Anti-HIV drugs promote ß-amyloid deposition and impair learning and memory in BALB/c mice.

OBJECTIVES: Growing evidence suggested that antiretroviral (ARV) drugs may promote amyloid beta (Aß) accumulation in HIV-1-infected brain and the persistence of HIV-associated neurocognitive disorders (HANDs). It has also been shown that lipid peroxidation upregulates ß-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) expression and subsequently promotes Aß peptide production. In the present study, we examined whether chronic exposure to the anti-HIV drugs tenofovir disoproxil fumarate (TDF) and nevirapine induces lipid peroxidation thereby promoting BACE1 and Aß generation and consequently impair cognitive function in mice. METHODS: TDF or nevirapine was orally administered to female BALB/c mice once a day for 8 weeks. On the 7th week of treatment, spatial learning and memory were assessed using the Morris water maze test. The levels of lipid peroxidation, BACE1, amyloid ß 1-42 (Aß1-42) and Aß deposits were measured in the hippocampal tissue upon completion of treatment. RESULTS: Chronic administration of nevirapine induced spatial learning and memory impairment in the Morris water maze test, whereas TDF did not have an effect. TDF and nevirapine administration increased hippocampal lipid peroxidation and Aß1-42 concentration. Nevirapine further upregulated BACE1 expression and Aß deposits. CONCLUSION: Our results suggest that chronic exposure to TDF and nevirapine contributes to hippocampal lipid peroxidation and Aß accumulation, respectively, as well as spatial learning and memory deficits in mice even in the absence of HIV infection. These findings further support a possible link between ARV drug toxicity, Aß accumulation and the persistence of HANDs.

Exposure to prenatal stress has deleterious effects on hippocampal function in a febrile seizure rat model.

Prenatal stress has been shown to result in the development of a number of neurological disorders in the offspring. Most of these disorders are a result of an altered HPA axis resulting in higher than normal glucocorticoid levels in the affected neonate. This leaves the offspring prone to immune challenges. Therefore the aim of the present study was to investigate the effects of prenatal stress and febrile seizures on behavior and hippocampal function. Pregnant dams were exposed to restraint stress during the third trimester. Following birth, febrile seizures were induced in two week old pups using lipopolysaccharide and kainic acid. A week later, anxiety-like behavior and navigational ability was assessed. Trunk blood was used to measure basal corticosterone concentration and hippocampal tissue was collected and analyzed. Our results show that exposure to prenatal stress increased basal corticosterone concentration. Exposure to prenatal stress exacerbated anxiety-like behavior and impaired the rat's navigational ability. Exposure to prenatal stress resulted in reduced hippocampal mass that was exacerbated by febrile seizures. However, exposure to febrile seizures did not affect hippocampal mass in the absence of prenatal stress. This suggests that febrile seizures are exacerbated by exposure to early life stressors and this may lead to the development of neurological symptoms associated with a malfunctioning hippocampus.

Exercise partly reverses the effect of maternal separation on hippocampal proteins in 6-hydroxydopamine-lesioned rat brain.

Animals subjected to maternal separation stress during the early stages of development display behavioural, endocrine and growth factor abnormalities that mirror the clinical findings in anxiety/depression. In addition, maternal separation has been shown to exacerbate the behavioural deficits induced by 6-hydroxydopamine (6-OHDA) in a rat model of Parkinson's disease. In contrast, voluntary exercise reduced the detrimental effects of 6-OHDA in the rat model. The beneficial effects of exercise appeared to be largely due to compensation in the non-lesioned hemisphere. The aim of the present study was to investigate whether voluntary exercise for 3 weeks could reverse the effects of maternal separation in rats challenged with the neurotoxin 6-OHDA infused into the medial forebrain bundle after 1 week of exercise, at postnatal day 60. The rats were killed 2 weeks later, at postnatal day 74. Their brains were dissected and the hippocampus rapidly removed for proteomic analysis by isobaric tagging (iTRAQ) and quantification of peptides by matrix-assisted laser desorption/ionization tandem mass spectrometry (MALDI-MS/MS). Maternal separation upregulated hippocampal proteins functionally involved in energy metabolism (nucleoside diphosphate kinase B, enolase and triosephosphate isomerase) and synaptic plasticity (α-synuclein, tenascin-R, Ba1-667, brevican and neurocan core protein) in the non-lesioned hemisphere. Exercise reversed many of these changes by downregulating the levels of hippocampal proteins functionally associated with energy metabolism (nucleoside diphosphate kinase B, enolase and triosephosphate isomerase) and synaptic plasticity (α-synuclein, tenascin-R, Ba1-667, brevican and neurocan core protein) in the non-lesioned hemisphere of rats subjected to maternal separation. Exercise and maternal separation therefore appeared to have opposing effects on the hippocampus in the non-lesioned hemisphere of the rat brain. Exercise seemed partly to reverse the effects of maternal separation stress on these proteins in the non-lesioned hemisphere. The partial reversal of maternal separation-induced proteins by exercise in the non-lesioned side sheds some insight into the mechanism by which exercise alters the molecular role players involved in determining the consequences of early life stress.

