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A search has been made for lepton-flavor-violating interactions of the type e ϩ p→lX, where l denotes a or with high transverse momentum, at a center-of-mass energy ͱs of 300 GeV with an integrated luminosity of 47.7 pb Ϫ1 using the ZEUS detector at HERA. No evidence was found for lepton-flavor violation and constraints were derived on leptoquarks ͑LQs͒ that could mediate such interactions. For LQ masses below ͱs, limits are set on eq 1 ͱ␤ lq , where eq 1 is the coupling of the LQ to an electron and a first-generation quark q 1 and ␤ lq is the branching ratio of the LQ to l and a quark. For LQ masses exceeding ͱs, limits are set on the four-fermion contact-interaction term eq ␣ lq ␤ /M LQ 2 for leptoquarks that couple to an electron and a quark q ␣ and also to l and a quark q ␤ . Some of the limits are also applicable to lepton-flavor-violating processes mediated by squarks in R-parity-violating supersymmetric models. In some cases involving heavy quarks and especially for lϭ, the ZEUS limits are the most stringent published to date.

Recently, apoptotic cell death has been reported in differentiated skeletal muscle, where apoptosis was generally assumed not to occur. To investigate whether apoptosis may contribute to the steroid-induced myopathy, rats treated with triamcinolone acetonide (TA) for 9 days were sacrificed for detecting apoptosis by in situ end-labelling (ISEL) and DNA electrophoresis in soleus muscles. Immunohistochemical stainings of Fas antigen and p53 protein were performed to examine whether apoptosis-related proteins were present in the myopathy. Muscle fibre necrosis and apoptotic myonuclei appeared in soleus muscles following administration of TA, while control muscles showed no evidences for apoptosis. Fas antigen was not detected in control muscles, but expressed in soleus muscles of steroid-induced myopathy. Some of the Fas antigen-expressing muscle fibres were positive for ISEL. p53 Protein was not detected in any muscle fibres. These findings indicate that TA can induce apoptosis in differentiated skeletal muscles, and Fas antigen might be partly related to apoptotic muscle death in steroid-induced myopathy.

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