Previous studies on ageing animal and human subjects have demonstrated a significant overall decline in neuronal numbers in the myenteric plexus of the enteric nervous system (ENS). Our study aimed to confirm this observation by counting myenteric neurons stained with the panneuronal markers PGP 9.5 and NADH-diaphorase. We also wished to examine the possibility that particular subpopulations of neurons are vulnerable. Therefore, we have immunostained and counted a number of nerve cell groups within the myenteric plexus of old and young Sprague Dawley rats using markers which reflect some of the neuronal phenotypes present, including ChAT and VIP. The number of neurons demonstrating NADH-diaphorase activity was significantly reduced (P<0.05) by approximately 15% in old rats. However, the number of neurons stained for PGP 9.5 immunohistochemistry was not reduced and demonstrated larger numbers of neurons than the NADH-diaphorase method. None of the other neuronal markers studied showed any significant reductions with age. In contrast to previous work, this study has gathered little evidence for extensive cell loss in the myenteric plexus of the aged rat, either in overall populations, or in any of the principal functional groups of neurons.

A fluorescence confocal microscopy technique was employed to obtain subsurface images of nerve and microvascular structure in the vas deferens and colon of the living rat. The use of dual labelling with vital dyes and 2-channel confocal acquisition allowed differentiation of microscopic structure at both low and higher magnification. Characteristic staining patterns of nerves and blood vessels were repeatedly obtained in each tissue, suggesting the potential of this technique for studying morphological changes associated with surgical procedures and/or models of neuronal or vascular pathology.

Wound healing has been studied in the surface ectoderm overlying the midbrain region of stages 16–20 chick embryos by light microscopy, scanning and transmission electron microscopy, and immunofluorescent techniques. The embryos were divided into 6 groups, i.e. stages 16–17 for groups I, V and VI, and stages 19–20 for groups II, III and IV. For groups I and II embryos, a longitudinal incision about 0.6 mm was made close to the dorsal midline and the embryos incubated for varying periods of time up to 24 h. To determine the role of actin in the process of healing, selected groups I and II embryos were stained with FITC phalloidin and the wound margins examined using a confocal microscope. Wounds of all embryos in group I and about 20% in group II healed completely within 24 h of reincubation. The process of healing involved a change in the shapes of the ectodermal cells at the wound ends. This appeared as a zipping-up of the wound from both ends. In about 80% of group II embryos where healing did not occur, wound gaping was marked. Intense actin staining (actin cable) was observed at the wound margins of groups I and II embryos suggesting that the actin purse-string mechanism may play a role during wound healing in this epithelial model. The role of tension in wound healing was also determined by placing 2 secondary wounds about 0.5–0.7 mm long close to, and at right angles to the ends of the primary wound in groups III and V embryos. The procedure decreased the tension within the ectodermal cells at the wound ends. Groups IV and VI embryos served as controls for groups III and V embryos, respectively. Healing of both primary and secondary wounds after reduction of tension was rapid. Most primary wounds in group V embryos healed completely within 3 h of reincubation and the rate of reepithelialisation after the reduction of tension was about 160% more than that in group VI (control) embryos. Similarly, most primary wounds in group III embryos were almost closed within 6 h of reincubation. Here, the rate of reepithelialisation was 80% more than that in group IV (controls). Thus tension is an important factor in wound healing in this model.

Rat liver ultrastructure was investigated after partial hepatectomy (PH), by scanning and transmission electron microscopy. Portal pressure was monitored before and after PH and, after killing performed at 6, 12, 24, 48 h and 10 d, regenerating livers were fixed by portal vein perfusion under haemodynamic conditions identical to those existing in vivo. An early and persistent increase in portal pressure after PH was found (P<0.01 for normal vs sham-operated controls). Ultrastructural study showed sinusoid dilatation and disappearance of the sieve-plate arrangement of small endothelial pores, thus leaving the parenchymal liver cell surface directly exposed to portal blood. Widening of sinusoids, endothelial fenestrations, intercellular spaces and spaces of Disse, was accompanied by dilatation of bile canaliculi. At 10 d, liver ultrastructure had returned to normal. Our observations suggest that a rise in portal pressure, as a consequence of PH, may be related to the observed ultrastructural changes in the liver.