Early maternal separation leads to down-regulation of cytokine gene expression.

Exposure to stressors may lead to subsequent alterations in the immune response. The precise mechanisms underlying such vulnerability are poorly understood, but may be hypothesized to include changes in cytokine systems. Maternal separation was used as a model of exposure to early life stressors. Subsequent cytokine gene expression was studied using a cytokine gene expression array. Maternal separation resulted in significant down-regulation of the expression of 6 cytokine genes; chemokine ligand 7, chemokine receptor 4, interleukin 10, interleukin-1beta, interleukin 5 receptor alpha and integrin alpha M. Specific cytokines may be involved in mediating the effects of early adversity on subsequent immunosuppression. Further work is needed to delineate fully the relationship between early adversity, immune alterations, and behavioural changes.

Maternal separation alters nerve growth factor and corticosterone levels but not the DNA methylation status of the exon 1(7) glucocorticoid receptor promoter region.

Separating rat pups from their mothers during the early stages of life is an animal model commonly used to study the development of psychiatric disorders such as anxiety and depression. The present study investigated how soon after the termination of the maternal separation period behavioural and neuroendocrine abnormalities relevant to above-mentioned illnesses would manifest. Sprague Dawley rat pups were subjected to maternal separation (3 h per day from postnatal day 2 through 14) and their behaviour and HPA axis activity determined 7 d later. We also measured nerve growth factor levels in their hippocampi and assessed the DNA methylation status of the promoter region of exon 1(7) of the glucocorticoid receptor in this brain region. As early as 7 d after the termination of the adverse event, a change in behaviour was observed that was associated with increased plasma corticosterone release and elevated nerve growth factor levels in the hippocampus. No alteration in the methylation status of the exon 1(7) glucocorticoid receptor promoter region was observed. Our data indicate that early life adversity may lead to the rapid development of abnormal behaviours and HPA axis dysregulation though no epigenetic changes to the exon 1(7) glucocorticoid receptor promoter region occurred. We further propose that the observed increased neurotrophin levels reflect compensatory mechanisms that attempt to combat the long-term deleterious effects of maternal separation.

Priming of rotational behavior by a dopamine receptor agonist in Hemiparkinsonian rats: movement-dependent induction.

Repetitive stimulation of dopamine receptors located in the basal ganglia may lead to the manifestation of sensitized, abnormal, motor responses in dopamine-denervated rats. In order to study the role of motor behavior execution on the expression of these altered motor responses, we evaluated how "priming", a phenomenon displaying neurochemical and behavioral features peculiar to a sensitized abnormal motor response in dopamine-denervated rats, depends on actual movement performance. To this end, unilaterally 6-hydroxydopamine-lesioned rats received apomorphine (0.2 mg/kg s.c.), being either allowed to move or immobilized (1 h) before, concomitantly to, or after its administration, respectively. Three days after apomorphine, the dopamine D(1) receptor agonist 1-Phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol (SKF 38393, 3 mg/kg s.c.) was administered to all animals. Rats that had performed rotational behavior following apomorphine administration displayed robust contraversive rotational behavior in response to SKF 38393, whereas rats that had been immobilized concomitantly to, but neither before nor after apomorphine, did not. To clarify whether stress, which may be increased by immobilization, mediated the results observed, additional rats received apomorphine paired with immobilization plus the corticosterone-synthesis inhibitor metyrapone (100 mg/kg i.p.), or apomorphine paired with a tail stressor, being not immobilized. Metyrapone did not affect the capacity of immobilization to prevent priming and tail stressor imposition did not affect priming magnitude, suggesting that stress has minimal or no effect on the results observed. This study demonstrates how movement performance following initial dopaminergic stimulation governs the occurrence of a sensitized, abnormal, motor response to a subsequent dopaminergic challenge in dopamine-denervated rats.

