Rapid Serial Sarcomere Loss Caused by Electrical Stimulation in Rabbit Triceps Surae Muscles

Muscle spasms, such as those observed in cerebral palsy patients, are involuntary muscle contractions that usually occur due to a lesion in the brain. These muscle spasms cause muscles to become hypoextensible, or very stiff. This hypoextensibility may be explained by a decrease in serial sarcomere number concomitant with a long stimulation period. In 1981, Tabary and Tardieu showed a 25% decrease in the number of serial sarcomeres in guinea pig Soleus muscles over a 12 hour stimulation period. As these results seem very extreme, it was necessary to try duplicating these results in our laboratory, as well as in a different animal model. The Medial Gastrocnemius, Plantaris, and Soleus muscles were stimulated via the tibial nerve in New Zealand White rabbits (n=3) for 10 hours in one of the legs (20 Hz at 3 times the α motoneuron threshold). The tibial nerve in the contralateral control leg was transected to ensure no cross- over training effects. After the stimulation period, the animals were sacrificed and the hind limbs were then placed in a 10% formalin solution at carefully controlled knee and ankle angles. Three to five samples were harvested from each muscle. After a digestion process, individual fascicles were teased out and mounted on prepared slides. These slides were then analyzed for fascicle length by using a camera system with specialized software and sarcomere lengths were determined using a laser diffraction method. Analysis showed that the serial sarcomere number decreased in the Medial Gastrocnemius by 23 ± 4.4%, in the Plantaris by 25 ± 2.9%, and the Soleus by 29 ± 7.0%. These numbers concur closely with the 25% loss of serial sarcomeres reported by Tabary and Tardieu in guinea pigs. These confirmed results will allow for more research to be done in this area

Two-frequency shell model for hypernuclei and meson-exchange hyperon-nucleon potentials

A two-frequency shell model is proposed for investigating the structure of hypernuclei starting with a hyperon-nucleon potential in free space. In a calculation using the folded-diagram method for Λ¹⁶O, the Λ single particle energy is found to have a saturation minimum at an oscillator frequency ħωΛ≈10MeV, for the Λ orbit, which is considerably smaller than ħωN=14MeV for the nucleon orbit. The spin-dependence parameters derived from the Nijmegen NSC89 and NSC97f potentials are similar, but both are rather different from those obtained with the Jülich-B potential. The ΛNN three-body interactions induced by ΛN-ΣN transitions are important for the spin parameters, but relatively unimportant for the low-lying states of Λ¹⁶O.Yiharn Tzeng, S. Y. Tsay Tzeng, T. T. S. Kuo, T.-S.H. Lee, and V. G. D. Stok

Angular correlation and coincidence studies of excited 0/sup +/ and other levels in the transitional Ce nuclides /sup 142/Ce, /sup 144/Ce, /sup 146/Ce, and /sup 148/Ce

The decays of the neutron-rich nuclides /sup 142/La, /sup 144/La, /sup 146/La and /sup 148/La to the levels of the transitional nuclides /sup 142/Ce, /sup 114/Ce, /sup 146/Ce and /sup 148/Ce, respectively, have been studied using mass-separated sources. Angular correlation studies have been employed to identify new excited 0/sup +/ levels in /sup 146 /Ce and support spin and parity assignments for 1/sup -/, 3/sup -/, 2 /sup +/, 3/sup +/, 4/sup +/ and 6/sup +/ levels in /sup 144/Ce and /sup 146/Ce. An excited 0/sup +/ level in /sup 148/Ce is indicated by coincidence ratios and electron studies, while no clear evidence can be found for the location of an excited 0/sup +/ level below 2 MeV in /sup 144/Ce. The resulting isotonic and isotopic systematics are discussed in terms of the transition from the closed shells at N=82 and Z=50 to the region of deformed nuclides. (13 refs)

Low-Dose Radiation-Induced Protective Process and Implications for Risk Assessment, Cancer Prevention, and Cancer Therapy

A low-dose protective apoptosis-mediated (PAM) process is discussed that appears to be turned on by low-dose gamma and X rays but not by low-dose alpha radiation. PAM is a bystander effect that involves cross-talk between genomically compromised [e.g., mutants, neoplastically transformed, micronucleated] cells and nongenomically compromised cells. A novel neoplastic cell transformation model, NEOTRANS3, is discussed that includes PAM. With NEOTRANS3, PAM is activated by low doses and inhibited by moderate or high doses and is, therefore, a hormetic process. A low-dose region of suppression of the transformation frequency below the spontaneous frequency relates to the hormetic zone over which PAM is presumed to operate. The magnitude of suppression relates to what is called the hormetic intensity. Both the hormetic intensity and width of the hormetic zone are expected to depend on dose rate, being more pronounced after low dose rates. It is expected that PAM likely had a significant role in the following observations after chronic irradiation: (1) what appears to be a tremendous reduction in the cancer incidence below the spontaneous level for Taiwanese citizens residing for years in cobalt-60 contaminated apartments; and (2) the published reductions in the lung cancer incidence below the spontaneous level in humans after protracted X irradiation and after chronic gamma plus alpha irradiation. Implications of PAM for cancer prevention and low-dose cancer therapy are briefly discussed