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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.

The purpose of the present study was to investigate the binding patterns of the plant lectin Bandeiraea simplicifolia I-isolectin B(4) (BSI-B(4)) to sensory neurones in seven mammalian species. The dorsal root ganglia and spinal cords of three rats, mice, guinea pigs, rabbits, flying foxes, cats, and marmoset monkeys were screened for BSI-B(4) using lectin histochemistry. BSI-B(4) binding was associated with the soma of predominantly small-diameter primary sensory neurones in the dorsal root ganglia and their axon terminals within laminae I and II of the superficial dorsal horn in all seven species. The similarities of lectin binding patterns in each of these species suggest that the glycoconjugate to which BSI-B(4) binds has a ubiquitous distribution in mammals, and supports the proposal that this lectin may preferentially bind to a subpopulation of sensory neurones with a similar functional role in each of these species., (Copyright 2002 Wiley-Liss, Inc.)

There is an increasing body of evidence to suggest that different functional classes of neurones express characteristic cell-surface carbohydrates. Previous studies have shown that the plant lectin Ulex europaeus agglutinin-I (UEA) binds to a population of small to medium diameter primary sensory neurones in rabbits and humans. This suggests that a fucose-containing glycoconjugate may be expressed by nociceptive primary sensory neurones. In order to determine the extent to which this glycoconjugate is expressed by other species, in the current study, we have examined the distribution of UEA-binding sites on primary sensory neurones in seven different mammals. Binding sites for UEA were associated with the plasma membrane and cytoplasmic granules of small to medium dorsal root ganglion cells and their axon terminals in laminae I-III of the grey matter of the spinal cord, in the rabbit, cat and marmoset monkey. However, no binding was observed in either the dorsal root ganglia or spinal cord in the mouse, rat, guinea pig or flying fox. These results indicate an inter-species variation in the expression of cell-surface glycoconjugates on mammalian primary sensory neurones.

The plant lectinBandeiraea simplicifoliaI-isolectin B4 (BSI-B4) identifies a galactose-containing, membrane-associated glycoconjugate expressed by a discrete subpopulation of unmyelinated primary sensory neurones in the rat. We have previously suggested that BSI-B4 selectively binds to primary sensory neurones that innervate the skin. However, in that study, the tracer diamidino yellow was applied to the cut ends of peripheral nerves to identify neurones innervating particular target tissues. In this study, we have avoided axotomy by retrogradely labelling primary sensory neurones from peripheral tissues using the carbocyanine dye 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbacyanine perchlorate (DiI). DiI was injected into the plantar skin, gastrocnemius muscle, and pyloric region of the stomach in rats. Corresponding ganglia were sectioned, incubated in BSI-B4 conjugated to fluorescein isothiocyanate, and examined with a fluorescence microscope. DiI-labelled cells were identified by red fluorescence within the cytoplasm, whereas cells binding BSI-B4 displayed green fluorescence associated with the plasma membrane and Golgi apparatus. Quantitative analysis revealed that 36.2% of cutaneous neurones, 7.6% of muscle neurones, and 6.8% of visceral neurones expressed the BSI-B4-binding site, indicating that a small but significant proportion of small-diameter primary sensory neurones innervating muscle and viscera also express BSI-B4-binding sites. [ABSTRACT FROM AUTHOR]