Maternal separation exaggerates the toxic effects of 6-hydroxydopamine in rats: implications for neurodegenerative disorders.

Many studies have shown that early life stress may lead to impaired brain development, and may be a risk factor for developing psychiatric pathologies such as depression. However, few studies have investigated the impact that early life stress might have on the onset and development of neurodegenerative disorders, such as Parkinson's disease, which is characterized in part by the degeneration of dopaminergic neurons in the nigrostriatal pathway. The present study subjected rat pups to a maternal separation paradigm that has been shown to model adverse early life events, and investigated the effects that it has on motor deficits induced by a unilateral, intrastriatal injection of 6-hydroxydopamine (12 microg/4 microl). The female rats were assessed for behavioral changes at 28 days post-lesion with a battery of tests that are sensitive to the degree of dopamine loss. The results showed that rats that had been subjected to maternal separation display significantly impaired performance in the vibrissae and single-limb akinesia test when compared to normally reared animals. In addition, there was a significant increase in the loss of tyrosine hydroxylase staining in maternally separated rats. Our results therefore suggest that adverse experiences sustained during early life contribute to making dopamine neurons more susceptible to subsequent insults occurring during more mature stages of life and may therefore play a role in the etiopathogenesis of Parkinson's disease.

Early pubertal female rats are more resistant than males to 6-hydroxydopamine neurotoxicity and behavioural deficits: a possible role for trophic factors.

PURPOSE: The infusion of 6-hydroxydopamine (6-OHDA) into the nigrostriatal pathway in rats is commonly used to produce an animal model of Parkinson's disease (PD). However, most studies use male adult animals only. The present study focused on possible gender differences in vulnerability to 6-OHDA during the early pubertal period when the effects exerted by gonadal steroid hormones are unpronounced. METHODS: Young Sprague-Dawley rats, 35 days of age, were given a low vs. a higher dose of 6-OHDA in the medial forebrain bundle (MFB). Control rats received equivalent saline infusions. At 14 days post-surgery the rats were evaluated for forelimb akinesia. RESULTS: For the higher dose of 6-OHDA the female rats were less impaired than males in making adjustment steps in response to a weight shift and in a vibrissae-evoked forelimb placing test. Tyrosine hydroxylase (TH) immunoreactivity was significantly higher for the female rats. CONCLUSION: Early gender differences in cell survival factors and/or other promoters of neuroplasticity may have contributed to the beneficial outcome in the females. For example, NGF was found to be higher in the female rats following administration of DA neurotoxin. It is unclear whether gonadal steroids are involved, and if so, whether female hormones are protective or whether male hormones are prodegenerative. Determining the mechanisms for the improved outcome in the young female rats may lead to potential treatment strategies in PD.

The effect of stress on the antioxidative potential of serum: implications for Alzheimer's disease.

There is growing consensus in the literature that oxidation status is increased in Alzheimer's disease (AD), and that antioxidant supplementation as prevention or treatment strategy should be investigated further. In the present study the total antioxidant status (TAS) was found to be highly significantly lower in 22 AD patients (p < 0.0001) than in 22 age- and gender matched non-demented controls. The TAS was also lower than controls in 22 patients with vascular dementia, but not significantly. The increased oxidation status in AD was verified using the benzoate hydroxylation method. The origin of the enhanced oxidation status in AD has not been elucidated. To determine whether a causal effect between stress and oxidative status of serum can be demonstrated, a rat model was used with two different kinds of stressors, swim stress (exercise) and restraint stress (non-exercise stress). Following swim stress the maximum oxidative effect was observed at one hour post stress (p < 0.001). At 24 h the oxidative status had recovered significantly to below control values. Restraint stress, however, showed progressively increased oxidation which attained significance after 24 h (p < 0.005). It is postulated that stress may contribute to the higher oxidation status in AD patients.

Early life trauma decreases glucocorticoid receptors in rat dentate gyrus upon adult re-stress: reversal by escitalopram.

