Luis Heredia

Assessing anxiety in C57BL/6J mice: a pharmacological characterization of the open-field and light/dark tests.

INTRODUCTIONnIn order to assess anxiety in mammals various tests and species are currently available. These current assays measure changes in anxiety-like behaviors. The open-field and the light/dark are anxiety tests based on the spontaneous behavior of the animals, with C57BL/6J mice being a frequently used strain in behavioral studies. However, the suitability of this strain as a choice in anxiety studies has been questioned. In this study, we performed two pharmacological characterizations of this strain in both the open-field and the light/dark tests.nnnMETHODSnWe examined the changes in the anxiety-like behaviors of C57BL/6J mice exposed to chlordiazepoxide (CDP), an anxiolytic drug, at doses of 5 and 10 mg/kg, picrotoxine (PTX), an anxiogenic drug, at doses of 0.5 and 1 mg/kg, and methylphenidate (MPH), a psychomotor stimulant drug, at doses of 5 and 10 mg/kg, in a first experiment. In a second experiment, we tested CDP at 2.5 mg/kg, PTX at 2 mg/kg and MPH at 2.5 mg/kg.nnnRESULTSnResults showed an absence of anxiolytic-like effects of CDP in open-field and light/dark tests. Light/dark test was more sensitive to the anxiogenic effects of PTX than the open-field test. Finally, a clear anxiogenic effect of MPH was observed in the two tests.nnnDISCUSSIONnAlthough C57BL/6J mice could not be a sensitive model to study anxiolytic effects in pharmacological or behavioral interventions, it might be a suitable model to test anxiogenic effects. Further studies are necessary to corroborate these results.

Perinatal exposure to BDE-99 causes learning disorders and decreases serum thyroid hormone levels and BDNF gene expression in hippocampus in rat offspring

Exposure of pregnant women to polybrominated diphenyl ethers (PBDEs) may mean serious health risks. The main goal of the present study was to examine the neurobehavioral changes in rat offspring that were perinatally exposed to one of the most prevalent PBDEs congeners found in humans, 2,2,4,4,5-pentaBDE (BDE-99). Rat dams were exposed to 0, 1 and 2mg/kg/day of BDE-99 from gestation day 6 to post-natal day 21. When pups were weaning, cortex and hippocampal gene expressions of brain-derived neurotrophic factor (BDNF) of the different isoforms of the thyroid hormone (TH) receptors (TRs) were evaluated. Serum TH levels were also determined. The remaining pups were assessed by neurobehavioral testing for learning and memory function. The results showed that maternal transference of BDE-99 produced a delay in the spatial learning task in the water maze test. Moreover, the open-field test revealed a significant dose-response anxiolytic effect. It was also found that the serum levels of triiodothyronine (T3), tetraiiodothyronine (T4) and free-T4 (FT4) decreased. Although no effect on the gene expression of the different isoforms of TRs was observed, the expression of the TH-mediated gene BDNF was down-regulated in the hippocampus. These results indicate a clear signal disruption of TH and reinforce previous studies in which neurotoxic effects of PBDEs in animal research were observed at levels comparable to those found in humans.

Individual housing and handling procedures modify anxiety levels of Tg2576 mice assessed in the zero maze test

The zero maze is an unconditioned anxiety test for mice, in which a number of environmental variables can modify the anxiety levels of the animals. In the present study, we have assessed how individual housing, handling procedure and interaction between individual housing and handling procedure affect the baseline anxiety of mice. Thirty-seven wild type mice and eighteen Tg2576 mice were used (obtained from crossing APPSWE hemizygous male C57BL6/SJL background with C57BL6/SJL female). Wild type mice were randomly assigned to four experimental groups: 1) group housed and unhandled, 2) group housed but handled, 3) individually housed, unhandled, and 4) individually housed and handled. In turn, Tg2576 mice were randomly assigned to two experimental groups: 1) individually housed, unhandled, and 2) individually housed and handled. The results show that individually housed mice exhibited more anxiety-related behaviors over a 5 min testing period than the other experimental groups. Use of the handling procedure was associated with a statistically significant reduction in anxiety-related behaviors among individually housed mice. No effects on anxiety-related behavior levels were observed when group housed animals were handled. When activity levels were significantly increased, a new parameter, Time by Entries, helped to prevent activity from influencing anxiety parameters such as time in the open section of the zero maze test. This knowledge can help to design more efficient experiments without bias from data obtained by means of unconditioned tests.

