slices were then frozen and CaM kinase II activity was measured in homogenates. Exposure of hippocampal slices to magnesium-free medium resulted in spontaneous epileptiform activity and a concurrent 38 +/- 5.47% decrease in CaM kinase II activity (range 38.8-75.4% of control; n = 7, P less than 0.001, paired Student's t test). The decrease in CaM kinase II activity was not reversible by treatment with protein phosphatases 1 and 2A (58.8 +/- 4.77% of control activity; range 28.6-69.7, P less than 0.01, paired Student's t-test), indicating that the decrease in CaM kinase II activity cannot be accounted for exclusively by autophosphorylation. The results demonstrate that magnesium-free medium treatment can induce spontaneous epileptiform activity and simultaneous changes in CaM kinase II activity.
Action Potentials↗
Regenerative, all-or-none electrographic seizures in the rat hippocampal slice in Mg-free and physiological medium.
All-or-none electrographic seizures (EGSs) were studied in hippocampal slices from young (21- to 38-day-old) rats in medium containing low (0 mM) or physiological (0.9 mM) levels of magnesium, with and without the GABAB agonist baclofen. Extracellular recording and stimulation were performed in stratum pyramidale and stratum radiatum of CA3, respectively. EGS activity was induced by exposure to low-Mg medium or by delivering repetitive stimulus trains in physiological Mg medium. After EGS activity had stabilized, the EGSs were tested for all-or-none behavior by varying the number of pulses in a train. An EGS was considered all-or-none if subthreshold stimulation produced no afterdischarge bursts, and if the EGS duration was largely independent of the number of suprathreshold stimulus pulses. According to this measure, EGSs in Mg-free + baclofen medium were all-or-none. EGSs evoked in physiological Mg medium were also all-or-none, although the threshold was higher, and the EGS duration lower, than in Mg-free medium. This all-or-none characteristic was observed whether the EGSs were induced by prior exposure to Mg-free medium or by repetitive stimulation, and in the presence and absence of baclofen. The all-or-none characteristic suggests that while the triggering mechanism for EGSs is strongly dependent on stimulus intensity, regenerative mechanisms--independent of stimulus intensity--are responsible for the maintenance of EGSs. EGSs are also terminated by mechanisms not dependent on stimulus intensity.
Action Potentials↗
Can mating preferences explain changes in mtDNA haplotype frequencies?
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Animals↗
DNA sequence evolution of the amylase multigene family in Drosophila pseudoobscura.
The alpha-Amylase locus in Drosophila pseudoobscura is a multigene family of one, two or three copies on the third chromosome. The nucleotide sequences of the three Amylase genes from a single chromosome of D. pseudoobscura are presented. The three Amylase genes differ at about 0.5% of their nucleotides. Each gene has a putative intron of 71 (Amy1) or 81 (Amy2 and Amy3) bp. In contrast, Drosophila melanogaster Amylase genes do not have an intron. The functional Amy1 gene of D. pseudoobscura differs from the Amy-p1 gene of D. melanogaster at an estimated 13.3% of the 1482 nucleotides in the coding region. The estimated rate of synonymous substitutions is 0.398 +/- 0.043, and the estimated rate of nonsynonymous substitutions is 0.068 +/- 0.008. From the sequence data we infer that Amy2 and Amy3 are more closely related to each other than either is to Amy1. From the pattern of nucleotide substitutions we reason that there is selection against synonymous substitutions within the Amy1 sequence; that there is selection against nonsynonymous substitutions within the Amy2 sequence, or that Amy2 has recently undergone a gene conversion with Amy1; and that Amy3 is nonfunctional and subject to random genetic drift.
Amylases↗
Amylase gene expression in intraspecific and interspecific somatic transformants of Drosophila.
