J. J. Dimatelis

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.

Behavioral changes after maternal separation are reversed by chronic constant light treatment

BACKGROUND Rats subjected to maternal separation display behavioral alterations (e.g. increased immobility in the forced swim test) and molecular changes (e.g. in growth factors and related signal transduction proteins). Light treatment has previously been shown to have antidepressant effects in rat models of depression, but has not been studied in a rodent model of maternal separation. METHODS This study focused on maternally separated rat pups. The aim of this study was to compare the effects of chronic constant light exposure during adolescence with the selective serotonin reuptake inhibitor (SSRI), escitalopram. Behavioral changes (exploratory activity in the open field and elevated plus maze, 22 kHz ultrasonic vocalizations, immobility in the forced swim test) and molecular changes (brain-derived neurotrophic factor (BDNF), mitogen-activated protein kinase phosphatase-1 (MKP-1) in the ventral hippocampus, and mu-opioid receptors in the nucleus accumbens) were measured. RESULTS Animals that had been subjected to maternal separation displayed an increased number and duration of 22 kHz vocalizations, increased immobility in the forced swim test, increased hippocampal BDNF, and decreased mu-opioid receptor levels in the nucleus accumbens in adulthood compared to controls. MKP-1 levels in the ventral hippocampus were not affected. After chronic light treatment, there was normalization of ultrasonic vocalizations, immobility on the forced swim test, and mu-opioid receptor levels in the nucleus accumbens. Chronic saline treatment reduced anxiety-like behavior and immobility in the forced swim test. Escitalopram did not have any significant effect in this rat model of depression. CONCLUSION Chronic constant light treatment reversed a number of the behavioral and molecular effects of maternal separation. Light-induced up-regulation of mu-opioid receptors in the nucleus accumbens may play a key role in mediating such effects.

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

•  What is the central question of this study? Maternal separation exacerbates behavioural deficits induced by 6‐hydroxydopamine lesioning in a rat model of Parkinsons disease. In contrast, voluntary exercise reduces these effects due to compensation in the non‐lesioned hemisphere. We have asked how maternal separation and exercise affect protein expression in lesioned and non‐lesioned hemispheres of the rat brain. •  What is the main finding and its importance? Using isobaric tagging and quantification of peptides by matrix‐assisted laser desorption/ionization tandem mass spectrometry, we show that exercise and maternal separation have opposing effects on the hippocampus in the non‐lesioned hemisphere, with exercise partially reversing effects of maternal separation on the levels of energy metabolism and synaptic plasticity proteins.

The effects of lobeline and naltrexone on methamphetamine-induced place preference and striatal dopamine and serotonin levels in adolescent rats with a history of maternal separation

Exposure to early life stress has been suggested to increase an individual’s vulnerability to methamphetamine (MA) dependence. Although there is no cure for drug dependence, the opioid and vesicular monoamine transporter 2 (VMAT2) systems may be useful targets for treatment insofar as they play pivotal roles in the neurochemistry of addiction. Here we investigated the effects of naltrexone (opioid antagonist) and lobeline (VMAT2 inhibitor) on MA-induced place preference in adolescent rodents subjected to early life trauma (maternal separation, MS) and controls, as well as the effects on dopamine and serotonin levels in the striatum. We found: (1) maternal separation attenuated methamphetamine-induced place preference; (2) lobeline and naltrexone treatment had differential effects on serotonin and dopamine concentrations in the striatum, naltrexone increased serotonin levels in the maternally separated animals. The hypothesized effect of early adversity increasing MA-induced place preference may not be apparent in adolescence. However the data are consistent with the hypothesis that early life stress influences neurochemical pathways that predispose an individual to drug dependence.

The interaction between stress and exercise, and its impact on brain function

In response to acute adversity, emotional signals shift the body into a state that permits rapid detection, identification, and appropriate response to a potential threat. The stress response involves the release of a variety of substances, including neurotransmitters, neurotrophic factors, hormones, and cytokines, that enable the body to deal with the challenges of daily life. The subsequent activation of various physiological systems can be both protective and damaging to the individual, depending on timing, intensity, and duration of the stressor. Successful recovery from stressful challenges during early life leads to strengthening of synaptic connections in health-promoting neural networks and reduced vulnerability to subsequent stressors that can be protective in later life. In contrast, chronic intense uncontrollable stress can be pathogenic and lead to disorders such as depression, anxiety, hypertension, Alzheimer’s disease, Parkinson’s disease, and an increased toxic response to additional stressors such as traumatic brain injury and stroke. This review briefly explores the interaction between stress experienced at different stages of development and exercise later in life.

