A stochastic model for interacting neurons in the olfactory bulb.

We focus on interacting neurons organized in a block-layered network devoted to the information processing from the sensory system to the brain. Specifically, we consider the firing activity of olfactory sensory neurons, periglomerular, granule and mitral cells in the context of the neuronal activity of the olfactory bulb. We propose and investigate a stochastic model of a layered and modular network to describe the dynamic behavior of each prototypical neuron, taking into account both its role (excitatory/inhibitory) and its location within the network. We adopt specific Gauss-Markov processes suitable to provide reliable estimates of the firing activity of the different neurons, given their linkages. Furthermore, we study the impact of selective excitation/inhibition on the information transmission by means of simulations and numerical estimates obtained through a Volterra integral approach.

A rare case of Hoffa's fat pad herniation in a young patient: dynamic ultrasound and MRI diagnosis.

Hoffa's fat pad (HFP) is part of the knee structure interposed between the joint capsule and the synovium. Recent studies have classified infrapatellar fat pad (IFP) disorders on a pathogenesis-based classification: traumatic disorders, post-traumatic disorders, lesions secondary to adjacent disorders. Masses or pseudo-masses may also be found within the IFP, however these alterations are much less frequent. Diagnostic imaging plays an important role in the diagnosis of masses and pseudo-masses of IFP and the first choice exam is a dynamic ultrasound study. We presented a rare case of Hoffa's fat pad herniation through the joint capsule, in a young child without history of knee injuries that has never been described before in the literature.

Linked Gauss-Diffusion processes for modeling a finite-size neuronal network.

A Leaky Integrate-and-Fire (LIF) model with stochastic current-based linkages is considered to describe the firing activity of neurons interacting in a (2×2)-size feed-forward network. In the subthreshold regime and under the assumption that no more than one spike is exchanged between coupled neurons, the stochastic evolution of the neuronal membrane voltage is subject to random jumps due to interactions in the network. Linked Gauss-Diffusion processes are proposed to describe this dynamics and to provide estimates of the firing probability density of each neuron. To this end, an iterated integral equation-based approach is applied to evaluate numerically the first passage time density of such processes through the firing threshold. Asymptotic approximations of the firing densities of surrounding neurons are used to obtain closed-form expressions for the mean of the involved processes and to simplify the numerical procedure. An extension of the model to an (N×N)-size network is also given. Histograms of firing times obtained by simulations of the LIF dynamics and numerical firings estimates are compared.

Ankle impingement: a review of multimodality imaging approach.

Ankle impingement is defined as entrapment of an anatomic structure that leads to pain and decreased range of motion of the ankle and can be classified as either soft tissue or osseous (Bassett et al. in J Bone Joint Surg Am 72:55-59, 1990). The impingement syndromes of the ankle are a group of painful disorders that limit full range of movement. Symptoms are due to compression of soft-tissues or osseous structures during particular movements (Ogilvie-Harris et al. in Arthroscopy 13:564-574, 1997). Osseous impingement can result from spur formation along the anterior margin of the distal tibia and talus or as a result of a prominent posterolateral talar process, the os trigonum. Soft-tissue impingement usually results from scarring and fibrosis associated with synovial, capsular, or ligamentous injury. Soft-tissue impingement most often occurs in the anterolateral gutter, the medial ankle, or in the region of the syndesmosis (Van den Bekerom and Raven in Knee Surg Sports Traumatol Arthrosc 15:465-471, 2007). The main impingement syndromes are anterolateral, anterior, anteromedial, posterior, and posteromedial impingement. These conditions arise from initial ankle injuries, which, in the subacute or chronic situation, lead to development of abnormal osseous and soft-tissue thickening within the ankle joint. The relative contributions of the osseous and soft-tissue abnormalities are variable, but whatever component is dominant there is physical impingement and painful limitation of ankle movement. Conventional radiography is usually the first imaging technique performer and allows assessment of any potential bone abnormality, particularly in anterior and posterior impingement. Computed tomography (CT) and isotope bone scanning have been largely superseded by magnetic resonance (MR) imaging. MR imaging can demonstrate osseous and soft-tissue edema in anterior or posterior impingement. MR imaging is the most useful imaging modality in evaluating suspected soft-tissue impingement or in excluding other ankle pathology such as an osteochondral lesion of the talus. MR imaging can reveal evidence of previous ligamentous injury and also can demonstrate thickened synovium, fibrosis, or adjacent reactive soft-tissue edema. Studies of conventional MR imaging have produced conflicting sensitivities and specificities in assessment of anterolateral impingement. CT and MR arthrographic techniques allow the most accurate assessment of the capsular recesses, albeit with important limitations in diagnosis of clinical impingement syndromes. In the majority of cases, ankle impingement is treated with conservative measures, with surgical debridement via arthroscopy or an open procedure reserved for patients who have refractory symptoms. In this article, we describe the clinical and potential imaging features, for the four main impingement syndromes of the ankle: anterolateral, anterior, anteromedial, posterior, and posteromedial impingement.

In vitro effects of ultraviolet A on histamine release from human basophils.

