Contextual fear conditioning in maternal separated rats: the amygdala as a site for alterations.

The first 2 weeks of life are a critical period for neural development in rats. Repeated long-term separation from the dam is considered to be one of the most potent stressors to which rat pups can be exposed, and permanently modifies neurobiological and behavioral parameters. Prolonged periods of maternal separation (MS) usually increase stress reactivity during adulthood, and enhance anxiety-like behavior. The aim of this study was to verify the effects of maternal separation during the neonatal period on memory as well as on biochemical parameters (Na(+), K(+)-ATPase and antioxidant enzymes activities) in the amygdala of adult rats. Females and male Wistar rats were subjected to repeated maternal separation (incubator at 32 °C, 3 h/day) during postnatal days 1-10. At 60 days of age, the subjects were exposed to a Contextual fear conditioning task. One week after the behavioral task, animals were sacrificed and the amygdala was dissected for evaluation of Na(+), K(+)-ATPase and antioxidant enzymes activities. Student-t test showed significant MS effect, causing an increase of freezing time in the three exposures to the aversive context in both sexes. Considering biochemical parameters Student-t test showed significant MS effect causing an increase of Na(+), K(+)-ATPase activity in both sexes. On the other hand, no differences were found among the groups on the antioxidant enzymes activities [superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT)] in male rats, but in females, we found a significant MS effect, causing an increase of CAT activity and no differences were found among the groups on SOD and GPx activities. Our results suggest a role of early rearing environment in programming fear learning and memory in adulthood. An early stress experience such as maternal separation may increase activity in the amygdala (as pointed by the increased activity of Na(+), K(+)-ATPase), affecting behaviors related to fear in adulthood, and this effect could be task-specific.

Long-lasting effects of maternal separation on an animal model of post-traumatic stress disorder: effects on memory and hippocampal oxidative stress.

Adverse early life events, such as periodic maternal separation, may alter the normal pattern of brain development and subsequently the vulnerability to a variety of mental disorders in adulthood. Patients with a history of early adversities show higher frequency of post-traumatic stress disorder (PTSD). This study was undertaken to verify if repeated long-term separation of pups from dams would affect memory and oxidative stress parameters after exposure to an animal model of PTSD. Nests of Wistar rats were divided into intact and subjected to maternal separation (incubator at 32°C, 3 h/day) during post-natal days 1-10. When adults, the animals were subdivided into exposed or not to a PTSD model consisting of exposure to inescapable footshock, followed by situational reminders. One month after exposure to the shock, the animals were exposed to a memory task (Morris water maze) and another month later animals were sacrificed and DNA breaks and antioxidant enzymes activities were measured in the hippocampus. Rats exposed to shock or maternal separation plus shock showed long-lasting effects on spatial memory, spending more time in the opposite quadrant of the water maze. This effect was higher in animals subjected to both maternal separation and shock. Both shock and maternal separation induced a higher score of DNA breaks in the hippocampus. No differences were observed on antioxidant enzymes activities. In conclusion, periodic maternal separation may increase the susceptibility to the effects of a stressor applied in adulthood on performance in the water maze. Increased DNA breaks in hippocampus was induced by both, maternal separation and exposure to shock.

Maternal depression model: long-lasting effects on the mother following separation from pups.

This study was carried out to ascertain the effects of maternal separation (3 h per day) of mothers from their pups in the neonatal period in rats, which has been suggested to induce a depressive-like state, would have long lasting effects on different parameters including hippocampal Na(+), K(+)-ATPase activity, NO production, free radical production and antioxidant enzymes activities in dams. Fourty-eight Wistar rats were divided into 3 groups: control, brief separation (10 min) and long separation (3 h). The neonatal interventions were done on postpartum days 1-10. At 35 days post-partum the dams were killed and the hippocampal Na(+), K(+)-ATPase activity were measured, as well as the activity of the antioxidant enzymes catalase, glutathione peroxidase, superoxide dismutase, free radicals production, and the production of nitric oxide. Hippocampal Na(+), K(+)-ATPase activity was decreased in the brief separated group and in dams subjected to 3 h separation from their pups. A reduction in nitric oxide levels in the hippocampus in dams of the long separated group was also observed. It is concluded that the withdrawal of pups from their mothers make the mothers more susceptible to the development of neurochemical alterations that could be related to depressive features.

Effects of chronic restraint stress and 17-ß-estradiol replacement on oxidative stress in the spinal cord of ovariectomized female rats.

