Search PubMed⌕ Search

Biomedical subjects

D Davidson

Publications and source records attributed to D Davidson.

At least 271 records · Page 15Linked to original sources
PubMed1971

5-Aminouracil treatment. A method for estimating G2.

Treatment of Vicia faba lateral roots with a range of concentrations of 5-aminouracil (5-AU) indicate that cells are stopped at a particular point in interphase. The timing of the fall in mitotic index suggests that cells are held at the S - G(2) transition. When cells are held at this point, treatments with 5-AU can be used to estimate the duration of G(2) + mitosis/2 of proliferating cells. Treatment with 5-AU can also be used to demonstrate the presence of subpopulations of dividing cells that differ in their G(2) duration. Using this method, 5-AU-induced inhibition, we have confirmed that in V. faba lateral roots there are two populations of dividing cells: (a) a fast-dividing population, which makes up approximately 85% of the proliferating cell population and has a G(2) + mitosis/2 duration of 3.3 hr, and (b) a slow-dividing population, which makes up approximately 15% of dividing cells and has a G(2) duration in excess of 12 hr. These estimates are similar to those obtained from percentage labeled mitosis (PLM) curves after incorporation of thymidine-(3)H.

Mitosis↗
PubMed1968

Evidence from thymidine-3H-labeled meristems of Vicia faba of two cell populations.

Treatments with tritiated thymidine (TdR-(3)H) have revealed the existence of two populations of mitotically active cells in meristems of lateral roots of Vicia faba. A rapidly dividing population, with a cycle time of 14 hr, constitutes about half the cells in the meristem. A second population of cells, with a cycle time in excess of 30 hr, is also present. Estimates of the relative size of this slowly dividing population are more difficult to make, but we calculate that this population includes 27-43% of meristem cells. The remaining fraction of the meristem is made up of cells that divide rarely or not at all. Since, at all times, both populations contribute to the mitotic index, the curve of the percentage of labeled mitoses that can be determined after a pulse label with TdR-(3)H differs from the curve expected of an ideal population in an important way: the peak value of the curve of the percentage of labeled mitoses is always less than 100%, usually between 75 and 80%. This heterogeneity within a meristem must be borne in mind in terms of the response of meristems to disruptive treatments, the mechanisms controlling mitotic cycle duration, and the spatial organization of a heterogeneous population in an organ that shows polarized growth.

Mitosis↗
PubMedDate not supplied

Effect of ethanol drinking and naltrexone on subsequent drinking in rats.

The effects of several days of oral ethanol drinking paired with naltrexone (NTX) on subsequent ethanol drinking were investigated in rats. We hypothesized that repeated pairings of NTX combined with forced oral ethanol intake would extinguish ethanol drinking so that when NTX injections were terminated, voluntary oral ethanol drinking would be suppressed. Thirty-two male. Long-Evans rats were provided with alternate days of either 8% ethanol solution or water as the sole source of fluid. Intraperitoneal injections of 0, 2.5, or 5.0 mg of NTX hydrochloride were administered on the ethanol days. Following the termination of injections, rats were returned to unrestricted access to water and ethanol and 24-h measurements of fluid intake were recorded. NTX decreased ethanol intake 4 h, but not 24 h, after NTX injections. Despite the consumption of significant amounts of ethanol during NTX treatment, there was no change in voluntary oral ethanol intake patterns after NTX injections were terminated (reinstatement of voluntary ethanol drinking). Thus, NTX's reduction in ethanol intake was limited in duration and did not result in long-term extinction of ethanol drinking behavior.

Alcohol Drinking↗