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Biomedical subjects

G R Holland

Publications and source records attributed to G R Holland.

At least 19 recordsLinked to original sources
PubMed1992

Periapical innervation of the ferret canine one year after pulpectomy.

Previous studies have shown that, following removal of the dental pulp and its replacement with a filling material, the nerves in the periapical region proliferate within an area of chronic inflammation. This study examined these responses in the ferret in more detail, both quantitatively and in three dimensions, 12 months after pulpectomy which was followed by obturation with gutta percha and zinc oxide and eugenol sealer. The results were compared with the responses after three months. The basic patterns, in terms of both inflammation and neural proliferation, were similar at the two time periods. Both the sizes of the inflammatory lesions and the degree of neural proliferation were lower at 12 months than at three, although the differences were not significantly different in the small number of specimens examined. Bacterial stains failed to show bacteria either in the apical root canal delta or in the periapical area. It is possible that the persistent inflammation was due to the irritant nature of the obturating materials used but not due to the original tissue damage, since extraction sites, by comparison, healed very quickly. Apparently, following endodontic treatment, chronic periapical inflammation and concomitant neural proliferation can continue for long periods.

Animals↗
PubMed1992

Axon populations in cat lingual and chorda tympani nerves.

The lingual and chorda tympani nerves from five cats were examined so that normal axonal populations could be determined. After perfusion fixation, the chorda tympani and lingual nerves were removed and processed, and sections were taken from individual and combined nerves for both light and electron microscopy. The chorda tympani remained as a distinct group of smaller axons for at least 4 mm distal to its junction with the lingual nerve. The mean number +/- S.D. of myelinated axons in the chorda tympani central to the junction was 1322 (+/- 268) and in the lingual nerve central to the junction, 3227 (+/- 510). The counts were not significantly different distal to the junction, and there were no side-to-side differences. Mean myelinated axon circumferences were significantly smaller in the chorda tympani (12.86 +/- 0.87) than in the lingual nerve (22.79 +/- 1.99; p less than 0.01). The mean size of axons in the chorda tympani was slightly but consistently larger on the left (13.1 +/- 0.73) than on the right side (12.61 +/- 1.01; p less than 0.05). Distal to the junction, the average proportion of non-myelinated axons was 44% in both chorda tympani and lingual nerves.

Animals↗
PubMed1991

Distribution and morphological characteristics of axons in the periodontal ligament of cat canine teeth and the changes observed after reinnervation.

The distribution and morphological characteristics of myelinated and non-myelinated axons innervating the lower canine periodontal ligament (PDL) in adult cats have been analysed. After perfusion fixation and decalcification, the teeth were slit transversely, divided into segments, and embedded in plastic. Ultrathin sections of each segment were examined in the electron microscope and used to reconstruct the whole PDL at 1, 4, 7, and 9 mm from the tooth apex. One millimeter from the tooth apex there were a mean of 920 myelinated axons and 1,415 non-myelinated axons. The numbers of axons declined toward the tooth crown. Bundles of myelinated and small non-myelinated axons lay adjacent to the blood vessels midway between the bone and cementum. Isolated myelinated axons appeared to have split away from these main nerve bundles and entered the avascular zone of the ligament, where they lost their myelin sheaths to become large non-myelinated axons rich in mitochondria. These non-myelinated axons sometimes appeared to be linked to collagen fibres and were thought to be the mechanoreceptor terminals. Twelve weeks after sectioning and inferior alveolar nerve, the total number of axons innervating the periodontal ligament was 50% of that found in the contralateral controls. The large non-myelinated axons had smaller mean diameters and contained fewer mitochondria, a change which may be consistent with a reduction in mechanoreceptor excitability.

Animals↗
PubMed1991

The effect of pulpectomy on the longitudinal distribution of nerve fibres in the periodontal ligament of the ferret.