Age-related effects of X-ray irradiation on mouse hippocampus

Therapeutic irradiation of pediatric and adult patients can profoundly affect adult neurogenesis, and cognitive impairment manifests as a deficit in hippocampal-dependent functions. Age plays a major role in susceptibility to radiation, and younger children are at higher risk of cognitive decay when compared to adults. Cranial irradiation affects hippocampal neurogenesis by induction of DNA damage in neural progenitors, through the disruption of the neurogenic microenvironment, and defective integration of newborn neurons into the neuronal network. Our goal here was to assess cellular and molecular alterations induced by cranial X-ray exposure to low/moderate doses (0.1 and 2 Gy) in the hippocampus of mice irradiated at the postnatal ages of day 10 or week 10, as well as the dependency of these phenomena on age at irradiation. To this aim, changes in the cellular composition of the dentate gyrus, mitochondrial functionality, proteomic profile in the hippocampus, as well as cognitive performance were evaluated by a multidisciplinary approach. Our results suggest the induction of specific alterations in hippocampal neurogenesis, microvascular density and mitochondrial functions, depending on age at irradiation. A better understanding of how irradiation impairs hippocampal neurogenesis at low and moderate doses is crucial to minimize adverse effects of therapeutic irradiation, contributing also to radiation safety regulations.

Behavioral effects of oral subacute exposure to BDE-209 in young adult mice: a preliminary study.

In this study, we examined the effects of an oral subacute exposure to 2,2,3,3,4,4,5,5,6,6-decabromodiphenyl ether (BDE-209) on young adult inbred wild type Tg2576 mice. BDE-209 was administered by gavage at doses of 0 and 20 mg/kg/day dissolved in sunflower oil for 15 days. Two behavioral endpoints were examined: anxiety-activity in a light/dark test and a zero maze test, and learning and spatial memory in a water maze test. Young adult mice exposed to BDE-209 showed a reduction in anxiety levels and a delayed learning in a spatial memory task. Although the results indicated that behavioral effects were present in a young adult exposed population of wild type Tg2576 mice, further studies on chronic exposure to BDE-209 are clearly necessary in order to corroborate these effects.

Neurobehavioral effects of concurrent exposure to cesium-137 and paraquat during neonatal development in mice.

As a result of nuclear power plants accidents such as Chernobyl or Fukushima, some people were exposed to external and internal ionizing radiation (IR). Human brain is highly sensitive to IR during fetal and postnatal period when the molecular processes are not completely finished. Various studies have shown that exposure to low doses of IR causes a higher incidence of cognitive impairment. On the other hand, in industrialized countries, people are daily exposed to a number of toxicant pollutants. Exposure to environmental chemicals, such as paraquat (PQ), may potentiate the toxic effects induced by radiation on brain development. In this study, we evaluated the cognitive effects of concomitant exposure to low doses of internal radiation ((137)Cs) and PQ during neonatal brain development. At the postnatal day 10 (PND10), two groups of mice (C57BL/6J) were exposed to (137)Cs (4000 and 8000 Bq/kg) and/or PQ (7 mg/kg). To investigate the spontaneous behavior, learning, memory capacities and anxiety, behavioral tests were conducted in the offspring at two months of age. The results showed that cognitive functions were not significantly affected when (137)Cs or PQ were administered alone. However, alterations in the working memory and anxiety were detected in mice exposed to (137)Cs combined with PQ.

Behavioral effects in mice of postnatal exposure to low-doses of 137-cesium and bisphenol A

Bisphenol A (BPA) is the most important plasticizer used in many household products such as polycarbonate plastics or epoxy resins. Public and scientific concerns exist regarding the possibility that the neonatal exposure to BPA may contribute to neurobehavioral disorders. On the other hand, there is little information on the effects of low doses of ionizing radiation during critical phases of postnatal brain development, as well as the combination of radiation and environmental chemicals. In this study, C57BL/6J mice were exposed to low doses of internal radiation ((137)Cs), and/or BPA on postnatal day 10 (PND10). At the age of two months, animals were submitted to several tests to assess anxiety, activity, learning, and memory. Results showed that exposure to (137)Cs, alone or in combination with BPA, increased the anxiety-like of the animals without changing the activity levels. Animals exposed to (137)Cs showed impaired learning, and spatial memory, an impairment that was not observed in the groups co-exposed to BPA.

