Footshock Session Research Articles

Compulsive methamphetamine self-administration in the presence of adverse consequences is associated with increased hippocampal mRNA expression of cellular adhesion molecules.

Methamphetamine (METH) is a popular but harmful psychostimulant. METH use disorder (MUD) is characterized by compulsive and continued use despite adverse life consequences. METH users experience impairments in learning and memory functions that are thought to be secondary to METH-induced abnormalities in the hippocampus. Recent studies have reported that about 50% of METH users develop MUD, suggesting that there may be differential molecular effects of METH between the brains of individuals who met criteria for addiction and those who did not after being exposed to the drug. The present study aimed at identifying potential transcriptional differences between compulsive and non-compulsive METH self-administering male rats by measuring global gene expression changes in the hippocampus using RNA sequencing. Herein, we used a model of METH self-administration (SA) accompanied by contingent foot-shock punishment. This approach led to the separation of animals into shock-resistant rats (compulsive) that continued to take METH and shock-sensitive rats (non-compulsive) that suppressed their METH intake in the presence of punished METH taking. Rats were euthanized 2 h after the last METH SA plus foot-shock session. Their hippocampi were immediately removed, frozen, and used later for RNA sequencing and qRT-PCR analyses. RNA sequencing analyses revealed differential expression of mRNAs encoding cell adhesion molecules (CAMs) between the two rat phenotypes. qRT-PCR analyses showed significant higher levels of Cdh1, Glycam1, and Mpzl2 mRNAs in the compulsive rats in comparison to non-compulsive rats. The present results implicate altered CAM expression in the hippocampus in the behavioral manifestations of continuous compulsive METH taking in the presence of adverse consequences. Our results raise the novel possibility that altered CAM expression might play a role in compulsive METH taking and the cognitive impairments observed in MUD patients.

Footshock‐induced abstinence from compulsive methamphetamine self‐administration is associated with increased expression of cannabinoid receptors (CB1 and CB2) in the rat hippocampus

Methamphetamine (METH) use disorder is characterized by compulsive and repeated drug intake despite negative life consequences. Large intake of METH in humans and animals is accompanied by dysfunctions in learning and memory and learning and by neurodegenerative changes in several brain regions. Because the endocannabinoid system (eCB) has been implicated in the manifestations of substance use disorders (SUDs), we sought to identify potential changes in various enzymes and the receptors (CB1 and CB2) that are involved in mediating the effects of endocannabinoids. To reach that end, we used a model of METH self-administration (SA) paradigm that includes a punishment phase (footshocks) that has helped to separate rats into a compulsive METH phenotype (shock-resistant, compulsive) that continues to take METH and a non-compulsive METH (shock-sensitive, abstinent) that suppressed or became abstinent in the presence of punishment. We then measured mRNA expression of cannabinoid receptors (CB/Cnr), synthetic (Dagl-a, Dagl-b, Nape-pld), as well as metabolizing enzymes (Mgll, Faah, Cox2) of the eCB signaling cascade in the dorsal striatum (DStr), nucleus accumbens (NAc), midbrain (MBr), and hippocampus (Hip) of rats euthanized two hours after the last METH SA plus footshock session. The abstinent rats exhibited significant increases in the expression of CB1 and CB2 in the hippocampus. The mRNA levels for the synthetic enzyme, Dagl-a, and the metabolic enzymes, Mgll, and Faah, were also increased in the hippocampus. In contrast, compulsive rats exhibited significant decreases in the expression of Faah in both the DStr and MBr but showed increased mRNA expression of Cox2 in the DStr. There were no significant changes in any of these in the nucleus accumbens. Taken together, these observations implicate, in part, the hippocampal endocannabinoid system in the suppression of METH intake in the presence of adverse consequences. Pharmacological agents that augment the activity of this system may be beneficial against METH use disorder in humans.

Early life sleep disruption is a risk factor for increased ethanol drinking after acute footshock stress in prairie voles.

