[Efferent connections of the caudate nucleus in cats]

The structural and ultrastructural changes in the frontal cortex and globus pallidus were investigated after local or extensive destructions of the caudate nucleus. Using the Fink-Heimer method few degenerating fibres of medium and small sizes were observed in the frontal cortex following the local destruction of the caudate nucleus with preliminary implanted electrodes (2-16 months prior to electrolytic destruction). The extensive destruction of the caudate nucleus without preliminary implanted electrodes is accompanied by mass degeneration of fibres with different calibre in the frontal cortex. Light and electron microscopy of the globus pallidus confirmed the existence of thin degenerating axons 0.5-0.6 mum in diameter after the local lesion of the caudate nucleus. Degenerating changes in axo-dendritic and axo-somatic terminals of the pallidal region occur by "dark" type. The degenerating fibres of the medium size in the frontal cortex following the caudate nucleus destruction are suggested to be the axons of thalamic neurons but not those of the destructed nucleus cells.