Assessing anxiety in C57BL/6J mice: A pharmacological characterization of the zero maze test

INTRODUCTIONnAnxiety disorders affect the quality of life and good health of millions of people over the world. Because clinical trials are expensive and frequently show high rates of placebo responses, animal models have become an important tool for drug discovery and brain research. Zero maze is a commonly used test to assess anxiety-like levels in mice, being the C57BL/6J strain one of the most widely used. However, only few studies have focused on the pharmacological characterization of this strain in the various anxiety tests.nnnMETHODSnIn this study, we analyzed the changes in the anxiety-like behaviors of mice exposed to chlordiazepoxide (CLZ), as an anxiolytic drug, at doses of 2.5, 5 and 10mg/kg, picrotoxine (PTX), as an anxiogenic drug, at doses of 0.5, 1 and 2mg/kg, and methylphenidate (MPH), as a psychomotor stimulant, at doses of 2.5, 5 and 10mg/kg. Data were hand recorded in situ by an observer and through a camcorder by computer software.nnnRESULTSnResults showed that CLZ and MPH had an anxiogenic effect at the two highest doses. Only CLZ at 2.5mg/kg reduced the anxiety-like levels of mice. Moreover, PTX exerted an anxiogenic effect in mice only at 2mg/kg. The drugs affecting the anxiety-like levels also affected the activity levels. Thus, the differences might have been mediated by changes in activity levels.nnnDISCUSSIONnGlobally, these data demonstrate that the results obtained from the zero maze test are difficult to interpret when the C57BL/6J strain is used. On the other hand, high doses of substances that interact with the GABAergic system, as CLZ, can produce sedation in these mice. In contrast, high doses of GABAA antagonists, as PTX, are necessary if anxiogenic effects should be observed. Further investigations with this strain are necessary in order to corroborate the results of the present study.

Motor and anxiety effects of PNU-282987, an alpha7 nicotinic receptor agonist, and stress in an animal model of Alzheimer's disease.

Behavioral and Psychological Symptoms in Dementia (BPSD) are also seen in Alzheimers disease (AD), being agitation and anxiety common symptoms. Since cholinergic agonists used to be the first pharmacological intervention in AD and this neurotransmission system have been related to cognitive and behavioral symptoms in this serious disease, we here address the question of a possible therapeutic role of PNU-282987 (PNU), an alpha7 nicotinic agonist, in motor activity and anxiety-like behaviors in an animal model of AD. On the other hand, since stress is an unavoidable condition in our daily activities, which activates physiological systems and deregulates bodys homeostasis, we also evaluated the possible precipitating effects of stress in the onset of behavioral deficits in animals with susceptibility to AD. A dose of 0 or 1 mg/kg of PNU was administered to transgenic mice under restrained stress or not, resulting in 4 experimental groups: SAL, PNU, SAL-STR, PNU-STR. The main goal of this study was to evaluate the possible therapeutic role of PNU- 282987 alpha7 nicotinic agonist in motor activity and anxiety-like behaviors, as well as the possible effects of stress in precipitating the onset of behavioral deficits in animals with susceptibility to AD. The present results suggest a differential effect of stress (p=0.011) and PNU (p= 0.009) on anxiety evaluated in an open field depending on genetic vulnerability. Moreover, PNU seems to reverse stress effects in the same apparatus. This was also observed when a more sensitive task such as the zero maze was used.

Effects of an Alpha7 Nicotinic Receptor Agonist and Stress on Spatial Memory in an Animal Model of Alzheimer's Disease

The aim of the present study was to test the effects of PNU-282987 on spatial learning and memory and hippocampal neurogenesis in both intact and chronically stressed transgenic mice. Transgenic mice with susceptibility to Alzheimers disease (AD) under immobilization stress and not-stressed animals receiving 0 and 1u2009mg/kg of PNU-282987 (PNU) were evaluated in a water maze task. The effects of PNU and stress on proliferation of new cells in the hippocampus of these animals were also assessed. The latency to escape the platform was significantly higher in transgenic stressed mice compared to those in the wild stressed group, as well as in transgenic animals without PNU compared to control wild group. On retention of the task, differences emerged on stressed wild animals, PNU wild group, and stressed wild mice receiving PNU. However, no significant differences were detected on new cell proliferation. The results of the present study did not show any impact of stress in acquisition of a spatial task both in wild and transgenic mice. No clear effects of PNU on acquisition of a spatial task in transgenic mice with susceptibility to AD were detected. Although PNU and stress effects were detected on retention of the task in wild animals, no changes were noted in transgenic mice.