Joseph Zohar

Long-term down-regulation of BDNF mRNA in rat hippocampal CA1 subregion correlates with PTSD-like behavioural stress response

Brain-derived neurotrophic factor (BDNF) and its intracellular kinase-activating receptor TrkB, have been implicated in the neurobiological mechanisms underlying the clinical manifestations of PTSD, especially those related to synaptic efficacy and neural plasticity. BDNF interacts with components of the stress response such as corticosterone, and plays an important role in growth, maintenance and functioning of several neuronal systems. This study employed an animal model of PTSD to investigate the relationship between prevalence rates of distinct patterns of behavioural responses to predator stress, circulating levels of corticosterone and local levels of mRNA for BDNF, TrkB and two other neurotrophic factors in selected brain areas. Animals whose behaviour was extremely disrupted by exposure selectively displayed significant down-regulation of mRNA for BDNF and up-regulation of TrkB mRNA in the CA1 subregion of the hippocampus, compared to animals whose behaviour was minimally or partially affected and to unexposed controls. The response was consistent throughout the entire study only in CA1. The consistent long-term the BDNF down-regulation and TrkB up-regulation associated with extreme behavioural compromise may be associated with chronic stress-induced psychopathological processes, especially in the hippocampus. The corresponding changes in neural plasticity and synaptic functioning may mediate clinical manifestations of PTSD.

Hippocampal Microinfusion of Oxytocin Attenuates the Behavioural Response to Stress by Means of Dynamic Interplay with the Glucocorticoid‐Catecholamine Responses

The neurohypophysial hormone oxytocin acts as a central nervous system neurotransmitter/neuromodulator. We evaluated the effects of oxytocin on behavioural responses to stress, as well as associated biophysiological responses, in a controlled, prospective animal model. The long‐term effects of exogenous oxytocin microinjected to the hippocampus of male rats were assessed. Animals were exposed to predator scent stress and treated 1 h or 7 days later with oxytocin or vehicle. Behaviours were assessed with the elevated plus‐maze and acoustic startle response tests, 7 days after microinjection and freezing behaviour upon exposure to a trauma‐related cue on day 8. These data served for classification into behavioural response groups. Trauma cue response, circulating corticosterone and oxytocin, hippocampal expression of glucocorticoid and mineralocorticoid receptors, and oxytocin receptor mRNA levels were assessed. The interplay between oxytocin, corticosterone and norepinephrine was assessed. Microinfusion of oxytocin both immediately after predator scent stress exposure or 7 days later, after exposure to trauma cue significantly reduced the prevalence rates of extreme responders and reduced trauma cue freezing responses. Post‐exposure treatment with oxytocin significantly corrected the corticosterone stress response, decreased glucocorticoid receptor expression and increased mineralocorticoid receptor expression in the hippocampus compared to vehicle treatment. High‐dose corticosterone administration together with norepinephrine caused release of plasma oxytocin and hippocampal oxytocin receptor. Oxytocin is actively involved in the neurobiological response to predator scent stress processes and thus warrants further study as a potential therapeutic avenue for the treatment of anxiety‐related disorders.

The Role of the Galaninergic System in Modulating Stress-Related Responses in an Animal Model of Posttraumatic Stress Disorder