Early postnatal experiences are important for shaping the development of the stress response and may contribute to the later emergence of alcohol use disorders. We have previously found that early life sleep disruption impairs social development and alters GABA neurons in the brain of adult prairie voles, a socially monogamous rodent that displays natural ethanol preference in the laboratory. However, it is unclear whether these effects on social behavior are due, in part, to overall anhedonia and/or altered behavioral response to stress. To address this question, litters containing prairie vole pups were sleep disrupted by gentle cage agitation for 7 consecutive days from postnatal days (P) 14 to 21 (early life sleep disruption, or ELSD group) or allowed to sleep undisturbed (Control). Adult voles underwent a 2-bottle choice ethanol drinking procedure integrated with a single session of footshocks. Ethanol intake after footshock was measured as well as c-Fos immunoreactivity in the lateral and central amygdala. ELSD animals showed increased ethanol consumption and increased neural activity in these amygdala regions after footshock compared to control animals. There were no differences in baseline ethanol drinking prior to exposure to a stressor. These results suggest that early life sleep disruption in prairie voles does not produce anhedonia but can have long-lasting effects on stress reactivity. In addition to shaping species-typical social behavior, early life sleep may be important in the development of stress induced ethanol consumption and the activation of limbic pathways associated with stress. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Escalated Oxycodone Self-Administration and Punishment: Differential Expression of Opioid Receptors and Immediate Early Genes in the Rat Dorsal Striatum and Prefrontal Cortex.

Opioid use disorder (OUD) is characterized by compulsive drug taking despite adverse life consequences. Here, we sought to identify neurobiological consequences associated with the behavioral effects of contingent footshocks administered after escalation of oxycodone self-administration. To reach these goals, Sprague-Dawley rats were trained to self-administer oxycodone for 4 weeks and were then exposed to contingent electric footshocks. This paradigm helped to dichotomize rats into two distinct behavioral phenotypes: (1) those that reduce lever pressing (shock-sensitive) and (2) others that continue lever pressing (shock-resistant) for oxycodone during contingent punishment. The rats were euthanized at 2-h after the last oxycodone plus footshock session. The dorsal striata and prefrontal cortices were dissected for use in western blot and RT-qPCR analyses. All oxycodone self-administration rats showed significant decreased expression of Mu and Kappa opioid receptor proteins only in the dorsal striatum. However, expression of Delta opioid receptor protein was decreased in both brain regions. RT-qPCR analyses documented significant decreases in the expression of c-fos, fosB, fra2, junB, egr1, and egr2 mRNAs in the dorsal striatum (but not in PFC) of the shock-sensitive rats. In the PFC, junD expression was reduced in both phenotypes. However, egr3 mRNA expression was increased in the PFC of only shock-resistant rats. These results reveal that, similar to psychostimulants and alcohol, footshocks can dichotomize rats that escalated their intake of oxycodone into two distinct behavioral phenotypes. These animals also show significant differences in the mRNA expression of immediate early genes, mainly, in the dorsal striatum. The increases in PFC egr3 expression in the shock-resistant rats suggest that Egr3 might be involved in the persistence of oxycodone-associated memory under aversive conditions. This punishment-driven model may help to identify neurobiological substrates of persistent oxycodone taking and abstinence in the presence of adverse consequences.

Selective Activation of Striatal NGF-TrkA/p75NTR/MAPK Intracellular Signaling in Rats That Show Suppression of Methamphetamine Intake 30 Days following Drug Abstinence.

BackgroundThe continuing epidemic of methamphetamine addiction has prompted research aimed at understanding striatal dysfunctions potentially associated with long-term methamphetamine use.MethodsHere, we investigated transcriptional and translational alterations in the expression of neurotrophic factors in the rat striatum at 30 days following methamphetamine self-administration and footshock punishment. Male Sprague–Dawley rats were trained to self-administer methamphetamine (0.1 mg/kg/injection, i.v.) or saline during twenty-two 9-hour sessions. Subsequently, rats were subjected to incremental footshocks for 13 additional methamphetamine self-administration sessions. This paradigm led to the identification of rats with shock-resistant and shock-sensitive phenotypes. Thirty days following the last footshock session, the dorsal striatum was dissected and processed for gene expression and protein analyses.ResultsPCR arrays revealed significant differences in neurotrophins and their receptors between the 2 phenotypes. Brain-derived neurotrophic factor and nerve growth factor protein levels were increased in the dorsal striatum of both shock-resistant and shock-sensitive rats. However, neurotrophic receptor tyrosine kinase 1 phosphorylation and nerve growth factor receptor protein expression were increased only in the shock-sensitive phenotype. Moreover, shock-sensitive rats showed increased abundance of several phosphorylated proteins known to participate in Ras/Raf/MEK/ERK signaling cascade including cRaf, ERK1/2, MSK1, and CREB.ConclusionsThese findings support the notion that animals with distinct phenotypes for methamphetamine intake in the presence of adverse consequences also display differential changes in an intracellular signaling cascade activated by nerve growth factor-TrkA/p75NTR interactions. Thus, the development of pharmacological agents that can activate nerve growth factor-dependent pathways may be a promising therapeutic approach to combat methamphetamine addiction.