Atrioventricular (AV) nodal conduction time is known to be modulated by the autonomic nervous system. The presence of numerous parasympathetic and sympathetic nerve fibres in association with conduction tissue in the heart is well authenticated. In this study, confocal microscopy was used to image the distribution of antibodies directed against the general neuronal marker PGP 9.5, tyrosine hydroxylase (TH), vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP) and β1 and β2-adrenoreceptors. Serial 12 μm sections of fresh frozen tissue taken from the frontal plane of the rat atrioventricular node, His bundle and bundle branches were processed for histology, acetylcholinesterase (AChE) activity and immunohistochemistry. It was found that the AV and ventricular conduction systems were more densely innervated than the atrial and ventricular myocardium as revealed by PGP 9.5 immunoreactivity. Furthermore, the transitional cell region was more densely innervated than the midnodal cell region, while spatial distribution of total innervation was uniform throughout all AV nodal regions. AChE-reactive nerve processes were found throughout the AV and ventricular conduction systems, the spatial distribution of which was nonuniform exhibiting a paucity of AChE-reactive nerve processes in the central midnodal cell region and a preponderance in the circumferential transitional cell region. TH-immunoreactivity was uniformly distributed throughout the AV and ventricular conduction systems including the central midnodal and circumferential transitional cell regions. β1-adrenoreceptors were found throughout the AV and ventricular conduction systems with a preponderance in the circumferential transitional cell region. β2-adrenoreceptors were localised predominantly in AV and ventricular conduction systems with a paucity of expression in the circumferential transitional cell region. These results demonstrate that the overall uniform distribution of total nerve processes is comprised of nonuniformly distributed subpopulations of parasympathetic and sympathetic nerve processes. The observation that the midnodal cell region exhibits a differential spatial pattern of parasympathetic and sympathetic innervation suggests multiple sites for modulation of impulse conduction within this region. Moreover, the localisation of β2-ARs in the AV conduction system, with an absence of expression in the circumferential transitional cell layer, suggests that subtype-specific pharmacological agents may have distinct effects upon AV nodal conduction.

Observations have been made on the rabbit sciatic nerve distal to a transection, with survival periods of up to 26 mo and prevention of reinnervation. It was confirmed that the nerve becomes compartmented by fibroblast processes and that a zone of fine collagen fibrils develops around the Schwann cell columns that constitute the Büngner bands. The Schwann cells become progressively more atrophic but after 6 mo of denervation still expressed low affinity p75 nerve growth factor receptor (NGFR), the latest stage at which this was examined. NGFR was also expressed by the processes of the fibroblasts producing the endoneurial compartmentation. By 26 mo after transection the site of previous nerve fibres was indicated by sharply demarcated domains of approximately circular outline in transverse section consisting of densely packed longitudinally oriented collagen fibrils. Some of these domains still possessed centrally situated Schwann cells or residual basal lamina but many were acellular. The central collagen fibrils in these domains were of smaller diameter than those situated peripherally but were of larger size than those that form around the Büngner bands during wallerian degeneration. The peripherally located fibrils in the domains were of the same calibre as for normal endoneurial collagen. The collagen domains were encircled by fibroblast processes or at times enclosed in a perineurial cell ensheathment. Long-standing axonal loss therefore leads to a striking reorganisation of the internal architecture of peripheral nerve trunks. The findings may be relevant for the interpretation of the appearances in chronic peripheral neuropathies in man.

The frequency of the Os zygomaticum bipartitum was examined in major human populations around the world. Eastern Asians have a higher frequency of the bipartite zygomatic bone than any other geographical groups. The arctic peoples, Amerindians and the Oceanians, who all may have derived from eastern Asian population stocks, have a considerably low frequency of this trait. The frequency distribution from East/Southeast Asia to Africa and Europe through South/Central/West Asia suggests some clinality for the bipartite zygomatic bone. The second peak in the frequency is seen in Subsaharan Africa. The clinal variation with no identifiable regulation by subsistence patterns and environmental factors suggested a genetic background for the occurrence of the Os zygomaticum bipartitum.

The occurrence and distribution of neuropeptide-containing nerve fibres in the human circumvallate papillae were examined by the peroxidase–antiperoxidase immunolocalisation method using surgical specimens that had not been subjected to radiotherapy, and the abundance of neuropeptide-containing fibres was expressed as the percentage of total nerve fibres demonstrated by protein gene product (PGP) 9.5 immunoreactivity for a quantitative representation of these peptidergic fibres. Substance P (SP) and calcitonin gene-related peptide (CGRP) immunoreactive (IR) nerve fibres were densely distributed in the connective tissue core of the circumvallate papillae, and some SP and CGRP-IR fibres were associated with the taste buds. A moderate number of vasoactive intestinal polypeptide (VIP)-IR fibres and a few galanin (GAL)-IR fibres were also seen in the connective tissue core and subepithelial layer. There were, however, no VIP-IR or GAL-IR fibres associated with the taste buds. Neuropeptide Y (NPY)-IR fibres were few and were associated with the blood vessels. Within the epithelium of the circumvallate papillae, no peptidergic fibres were found, although a number of PGP 9.5-IR fibres were detected. The abundance of SP, CGRP, VIP, and GAL-IR fibres expressed as the percentage of total PGP 9.5 IR fibres was 25.35±3.45%, 22.18±3.26%, 10.23±1.18%, and 4.12±1.05%, respectively. The percentage of NPY-IR fibres was below 3%. In a deeper layer of the papillae, a few VIP, GAL, and NPY-IR ganglion cells were found, and VIP immunoreactivity was detected in a few cells of the taste buds. There was no somatostatin, leucine enkephalin, or methionine enkephalin immunoreactivity in the circumvallate papillae. These results suggest that the dense SP and CGRP-IR fibres within the connective tissue core of the human circumvallate papillae may be involved in the deep sensation of the tongue.

