Stochastic models of neuronal dynamics

Cortical activity is the product of interactions among neuronal populations. Macroscopic electrophysiological phenomena are generated by these interactions. In principle, the mechanisms of these interactions afford constraints on biologically plausible models of electrophysiological responses. In other words, the macroscopic features of cortical activity can be modelled in terms of the microscopic behaviour of neurons. An evoked response potential (ERP) is the mean electrical potential measured from an electrode on the scalp, in response to some event. The purpose of this paper is to outline a population density approach to modelling ERPs. We propose a biologically plausible model of neuronal activity that enables the estimation of physiologically meaningful parameters from electrophysiological data. The model encompasses four basic characteristics of neuronal activity and organization: (i) neurons are dynamic units, (ii) driven by stochastic forces, (iii) organized into populations with similar biophysical properties and response characteristics and (iv) multiple populations interact to form functional networks. This leads to a formulation of population dynamics in terms of the Fokker-Planck equation. The solution of this equation is the temporal evolution of a probability density over state-space, representing the distribution of an ensemble of trajectories. Each trajectory corresponds to the changing state of a neuron. Measurements can be modelled by taking expectations over this density, e.g. mean membrane potential, firing rate or energy consumption per neuron. The key motivation behind our approach is that ERPs represent an average response over many neurons. This means it is sufficient to model the probability density over neurons, because this implicitly models their average state. Although the dynamics of each neuron can be highly stochastic, the dynamics of the density is not. This means we can use Bayesian inference and estimation tools that have already been established for deterministic systems. The potential importance of modelling density dynamics (as opposed to more conventional neural mass models) is that they include interactions among the moments of neuronal states (e.g. the mean depolarization may depend on the variance of synaptic currents through nonlinear mechanisms).Here, we formulate a population model, based on biologically informed model-neurons with spike-rate adaptation and synaptic dynamics. Neuronal sub-populations are coupled to form an observation model, with the aim of estimating and making inferences about coupling among sub-populations using real data. We approximate the time-dependent solution of the system using a bi-orthogonal set and first-order perturbation expansion. For didactic purposes, the model is developed first in the context of deterministic input, and then extended to include stochastic effects. The approach is demonstrated using synthetic data, where model parameters are identified using a Bayesian estimation scheme we have described previously.

Hydrogen transfer in excited pyrrole–ammonia clusters

The excited state hydrogen atom transfer reaction (ESHT) has been studied in pyrrole-ammonia clusters [PyH-(NH(3))(n)+hnu-->Py.+.NH(4)(NH(3))(n-1)]. The reaction is clearly evidenced through two-color R2P1 experiments using delayed ionization and presents a threshold around 235 nm (5.3 eV). The cluster dynamics has also been explored by picosecond time scale experiments. The clusters decay in the 10-30 ps range with lifetimes increasing with the cluster size. The appearance times for the reaction products are similar to the decay times of the parent clusters. Evaporation processes are also observed in competition with the reaction, and the cluster lifetime after evaporation is estimated to be around 10 ns. The kinetic energy of the reaction products is fairly large and the energy distribution seems quasi mono kinetic. These experimental results rule out the hypothesis that the reaction proceeds through a direct N-H bond rupture but rather imply the existence of a fairly long-lived intermediate state. Calculations performed at the CASSCF/CASMP2 level confirm the experimental observations, and provide some hints regarding the reaction mechanism.

Functional studies on nine different haemoglobins with high oxygen affinity

Nine carriers of beta-abnormal haemoglobins with increased oxygen affinity (Hb X) were examined. Their oxygen dissociation curves from whole blood were more or less left-shifted, with six of nine also characterized by biphasism. This refers to an 'inflection point' usually positioned at about 50-60% of Hb O(2) saturation, commonly believed to be a limit between oxygenation of the normal and abnormal components. In effect, the inflection does not always correspond to the Hb X level, which sometimes is much lower than 50% of the total Hb. Moreover, the upper half segment of the dissociation curve could not only be an expression of Hb A oxygenation, since it is always left-shifted. However, a high Hb A level is commonly believed to be the main compensatory factor of these subjects, but many indications suggest that often they have at least three, and not only two, main haemoglobin species: Hb A, Hb X plus hybrids of the type alpha(2)beta(A)beta(X). These would oxygenate after Hb X, but before Hb A. Finally, the interaction of 2,3-diphosphoglycerate with Hb X and/or hybrid tetramers must be altered, and the releasing of oxygen from both is more or less reduced. Unfortunately, it is difficult to demonstrate the presence of hybrids directly, i.e. with amino acid analysis of the abnormal beta-globin.