BACKGROUND Converging evidence implicates the regulatory neuropeptide galanin in anxiety- and depression-related behaviors, through modulation of neuroendocrine, serotonergic, and noradrenergic systems. This study examined the relationship between stress-induced posttraumatic stress disorder (PTSD)-like behavioral response patterns in rats and galanin mRNA levels in key brain areas and the effects of acute phase pharmacologic manipulation using an agonist (galnon) on behavioral, physiologic, and response patterns of brain-derived neurotrophic factor (BDNF) and 5-hydroxytryptamine-1A (5HT-1A). METHOD Galanin mRNA expression was assessed in the frontal cortex and hippocampus in the short- and long-term (30 min and 7 days) after exposure to predator scent stress. The effects of intraperitoneal galnon .5 mg/kg versus saline 1 hour postexposure on behavioral tests (elevated plus maze and acoustic startle response) were evaluated 7 days later. Trauma-cue response, circulating corticosterone, and localized brain expression of 5HT-1A receptors and BDNF were subsequently assessed. All data were analyzed in relation to individual behavior patterns. RESULTS Whereas animals with minimal behavioral disruption displayed a lasting upregulation of galanin mRNA in the hippocampal CA1 area, those with extreme behavioral responses displayed downregulation in both CA1 and frontal cortex. Immediate postexposure treatment with galnon significantly reduced prevalence rates of extreme responders, reduced trauma-cue freezing responses, corrected the corticosterone response, and increased CA1 expression of 5HT-1A and BDNF mRNA compared with saline controls. CONCLUSIONS Galanin is actively involved in the neurobiological response to predator scent stress with resilience/recovery after stress exposure and thus warrants further study as a potential therapeutic avenue for the treatment of anxiety-related disorders.

Distinctive hippocampal and amygdalar cytoarchitectural changes underlie specific patterns of behavioral disruption following stress exposure in an animal model of PTSD

Alterations in cytoarchitecture and molecular signaling have been observed in adaptive and maladaptive responses to stress and presumably underlie the physiological and behavioral changes observed. The relationship between behavioral responses to stress exposure and changes in cytoarchitecture of subregions of the hippocampus and amygdala was investigated in an animal model of PTSD. Behaviors in elevated plus-maze and acoustic startle response tests were assessed in rats 7 days after exposure to predator scent stress. Brains were harvested 24h later. Neurons from CA1, CA3, and dentate gyrus subregions and basolateral amygdala were reconstructed and subjected to Sholl analysis and spine density estimation. Glucocorticoid receptor, brain-derived neurotrophic factor, phospho-NR1-Ser-889, phospho-GluR1-Ser-845, phospho-calcium/calmodulin dependent protein kinase II-Thy-286, post-synaptic density protein 95 and phospho-CREB-Ser-133 were evaluated in the hippocampus. Data were analyzed by retrospective classification of individual rats into three behavioral response groups. The extent and distribution of changes in the morphology of hippocampal and amygdalar dendrites was significantly associated with stress-induced behavioral response classification. Extreme (PTSD-like) behavioral disruption was associated with extensive neuronal retraction in the hippocampus and proliferation in the amygdala. Neither structure displayed such changes in minimal behavioral responders. Partial behavioral response was associated with identical changes in the hippocampus only. Patterns of change in requisite molecular signaling genes and endophenotypic markers corresponded to the structural and behavioral responses. The extent and distribution of changes in the cytoarchitecture of hippocampal and amygdalar subregions is directly related to the pattern of behavioral response of the individual to stress exposure.

An association between stress-induced disruption of the hypothalamic-pituitary-adrenal axis and disordered glucose metabolism in an animal model of post-traumatic stress disorder.

Retrospective clinical reports suggesting that traumatic stress populations display an increased propensity for glucose metabolism disorders were examined in a controlled prospective animal model. Stress‐induced behavioural and hypothalamic‐pituitary‐adrenal (HPA) axis response patterns were correlated to central and peripheral parameters of glucose metabolism and signalling, and to body measurements in Sprague–Dawley rats exposed to predator scent stress. Forty days post‐exposure, fasting blood glucose and insulin levels, oral glucose tolerance test, body weight and white adipose tissue mass, systemic corticosterone levels and brain expression of insulin receptor (IR) and insulin‐sensitive glucose transporter 4 (GLUT4) protein levels were evaluated. In a second experiment inbred strains with hyper‐ (Fischer) and hypo‐ (Lewis) reactive HPA axes were employed to assess the association of metabolic data with behavioural phenomenology versus HPA axis response profile. For data analysis, animals were classified according to their individual behavioural response patterns (assessed at day 7) into extreme, partial and minimal response groups. The exposed Sprague–Dawley rats fulfilling criteria for extreme behavioural response (EBR) (20.55%) also exhibited significant increases in body weight, abdominal circumference and abdominal white adipose tissue mass; a hyperglycaemic oral glucose tolerance test; and fasting hyperglycaemia, hyperinsulinaemia and hypercorticosteronemia, whereas minimal responders (MBR) and control animals displayed no such disturbances. Hippocampal and hypothalamic expression of IR and GLUT4 protein were significantly lower in EBR than in MBR and control rats. The inbred strains showed no metabolic differences at baseline. Exposed Fischer rats displayed hyperglycaemia and hyperinsulinaemia, whereas Lewis rats did not. A significant protracted disorder of glucose metabolism was induced by exposure to a stress paradigm. This metabolic response was associated with the characteristic pattern of HPA axis (corticosterone) response, which underlies the behavioural response to stress.

