Individual variability of pathological parameters in chemically induced rat colon tumors.

The development of tumorigenic conditions in the carcinogen-exposed rat colon was studied using selected morphological, histochemical, immunohistochemical and biochemical methods of analysis. Rats were treated with two carcinogens: 1,2-dimethylhydrazine and N-methyl-N'-nitro-N-nitrosoguanidine alone or with deoxycholic acid as a tumor promoter. It was found that 3 months after treatment of animals with the carcinogens the following changes were developed in colonic tissue: infiltration of lymphocytes in the mucous membrane, high increase in mitotic index among epithelial cells, negative reactions of colonic cells for neutral mucopolysaccharides and sulfomucins and positive reactions to carboxyl groups, nonsulfated acid mucosubstances and tissue polypeptide antigens. An increase in the activity of ornithine decarboxylase in colonic tissue was developed within the same time period and has been seen only in those tissues which were characterized by the development of precancerous conditions. Individual variations were observed in the manifestation of the studied parameters in rat neoplastic colonic tissues. It is suggested that these differences reflect an individual sensitivity of animals to carcinogens and the magnitude of the dysplastic processes induced in the colon.     

Maturation of locust corpora allata during the reproductive cycle: Effect of reserpine on allatotropic activity,juvenile hormone-III biosynthesis,and oocyte development

Reserpine, at doses of 20–175 μg per g body weight, severely retards oogenesis in newly emerged adult female migratory locusts (Locusta migratoria migratorioides) but does not increase mortality during the first 9 days and only slightly delays somatic growth. Total protein, and hemolymph vitellogenin content particularly, are significantly reduced in reserpine-treated locusts. The synthesis of juvenile hormone III (JH-III) following adult emergence, essential for induction of vitellogenesis and subsequent oogenesis, is dependent on the maturation and activation of the corpora allata (CA). CA of 7- to 8-day-old female locusts, treated with reserpine at day 1 after adult emergence, are only marginally active in vitro and are only slightly stimulated by an allatotropic factor. The basal activity and response of CA from the reserpine-treated locusts resembles that of newly emerged locusts, suggesting that reserpine specifically retards the initial maturation of the locust CA. Recovery of basal CA activity is evident on days 12–13 in reserpine-treated locusts, but responsiveness to the allatotropic factor is not recovered. Starvation of newly emerged females for 3 days and subsequent feeding did not effect ooctye development or CA activity. Cerebral content of the allatotropic factor, assayed on days 7–8, is not reduced by the reserpine treatment.     

Partial purification and characterization of locust allatotropin I

Methanol extracts of locust brains, corpora cardiaca (CC), and suboesophageal ganglia (SOG) were separated by gradient and/or isocratic reverse-phase high-performance liquid chromatography (HPLC) and allatotropic activity monitored in the eluted fractions. A major peak of activity, separated by isocratic separation with 12% 2-propanol, designated allatotropin I, exhibited identical retention times in the three tissue extracts. Doseresponse curves of allatotropin I indicate similar content in brain and CC-equivalents, whereas optic lobes, similarly separated by isocratic HPLC, contain only one-tenth of this amount of allatotropin. Allatotropin I is resistant to boiling and is susceptible to tryptic and chymotryptic digestion. Methanol extracts of thoracic muscle, Malpighian tubules, fat body or ovaries, similarly prepared and boiled, did not exhibit allatotropic activity at high doses of tissue equivalents.     

Comparison of the predicted structure for the activated form of the P21 protein with the X-ray crystal structure

The predicted conformation and position of the central transforming region (residues 55–67) of the p21 protein are compared with the conformation and position of this segment in a recently determined X-ray crystal structure of residues 1–166 of this protein in the activated state bound to a nonhydrolyzable GTP derivative. We previously predicted that this segment of the protein would adopt a roughly extended conformation from Ile 55-Thr 58, a reverse turn at Ala 59-Gln 61, followed by an -helix from Glu 62-Met 67. We further predicted that this region of the activated protein occupies a position that is virtually identical to corresponding regions in the homologous purine nucleotide-binding proteins, bacterial elongation factor (EF-tu), and adenylate kinase (ADK). We find that there is a close correspondence between the conformation and position of our predicted structure and those found in the X-ray crystal structure. A mechanism for activation of the protein is proposed and is corroborated by X-ray crystallographic data.     

Importance of cell-aggregation during induction of neural differentiation in PCC-7 embryonal carcinoma cells.