Knowledge of the structure and function of the central canal of the human spinal cord is important in understanding the pathogenesis of syringomyelia. Analysis of the morphology of the central canal is difficult using isolated histological sections. A 3-dimensional reconstruction technique using digitised histological sections was therefore developed to visualise the morphology of the central canal. The technique was used to study the canal in the conus medullaris and filum terminale of 1 sheep and 4 human spinal cords. A variety of morphological features were demonstrated including canal duplication, a terminal ventricle and openings from the canal lumen into the subarachnoid space. The findings suggest the possibility of a functionally important fluid communication in the caudal spinal cord which may have a sink function.

The bicuspid (mitral) valve complex of the human heart consists of functional units which include the valve leaflets, chordae tendineae and the papillary muscles. The mechanical properties of these functional units depend to a large extent on the link between the muscle and the valve. This link is usually arranged in a branching network of avascular tendinous chordae composed of collagen and elastic fibres, which transmit contractions of the papillary muscle to the valve leaflets. In order to perform their function efficiently, the chordae have to possess a high degree of elasticity, as well as considerable strength and endurance. Human chordae tendineae originating from the left ventricles were obtained from 7 embalmed cadavers and 6 postmortem subjects of various ages. Samples washed in saline were fixed or postfixed in 9% formol saline. Observations were made by illuminating the chordae along their axes. The reflected images originating from the superficial collagenous layers of the relaxed chordae showed a striped pattern 11 μm in width. Scanning electron and light microscopy of the chordae confirmed an undulating pattern of collagen fibrils arranged in bundles of planar waves in register and around the entire circumference of the chorda. The dimensions of the waves correlated with those of the striped reflected pattern. The observed undulating arrangement of the collagen fibrils appears to produce an inherent built-in elasticity which is likely to be of considerable advantage for a tissue which is under continuous repetitive stress. The chordae were covered by endocardium composed of a superficial layer of smooth squamous endothelial cells and an underlying dense layer of elastic fibres. It is suggested that the relaxed striped chordae, consisting of undulating collagen fibrils, straighten when the chordae become stretched by papillary muscle contraction, thereby mitigating the peak stress developed during muscle contraction. On relaxation the elastic tissue tends to return the collagen to its wavy configuration. It is also suggested that the regular wavy pattern of collagen seen in young individuals gradually changes with age by elongation of the wave pattern which eventually becomes randomised. In addition, with increasing age, substantial cushions of connective tissue appear below endocardium while the dense collagenous core has a reduced cross-sectional area which may lead to stretching and eventual rupture of the chordae.

Connexin 43 (Cx43) has been reported to be expressed in vascular smooth muscle cells and endothelial cells. Evidence for possible variations in Cx43 distribution within different parts of the vascular system is limited. We have therefore investigated the expression of Cx43 in the endothelia and media of 11 vessels of different size and function in the rat, using immunofluorescence and confocal laser scanning microscopy. The results showed that punctate Cx43 staining was abundant in the endothelia and media of all of the 5 elastic arteries examined. In the media, the amount of Cx43 staining decreased as the size of the elastic arteries became smaller. In the 6 muscular arteries examined, 2 different patterns of Cx43 staining were observed. In the first type, Cx43 expression was high in the endothelium but virtually absent from the media. Mesenteric resistance, hepatic and tail arteries were examples. In the second type, Cx43 staining was absent from both the media and the endothelia. The coronary, basilar, and middle cerebral arteries showed this appearance. The results suggest that expression of Cx43 is largely restricted to elastic arteries in the arterial system of the rat. The lack of immunodetectable Cx43 from the media of all muscular arteries examined, and from the endothelia of some of these arteries, raises the possibility of significant differences in the form of expression of Cx43 in these vessels or the presence of other connexins.