Microinfusion of a Corticotrophin-Releasing Hormone Receptor 1 Antisense Oligodeoxynucleotide into the Dorsal Hippocampus Attenuates Stress Responses at Specific Times After Stress Exposure

Corticotrophin‐releasing hormone (CRH) plays a key role in the adjustment of neuroendocrine and behavioural adaptations to stress. Dysregulation in CRH systems has been implicated in a variety of stress‐related psychiatric disorders such as post‐traumatic stress disorder (PTSD). The present study examined the relationship between stress‐induced PTSD‐like behavioural response patterns and levels of CRH, CRH receptor (CHR‐R)1 and phosphorylated extracellular signal‐regulated kinase (pERK1/2) in the rat hippocampus subregions. The effects of pharmacological manipulations on behavioural, physiological and response patterns of brain‐derived neurotrophic factor (BDNF) and pERK1/2 expression using a CRH receptor (CRH‐R)1‐antisense oligodeoxynucleotide (CRH‐R1‐ASODN) were evaluated. CRH and CRH‐R1 mRNA and pERK1/2 protein levels were assessed in the hippocampus subregions 7 days after exposure to predator scent stress (PSS). The effects of CRH‐ASODN versus CRH‐Scrambled‐ODN microinfusion to the dorsal hippocampus either 1 h or 48 h post‐exposure on behavioural tests (elevated plus maze and acoustic startle response) were evaluated 7 days later, 14 days after PSS exposure. Localised brain expression of BDNF and ERK1/2 was subsequently assessed. All data were analysed in relation to individual behaviour patterns. A distinct pattern associated with extreme behavioural response (EBR) was revealed in the bioassay of behavioural study subjects, classified according to their individual patterns of behavioural response at 7 days. These EBR individuals displayed significantly higher CRH and CRH‐R1 mRNA levels in the CA1 and CA3 areas, mediating down‐regulation of pERK1/2 protein levels. Microinfusion of a CRH‐R1‐ASODN into the dorsal hippocampus 48 h after stress exposure, although not immediately after exposure (1 h), significantly reduced behavioural disruption and was associated with concomitant up‐regulation of BDNF and pERK1/2 protein levels compared to CRH‐R1‐Scrambled ‐ODN controls. CRH/CRH‐R1 is actively involved in the neurobiological response to predator scent stress processes and thus warrants further study as a potential therapeutic avenue for the treatment of anxiety‐related disorders.

Predator-scent stress, ethanol consumption and the opioid system in an animal model of PTSD.

