An integrate-and-fire model for synchronized bursting in a network of cultured cortical neurons.

It has been suggested that spontaneous synchronous neuronal activity is an essential step in the formation of functional networks in the central nervous system. The key features of this type of activity consist of bursts of action potentials with associated spikes of elevated cytoplasmic calcium. These features are also observed in networks of rat cortical neurons that have been formed in culture. Experimental studies of these cultured networks have led to several hypotheses for the mechanisms underlying the observed synchronized oscillations. In this paper, bursting integrate-and-fire type mathematical models for regular spiking (RS) and intrinsic bursting (IB) neurons are introduced and incorporated through a small-world connection scheme into a two-dimensional excitatory network similar to those in the cultured network. This computer model exhibits spontaneous synchronous activity through mechanisms similar to those hypothesized for the cultured experimental networks. Traces of the membrane potential and cytoplasmic calcium from the model closely match those obtained from experiments. We also consider the impact on network behavior of the IB neurons, the geometry and the small world connection scheme.

Soft tissue emergency in adult horses.

Equine practitioners are frequently called to attend to soft tissue injuries. The majority of these cases are routine and straightforward; however, a certain percentage may present as a life-threatening situation with potentially serious complications. Client communication, adequate preparation, patient stabilization, accurate injury assessment and appropriate wound preparation are key factors to expedite recovery and achieve a favorable outcome. Understanding the limitations of field therapy and deciding when to transport the case to a clinic or referral center plays an important role in the successful management of these cases.

A new bioprosthesis in large abdominal wall defects.

A collagen-coated Vicryl mesh bioprosthesis was used to repair a 4 x 4 cm full-thickness abdominal wall defect, created in experimental rats. The tensile strength of the repair at 6 months reached 70% of the original abdominal wall. Implant collagen could not be differentiated from host collagen after 2 weeks. The increase in collagen content of the repair was responsible for the increasing tensile strength of the wound with time. All histological sections showed good tolerance of the implant. These results support the use of collagen Vicryl membrane to repair large abdominal wall defects. Clinical trials are indicated.

Collagen vicryl--a new dural prosthesis.

No ideal dural grafting material is currently available. Many materials have been evaluated in this role, and for many neurosurgeons cadaveric human lyophilized dura has been popular. Recently this material has been putatively associated with Creutzfeldt-Jakob disease. In this study we compared three degradable materials, collagen vicryl (Bovine collagen coated vicryl mesh), Zenoderm (Porcine dermis) and Lyodura (Lyophilized human cadaveric dura) as dural substitutes. In an experimental model using the New Zealand White Rabbit the materials were implanted into dural defects of dimensions 1.7 cm by 1 cm. In the control group the dura was not repaired. In total 47 animals were used and sacrificed at time intervals of 2, 4, 8, 12, and 24 weeks. On gross examination the collagen vicryl produced few adhesions to the cerebral cortex and was replaced by a neomembrane which showed good union with the host dura. In the control group no new layer was formed and there were severe cortical adhesions. Zenoderm and Lyodura remained undegraded and produced more adherence to the cerebral cortex than the collagen vicryl implant. The histological examination showed collagen vicryl to support ingrowth of fibroblasts and the production of a new collagen layer which by 3 months resembled the original host dura. The inflammatory response to the implant did not persist after 3 months. The other substitutes were revitalized by host cells but remained undegraded at 6 months with ingrowth of woven bone and persistence of inflammatory and foreign body response. The results show collagen vicryl to be a suitable dural substitute with potential advantages over other currently used degradable materials, and should be evaluated more fully, both in laboratory studies and clinically.

Use of a collagen coated vicryl tube in reconstruction of the porcine esophagus.