The innervation density of the periodontal ligament was measured at a series of levels around the mandibular canines of 6 ferrets, in 5 of the which the pulp of one of each of these pairs of teeth had been removed 3 months earlier. In control (unoperated) teeth the density of innervation was greatest in the apical third and lowest in the coronal third. The pattern around the pulpectomized teeth was similar. There was no statistically significant difference between density values for control and operated teeth. Pulpectomy thus does not affect the incidence or distribution pattern of nerves in the periodontal ligament.

Animals↗
PubMed1991

Innervation of the pulp-predentin border zone of the cat following denervation and reinnervation.

Under general anesthesia the inferior alveolar nerves of 8 cats were transected unilaterally and the cut ends reapposed. Two of these animals were, under general anesthesia, perfused with fixative 2 days later and 6 animals 12 or 15 weeks later, and the crowns of the mandibular canine teeth were prepared for ultrastructural examination. The distribution of axons at the pulp-predentin border and in the predentinal tubules was measured on the operated and control sides. In unoperated teeth the innervation at the pulp-predentin border paralleled that in the predentinal tubules being denser more coronally. The axons at the pulp-predentin border had disappeared by 2 days after denervation but had returned by 12 weeks and later with a density and distribution similar to that of the control sides.

Animals↗
PubMed1990

The number and size of axons central and peripheral to inferior alveolar nerve injuries in the cat.

We have observed the effect of three different lesions on the inferior alveolar nerve of the cat. If the nerve is transected and the cut ends reapposed there is no significant difference between the number of myelinated axons in the nerve proximal to the lesion and the number in contralateral control nerves at 9 or 15 weeks post-operatively. Counts distal to the lesion also do not differ significantly from control values although the size of the myelinated axons is reduced. If recovery is impeded, but not completely blocked, the number of proximal myelinated axons remains at control values but the number of non-myelinated axons is reduced by 74%. If recovery is completely blocked a neuroma forms in the proximal stump and is characterised by large numbers of small myelinated axons and a relative increase in the number of non-myelinated axons. The additional axons are presumably sprouts and recurrent loops. No effects on the contralateral inferior alveolar nerve were detected. The ability to accurately reappose the cut ends of the nerve within the bony canal counts for the high level of recovery. Changes in the nerve are clearly related to the nature and extent of the injury.

Animals↗
PubMed1990

Cell counts in the trigeminal ganglion of the cat after inferior alveolar nerve injuries.

This investigation was designed to determine the change in cell numbers in the trigeminal ganglia following unilateral section of one of its peripheral branches. In 9 young adult cats, under general anesthesia, the inferior alveolar nerve was transected. In 3 of the animals the cut ends were reapposed and in the other 6 regeneration was blocked. After 15 weeks the trigeminal ganglia were removed, and the number of neurons present estimated by counting nucleoli in every third section. The counts were compared with those obtained from 3 unoperated control animals. The mean number of cells in the ganglia of control animals was 14,324 with no statistically significant difference between sides. There was no significant difference between counts from opposite sides of cats whose nerves were allowed to regenerate. In the animals in which regeneration was prevented the mean count on the operated side was 13,874 and on the unoperated 18,374. These differences were statistically significant and appeared to result from an increase in cell counts on the unoperated side rather than a reduction in the counts on the operated side. This may be explained by the presence of neurons with inconspicuous nucleoli in normal ganglia, which are stimulated to enlarge and become more prominent following peripheral nerve injury. This change could occur on both sides and would mask cell loss on the operated side and produce an apparent increase in the count on the unoperated side.

Age Factors↗
PubMed1989

Sympathetic-sensory axon to axon contacts in the dental pulp.

