The termination of the spinothalamic tract in the cat an experimental study with silver impregnation methods

Abstract

The termination of the spinothalamic tract (STT) in the cat has been studied light microscopically in Fink-Heimer and Nauta impregnated sections. Following lesions of the STT at various rostrocaudal levels of the spinal cord the degenerating fibres in the thalamus and subthalamus were mapped, mainly in transverse sections. The cervicothalamic tract was not injured by the lesions. The spinothalamic fibres enter the diencephalon through the mesencephalic reticular formation and terminate in the following regions: the medial portion of the magnocellular part of the medial geniculate body (MGmc), the ventrolateral portion of the medial part of the posterior nuclear complex (POm), the caudolateral and medial parts of the zona incerta (ZI), the nucleus centralis medialis (CeM), the nucleus parafascicularis (Pf), the lateral part of the nucleus centralis lateralis (CL), the medial and rostrolateral parts of the nucleus ventralis lateralis (VL). To reach these regions the fibres pass through the nucleus centrum medianum (CM), the nucleus subparafascicularis (SPf) and the nucleus paracentralis (Pc). The fibres that terminate in the VL pass through Forel's field H1 and the external medullated lamina (EML). Conclusive results were not obtained concerning a termination in the CM. The spinothalamic fibres do not pass through nor terminate in the nucleus ventralis posterolateralis (VPL) and the nucleus reticularis (R). The VPL, defined as that portion of the ventral thalamus that receives terminal fibres from the dorsal column nuclei, has been found to extend rostrally only as far as Horsley-Clarke level anterior 10.5. The results strongly support the view that all the spinothalamic fibres terminate ipsilateral to their course in the ventral quadrant of the spinal cord. No signs of a somatotopical organization of the termination of the STT were found.