Behavioural and biochemical changes in maternally separated Sprague–Dawley rats exposed to restraint stress

Early life adversity has been associated with the development of various neuropsychiatric disorders in adulthood such as depression and anxiety. The aim of this study was to determine if stress during adulthood can exaggerate the depression-/anxiety-like behaviour observed in the widely accepted maternally separated (MS) Sprague–Dawley (SD) rat model of depression. A further aim was to determine whether the behavioural changes were accompanied by changes in hippocampal brain-derived neurotrophic factor (BDNF) and the protein profile of the prefrontal cortex (PFC). Depression-/anxiety-like behaviour was measured in the elevated plus maze, open field and forced swim test (FST) in the MS SD rats exposed to chronic restraint stress in adulthood. As expected, MS increased immobility of SD rats in the FST but restraint stress did not enhance this effect of MS on SD rats. A proteomic analysis of the PFC revealed a decrease in actin-related proteins in MS and non-separated rats subjected to restraint stress as well as a decrease in mitochondrial energy-related proteins in the stressed rat groups. Since MS during early development causes a disruption in the hypothalamic‐pituitary‐adrenal axis and long-term changes in the response to subsequent stress, it may have prevented restraint stress from exerting its effects on behaviour. Moreover, the decrease in proteins related to mitochondrial energy metabolism in MS rats with or without subsequent restraint stress may be related to stress per se and not depression-like behaviour, because rats subjected to restraint stress displayed similar decreases in energy-related proteins and spent less time immobile in the FST than control rats.

Effects of maternal separation and methamphetamine exposure on protein expression in the nucleus accumbens shell and core

Early life adversity has been suggested to predispose an individual to later drug abuse. The core and shell sub-regions of the nucleus accumbens are differentially affected by both stressors and methamphetamine. This study aimed to characterize and quantify methamphetamine-induced protein expression in the shell and core of the nucleus accumbens in animals exposed to maternal separation during early development. Isobaric tagging (iTRAQ) which enables simultaneous identification and quantification of peptides with tandem mass spectrometry (MS/MS) was used. We found that maternal separation altered more proteins involved in structure and redox regulation in the shell than in the core of the nucleus accumbens, and that maternal separation and methamphetamine had differential effects on signaling proteins in the shell and core. Compared to maternal separation or methamphetamine alone, the maternal separation/methamphetamine combination altered more proteins involved in energy metabolism, redox regulatory processes and neurotrophic proteins. Methamphetamine treatment of rats subjected to maternal separation caused a reduction of cytoskeletal proteins in the shell and altered cytoskeletal, signaling, energy metabolism and redox proteins in the core. Comparison of maternal separation/methamphetamine to methamphetamine alone resulted in decreased cytoskeletal proteins in both the shell and core and increased neurotrophic proteins in the core. This study confirms that both early life stress and methamphetamine differentially affect the shell and core of the nucleus accumbens and demonstrates that the combination of early life adversity and later methamphetamine use results in more proteins being affected in the nucleus accumbens than either treatment alone.

Early ethanol exposure and vinpocetine treatment alter learning- and memory-related proteins in the rat hippocampus and prefrontal cortex.

This study investigates the effects of early exposure to ethanol on cognitive function and neural plasticity‐related proteins in the rat brain. Sprague‐Dawley rats were administered 12% ethanol solution (4 g/kg/day i.p.) or saline from P4 to P9. Vinpocetine, a phosphodiesterase type 1 inhibitor, was tested to determine whether it could reverse any changes induced by early ethanol exposure. Hence, from P25 to P31, ethanol‐exposed male rats were injected with vinpocetine (20 mg/kg/day i.p.) or vehicle (DMSO) prior to undergoing behavioral testing in the open field and Morris water maze (MWM) tests. Ethanol exposure did not adversely affect spatial memory in the MWM. A key finding in this study was a significant ethanol‐induced change in the function of the phosphorylated extracellular signal‐related kinase (P‐ERK) signaling pathway in the prefrontal cortex (PFC) and dorsal hippocampus (DH) of rats that did not display overt behavioral deficits. The P‐ERK/ERK ratio was decreased in the PFC and increased in the DH of ethanol‐exposed rats compared with controls. Rats that received vinpocetine in addition to ethanol did not display any behavioral changes but did show alterations in neural plasticity‐related proteins. Mitogen‐activated protein kinase phosphatase was increased, whereas brain‐derived neurotrophic factor was decreased, in the PFC of vinpocetine‐treated ethanol‐exposed rats, and phosphorylated‐glycogen synthase kinase β and synaptophysin were increased in the DH of these rats. This study provides insight into the long‐term effects of early ethanol exposure and its interaction with vinpocetine in the rat brain.