The activity in stimulated intrapulpal sensory nerve fibres can be increased by simultaneous stimulation of the sympathetic system. The anatomical basis for this interaction is unknown. Unmyelinated nerve fibres in the dental pulp are characterized by incomplete isolation and ensheathment. Individual pockets of Schwann cells often contain several axons in close contact within a confined space. If a pocket contained both sensory and adrenergic axons it is possible that activity in one could affect the properties of the other. Four young adult ferrets were, under general anesthesia injected intraperitoneally with the false neurotransmitter 6-hydroxydopamine which accumulates as dark vesicles within adrenergic axons. The animals were, still under general anesthesia, perfused four hours later with a fixative mixture. The canine teeth were removed, decalcified and prepared for electron microscopy. Ultrathin sections of the dental pulp were examined in the electron microscope. Convincingly labelled axons were rare. Labelled sympathetic axons were found in common Schwann cell pockets with unlabelled, presumably sensory, axons. This confirms studies in which degeneration has been observed following either surgical removal of the superior cervical ganglion or chemical sympathectomy. While this "axonal mingling" probably occurs in other sites it may be more extensive in the dental pulp.

Adrenergic Fibers↗
PubMed1988

Periapical innervation of the ferret canine and the local retrograde neural changes after pulpectomy.

The amputation of the dental pulp severs a population of axons that are predominantly in the A delta and C fiber size range and are principally involved in nociception. Local periapical neuromas, if they are formed after pulpectomy, may be the sites of spontaneous nervous activity that may, in some circumstances, be involved in the genesis of chronic pain. The periapical tissues from the mandibular canines of four ferrets were examined 3 months after pulpectomies. Silver-stained paraffin sections were examined in three dimensions at the light microscope level. Ultrathin sections were examined at the electron microscope level. Compared with contralateral and independent controls, the principal changes were the loss of the periodontal plexus around the root apex, the extension of damage well below the apical foramen, and the persistence of inflammation 12 weeks postoperatively. While a somewhat disorderly mass of nerve fibers develops subapically, the arrangement has only some of the features usually associated with neuromas.

Animals↗
PubMed1988

Nucleolar eccentricity in trigeminal ganglion neurons.

The aim of this study was to determine if measuring trigeminal ganglion neuron profiles containing nucleoli in histological sections gave a reasonable estimation of cell size. Serial sections of ferret trigeminal ganglia were prepared, and neuron profiles traced with the aid of a camera lucida. The cross sectional area of the profiles was measured. Profiles containing nucleoli formed the upper part of the size spectrum and were significantly larger than the profiles that did not contain nucleoli. When serial profiles of individual neurons were examined the largest profile contained the nucleolus in 20 of 27 cases, and the mean sizes of 'largest' and 'nucleolus-containing' profiles did not differ significantly. Computer reconstructions of individual cells show the nucleolus to be central in almost all cells viewed from almost every projection. It is concluded that the nucleolus lies at, or very near to, the centre of the neuron and at its widest dimension. Measuring the size of profiles containing nucleoli gives a satisfactory representation of cell size.

Animals↗
PubMed1987

The effect of nerve section on the incidence and distribution of gap junctions in the odontoblast layer of the cat.

Gap junctions are numerous in the odontoblast layer of the dental pulp and may link sensory axons to odontoblasts. If these junctions do link axons and odontoblasts, they, together with the axons, should disappear after cutting the pulpal nerves centrally. Under general anesthesia the inferior alveolar nerve on one side of two young adult cats was sectioned. Under general anesthesia the animals were perfused with fixative 56 hours later and the coronal dental pulp prepared for electron microscopy. Ultrathin sections were examined from the level of the pulpal cornu and levels approximately one, two, and three mm below this. The incidence of cell processes and gap junctions was measured at different distances from the pulp predentin junction, and operated and control sides compared. The odontoblast layer at the level of the cornu differed from elsewhere in having, on the control side, a greater density of cell processes and gap junctions and in having clearly recognizable axons approaching to within 5 to 10 micron of the predentin. The only statistically significant changes after nerve section occurred in this layer and consisted of a decline in the incidence of cell processes and of gap junctions that link one cell process to another. There was no significant difference between the operated and control sides in the number of gap junctions linking cell processes to recognizable cell bodies. The odontoblast layer in the pulpal cornu contained substantial numbers of unsheathed axons, many presumably en route to the dentin. These axons may participate in gap junctions that link them to other cell processes, possibly even other axons.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Pulp re-innervation in re-implanted canine teeth of the cat.