This experimental study assessed the use of a collagen-coated vicryl mesh tube to reconstruct the esophagus in growing piglets. Initial experiments, in which a segment of thoracic esophagus was excised and replaced by this prosthetic tube, resulted in all the animals succumbing to mediastinitis within the first 3-4 days. This was shown, at post-mortem, to be due to leakage of the prosthesis, secondary to acid reflux, resulting in dissolution of the prosthesis. The collagen-coated vicryl mesh was thereafter treated with glutaraldehyde and in-vitro studies showed that the glutaraldehyde-treated material exhibited a higher resistance to 0.01 M HCl at pH 2.0, when compared with untreated material. In addition, the glutaraldehyde-treated material also showed an increased resistance to digestion by bacterial collagenase. Further experiments to reconstruct the cervical esophagus in growing piglets were performed using the revised glutaraldehyde cross-linked collagen coated vicryl mesh tube. All the animals survived the procedure and the prosthesis were leakproof immediately post-operatively. The animals, however, developed severe stenosis at a mean of 11 days post-operatively. Attempts at neo-epithelialization of the graft were seen histologically. There was considerable granulation tissue and scar tissue formation on the mediastinal aspect of the graft. It is suggested that collagen coated vicryl mesh tube may find applications in the treatment of esophageal atresia only if the problem of stenosis of the prosthesis can be solved.

Treatment of equine leg wounds using skin grafts: Thirty-five cases, 1975-1988.

A retrospective study was conducted on 35 equine patients with lower leg wounds that were managed utilizing skin graft procedures. Two pinch graft, five punch graft, seven tunnel graft, eight split-thickness mesh graft and thirteen full-thickness mesh expansion graft procedures were performed in the initial treatment. The average wound size was 188 cm(2). Twentyfour cases had pregrafting complications: 10 wounds developed sequestra; three wounds were grossly contaminated and infected; and 11 cases developed granulation tissue complications prior to grafting. Graft failure following the initial procedure was seen in 12 cases and occurred with all techniques except pinch grafting. Graft failure was often attributable to poor quality of granulation tissue as well as anatomic site, especially the dorsal surface of the tarsus. An average of two additional grafting procedures was required to successfully treat initial failures. Pinch grafts took the longest time to epithelialize (70 days), followed by punch grafts (47 days). Both were similar in terms of being the least durable and least cosmetically acceptable of all techniques used. Split-thickness and full-thickness mesh expansion grafts were technically the most difficult, but showed the most rapid epithelialization (28 days), greatest durability, and the best cosmetic appearance. Tunnel grafts provided a practical technique for grafting cases which were either not suited for, or which had failed with, mesh expansion grafts.

In vivo evaluation and comparison of collagen, acetylated collagen and collagen/glycosaminoglycan composite films and sponges as candidate biomaterials.

Native collagen, acetylated collagen, collagen/10% chondroitin sulphate, collagen/2.5% hyaluronic acid and collagen/20% hyaluronic acid were implanted both as film and as sponge into rat lumbar muscle for 7 and 14 d. After 7 d implantation, all materials elicited an acute inflammatory cell response characterized by numerous polymorphs and histocytes. The cell population after 14 d was principally mononuclear, i.e. leucocytes, neutrophils, macrophages, lymphocytes and fibroblasts. Both films and sponges followed a similar pattern. Native collagen elicited a subacute inflammatory response after 7 d. However, 14 d after implantation, a marked infiltration by neutrophils was apparent with subsequent degradation of existing collagen material. Acetylated collagen film evoked a much greater inflammatory cell response than native collagen. Both collagen/hyaluronic acid composites elicited a similar response. The collagen/10% chondroitin sulphate composite elicited the least inflammatory cell response at 7 d, whereas infiltration by host fibroblasts after 14 d implantation was clearly seen.

Cellular invasion and breakdown of three different collagen films in the lumbar muscle of the rat.

Collagen films were prepared by three different methods involving acid homogenization at pH 3.0 of a collagen suspension for 1.5 min (film A) and 15 min (film B) and alkaline homogenization at pH 10 for 15 min (film C), after which the resulting slurries were degassed and dried over sterile air. Subsequent examination by scanning electron microscope (SEM) revealed that all samples showed a distinctly layered structure which was much finer in the acid films. Implantation into the lumbar muscle of rats followed by histology and SEM studies revealed that film B was completely resorbed at 14 d whereas remnants of film A could still be seen at this period. The slowest rate of resorption was observed with film C, traces of which could still be found at 70 d. Invading inflammatory cells moved into the collagen films between the layers from the edges only causing the whole structure to 'ribbon out'. The surfaces of all three films appeared to be impenetrable to cells. Incubation of the three films with bacterial collagenase revealed similar relative rates of degradation to those observed in vivo.

