The role of nutrition in the development of evoked cortical responses in rat

Abstract

Following lesions of varying size in different parts of the cerebral cortex in 24 adult cats the ensuing preterminal and terminal degeneration in the lateral reticular nucleus (nucleus of the lateral funiculus) has been studied by means of the Nauta silver impregnation method. The majority of cortical efferents terminating within the nucleus are derived from the anterior sigmoid gyrus. Scanty projections arise in the posterior sigmoid, the coronal and the anterior ectosylvian gyri. In addition some fibres are derived from the gyrus proreus and parts of the medial wall of the hemisphere below the cruciate sulcus. Evidence for fibres from the occipital, temporal, and parietal cortices and part of the cingulate gyrus was not obtained. The cortical fibres are distributed mainly to the nucleus contralateral to the lesion; only a few terminate in the ipsilateral nucleus. Regardless of the site of the lesion, if degeneration is present, it is found to be restricted to the rostrodorsal part of the magnocellular division of the lateral reticular nucleus. The subtrigeminal and the parvicellular divisions do not receive cortical afferents. Following small lesions placed in various parts of the sensorimotor cortex, no evidence in favour of a somatotopical organization of the projection was found. Only few degenerating fragments are seen close to the soma of the cells, indicating that that most synaptic contacts are presumably axodendritic. The sites of origin of the cortical projection to the lateral reticular nucleus are discussed with reference to present knowledge about the functional and cytoarchitectonic localization within the cerebral cortex and other corticofugal fibre tracts. The area of termination of the cortical fibres overlaps to some extent with the terminal areas of other afferents to the nucleus (from the spinal cord, the red nucleus and the fastigial nucleus). From a functional point of view it is of interest that the cortical fibres to the red nucleus are derived from the same regions as those to the lateral reticular nucleus. Even if the fibres to the latter from the red nucleus have a somewhat different area of termination within the magnocellular division, both connections (the direct corticoreticular and the cortico-rubro-reticular) may serve as links in a cerebro-cerebellar pathway. However, both projections may also be imagined to influence the spinal input to the cerebellum via the lateral reticular nucleus.