Biomedical subjects

A Milgram

Publications and source records attributed to A Milgram.

4 recordsLinked to original sources

PubMed2001

The Rhodobacter capsulatus genome.

The genome of Rhodobacter capsulatus has been completely sequenced. It consists of a single chromosome containing 3.5 Mb and a circular plasmid of 134 kb. This effort, started in 1992, began with a fine-structure restriction map of an overlapping set of cosmids that covered the genome. Cosmid sequencing led to a gapped genome that was filled by primer walking on the chromosome and by using lambda clones. Methods had to be developed to handle strong stops in the high GC (68%) inserts. Annotation was done with the ERGO system at Integrated Genomics, as was the reconstruction of the cell's metabolism. It was possible to recognize 3709 orfs of which functional assignments could be made with high confidence to 2392 (65%). Unusual features include the presence of numerous cryptic phage genomes embedded in the chromosome.

Journal Article↗

PubMed1991

Cortical cells' physiology following visual split brain in developing cats.

We have studied physiologically whether visual cortex cells in areas 17 and 18 of split-brain cats preserve their performance despite the blockage of both binocularity and of interhemispheric communication. The absolute majority of the cells in cats underwent split-brain surgery as kittens and adults and were driven by the ipsilateral eye, resulting in the absence of interhemispheric interaction. Similar results were found in cats and kittens that underwent only chiasm split surgery, although some recovery of callosal transfer was found in the latter. A remarkable loss of binocularity was found when only callosal transection was performed, both in adult cats and in kittens, although some ipsilateral eye dominance was observed in the latter. As to the deprived cats, while in the inexperienced hemisphere (ipsilateral to the deprived eye), the majority of the cells was visually unresponsive, in the contralateral (experienced) hemisphere, the majority was responsive. A considerable reduction in responsiveness was found in the callosally transected cats and kittens. Generally, a degradation of function was found in the various properties as a result of chiasmal and/or callosal transection. The main effect is the increased number of cells with diffuse and incomplete receptive fields. There was also a reduction in the proportion of orientation-selective cells, mainly in the split-brain cats. It was concluded that, despite the high amount of hemispheric independency in the normal brain, the integrity and simultaneous action of the two hemispheres are needed for the normal functioning of visual cortex cells.

Aging↗

PubMed1990

The ocular dominance and receptive field properties of visual cortex cells of cats following long-term transection of the optic chiasm and monocular deprivation during adulthood.

Plasticity-induced interhemispheric transfer of visual information to cortical cells was studied in adult cats. The direct contralateral visual pathway was surgically eliminated permitting binocularity only by callosal transfer. In order to enhance the interhemispheric transfer, one hemisphere was made less visually active by depriving it chronically from visual input. Single cell recording was made in areas 17-18 boundary, the callosal projection zone, of operated (OC), operated and deprived (OCMD), and normal control cats. In the OCMD cats, greater than 90% of the cells in each hemisphere reacted ipsilaterally to the deprived or non-deprived eye. Only 3.1% of the cells in both hemispheres of the OCMD cats and 3.9% in the OC cats had contralateral input via the corpus callosum. The two hemispheres were similar in the selectivity of their cells to stimulus orientation and direction. The average receptive field area of the OCMD cats was also similar for the ipsilaterally driven cells in the two hemispheres; it was 1.2 degrees 2 for the deprived eye and 1.1 degrees 2 for the normal eye. The receptive fields (greater than 95%) of both eyes of the OCMD cats were found in the nasal visual hemifields and greater than 70% of them were at eccentricities of less than 5 degrees from the vertical meridian. The disappearance of the temporal (contralateral) hemifields in these cats and the physiological properties of their cortical cells were determined merely by the chiasm transection which had thus induced nearly complete interhemispheric separation. No effect of the monocular deprivation, in normal adult cats or in cats with chiasm transection was found, even after long periods (greater than 7 months). Therefore, plasticity-induced interhemispheric transfer of visual information was not found during adulthood.

Animals↗

PubMed1990

Hydrocephalus in developing cats: physiological properties of visual cortex cells.

We have studied electrophysiologically by single cell recording in the visual cortex, whether modification of the visual system in developing and in adult cats by hydrocephalus has an effect on processing of visual information. One of our cats (H1) had developed a complete hydrocephalus and the others partial, as proved by either complete or partial dilation of the lateral ventricles, respectively and by the thinning of the cortex. Despite this, the horizontal lamination and the vertical organization of the cortex were fully preserved. Except for the optic radiation and the corpus callosum which was remarkably modified, the optic tract, chiasm, nerve and retina were morphologically and histologically normal. The visual behavior of the hydrocephalic cats was normal. This was also reflected, by and large, in the physiological properties of the visual cortex. However, in cat H1 there were many more visually unresponsive cortical cells in comparison to its matched controls (C1) and the normal cats. A reduced responsiveness was also found in cat H2 with partial hydrocephalus but not in the other partial hydrocephalic cats. Similarly, the ocular dominance distribution of the cells was affected in cat H1 in comparison to the control cats as indicated by the changes found in the relative proportions of contralaterally and ipsilaterally driven cells in the two hemispheres. No change was, however, found in the partially hydrocephalic cats. Most of the cells in the hydrocephalic cats were orientation specific, similarly to the result of their matched controls. Direction specific cells were much smaller in proportion in cat H1 but not in the other cats, in comparison with their matched controls. In keeping with this, a large increase was found in the receptive field area of cat H1, a smaller one in cat H2 and none in the other hydrocephalic cats in comparison to the matched controls. The eccentricity distribution of the receptive fields in the hydrocephalic cats was the same as expected under normal conditions. It was concluded that in the way hydrocephalus had modified the brain of several of our cats, a quantitative effect was induced in visual cortex cells leading to some degradation of function; this change, however, did not interfere with their basic visual properties.

Animals↗