The ultrastructure of sensory nerve endings in the human periodontal ligament from 43 extracted teeth was studied using serial sections. Three types of nerve endings were found: free nerve endings (FNE), Ruffini-like endings and lamellated corpuscles. Free nerve endings stem from unmyelinated or from myelinated nerve fibers. The endings contain neurotubuli, neurofilaments and vesicles. Ruffini-like receptors were mostly found in the apical part of the periodontal ligament. In these Ruffini-like receptors a particularly abundant concentration of mitochondria appears. In some cases desmosome-like junctions are present between neurite and ensheathing cell. Lamellated corpuscles were also found in the periodontal ligament. The lamellae are extremely endocytotic and are in close contact with each other.

Animal models have been developed in which the role of Helicobacter pylori in the pathogenesis of different gastroduodenal diseases can be investigated. The gnotobiotic pig was one of the first animal models used. In this model, Helicobacter pylori infection causes gastritis, which shows some similarities to that in humans, such as the development of mucosa-associated lymphoid tissue (MALT). Hence, this animal model can be used to study the development of MALT in the normal stomach. The aim of our study is to see if lymphoid tissue is present or absent in the normal stomach of gnotobiotic pigs before birth and if so, to investigate its development and composition as a function of gestational age and location in the stomach. Therefore, we studied 82 foetal piglets using routine histology and immunohistochemistry. Our findings show that lymphoid tissue is present at birth. It is composed of lymphoid nodules, a diffuse mononuclear infiltrate and intra-epithelial lymphocytes. The development is a sequential process. The lymphoid tissue in the stomach at birth is composed of the immunohistochemically different immunocompetent cells normally present. In conclusion, MALT is present in normal foetal gnotobiotic pig gastric mucosa, and in this model the stomach is no exception to the rest of the gastrointestinal tract.

The innervation of the human lumbar facet joint capsule was studied by light and electron microscopy. Small numbers of encapsulated corpuscular endings were identified in the dense fibrous layer. Clusters of 2 types of endings were found : small cylindrical corpuscles (type 1) and large fusiform corpuscles (type 2). The corpuscles were classified structurally as Ruffini-type endings. The 1st type was predominant and characterised by a compartmentalised receptor complex, a thin perineurial capsule and a narrow subcapsular space. The 2nd type was characterised by a thicker perineurial capsule, a ' spindle-like ' receptive complex, and an extensive subcapsular space with capillaries and concentrically oriented fibroblast-like cells. Both types of endings were innervated mainly by thinly myelinated group III (A delta) and unmyelinated group IV (C) nerve fibres that branched and terminated in the receptor complex. Their sensory endings were intimately related to the collagen fibre bundles as multiple enlarged axonal segments (' beads ') with ultrastructural features which were characteristic of receptive sites : an accumulation of mitochondria and vesicles, and ' bare ' areas of axolemma lacking a Schwann cell investment but covered by a thin basal lamina. Some beads in the 2nd type of ending contained granular vesicles, 30-60 mm in diameter, resembling sympathetic nerve endings. Small diameter collagen fibrils situated within multilayered basal laminae were found among the multiple receptive sites in the receptive complex in both types of ending. Their possible functional significance in mechanoreception is discussed. Particular attention has been given to their apparent variable orientation to the mechanoreceptive site.

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