Variations in maternal care associated with differences in female rat reproductive behavior in a group-mating environment.

Maternal care influences the development of sexual behavior in pair mating rats, under laboratory conditions. This study examined the effect of variations in maternal care in a group-mating condition. Groups of two low and two high licking/grooming (LG) female offspring mated with two males in a large pacing chamber for 36 hr. Sexual behaviors were scored for the first 15 vaginal-cervical stimulations (VCS) and the entire 36 hr. Low LG females spent more time mating, required more time to receive an intromission after entering the male compartment. They also received more ejaculations compared to high LG females during the first 15 VCS. This difference disappeared as mating continued. Males were more responsive to high than low females. No pregnancy rate difference was seen between the two female phenotypes, demonstrating that variation in maternal care received results in two mating strategies that are both reproductively successful under group-mating conditions.

Resolving the contributions of the membrane-bound and periplasmic nitrate reductase systems to nitric oxide and nitrous oxide production in Salmonella enterica serovar Typhimurium.

The production of cytotoxic nitric oxide (NO) and conversion into the neuropharmacological agent and potent greenhouse gas nitrous oxide (N2O) is linked with anoxic nitrate catabolism by Salmonella enterica serovar Typhimurium. Salmonella can synthesize two types of nitrate reductase: a membrane-bound form (Nar) and a periplasmic form (Nap). Nitrate catabolism was studied under nitrate-rich and nitrate-limited conditions in chemostat cultures following transition from oxic to anoxic conditions. Intracellular NO production was reported qualitatively by assessing transcription of the NO-regulated genes encoding flavohaemoglobin (Hmp), flavorubredoxin (NorV) and hybrid cluster protein (Hcp). A more quantitative analysis of the extent of NO formation was gained by measuring production of N2O, the end-product of anoxic NO-detoxification. Under nitrate-rich conditions, the nar, nap, hmp, norV and hcp genes were all induced following transition from the oxic to anoxic state, and 20% of nitrate consumed in steady-state was released as N2O when nitrite had accumulated to millimolar levels. The kinetics of nitrate consumption, nitrite accumulation and N2O production were similar to those of wild-type in nitrate-sufficient cultures of a nap mutant. In contrast, in a narG mutant, the steady-state rate of N2O production was ~30-fold lower than that of the wild-type. Under nitrate-limited conditions, nap, but not nar, was up-regulated following transition from oxic to anoxic metabolism and very little N2O production was observed. Thus a combination of nitrate-sufficiency, nitrite accumulation and an active Nar-type nitrate reductase leads to NO and thence N2O production, and this can account for up to 20% of the nitrate catabolized.