Commencement Of Stress Research Articles

Central noradrenergic depletion by DSP-4 prevents stress-induced memory impairments in the object recognition task

Environmental stress produces adverse affects on memory in humans and rodents. Increased noradrenergic neurotransmission is a major component of the response to stress and noradrenaline (NA) plays an important role in modulating processes involved in learning and memory. The present study investigated the effect of NA depletion on stress-induced changes on memory performance in the mouse. Central NA depletion was induced using the selective neurotoxin N-(2-chloroethyl)- N-ethyl-2 bromobenzylamine (DSP-4) and verified by high performance liquid chromatography (HPLC). A novel cage stress procedure involving exposure to a new clean cage for 1 h per day, 4 days per week for 4 weeks, was used to produce stress-induced memory deficits measured using the object recognition task. 50 mg/kg DSP-4 produced large and sustained reductions in NA levels in the frontal cortex and hippocampus measured 24 h, 1 week and 5 weeks after treatment. Four weeks of exposure to novel cage stress induced a memory deficit in the object recognition task which was prevented by DSP-4 pre-treatment (50 mg/kg 1 week before the commencement of stress).These findings indicate that chronic environmental stress adversely affects recognition memory and that this effect is, in part, mediated by the noradrenergic stress response. The implication of these findings is that drugs targeting the noradrenergic system to reduce over-activity may be beneficial in the treatment of stress-related mental disorders such as post-traumatic stress disorder or anxiety in which memory is affected.

Aluminum stress induces up-regulation of an efficient antioxidant system in the Al-tolerant maize line but not in the Al-sensitive line

The response of the antioxidant enzymes, superoxide dismutase (SOD; EC 1.15.1.1) and peroxidase (POD; EC 1.11.1.7), to Aluminum (Al) stress was studied in roots of two inbred lines of maize ( Zea mays L.) differing in their tolerance to Al. In addition, the production of malondialdehyde (MDA) was measured to evaluate the level of lipid peroxidation as well as the accumulation of proline (Pro) and carbohydrates under 72 h Al stress. Roots of Al (0, 120, 240, 360 and 480 μM, at pH 4.2) -treated plants were sampled at various times (12, 24, 48, 72 h) after commencement of stress. A major difference in the antioxidant enzymes between the two maize lines associated with Al tolerance was observed after 24 h of Al exposure. A gradual increase in the membrane lipid peroxidation in Al-stressed root of the susceptible maize line was accompanied by decreased activities of the antioxidant enzymes SOD and POD. In contrast, increased activities of the SOD and POD were found in Al-treated roots of the tolerant maize line, in which the level of membrane lipid peroxidation remained almost unchanged. After 72 h exposure to 480 μM Al the accumulation of Al in roots was almost from 90 times (tolerant) to 140 times (sensitive) than the control (without Al), while at the same time Al treatment resulted in 2.2 to 2.5-fold (at 240, 360 and 480 μM Al) increased Pro content in the roots of the tolerant line compared to 0 μM Al. Yet, 72 h exposure to 480 μM Al increased 1.7-fold the carbohydrate concentration in the roots of the Al tolerant maize line VA-22 while in the sensitive line A 4/67 remained almost unchanged. These data provide evidence of an internal mechanism of tolerance that increase the antioxidant system activity in order to limit cellular damages and possibly linked to the Al tolerance of the maize line VA-22. Analyses of the 12, 24, 48, and 72 h POD and SOD isoforms showed that in the Al-tolerant maize plants the anionic POD isoforms A 1, A 3 and A 4 and the SOD isoforms SOD 1 and SOD 2 were induced by increased Al-stress. It seemed that in the Al tolerant maize line, the anionic POD isoforms A 1, A 3 and A 4 and the SOD isoforms SOD 1 and SOD 2 were required for adaptation as the oxidant level increased by the increased Al stress. Our results suggest that Al toxicity may be mediated by oxidative stress and that the better protection of the Al tolerant maize roots from Al-induced oxidative damage results, at least partially, from the increased activity of their antioxidative system.

