Habituation and inhibition of the crayfish lateral giant fibre escape response

1. Decrement of the lateral giant fibre escape response was studied in intact, restrained, crayfish and in those with the ventral nerve cord transected at the thoracic-abdominal level. 2. Taps (delivered at rates of 1 per 5 min to the abdomen) depressed responsiveness to about 50% of its inital value in 10 trials, for both intact and operated animals. 3. With additional stimulation, responsiveness dropped to near zero for both groups. Recovery was negligible 2 h later, but nearly complete after an additional 24 h rest. 4. Protection against response decrement in this situation was obtained by directly activating the cord giant fibres 30 msec prior to the tactile stimulus. The directly-elicited giant fibre spikes which follow the tactile stimulus do not influence the course of response decrement. 5. The results establish the decrement as centrally mediated habituation, and minimize the role of receptor alterations or descending neuronal influences in the behavioural change. 6. A comparison is made between the properties of hibituation and the homosynaptic depression of afferent to interneurone synapses that is presumed to be the physiological mechanism of habituation in this situation.

Mitogenic action of oestradiol-17 beta on human myometrial and endometrial cells in long-term tissue cultures

Dispersed human endometrial and myometrial cells grown for up to 4 months as monolayer cultures responded to addition of oestradiol-17β (1 × 10−9 mol/l) to the medium by increased [3H]thymidine incorporation into DNA, and an increased rate of cell division. Cultures derived from uterine leiomyomata showed a less consistent mitotic response to the hormone.

Normal endometrial and myometrial cells grown in the oestradiolenriched medium showed a significantly higher efficacy of colony formation (increases of about 60 and 90%, respectively) than cells grown in control medium throughout the experimental period. Exposure to the hormone for 3–4 days was sufficient to induce this effect, which suggests that it does not depend on selection of hormone-sensitive cells. The mitogenic effect of oestradiol, as expressed by increased cloning efficacy, persisted for several days after transfer of the cells to a hormone-free medium. Cultures of foetal rat skeletal muscle failed to respond to oestradiol-17β in the cloning test, and oestradiol-17α was without effect on uterine cells.

It is concluded that oestradiol-17β exerts a direct mitogenic action on some cellular components of the human endometrium and myometrium in vitro.

Further studies of the effect of bone marrow cells on chemically induced lymphoma in C57BL-6 mice

Injection of syngeneic bone marrow cell to adult C57BL/6 mice treated DMBA intragastrically failed to prevent lymphoma induced by the chemical.The present result seem to indicate that bone marrow cells do not hasten the regeneration of the transient injuried thymus by DMBA as compared with their effect in irradiated mice.IT APPEARS THAT, UNDER THE CONDITIONS USED, DMBA DOES NOT CAUSE SIGNIFICANT DAMAGE TO THE BONE MARROW SINCE MARROW CELLS FROM CHEMICALLY TREATED MICE WERE AS EFFECTIVE AS NORMAL MARROW CELLS IN: (a) preventing radiogenic leukaemia, (b) repairing radiation damage of the thymus, (c) preventing the lethal action of high doses of irradiation.Marrow cells failed to restore antibody formation to Shigella depressed by DMBA as they do in irradiated mice.The result strengthen our previous view on the critical role of bone marrow on the effects caused by irradiation and not in the leukaemia process as such.

Investigations of the marine algae of Nova Scotia. VIII. The flora of Digby Neck Peninsula, Bay of Fundy

The algal flora at two selected sites on the Digby Neck Peninsula, Bay of Fundy, was examined at monthly intervals for a year. One hundred and eighty-seven species and varieties were recorded; of these 76 are newly recorded for the Bay of Fundy and 11 are new records for North America. A taxonomic listing, inclusive of reproductive structures found during the year, is given. Seasonal changes and vertical migration of the algae are discussed.

SPORANGIA OF RALFSIA FUNGIFORMIS (GUNN.) SETCHELL ET GARDNER(1) (2)

Unilocular and plurilocular sporangia of Ralfsia fungiformis are, for the first time, recorded for North America. The validity of certain types of structures, considered by some authors as plurilocular sporangia, is discussed.