The 3-dimensional ultrastructure of mouse renal glomeruli under normal haemodynamic conditions was studied by scanning electron microscopy using an in vivo cryotechnique followed by freeze-substitution, and compared with glomeruli prepared by conventional fixation methods. Mouse kidneys were frozen with a cryoknife apparatus and a liquid isopentane-propane mixture (−193°C). Surface areas of the frozen tissues were freeze-fractured with a scalpel in liquid nitrogen. The specimens were routinely freeze-substituted, freeze-dried, ion-sputtered, and then observed in a scanning electron microscope at an accelerating voltage of 5 kV. Renal glomeruli showed good ultrastructural preservation of the surface tissues. Podocytes with interdigitating foot processes covering capillary loops exhibited smooth surface contours and their cell surfaces were arranged more tightly than those seen by the conventional fixation method. Filtration slits between foot processes were found to be narrow. The internal structure of the glomerular tuft was seen in the freeze-fracture faces. The capillary lumen with variously shaped erythrocytes was kept open in frozen glomeruli under normal blood circulation conditions. The ultrastructure of renal glomeruli, as revealed by the in vivo cryotechnique with freeze-substitution, appears to be closer to that of the living state.

Traumatic avulsions of ligament or tendon insertions rarely occur at the actual interface with bone, which suggests that this attachment is strong or otherwise protected from injury by the structure of the insertion complex. In this study we describe the terminal extent of quadriceps tendon fibres where they insert into the patellae of adult rabbits, humans, dogs and sheep. Specimens were examined by scanning electron microscopy (SEM) and light microscopy (LM). To facilitate tracing of tendon fibres the specimens were decalcified for SEM, and polarised light microscopy (PLM) was used in the LM segment of the study. By SEM it was possible to identify mature bone by the presence of osteocytes and a lamellar organisation. PLM and SEM showed that, unlike tendon fibres elsewhere, those in the calcified fibrocartilage were not crimped. No specific cement line was identified by SEM. Tendon fibres interdigitated among separate bone lamellar systems, (osteons or marrow spaces), but did not merge with the collagen systems of individual lamellae. The interdigitation was more extensive and the margin between tendon and bone was less distinct in the anterior third of the insertion. The segment of calcified tendon which interdigitated with bone stained less intensely blue and was less cellular than the more proximal calcified fibrocartilage zone adjacent to the tidemark. Lamellar collagen fibres of the bony trabeculae in the anterior patella were unusually parallel and longitudinal in orientation, making distinction of interposed tendon fibres difficult on LM and PLM sections. LM, SEM and transmission electron microscopy of rabbit patellae at birth revealed that anterior quadriceps tendon fibres extended over the patella in a fibrous cellular layer. By 2 wk of age, this layer had acquired chondroid features (i.e. cell lacunae and metachromasia) and contained vessels extending from patellar marrow. At 6 wk of age, part of this fibrocartilaginous layer was replaced by mature bone and osteoid. In the young adult animal, the quadriceps tension interdigitates extensively with the patellar bone. This segment of the insertion is perhaps the remnant of calcified fibrocartilage which has been remodelled by bone formation.

A study was carried out on the discomalleolar ligament by dissection of adult human cadavers. The ligament corresponds to the most internal portion of the superior lamina of the temporomandibular joint capsule. It extends from the posterointernal portion of the temporomandibular joint disc, penetrates the petrotympanic fissure and reaches the malleus of the middle ear. Because of its morphology and anatomical arrangement the discomalleolar ligament should be considered as an intrinsic ligament of the temporomandibular joint and distinguished from the tympanic portion of the sphenomandibular ligament (anterior ligament of the malleus).

Anatomical Society of Great Britain and Ireland

Madrid, 26–27 November 1998. Joint Symposium between the Spanish Anatomical Society and the Anatomical Society of Great Britain and Ireland on morphogenetic and genetic analysis of vertebrate development.

Winter meeting, 5–7 January 1999. This will be held at the University of Leeds and will include a one and a half day symposium on ‘Structure and function of molecular motors’. Further information can be obtained from Dr Roger Soames, Centre for Human Biology, University of Leeds, Leeds LS2 9JT.

Summer meeting, 13–15 July 1999. This will be held in Glasgow. The title of the Symposium will be announced later.

Summer meeting, 24–26 July 2000. This will be held at the University of Cambridge.

Research Studentships

Grant funding is available for Research Studentships in the anatomical sciences, commencing October 1999. Project applications are invited from Society Members who hold academic positions in Departments of Anatomical and related Sciences in the UK and Ireland.

Further particulars and application forms are available from Dr D. J. Watt, Department of Neuromuscular Diseases, Division of Neuroscience and Psychological Medicine, Imperial College School of Medicine, Charing Cross Campus, St Dunstan's Road, London W6 8RP (e-mail: d.watt@cxwms.ac.uk). The closing date for applications is 9 October 1998.