scholarly journals Analysis of an Experimental Cortical Network: ii) Connections of Visual Areas 17 and 18 After Neonatal Injections of Ibotenic Acid

1991 ◽  
Vol 2 (1) ◽  
pp. 29-54 ◽  
Author(s):  
G. M. Innocenti ◽  
P. Berbel
Keyword(s):  
Horseradish Peroxidase ◽  
Corpus Callosum ◽  
Wheat Germ Agglutinin ◽  
Wheat Germ ◽  
Ibotenic Acid ◽  
Contralateral Hemisphere ◽  
Cortical Areas ◽  
Visual Areas ◽  
Local Injections ◽  
Areas 17 And 18

Lesions of cortical areas 17 and 18 were produced in newborn kittens by local injections of the excitotoxin ibotenic acid. In the adult this results in a microcortex which consists of superficial layers I, II and III, in the absence of granular and infragranular layers. Horseradish peroxidase, alone or wheat germ agglutinin conjugated, was injected in the microcortex or in the contralateral, intact areas 17 and 18. The microcortex maintains several connections characteristic of normal areas 17 and 18 of the cat. It receives afferents from the dLGN, and several visual areas of the ipsilateral and contralateral hemisphere. However, it has lost its projections to dLGN, superior colliculus, and, at least in part, those to contralateral visual areas. Thus some parts of the microcortex receive from, but do not project into, the corpus callosum. In addition, the microcortex maintains afferents from ipsilateral and contralateral auditory areas AI and AII which are normally eliminated in development.

scholarly journals Analysis of an Experimental Cortical Network: i) Architectonics of Visual Areas 17 and 18 After Neonatal Injections of Ibotenic Acid; Similarities with Human Microgyria

1991 ◽  
Vol 2 (1) ◽  
pp. 1-28 ◽  
Author(s):  
G. M. Innocenti ◽  
P. Berbel
Keyword(s):  
Radial Glia ◽  
Thick Layer ◽  
Ibotenic Acid ◽  
Cortical Areas ◽  
Visual Areas ◽  
Local Injections ◽  
Layer I ◽  
Areas 17 And 18 ◽  
Normal Cortex ◽  
Severe Destruction

Lesions of cortical areas 17 and 18 have been produced in newborn kittens by local injections of the excitotoxin ibotenic acid (ibo). Twenty-four hours after an injection on postnatal days 2 or 3, the gray matter of areas 17 and 18 near the center of the injection appears completely destroyed, with the exception of a one-to-two cell-thick layer at the bottom of layer I. Intact migrating neurons and radial glia can be found light- and electron-microscopically in the region affected. During the following weeks a several hundred micron thick cortex reforms. In the adult, this cortex consists of superficial layers I, II and III as proven by cytoarchitectonics, continuity with the corresponding layers of the normal cortex and cellular composition. We believe that the recovery is due to completion of migration by neurons spared by the ibo injection. More severe destruction of cerebral cortex, i.e. complete loss of the neuronal layers or their reduction to a few cell-thick mantles can be obtained with ibo injections at the end of the second or, respectively, first postnatal week. Severity of lesion also depends on the dose of ibo injected. There are interesting similarities between the ibo-injured cortex and two human neocortical displasias: microgyria and ulegyria.

Structural basis of cortical synchronization. II. Effects of cortical lesions

1995 ◽  
Vol 74 (6) ◽  
pp. 2401-2414 ◽  
Author(s):  
M. H. Munk ◽  
L. G. Nowak ◽  
J. I. Nelson ◽  
J. Bullier
Keyword(s):  
Corpus Callosum ◽  
Posterior Part ◽  
Preceding Paper ◽  
Ibotenic Acid ◽  
Border Region ◽  
Extrastriate Cortex ◽  
Structural Basis ◽  
Encounter Rate ◽  
Cortical Areas ◽  
Reciprocal Connections

1. To understand the structural basis of the different types of interhemispheric synchronizations described in the preceding paper, we made sections of the corpus callosum and lesions of extrastriate cortex. We measured the effects of such operations on the frequency of encounter, width and strength of T, C, and H peaks in cross-correlation histograms computed from single-unit and multiunit recordings from areas 17-18 of opposite cortical hemispheres in the cat. 2. Sectioning of the corpus callosum led to a complete abolition of T and C couplings and a strong reduction of encounter rate and strength of H coupling. A section limited to the posterior half of the corpus callosum abolished T and C couplings completely. This suggests that T and C couplings are mediated by the direct reciprocal connections between visual cortical areas circulating through the posterior part of the corpus callosum. 3. The encounter rate of H peaks depended on the extent of the callosal cut. Larger lesions gave a more pronounced reduction of the number of H peaks. From this observation we conclude that H peaks are at least partially mediated by polysynaptic pathways involving widely distributed cortical regions. 4. Extensive lesions of extrastriate cortex were made by aspiration of the gray matter or injections of ibotenic acid. These lesions removed the direct inputs from cortical areas sending ipsilateral as well as contralateral inputs to the area 17-18 border region. Encounter rate and coupling strength of C and H peaks were decreased, whereas little effect was observed on T peaks. 5. These results demonstrate that all types of interhemispheric synchronization are mediated by corticocortical connections and that T and C peaks are generated by reciprocal connections between areas 17 and 18 of each hemisphere. Feedback connections play a role in mediating or facilitating the C and H types of interhemispheric synchronization.

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