BACKGROUND: As long-wave ultraviolet (UV) radiation penetrates the dermis, connective tissue cellular components and circulating blood cells can be possible targets for solar UVA. Basophils, involved in the effector phase of the inflammatory response, play a part in skin diseases such as chronic urticaria, psoriasis, atopic dermatitis, fixed drug eruption, allergic contact dermatitis, urticaria pigmentosa, systemic sclerosis and bullous pemphigoid. OBJECTIVE: The evaluation of the in vitro effect of UVA on histamine release from human basophils. METHODS: Basophils from healthy human volunteers were irradiated, respectively, with UVA at doses of 2.5, 5, 7.5, 10, 20 and 50 J/cm2 and then incubated with an anti-IgE serum. A fluorimetric technique was employed to determine histamine release from samples: (i) incubated with 2% HClO4 (complete lysis of basophils); (ii) irradiated with increasing doses of UVA; and (iii) unirradiated (controls). RESULTS: Histamine release was: 100% for HClO4 incubated basophils, 30% for unirradiated and anti-IgE incubated cells (controls) and 27%, 24%, 34%, 41%, 60% and 70% for basophils irradiated with UVA doses, respectively, of 2.5, 5, 7.5, 10, 20 and 50 J/cm2 and incubated with anti-IgE. Histamine releasability from irradiated samples was statistically significant (P < 0.05), in comparison with controls, at UVA doses equal to 5, 10, 20 and 50 J/cm2. CONCLUSIONS: UVA exerts, at least in vitro, a biphasic dose-dependent action on histamine release from human basophils incubated with an anti-IgE serum: at the lowest irradiation doses (< 5 J/cm2) it exerts an inhibitory effect and at the highest doses (> or = 10 J/cm2) histamine release increases significantly.

Expression of the chemokine receptor CCR3 on human mast cells.

BACKGROUND: The aim of this study was to investigate whether human mast cells express functional active CCR3 receptors, which are activated by CC chemokines. These ligands include the CCR3-selective chemokines eotaxin and eotaxin-2 and the more promiscuous CC chemokines, MCP-4, MCP-3, MCP-2 and RANTES. METHODS: Immunohistochemical analysis was performed on skin, gut and lung specimens. Double immunostaining was performed with anti-CCR3 and antitryptase, and anti-CCR3 and antichymase antibody (Ab) by using the avidin-biotin-peroxidase system with two different substrates. Mast cells were isolated and purified from human lung parenchyma (HLMC) by countercurrent elutriation followed by discontinuous Percoll density gradient. Flow-cytometric analysis of HLMC surface CCR3 expression was performed with the monoclonal Ab anti-CCR3 (7B11). Functional activation of HLMC was verified by the ability of cells to release histamine and/or migrate in response to eotaxin. RESULTS: High percentages (>70%) of tryptase-positive cells showing CCR3 expression were found in the skin and in the intestinal submucosa, whereas much lower percentages (< or = 20%) were found in the intestinal mucosa and in the lung interstitium. Eotaxin (1-100 nM) neither induced histamine release from HLMC nor enhanced anti-IgE-induced histamine release. In contrast, eotaxin (10-100 nM) and RANTES (10-100 nM) induced HLMC chemotaxis in vitro. Preincubation of HLMC with antibody anti-CCR3 (5 microg/ml) before loading into the chemotaxis chamber abrogated chemotaxis elicited by eotaxin. Double immunostaining with anti-CCR3 and anti-chymase antibody showed that the vast majority of CCR3-expressing mast cells in the various human tissues examined were tryptase-chymase double-positive. CONCLUSIONS: These results indicate that CCR3 is expressed on human mast cells and that these cells are attracted by CCR3-binding chemokines.

Tat protein is an HIV-1-encoded beta-chemokine homolog that promotes migration and up-regulates CCR3 expression on human Fc epsilon RI+ cells.

Human basophils and mast cells express the chemokine receptor CCR3, which binds the chemokines eotaxin and RANTES. HIV-1 Tat protein is a potent chemoattractant for basophils and lung mast cells obtained from healthy individuals seronegative for Abs to HIV-1 and HIV-2. Tat protein induced a rapid and transient Ca(2+) influx in basophils and mast cells, analogous to beta-chemokines. Tat protein neither induced histamine release from human basophils and mast cells nor increased IL-3-stimulated histamine secretion from basophils. The chemotactic activity of Tat protein was blocked by preincubation of FcepsilonRI(+) cells with anti-CCR3 Ab. Preincubation of Tat with a mAb anti-Tat (aa 1-86) blocked the migration induced by Tat. In contrast, a mAb specific for the basic region (aa 46-60) did not inhibit the chemotactic effect of Tat protein. Tat protein or eotaxin desensitized basophils to a subsequent challenge with the autologous or the heterologous stimulus. Preincubation of basophils with Tat protein up-regulated the level of CCR3 mRNA and the surface expression of the CCR3 receptor. Tat protein is the first identified HIV-1-encoded beta-chemokine homologue that influences the directional migration of human FcepsilonRI(+) cells and the expression of surface receptor CCR3 on these cells.

Objective algorithms for the aerosol problem.

Retrieval of the aerosol size distribution from optical measurements at ground level is well known to be a difficult problem. Nowadays objective techniques that can give a solution without the intervention of the researcher do not exist. We propose several objective methods that are well based in the mathematical and physical points of view. Their accuracy is evaluated and the top performance of the objective inversion techniques is presented. Moreover physical and experimental suggestions can be drawn to improve the accuracy. Inversions with experimental optical depths are also shown.