Evaluation of formalin-fixed paraffin-embedded tissues from vaccine site-associated sarcomas of cats for polyomavirus DNA and antigen

OBJECTIVE

To determine whether vaccine site-associated sarcomas (VSS) from cats contain polyomavirus antigen or DNA.

SAMPLE POPULATION

50 formalin-fixed paraffin-embedded tissue blocks of VSS from cats.

PROCEDURE

Sections from each tissue block were evaluated for polyomavirus antigen by use of an avidin-biotin-complex immunohistochemical staining method, using rabbit anti-murine polyomavirus polyclonal antiserum as the primary antibody. The DNA was extracted from sections of each tissue block, and a polymerase chain reaction assay was performed, using primers designed to amplify regions of the bovine polyomavirus genome and consensus polyomavirus primers designed to detect unknown polyomaviruses.

RESULTS

Polyomavirus antigen and DNA were not detected in any of the VSS.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that polyomaviruses likely do not have any direct involvement in the pathogenesis of VSS in cats.

Modulation of absence seizures by the GABA(A) receptor: a critical rolefor metabotropic glutamate receptor 4 (mGluR4)

Experimental absence seizures are associated with perturbations in the presynaptic release of GABA and glutamate within thalamocortical circuitry. The release of both glutamate and GABA is regulated by group III metabotropic glutamate receptors (mGluRs). Therefore, we examined the susceptibility of mice lacking the mGluR4 subtype of mGluR (mGluR4(-/-)) versus their wild-type controls (mGluR4(+/+)) to absence seizures induced either by gamma-hydroxybutyrate (GHB) or the GABA(B) agonist (-) baclofen or by low doses of the GABA(A) receptor (GABA(A)R) antagonists pentylenetetrazole, bicuculline, or picrotoxin. There was no difference between mGluR4(-/-) and mGluR4(+/+) mice in threshold to absence seizures induced by either GHB or (-) baclofen. In contrast, the mGluR4(-/-) mice were markedly resistant to absence seizures induced by low doses of GABA(A)R antagonists. No differences were observed between mGluR4(-/-) and mGluR4(+/+) mice in threshold to clonic or tonic seizures induced by higher doses of GABA(A)R antagonists, strychnine, or electroshock, indicating that seizure resistance in the mGluR4(-/-) mice was restricted solely to absence seizures. The resistance of mGluR4(-/-) mice to absence seizures induced by GABA(A)R antagonists was mimicked by bilateral administration of a mGluR4 antagonist into the nucleus reticularis thalami (nRT) of mGluR4(+/+) mice. Conversely, intra-nRT administration of a mGluR4 agonist in mGluR4(+/+) mice exacerbated GABA(A)R-induced absence seizures. These data indicate that the presence of mGluR4 within nRT is critical to GABAergic modulation of thalamocortical synchronization in normal and pathological states, such as generalized absence epilepsy.

Calmodulin regulates the disassembly of cortical F-actin in mast cells but is not required for secretion

Secretion is dependent on a rise in cytosolic Ca(2+)concentration and is associated with dramatic changes in actin organization. The actin cortex may act as a barrier between secretory vesicles and plasma membrane. Thus, disassembly of this cortex should precede late steps of exocytosis. Here we investigate regulation of both the actin cytoskeleton and secretion by calmodulin. Ca(2+), together with ATP, induces cortical F-actin disassembly in permeabilized rat peritoneal mast cells. This effect is strongly inhibited by removing endogenous calmodulin (using calmodulin inhibitory peptides), and increased by exogenous calmodulin. Neither treatment, however, affects secretion. Low concentrations ( approximately 1 microM) of a specific inhibitor of myosin light chain kinase, ML-7, prevent F-actin disassembly, but not secretion. In contrast, a myosin inhibitor affecting both conventional and unconventional myosins, BDM, decreases cortical disassembly as well as secretion. Observations of fluorescein-calmodulin, introduced into permeabilized cells, confirmed a strong (Ca(2+)-independent) association of calmodulin with the actin cortex. In addition, fluorescein-calmodulin enters the nuclei in a Ca(2+)-dependent manner. In conclusion, calmodulin promotes myosin II-based contraction of the membrane cytoskeleton, which is a prerequisite for its disassembly. The late steps of exocytosis, however, require neither calmodulin nor cortical F-actin disassembly, but may be modulated by unconventional myosin(s).

Validation of retroviral detection for rodent cell-derived products and gene therapy applications

The availability of sensitive assays for detecting infectious murine retroviruses has become critical for the development and acceptance of a number of biopharmaceuticals, including monoclonal antibody-derived products and gene therapy vectors. Comparative studies demonstrated that the PG4 S+L- retrovirus infectivity test routinely yields higher titres than the mink cell test for xenotropic, amphotrophic and MCF murine retroviruses. A validation study for the PG4 S+L- assay demonstrated very good linearity (r2 of 0.95 to 0.99), reproducibility within a study (+/-0.35 log10 units), and precision between tests (+/-0.45 log10 units). Interference (or selectivity) in the presence of a non-specific antibody was insignificant (less than 0.2 log10 units). Sensitivity levels established from measurements as virus titres approach zero demonstrated a threshold value of 2-3 focus forming units (FFU)/ml. Two methods for increasing assay sensitivity were used including: (i) increased product samplings combined with a Poisson distribution analysis, and (ii) a 14-day co-cultivation with Mus dunni cells. Each of these methods was shown to increase sensitivity by at least one log10 unit. Murine retroviruses may also be detected by a less sensitive immunofluorescence assay (IFA) using specific monoclonal antibodies; this assay is essential for detecting certain recombinant ecotropic MuLVs. In summary, murine retroviral detection ranked by sensitivity is mink S+L- < IFA with monoclonal antibodies < PG4 S+L- < Mus dunni co-cultivation followed by PG4 S+L-.

A post-anaesthetic follow-up program

Experience with an in-hospital post-anaesthetic follow-up program is reported. Visits are made by a Registered Nurse, a hospital employee working under the direction of the Head of the Department of Anesthesia. Over a three-year period 21,116 of 39,239 patients receiving anaesthetics were visited. Those not visited were mainly outpatients or patients discharged early following minor surgery. Anaesthetic related minor complications were noted in 8.15% of the patients seen in follow-up. Major complications occurred in 0.37% of patients seen.

Closing capacity measurement during general anesthesia

A modification of the single-breath nitrogen closing volume (CV) test allows measurement of closing capacity (CC) during general anesthesia. In the modification, inspiration and expiration are mechanically produced by a hydraulically powered cylinder. For 14 awake, normal subjects results of the CV test performed using this mechanical method differed that those obtained following spontaneous inspiration and expiration. Mean (+/-SE) CC's were 2.25 (+/-0.15) and 2.42 1 (+/-0.14) (P less than 0.01) using spontaneous and mechanical methods, respectively. The slopes of Phase III of the CV traces were 2.24 (+/-0.27) and 2.66 per cent N2/L (+/-0.32) (P less than 0.01), respectively. To eliminate differences due to measurement technique, the modified CV test was used both before and during anesthesia with halothane in 70 per cent N2 in 11 normal, supine, spontaneously breathing subjects. CC's were 1.89 l (+/-0.16) before and 1.84 l (+/-0.15) during anesthesia (P greater than .5). Mean functional residual capacities (FRC) by the closed-circuit helium method were 1.77 l (+/-0.15) before and 1.45 l (+/-0.17) during anesthesia (P less than .001). With CC unchanged and FRC decreased following induction, CC/FRC increased from 1.07 (+/-0.08) to 1.37 (+/-0.11) (P less than .005), suggesting increased small-airway closure during anesthesia.