96 research outputs found
Quantitative changes in mitochondria of spinal ganglion neurons in aged rabbits
No full textWithin the context of our research on the age-related structural changes in spinal ganglia, we studied the mitochondria of the neuronal perikaryon in the spinal ganglia of 12-, 42-, and 79-month-old rabbits. Both the volume of the perikaryon and the total mitochondrial mass within the perikaryon increased significantly passing from young adult to old animals. Hence, there is no net loss of mitochondria in these neurons with age. Since, however, the volume of the perikaryon increased by more than 63% while the total mitochondrial mass within the perikaryon increased by only 18%, the mean percentage of perikaryal volume occupied by mitochondria decreased with age. This decrease is only in very minor part a consequence of lipofuscin accumulation, so that the ratio between the total mitochondrial mass and the functionally active volume of cytoplasm decreased with age. Possible causes of this decrease are discussed briefly. Moreover, while the mitochondrial structure did not change, mitochondrial size increased with age. Finally, in each of the three age groups both the mean percentage volume of mitochondria and the mean mitochondrial size were very similar in large light and in small dark neurons. Copyrigh
Modellare i discenti : ottimizzare formazione, valutazione e testing
No full textGli autori stanno sperimentando una procedura innovativa per profilare gli utenti di una piattaforma di e-learning per predire chi porterà a termine il corso con successo e aiutare i tutor ad organizzare le loro mansioni fin dall’inizio. La modellazione predittiva dei discenti è proposta come uno strumento per programmare strategie di tutoraggio orientate all’individuo,
allo scopo di aumentare non solo le probabilità di completamento del corso ma anche il ritorno sugli investimenti della formazione. Infatti creando un proflo dei discenti è possibile sapere in anticipo chi tra loro terminerà il corso
con successo, chi abbandonerà comunque il corso e chi ha bisogno di più aiuto per completarlo. Il fatto di sapere dove i discenti siano più propensi ad avere successo aiuterà inoltre l’ottimizzazione della valutazione e della fase di formazione
Ratios between number of neuroglial cells and number and volume of nerve cells in the spinal ganglia of two species of reptiles and three species of mammals
No full textWe studied the ratios between number of neuroglial (=satellite) cells and number and volume of neurons with which they are associated in the spinal ganglia of two species of reptiles (lizard and gecko) and three species of mammals (mouse, rat, and rabbit). In all five species, we found that the number of satellite cells associated with a nerve cell body increased with increasing volume of the latter. This result shows that there is a quantitative balance between neuroglia and nerve tissue in spinal ganglia. This balance seems to be maintained by a tight regulation of the number of satellite cells. We also found that the mean volume of nerve cell body corresponding to a satellite cell was lower for small neurons than for large ones. Since satellite cells metabolically support spinal ganglion neurons, the metabolic needs of small neurons are better satisfied than those of large ones. For a nerve cell body of a given size, the number of associated satellite cells did not differ between the lizard and gecko, nor between the mouse, rat, and rabbit. However, this number was significantly smaller in the reptiles than in the mammals. This result could be explained by the lower metabolic rate in the nervous system of poikilotherms than mammals, or could have a phylogenetic significance. These two interpretations are not mutually exclusive
Relazioni quantitative fra cellule satelliti e neuroni nei gangli spinali di alcune specie di vertebrati
No full text
Learner modelling : optimizing training, assessment and testing
No full textThe authors are experimenting an innovative procedure to profile learners
using an e-learning platform to predict if they will successfully end their
training (or education activities) and to help tutors organize their tasks from
the very beginning. Predictive learner modelling is proposed as an instrument
for planning individual-oriented tutoring strategies to increase not only the
probability of completion but also the return on investments of the training
activities. In fact, by modelling learners’ profiles it is possible to know in
advance who of them will successfully complete their courses, who will
leave the training anyway and who needs more help to complete their
courses, according to their profiles. Knowing where learners are more likely
to succeed will also help optimizing the assessment and training phases
A mutually stimulating loop involving emx2 and canonical wnt signalling specifically promotes expansion of occipital cortex and hippocampus.
No full textThe correct size of the different areas composing the mature cerebral cortex depends on the proper early allocation of cortical progenitors to their distinctive areal fates, as well as on appropriate subsequent tuning of their area-specific proliferation-differentiation profiles. Whereas much is known about the genetics of the former process, the molecular mechanisms regulating proliferation and differentiation rates within distinctive cortical proto-areas are still largely obscure. Here we show that a mutual stimulating loop, involving Emx2 and canonical Wnt signalling, specifically promotes expansion of the occipito-hippocampal anlage. Collapse of this loop occurring in Emx2-/- mutants leads progenitors within this region to slow down DNA synthesis and exit prematurely from the cell cycle, due to misregulation of cell cycle-, proneural- and lateral inhibition-molecular machineries, and eventually results in dramatic and selective size-reduction of occipital cortex and hippocampus. Reactivation of canonical Wnt signalling in the same mutants rescues a subset of molecular abnormalities and corrects differentiation rates of occipito-hippocampal progenitors
Density and distribution of microtubules in the axons of the lizard dorsal roots
No full textThe number, density and distribution of microtubules were determined in cross-sections of unmyelinated and myelinated axons of lizard (Lacerta muralis) spinal dorsal roots. In both unmyelinated and myelinated axons the average number and density of microtubules were found to be related to the axonal size. The average number of microtubules rose, while the microtubular density decreased with an increase in the cross sectional area of the axon. More precisely, a linear relationship was observed between the logarithm of the microtubular density and the cross-sectional area of the axon. The average microtubular densities were found to be the same in two samples of unmyelinated and myelinated axons of corresponding size. Therefore, it can be hypothesized that the different microtubular densities usually found in unmyelinated and myelinated axons are correlated with the different size range of the two types of axon rather than with the absence or presence of a myelin sheath. The microtubular densities nearly always proved higher in the sub-axolemmal band and around the mitochondria than in the rest of the axoplasm
Mitochondria in perineuronal satellite cell sheaths of rabbit spinal ganglia : quantitative changes during life
No full textWe studied quantitative changes in mitochondria of perineuronal satellite cell sheaths (SCSs) of rabbit spinal ganglia from young to extremely advanced age (1, 3.6, 6.7 and 8.8 years). The mitochondrial structure did not differ in the four age groups, while mitochondrial size increased progressively and significantly with age. The mean percentage of cytoplasmic volume occupied by mitochondria decreased progressively and significantly from young to old animals. This decrease was mainly due to a progressive and significant reduction in the total mitochondrial volume. Lipofuscin accumulation had a negligible influence on this reduction. These results suggest that the ability of SCSs to produce energy decreases with age and that the reduced ability of spinal ganglion neurons to respond to high energy demands in old age may be in part due to the diminished contribution of perineuronal satellite cells
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