The importance of cell-aggregation during retinoic acid-induced neural differentiation of embryonal carcinoma cells was studied on the PCC-7 cell line. These cells were chosen as they display low tendency for spontaneous aggregation, and they develop preferentially to neurons upon induced in vitro differentiation. Forced aggregation of these cells, in the absence of retinoic acid, did not result in development of neuron- or glial-like cells. Application of retinoic acid prior to or after the cell-aggregation did not result in neural tissue-like differentiation, either. Irreversible induction of neural development was achieved if cell-aggregation and retinonic acid acted simultaneously, and for a period longer than 48 h. Retinoic acid, on the other hand, was found to be toxic on non-aggregated PCC-7 cells. Our data suggest that cell to cell contacts alter the response of these cells to retinoic acid, and their close apposition is a prerequisite for the retinoic acid-induced neural differentiation.     

IL-2 influences the balance between immunity and unresponsiveness in the picryl (TNP) contact sensitivity system by blocking the development or action of an Lyt-2+, I-J+ T suppressor cell

Mice injected with antigen (picrylated spleen cells) intravenously fail to develop contact sensitivity. However, contact sensitivity occurs if these mice are injected with IL-2. This effect of IL-2 was reproduced in vitro by taking spleen cells 2 days after injecting antigen intravenously and culturing them with either 150 u/ml recombinant IL-2 for 2 days or by pulsing with 600-1200 u/ml IL-2 at 4 degrees C for 1 hr. After 2 days in culture these antigen-exposed cells transfer contact sensitivity to naive recipients in a 24-hr experiment. However, the ability of antigen-exposed cells, pulsed with IL-2, to transfer contact sensitivity is abolished when they are incubated with unpulsed antigen-exposed cells and as few as 1/16 of their number have a significant effect. This phenomenon is specific, as normal cell or cells from mice injected with oxazolonated cells intravenously have no effect. The suppressor cells were Thy-1+, Lyt-1-, 2+, I-J+ T cells. It was concluded that IL-2 prevents the development/action of antigen-specific T suppressor cells.     

Multielectrode culture chamber: a device for long-term recording of bioelectric activities in vitro

A multi-microelectrode culture chamber system was constructed for monitoring simultaneously morphological and electrophysiological development of neural cells in vitro. The setup consisted of a pattern of gold conductor lines evaporated onto a glass substrate and insulated with polyamide. The width of each electrode was 10 microns, and the distance between the electrodes was 60 microns. The electrode patterns were constructed and the uncovering of the electrode tips were carried out by photo-etching. This system allowed us to record spontaneous activities in both explant- and primary monolayer cultures of either rat or mouse spinal cords and forebrains, during neuronal regeneration and maturation.     

A quantitative description of vitellogenesis in Locusta migratoria migratorioides

During the main period of development of the oöcytes in Locusta migratoria migratorioides from 1.5 mm to 5.5 mm in length, a steady-state level of about 8 mg/ml VG (vitellogenin)² is maintained. During this period, total uptake rate of VG by the terminal oocytes was calculated to increase linearly from about 0.05 mg/hr to about 0.5 mg/hr. This increase is matched by an increase in the rate of VG synthesis, as determined by ³H-leucine incorporation rates, while the rate of synthesis of nonvitellogenic proteins at the same time remains constant.     

Analysis of gamma-carboxyglutamic acid via amino acid analysis.

Modifications of the analysis of protein-bound residues of γ-carboxyglutamic acid (Gla) via alkaline hydrolysis are presented. The method described allows easier sample manipulation than that heretofore required and insures quantitative recovery of hydrolyzed amino acids. A possible explanation of the shoulder which sometimes appears near Gla on some amino acid analyzers is presented.     

The influence of canavanine and related compounds on the water balance system of locusts

In vivo increase in haemolymph volume of canavanine-treated locusts substantiates our previous in vitro findings that canavanine inhibits fluid secretion by locust Malpighian tubules. Furthermore when diuretic hormone is applied in vivo after canavanine treatment haemolymph volume is drastically reduced below levels retained in locusts untreated with canavanine. Again this is in accord with canavanine potentiation of semi-isolated Malpighian tubules and enhanced fluid secretion in vitro. The response is specific to canavanine; compounds similar in structure (arginine, argininic acid, citrulline, canaline, ornithine and homoserine) have no effect on the rate of fluid secreted by Malpighian tubules. Only partial competition is obtained with uridine homoserine.