Long-Term Sertraline Intake Reverses the Behavioral Changes Induced by Prenatal Stress in Rats in a Sex-Dependent Way.

Early life stress is a major factor underlying the vulnerability to respond to stressful events later in life. The present study attempted to evaluate the role of prenatal stress affecting the development of stress-related disorders and their reversion by postnatal exposure to Sertraline (SERT), a front-line medication for medication for posttraumatic stress disorder (PTSD) in humans. To achieve this, adult male and female prenatally stressed (PS) or unstressed (Controls) offspring rats, following oral chronic treatment with SERT (5 mg/kg/day; from 1 month to 4 months old), or not, were studied prior to and after a traumatic event. First, anxiety-like behavior during the prepulse inhibition (PPI) test, a modulation of the startle reflex, was examined in all animals. Subsequently, the animals were subjected to a session of mild inescapable footshocks (IS; 0.35 mA, 5 s) in a shuttle box that was followed by 4 days of situational reminders in the aversive context. Prior to the footshocks no effects of PS or SERT were shown, and no changes in PPI and the habituation to the shuttle box were found. After them, PS led animals to exhibit behavioral alterations. When compared to the Controls, PS animals of both sexes displayed less rearing activity in the aversive environment. PS males responded less to footshock delivery and, in most of the animals, fear extinction was impaired. Moreover, the early postnatal exposure to SERT lessened the behavioral impact of PS in females, while in males it had no effect. Current results extend previous data from our laboratory, showing that PS heightened vulnerability to stress later on, and that SERT acts differently in males and females.

Functional β2-adrenoceptors in rat left atria: effect of foot-shock stress.

Altered sensitivity to the chronotropic effect of catecholamines and a reduction in the β1/β2-adrenoceptor ratio have previously been reported in right atria of stressed rats, human failing heart, and aging. In this report, we investigated whether left atrial inotropism was affected by foot-shock stress. Male rats were submitted to 3 foot-shock sessions and the left atrial inotropic response, adenylyl cyclase activity, and β-adrenoceptor expression were investigated. Left atria of stressed rats were supersensitive to isoprenaline when compared with control rats and this effect was abolished by ICI118,551, a selective β2-receptor antagonist. Schild plot slopes for the antagonism between CGP20712A (a selective β1-receptor antagonist) and isoprenaline differed from unity in atria of stressed but not control rats. Atrial sensitivity to norepinephrine, as well as basal and forskolin- or isoprenaline-stimulated adenylyl cyclase activities were not altered by stress. The effect of isoprenaline on adenylyl cyclase stimulation was partially blocked by ICI118,551 in atrial membranes of stressed rats. These findings indicate that foot-shock stress equally affects inotropism and chronotropism and that β2-adrenoceptor upregulation contributes to the enhanced inotropic response to isoprenaline.

Temporal changes in c-Fos activation patterns induced by conditioned fear

Mechanisms underlying shock-induced conditioned fear - a paradigm frequently used to model posttraumatic stress disorder, PTSD - are usually studied shortly after shocks. Some of the brain regions relevant to conditioned fear were activated in all the c-Fos studies published so far, but the overlap between the activated regions was small across studies. We hypothesized that discrepant findings were due to dynamic neural changes that followed shocks, and a more consistent picture would emerge if consequences were studied after a longer interval. Therefore, we exposed rats to a single session of footshocks and studied their behavioral and neural responses one and 28 days later. The neuronal activation marker c-Fos was studied in 24 brain regions relevant for conditioned fear, e.g. in subdivisions of the prefrontal cortex, hippocampus, amygdala, hypothalamic defensive system, brainstem monoaminergic nuclei and periaqueductal gray. The intensity of conditioned fear (as shown by the duration of contextual freezing) was similar at the two time-points, but the associated neuronal changes were qualitatively different. Surprisingly, however, Multiple Regression Analyses suggested that conditioned fear-induced changes in neuronal activation patterns predicted the duration of freezing with high accuracy at both time points. We suggest that exposure to electric shocks is followed by a period of plasticity where the mechanisms that sustain conditioned fear undergo qualitative changes. Neuronal changes observed 28 days but not 1 day after shocks were consistent with those observed in human studies performed in PTSD patients.