The effect of exercise on the healing of articular cartilage defects in the equine carpus.

Arthroscopic surgery was performed on 12 horses (2-4 years of age) to create a 7 x 14 mm full-thickness cartilage defect in one radial carpal bone and in the contralateral third carpal bone. Six horses remained confined to a small paddock and six horses underwent a program of increasing exercise consisting of walking, trotting, and cantering for 13 weeks. All lesions showed evidence of healing at week 6 that progressed to more complete healing at week 13. There was no difference in the amount of repair tissue covering the defect. Histologically, the lesions healed with a combination of fibrous tissue and fibrocartilage. The repair tissue was significantly thicker in the exercised horses but there was no difference in repair quality. It was concluded that radial carpal and third carpal lesions have an equal ability to heal and that early postoperative exercise is not detrimental to the repair tissue within these carpal cartilage defects.

Use of a bioprosthesis to relieve tension in oesophageal anastomosis: an experimental study.

Collagen-coated Vicryl mesh was assessed as a prosthetic repair material in the oesophagus of growing piglets. In a group of six piglets (group A), a full thickness defect was created in the oesophagus without fully transecting the organ. The removed tissue was subsequently replaced with a patch of collagen-coated Vicryl mesh. Animals were killed at 4 weeks and in the five surviving piglets the prosthesis had been replaced by host scar tissue with a normal epithelial lining. Two further groups of six piglets (groups B and C) were used as controls. In group B the oesophagus was either partly transected (four animals) or completely transected (two animals) and an anastomosis was performed, whereas in group C a 2.5-cm length of oesophagus was removed so that the anastomosis was performed under tension. In group B, all six piglets survived, whereas in group C, where the anastomosis was performed under tension, only two piglets survived. Microscopic and macroscopic examination of all groups showed that the collagen-coated Vicryl prosthesis was replaced by scar tissue; moderate stenosis was observed in only one animal in group A. Collagen-coated Vicryl mesh may be used either to reinforce an anastomosis performed under tension or may find use in tubular form to bridge the gap between the two ends of the oesophagus to be joined. It is envisaged that such a material may find applications in the treatment of oesophageal atresia.

Removal of a retropharyngeal foreign body in a horse, with the aid of ultrasonography during surgery.

Diagnostic ultrasonography was used during surgery to assist in the removal of a piece of wire from the retropharyngeal region. A 3-year-old Quarter Horse mare was referred with dysphagia of 2 days' duration. Radiography revealed a 9-cm piece of wire located caudodorsal to the larynx. A ventral surgical approach was performed, dissecting along the right side of the larynx and trachea. The surgical field was filled with 0.85% sterile physiologic saline solution. A 5 MHz-mm sector scanner probe immersed in the fluid was able to locate the wire and facilitate the direction and depth of dissection to where the wire was identified and removed.

Some observations on the regeneration of smooth muscle in the repaired urinary bladder of the rabbit.

The regeneration of smooth muscle appears to take place within the fibrous tissue characteristically found when a biodegradable collagen/Vicryl prosthesis is used to repair full thickness defects in the rabbit urinary bladder. The question of whether the central smooth muscle was the result of myoblastic differentiation in the fibrous tissue or arose from healthy pre-existing detrusor muscle was resolved by serial sectioning and specific staining. Only in situ transmutation, or differentiation, explains the morphology, and the results therefore strongly suggest that this central smooth muscle regenerated from within the repair area.

The evolution of a biodegradable membrane for use in urological surgery. A summary of 109 in vivo experiments.

The evolution of a collagen/vicryl composite membrane designed as a prosthetic material for use in urinary tract surgery is described. The early experiments in which collagen film alone was used to repair experimental ureterotomies are reviewed together with our first experiments with the collagen/vicryl prosthesis in the repair of partial nephrectomies and of full thickness defects created in the urinary bladder of experimental rabbits. These early results led to the preparation of a composite using a more highly purified collagen and employing a method of sterilisation (gamma irradiation) which would be acceptable for regular use in medical products. The results of a further series of partial nephrectomy and full thickness bladder repairs show that irradiation does not compromise the efficacy of the collagen/vicryl composite in vivo.

