[Location of neurons giving rise to certain descending fiber systems in the sensomotor and orbitofrontal cortex].

By means of the horseradish peroxidase (HP) retrograde axonal transport method localization of HP-labelled neurons in the forebrain cortex making projections on some somatic (motor and sensory) spinal and truncal centers, as well as on the retucular formation, substantia nigra and hypothalamus has been studied. Certain peculiarities in localization of the neurons giving origin to various fibre systems in the forebrain cortex have been revealed. Differences are especially noticeable in the area of sulcus chiasmaticus. Only when HP is infected into the spinal cord there is nearly no labelled neurons in the orbital-frontal cortex, while if the enzyme is injected into other structures studied HP-positive cells are revealed in this cortical area. Numerous labelled neurons are noted in the orbital-frontal cortex when HP is injected into the reticular formation and nuclei of the midbrain--the red nucleus and substantia nigra. In the lateal sulcus area HP-positive neurons are revealed when the enzyme is injected into the spinal cord and substantia nigra. Neurons giving origin to the fibre systems running to the spinal cord and to a number of subcortical formations are situated in the layer V. Cortico-hypothalamic neurons, that localized not only in the layer V, but also in the layers III--IV of the frontal cortex and in the layer VI of the orbital cortex--in the presylvian fissure are, make the exception to the rule.