Not all stressors are equal: behavioral and endocrine evidence for development of contextual fear conditioning after a single session of footshocks but not of immobilization.

Exposure of animals to footshocks (FS) in absence of any specific cue results in the development of fear to the compartment where shocks were given (contextual fear conditioning), and this is usually evaluated by time spent freezing. However, the extent to which contextual fear conditioning always develops when animals are exposed to other stressors is not known. In the present work we firstly demonstrated, using freezing, that exposure of adult rats to a single session of FS resulted in short-term and long-term contextual fear conditioning (freezing) that was paralleled by increased hypothalamic-pituitary-adrenal (HPA) activation. In contrast, using a similar design, no HPA or behavioral evidence for such conditioning was found after exposure to immobilization on boards (IMO), despite this stressor being of similar severity as FS on the basis of standard physiological measures of stress, including HPA activation. In a final experiment we directly compared the exposure to the two stressors in the same type of context and tested for the development of conditioning to the context and to a specific cue for IMO (the board). We observed the expected high levels of freezing and the conditioned HPA activation after FS, but not after IMO, regardless of the presence of the board during testing. Therefore, it can be concluded that development of fear conditioning to context or particular cues, as evaluated by either behavioral or endocrine measures, appears to be dependent on the nature of the aversive stimuli, likely to be related to biologically preparedness to establish specific associations.

Metyrapone and fluoxetine suppress behavioural but not cardiac effects of sub‐chronic stress in rats

To determine whether repetitive aversive episodes have enduring effects on cardiac autonomic control, male Sprague-Dawley rats (n=35) instrumented for telemetric recording of heart rate (HR) and locomotor activity (LOC) were subjected to footshock sessions on five consecutive days. During post-stress week, HR was reduced in the active (ΔHR=-23±3 bpm) and the inactive (ΔHR=−20±3 bpm) phases of the light/dark cycle, and LOC was reduced in the active phase (Δ= −0.9±0.1 cpm). Bradycardic effect was not related to reduced LOC, and persisted after sympathetic blockade with atenolol. Vagal blockade (scopomamine) was performed before and after the stress period; in both instances HR increased to the same level suggesting that stress-induced bradycardia was vagally-mediated. In different groups (n=7 each), SSRI Fluoxetine and inhibitor of corticosterone synthesis Metyrapone did not affect stress-induced cardiac changes but prevented reduction in LOC. We conclude that: i) behavioural effects (LOC) of chronic stress are mediated by stress-induced rises of corticosterone whereas cardiac effects are not; and ii) these locomotor could be prevented by SSRI treatment. Supported by NHMRC.

Footshock stress differentially affects responses of two subpopulations of spinal dorsal horn neurons to urinary bladder distension in rats

This investigation examined the effect of footshock on responses of 283 spinal dorsal horn neurons (DHNs) to urinary bladder distension (UBD). Female rats were treated with seven daily sessions of footshock (chronic footshock, CFS), six accommodation sessions followed by one exposure to footshock (acute footshock, AFS) or handled similarly without receiving any footshock (no footshock, NFS). After the final footshock or NFS session, rats were anesthetized, a laminectomy performed and extracellular single-unit recordings of L6–S1 DHNs obtained in intact or spinalized preparations. Neurons were classified as Type I—inhibited by heterotopic noxious conditioning stimuli (HNCS) or as Type II—not inhibited by HNCS—and characterized for spontaneous activity and for neuronal discharges evoked by graded UBD. A differential effect of footshock-induced stress was noted on neuronal subgroups. In intact preparations, Type I neurons were less responsive to UBD after either chronic or acute stress, while Type II neurons demonstrated significantly augmented responses to UBD. This enhanced neuronal responsiveness to UBD was present in spinalized preparations following exposure to CFS but not AFS. Type I neurons were still less responsive to stress in spinalized preparations following CFS and AFS. This study provides further evidence that (1) at least two populations of spinal neurons exist which encode for visceral stimuli and are likely to have distinct roles in visceral nociception, and that (2) the chronic stress-induced enhancement of DHN responses to UBD involves changes at the spinal level while the acute stress effects are dependent on a supraspinal substrate.