An assessment of a collagen/vicryl composite membrane to repair defects of the urinary bladder in rabbits.

Collagen/vicryl (Polyglactin) composite membrane has been used to repair full-thickness defects in the urinary bladder of rabbits. The material has been shown to be biodegradable, prevent leakage of urine, and is readily replaced by collagenous scar tissue lined with a urothelium. Regeneration of smooth muscle has been observed in the repair area of some animals. The results suggest that such a material may well be of use to urologists wishing to augment contracted bladders or in the repair of bladder fistulae in human subjects, thereby avoiding the use of bowel or other material e.g. omentum.

The use of a biodegradable collagen/vicryl composite membrane to repair partial nephrectomy in rabbits.

A composite membrane produced from collagen and vicryl mesh has been used to cover the kidney surface following partial nephrectomy in rabbits. The membrane readily held sutures, gave satisfactory haemostasis, and prevented leakage of urine. The experiments showed that the prosthesis biodegraded in less than twenty weeks. The only observed long-term effect of the material was thickening of the renal capsule. The results indicate that this membrane may be a suitable reparative material for use in traumatised kidneys in humans.

Assessment of collagen film for use in urinary tract surgery.

This investigation assessed a biodegradable collagen membrane which can be sutured around the ureter to prevent urine leakage, thus permitting healing to proceed more rapidly while the membrane itself is resorbed. Following an early in vitro investigation in which collagen was assessed, a more comprehensive survey has now been carried out. Tissue compatibility and biodegradation were assessed by implanting the film into the lumbar muscles of rats; it was then used to cover experimental ureterotomies in New Zealand White rabbits. The data obtained from the rabbits confirmed that a collagen membrane can prevent leakage of urine from the ureter during healing while it itself is biodegraded, indicating that a collagen membrane could be used to repair the injured urinary tract.

Microsurgical reconstruction of the trachea in rats (an experimental study).

This study was carried out to evaluate the use of 'Zenoderm' (enzyme treated procine dermis) as a patch for the repair of tracheal defects in rats, with particular reference to its application in the treatment of some cases of tracheal stenosis. Fifty-three rats were included in the study. Using microsurgical techniques, a defect was created in the cervical trachea and repaired using a suitable patch of 'Zenoderm' (two groups with different sized defects). In a further group of rats, healing of the trachea was studied after excision of a segment and end to end anastomosis. A set number of rats were sacrificed after intervals of 14, 28, 91 and 182 days when the trachea was excised and evaluated. Healing of the tracheae following end to end anastomosis was satisfactory in all cases with no evidence of stenosis. The two groups of tracheae with Zenoderm patches showed progressive stenosis at the area of the repair but there was no evidence of respiratory obstruction or distress. The Zenoderm patch and the regenerating epithelium were both evaluated by light microscopy and scanning electromicroscopy. The Zenoderm patch showed gradual absorption and was replaced by host collagen. There was gradual regeneration of epithelium which showed slow maturation from flat non-ciliated epithelium to partially cuboidal and columnar epithelium with some cilia showing early differentiation to respiratory epithelium. In conclusion, this experimental study confirmed the biocompatibility of 'Zenoderm' in rats. It provided a suitable surface for regeneration of tracheal epithelium. Replacement of the patch by the host collagen is promising but requires further study to assess its rigidity and ability to withstand pressure changes in the trachea.

Properties of bovine fibrin absorbable implants.

The assimilation characteristics of absorbable bovine fibrin implants in an experimental situation are described, and the effect of delaying absorption with formaldehyde treatment is demonstrated. Essentially, in vivo in the rat, Biethium fibrin implants are absorbed in approximately four to eight weeks because of the polymorphonuclear leukocyte digestion. An indication of the clinical uses in stress incontinence and hemorrhage of the liver are given, together with a look at the future of some of the other areas in which this absorbable, biologic plastic may fit into the surgeon's armamentarium to replace deficient or destroyed tissue.