Early exposure to adverse experiences may lead to specific changes in hippocampal glucocorticoid function resulting in abnormalities within the hypothalamic-adrenal axis. Given interactions between the neuroendocrine and central serotonergic systems, we hypothesized that exposure to early trauma would lead to abnormal hypothalamic-adrenal axis activity that would be normalized by pretreatment with a selective serotonin re-uptake inhibitor. Hypothalamic-adrenal axis function was assessed by determining basal corticosterone levels and hippocampal glucocorticoid receptor immunoreactivity. Rats were subjected to a triple stressor on postnatal day 28, and again to a single swim re-stress session on postnatal day 35 and postnatal day 60. On postnatal day 61 i.e. 24 h after the last re-stress, trunk blood was collected for serum corticosterone determinations and hippocampal tissue was collected for immunohistochemistry of glucocorticoid receptors. Escitalopram (5mg/kg) or saline vehicle was administered from postnatal day 47-postnatal day 60 via osmotic mini-pumps. Animals exposed to early life trauma showed an increase in basal corticosterone levels, and a significant decrease in the ratio of glucocorticoid receptor positive cells to total cells in the hilus, granule cell layer and the dentate gyrus. Both the increase in basal corticosterone and decrease in glucocorticoid receptor immunoreactivity were reversed by escitalopram pretreatment. These data confirm alterations in hypothalamic-adrenalaxis function that may stem from decreases in glucocorticoid receptor levels, in response to early adverse experiences, and demonstrate that these alterations are reversed by serotonin re-uptake inhibitor pretreatment.

Maternal separation in rats leads to anxiety-like behavior and a blunted ACTH response and altered neurotransmitter levels in response to a subsequent stressor.

Adverse early life experiences can have a negative impact on behavior later in life. We subjected rat pups to maternal separation and determined the effect's thereof on adult behavior. We removed rat pups from their mothers for 3 h daily from postnatal days 2 to 14. While controls were reared normally on day 60, the behaviors of the rats were tested using the elevated plus-maze. Some rats were subsequently subjected to restraint stress for a 10-min period. Trunk blood was collected for basal, as well as 15- and 60-min postrestraint stress ACTH determinations. Neurotransmitter levels (noradrenaline (NA), serotonin (5HT), and their metabolites, MHPG and 5HIAA, respectively) were also determined at basal, immediately and 15-min post-restraint stress in the hypothalamus, hippocampus, and frontal cortex in another group of animals. The amount of entries into the arms of the elevated plus-maze was significantly reduced in the separated animals, indicating decreased locomotion. They spent significantly more time in the closed arms of the maze. A significant increase in defecation frequency was noted. These observations suggested anxious behavior. Basal ACTH levels were significantly higher in separated animals. At 15-min post-restraint stress, the ACTH levels were significantly lower than controls, indicating a blunted stress response. A decrease in noradrenaline was noted first in limbic regions and an increase in 5HIAA levels was found in the frontal cortex and hippocampus. We conclude that maternal separation induced abnormal behaviors and stress responses that were associated with altered neurotransmitter levels.

The effects of repeated intra-amygdala CRF injections on rat behavior and HPA axis function after stress.

Patients diagnosed with certain anxiety disorders or depression show symptoms of a dysregulated HPA-axis secondary to increased release of corticotropin releasing factor (CRF). Male Wistar rats were injected with CRF (100 ng/microL) in the basolateral amygdala (BLA) for 5 days. Measurement of behavior was performed on the elevated plus maze and open field test. Behavioral and neuroendocrine response to restraint stress was also evaluated. Chronic treatment of CRF resulted in a significant increase in grooming after restraint stress in the Open Field test. Basal plasma corticosterone concentrations were significantly lower in the CRF-injected rats. These animals also showed greater and longer increase in corticosterone levels following the restraint stress than controls, but had comparable ACTH responses to restraint stress. Our results indicate that chronic administration of CRF into the basolateral amygdala may promote stress-induced grooming behavior in rats. In addition the data suggests that increased CRF in the amygdala may contribute to the dysregulation of corticosterone secretion. These findings may have important implications for patients suffering from psychiatric illnesses such as posttraumatic stress disorder and depression that are characterized by abnormalities in cortisol release.