Inhibition of FAAH during a trauma prevents the development of sleep disturbances

Event Abstract Back to Event Inhibition of FAAH during a trauma prevents the development of sleep disturbances K. Spitzer1*, V. Humli1, T. T. Nguyen2, A. Szőke2, J. Haller3 and S. Kántor4 1 Eotvos Lorand University, Hungary 2 Semmelweis University, Hungary 3 Hungarian Academy of Sciences, Department of Behavioral Neuroscience, Institute of Experimental Medicine, Hungary 4 Pazmany Peter Catholic University, Hungary Post-traumatic stress disorder (PTSD) is an anxiety disorder that results from exposure to a traumatic event. Besides distress, PTSD is characterized by cognitive dysfunctions and severe sleep disturbances. Since the cannabinoid CB1 receptor play a central role in trauma-induced plastic changes in the brain that lead to PTSD and CB1 receptors are present in sleep-wake centers of the brain, we hypothesized that an enhanced endocannabinoid signaling during a traumatic event affects the development of PTSD sleep symptoms. To test our hypothesis, we studied the effect of the fatty acid amide hydrolase enzyme inhibitor URB-597 on contextual conditioned fear responses in mice. We instrumented 18 weeks old, male, CD1 mice with EEG/EMG electrodes, and after recovery, we exposed them to a brief session of electric foot-shocks. 40 min before shock exposure, we injected the mice with URB-597 (0.3 mg/kg, i.p.) or vehicle. Sleep/wake behavior was recorded in mice for 24 hours in their home cages a day before (baseline day), a day after and 14 days after the trauma. The re-exposure to the shock context caused hypervigilance in vehicle but not in URB597 treated mice 14 days after the trauma. REM sleep was also reduced in these mice, which effect was prevented by URB597 treatment. These results suggest that an increased endocannabinoid signaling during the trauma alleviates the sleep symptoms of a subsequent PTSD and may explain the interindividual differences in responses to traumatic events. Keywords: disorders, Neuroscience Conference: 13th Conference of the Hungarian Neuroscience Society (MITT), Budapest, Hungary, 20 Jan - 22 Jan, 2011. Presentation Type: Abstract Topic: Disorders Citation: Spitzer K, Humli V, Nguyen TT, Szőke A, Haller J and Kántor S (2011). Inhibition of FAAH during a trauma prevents the development of sleep disturbances. Front. Neurosci. Conference Abstract: 13th Conference of the Hungarian Neuroscience Society (MITT). doi: 10.3389/conf.fnins.2011.84.00035 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 03 Mar 2011; Published Online: 23 Mar 2011. * Correspondence: Dr. K. Spitzer, Eotvos Lorand University, Budapest, Hungary, klaudia.spitzer@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers K. Spitzer V. Humli T. T Nguyen A. Szőke J. Haller S. Kántor Google K. Spitzer V. Humli T. T Nguyen A. Szőke J. Haller S. Kántor Google Scholar K. Spitzer V. Humli T. T Nguyen A. Szőke J. Haller S. Kántor PubMed K. Spitzer V. Humli T. T Nguyen A. Szőke J. Haller S. Kántor Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Neurobiological examination of distress provoked by trauma experience in an animal model: short- and long-term effects