Genetic predisposition and early life experience interact to determine glutamate transporter (GLT1) and solute carrier family 12 member 5 (KCC2) levels in rat hippocampus

Attention-deficit/hyperactivity disorder (ADHD) is one of the most common child psychiatric disorders. While it is typically treated with medications that target dopamine and norepinephrine transmission, there is increasing evidence that other neurotransmitter systems, such as glutamate and GABA, may be involved. The aetiology of ADHD is unknown; however, there is evidence that early life stress may contribute to the development of the disorder. In the present study we used proteomic analysis (iTRAQ) followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blot analysis to investigate hippocampal protein profiles of three rat strains: an animal model of ADHD, spontaneously hypertensive rats (SHR), their control Wistar-Kyoto rats (WKY), and Sprague-Dawley rats (SD). We additionally investigated how these protein profiles are affected by maternal separation, a model of early life stress. Our findings show that solute carrier family 12 member 5 (KCC2) is increased in SHR hippocampus. The glutamate transporter GLT1 splice variant, GLT1b, was increased (proteomic analysis) while total GLT1 (comprised mostly of GLT1a splice variant) was reduced (Western blot analysis) in SHR hippocampus, compared to WKY and SD – a pattern that is consistent with elevated extracellular glutamate levels. Maternal separation increased total GLT1 in hippocampi of SHR, WKY, and SD, and reduced GLT1b in SHR hippocampus. Together these findings provide evidence for disturbed glutamatergic and GABAergic transmission in SHR hippocampus, maternal separation effects on glutamate uptake in hippocampi of all three strains, as well a unique effect of maternal separation on GLT1b levels in SHR hippocampus. These data suggest significant involvement of glutamatergic and GABAergic transmission in the neuropathophysiology of ADHD, and implicates changes in glutamatergic transmission as a result of early life stress.

Proteomic analysis of maternal separation-induced striatal changes in a rat model of ADHD: The spontaneously hypertensive rat.

BACKGROUND Developmental stress increases the risk of developing psychological disturbances and is modelled in rodents by maternal separation (MS). Attention-deficit/hyperactivity disorder (ADHD) is characterised by inattention, hyperactivity and impulsivity and is studied using the spontaneously hypertensive rat (SHR). Previous studies suggested that SHR differ from their progenitor strain, the Wistar-Kyoto (WKY), in their response to developmental stress. This study sought to investigate the effects of MS on striatal protein expression, a brain area implicated in the pathophysiology of ADHD and susceptible to developmental stress, in SHR, WKY and Sprague-Dawley (SD) rat strains. METHOD Dissected striata of separated and non-separated SHR, WKY and SD (n = 6 per group) were assessed for MS-induced changes in protein expression using isobaric tagging (iTRAQ) and peptide quantification via matrix-assisted laser desorption/ionisation (MALDI) tandem mass spectrometry. RESULTS Strain and MS-induced differences were observed in proteins related to energy metabolism, neuroprotection, protein folding, protein metabolism, signalling and structure. Striatal SHR protein levels were consistent with delayed neuronal maturation and altered neurotransmission and energy metabolism. MS produced mostly opposite effects on SHR striatal proteins compared to WKY and SD. COMPARISON WITH EXISTING METHODS Proteomic profiling of protein expression in selected brain areas provides an assessment of overall changes in metabolic pathways that cannot be determined using standard protein isolation techniques. Furthermore, MS-induced changes in protein expression in the striatum of SHR, WKY and SD have not been reported. CONCLUSIONS The results suggest that energy metabolism, neurotransmission and neural development are altered in SHR striatum and that WKY and SD are suitable comparator strains for SHR. The strain-dependent effects of MS on striatal protein expression reinforce the importance of gene × environment interactions in determining behavioural outcome.