[Use of recombinant human erythropoietin in newborns with very low weight: efficacy monitoring]

Chronic anemia is very frequent in very low birth weight (VLBW) infants. Lowered red cells life span, hemolysis, low production of erythropoietin, phlebotomies, excessive body growth are its most important causes. A reduction of the number of transfusions to babies with chronic anemia was obtained through r-HuEpo. A serie accounting for 89 newborns < 1500 g (18 < 1000 g) with a mean weight of 1069 g (+/- 238) in whom early treatment with r-HuEpo was performed (from 9.55 +/- 3.04 day), 300 UI three times a week s.c., is presented. Therapy with r-HuEpo was carried out for 6 weeks, or until the baby weighed 1800 g. During the treatment, each baby received iron, folic acid, multivitaminic supplements. Patients were monitored with red blood cells count, comprehensive of reticolocytes, ipochromic cells (Ipo-cells), content of hemoglobin of reticolocytes (CHr), each week. Iron, ferritine and transferrine were obtained only twice a month, as they required further blood sampling. 10.1% neonates received transfusions: the percentage of transfused VLBW infants was much higher (55.5%) before than after the introduction of r-HuEpo (p = 0.0002). 33.3% extremely low birth weight (ELBW) infants required transfusions (vs 95.5% in pre r-HuEpo period) (p < 0.0001). Our results confirm the importance of Ipo-cells and CHr to monitor early alterations of iron cellular employment.

Akt and PTEN: new diagnostic markers of non-small cell lung cancer?

We are particularly interested in testing the principles of cell proliferation and apoptosis in the microenvironment of human lung cancers with respect to the cell survival protein Akt 1 and PTEN 2. Akt is a cytosolic protein which promotes cell survival by phosphorylative inactivation of targets in apoptotic pathways. Akt has been found to play a role in the survival of experimental cancer cell lines in breast, prostate, ovary, lung and brain tissue. PTEN is a tumor suppressor gene whose protein product is expressed in inverse proportion to phosphorylated Akt in endometrial and breast cancer cell lines. No studies of the diagnostic significance of Akt and PTEN in human lung cancers have been reported.

Optimal complete block designs to adjust for interplot competition with a covariance analysis

Optimal complete block designs are given for variety trials with interplot competition. In the paper, competition is modeled using height differences between neighboring varieties. When variety heights are known at the design stage, a simulated annealing algorithm is proposed. The optimal designs tend to reduce height differences between neighboring varieties. When variety heights are not known in advance, neighbor-balanced designs at distances 1 and 2 are shown to have optimality properties.

Limited value of zinc protoporphyrin as a marker of iron status in chronic hemodialysis patients

BACKGROUND

In an attempt to find new parameters able to evaluate the actual iron availability by bone marrow cells, zinc protoporphyrin (ZnPP), a metabolic intermediate generated in the red blood cell by the incorporation of zinc instead of iron, has been proposed. ZnPP is a good marker of iron-deficiency anemia in non-uremic people, as red blood cell ZnPP concentration rises specifically (except for lead intoxication) in this condition. Existing data on ZnPP as a marker of iron deficiency in uremic patients comes mainly from cross sectional studies on chronic hemodialysis and has produced conflicting results.

SUBJECTS AND METHODS

Therefore, we prospectively studied 42 HID patients, 28-88 years old, 13-346 months of dialysis age, beginning from a period of maximal iron deficiency, due to the lack of parenteral iron compounds (T0) up to the end of more than one year of follow-up with continuous parenteral iron supplementation (T4). ZnPP, hemoglobin, transferrin saturation and ferritin were serially determined before and after six weeks (T1), four months (T2), seven months (T3) and 14 months (T4) of parenteral iron supplementation at a maintenance dose of 0.5-1 mg/kg/week.

RESULTS

In comparison with baseline values (95+/-37 micromol/mol heme) there were no significant changes in ZnPP levels at T1 and T2 despite a continuous increase in both transferrin saturation and ferritin values, while ZnPP significantly decreased at T4 (63+/-37 micromol/mol heme, p<0.001). There was no correlation between ZnPP and both transferrin saturation and ferritin at any time during the study, the same was true for ZnPP and zinc and lead serum concentration, fibrinogen and reactive C protein levels at T1 and T4, respectively. At T4, only 2/10 patients who still showed ZnPP levels >80 micromol/mol heme had absolute or functional iron deficiency, when the percentage of hypochromic red cells were measured.

CONCLUSION

We conclude that ZnPP untimely parallels a change in iron balance in only a proportion of uremic people, in as much as confounding factors, such as chronic inflammation and uremia in itself may obscure its relationship with iron status. Therefore, ZnPP cannot be assumed to be a first-line diagnostic marker of iron balance in uremic patients.

