Interspecific agonistic behaviour in small mammals in a Mexican high-elevational grassland

Field trials were conducted throughout an annual cycle to study the role of agonistic behaviour in explaining the relative abundance of the volcano mouse ( Neotomodon alstoni ) in a small mammal community in high-altitude grasslands of central Mexico. Intrasexual contests between N. alstoni and three other sympatric rodents ( Peromyscus melanotis, Microtus mexicanus, and Reithrodontomys megalotis ) were performed. Male and female P. melanotis (100 and 67% of contests, respectively) and M. mexicanus (82 and 100%) were aggressively dominant over N. alstoni , whereas R. megalotis (80 and 100%) were not aggressive. Agonistic behaviour in this species did not explain its greater abundance in the community.     

Base sequence damage in DNA from X-irradiated monkey CV-1 cells

Two kinds of 3'-ends were detected in DNA scission fragments of highly repetitive primate component alpha DNA which were isolated from irradiated monkey CV-1 cells. The fragments' 3'-ends were characterized by 5'-32P-end labelling the DNA, followed by examination in high-resolution polyacrylamide gels under denaturing conditions. Hydrolysis of the labelled fragments' termini with exonuclease III of E. coli or by the 3'-phosphatase activity of T4 polynucleotide kinase generated a third, slowest migrating species in each mobility size class. Reference to mobility size class standards makes it highly probable that the fragment ends generated by X-rays in cells are 3'-phosphoryl and 3'-phosphoglycolate, and that they are converted to slower migrating fragments with 3'-OH ends, similar to results obtained with DNA irradiated in water (Henner et al. 1982, 1983 a, b). Densitometer measurements of gel autoradiograms showed that X-ray induction of DNA fragments with 3'-phosphoryl and 3'-phosphoglycolate ends was dose-dependent over a range 100-900 Gy. In CV-1 cells the frequency of single-strand breaks in alpha DNA was 8.6 x 10(-7) breaks/nt/Gy. The two kinds of ends disappeared in post-radiation incubation with a half-time of 1.6 h. These results provide a new means to study X-ray damage and repair of specific sequences in animal cells.     

Clinical Use of a New Mitral Disc Valve

A disc valve of new design was used successfully for the replacement of the mitral valve in patients with rheumatic mitral valve disease. This valve would appear to have the following advantages over the mitral ball valve prosthesis:• Lower left atrial pressure after replacement.• Elimination of the hazard of left ventricular outflow tract obstruction with mitral valve replacement.• Decreased incidence of thromboembolization.• Abolition of possibility of ventricular septal irritation.Despite the better outlook for this valve compared with the ball valve for mitral valve substitution, the mitral valve should always be repaired whenever feasible. Repair is possible in the majority of patients.     

Patterns of sequence variation in the mitochondrial D-loop region of shrews

Direct sequencing of the mitochondrial displacement loop (D-loop) of shrews (genus Sorex) for the region between the tRNA(Pro) and the conserved sequence block-F revealed variable numbers of 79-bp tandem repeats. These repeats were found in all 19 individuals sequenced, representing three subspecies and one closely related species of the masked shrew group (Sorex cinereus cinereus, S. c. miscix, S. c. acadicus, and S. haydeni) and an outgroup, the pygmy shrew (S. hoyi). Each specimen also possessed an adjacent 76-bp imperfect copy of the tandem repeats. One individual was heteroplasmic for length variants consisting of five and seven copies of the 79-bp tandem repeat. The sequence of the repeats is conducive to the formation of secondary structure. A termination-associated sequence is present in each of the repeats and in a unique sequence region 5' to the tandem array as well. Mean genetic distance between the masked shrew taxa and the pygmy shrew was calculated separately for the unique sequence region, one of the tandem repeats, the imperfect repeat, and these three regions combined. The unique sequence region evolved more rapidly than the tandem repeats or the imperfect repeat. The small genetic distance between pairs of tandem repeats within an individual is consistent with a model of concerted evolution. Repeats are apparently duplicated and lost at a high rate, which tends to homogenize the tandem array. The rate of D- loop sequence divergence between the masked and pygmy shrews is estimated to be 15%-20%/Myr, the highest rate observed in D-loops of mammals. Rapid sequence evolution in shrews may be due either to their high metabolic rate and short generation time or to the presence of variable numbers of tandem repeats.      

大鼠胼胝体内神经肽Y免疫反应阳性纤维的发育

本实验用免疫组织化学ＡＢＣ法研究了大鼠胼胝体内神经肽Ｙ免疫反应阳性（ＮＰＹ－ＩＲ）纤维的生后发育。结果发现,许多ＮＰＹ－ＩＲ纤维在大鼠出生时便存在于胼胝体内。ＮＰＹ－ＩＲ胼胝体纤维的密度在生后１周内继续逐渐增高,在第２周内达到最高峰。之后,ＮＰＹ－ＩＲ胼胝体纤维的密度逐渐下降,至第３周末时接近成年时的水平,即仅有少量ＮＰＹ－ＩＲ纤维存在于胼胝体内。这些结果提示在大鼠早期生后发育过程中许多ＮＰＹ－ＩＲ胼胝体纤维是暂时性的,其作用可能与大脑皮质的机能发育有关。