Sylvie Gaillet

The involvement of noradrenergic ascending pathways in the stress-induced activation of ACTH and corticosterone secretions is dependent on the nature of stressors

SummaryThe aim of the present study was to explore in male rats the role of the catecholaminergic innervation of the hypothalamus in corticotropic and adrenal responses to different kinds of stress conditions. For this purpose, 6-hydroxydopamine (3 μg in 0.2 μl saline) was stereotaxically and bilaterally infused at two levels of the main noradrenergic ascending brain stem bundle (NAB-X). The efficiency of catecholaminergic denervation of the hypothalamus was checked by measuring noradrenaline concentrations in paraventricular nuclei punches by HPLC and was confirmed by a 86% fall in noradrenaline levels of NAB-X rats killed after the stress experiments. Seven days after lesioning the NAB, sham operated controls and NAB-X lesioned animals were divided into 4 groups and submitted to 4 different stressors, i.e.: 2 min ether vapors (n = 5), 1 h immobilization (n = 7), i.v. histamine (2 mg/kg; n = 7) or i.v. insuline (10 I.U./kg; n = 8) injections. ACTH and corticosterone were measured in blood samples sequentially taken from a chronic carotid cannula, before stress and at short intervals over the 2 following hours. In comparison to the respective control groups, NAB-X dramatically reduced the ACTH response to ether (-78%) and to restraint (-53%) stress whereas the corticosterone response was affected to a lesser extent. In contrast, NAB-X slightly altered these responses in the histamine-treated group, although, surprisingly, the ACTH response tended to decrease and that of corticosterone to increase. Finally, NAB-X provoked a biphasic response to insulineinduced hypoglycemia, with a very early (5 min) rise in ACTH and corticosterone in comparison to the control group, followed by a trend to low hormonal levels up to 120 min. These results strongly suggest a differential involvement of the hypothalamic noradrenergic innervation upon the hypothalamic-pituitary-adrenal axis according to the nature of stress conditions.

Sex differences in learning deficits induced by prenatal stress in juvenile rats

Stress during pregnancy results in neurochemical and behavioral alterations observed throughout adulthood and aging. We here examined the impact of prenatal stress (PS) on cognitive functions in juvenile-4-week-old-rats, focusing on putative sex differences. Dams received an unpredictable 90-min duration contention stress between gestational day E17 and E20. Locomotion and learning ability were examined in offsprings between day P24 and P29 using actimetry, spontaneous alternation in the Y-maze, delayed alternation in the T-maze, and passive avoidance. Both male and female PS rats showed increased activity. In the Y-maze, diminished spontaneous alternation (males: -20%; females: -29%) were seen for PS rats compared to non-PS rats. The number of arm entries was unchanged among groups. In the T-maze, PS rats failed to perform delayed alternation, as shown by equal time spent and number of entries in both the novel and previously explored arms. In the passive avoidance test, PS resulted in significant impairments for female offspring only of both step-through latency and percentage of animals to criterion. PS thus induced severe learning impairments affecting both short-term and long-term memories that could be observed early in lifetime, in 4-week-old, juvenile rats. In addition, marked sex differences were evidenced, particularly in the passive avoidance response that may reflect differential developmental neuroadaptations in precise brain structures.

Differential Early Time Course Activation of the Brainstem Catecholaminergic Groups in Response to Various Stresses

The effects of various stressors (restraint, ether, histamine and insulin-induced hypoglycemia stress) on the early time course activation of the different catecholaminergic (CA) cell groups A1/C1, A2/C2 and locus ceruleus (LC) from the brainstem were studied. The activity of the central noradrenergic neurons was assessed by measuring in tissue punches the 3,4-dihydroxyphenylacetic acid (DOPAC) level, a side metabolite of noradrenaline (NA) and adrenaline biosynthesis that is thought to reflect the activity of NA cells. Short 5 min restraint stress led to an immediate increase of DOPAC level in the three CA groups. In the A1/C1 and A2/C2 groups the maximal increase, respectively +75 and +50%, was already reached at the end of the application of the stress while for the LC the maximum (+84%) was obtained 15 min after the onset of the stress. Return to baseline level was achieved within 2 h. Continuous immobilization stress did not further alter the DOPAC concentration in the LC and the A1/C1 while a progressive increase up to 85% in the A2/C2 group was seen over 20 min. Following a 2-min exposure to ether, DOPAC was increased in all three structures within 5 min. At this time the maximum was already reached in the A1/C1 and LC, respectively +99 and +43%. After histamine or insulin injection DOPAC level increased in the A1/C1 and A2/C2 in the +25/+50% range but was not significantly affected in the LC. In all the stress situations studied the increase in DOPAC level, particularly in the A1/C1 group always preceded or was concomitant to the increase of plasma corticosterone.(ABSTRACT TRUNCATED AT 250 WORDS)