Multifocal granular cell tumor of the esophagus and proximal stomach with infiltrative pattern: a case report and review of the literature

The granular cell tumor is a solitary painless nodule that arises most commonly on the skin or the tongue. The vast majority are benign. Approximately 5% to 9% of granular cell tumors have been reported in the gastrointestinal tract, most commonly in the esophagus. We report a case of a 45-year-old African American woman with multifocal granular cell tumors of the esophagus and proximal stomach. Two lesions within the distal esophagus and proximal stomach were characteristic nodular granular cell tumors. Within the mid esophagus there was poorly defined transmural involvement by benign-appearing granular cells. This pattern of infiltration by benign cells is uncharacteristic. A review of the literature with emphasis on the determination of malignancy is also presented.

Confusional consequences of illogical interaction

A personality theory rooted in interpersonal interaction is presented herein. The theory rests on a simple reward-punishment paradigm in which interpersonal interactions are viewed not as a series of discrete phenomena but as continuously recurrent experiences. Effects of interaction patterns thus reflect an accumulated experience rather than individual, discontinuous events. This basic learning paradigm keeps intact a simplicity and appealing logic. At the same time, invoking a cumulative learning experience, rather than the more common view, a series of individually discrete events, invests the theory with a conceptual underpinning sufficient to explain the role of interaction patterns in forming the complexity of thought, emotion, and behavior that is the reality of the human condition. Major dimensions of this identity-acquiring process are described herein. These vary hugely and are understood to underwrite in a direct, logical, ultimately simple way the various attributes that are the basis of identity. This applies to normal identity and can be applied as well to those identities that may form the core of such conditions as mania, depression, and even schizophrenia. The manner in which this theory incorporates tenets of other extant interactive theories is also described.

Pancreatic masses: a multi-institutional study of 364 fine-needle aspiration biopsies with histopathologic correlation

Only 15% of primary malignant tumors are confined to the gland at the time of presentation. Fine-needle aspiration (FNA) is valuable in confirming the malignant nature of these unresectable lesions. Benign pancreatic lesions and metastatic neoplasms can also be evaluated by fine-needle aspiration. We undertook a retrospective study to evaluate the efficacy of FNA in assessing pancreatic masses. Three hundred and sixty-four radiologically guided FNAs of the pancreas performed between 1986-1996 were reviewed. Surgical material was also evaluated when available and compared to the FNA material. There were 223 men and 141 women. Their ages ranged from 23-90, with a mean of 64 yr. Two hundred and twelve patients (58%) had primary malignant tumors, 183 had adenocarcinomas, 15 had mucinous cystadenocarcinomas, 12 had neuroendocrine tumors, and 2 had pleomorphic giant-cell carcinomas. Ninety-one (43%) had available surgical material which showed adenocarcinoma. Ninety-one patients (25%) had benign aspirates, including 53 showing benign ductal epithelium, 23 showing pancreatitis/inflammation. 10 showing pseudocysts, and 7 showing serous cystadenomas. Surgical material was available in 24 (26%) of these patients. Two of these showed adenocarcinoma. Sixteen aspirates (4%) were suspicious for malignancy, 13 (81%) of which showed adenocarcinoma on follow-up biopsies. Twenty-two aspirates (6%) showed metastatic neoplasms. Twenty-three (6%) had unsatisfactory specimens. Ten (43%) of these had follow-up biopsies, 3 of which were malignant. FNA of primary benign and malignant pancreatic masses is highly sensitive (98%) and specific (100%). Eighty-one percent of the suspicious lesions showed adenocarcinoma on follow-up biopsy. FNA of metastatic neoplasms to the pancreas is also very accurate. This technique can be useful in avoiding unnecessary surgery.

Genetic variation within a parthenogenetic lineage

A clone of the grain aphid Sitobion avenae F. was maintained parthenogenetically over thirty-two generations (n = 344) in a constant environment: a new generation being set up by a female selected at random from the preceding generation. Genomic DNA from individual aphids was screened for genetic stability using RAPD-PCR with a previously tested ten-mer primer. A putative germ-line mutation was noted in generation 14 and somatic mutations were noted in generations 12, 25, 27 and 29. There were no differences in the RAPD-PCR profiles of winged and wingless morphs and samples tested for symbiotic DNA. No endoblotic fungal organism was associated with the clone. Southern blotting and hybridization studies indicated that band additions were of aphid origin. However, the RAPD-PCR profiles of the germ-line and somatic mutation samples were unique from other aphid clones cultured during the experimental period. This paper documents discernible genetic changes occurring within an animal clonal lineage over time and Impacts on the consequences this may have for clonal systems.

