Comparison of in vitro cytotoxicity of Fusarium mycotoxins,deoxynivalenol, T-2 toxin and zearalenone on selected human epithelial cell lines.

Three human epithelial cell lines (CaCo-2, HEp-2 and HeLa) implicated as potential targets for three Fusarium toxins were tested for the extent of survival on exposure to increasing toxin concentration and incubation periods. Cytotoxicity assay using 3(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide (MTT) was carried out with deoxynivalenol (DON), T-2 toxins and zearalenone (ZON) on CaCo-2, HEp-2 and HeLa cell lines. Of the three cell lines used, HeLa was the most sensitive, eliciting cell death after 2 days exposure at 100 ng ml(-1)with T-2 toxin. HeLa was the only cell line to exhibit cytotoxicity towards ZON showing cell death at 1000 ng ml(-1)after 2 days which increased to 4 days, showing substantial cell death at 200 ng ml(-1). HEp-2 was sensitive to DON showing cell death after 2 days (100 ng ml(-1)) with complete cell death occurring at 200 ng ml(-1) after 4 days of exposure. Substantial cytoxicity of T-2 towards HEp-2 occurred after 2 days at 1000 ng ml(-1) and complete cell death occurred with 100 ng ml(-1) at day 4. The CaCo-2 cell line was generally resistant to the mycotoxins tested between 100 and 1000 ng ml(-1). This study shows that cytotoxicity of Fusarium toxins to epithelium cell lines is concentration- and time- dependant and results from ZON-HeLa interaction indicate possible cell type-mycotoxin specificity.

Model of a pattern generator for locomotion in mammals.

This paper presents an analytic model of a limb pattern generator that can produce complex muscle activation patterns such as those shown to control the limbs of cats. The limb pattern generator is considered to have a tonic input and six outputs; this provides for flexion and extension of representative muscles for each of the three joints of the limb. The pattern generator functions as a community of labile synthesized relaxation oscillators that alters its output in response to input. This model was studied using electromyographic data from an experiment conducted on an acute postmammillary cat preparation. The results suggest that the limb pattern generator can be represented as three subsystems: an oscillator that produces the fundamental frequency of the output in response to the tonic signal, nonlinear shaping functions that mold the oscillator output into the basic complex pattern, and appropriate weighting functions that generate the muscle activity pattern from basic waveforms. The model can account for speed changes in locomotion with a relatively smooth change of system parameters. The pattern generator model is generative, amenable to simulation studies, and can be realized by a neural network.

Mechanical resonance of the human body during voluntary oscillations about the ankle joint.

Viscoelastic models of the musculoskeletal system suggest resonant frequencies of oscillatory movement at which maximal output is realized with minimal energy expenditure. To investigate this, resonance at the human ankle joint was explored by comparing predicted and experimental gain/frequency and phase frequency functions. These functions were predicted from viscous (B) and elastic (K) coefficients of ankle extensors which were determined from the damped sinusoidal force produced after landing with muscles in sustained contraction (B = 3986 kg/s, K = 31,898 kg/s2). Experimental input/output functions were determined from Fourier analysis of force (output) and rectified, filtered EMG (input) obtained during voluntary sinusoidal oscillations of ground reaction force of a specified magnitude and frequency. Correlations between predicted and experimental functions were significant (p less than 0.02) in four of five subjects. The average resonant frequency was 3.33 +/- 0.15 Hz. The mechanical properties of muscle are considered to be as important as the nervous system in determining the choice of both the movement pattern and the strategy which is adopted in response to changing conditions.

Planning for future performance: implications for long term training.

The contribution of cardio-respiratory endurance and strength to elite performance in swimming has been quantitated in a unit of training termed the Training Impulse (TRIMP). The Training Impulse has been used to construct a model for predicting performance in swimming based upon the degree of balance between fitness and fatigue that training engenders.

Distribution coding in the visual pathway.

Although a variety of types of spike interval histograms have been reported, little attention has been given to the spike interval distribution as a neural code and to how different distributions are transmitted through neural networks. In this paper we present experimental results showing spike interval histograms recorded from retinal ganglion cells of the cat. These results exhibit a clear correlation between spike interval distribution and stimulus condition at the retinal ganglion cell level. The averaged mean rates of the cells studied were nearly the same in light as in darkness whereas the spike interval histograms were much more regular in light than in darkness. We present theoretical models which illustrate how such a distribution coding at the retinal level could be "interpreted" or recorded at some higher level of the nervous system such as the lateral geniculate nucleus. Interpretation is an essential requirement of a neural code which has often been overlooked in modeling studies. Analytical expressions are derived describing the role of distribution coding in determining the transfer characteristics of a simple interaction model and of a lateral inhibition network. Our work suggests that distribution coding might be interpreted by simply interconnected neural networks such as relay cell networks, in general, and the primary thalamic sensory nuclei in particular.