Two-Loop Four-Fermion Scattering Amplitude in QED.

We present the first fully analytic evaluation of the transition amplitude for the scattering of a massless into a massive pair of fermions at the two-loop level in quantum electrodynamics. Our result is an essential ingredient for the determination of the electromagnetic coupling within scattering reactions, beyond the currently known accuracy, which has a crucial impact on the evaluation of the anomalous magnetic moment of the muon. It will allow, in particular, for a precise determination of the leading hadronic contribution to the (g-2)_{µ} in the MUonE experiment at CERN, and therefore can be used to shed light on the current discrepancy between the standard model prediction and the experimental measurement for this important physical observable.

Electron spectroscopic imaging for high-resolution immunocytochemistry: use of boronated protein A.

In the present study we adapted electron spectroscopic imaging (ESI) for high-resolution immunocytochemistry. To accomplish this, we applied boronated protein A (B-pA) for indirect detection of specific antigenic sites using pre-embedding and post-embedding protocols. Isolated acinar cells were exposed to wheat germ agglutinin (WGA) and anti-WGA, followed by B-pA, to reveal WGA binding sites at the level of the plasma membrane. The cells were then embedded in Epon and unstained ultra-thin sections were examined by electron microscopy using the ESI mode. For post-embedding, ultra-thin sections of glutaraldehyde-fixed, Lowicryl-embedded pancreatic tissue were exposed to specific antibodies (anti-insulin or anti-amylase), followed by B-pA. The unstained sections were examined using the ESI mode. In both cases, boron was detected with high resolution either at the level of the plasma membrane of acinar cells, demonstrating WGA binding sites, or over secretory granules in pancreatic insulin-secreting cells or acinar cells, demonstrating insulin and amylase, respectively. These findings were compared to those obtained with the protein A-gold technique, and have demonstrated the analogy of both types of labeling. In addition, several control experiments assessed this novel approach. They have demonstrated the specificity of labeling and the high reactivity of B-pA, as well as its antibody-binding properties. Finally, electron energy loss spectral analysis confirmed the presence of boron in the tissue sections at sites where immunolabeling was detected. These results demonstrate that ESI is an appropriate approach for cytochemistry. Since the technique is based on detection of elements, spatial resolution is considered to be in the magnitude of 0.5 nm, which represents a major improvement in resolution over actual electron microscopic cytochemical techniques.

Cachexia secondary to intracranial anaplastic (malignant) ependymoma in a boxer dog.

An eight-year-old female boxer was referred because of weight loss of several months' duration. On physical examination, cachexia was the only reported abnormality. Neurological symptoms were shown only in the last days preceding death and consisted of altered mental status, compulsive behaviour and left rear proprioception deficit. At post-mortem examination, a voluminous, soft, haemorrhagic mass was found invading the floor of the brain. Based on the morphological features of the tumour, marked parenchymal invasion, extensive necrosis and cellular atypia, the mass was classified as an anaplastic ependymoma. This case report shows similarities to the diencephalic syndrome reported in human paediatric medicine in which the main clinical sign is a profound emaciation in spite of normal or slightly diminished caloric intake. Weight loss and cachexia are clinically relevant problems in small animals and these clinical signs should raise a suspicion, among the other differentials, of a brain tumour, even in absence of neurologic signs.