Event Abstract Back to Event Neurobiological examination of distress provoked by trauma experience in an animal model: short- and long-term effects P. Sörös1*, Á. Tulogdi1, R. Nagy1, M. Tóth1, L. Bíró1, M. Aliczki1, B. Klausz1, É. Mikics1 and J. Haller1 1 Institute of Experimental Medicine of the Hungarian Academy of Sciences, Hungary Mechanisms underlying shock-induced conditioned fear -a laboratory model of post-traumatic stress disorder, PTSD- are usually studied shortly after shock exposure. As PTSD develops after a long incubation time, we hypothesized that a more consistent picture would be obtained at later time-points. Therefore, we exposed rats to a single session of footshocks and studied their conditioned fear response one and 28 days later. The neuronal activation patterns were studied by c-Fos immunocytochemistry in 29 brain regions relevant for the expression of conditioned fear. The duration of contextual freezing was similar at the two time points, but the associated neuronal changes were qualitatively different. A restricted number of brain areas were affected one day after shocks; freezing was associated with, and likely due to an enhanced activation of the anterior hypothalamus, and/or to changed periaqueductal gray activation. 28 days after shocks, almost all the systems involved in conditioned fear were activated. Increased activations were seen in the medial prefrontal cortex, hippocampus, medial and basolateral amygdala, ventromedial hypothalamic nucleus, hypothalamic paraventricular nucleus, dorsomedial periaqueductal grey, median raphe and locus coeruleus. The sharp contrast between the similarity in behavior and the markedly different neuronal activation patterns are discussed in conjunction with the temporal evolution of shock-induced changes and the relevance of incubation time. Keywords: disorders, Neuroscience Conference: 13th Conference of the Hungarian Neuroscience Society (MITT), Budapest, Hungary, 20 Jan - 22 Jan, 2011. Presentation Type: Abstract Topic: Disorders Citation: Sörös P, Tulogdi Á, Nagy R, Tóth M, Bíró L, Aliczki M, Klausz B, Mikics É and Haller J (2011). Neurobiological examination of distress provoked by trauma experience in an animal model: short- and long-term effects. Front. Neurosci. Conference Abstract: 13th Conference of the Hungarian Neuroscience Society (MITT). doi: 10.3389/conf.fnins.2011.84.00034 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 03 Mar 2011; Published Online: 23 Mar 2011. * Correspondence: Dr. P. Sörös, Institute of Experimental Medicine of the Hungarian Academy of Sciences, Budapest, Hungary, petra.soros@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers P. Sörös Á. Tulogdi R. Nagy M. Tóth L. Bíró M. Aliczki B. Klausz É. Mikics J. Haller Google P. Sörös Á. Tulogdi R. Nagy M. Tóth L. Bíró M. Aliczki B. Klausz É. Mikics J. Haller Google Scholar P. Sörös Á. Tulogdi R. Nagy M. Tóth L. Bíró M. Aliczki B. Klausz É. Mikics J. Haller PubMed P. Sörös Á. Tulogdi R. Nagy M. Tóth L. Bíró M. Aliczki B. Klausz É. Mikics J. Haller Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The role of neuroinflammation in the release of aversive odor cues from footshock-stressed rats: Implications for the neural mechanism of alarm pheromone

Stressed animals have been known to release aversive chemosignals toward which conspecifics show avoidance-like responses. The present studies assessed whether inflammatory cytokine responses provoked by footshock stress modulate odor signals released from male rats. Male rats were exposed to 30min of intermittent footshock (60 shocks, 1.0mA, 100ms each, variable ITI of 30s) or remained in their home cages as non-stressed controls. Real time RT-PCR analysis of brain tissues indicated that footshock increased the pro-inflammatory cytokine, IL-1β and hnCRH as well as c-fos mRNA expressions in the paraventricular nucleus, and the bed nucleus of the stria terminalis, and increased plasma corticosterone levels. Soiled bedding collected from rats exposed to 30-min, but not 5-min, of footshock elicited a differential response, as expressed by decreased sniffing and increased avoidance in male test subjects. Soiled bedding from rats given corticosterone injection (s.c. 1.25 or 3.75mg/ml) 3h before bedding collection evoked no avoidance response in odor-recipients. Furthermore, ICV infusion of the anti-inflammatory cytokine IL-10 (20 or 200ng) into the stimulus animals 30-min before a 30-min footshock session, had no effect on plasma corticosterone levels in the stimulus animals, but attenuated the release of aversive odor as indicated by dose-dependently diminished avoidance in odor-recipient rats. These results demonstrated that stressed rats release odorant cues that cause other rats to move away from the source of the signal. Such stress-induced chemosignals may be mediated by inflammatory cytokine responses in the brain.

A single footshock causes long-lasting hypoactivity in unknown environments that is dependent on the development of contextual fear conditioning

