Cytokinin-induced switch in development in excised cotyledons of radiata pine cultured in vitro

Cotyledons of Pinus radiata D. Don were cultured under shoot-forming (plus cytokinin) and elongating (minus cytokinin) conditions. Using. autoradiographic and precursor incorporation techniques, the sites and rate of macromolecular synthesis were examined during the first five days in culture. Active incorporation of ³H-thymidine, ³ H-uridine and ³H-leucine occurred. In shoot-forming cotyledons the incorporation became preferentially located in the epidermal and sub-epidermal cell layers in contact with the medium. In elongating cotyledons, in contrast, incorporation was randomly distributed, and the amount of incorporation declined with time. Biochemically, differences in DNA, RNA and total protein synthetic patterns were observed. In elongating cotyledons the rates of RNA and protein synthesis were higher during the first 48 h than in shoot-forming tissues, after which the synthetic rates were similar. Two peaks of newly formed DNA were observed in both tissues. These findings indicate that the cytokinin-induced changes in developmental pathways began within 24 h in culture.     

Direct interaction of tricyclic antidepressants with opiate binding sites in the bovine adrenal medulla

This note reports the interaction of three currently used tricyclic antidepressant drugs (clomipramine, imipramine and amitriptyline) with delta, mu and kappa opioid binding sites in the bovine adrenal medulla. Clomipramine was the only drug interacting with delta and mu sites. On the contrary, all three drugs showed a significant interactions with subtypes of the kappa binding site. Clomipramine was the most active on the kappa 2 and kappa 3 subtypes while amitriptyline showed the highest interaction with the kappa 1 subtype. On the contrary the tricyclic cyproheptadine did not present any interaction with opioid binding sites in our system. This interaction between tricyclic antidepressants and opioid binding sites might be the origin of their analgesic action.     

Regulation of fibronectin biosynthesis by glucocorticoids in human fibrosarcoma cells and normal fibroblasts

When treated with the synthetic glucocorticoid dexamethasone, HT1080 human fibrosarcoma cells show changes in morphology, adhesion, and the extracellular matrix. Dexamethasone treatment results in a tenfold increase in the rate of fibronectin biosynthesis in HT1080 cells and a twofold increase in untransformed, normal human fibroblasts. Maximal induction levels are attained within one cell generation, while decay of the response requires several cell cycles. Pulse-chase studies showed that most of the newly synthesized fibronectin is secreted into the medium. The glucocorticoid antagonist, RU-486, blocks the dexamethasone-induced changes but does not alter the basal rate of fibronectin production. Therefore, fibronectin biosynthesis appears to be controlled by two distinct mechanisms--one, regulating basal rates of fibronectin production, which is transformation-sensitive and glucocorticoid-independent; and another, which is mediated by the glucocorticoid receptor, resulting in elevated rates of fibronectin biosynthesis upon dexamethasone treatment both in normal fibroblasts and in HT1080 cells.     

Histology and fine structure of spermatozoa and egg passage in the female tract of Dermacentro andersoni stiles (acari-Ixodidae)

The final phase of spermiogenesis in the hard tick Dermacentor andersoni occurs in the seminal receptacle of engorged females. This phase is characterized mainly by rupture of the outer sheath of advanced spermatids at their pointed tips, and subsequent elongation as the internal column of these cells evaginates. The sheath invaginates at the opposite end to form the narrow posterior half of the sperm cell. Rupture of the endospermatophoric wall releases the large mass of contained spermatozoa, which begin migration up one or both oviducts. During the migration to the ovarian lumen, spermatozoa exhibit a propensity for active penetration of epithelial cells lining the oviducts. This phenomenon is also observed with spermatozoa in the ovarian lumen. Penetration of epithelial cells by spermatozoa is interpreted to be a response by the latter in seeking eggs for penetration and fertilization.     

Activity of phenol oxidases at the puparium formation stage in development of nineteen lozenge mutants of Drosophila melanogaster

Phenol oxidase activity of activated A₁ and A₂ (A₃) electrophoretic components from 19 lozenge mutant and three lozenge double mutant strains was compared to that of wild type flies. Melanin production by the activated A components with tyrosine as substrate was compared to activity in the same acrylamide gels with dopa as substrate. Melanin production decreased, first in the A₁ band and then in the A₂ (A₃) band, with increased morphological expression of the mutant genes. No melanin bands were obtained with either substrate in five of the more severely affected mutants. A possible correlation between phenol oxidase activity and quinone production necessary for normal development of eyes, female accessory sex organs, and claws is discussed.Supported by PHS grant AM-08331-05.