Stimulation induced recurrent epileptiform discharges block cortical and subcortical spreading depression in rats

Blockade of the spread depression [SD] in chemically or electrically stimulated areas of the cerebral cortex was analyzed in a series of experiments performed in 40 curarized, locally anaesthetised rats. Longlasting stimulation of the cerebral cortex (0.5 to 1.7 mA, 6 Hz, 0.1 ms) elicited recurrent episodes of enhanced evoked potentials propagating to remote cortical areas [Co], the caudate nucleus [Cd], the hippocampus [Hi] and the thalamus [Th] and was accompanied by marked slow potential shifts (4-6 mV amplitude, 2-3 min duration, at 2-5 min intervals]. The projected discharge interfered with SD initiation and propagation in all the examined structures. The SD blockade was most pronounced during the episodes and almost absent in the intervals between them. The block was manifested by reduced amplitude and duration of the slow potential of SD. Pentobarbital [20 mg/kg] suppressed the recurrent discharges and eliminated the corresponding SD blockade. Recurrent excitability changes induced by Cd and Th stimulation elicited similar effects but the threshold was higher in Cd and Th than in Co. SD was less effectively blocked by the projected discharge than by stimulation of the same structure, particularly in the vicinity of the recording electrodes, where the blockade could be observed even under pentobarbital. The SD blockade outlasted stimulation by a considerably longer period of time in Th (about 10 min) than in the Cd (about 3 min). The onset of stimulation and the projected episodes sometimes elicited SD waves but SD blockade prevailed with continued stimulation. The present findings support the hypothesis that excessive neural activity increases the potassium clearance and thus prevents the autoregenerative accumulation of potassium ions, mediating SD propagation.     

Genetic analysis of the predisposition to uterine myoma. Prevalence and morbidity

Prevalence of uterine myoma (MU) was estimated in several Moscow districts. The overall average estimate of the MU prevalence is 2.45% among women of all groups. The prevalence MU estimates increase with the age, its maximum value reaching 8.31% at the age of 50 years. The morbidity risk estimates increased with the age as well, the maximum value being 2.98% at the age of 40-44 years. The value of "cumulative" morbidity risks, i. e. the probability to be affected, is 9.74% for a population living long enough, this value being based on the age-specific estimates of morbidity risks. Taking into consideration the autopsy data, indicating that frequency of MU, including small myomatous nodes, is 20%, the conclusion is made that MU is manifested by clinically expressed disturbances (urging a woman to address to a doctor) in 50% of cases only. Epidemiological data obtained are to be used later for genetic analysis of familial data on MU.     

The electrophysiological characteristics and behavioral manifestations of hippocampal and thalamic spreading depression]

Behavioral manifestations of spreading depression (SD) were compared with SD electrophysiological characteristics in these structures. Carbon electrodes were suitable for recording DC slow potential changes in freely moving animal. It was shown that short (0.1 s) high-frequency (200 Hz) electrical stimulation of thalamus and hippocampus with intensity 50-300 microA easily triggered SD wave in these structures in narcotized and awake rats. The threshold of SD occurrence in dorsal hippocampus was the same or sometimes lower than that of the primary afterdischarge. Penetrating SD into ventral hippocampus provoked long latency seizure discharge and wet-dog shakings in awake rats. Intensity of locomotor activity accompanying bilateral hippocampal SD exceeded orienting response significantly. Contrary to hippocampus, thalamic SD was usually subseizure and unilateral phenomenon and had a clear tranquil effect on the rat locomotor activity. It was found that the rats didn't change the compartment preference after 20-45 SD waves in the thalamus or in the hippocampus.     

Properties of spreading depression during different phases of cyclic excitation of the rat neocortex

Properties of cortical spreading depression were studied during different phases of cyclic excitation developing in the neocortex of rats under the influence of low-frequency electrical stimulation. Waves of spreading depression appeared in the cortex spontaneously or after microinjection of potassium chloride. During each excitation cycle a state preventing the passage and appearance of these waves developed in the region of electrical stimulation. The degree of blocking in other areas of the cortex outside the region of stimulation depended on the distance from the site of electrical stimulation and on generalization of excitatation over the cortex. After the end of the excitation phase, while the current continued to act, the ability of the cortex to conduct the depression wave was restored. In intervals of cyclic excitation the duration of the waves of spreading depression remained on average only half its duration in the absence of stimulation. The time course of development and the character of recovery of depression during the intervals confirm the hypothesis that activation of the potassium-sodium pump may have a role in the blocking mechanism and enable the temporal parameters of this process to be estimated.     

