Phenotypic Analysis of the Plp-Deficient Mouse

The myelin proteolipid protein (Plp) gene encodes the major protein components of compact central nervous system myelin. Mutations of this gene lead to severe dysmyelinating disease and oligodendrocyte death suggesting roles for Plp gene products as vital structural components of compact myelin and as oligodendrocyte maturation or survival factors. The Plp gene knockout mouse was generated (Klugmann et al., 1997) to study the effects of loss of Plp gene function on oligodendrocyte development and myelination in the central nervous system. Surprisingly the Plp gene knockout mouse showed no gross evidence of dysmyelination but did develop a late onset phenotype associated with progressive axonal changes. This study characterised the phenotype of these mice and assessed the ability of Plp gene isoforms to modify the phenotype of Plp gene knockout mice by transgenic complementation. The Plp gene knockout mouse formed large volumes of myelin and maintained oligodendrocyte numbers into adulthood. However, in the central nervous system, myelin was ultrastructurally abnormal and a proportion of small diameter axons failed to acquire myelin sheaths. Axonal changes consisted of swollen and degenerate axons and were confined to myelinated regions of the central nervous system where small diameter fibres appeared to be preferentially affected. Transgenic complementation with constructs expressing all of the components of the Plp gene ameliorated the phenotype of the Plp gene knockout mouse demonstrating that these changes were the direct result of loss of Plp gene function. These results indicate that, although the Plp gene products play roles in initiating myelination and in stabilising myelin lamellae, they are not vital components for oligodendrocyte development or myelin formation. The development of axonal changes appears to depend on the presence of myelin and demonstrates a potential role for the Plp gene in axoglial interaction. In addition, the changes in the Plp gene knockout mouse highlight the increasingly recognised role of gene dosage in the pathogenesis of Plp gene-related disease

Grass as a linear gastrointestinal foreign body obstruction in four dogs

Four dogs presented with linear gastrointestinal foreign body (FB) obstruction caused by impacted grass fibres. The material had become anchored within the pylorus in three dogs, causing necrosis and perforation of the mesenteric border of the affected intestinal segment. Gastrotomy and intestinal resection and anastomosis were performed. The fourth case presented acutely with no intestinal necrosis or perforation, with the fibres removed via enterotomy. One dog suffered severe postoperative ileus that failed to respond to medical management. Continued deterioration prompted euthanasia 12 days postoperatively. The other three dogs survived and were discharged without complication. Grass has not previously been reported as a cause of linear gastrointestinal obstruction in dogs. It has, however, the potential to cause severe necrosis and perforation of the intestine and should be recognised as a potential linear FB in dogs

Studies on the inhibition of feline EGFR in squamous cell carcinoma:Enhancement of radiosensitivity and rescue of resistance to small molecule inhibitors

This study investigated different methods of EGFR (Epithelial Growth Factor Receptor) targeting in feline squamous cell carcinoma with the ultimate aim of establishing a large animal model of human head and neck cancer. Both small molecule receptor tyrosine kinase inhibitor (TKI) and RNA interference (RNAi) techniques were employed to target the feline EGFR. We demonstrated that the human drug gefitinib caused a reduction in cell proliferation and migration in a feline cell line. However, we also document the development of resistance that was not associated with mutation in the kinase domain. RNAi caused a potent reduction in EGFR activity and was able to overcome acquired gefitinib resistance. In addition, RNAi targeting of EGFR, but not gefitinib, caused an additive effect on cell killing when combined with radiation. These results support the use of feline SCC as a model of head and neck cancer in man in the search for novel and effective treatments for both tumors

Oligodendroglial modulation of fast axonal transport in a mouse model of hereditary spastic paraplegia

Oligodendrocytes are critical for the development of the plasma membrane and cytoskeleton of the axon. In this paper, we show that fast axonal transport is also dependent on the oligodendrocyte. Using a mouse model of hereditary spastic paraplegia type 2 due to a null mutation of the myelin Plp gene, we find a progressive impairment in fast retrograde and anterograde transport. Increased levels of retrograde motor protein subunits are associated with accumulation of membranous organelles distal to nodal complexes. Using cell transplantation, we show categorically that the axonal phenotype is related to the presence of the overlying Plp null myelin. Our data demonstrate a novel role for oligodendrocytes in the local regulation of axonal function and have implications for the axonal loss associated with secondary progressive multiple sclerosis

Postattenuation neurologic signs after surgical attenuation of congenital portosystemic shunts in dogs:A review