Silver nanoparticles: Their potential toxic effects after oral exposure and underlying mechanisms – A review

Because of their antimicrobial properties, the use of silver nanoparticles (AgNPs) is increasing fast in industry, food, and medicine. In the food industry, nanoparticles are used in packaging to enable better conservation products such as sensors to track their lifetime, and as food additives, such as anti-caking agents and clarifying agents for fruit juices. Nanoemulsions, used to encapsulate, protect and deliver additives are also actively developed. Nanomaterials in foods will be ingested and passed through the digestive tract. Those incorporated in food packaging may also be released unintentionally into food, ending up in the gastrointestinal tract. It is therefore important to make a risk assessment of nanomaterials to the consumer. Thus, exposure to AgNPs is increasing in quantity and it is imperative to know their adverse effects in man. However, controversies still remain with respect to their toxic effects and their mechanisms. Understanding the toxic effects and the interactions of AgNPs with biological systems is necessary to handle these nanoparticles and their use. They usually generate reactive oxygen species resulting in increased pro-inflammatory reactions and oxidative stress via intracellular signalling pathways. Here, we mainly focus on the routes of exposure of AgNPs, toxic effects and the mechanisms underlying the induced toxicity.

Dietary exposure to silver nanoparticles in Sprague–Dawley rats: Effects on oxidative stress and inflammation

Due to undesirable hazardous interactions with biological systems, we evaluated the effect of silver nanoparticles (AgNPs) intake on oxidative stress and inflammation. Rats received for 81 days a standard diet (Controls) or a standard diet plus 500 mg/d/kg BW AgNPs. We assayed plasma lipids, and oxidative stress was assessed by measuring liver and heart superoxide anion production (O₂°⁻) and liver malondialdehyde levels (MDA). Antioxidant status was appraised using plasma paraoxonase activity (PON), plasma antioxidant capacity (PAC) and liver superoxide dismutase activity (SOD). Liver inflammatory cytokines TNFα and IL-6 levels and plasma alanine aminotransferase (ALT) were assayed. Compared with Controls, AgNPs raised cholesterolemia (9.5%), LDL-cholesterol (30%), and lowered triglycerides (41%). They also increased liver (30%) and cardiac (41%) O₂°⁻ production, reduced PON activity (15%) and raised liver TNFα (9%) and IL-6 (∼12%). Plasma ALT activity rose (12%) after treatment with AgNPs. However, PAC and liver MDA and SOD activity were unchanged. These features indicate that exposure to 500 mg/d/kg BW of AgNPs results in liver damage by a dysregulation of lipid metabolism, highlighting liver and heart as the most sensitive organs to the deleterious effects. Our findings also demonstrate for the first time the oxidative and inflammatory effects of dietary AgNPs.

Cafeteria diet induces obesity and insulin resistance associated with oxidative stress but not with inflammation: improvement by dietary supplementation with a melon superoxide dismutase