Exposure to a single session of footshocks induces long-lasting inhibition of activity in unknown environments that markedly differ from the shock context. Interestingly, these effects are not necessarily associated to an enhanced anxiety and interpretation of this hypoactivity remains unclear. In the present experiment we further studied this phenomenon in male Sprague–Dawley rats. In a first experiment, a session of three shocks resulted in hypoactivity during exposure, 6–12 days later, to three different unknown environments. This altered behaviour was not accompanied by a greater hypothalamic–pituitary–adrenal (HPA) activation, although greater HPA activation paralleling higher levels of freezing was observed in the shock context. In a second experiment we used a single shock and two procedures, one with pre-exposure to the context before the shock and another with immediate shock that did not induce contextual fear conditioning. Hypoactivity and a certain level of generalization of fear (freezing) to the unknown environments only appeared in the group that developed fear conditioning, but no evidence for enhanced anxiety in the elevated plus-maze was found in any group. The results suggest that if animals are able to associate an aversive experience with a distinct unknown environment, they would display more cautious behaviour in any unknown environment and such strategy persists despite repeated experience with different environments. This long-lasting cautious behaviour was not associated to greater HPA response to the unknown environment that was however observed in the shock context. The present findings raised some concerns about interpretation of long-lasting behavioural changes caused by brief stressors.

AT1A receptor deficiency attenuates cardiovascular reactivity to contextual fear conditioning but not anxiety‐like behavior in mice

Angiotensin AT1 receptors are important in regulating blood pressure (BP) reactivity to unconditioned aversive stimuli. In this study, we examined the influence of AT1A receptors on cardiovascular and behavioral effects of contextual fear conditioning. AT1A receptor knockout (AT1A−/−) and AT1A+/+ mice were implanted with BP telemetry devices and subjected to a 5‐min footshock session consisted of 4 brief electric footshocks. Mice were then re‐exposed to the same context (the footshock chamber) 4 hours and 1–4 days after the footshock, and their behavior was analyzed by a computerized video‐tracking system. The BP rise during the re‐exposure sessions was consistently lower in AT1A−/− than AT1A+/+mice (+24±4 and +37±2 mmHg, respectively, n=5–6). However, immobility duration (freezing) was similar between groups. Unexpectedly, AT1A−/− mice displayed increased anxiety‐like behavior as evidenced by reduced time spent in the centre of the footshock chamber. Likewise, the BP rise during the elevated plus maze test was lower by 25% in AT1A−/− mice, although anxiety scores increased. These data indicate that AT1A receptor deficiency in mice attenuates the BP responsiveness to conditioned contextual fear. This attenuation cannot be ascribed to reduced emotional reactivity or anxiety, and may thus relate principally to dysfunctions in central autonomic regulation. NHMRC (Australia)

Increased spontaneous activity and reduced inotropic response to catecholamines in ventricular myocytes from footshock-stressed rats

Exposure to stressors has been shown to change atrial responsiveness to catecholamines, but it is not clear yet how it affects the ventricular myocardium, which plays a major role in the catecholamine-stimulated increase in cardiac output. Adult male rats were submitted to restraint (RST) or footshock (FS) sessions for 3 days. Reactivity to agonists of the β-adrenergic pathway was analyzed in left ventricular myocytes isolated from stressed and control rats (CTR). Whereas no significant changes were detected after RST, enhancement of catecholamine-induced spontaneous activity, accompanied by decrease in inotropic maximal response, was observed in myocytes from FS rats. Changes were reversed by β1-, but not by α1- or β2-adrenoceptor (AR) blockade. Similar alterations were seen in response to forskolin. However, responsiveness to 3-isobutyl-1-methylxanthine and CaCl2 was comparable in control and FS groups. A significant negative correlation was observed between the maximally stimulated spontaneous activity rate and contraction amplitude. Results indicate that: (a) enhanced automatism during adrenergic stimulation of myocytes from FS rats is mediated by β1-ARs and seems to involve post-receptor mechanisms, probably decreased cAMP degradation; (b) the exaggerated spontaneous activity, which may contribute to generation of catecholaminergic arrhythmias, might limit the development of the inotropic response.

Age‐ and Sex‐Dependent Effects of Footshock Stress on Subsequent Alcohol Drinking and Acoustic Startle Behavior in Mice Selectively Bred for High‐Alcohol Preference

