Elsevier

Neuroscience

Volume 127, Issue 1, 2004, Pages 165-175
Neuroscience

Ultrastructural analysis of the central terminals of primary sensory neurones labelled by transganglionic transport of bandeiraea simplicifolia i-isolectin B4

https://doi.org/10.1016/j.neuroscience.2004.05.008Get rights and content

Abstract

In this study the ultrastructural appearance of primary sensory neurones labelled by the injection of the plant lectin Bandeiraea simplicifolia I-isolectin B4 (BSI-B4) into a peripheral nerve has been examined in the rat. Electron microscopy of the somata of retrogradely labelled neurones showed the lectin to be associated with the inner surface of cytoplasmic vesicles, supporting the premise that the uptake of BSI-B4 into sensory neurones is by the process of receptor-mediated endocytosis. Light and electron microscopic analysis of the spinal cord revealed transganglionically transported lectin in unmyelinated axons in the dorsolateral funiculus and axon terminals concentrated mainly within lamina II of the dorsal horn. Detailed analysis of 1377 of these axon terminals revealed that the majority were glomerular in shape and surrounded by up to 14 other unlabelled profiles. These findings suggest that primary sensory neurones which transganglionically transport BSI-B4 have a synaptic ultrastructure similar to that which has been previously reported for unmyelinated primary sensory neurones. Moreover, it appears that the axon terminals of these neurones are subjected to extensive modulation. Examination of the vesicle content of lectin labelled axon terminals revealed that the majority contained small agranular vesicles while large granular vesicles were observed only occasionally. These findings support the suggestion that the populations of neurones expressing binding sites for BSI-B4 are fairly distinct from those containing neuroactive peptides. In conclusion, the results of the current study suggest that the lectin BSI-B4 can be used as a histological marker for a subpopulation of small diameter primary sensory neurones and provide further evidence for the potential of this lectin as a useful tool in the study of pain.

Section snippets

Animals

Three adult Wistar strain rats with body weights ranging from 240 to 430 g were used in this study. All animal work was carried out in accordance with the National Institute of Health Guide for the Care and Use of Laboratory Animals and the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes and with the approval of the University Research Ethics Committee. All efforts were made to minimise the number of animals used in this experiment and their suffering.

Dorsal root ganglia

Light microscopic examination of vibratome sections of the L4 dorsal root ganglia in all three animals revealed a dense reaction product associated with a large number of neurones indicating that lectin transport had been successful. Although no detailed morphometric analysis was performed, it was clear that lectin transport was restricted to a subpopulation of small diameter neurones (Fig. 1A).

Examination at higher magnification, and with the aid of an oil-immersion objective, revealed that

Discussion

This study constitutes the first detailed analysis of the ultrastructural appearance of the central terminals of primary sensory neurones labelled by transganglionic transport of BSI-B4. The results raise a number of interesting issues regarding the mode of transport of the lectin and the features of the neurones that it labels.

Acknowledgements

This study was supported by an Australian Postgraduate Award from the Commonwealth Department of Education, Science and Training to M.B.G. and a Queensland University of Technology Research Encouragement Award to M.B.P.

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