Oxidative stress is involved in obesity. However, dietary antioxidants could prevent oxidative stress-induced damage. We have previously shown the preventive effects of a melon superoxide dismutase (SODB) on oxidative stress. However, the mechanism of action of SODB is still unknown. Here, we evaluated the effects of a 1-month curative supplementation with SODB on the liver of obese hamsters. Golden Syrian hamsters received either a standard diet or a cafeteria diet composed of high-fat, high-sugar, and high-salt supermarket products, for 15 weeks. This diet resulted in insulin resistance and in increased oxidative stress in the liver. However, inflammatory markers (IL-6, TNF-α, and NF-κB) were not enhanced and no liver steatosis was detected, although these are usually described in obesity-induced insulin resistance models. After the 1-month supplementation with SODB, body weight and insulin resistance induced by the cafeteria diet were reduced and hepatic oxidative stress was corrected. This could be due to the increased expression of the liver antioxidant defense proteins (manganese and copper/zinc superoxide dismutase, catalase, and glutathione peroxidase). Even though no inflammation was detected in the obese hamsters, inflammatory markers were decreased after SODB supplementation, probably through the reduction of oxidative stress. These findings suggest for the first time that SODB could exert its antioxidant properties by inducing the endogenous antioxidant defense. The mechanisms underlying this induction need to be further investigated.

Lesions of the Afferent Catecholaminergic Pathways Inhibit the Temporal Activation of the CRH and POMC Gene Expression and ACTH Release Induced by Human Interleukin-1β in the Male Rat

A number of recent studies have suggested that interleukin-1beta (IL-1beta) is a major mediator contributing to the recruitment of the hypothalamo-pituitary-adrenal (HPA) axis following infectious aggressions. Central catecholamines modulate the response of the HPA axis. To investigate the importance of the afferent catecholaminergic pathways in a pathophysiological situation, we used the intraperitoneal (i.p.) IL-1beta injection (mimicking peripheral infections) and we investigated the effects on the HPA responses to IL-1beta of bilateral neurotoxic (6-OHDA) deletion of the ventral noradrenergic ascending bundle (VNAB-X). The VNAB is an essential stimulating pathway linking the brainstem and the paraventricular nucleus (PVN). We determined the time courses of a number of HPA variables up to 240 min after i.p. injection of IL-1beta. We followed: plasma ACTH and corticosterone (CORT) concentrations, AP POMC nuclear primary RNA transcripts, AP POMC nuclear intermediate transcript RNA, AP POMC cytoplasmic mRNA, and hypothalamus (HT) CRH cytoplasmic mRNA. Compared to sham-lesioned male rats, VNAB-X animals displayed: (1) a reduced increase in plasma ACTH, and to a lesser extent in CORT throughout the experimental period with a 85% inhibition at the peak (90 min); (2) an increase in AP POMC primary nuclear transcript and in AP POMC nuclear intermediate transcript RNAs which last 60 min, instead of sustained significantly higher levels up to 240 min; (3) a similar, although reduced inhibition in the corresponding POMC cytoplasmic mRNA; (4) an almost complete abolishment of the marked biphasic rise in HT CRH mRNA. In conclusion, activation of the HPA axis by peritoneal IL-1beta challenge involves CRH-producing neurons, and afferent catecholaminergic innervation of the PVN plays a crucial role in the signaling machinery linking the peritoneal aggression to the HPA axis.

Vineatrol and Cardiovascular Disease: Beneficial Effects of a Vine-Shoot Phenolic Extract in a Hamster Atherosclerosis Model

We evaluated the effect of the intake of a grapevine-shoot phenolic extract (Vineatrol 30) on early atherosclerosis in hamsters fed a hyperlipidic diet. Golden Syrian hamsters received for 13 weeks either a standard diet, a high-fat (HF) diet, or the HF diet plus Vineatrol 30 at 0.04, 0.2, or 1.0 mg/(kg body weight/d). We measured plasma lipids and glucose, insulin, leptin and adiponectin, as well as liver TNF-α and IL-6 levels. Oxidative stress was assessed by measuring plasma paraoxonase activity (PON) and liver superoxide anion production (O(2)(•-)). The aortic fatty streak area (AFSA) was also determined. In comparison with HF group, we demonstrated that the highest dose of Vineatrol 30 was capable of decreasing AFSA (67%), insulinemia (40%), and leptinemia (8.7%), which were increased by the HF diet. We also showed increased O(2)(•-) production (35%) and a rise in levels of the liver proinflammatory cytokines TNF-α (22%) and IL-6 (21%), accompanied by a fall in PON activity (56%) due to the HF diet versus the standard diet. In contrast, except plasma adiponectin levels that are not changed, Vineatrol 30 treatment lowered AFSA (67%), O(2)(•-) production (36%), insulin resistance (42%), leptinemia (9%), liver TNF-α (18%) and IL-6 (15%), while it rose PON activity (29%). These findings demonstrate the preventive effects of polyphenols present in Vineatrol 30 in managing cardiovascular, metabolic, and inflammatory risk factors.