This was investigated 24 weeks post-operatively by light and electron microscopy. The number of axons in the pulp at the root apex ranged from 7.5 to 76.2 per cent of the number in the contralateral control tooth. The myelinated fibres were smaller and did not penetrate as far as the coronal pulp.

Animals↗
PubMed1987

A morphological study of the collateral reinnervation of the cat's canine tooth.

We examined the morphologic characteristics of the collateral reinnervation of the cat's canine tooth pulp. Collateral reinnervation was stimulated in six adult cats by transecting the ipsilateral inferior alveolar nerve and preventing it from regenerating by sealing the ligated nerve inside a nylon tube. The apices of the canine teeth were examined after 15 weeks using electron microscopy and each axon was counted and measured. Compared with contralateral control teeth, the collateral reinnervation consisted of fewer myelinated fibers and in five animals the number of nonmyelinated fibers was also smaller. In one animal the nonmyelinated count on the operated side exceeded that on the control side. The total number of axons was 33.5% of the number in control teeth, considerably fewer than seen after reinnervation by regenerating fibers in previous experiments. The structural characteristics of the collateral fibers were similar to those of regenerating nerve fibers. Compared with controls the myelinated collateral fibers were smaller and had thinner myelin sheaths. There were more nonmyelinated fibers containing only one axon. More nonmyelinated fibers had exposure of part of their axolemma to the extracellular space and there was also an increase in axoaxonal apposition.

Animals↗
PubMed1987

An electrophysiological and morphological study of the innervation and reinnervation of cat dentine.

1. Experiments were carried out to determine which, if any, of the cellular processes in cat dentine are nerves. This was done by examining in the electron microscope the contents of the dentinal tubules in control teeth and in teeth that had been denervated 56 h previously. The extent of any reinnervation, and associated return of neural responses to dentine stimulation were investigated 12 weeks after denervation. 2. In five cats, the inferior alveolar nerve was sectioned on one side and the cut ends reapposed. 3. Each of the tubules in the predentine of control teeth contained one process with a cross-sectional area of 0.21-1.14 micron2 and up to eight other, secondary processes which were generally smaller. The proportion which contained secondary processes was highest (83%) near the tip of the pulp and decreased further down the side of the crown of the tooth. 4. 56 h after denervation, almost all the secondary processes had disappeared, leaving just one of the larger processes in each tubule. It is concluded that these larger processes are odontoblast processes and that all the secondary processes are nerve terminals. 5. 12 weeks after denervation, small processes were again present in some tubules. Recordings in three cats showed that inferior alveolar nerve fibres had regenerated into the canine pulp and that some of these had re-established receptor properties similar to those in normal teeth.

Action Potentials↗
PubMed1986

Reinnervation of teeth after segmental osteotomy.

The reinnervation of 8 canine teeth denervated by segmental osteotomy has been investigated in cats by using electron microscopy. 12 weeks after osteotomy, the mean total number of axons at the canine apices was 36% of that found in normal animals. The myelinated axons were smaller than normal with thinner myelin sheaths. In non-myelinated fibres, there were fewer axons per fibre (Remak bundle) and more fibres containing only one axon. The proportions of myelinated and non-myelinated fibres were normal.

Animals↗
PubMed1985

Reinnervation of the canine tooth pulp after section of the inferior alveolar nerve in the cat.

The apices of lower canine teeth have been examined 9 weeks after unilateral section of the inferior alveolar nerve. The teeth were extensively reinnervated although there was considerable variation in the number of axons present. The myelinated axons were smaller than normal with thinner myelin sheaths. There were fewer axons per non-myelinated fibre (Remak bundle). The proportions of myelinated and non-myelinated fibres were normal.

Action Potentials↗