The development of postattenuation neurologic signs (PANS) is a poorly understood and potentially devastating complication after surgical attenuation of congenital portosystemic shunts in dogs. Postattenuation neurologic signs include seizures but also more subtle neurologic signs such as depression, behavioral changes, tremors, and twitching. They most commonly occur within 7 days postoperatively and are typically unrelated to hyperammonemia, hypoglycemia, or electrolyte disturbances. This narrative review summarizes the findings of 50 publications from 1988-2020 that report occurrence of PANS. While most published reports included only dogs affected by postattenuation seizures (PAS), others included dogs with any form of PANS. Overall, PANS (including PAS) affected 1.6%-27.3% of dogs, whereas incidence of PAS ranged from 0%-18.2%. The etiology of PANS remains unknown; however, several theories have been proposed. Risk factors include preoperative hepatic encephalopathy, increasing age, and possibly certain breeds and extrahepatic shunt morphology. There is increasing evidence that prophylactic antiepileptic drugs do not prevent PANS. Treatment is centered around controlling neurologic signs with antiepileptic drugs and providing supportive intensive care. The 30-day survival rate in studies that included a minimum of four dogs affected by PANS was 0%-100% (median, 50.0%) and 0%-75.0% (median, 37.5%) for those with PAS. Mortality associated with PANS was typically related to occurrence of generalized seizure activity. Prognostic factors positively associated with short-term survival included having a history of preoperative seizures and development of focal seizures only. If affected dogs survived to discharge, survival for several years was possible, and the majority of neurologic signs manifested as part of the phenomenon of PANS appeared to resolve

The effect of prophylactic treatment with levetiracetam on the incidence of post-attenuation seizures in dogs undergoing surgical management of single congenital extrahepatic portosystemic shunts

Objectives: To report (1) the incidence of post-attenuation seizures (PAS) in dogs that underwent single congenital extrahepatic portosystemic shunt (cEHPSS) attenuation and (2) to compare incidence of PAS in dogs that either did or did not receive prophylactic treatment with levetiracetam (LEV).Study Design: Multi-institutional retrospective study.Sample Population: Nine-hundred-and-forty dogs.Methods: Medical records were reviewed to identify dogs that underwent surgical attenuation of a single cEHPSS from January 2005 through July 2017 and developed PAS within seven days postoperatively. Dogs were divided into three groups: no LEV (LEV-); LEV at >15mg/kg TID for >24 hours or a 60mg/kg intravenous loading dose preoperatively, followed by >15mg/kg TID postoperatively (LEV1); ); and LEV at less than 15mg/kg TID, for less than 24 hours preoperatively, or continued at less than 15mg/kg TID postoperatively (LEV2).Results: Nine-hundred-and-forty dogs were included. Seventy-five (8.0%) developed PAS. Incidence of PAS was 35/523 (6.7%), 21/188 (11.2%) and 19/228 (8.3%) in groups LEV-, LEV1 and LEV2, respectively. This difference was not statistically significant (p=0.14). No significant differences between groups of dogs that seized with respect to variables investigated were identified.Conclusions: The overall incidence of PAS was low (8%). Prophylactic treatment with LEV according to the protocols investigated in our study was not associated with a reduced incidence of PAS.Clinical Significance: Prophylactic treatment with LEV does not afford protection against development of PAS. Surgically treated dogs should continue to be monitored closely during the first seven days postoperatively for seizures

Prognostic factors for short‐term survival of dogs that experience postattenuation seizures after surgical correction of single congenital extrahepatic portosystemic shunts: 93 cases (2005‐2018)

© 2020 The American College of Veterinary Surgeons Objective: To identify prognostic factors for short-term survival of dogs that experience seizures within 7 days after surgical correction of single congenital extrahepatic portosystemic shunts (cEHPSS). Study design: Multi-institutional retrospective study. Sample population: Ninety-three client-owned dogs. Methods: Medical records at 14 veterinary institutions were reviewed to identify dogs that underwent surgical attenuation of a single cEHPSS from January 1, 2005 through February 28, 2018 and experienced postattenuation seizures (PAS) within 7 days postoperatively. Logistic regression analysis was performed to identify factors associated with 1-month survival. Factors investigated included participating institution, signalment, shunt morphology, concurrent/historical conditions, presence of preoperative neurologic signs, presence of preoperative seizures, aspects of preoperative medical management, surgical details including method and degree of shunt attenuation, type of PAS (focal only or generalized ± focal), drugs administered as part of the treatment of PAS, and development of complications during treatment of PAS. Results: Thirty (32.3%) dogs survived to 30 days. Seventy-six (81.7%) dogs experienced generalized PAS. Factors positively associated with short-term survival included having a history of preoperative seizures (P =.004) and development of focal PAS only (P =.0003). Most nonsurvivors were humanely euthanized because of uncontrolled or recurrent seizures. Conclusion: Dogs that experienced PAS that had a history of preoperative seizures and those that experienced focal PAS only had significantly improved short-term survival. Clinical significance: The results of this study provide information that will help in the counseling of owners who seek treatment for PAS after surgical correction of cEHPSS. © 2020 The American College of Veterinary Surgeons