Isolation and characterization of a large,neurite-associated glycoconjugate from neuroblastoma cells

A high molecular weight glycoconjugate has been isolated from neurite-producing neuronal tumor cells in culture and has been designated as I(0) based on its elution characteristics in gel filtration chromatography. This molecule cannot be found in a variety of nonneuronal cells. I(0) is found in the substratum-attached material or cell fraction of neurite-producing neuroblastoma cells, depending upon culture conditions. It is found in the substratum-bound fraction of B104 rat neuroblastoma cells during serum starvation and in the EGTA-detached cell fraction of B104 cells grown in chemically defined N2 medium. It occurs only in the cell fraction of the human neuroblastoma line Platt. Examination of behavioral variants of the B104 rat line further strengthens the association of I(0) with neurite production; the constitutive neurite-producing E(R)B9 variant contains I(0) while the non-neurite-producing E(R)A11 variant does not. I(0) is large, eluting in the void volume of sepharose-CL2B columns. Radioiodination of intact cells with lactoperoxidase shows I(0) to be a cell surface component. Metabolic radiolabeling studies show that it contains a high proportion of polysaccharide to protein, does not contain mannose, and is unsulfated. Alkaline borohydride reduction release two size classes of large polysaccharide chain. The alkaline reduction results, along with the mannose incorporation studies, show the presence of O-glycosidic linkages and few, if any, N-linkages. Resistance to nitrous acid deamination, insensitivity to glycosaminoglycan lyases, and the absence of sulfation, indicate that I(0) does not contain the glycosaminoglycans hyaluronic acid, chondroitin-, dermatan-, or heparin- sulfates. Affinity column chromatography reveals high binding affinity of I(0) to polyornithine and no binding to gelatin (collagen) or the glycosaminoglycans hyaluronate and heparin. These studies describe a unique high molecular weight glycoconjugate on the surface of neurite-producing neuroblastoma cell lines from two species.     

Relative apparent synapomorphy analysis (RASA). I: The statistical measurement of phylogenetic signal

We have developed a new approach to the measurement of phylogenetic signal in character state matrices called relative apparent synapomorphy analysis (RASA). RASA provides a deterministic, statistical measure of natural cladistic hierarchy (phylogenetic signal) in character state matrices. The method works by determining whether a measure of the rate of increase of cladistic similarity among pairs of taxa as a function of phenetic similarity is greater than a null equiprobable rate of increase. Our investigation of the utility and limitations of RASA using simulated and bacteriophage T7 data sets indicates that the method has numerous advantages over existing measures of signal. A first advantage is computational efficiency. A second advantage is that RASA employs known methods of statistical inference, providing measurable sensitivity and power. The performance of RASA is examined under various conditions of branching evolution as the number of characters, character states per character, and mutations per branch length are varied. RASA appears to provide an unbiased and reliable measure of phylogenetic signal, and the general approach promises to be useful in the development of new techniques that should increase the rigor and reliability of phylogenetic estimates.      

Molecular evolution of voltage-sensitive ion channel genes: on the origins of electrical excitability

We have analyzed nucleic acid and amino acid sequence alignments of a variety of voltage-sensitive ion channels, using several methods for phylogenetic tree reconstruction. Ancient duplications within this family gave rise to three distantly related groups, one consisting of the Na+ and Ca++ channels, another the K+ channels, and a third including the cyclic nucleotide-binding channels. A series of gene duplications produced at least seven mammalian homologues of the Drosophila Shaker K+ channel; clones of only three of these genes are available from all three mammalian species examined (mouse, rat, and human), pointing to specific genes that have yet to be recovered in one or another of these species. The Shaw-related K+ channels and the Na+ channel family have also undergone considerable expansion in mammals, relative to flies. These expansions presumably reflect the needs of the high degree of physiological and neuronal complexity of mammals. Analysis of the separate domains of the four-domain channels (Ca++ and Na+) supports their having evolved by two sequential gene duplications and implies the historical existence of a functional two-domain channel.