Four black rats collected in the Mauritius Island lying in Indian Ocean have the karyotype basically categorized in the Oceanian type containing large metacentric M1 and M2 pairs, but 2n-number is 42 in 3 specimens and 43 in one. The increase of the chromosome number resulted from the presence of 8 small acrocentrics. These excessive acrocentrics are formed by the Robertsonian fission-type mechanism of 4 small metacentrics. One rat with 43 chromosomes has a similar karyotype to the above, except for the presence of one extra chromosome which results from the Robertsonian fission of one of the large metacentric M1 pair.
Serial chromosome investigations in a fibroblast strain from Hurler syndrome and two strains from Tay Sachs disease have resulted in striking similarity of chromosome aberration profiles, with a marked increase in anueploidy, polyploidy, and dicentrics in the senescent phase. In addition, a high frequency of nuclear alterations and metaphases with shrinked chromosomes is noted in the three senescent fibroblast cell cultures.
Deoxyribonucleoprotein (DNP) is extracted from calf thymus. The DNP solution is sprayed onto a specially designed specimen holder which is precooled with liquid nitrogen. The frozen specimen is deeply etched by rewarming upto -90°C at 1×10-5 Torr, and subsequently shadowed with platinum-palladium. The freezereplica of the DNP is examined under an electron microscope. The DNP fibers with a mean diameter of 183Å are formed by a coiling of fine fibrils, 23Å in mean diameter.
Using the anterograde degeneration method, the accessory optic system was analized and divided into the inferior and superior accessory optic tracts in the rat. The inferior accessory optic tract terminal is sent bilaterally into the medial treminal nucleus. The superior accessory optic tract fibers are contralaterally projected into the lateral and dorsal terminal nuclei.
A direct fiber connection of the retino-suprachiasmatic pathway was examined by the Fink-Heimer and Nauta-Gygax techniques. It was obtained that the retino-suprachiasmatic fibers were distributed bilaterally into the suprachiasmatic nucleus in the rat. The significance of the optic-hypothalamic connection is concerned.