The Amylase locus in Drosophila melanogaster normally contains two copies of the structural gene for alpha-amylase, a centromere-proximal copy, Amy-p, and a distal copy, Amy-d. Products of the two genes may display discrete electrophoretic mobilities, but many strains known to carry the Amy duplication are characterized by a single amylase electromorph, e.g., Oregon-R, which produces the mobility variant AMY-1. A transient expression assay was used in somatic transformation experiments to test the functional status of the Amy genes from an Oregon-R strain. Plasmid constructs containing either the proximal or distal copy were tested in amylase-null hosts. Both genes produced a functional AMY-1 isozyme. Constructs were tested against an AMY-3 reference activity produced by a coinjected plasmid that contains the Amy-d3 allele from a Canton-S strain. With reference to the internal control, the Amy-p and Amy-d genes from Oregon-R expressed different relative activity levels for AMY-1 in transient assays. The transient expression assay was successfully used to test the functional status of Amy-homologous sequences from strains of other species of Drosophila characterized by a single amylase elctromorph, namely, Drosophila pseudoobscura ST and Drosophila miranda S 204. The amylase-null strain of D. melanogaster provided the hosts for these interspecific somatic transformation experiments.
Amylases↗
NMDA antagonists differentiate epileptogenesis from seizure expression in an in vitro model.
In an electrographic model of seizures in the hippocampal slice, both of the N-methyl-D-aspartate (NMDA) antagonists 2-amino-5-phosphonovaleric acid and 5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine maleate (MK-801) prevented the progressive development of seizures but did not block previously induced seizures. Thus, a process dependent on the NMDA receptor-ionophore complex establishes a long-lasting, seizure-prone state; thereafter the seizures depend on non-NMDA receptor-ionophore mechanisms. This suggests that there is an important distinction between epileptogenesis and seizure expression and between antiepileptogenic and anticonvulsant pharmacological agents.
2-Amino-5-phosphonovalerate↗
The drug MK-801 attenuates the development, but not the expression, of long-term potentiation and stimulus train-induced bursting in hippocampal slices.
Recent studies have demonstrated that (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801), a use-dependent blocker of N-methyl-D-aspartate (NMDA)-activated membrane channels, attenuates the development of long-term potentiation in vitro and kindling in vivo. Both of these phenomena are manifestations of physiological plasticity related to behavioural states and the results of these studies add to the gathering evidence for the involvement of the NMDA receptor/channel system in such processes. In the present experiment, slices of hippocampus, prepared from rats, were electrically stimulated to produce either long-term potentiation of the CA1 population spike or stimulus train-induced epileptiform bursting in area CA3. At 10 microM, MK-801 attenuated the development of long-term potentiation, but had no attenuating effect upon the previously-potentiated population spike. Similarly, 10 microM MK-801 attenuated the development of epileptiform activity in area CA3, but had little or no effect on the previously-established bursting in area CA3. These data support the suggestion that MK-801 exerts an antiepileptogenic, but not an anticonvulsant effect, at concentrations which also inhibit long-term potentiation.
Animals↗
Selection in natural and experimental populations of Drosophila pseudoobscura.
The inverted gene arrangements of Drosophila pseudoobscura were used by Th. Dobzhansky in pioneering analyses of natural selection. Recent experiments have shed light on the mechanisms of selection contributing to the balanced polymorphism for the gene arrangements. In experimental populations, both major components of fitness, viability and fertility, are frequency dependent, and rare genotypes often have a selective advantage. Viabilities are also density dependent. The frequency dependence and density dependence of the fitness components are not universal. Some karyotypes are strongly influenced by frequency or density, some are slightly influenced, and some do not appear to be influenced at all. The role of heterozygote advantage in the selection on the gene arrangements is not clear. It is probably one important element in the overall selection, but viability and fertility do not always show a heterozygote advantage. Viability and fertility components of selection seem to be about equally important in changing inversion frequencies. Male mating success is an important component of selection in natural populations, and in one population rare male karyotypes have been found to have a pronounced mating advantage.
Animals↗
Thai and American perspectives on over- and undercontrolled child behavior problems: exploring the threshold model among parents, teachers, and psychologists.
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Aggression↗
Rare male mating advantage in a natural population of Drosophila pseudoobscura.