Complex catecholaminergic modulation of the stimulatory effect of interleukin-1β on the corticotropic axis

We recently showed that bilateral neurotoxic microlesions (6-OH-DA) of the ventral noradrenergic ascending bundle (VNAB-X) at stereotaxic coordinates that blocked corticotropic stress responses did not affect the ACTH surge after bilateral intra-paraventricular (i.PVN) injections of interleukin-1 beta (IL-1 beta), and that lesioning at these stereotaxic coordinates obliterated the dorsal axonal populations of the VNAB (dVNAB-X), but spared the bundles most ventral axons (vVNAB). The present study compares the effects of IL-1 beta given i.PVN (2 x 5 ng) of intra-arterially (i.a.) (100 ng) on plasma ACTH in rats with bilateral 6-OH-DA microlesions placed in the dVNAB or the vVNAB, or in an intermediary central position (cVNAB-X). Unlike our previous results, in which dVNAB-X did not alter the biphasic ACTH response to i.PVN IL-1 beta, both vVNAB-X and cVNAB-X reduced by 50-75% the early and delayed ACTH surges which are typical of the i.PVN route. On the other hand the swift monophasic ACTH surge usually occurring after an i.a. injection of IL-1 beta was 65% smaller after dVNAB-X, but was doubled after vVNAB-X or cVNAB-X. Hence, the release of ACTH after both i.PVN or i.a. IL-1 beta requires brainstem afferences conveyed to the hypothalamus by the VNAB. However, the VNAB appears to include at least two functionally different subsets of axons, the roles of which in the ACTH response to IL-1 beta depend on the route by which the cytokine is given.

Transient increase in the high affinity [3H]-l-glutamate uptake activity during in vitro development of hippocampal neurons in culture

The glial GLAST and GLT-1 glutamate transporters are transiently expressed in hippocampal neurons as shown by immunocytochemistry (Plachez et al., 2000. J. Neurosci. Res., 59, 587-593). In order to test if this transient expression is associated to a transient glutamate uptake activity, [3H]-glutamate uptake was studied during the in vitro development of embryonic hippocampal neurons cultured in a defined (serum free) medium. In these cultures, the ratio of the number of glial cells to the number of neurons increased from 1.7 to 11.3% during the first 10 days of culture, while 77% of the neurons died. The number of neurons then remains stable up to 23 days of culture. The initial glutamate uptake velocity at 20 and 200 microM [3H]-glutamate usually increased about five times between 1 and 10 days in vitro (DIV). Interestingly, at 2 microM [3H]-glutamate, the uptake initial velocity showed a biphasic pattern, with a transient peak between 1 and 6 DIV, the maximum being reached at 2 DIV and a delayed regular increase from 8 to 23 DIV. The concentration-dependent curves were best fitted with two saturable sites high and low affinities, at both 2 and 10 DIV. To pharmacologically characterize the transient increased glutamate uptake activity, four uptake inhibitors, L-threo-3-hydroxy-aspartic acid (THA), L-trans-pyrrolidine-2,4-dicarboxylic acid (L-trans-2,4-PDC), dihydrokainate (DHK), and DL-threo-beta-benzyloxyaspartate (TBOA) were tested. THA, L-trans-2,4-PDC and DL-TBOA inhibited glutamate uptake both at 2 and 10 DIV, while the GLT-1 selective uptake inhibitor DHK neither strongly affected the uptake at 2, nor at 10 DIV. These data indicated that, besides the regular increase in the glial-dependent glutamate uptake activity, a transient high-affinity, DHK insensitive, glutamate transport activity in hippocampal neurons in culture is present. This latter activity could potentially be related to the transient expression of the glial GLAST transporter in neurons.