Biomedical subjects
Publications and source records attributed to B Doubleday.
This paper incorporates a brief review of impression materials currently available for use by the orthodontic profession; subjective assessments of a selection of alginates, silicones and bite registration materials in a clinical setting; and a list of prices and retailers of impression materials.
Following nerve section, regenerating axons from the proximal stump grow preferentially towards the distal stump. It has been postulated that this may result from the release of a neurotropic factor. To investigate whether the protein nerve growth factor (NGF) plays such a role, we immunised adult rats against NGF and examined the effect on regeneration of sectioned nerves through Y-shaped silastic tubes towards either the distal stump or an empty arm. Regeneration through the tubes was assessed electrophysiologically and the number of myelinated and nonmyelinated fibres at different sites was quantified using electron microscopy. There was electrophysiological evidence of regeneration towards the distal nerve stump in all the animals and there was no significant difference between the immunised and control animals in the size of compound action potential (CAP) ratios. Histologically, the majority of axons were found to have regenerated towards the distal nerve stump in 9/10 of the control animals and 7/9 of the immunised animals and there was no significant difference between the two groups in the numbers of regenerating myelinated or unmyelinated axons. However, in the immunised animals both myelinated and unmyelinated axons were slightly but significantly smaller and the myelin sheaths were thinner than in the control animals. In 2 immunised animals and none of the controls a small CAP was recorded while stimulating distal to the 'empty arm' and the presence of a small number of myelinated and unmyelinated axons was confirmed histologically. We conclude that as depletion of NGF does not block the preferential growth of regenerating axons towards the distal nerve stump it does not play the major neurotropic role in nerve regeneration. The reduction in size and myelin thickness of the regenerated axons after immunisation confirms the neurotrophic effects of NGF.
1. Electrophysiological experiments were carried out to determine whether or not collateral sprouting of cutaneous low-threshold mechanoreceptive fibres could be detected and to investigate the effect of nerve growth factor (NGF) deprivation on the sprouting of these fibres and the fibres innervating tooth pulps. 2. In twenty-one ferrets (eleven of which had been autoimmunized against NGF) the right inferior alveolar nerve (IAN) was sectioned and prevented from regenerating. After 12 weeks, transmedian innervation from the left IAN was determined by stimulating the nerve whilst recording from electrodes implanted in the contralateral anterior teeth and also by single unit recordings from the nerve whilst mechanically and electrically stimulating the skin. The results were compared with those from ten control animals. 3. Transmedian innervation of contralateral teeth was found in none of the control animals; in all ten of the animals which had undergone denervation without immunization (4/10 canines, 17/20 incisors); but in only six of the eleven immunized and denervated animals (0/11 canines, 7/22 incisors). 4. Of 270 cutaneous mechanoreceptive units sampled in the controls, only four units had transmedian receptive fields, extending a maximum of 1 mm across the mid-line. After denervation, significantly more units (42 of 274) crossed the mid-line and extended up to 4 mm. After immunization and denervation only eleven of 305 units crossed the midline by a maximum of 1 mm. 5. These data show that cutaneous low-threshold mechanoreceptive A beta and A delta fibres, as well as A delta tooth pulp fibres, are able to undergo collateral sprouting. This sprouting is partially blocked by NGF depletion, suggesting that NGF plays an essential role in the process.
1. The effects of depressed sympathetic function on the inotropic responses of the heart to sympathomimetic amines have been examined in rats immunized against nerve growth factor (NGF) 6 weeks prior to the isolation of cardiac tissues. 2. The activity of tyrosine hydroxylase in cervical sympathetic ganglia and the levels of noradrenaline in ventricular tissue were significantly reduced in NGF-immunized rats. 3. Left atria and papillary muscles from NGF-immunized rats were supersensitive to the beta-adrenoceptor agonist isoprenaline when compared with controls. 4. The responses of cardiac tissues to the alpha-adrenoceptor agonist phenylephrine were unaffected by immunization. 5. These results support the hypothesis that cardiac beta- but not alpha-adrenoceptor sensitivity is regulated by the sympathetic nervous system.
We have investigated whether chronic nerve growth factor (NGF) depletion affects the development of transmedian collateral reinnervation by C-fibres. Using a dye-labelled plasma extravasation technique in rats, the extent of transmedian innervation of the skin by C-fibres in the inferior alveolar nerve (IAN) was determined 8-10 weeks after sectioning and preventing regeneration of the contralateral IAN. Another group of animals were immunised against NGF prior to the nerve section and a third group acted as unoperated controls. A small but significant transmedian collateral reinnervation by C-fibres developed after contralateral denervation alone, but was not found in the animals also immunised against NGF. These results suggest that NGF is essential for the development of collateral reinnervation from cutaneous C-fibres.
The local gingival antibody response was examined in actively-immunized rhesus monkeys and in human natural immunization to the cell-surface streptococcal antigen (SA I/II). A technique was developed to collect gingival capillary and crevicular fluid washings (GCCFW) from monkeys and human subjects with clinically normal gingiva. The thin crevicular epithelium and the adjacent capillary plexus are pierced with a probe and the resulting mixture of capillary blood, tissue fluid and crevicular fluid are collected by repeated washing of the gingival crevice. Antibodies measured by a solid-phase radioimmunoassay revealed that the IgG class of anti-SA I/II antibodies in GCCFW from the entire gingiva were positively correlated with the corresponding serum antibodies. Antibody levels from six defined dento-gingival units showed a progressive increase in the anti-SA I/II antibody level from the incisor to the premolar and molar units. A significant negative correlation was found between the antibody level of the total GCCFW and past caries experience. A similar negative correlation was found between antibodies from the GCCFW and the DMFS index of the molar teeth. The results are consistent with the hypothesis that there is an independent local immune response in the dento-gingival unit, which is superimposed on the common circulating serum antibodies and sensitized lymphocytes.