Emerging literature points to stress exposure as a potential contributor to the development of alcohol abuse, but animal models have yielded inconsistent results. Converging experimental data indicate that the endogenous opioid system modulates alcohol consumption and stress regulation. The aim of the present study is to examine the interplay between stress exposure, behavioral stress responses, ethanol (EtOH) consumption and the endogenous opioid system in an animal model of posttraumatic stress disorder. Rats were exposed to stress and then tested in a two-bottle free choice (TBC) assay or in a conditioned place preference paradigm. In some experiments, the endogenous opioid system was pharmacologically manipulated prior to stress exposure. The behavioral outcomes of stress exposure were assessed in an elevated plus-maze, with the acoustic startle response, and by monitoring the freezing response to trauma reminder. Immunoreactivity of phosphorylated opioid receptors in hippocampal subregions was also measured. Stress significantly increased the consumption of EtOH in the TBC assay. The severity of the behavioral response to stress was associated with EtOH consumption, cue-triggered freezing response to a trauma reminder, and endogenous levels of phosphorylated opioid receptors in the hippocampus. Pharmacologically manipulating the endogenous opioid system prior to stress exposure attenuated trauma cue-triggered freezing responses and blocked predator scent stress-induced potentiation of EtOH consumption. These data demonstrate a stress-induced potentiation of EtOH self-administration and reveal a clear association between individual patterns of the behavioral response to stress and alcohol preference, while indicating a role for the endogenous opioid system in the neurobiological response to stress.

Preventing sleep on the first resting phase following a traumatic event attenuates anxiety-related responses

HighlightsRecurring memories of a traumatic event are a fundamental feature of PTSD.Sleep immediately following learning result in the long‐term preservation of emotional memories.Sleep deprivation following a potentially traumatic event may prevent the consolidation of event‐related memories.Preventing sleep on the first resting phase following a traumatic event attenuates posttraumatic symptoms. ABSTRACT Sleep deprivation (SD) in the early aftermath of stress exposure at the onset of the inactive (resting)‐phase, has been shown to ameliorate stress‐related sequelae. We examined whether this effect is affected by the temporal proximity between SD and the stressful event or whether it was related to the prevention of sleep in the first resting phase following the exposure. Rats were exposed to stress at the onset of their active phase. Then, they were prevented from sleeping immediately thereafter [forced wakefulness (FW)], or during the first resting phase (SD). The behavior in the elevated plus‐maze and acoustic startle response paradigms were assessed seven days post‐exposure for retrospective classification into behavioral response groups. We found that resting phase SD (with or without FW) decreased PTSD‐like phenotype, whereas immediate FW had no significant effect. The long‐term anxiolytic effects of SD appear to stem from a diurnal cycle‐dependent mechanism, such that preventing sleep during the first natural resting phase following the traumatic exposure is beneficial in preventing the traumatic sequelae.

Distinctive cardiac autonomic dysfunction following stress exposure in both sexes in an animal model of PTSD.

It is unclear whether the poor autonomic flexibility or dysregulation observed in patients with posttraumatic stress disorder (PTSD) represents a pre-trauma vulnerability factor or results from exposure to trauma. We used an animal model of PTSD to assess the association between the behavioral response to predator scent stress (PSS) and the cardiac autonomic modulation in male and female rats. The rats were surgically implanted with radiotelemetry devices to measure their electrocardiograms and locomotor activity (LMA). Following baseline telemetric monitoring, the animals were exposed to PSS or sham-PSS. Continuous telemetric monitoring (24h/day sampling) was performed over the course of 7days. The electrocardiographic recordings were analyzed using the time- and frequency-domain indexes of heart rate variability (HRV). The behavioral response patterns were assessed using the elevated plus maze and acoustic startle response paradigms for the retrospective classification of individuals according to the PTSD-related cut-off behavioral criteria. During resting conditions, the male rats had significantly higher heart rates (HR) and lower HRV parameters than the female rats during both the active and inactive phases of the daily cycle. Immediately after PSS exposure, both the female and male rats demonstrated a robust increase in HR and a marked drop in HRV parameters, with a shift of sympathovagal balance towards sympathetic predominance. In both sexes, autonomic system habituation and recovery were selectively inhibited in the rats whose behavior was extremely disrupted after exposure to PSS. However, in the female rats, exposure to the PSS produced fewer EBR rats, with a more rapid recovery curve than that of the male rats. PSS did not induce changes to the circadian rhythm of the LMA. According to our results, PTSD can be conceptualized as a disorder that is related to failure-of-recovery mechanisms that impede the restitution of physiological homeostasis.