The Influence of Synaptic Weight Distribution on Neuronal Population Dynamics

The manner in which different distributions of synaptic weights onto cortical neurons shape their spiking activity remains open. To characterize a homogeneous neuronal population, we use the master equation for generalized leaky integrate-and-fire neurons with shot-noise synapses. We develop fast semi-analytic numerical methods to solve this equation for either current or conductance synapses, with and without synaptic depression. We show that its solutions match simulations of equivalent neuronal networks better than those of the Fokker-Planck equation and we compute bounds on the network response to non-instantaneous synapses. We apply these methods to study different synaptic weight distributions in feed-forward networks. We characterize the synaptic amplitude distributions using a set of measures, called tail weight numbers, designed to quantify the preponderance of very strong synapses. Even if synaptic amplitude distributions are equated for both the total current and average synaptic weight, distributions with sparse but strong synapses produce higher responses for small inputs, leading to a larger operating range. Furthermore, despite their small number, such synapses enable the network to respond faster and with more stability in the face of external fluctuations.     

Improved Procedure for the Reduction of N - 1 Content in Synthetic Oligonucleotides

Abstract

By incorporating a “capping step” at the start of an oligonucleotide synthesis (“pre-cap”) and following a “SUP” work-up protocol with ammonium hydroxide, an overall improvement is observed in the quality of oligonucleotides synthesized on a large scale on controlled pore glass support (CPG). Rationalization of these results is provided.     

A Novel Plasmid Gene Involved in Bacteriophage PRD1 Infection and Conjugative Host-Range

PRD1 infects bacteria carrying IncN plasmids by binding to their conjugative pili. Mutations in a plasmid locuskikAclose to the pilus region result in PRD1 resistance and reduced conjugation proficiency toKlebsiellabut not toEscherichia coli.One of the two genes ofkikAis sufficient to restore both normal phenotypes. PRD1 binds to cells carrying the mutant plasmid but fails to inject its genome.     

Search for peptide immunogens of the beta-subunit of human chorionic gonadotropin (hCG) capable of eliciting hormone specific and neutralizing antisera. Identification of an undecapeptide eliciting hCG-specific antisera.

The work reported herein describes our attempts to identify peptide immunogens of the beta-subunit of the pregnancy-specific placental hormone, human chorionic gonadotropin (hCG), capable of eliciting hormone specific and neutralizing antisera. Hydrophilicity profiles of the beta-subunits of hCG and the homologous pituitary hormone, human luteinizing hormone (hLH) were compared and two sequences which are hydrophilic but unique to hCG-beta were identified. They are 6-12 and 109-119 of hCG-beta. Results of the studies with the undecapeptide 109-119 of hCG-beta are reported in this paper. The undecapeptide amide was synthesized using the p-(acyloxy) benzhydrylamine resin and antisera to the peptide were elicited in rabbits using the peptide-diphtheria toxoid conjugate. The peptide is highly immunogenic as both the rabbits responded with high titers of antibodies to the peptide. The antipeptide antibodies bound to hCG but not to hLH showing thereby that the region 109-119 of hCG-beta is a unique determinant of hCG. However, the antibodies were found not to neutralize the biological activity of hCG.     

Interaction between gabaergic and opioid pathways in the regulation of gonadotropin secretion in males

The effects of naloxone infusion given together with an infusion of LRH on gonadotropin secretion, were studied in 6 normal male volunteers before and after pretreatment with the GABA-transaminase inhibitor, valproic acid. In concordance with previous studies, naloxone infusion augmented the LRH-stimulated secretion of LH. Baseline serum LH concentrations were not significantly different after valproic acid pretreatment compared to control values. Similarly, valproic acid pretreatment failed to blunt the naloxone-augmented LRH-stimulated secretion of LH. Our data suggest that the previously reported animal studies on the central suppressive effect of GABA on endogenous LRH release is less prominent than the suppressive effect of opioidergic regulatory mechanisms in the human male.     

Effect of selenium on lead-induced alterations in rat brain

The effects of lead (Pb) and selenium (Se) interactions on central nervous system (CNS) functions were seen in adult rats by both biochemical and histologic pathological alterations. Pb administration of 20 mg/kg body wt for 8 wk showed degenerative changes only in the cerebral cortex. The changes in the cerebellar regions were not significant. Biochemically a marked decrease in the DNA, RNA, and protein content was seen following lead treatment. These decreases were significant in both the regions of the brain. During the concomitant administration of Pb and Se, the alterations in the transverse section of cerebral cortex showed only marginal changes. The values of DNA and RNA content showed significant improvement in both regions of the brain compared to the Pb treated group.