The influence of B chromosomes on rDNA organization in rye interphase nuclei

Patterns of rye rDNA organization in interphase nuclei were studied through the use ofin situ hybridization in spreads of root meristem cells from plants with and without B chromosomes (Bs). In cells from plants without Bs each rDNA locus is organized as a single perinucleolar knob of condensed chromatin with decondensed chromatin inside the nucleolus. In plants with Bs there is a marked modification of the pattern, found in more than 23% of nuclei, which involves several regions of condensed chromatin interspersed with decondensed chromatin inside the nucleolus. This B-induced alteration in rDNA interphase organization suggests a change in expression of the rRNA genes located on the A chromosomes probably related to the reduction in nuclear RNA observed previously in plants with Bs. The influence of the Bs on the expression of A chromosome genes, through rearrangement of interphase chromatin, could provide the basis of an explanation for some of the known phenotypic effects of B chromosomes in rye.     

The effects of the experience of forming visual images on the spatial organization of the EEG

The spatial organization of biopotentials in the cerebral cortex of 23 subjects who were students at the Faculty of Graphic Arts (“professionals”) as well as 39 subjects lacking systematic experience of visual images (“non-professionals”) was compared with the aim of identifying EEG correlates of the experience of visual images (image formation) in humans. Changes in measures of the spatial organization of biopotentials (spatial synchronization, spatial disordering, coherence, and spectral power) were analyzed as subjects mentally composed visual images consisting of two simple graphic elements — right angles and oblique lines. The total number of image elements increased in each of four sequential tasks, from a number which could be analyzed at the conscious level (4–7 elements) to a number exceeding analysis at the conscious level (8–16). Intergroup differences, particularly increases in the spatial disordering of biopotentials (non-linear processes), were detected when large numbers of elements were used (tasks 3 and 4). This measure increased more markedly in professionals than in non-professionals. Changes were significant in the anterior areas of the right hemisphere. Spatial synchronization of biopotentials (linear processes) increased in non-professionals in the posterior areas of the right hemisphere. Coherence and spectral power increased in professionals in a larger number of narrow-band EEG frequency subranges than in non-professionals. These data show that experience of visual imagery results in a more complex neurodynamic process during the activity, with non-linear dynamics and a multitude of EEG resonance systems at different frequencies. __________ Translated from Zhurnal Vysshei Nervnoi Deyatel’nosti imeni I. P. Pavlova, Vol. 55, No. 6, pp. 812–821, November–December, 2005.     

The spatial organization of the excitatory regions in the visual receptive fields of the pigeon's optic tectum

Summary The spatial location of the excitatory regions in the receptive field of cells in the pigeon's optic tectum was analyzed with light and dark edges moving at a constant velocity. The tectal cells were classified into two main groups: 1-cells showing spatially overlapping light and dark excitatory regions in their receptive field (60%); cells showing spatially separated light and dark excitatory regions in their receptive field (32%). A small number of cells discharged only to one sign of contrast. These results were confirmed by testing the cells with light bars of various widths. Latency studies were carried out with single edges moving at a series of constant velocities. In most cases, for any given cell the light and the dark edge discharges were shown to have similar latencies. These results also indicate that the relative location of the excitatory regions in the receptive field of most tectal cells was not significantly affected by the latency of the discharges.Supported by grants from the CNRS (ERA No. 333; ATP No. 4185) and from DGRST (79.7.1075)