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R T Robertson

Publications and source records attributed to R T Robertson.

113 records · Page 7Linked to original sources
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Thalamic projections to visually responsive regions of parietal cortex.

Thalamic efferents to visually responsive regions of parietal cortex of the cat were investigated by experimental retrograde tracing techniques. Two classes of photically evoked potentials recorded from the middle suprasylvian gyrus could be distinguished on the basis of waveform and latency. Type 1 responses were recorded from the Clare-Bishop area at the lateral border of the suprasylvian gyrus and Type 2 responses were recorded from association response areas on the crown of the suprasylvian gyrus. Studies of retrograde degeneration in kittens and adult cats and retrograde transport of intracortically injected horseradish peroxidase indicate that afferents to the electrophysiologically identified Clare-Bishop area originate in the lateroposterior nucleus, the posterior nucleus, and the medial interlaminar nucleus of the lateral geniculate body. Afferents to electrophysiologically identified association response areas originate in the lateroposterior nucleus, ventroanterior nucleus, the pulvinar, the laterodorsal nucleus, and the central lateral nucleus. Studies of orthograde degeneration following placement of parietal lesions indicate a close reciprocity of corticothalamic and thalamocortical projections.

Age Factors↗
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An inbred epilepsy-prone substrain of BALB/c mice shows absence of the corpus callosum, an abnormal projection to the basal forebrain, and bilateral projections to the thalamus.

BALB/c mice lack a corpus callosum in about 11% of the population. Two inbred substrains of BALB/c mice, epilepsy-prone (EP) and epilepsy-resistant (ER), have been examined to determine whether these substrains differ in regard to corpus callosum morphology. Further, this study addressed the issue of whether misrouted cortical axons form an aberrant pathway instead of the corpus callosum. Initial studies that examined fresh brain tissue of adult animals revealed normal corpora callosa in all ER mice but deficient or absent corpora callosa in all EP mice. Subsequently, Dil crystals were placed in the motor cortices of aldehyde-fixed brains of 2-week-old animals to investigate cortical projections in both inbred substrains of mice. Fluorescent microscopy revealed that all of the ER animals had normal corpora callosa, whereas all EP animals exhibited either reduced corpora callosa (partially callosal) or an absence (acallosal) of this structure. Both acallosal and partially callosal EP mice displayed an extensive, aberrant projection to the basal forebrain as well as bilateral projections to midline and intralaminar thalamic nuclei. The fibers projecting to the basal forebrain arose from the cortex, coursed toward the midline before turning ventrally along the midline, and appeared to terminate in the medial septal nucleus and the nucleus of the diagonal band. ER animals lacked this aberrant cortical projection to the basal forebrain. Electron microscopic results obtained from EP mice indicated that labeled axons in this aberrant pathway formed axosomatic, axodendritic, and axospinous synapses with the neurons in the medial septal/diagonal band complex. The function of the aberrant projection to the basal forebrain remains unknown but it may provide an abnormal excitatory input to a region that provides cholinergic and GABAergic input to the cerebral cortex and hippocampus. The additional projections to midline and contralateral intralaminar thalamic nuclei in EP mice may function to intensify the synchronization of bilateral discharges.

Agenesis of Corpus Callosum↗