On the Use of Bayesian Methods for Evaluating Compartmental Neural Models

Computational modeling is being used increasingly in neuroscience. In deriving such models, inference issues such as model selection, model complexity, and model comparison must be addressed constantly. In this article we present briefly the Bayesian approach to inference. Under a simple set of commonsense axioms, there exists essentially a unique way of reasoning under uncertainty by assigning a degree of confidence to any hypothesis or model, given the available data and prior information. Such degrees of confidence must obey all the rules governing probabilities and can be updated accordingly as more data becomes available. While the Bayesian methodology can be applied to any type of model, as an example we outline its use for an important, and increasingly standard, class of models in computational neuroscience—compartmental models of single neurons. Inference issues are particularly relevant for these models: their parameter spaces are typically very large, neurophysiological and neuroanatomical data are still sparse, and probabilistic aspects are often ignored. As a tutorial, we demonstrate the Bayesian approach on a class of one-compartment models with varying numbers of conductances. We then apply Bayesian methods on a compartmental model of a real neuron to determine the optimal amount of noise to add to the model to give it a level of spike time variability comparable to that found in the real cell.     

Changes of plasma insulin, urea, amino acids and rumen metabolites in somatotropin treated dairy cows

Summary An experiment was performed to evaluate the effects of somatotropin on plasma free amino acid, urea and insulin concentrations and rumen fermentation pattern and to assess their relationships. Four Italian Friesian dairy cows fitted with rumen cannulae were used in a switch-back design. Slow releasing recombinant bovine somatotropin (640 mg/cow) was injected every 28 days for two consecutive periods. Rumen fluid and blood samples were collected before and after feeding at 0, 7 and 21 days after rbST injection. Exogenous rbST increased plasma insulin concentration and the insulin response to feeding, and decreased plasma urea and free essential and branched chain amino acid concentrations. rbST did not affect rumen fermentation pattern. No correlation was found between rumen and plasma parameters measured after feeding. Our results are consistent with the notion that the main effect of somatotropin is post-absorptive.     

N-Linked glycosylation of a baculovirus-expressed recombinant glycoprotein in insect larvae and tissue culture cells

The potential of insect cell cultures and larvae infected with recombinant baculoviruses to produce authentic recombinant glycoproteins cloned from mammalian sources was investigated. A comparison was made of the N-linked glycans attached to secreted alkaline phosphatase (SEAP) produced in four species of insect larvae and their derived cell lines plus one additional insect cell line and larvae of one additional species. These data survey N-linked oligosaccharides produced in four families and six genera of the order Lepidoptera. Recombinant SEAP expressed by recombinant isolates of Autographa californica and Bombyx mori nucleopolyhedroviruses was purified from cell culture medium, larval hemolymph or larval homogenates by phosphate affinity chromatography. The N-linked oligosaccharides were released with PNGase-F, labeled with 8- aminonaphthalene-1-3-6-trisulfonic acid, fractionated by polyacrylamide gel electrophoresis, and analyzed by fluorescence imaging. The oligosaccharide structures were confirmed with exoglycosidase digestions. Recombinant SEAP produced in cell lines of Lymantria dispar (IPLB-LdEIta), Heliothis virescens (IPLB-HvT1), and Bombyx mori (BmN) and larvae of Spodoptera frugiperda, Trichoplusia ni , H.virescens , B.mori , and Danaus plexippus contained oligosaccharides that were structurally identical to the 10 oligosaccharides attached to SEAP produced in T.ni cell lines. The oligosaccharide structures were all mannose-terminated. Structures containing two or three mannose residues, with and without core fucosylation, constituted more than 75% of the oligosaccharides from the cell culture and larval samples.      

Binding of estradiol receptor complexes to isolated human breast chromatin

Summary The interaction of estradiol-receptor complexes and isolated human breast tumor chromatin was studied under equilibrium conditions.The estradiol-receptor complexes bound specifically to the chromatin of hormone dependent tumors and showed a single class of binding sites with a Ka of 0.96 × 10¹⁰ m ^–1 and a binding capacity of 1.5 pmoles/mg DNA. The binding was a temperature-dependent process and involved a transformation of the receptor protein.The heat-activated hormone-receptor com-plex was more active than the 8S form in the binding phenomenon. The specific interaction of estradiol-receptor complex with isolated chromatin was saturable and sensitive to conditions of temperature and ionic strength. Furthermore under optimal conditions no acceptor sites were detected in chromatin of hormone independent tumors.Dedicated to ProfessorLuis F. Leloir on the occasion of his 70th birthday.     

Particulate DNA polymerase from the cytoplasm of Xenopus laevis oocytes

A DNA polymerase has been partially purified and characterized from Xenopus laevis stage 6 oocytes. The enzyme is present only in the cytoplasm and has been shown to be able to copy Poly(A) x oligo(dT), to be sensitive to N-ethylmaleimide, and to sediment faster than 4 S in high salt glycerol gradient. The enzyme can be extracted from particulate material which has a density in sucrose gradient ranging from 1.200 to 1.225 g/cc. This particulate material is identified by its ability to use Poly(A) x oligo(dT) as template in an exogenous DNA polymerase reaction and by its endogenous DNA synthesizing capacity.