W. M. U. Daniels

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 effects 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.

Maternal separation of rat pups increases the risk of developing depressive-like behavior after subsequent chronic stress by altering corticosterone and neurotrophin levels in the hippocampus

Children that are abused have an increased risk for developing psychiatric disorders later in life, because of the negative effects of stress on the developing brain. We used a maternal separation model in rats to see how neurotrophins, stress hormones, behavior and the anti-oxidant potential of serum are affected. Rat pups were separated from their mothers for 3h/day on days 2-14. Maternal separation caused changes in levels of NGF and NT-3 in the dorsal and ventral hippocampus, increased basal corticosterone levels and decreased ACTH levels after acute restraint stress. The anti-oxidant potential of the rat serum was significantly lower in the maternal separation group. Depressive-like behavior, measured during a forced swim test, was seen in maternally separated rats after additional chronic stress during adulthood. Maternal separation caused downregulation of neurotrophins in the ventral hippocampus, possibly as an effect of high corticosterone levels, but compensatory mechanisms against cell death may be involved as neurotrophin levels increased in the dorsal hippocampus. Decreased anti-oxidant potential of serum could have been an effect of downregulated neurotrophin levels.

Melatonin prevents β‐amyloid‐induced lipid peroxidation

Daniels WMU, van Rensburg SJ, van Zyl JM, Taljaard JJF. Melatonin prevents β‐amyloid‐induced lipid peroxidation. J. Pineal Res. 1998; 24:78–82.

Early maternal separation alters the response to traumatization: resulting in increased levels of hippocampal neurotrophic factors.

Early life adversity predisposes individuals to the development of psychopathology in later life, especially depression and anxiety disorders. Prior history of stressors may also be a vulnerability factor for developing posttraumatic stress disorder (PTSD) in response to trauma. We examined the mechanisms underlying this phenomenon by employing two animal stress models, early maternal separation followed by later time-dependent sensitization (TDS). In animals exposed to adult TDS, those with prior early adversity did not differ from controls on tests of anxiety (elevated plus maze, open field), or HPA function (ACTH and corticosterone levels). However, those with prior early adversity had increased levels of neurotrophic factors (BDNF, NGF and NT-3) in both the dorsal and ventral hippocampus. Although early adversity is known to be associated with negative effects on neuronal function, it may also be associated with an increased ability to respond to subsequent stressors with compensatory mechanisms such as increased neurotrophic factor release.

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.

The role of the MAP-kinase superfamily in β-amyloid toxicity

The mitogen-activated protein kinase (MAP kinase) pathway participates in a number of reactions of the cell when responding to various external stimuli. These stimuli include growth factor binding to its receptor as well as stressful situations such as hypoxia and oxidative stress. It has been postulated that one of the mechanisms by which β-amyloid exerts its toxic effects is to produce oxidative stress. This study therefore investigated whether the MAP-kinase pathway was activated in cells following exposure to β-amyloid. Neuroblastoma (N2α) cells were used in all experiments. The cells were exposed to 50, 100, and 500 μM glutamate, and 10, 30, and 50 μM β-amyloid, for 24 h. The methyl–thiazolyl tetrazolium salt (MTT) assay was performed to determine the degree of toxicity. The generation of hydrogen peroxide was detected by fluorescence microscopy using the dye dihydrochlorofluorescein diacetate (DCDHF). Extracellular-signal-regulated kinase (ERK) and p38 MAP-kinase phosphorylation, as representatives of the MAP-kinase pathway, was determined. Treating N2α cells with β-amyloid resulted in a greater than 50% reduction in cell viability. These cells also showed a significantly higher presence of hydrogen peroxide. Western Blot analysis revealed that the phosphorylation of p38 MAP kinase was dose-dependently increased in cells exposed to glutamate and β-amyloid. On the other hand, the phosphorylation of ERK was significantly reduced in these cells. These data therefore suggest that the toxic effects of β-amyloid involve the generation of hydrogen peroxide, leading to the activation of p38 and the down-regulation of ERK.

