Selective Nerve Root Transection in the Rat Produces Permanent, Partial Nerve Injury Models with Variable Levels of Functional Deficit.

BACKGROUND: The goal of this study was to develop a partial, nonregenerative nerve injury model in a rat that results in permanently reduced motoneuron numbers and function. This model could serve as a platform for the study of therapeutics, such as a reverse end-to-side nerve transfer (i.e., supercharge). The authors hypothesized that transection of one or more of the L4 to L6 nerve roots supplying the sciatic nerve would cause a permanent reduction in muscle force. METHODS: Rats were randomized into five groups that underwent variations of nerve root transections or sham injury. The L4 to L6 nerve roots were selectively transected and capped to prevent regeneration. Tibial and common peroneal nerves were harvested for quantitative histology and retrograde-labeled to assess the number of motoneurons projecting axons. Muscle force and relative muscle mass were assessed as metrics of postinjury motor function. RESULTS: At 6 months, the number of motoneurons projecting axons and myelinated axon counts were reduced in both the tibial and common peroneal nerves after injury in all groups. Transecting both L4 and L5 or both L4 and L6 reduced motoneuron numbers sufficiently below sham numbers to reduce muscle force and mass in major muscles of the hindlimb innervated by both nerves. Transecting L4 reduced muscle force and mass in common peroneal-innervated muscles, whereas transecting L5 reduced muscle force and mass in tibial-innervated muscles. These findings were stable over time. CONCLUSION: Transection of nerve roots produces stable (time-independent) partial nerve injury models with a selective decrease in motor function.

Intrahepatic Vascular Anatomy in Rats and Mice--Variations and Surgical Implications.

INTRODUCTION: The intra-hepatic vascular anatomy in rodents, its variations and corresponding supplying and draining territories in respect to the lobar structure of the liver have not been described. We performed a detailed anatomical imaging study in rats and mice to allow for further refinement of experimental surgical approaches. METHODS: LEWIS-Rats and C57Bl/6N-Mice were subjected to ex-vivo imaging using µCT. The image data were used for semi-automated segmentation to extract the hepatic vascular tree as prerequisite for 3D visualization. The underlying vascular anatomy was reconstructed, analysed and used for determining hepatic vascular territories. RESULTS: The four major liver lobes have their own lobar portal supply and hepatic drainage territories. In contrast, the paracaval liver is supplied by various small branches from right and caudate portal veins and drains directly into the vena cava. Variations in hepatic vascular anatomy were observed in terms of branching pattern and distance of branches to each other. The portal vein anatomy is more variable than the hepatic vein anatomy. Surgically relevant variations were primarily observed in portal venous supply. CONCLUSIONS: For the first time the key variations of intrahepatic vascular anatomy in mice and rats and their surgical implications were described. We showed that lobar borders of the liver do not always match vascular territorial borders. These findings are of importance for the design of new surgical procedures and for understanding eventual complications following hepatic surgery.

How similar are inbred rats? The influence of anatomical variations, shipment and sampling time on experimental surgery.

Variations among inbred rats in terms of anatomy and routine laboratory values can potentially blur surgical experimental results. Therefore, a retrospective analysis aiming at investigating hepatic and perihepatic anatomical variations, liver weight, body weight, liver weight/body weight ratio (LBWR), variations in routine laboratory values, and the influence of shipment and repeated sampling was performed. In our study, liver weight of rats seemed to be strain-specific. LBWR was weakly and negatively correlated with body weight in rats. A statistically significant difference in routine blood tests was found among normal rats grouped by different body weight or shipment. Weekly repeated sampling from the same rats revealed a statistically significant difference in a blood test. In conclusion, the fact that variation among rats or their environment can blur the results of a surgical experimental study should be kept in mind.

Immunosuppressive effect of total body irradiation and cyclosporine A on graft survival and the lymphatic system in a cardiac hamster-to-rat transplantation model.