The natural selection acting on chromosomal inversions was studied in a natural population of Drosophila pseudoobscura. Females from this population were allowed to produce offspring from their matings in nature. They were then remated to males from a laboratory strain and again allowed to produce offspring. Offspring were also produced from matings of males from nature to laboratory females. Diagnosis of salivary chromosomes in these several sets of larval offspring allowed us to deduce the karyotypes of adult females and males from nature as well as the karyotypes of the offspring of these females by their matings in nature. We reason that the males collected with the females are a reasonable sample of those that mated the females and deposited the sperm they carried on capture. Chromosome frequencies in the offspring of wild females by their matings in nature were decomposed into male and female parental contributions. Changes in chromosome frequency due to male mating success were calculated by comparing chromosomal frequencies in adult males with those in the chromosomes they contributed to their offspring. These changes were sizable and provide direct evidence that male sexual selection is an important component of selection on the inversions in this natural population. We proceeded further to classify karyotypes on the basis of their frequencies and to calculate the fraction of offspring fathered by rare or common males. Rare male karyotypes as a group had a selective value nearly twice that of the common male karyotypes.
Animals↗
Evidence for non-neutrality of mitochondrial DNA haplotypes in Drosophila pseudoobscura.
Mitochondrial DNA (mtDNA) haplotypes usually are assumed to be neutral, unselected markers of evolving female lineages. This assumption was tested by monitoring haplotype frequencies in 12 experimental populations of Drosophila pseudoobscura which were polymorphic for mtDNA haplotypes. Populations were maintained for at least 10 generations, and in one case for 32 generations, while tests of mtDNA selective neutrality were conducted. In an initial population, formed from a mixture of two strains with different mitochondrial haplotypes, the frequency of the Bogota haplotype increased 46% in 3 generations, reaching an apparent equilibrium frequency of 82% after 32 generations. Perturbation of this equilibrium by addition of the less common haplotype resulted in a rapid, dramatic increase in frequency of the second haplotype, and a return to essentially the same equilibrium frequency as before perturbation. This behavior is not consistent with mtDNA neutrality, nor is the equilibrium consistent with a simple model of constant selection on the haploid mtDNAs. Replicate cage experiments with mtDNA haplotypes did not always generate the same result as the initial cage. Several lines of evidence, including manipulations of the nuclear genome, support the idea that both nuclear and mitochondrial genomes are involved in the dramatic mtDNA frequency changes. In another experiment, strong female viability selection was implicated via mtDNA frequency changes. Although the causes of the dramatic mtDNA frequency changes in our populations are not obvious, it is clear that Drosophila mitochondrial haplotypes are not always simply neutral markers. Our findings are relevant to the introduction of a novel mtDNA variant from one species or one population into another. Such introductions could be strongly favored by selection, even if it is sporadic.
Animals↗
Seizure-like events in brain slices: suppression by interictal activity.
A major concern in epilepsy research is the relationship between ictal (seizure) electrophysiological activity and interictal (between seizure) activity. Much research is carried out in vitro using brain slice models. Although they allow detailed electrophysiology, the events recorded are generally more similar to interictal than ictal activity. We have described an in vitro model of epileptiform activity in the hippocampal slice (exposure to artificial cerebrospinal fluid containing no added magnesium) in which the events closely resemble those seen in vivo during seizures. However, this model is limited by the brief period during which this ictaform activity occurs before it is replaced by interictal-like activity. We now report that as the frequency of the interictal activity is suppressed by the GABAB agonist baclofen, the ictal activity returns. Moreover, when frequent interictal activity is reinduced, the ictal activity again is suppressed. These results suggest that interictal activity may decrease the probability of a seizure. Furthermore, they suggest that substances which may be shown to inhibit interictal activity in various models of epilepsy may not necessarily inhibit ictal activity.
Action Potentials↗
Restriction-map variation in the alcohol dehydrogenase region of Drosophila pseudoobscura.
