[Demonstration of the sources of several descending forebrain systems using the horseradish peroxidase retrograde axonal transport technic].

Cells of cortical and diencephalic fibres descending to the mesencephalic and bulbar reticular formation and to the dorsal column nuclei were identified. According to findings neurons sending fibres to the mesencephalic reticular formation are located in orbitofrontal pole and in area 6 of the pericruciate cortex, mainly ipsilaterally. Neurons which distribute fibres to the bulbar reticular formation are concentrated mainly in area 6 and 4 of the both hemispheres, while those distributing fibres to dorsal column nuclei are arranged in areas 1, 2, 3 and 4, mainly contralaterally. Fibres descending to reticular formation from the limbic cortex, septum, substantia innominata and amygdala were also found. The functional significance of the investigated descending pathways of forebrain is discussed.