The aim of the study was to evaluate the effect of total body irradiation (TBI) and cyclosporine A (CyA) on graft survival and the lymphatic system in a concordant hamster-to-rat heart transplantation model, and to compare these effects with those of total lymphoid irradiation (TLI). Preoperatively TBI was given as a single dose of 5 Gy, CyA was given intramuscularly at a dose of 10 mg/kg/day. TBI prolonged graft survival to seven days. Combined TBI and CyA prolonged graft survival to ten days. The effect of TBI on graft survival, total white blood cell count (WBC) and differential counts was reproducible but not as distinct as the effect of TLI. Analysis of changes in WBC and differential counts combined with the morphology of the grafts at rejection and of spleens from TBI- and CyA-treated animals indicates a reproducible immunosuppressive effect of TBI and a severe type of acute humoral rejection with vasculitis and cellular infiltrates dominated by macrophages and neutrophilic granulocytes. In conclusion, we find TBI a simple pretreatment which may be useful in combination with other immunosuppressive treatment as preoperative induction and depletion therapy.

The de-endothelialized rat carotid arterial graft: a versatile experimental model for the investigation of arterial thrombosis.

A novel model of arterial thrombosis was developed. A mechanical endothelium-denuding injury was created (using a scalpel blade) on harvested, freezer-stored rat carotid arteries. Vessel length of 5 mm. were grafted into the femoral arteries of recipient Sprague-Dawley rats using microvascular anastomotic technique. Patency rates in untreated animals were compared with those in animals receiving systemic aspirin or heparin. The control group patency after 2 hours of flow was 15%, while grafts in aspirin- and heparin-treated animals achieved 35% and 95% patency rates, respectively. Uninjured non-frozen carotid grafts in untreated animals yielded a 95% patency rate, while frozen grafts achieved an 80% patency. Therapeutic levels of aspirin, heparin, and urokinase were confirmed through tail bleeding and whole blood clotting tests, as well as platelet aggregation studies and scanning electron microscopy of the graft lumenal surfaces. A long-term series using syngeneic grafts placed in recipients (Lewis-to-Lewis) and employing systemic heparinization demonstrated maintenance of patency for 4 weeks. Scanning electron microscopy revealed good re-endothelialization, well advanced by one week. Histology confirmed the regrowth of endothelial cells, but showed sparse cellular repopulation of medial and adventitial layers. The mechanical injury model was compared to enzymatic de-endothelialization (using trypsin or collagenase), for which patency rates were similar (10% and 0%, respectively). Trypsin de-endothelialized vessels were tested in vitro for the amount of active trypsin remaining bound to the lumenal surface; no detectable activity was found when trypsin inhibitor was applied following trypsin treatment. The versatility of allowing both in vitro evaluation and in vivo patency assessment demonstrates the uniqueness and value of this new model, offering an avenue toward more direct investigations of surface-mediated thrombotic processes.

Experiments with a biological material for the closure of incisional hernias.

A new preparation process was studied which should allow the implantation of collagen type I in its native structure in reconstructive surgery, in this special case for closure of incisional hernias. As experimental animals we used 30 female Lewis rats. A defect of the anterior abdominal wall measuring 3 cm X 4 cm was closed with our collagen substitute. Biopsies taken after 4, 6 and 8 weeks were examined morphologically. As criteria for revitalization and revascularization we used the type of infiltrating cells, the depth and density of infiltration and the formation of new blood vessels. After 4 weeks the implants were infiltrated by fibroblasts that decreased in density towards the centre. Good revascularization could be seen on the muscle-implant interface. After 6 weeks the density of infiltrating cells had increased markedly even to the centre of the collagen implant. Sporadically small vessels could be seen. Eight weeks after implantation the density of infiltrated cells was at the same high level, and capillary bundles could be seen within the whole implant. We believe that this collagen implant is suitable for the closure of hernias as shown by its physical and morphological properties. In particular it appears to guarantee and earlier and tighter closure of hernias than other materials.