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G Vrensen

Publications and source records attributed to G Vrensen.

44 records · Page 3Linked to original sources
PubMed1977

Quantitative aspects of the synaptic organization of the superior colliculus in control and dark-reared rabbits.

Fine structural and quantitative aspects of the synaptic organization of the superior colliculus of the rabbit were studied. The synaptic density, the frequency of the distinct types of terminals, the length of the contact zones, the percentage of serial contacts and the number of synaptic vesicles per terminal were estimated in control, dark-reared and dark-reared-recovered animals. The ultrastructure of the synaptic terminals and the complex interconnectivity correspond to that described for other species. The depth distribution of terminals with round synaptic vesicles agrees quite well with the distribution of cortical and retinal afferents found in lesion experiments. Dark-rearing has little effect on the quantitative organization of the synaptic terminals. In contrast with previous observations in the visual cortex of the same animals37 no changes in the density of synaptic vesicles is observed in the superior colliculus after long term dark-rearing.

Animals↗
PubMed1975

The effects of monocular deprivation on synaptic terminals in the visual cortex of rabbits. A quantitative electron microscopic study.

The effect of prolonged (7 month) monocular deprivation (right eye sutured) on the density of synapses (NA) and the number of synaptic vesicles (Nves) in the visual cortex of rabbits is studied. The results can be summarized as follows: (1) No changes (NA and Nves) are observed in the non-deprived hemisphere (visual areas I and II, motor cortex) as compared to control animals. (2) NA has not changed, as compared to control animals, in the binocular field of the deprived visual cortex. (3) A significant rise in NA, as compared to control animals, is observed in the monocular field of area I and in the motor cortex of the deprived cortex. This rise is similar to that found after recovery from prolonged dark rearing. (4) The increase in NA is mainly restricted to the laminae I-II, indicating that, most likely, we are not dealing with an increase in specific visual afferents. (5) The deprived visual cortex shows a significant decrease (16%) in NVes. This decrease is less pronounced than after dark rearing (40%). This probably points to the fact that eye suturing does not fully prevent light penetration. The results are discussed in the light of recent discussions on the plasticity of synapses and the effect of retinal input on the development of the visual system.

Animals↗
PubMedDate not supplied

Visual performance and synapses in the visual cortex of rabbits.

The density of synaptic connections, the length of the contact zones and the number of synaptic vesicles are quantitatively studied in the left and right hemisphere of a group of rabbits a number of which showed marked ocular dominance. No systematic differences in the parameters studied could be observed in the visual cortex between symmetric animals, indicating that the ocular dominance cannot be explained by hemispheric differences in density of synapses.

Animals↗