Biomedical subjects

F Giannakopoulos

Publications and source records attributed to F Giannakopoulos.

5 recordsLinked to original sources

PubMed2004

Evaluation of bone mineral density of the peripheral skeleton in pre- and postmenopausal women with newly diagnosed endogenous Cushing's syndrome.

OBJECTIVE: Cushing's syndrome (CS) is a well recognized cause of bone loss. Although many previous studies have shown decreased bone mineral density (BMD) in the lumbar spina and proximal femur of patients with endogenous CS, so far, the data estimating BMD in their peripheral skeleton are sparse. The aim of the present study was to evaluate BMD in the forearm and heel of women with newly diagnosed CS and to investigate its possible correlation with serum osteocalcin (BGP) and 24-hour urinary free cortisol levels (UFC). PATIENTS AND METHODS: BMD in the forearm (distal and ultradistal area) of 29 (13 premenopausal and 16 postmenopausal) women with newly diagnosed CS (18 with pituitary adenoma, 10 with adrenal tumor and 1 with ectopic) was measured by dual x-ray absorptiometry (DEXA) and was compared with BMD of 29 age, body mass index (BMI)- and oestrogen status matched healthy controls. Furthermore, in 18 (9 premenopausal and 9 postmenopausal) of the above patients (14 with pituitary adenoma, 5 with adrenal tumor and 1 with ectopic) broadband ultrasound attenuation (BUA) by quantitative ultrasound (QUS) of the heel was estimated and 18 age-, BMI- and oestrogen status matched healthy women served as controls. In all the patients serum BGP and UFC were measured at the time of diagnosis of CS. RESULTS: Compared to their matched controls, BMD in the forearm and BUA values in the heel did not differ in the premenopausal women with CS, while in the postmenopausal group BMD in the forearm was decreased (P < 0.05) but not BUA. Apart from a weak negative correlation between serum BGP and BMD in the ultradistal site of the forearm in premenopausal women (P = 0.05), serum BGP and UFC did not show significant correlation with BMD or BUA. CONCLUSIONS: BMD in the forearm is reduced only in postmenopausal women with newly diagnosed endogenous CS, while BUA in the heel is unaffected in both pre- and postmenopausal patients. Moreover, serum BGP and UFC do not seem to be relevant markers for assessing bone loss in the peripheral skeleton at the time of diagnosis of hypercortisolemia.

Absorptiometry, Photon↗

PubMed2003

Association of vitamin D receptor gene polymorphisms with bone mineral density in postmenopausal women of Hellenic origin.

OBJECTIVES: There are numerous indications that genetic factors play an important role in the pathogenesis of osteoporosis, a common condition characterized by reduced bone mass and increased fracture risk. The vitamin D receptor (VDR) gene has been suggested as a possible candidate gene for the regulation of bone mass but the relationship between VDR polymorphisms and bone mineral density (BMD) is controversial and has not been confirmed by all workers in different ethnic groups studied. METHODS: In order to evaluate the contribution of the VDR alleles in bone mass loss, the BsmI, ApaI and TaqI polymorphisms in the VDR gene were studied in 126 postmenopausal women. RESULTS: It was found that the bb, aa and TT genotypes and the bAT and baT haplotypes were associated with a lower BMD measured at the forearm. CONCLUSIONS: Our analysis reveals a significant association between VDR gene alleles and bone mass in the population studied.

Bone Density↗

PubMed2001

Epileptiform activity in a neocortical network: a mathematical model.

A simple mathematical model describing the generation and propagation of epileptiform activity in a cerebral cortical network is presented. The model consists of a system of nonlinear delay differential equations. Physiological properties are taken into account as nonlinear transmission of signals at the synapse, temporal and spatial summation of incoming signals at the soma, active membrane characteristics, and dendritic and axonal propagation times. The influence of the connectivity and the temporal parameters on the oscillatory properties of the model is studied. The computer simulations are in agreement with experimental observations in cortical networks: whereas a weak excitatory or strong inhibitory synaptic connection strength produces a stationary status with short-lasting responses to external stimuli, increases in excitation or decreases in inhibition induce spontaneous and stimulus-evoked rhythmic discharges. Synaptic burst-like activity is observed only for an intermediate range of excitatory and inhibitory connection strengths and external inputs. The form and duration of the bursts can also be controlled by the temporal parameters. The results demonstrate that relatively simple mathematical equations are sufficient to model some of the network properties underlying the generation and propagation of epileptiform activity.

Epilepsy↗

PubMed1996

Population networks: a large-scale framework for modelling cortical neural networks.

Artificial neural networks are usually built on rather few elements such as activation functions, learning rules, and the network topology. When modelling the more complex properties of realistic networks, however, a number of higher-level structural principles become important. In this paper we present a theoretical framework for modelling cortical networks at a high level of abstraction. Based on the notion of a population of neurons, this framework can accommodate the common features of cortical architecture, such as lamination, multiple areas and topographic maps, input segregation, and local variations of the frequency of different cell types (e.g., cytochrome oxidase blobs). The framework is meant primarily for the simulation of activation dynamics; it can also be used to model the neural environment of single cells in a multiscale approach.

Animals↗

PubMed1987

Characteristics of neuronal systems in the visual cortex.

The coupling complexity of cortical areas makes it very difficult to analyse them experimentally. Studies of model systems provide the possibility of adapting the analysis to the available data base and elaborating the fundamental properties that depend on the structure of the system. We propose a model system of variable complexity that is spatially two-dimensional and time-dependent, uses feedback for iteration and smoothing, includes the mapping of the cortical networks and can be nonlinear as the case requires. Combining such elementary systems on the basis of neuroanatomical findings enables us to simulate cortical mappings and to interpret neurophysiological data. The decisive factor is that the dynamics of the system and the neuroanatomically based spatial coupling are closely connected with each other.

Animals↗