The locust olfactory system as a case study for modeling dynamics of neurobiological networks: from discrete time neurons to continuous time neurons.

Both chaotic and periodic activities are observed in networks of the central nervous systems. We choose the locust olfactory system as a good case study to analyze the relationships between networks' structure and the types of dynamics involved in coding mechanisms. In our modeling approach, we first build a fully connected recurrent network of synchronously updated McCulloch and Pitts neurons (MC-P type). In order to measure the use of the temporal dimension in the complex spatio-temporal patterns produced by the networks, we have defined an index the Normalized Euclidian Distance NED. We find that for appropriate parameters of input and connectivity, when adding some strong connections to the initial random synaptic matrices, it was easy to get the emergence of both robust oscillations and distributed synchrony in the spatiotemporal patterns. Then, in order to validate the MC-P model as a tool for analysis for network properties, we examine the dynamic behavior of networks of continuous time model neuron (Izhikevitch Integrate and Fire model -IFI-), implementing the same network characteristics. In both models, similarly to biological PN, the activity of excitatory neurons are phase-locked to different cycles of oscillations which remind the ones of the local field potential (LFP), and nevertheless exhibit dynamic behavior complex enough to be the basis of spatio-temporal codes.

Statistical analysis and parsimonious modelling of dendrograms of in vitro neurones.

The processes whereby developing neurones acquire morphological features that are common to entire populations (thereby allowing the definition of neuronal types) are still poorly understood. A mathematical model of neuronal arborizations may be useful to extract basic parameters or organization rules, hence helping to achieve a better understanding of the underlying growth processes. We present a parsimonious statistical model, intended to describe the topological organization of neuritic arborizations with a minimal number of parameters. It is based on a probability of splitting which depends only on the centrifugal order of segments. We compare the predictions made by the model of several topological properties of neurones with the corresponding actual values measured on a sample of honeybee (olfactory) antennal lobe neurones grown in primary culture, described in a previous study. The comparison is performed for three populations of segments corresponding to three neuronal morphological types previously identified and described in this sample. We show that simple assumptions together with the knowledge of a very small number of parameters allow the topological reconstruction of representative (bi-dimensional) biological neurones. We discuss the biological significance (in terms of possible factors involved in the determinism of neuronal types) of both common properties and cell-type specific features, observed on the neurones and predicted by the model.

Classification of fusiform neocortical interneurons based on unsupervised clustering.

A classification of fusiform neocortical interneurons (n = 60) was performed with an unsupervised cluster analysis based on the comparison of multiple electrophysiological and molecular parameters studied by patch-clamp and single-cell multiplex reverse transcription-PCR in rat neocortical acute slices. The multiplex reverse transcription-PCR protocol was designed to detect simultaneously the expression of GAD65, GAD67, calbindin, parvalbumin, calretinin, neuropeptide Y, vasoactive intestinal peptide (VIP), somatostatin (SS), cholecystokinin, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, kainate, N-methyl-d-aspartate, and metabotropic glutamate receptor subtypes. Three groups of fusiform interneurons with distinctive features were disclosed by the cluster analysis. The first type of fusiform neuron (n = 12), termed regular spiking nonpyramidal (RSNP)-SS cluster, was characterized by a firing pattern of RSNP cells and by a high occurrence of SS. The second type of fusiform neuron (n = 32), termed RSNP-VIP cluster, predominantly expressed VIP and also showed firing properties of RSNP neurons with accommodation profiles different from those of RSNP-SS cells. Finally, the last type of fusiform neuron (n = 16) contained a majority of irregular spiking-VIPergic neurons. In addition, the analysis of glutamate receptors revealed cell-type-specific expression profiles. This study shows that combinations of multiple independent criteria define distinct neocortical populations of interneurons potentially involved in specific functions.

A morphometric classification of pupal honeybee antennal lobe neurones in culture.

Both intrinsic (programmed) and extrinsic (non-programmed) factors are thought to play a role in the morphogenesis of neurones in the honeybee antennal lobe (the first relay station in the olfactory pathway) during development. We present here a morphometric and statistical analysis of a large population of pupal honeybee antennal lobe neurones grown in primary culture. Quantitative parameters were used to characterize neuronal shapes. On the basis of such morphometric measurements, an automatic classification allowed three morphological types to be distinguished. Their main characteristics are presented and the role of intrinsic and extrinsic factors in their determination is discussed.

[A one-year prospective study of disodium etidronate versus 17 beta estradiol in the prevention of postmenopausal osteoporosis]. / Etude prospective versus 17 beta estradiol de l'étidronate disodique en prévention de l'ostéoporose post-ménopausique. Etude sur un an.

This prospective, controlled, nonrandomized, one-year trial in women included less than ten years after menopause was designed to compare the preventive efficacy on postmenopausal bone loss of replacement percutaneous 17 beta estradiol versus intermittent disodium etidronate. Twenty-five patients took oral disodium etidronate in a daily dosage of 200 mg in two-month courses separated by two-month intervals, with 1 g/day elemental calcium. Twenty-three patients used percutaneous 17 beta estradiol in daily dosage of 1.5 mg for the first twenty days of each month, then 20 mg oral dydrogesterone for the remaining ten days. At baseline the two groups were comparable as concerns age, mean time since menopause (5.1 versus 4.3 years), weight, height, and lumbar bone mineral density as measured by dual-photon X-ray absorptiometry. After one year of treatment, in both groups, bone mineral density was unchanged as compared with baseline, whereas serum alkaline phosphatase levels were significantly reduced. In the estrogen group, biochemical markers for bone turnover showed no significant changes, where as in the etidronate group urinary calcium and urinary hydroxyproline were significantly reduced. These data suggest that disodium etidronate is a satisfactory alternative to estrogens for the short-term prevention of postmenopausal bone loss when hormone replacement therapy is contraindicated or refused by the patient and when preventive therapy is warranted on the basis of measurable risk markers.

[Fibroblastic rheumatism. A clinical and histological entity]. / Le rhumatisme fibroblastique. Une entité clinique et histologique.

In 1980 was described for the first time a disease which seemed unknown until then. From that time three cases have been published. The current study summarizes their common characteristic, combining joint involvements to nodular-type involvements to systemic involvement, i.e. a specific histology. This entity has been named fibroblastic rheumatism. Nosologically, it is situated between juvenile fibroblastoses without joint involvement and with nodules, and adult sclerodermis with joint and systemic involvement without nodules.