Dressed neurons: modeling neural-glial interactions

Based on recent experimental data, we design a model for neuronal membrane potentials that incorporates the influence of the surrounding glia (dressed neurons). A neurotransmitter released into the synaptic cleft triggers a Ca(2+) response in nearby glial cells that spreads as a Ca(2+) wave and interacts with other synapses via the release of glutamate from astrocytes. We consider the simple case of a neuron-glia circuit that consists of a single neuron that triggers a Ca(2+) response in the glial cell which in turn feeds back into synapses of the same neuron. It is shown that persistent spiking can occur if the glutamate receptors on the astrocytes are overexpressed--a condition that has been reported from patients suffering from mesial-lobe epilepsy.     

Parallel computation and FASTA: confronting the problem of parallel database search for a fast sequence comparison algorithm

We have parallelized the FASTA algorithm for biological sequencecomparison using Linda, a machine-independent parallel programminglanguage. The resulting parallel program runs on a variety ofdifferent parallel machines. A straightforward parallelizationstrategy works well if the amount of computation to be doneis relatively large. When the amount of computation is reduced,however, disk I/O becomes a bottleneck which may prevent additionalspeed-up as the number of processors is increased. The paperdescribes the parallelization of FASTA, and uses FASTA to illustratethe I/O bottleneck problem that may arise when performing paralleldatabase search with a fast sequence comparison algorithm. Thepaper also describes several program design strategies thatcan help with this problem. The paper discusses how this bottleneckis an example of a general problem that may occur when parallelizing,or otherwise speeding up, a time-consuming computation. Received on July 25, 1990; accepted on October 15, 1990     

Characterization of a novel mutation in the cardiac ryanodine receptor that results in catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an arrhythmogenic disease that manifests as syncope or sudden death during high adrenergic tone in the absence of structural heart defects. It is primarily caused by mutations in the cardiac ryanodine receptor (RyR2). The mechanism by which these mutations cause arrhythmia remains controversial, with discrepant findings related to the role of the RyR2 binding protein FKBP12.6. The purpose of this study was to characterize a novel RyR2 mutation identified in a kindred with clinically diagnosed CPVT.Single-strand conformational polymorphism analysis and direct DNA sequencing were used to screen the RyR2 gene for mutations. Site-directed mutagenesis was employed to introduce the mutation into the mouse RyR2 cDNA. The impact of the mutation on the interaction between RyR2 and a 12.6 kDa FK506 binding protein (FKBP12.6) was determined by immunoprecipitation and immunoblotting and its effect on RyR2 function was characterized by single cell Ca²⁺ imaging and [³H]ryanodine binding.A novel CPVT mutation, E189D, was identified. The E189D mutation does not alter the affinity of the channel for FKBP12.6, but it increases the propensity for store-overload-induced Ca²⁺ release (SOICR). Furthermore, the E189D mutation enhances the basal channel activity of RyR2 and its sensitivity to activation by caffeine.The E189D RyR2 mutation is causative for CPVT and functionally increases the propensity for SOICR without altering the affinity for FKBP12.6. These observations strengthen the notion that enhanced SOICR, but not altered FKBP12.6 binding, is a common mechanism by which RyR2 mutations cause arrhythmias.Key words: arrhythmia, calcium, death sudden, genetics, ion channels     

Effect of LH, FSH, LH + FSH and homoplastic pituitary extract on developing testis and epididymis of pigeon Columba livia

Ovine LH is needed for differentiation of juvenile Leydig cells and for their maintenance and steroidogenic potential, while FSH is necessary for Sertoli cell activity and spermatogonial multiplication suggesting that LH is steroidogenic hormone and FSH is gametogenic in the developing pigeon, C. livia. Homoplastic pituitary extract is more potent than ovine LH + FSH in stimulating gametogenic and endocrine components of the developing testis.     

Evaluation of immunomodulatory activity of Suvarnamalini vasant, a generic Ayurvedic herbomineral formulation

Suvarnamalini vasant-a generic Ayurvedic herbomineral preparation was studied for its immunomodulatory activity by 1) evaluating it's effect on phagocytic function of polymorphonuclear white blood cells of rats and 2) it's effect in E.coli-induced peritonitis in albino mice. Pretreatment of rats with Suvarnamalini vasant improved the phagocytic function of polymorphonuclear white blood cells and also protected mice against E.coli-induced peritonitis. The results indicate the potential of Suvarnamalini vasant as an immunomodulator.     

Root biomass distribution in a moist tropical montane forest

Effects of N sources (ammonium, nitrate and ammonitrate) and VA mycorrhizae (Glomus intraradices) on rhizosphere soil characteristics (pH, exchangeable acidity, exchangeable cations, inorganic N concentrations) growth and nutrient acquisition of coffee seedlings (Coffea arabica L. cv guatemala) were investigated in a pot study with an acid soil (Red Bluff Loam) sterilized by autoclaving. Ammonium addition decreased rhizosphere pH while nitrate and ammonitrate additions both increased rhizosphere pH. Mycorrhizae induced a higher pH, a lower exchangeable acidity and higher values of exchangeable cations in the rhizosphere. Ammonium addition resulted in a lower mycorrhizal infection than the two other N sources. Mycorrhizal plants grew better and accumulated more N, Ca and Mg than non-mycorrhizal plants.