Mast cells alter granular properties and spatial relation to nerve fibres in spondylitis of adjuvant-treated rats.

It has been long implicated that mast cells (MCs) have a close spatial relationship to the peripheral nerve fibres. In the present study, which used spondylitis of adjuvant-treated rats, we investigated the behaviour of MCs in relation to peripheral nerve fibres and other inflammatory cells. Rat MCs with staining properties like connective tissue MCs decreased in number as inflammation progressed. With additional electron microscopic studies it was possible to observe the sequence of changes in their granular ultrastructure during active inflammation. Thus, the decrement of MCs with staining properties like connective tissue MCs was attributable to the changes in their granular conformation. In contrast, enzyme histochemistry of nerve fibres indicated that the percentages of MCs which were distant from nerve fibres increased significantly during the early stage of inflammation (p < 0.01). We speculate that while other inflammatory cells infiltrate, MCs deviate actively form nerve fibres and release their granular content.