Analysis of the unmyelinated primary sensory neurone projection through the dorsal columns of the rat spinal cord using transganglionic transport of the plant lectin Bandeiraea simplicifolia I-isolectin B4

Abstract

We have examined the projection of unmyelinated primary sensory neurones through the dorsal columns of the rat spinal cord using transganglionic transport of the plant lectin Bandeiraea simplicifolia I-isolectin B4. A small volume of the lectin was injected into the sciatic nerve of anaesthetised rats to label the central terminals of nociceptive primary sensory neurones. Following a survival period of 7 days, transverse and longitudinal sections of the superficial dorsal horn, dorsolateral funiculus and the dorsal columns from spinal segments L4 through to T13 were screened for lectin transport using light and electron microscopy. Longitudinal sections of the thoraco-lumbar region of spinal cord were also examined for lectin binding. Light and electron microscopy revealed transganglionically transported and bound lectin in the superficial dorsal horn and dorsolateral funiculus of the L3 and L4 segments of spinal cord. However, no lectin transport or binding was observed within the dorsal columns at any level of spinal cord examined. From these results, we suggest that the unmyelinated neurones within the dorsal columns do not express the binding site for BSI-B4 and, as such, may be responsible for visceral rather than cutaneous sensation. In line with the theories regarding a postsynaptic dorsal column pathway, these results suggest that nociceptors that bind BSI-B4 are not involved in a direct ascending projection through the dorsal columns.