Malignant cutaneous and subcutaneous abdominal wall lesions: a fine-needle aspiration study

Cutaneous and subcutaneous masses of the abdominal wall are uncommon. However, a variety of benign and neoplastic entities can be encountered in this region. We report a series of 22 fine-needle aspirations (FNA) of malignant cutaneous and subcutaneous lesions involving the abdominal wall. All of these lesions were metastatic neoplasms. There were 14 females and eight males, with an age range of 35-83 years (mean 65 years). Twenty-one had a previous history of malignancy. The mean interval between the primary diagnosis and FNA was 26 months (range 1.5-128 months). The sites of origin in order of decreasing frequency were colon (n = 4), ovary (n = 4), breast (n = 3), endometrium (n = 2), melanoma (n = 2), and one case each of cervix, urinary bladder, kidney, pancreas, gallbladder, and lymphoma. One case was a squamous-cell carcinoma of unknown origin. Fourteen of the 22 patients were dead at the end of this study, with a mean survival of 8.4 months (range 0.5-44 months) following FNA. One patient was alive with disease at 13 months, and seven patients were lost to follow-up. Based on this data and on review of the literature we conclude that the majority of malignant cutaneous and subcutaneous lesions of the abdominal wall subject to FNA biopsy are metastatic tumors which originate from intra-abdominal, pelvic, and retroperitoneal organs and that FNA is a highly useful technique in the assessment of these lesions of the abdominal wall.

Hemoglobin Agenogi [beta 90 (F6) Glu-->Lys] found in Piedmont. Case report

An electrophoretically slow-moving hemoglobin, with abnormal beta chains, has been found in a young woman and in three members of her family. This variant amounted to 41% of the total Hb, and did not cause important clinical manifestations, although characterized by decreased oxygen affinity. Structural and aminoacid analyses revealed the mutation of Hb-Agenogi: 90 (F6) Glu-->Lys, a rare variant so far detected in unrelated racial and ethnic groups. This is the first affected family of ascertained Piedmontese ancestry.

[Functional analysis of diluted solutions of human hemoglobin by using Oximeter-3000 WTW equipped with Trioxmatic-300 electrode]

The oxygen carrying capacity of dilute solutions of hemoglobin from normal human adults was examined, by using the above indicated Oximeter. The results show that, if the pO2s are compared with those drawn from the Oximeter-539 WTW (a simpler instrument) carrying the same oxygen electrode, there is a good correspondence between the data drawn from both the instruments. The advantage of the former is that pO2s are measure in mBr, whereas the latter measures the oxygen of the aqueous solutions in mg/l; then mg must be converted into Torr pO2. Since both instruments are usually employed in the oxygen measurement of waste waters of earth, another conclusion is that their sensitivity also allows the use in the bio-medical (and zoological) field. In fact, the data obtained agree with those of recent literature on the subject, which are mainly drawn from automated and sophisticated apparatuses specifically built at this purpose.

Studies on the oxygen transport in the clinical association between Hb-S and Hb-C

The whole blood oxygen affinity of a Negro carrier of SC disease was found to be characterized by some right-shifted p50 and clearly increased Bohr effect, whereas the isolated and purified Hb-S and Hb-C exhibited slight deficiencies mainly of the Bohr effect. The right-shifted p50 from whole blood can be easily explained by the mild anemia with a parallel increase of 2,3-diphosphoglycerate (DPG), whereas the functional discrepancies between whole blood function and that of the purified Hb-S and C could be due, at least in part, to the presence in vivo of consistent amounts of hybrid Hb tetramers of the type alpha alpha beta S beta C. Unfortunately, the mechanism promoting the formation (or dissolution) of hybrids are fundamentally unknown; so, either their presence and functional properties are very difficult to be explored.

A new fast-moving variant causing erythrocytosis and mild hemolysis: Hb Gàmbara [beta 82(EF6)Lys-->Glu]

Hb Gàmbara is a new hemoglobin variant with abnormal beta chains that has been found in three out of four members of a family of Lombardy origin (Gàmbara, Brescia, Northern Italy). The affected subjects led a normal life, but they had modest erythrocytosis and mild (compensated) hemolysis with slight splenomegaly. Their abnormal hemoglobin was about 52% of the total hemoglobin, and was shown to be stable by the isopropanol test. Whole blood P50 of the proband was 19.3 Torr, Bohr effect was decreased (-0.25), as well as the molar ratio between the 2,3-diphosphoglycerate level and total hemoglobin of erythrocytes (0.68). The purified abnormal hemoglobin was characterized by an altered oxygen affinity, low n-factor, chloride, and 2,3-diphosphoglycerate effects. The Bohr effect was about 40% of the normal control. The abnormal hemoglobin moved faster than Hb A at alkaline electrophoresis, and split into two fractions, probably due to the formation of hybrid tetramers (alpha 2 beta A beta X). The reversed phase high performance liquid chromatogram from the tryptic digest of the aminoethylated abnormal beta chain subunits indicated the presence of an extra peptide, beta T-9, 10, replacing the individual peptides beta T-9 and beta T-10. Finally, the proband's DNA, drawn from a suitable segment of the beta structural gene (exon 2), revealed a nucleotide sequence carrying the heterozygous mutation AAG-->GAG at codon 82. This led to a Lys-->Glu substitution at position 82(EF6) of the beta chain.