A 32-kb region including the Adh structural gene was analyzed with six restriction endonucleases in 20 lines of Drosophila pseudoobscura, one line of D. persimilis, and one line of D. miranda. Nineteen lines of D. pseudoobscura from a single population were estimated to be polymorphic at one in every 15 nucleotides (p = 0.066). Any two homologous chromosomes chosen at random were heterozygous at one in 48 (H = 0.021) nucleotides. Two small insertions of 50 and 200 bp were found approximately 7 kb upstream from the Adh transcript. High haplotype diversity and low linkage disequilibrium suggest that the polymorphic restriction sites around Adh have segregated almost randomly during the history of this D. pseudoobscura population and that the effects of inbreeding and periodic reduction of population size have been negligible. The restriction-endonuclease analysis for the Adh region of D. pseudoobscura stands in sharp contrast to the strong linkage disequilibrium, high levels of insertion/deletion polymorphism, and lower estimates of nucleotide polymorphism found for this same region in D. melanogaster. A phylogeny for the Adh haplotypes is consistent with an early divergence of D. miranda, while D. persimilis falls within the cluster of D. pseudoobscura haplotypes.
Alcohol Dehydrogenase↗
The NMDA receptor antagonist 2-amino-5-phosphonovalerate blocks stimulus train-induced epileptogenesis but not epileptiform bursting in the rat hippocampal slice.
The role of N-methyl-D-aspartate (NMDA) receptors in producing stimulus train-induced bursting (STIB) was examined in area CA3 of the rat hippocampus. Extracellular recordings were made from the CA3 pyramidal cell layer. Bursting was induced by trains of electrical stimuli delivered to the stratum radiatum of CA3, or by bath application of NMDA. The specific NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid (APV) was then bath applied to test its ability to block STIB and NMDA activated bursting. A dose-response relation for NMDA activation indicated that bath application of 1 and 5 microM NMDA had little or no effect on the response to a paired stimulus pulse (triggered response) and did not induce spontaneous bursting. Ten micromolar NMDA induced strong triggered and spontaneous bursting during the application of NMDA in 72% of the slices. Fifty to one hundred micromolar NMDA caused the abolition of the excitatory postsynaptic potential (EPSP) and orthodromic population spike and the decrease or abolition of the antidromic population spike. In the normal medium wash following 10 microM NMDA, those slices that produced triggered and spontaneous bursting in 10 microM NMDA underwent an early phase of decreased excitability in which spontaneous bursting occurred in only 6% of the slices that were bursting in NMDA. Later in the wash spontaneous bursting began occurring in half of the slices that were bursting in NMDA, and the excitability of the triggered bursts increased slightly. The ability of the NMDA receptor antagonist APV to block NMDA-activated bursting was tested. Bath application of 100 or 200 microM APV alone caused little change in the normal triggered response. When 10 microM NMDA was added to the APV solution, there was little or no change in the triggered response, and no spontaneous bursting occurred. However, when 100 or 500 APV was added to the NMDA solution after NMDA burst activation had occurred, triggered bursting was reduced, but not blocked, although spontaneous bursting was blocked. In those slices that continued bursting after the washout of NMDA, bath application of 100 or 500 microM APV reduced, but did not block, triggered bursting. Spontaneous bursting continued in all slices. The ability of APV to block the induction of bursting by trains of electrical stimuli was then tested.(ABSTRACT TRUNCATED AT 400 WORDS)
2-Amino-5-phosphonovalerate↗
Magnesium-free medium activates seizure-like events in the rat hippocampal slice.
The effect of magnesium-free medium on the electrical activity in CA3 of the rat hippocampal slice was examined. Magnesium removal resulted in the development of spontaneous and triggered interictal-like bursting, followed by spontaneous ictal-like events and finally periodic clustered bursts. The ictal-like events consisted of a tonic firing phase and a phase of clustered burst discharges resembling the tonic and clonic phases of seizures. The return to normal medium resulted in spontaneous and triggered interictal-like bursts.
Action Potentials↗