Early maternal separation followed by later stressors leads to dysregulation of the HPA-axis and increases in hippocampal NGF and NT-3 levels in a rat model

Early adverse life events, followed by subsequent stressors, appear to increase susceptibility for subsequent onset of psychiatric disorders in humans. The molecular mechanisms that underlie this phenomenon remain unclear, but dysregulation of the HPA axis and alterations in neurotrophic factors have been implicated. The present study investigated the effects in rodents of early maternal separation, followed by stress in adolescence and adulthood on later HPA-axis activity and hippocampal neurotrophin levels (brain-derived neurotrophic factor, nerve growth factor, and neurotrophin-3). Animals subjected to repeated stressors showed a significant decrease in basal ACTH (p < 0.05) and CORT (p < 0.05) levels when compared to controls, as well as significantly increased levels of NGF in the dorsal (p < 0.001) and ventral hippocampus (p < 0.01), and of NT-3 in the dorsal hippocampus (p < 0.01). Dysregulation of the HPA axis after multiple stressors is consistent with previous preclinical and clinical work. Given that neurotrophins are important in neuronal survival and plasticity, it is possible to speculate that their elevation reflects a compensatory mechanism.

Developmental Trauma is Associated with Behavioral Hyperarousal, Altered HPA Axis Activity, and Decreased Hippocampal Neurotrophin Expression in the Adult Rat

Abstract:  Effects of early‐life trauma on adult behavioral responses, corticosterone (CORT) concentration, and levels of nerve growth factor (NGF), brain‐derived neutrophic factor (BDNF), and neurotrophin‐3 (NT‐3) in hippocampus and frontal cortex were investigated. Traumatized animals showed an increase in rearing in both the elevated plus maze and open field after adult restress, higher basal levels of CORT, lower levels of BDNF in dorsal hippocampus, and lower levels of NT‐3 in dorsal and ventral hippocampus. Trauma‐related behavioral hyperarousal and altered hypothalamic‐pituitary‐adrenal (HPA) axis activity may be mediated by decreases in hippocampal neurotrophin expression.

fluoxetine decreases stereotypic behavior in primates

BACKGROUND Primates reared in captivity may display stereotypic behaviors. These behaviors are arguably reminiscent of human obsessive-compulsive or posttraumatic symptoms, which respond to selective serotonin reuptake inhibitors (SSRIs). Captive primates with marked stereotypic behaviors were entered into a randomized controlled study of the SSRI, fluoxetine. METHODS A sample of 10 vervet monkeys with behaviors such as marked saluting, somersaulting, weaving, or head tossing was selected. Subjects were randomized to receive fluoxetine 1 mg/kg for 6 weeks (n=5) or no treatment (n=5). A rater blind to the medication status of subjects noted the frequency of the stereotypic behaviors. RESULTS Repeated-measures analysis of variance (RM-ANOVA) demonstrated a significant GroupxTime difference with significantly fewer stereotypic symptoms in the fluoxetine group by endpoint. At this time, three of the five fluoxetine-treated subjects (but none of the no-treatment subjects) were responders on the Clinical Global Impressions (CGI) change item (CGI < or =2). CONCLUSIONS Stereotypic behaviors in captive vervets gradually and partially decrease in response to administration of an SSRI, paralleling research on human anxiety symptoms. Further research on animal stereotypies may be useful in providing appropriate veterinary care, and in exploring the underlying neurobiology of certain psychiatric disorders.

Free radical scavenging effects of melatonin and serotonin: possible mechanism.

Melatonin has been reported to be a potent free radical scavenger, but the mechanism by which it protects membranes from lipid peroxidation is poorly understood. The present study addresses this problem by comparing the free radical scavenging properties of melatonin and serotonin, two indoles with similar structure, but differing solubilities. Both serotonin and melatonin significantly prevented lipid peroxidation of platelet membranes. Additionally, melatonin significantly decreased the microviscosity (increased the fluidity) of platelet membranes, while serotonin had the opposite effect. These data led us to postulate that serotonin exerts its free radical scavenging action in the aqueous phase, or at the water-membrane interface, while melatonin positions itself within the lipid bilayer where it protects membrane phospholipids against free radical attack.