Previous studies have shown sex-specific oxidative changes in spinal cord of rats submitted to chronic stress, which may be due to gonadal hormones. Here, we assessed total radical-trapping potential (TRAP), superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities and lipid peroxidation (evaluated by the TBARS test) in the spinal cord of ovariectomized (OVX) female rats. Female rats were subjected to OVX, and half of the animals received estradiol replacement. Animals were subdivided into controls and chronically stressed (for 40 days). Our findings demonstrate that chronic stress decreased TRAP, and increased SOD activity in spinal cord homogenates from ovariectomized female rats and had no effect on GPx activity. On the other hand, groups receiving 17ß-estradiol replacement presented a decreased GPx activity, but no alteration in TRAP and in SOD activity. No differences in the TBARS test were found in any of the groups analyzed. In conclusion, our results support the idea that chronic stress induces an imbalance between SOD and GPx activities, additionally decreasing TRAP. Estradiol replacement did not reverse the effects of chronic stress, but induced a decrease in GPx activity. Therefore, estradiol replacement in ovariectomized chronically stressed rats could make the spinal cord more susceptible to oxidative injury.

Effect of chronic administration of tamoxifen and/or estradiol on feeding behavior, palatable food and metabolic parameters in ovariectomized rats.

Tamoxifen (TAM) is a selective estrogen receptor modulator (SERM) used in the treatment of breast cancer; however many women complain of weight gain during TAM treatment. The anorectic effects of estradiol (E) and TAM are well known, although the effects of E on the consumption of palatable food are controversial and there is no information regarding the effects of TAM on palatable food consumption. The aim of this study was to investigate the effects of chronic treatment with estradiol and/or tamoxifen on feeding behavior in ovariectomized rats exposed to standard chow and palatable foods (Froot Loops® or chocolate). Additionally, parameters such as body weight, uterine weight, lipid profile and plasma glucose were also measured. Wistar rats were ovariectomized (OVX) and subsequently injected (ip.) for 40 days with: E, TAM, E+TAM or vehicle (OVX and SHAM - controls). Behavioral tests were initiated 25 days after the start of treatment. Froot Loops® consumption was evaluated in a novel environment for 3 min. Standard chow intake was evaluated for two days and chocolate intake for 7 days in the home cage in a free choice model (chocolate or standard chow). Rats injected with E, TAM and E+TAM groups showed a reduction in body weight and standard chow intake, compared with control groups. With regard to palatable food intake, the E, TAM and E+TAM groups demonstrated increased consumption of Froot Loops®, compared with the SHAM and OVX groups. In contrast, all groups increased their consumption of chocolate, compared with standard chow; however the E group consumed more chocolate than the OVX, TAM and E+TAM groups. Despite these differences in chocolate consumption, all groups showed the same caloric intake during the chocolate exposure period; however the TAM and E+TAM groups presented decreased body weight. Treatment with estradiol and tamoxifen showed a favorable lipid profile with low levels of TC, LDL, LDL/HDL ratio and lower levels of plasma glucose. The E group presented high levels of TG and HDL, when compared with the TAM and E+TAM groups. Taken together, results suggest that TAM acted in an estrogen-like manner on the majority of parameters analyzed. However, tamoxifen acts in a different manner depending on the type of palatable food and the exposure. In addition, the TAM group demonstrated weight loss, compared with other groups independently of the type of food presented (palatable food or standard chow), showing a low caloric efficiency.

Caloric restriction improves basal redox parameters in hippocampus and cerebral cortex of Wistar rats.

Caloric restriction (CR) has been shown to either decrease or prevent the progression of several age-related pathologies. In previous work, we demonstrated that CR modulates astrocyte functions, suggesting that CR may exert neuroglial modulation. Here, we investigated the effects of CR on hippocampal (Hc) and cortical (Cx) oxidative stress parameters of male Wistar rats. Our results showed that CR-fed rats had 17% less body weight gain after 12 weeks of treatment. CR improved locomotion performance, increased glutathione levels and decreased glutathione peroxidase activity and the production of reactive oxygen species. However, no changes were observed in lipid peroxidation, nitric oxide content and catalase activity. Single cell gel electrophoresis assay (comet assay) revealed a reduction in the extent of basal DNA damage upon CR. Our data suggest that dietary CR could induce both hippocampal and cortical modulation resulting in metabolic changes and as a consequence, significant improvement of cellular defense-associated parameters.

Could preference for palatable foods in neonatally handled rats alter metabolic patterns in adult life?

Previous studies indicate that, in adulthood, neonatally handled rats consume more sweet food than nonhandled rats. The aim of the present study was to assess the effects of the chronic exposure to a palatable diet (chocolate) in adult neonatally handled rats. We measured the consumption of foods (standard lab chow and chocolate), body weight gain, abdominal fat deposition, and levels of plasma lipids, glucose, insulin, and corticosterone in adult neonatally handled (10 min/d, first 10 d of life) and nonhandled rats. We found an increased intake of chocolate in handled rats, but this consumption decreased over time. Handled male animals exhibited higher body weight, higher caloric efficiency, and lower triglyceride levels. Nonhandled females that were exposed long-term to the highly caloric diet had increased abdominal fat deposition compared with handled females. Overall female rats had increased abdominal fat deposition, higher total cholesterol and glucose levels, and lower insulin in comparison with males. Interestingly, chocolate consumption diminished the weight of the adrenal glands in both handled and nonhandled animals. These findings suggest that neonatal handling induces a particular metabolic pattern that is sex specific.