Seasonal differences in the effect of isolation and restraint stress on the luteinizing hormone response to gonadotropin-releasing hormone in hypothalamopituitary disconnected, gonadectomized rams and ewes.

Stress responses are thought to act within the hypothalamopituitary unit to impair the reproductive system, and the sites of action may differ between sexes. The effect of isolation and restraint stress on pituitary responsiveness to GnRH in sheep was investigated, with emphasis on possible sex differences. Experiments were conducted during the breeding season and the nonbreeding season. In both experiments, 125 ng of GnRH was injected i.v. every 2 h into hypothalamopituitary disconnected, gonadectomized rams and ewes on 3 experimental days, with each day divided into two periods. During the second period on Day 2, isolation and restraint stress was imposed for 5.5 h. Plasma concentrations of LH and cortisol were measured in samples of blood collected from the jugular vein. In the second experiment (nonbreeding season), plasma concentrations of epinephrine, norepinephrine, 3,4-dihydroxyphenylalanine, and 3,4-dihydroxyphenylglycol were also measured. In both experiments, there was no effect of isolation and restraint stress on plasma concentrations of cortisol in either sex. During the breeding season, there was no effect of isolation and restraint stress on plasma concentrations of LH in either sex. During the nonbreeding season, the amplitude of the first LH pulse after the commencement of stress was significantly reduced (P < 0.05) in rams and ewes. In the second experiment, during stress there was a significant increase (P < 0.05) in plasma concentrations of epinephrine in rams and ewes and significantly higher (P < 0.05) basal concentrations of norepinephrine in ewes than in rams. These results suggest that in sheep stress reduces responsiveness of the pituitary gland to exogenous GnRH during the nonbreeding season but not during the breeding season, possibly because of mediators of the stress response other than those of the hypothalamus-pituitary-adrenal gland axis.

Effects of soil water deficit at different growth stages on rice growth and yield under upland conditions. 1. Growth during drought

Upland rice can be subject to drought at any time during growth, and responses of various growth processes to water stress may depend on the timing of drought in relation to crop growth stages. In two experiments, rice plants at three or four growth stages were subjected to drought periods of 23–35 days to examine the response of shoot dry matter (SDM) production and associated processes to water stress. Young plants, 33 days old at the commencement of stress, maintained high leaf water potential during the stress period because of the low demand for water. Radiation-use efficiency (i.e. SDM production per unit intercepted radiation) of the young plants in the drought treatment was similar to that in the irrigated control, but SDM production was reduced by 71% because of 68% reduction in radiation interception. The young plants extracted water more slowly than older plants immediately after stress was imposed, whereas the total water extraction during the stress period was not significantly different from that of the older plants. The young plants produced less SDM than the older plants (90 versus 300 g m −2), and hence had lower water-use efficiency (i.e. SDM production per unit water used 1.4 versus 4.2 g kg −1). During early growth stages, root length growth was very sensitive to soil water deficit. When stress developed in the older plants with the canopy intercepting greater than about 60% of full solar radiation, reduction in SDM production was mostly due to reduced radiation-use efficiency (1.2 versus 2.3 g MJ −1). The plants extracted water more rapidly and from deeper soils, and leaf water potential decreased rapidly with the large demand for transpiration water. The results therefore show that rice responds to drought in a manner depending on the stage of canopy development.

An immediate kidney response to acute stress.

LITTLE is known about non-specific changes in the kidney structure of animals exposed to acute stress. Selye (1937) frequently observed cloudy swelling in the renal tubules of rats during the alarm reaction. Leduc and Guillemin (1949) reported that while the dry weight of most organs is diminished during acute cold exposure, that of the kidney, the heart and the brain remains constant. In the course of a nutritional study of the alarm reaction we observed that the kidney, like the adrenal, reacts to every type of acute stress with an immediate rise of its weight (Constantinides 1950). The increment becomes measurable as rapidly as 20 hours after commencement of stress but it is of a small order of magnitude. The data of the present paper show that a renal enlargement is an integral part of the alarm reaction,