Exposure to stress during adolescence is known to be a risk factor for alcohol-use and anxiety disorders. This study examined the effects of footshock stress during adolescence on subsequent alcohol drinking in male and female mice selectively bred for high-alcohol preference (HAP1 lines). Acoustic startle responses and prepulse inhibition (PPI) were also assessed in the absence of, and immediately following, subsequent footshock stress exposures to determine whether a prior history of footshock stress during adolescence would produce enduring effects on anxiety-related behavior and sensorimotor gating. Alcohol-naïve, adolescent (male, n = 27; female, n = 23) and adult (male, n = 30; female, n = 30) HAP1 mice were randomly assigned to a stress or no stress group. The study consisted of 5 phases: (1) 10 consecutive days of exposure to a 30-minute footshock session, (2) 1 startle test, (3) one 30-minute footshock session immediately followed by 1 startle test, (4) 30 days of free-choice alcohol consumption, and (5) one 30-minute footshock session immediately followed by 1 startle test. Footshock stress exposure during adolescence, but not adulthood, robustly increased alcohol drinking behavior in both male and female HAP1 mice. Before alcohol drinking, females in both the adolescent and adult stress groups showed greater startle in phases 2 and 3; whereas males in the adolescent stress group showed greater startle only in phase 3. After alcohol drinking, in phase 5, enhanced startle was no longer apparent in any stress group. Males in the adult stress group showed reduced startle in phases 2 and 5. PPI was generally unchanged, except that males in the adolescent stress group showed increased PPI in phase 3 and females in the adolescent stress group showed decreased PPI in phase 5. Adolescent HAP1 mice appear to be more vulnerable to the effects of footshock stress than adult mice, as manifested by increased alcohol drinking and anxiety-related behavior in adulthood. These results in mice suggest that stress exposure during adolescence may increase the risk for developing an alcohol-use and/or anxiety disorder in individuals with a genetic predisposition toward high alcohol consumption.

Chronic stress during paradoxical sleep deprivation increases paradoxical sleep rebound: Association with prolactin plasma levels and brain serotonin content

Previous studies suggest that stress associated to sleep deprivation methods can affect the expression of sleep rebound. In order to examine this association and possible mechanisms, rats were exposed to footshock stress during or immediately after a 96-h period of paradoxical sleep deprivation (PSD) and their sleep and heart rate were recorded. Control rats (maintained in individual home cages) and paradoxical sleep-deprived (PS-deprived) rats were distributed in three conditions (1) no footshock--NF; (2) single footshock--SFS: one single footshock session at the end of the PSD period (6-8 shocks per minute; 100 ms; 2 mA; for 40 min); and (3) multiple footshock--MFS: footshock sessions with the same characteristics as described above, twice a day throughout PSD (at 7:00 h and 19:00 h) and one extra session before the recovery period. After PSD, animals were allowed to sleep freely for 72 h. Additional groups were sacrificed at the end of the sleep deprivation period for blood sampling (ACTH, corticosterone, prolactin and catecholamine levels) and brain harvesting (monoamines and metabolites). Neither SFS nor MFS produced significant alterations in the sleep patterns of control rats. All PS-deprived groups exhibited increased heart rate which could be explained by increased dopaminergic activity in the medulla. As expected, PS deprivation induced rebound of paradoxical sleep in the first day of recovery; however, PSD+MFS group showed the highest rebound (327.3% above the baseline). This group also showed intermediate levels of corticosterone and the highest levels of prolactin, which were positively correlated with the length of PS episodes. Moreover, paradoxical sleep deprivation resulted in elevation of the serotonergic turnover in the hypothalamus, which partly explained the hormonal results, and in the hippocampus, which appears to be related to adaptive responses to stress. The data are discussed in the realm of a prospective importance of paradoxical sleep for processing of traumatic events.

A single exposure to immobilization causes long-lasting pituitary-adrenal and behavioral sensitization to mild stressors

We have previously reported that a single exposure to immobilization (IMO) in rats causes a long-term desensitization of the hypothalamic-pituitary-adrenal (HPA) response to the same (homotypic) stressor. Since there are reports showing that a single exposure to other stressors causes sensitization of the HPA response to heterotypic stressors and increases anxiety-like behavior, we studied in the present work the long-term effects of IMO on behavioral and HPA response to mild superimposed stressors. In Experiments 1 and 2, adult male Sprague–Dawley rats were subjected to 2 h of IMO and then exposed for 5 min to the elevated plus-maze (EPM) at 1, 3 or 7 days after IMO. Blood samples were taken at 15 min after initial exposure to the EPM. Increases in anxiety-like behavior and HPA responsiveness to the EPM were found at all times post-IMO. Changes in the resting levels of HPA hormones did not explain the enhanced HPA responsiveness to the EPM (Experiment 3). In Experiments 4 and 5, we studied the effects of a single exposure to a shorter session of IMO (1 h) on behavioral and HPA responses to a brief and mild session of foot-shocks done 10 days after IMO. Neither previous IMO nor exposure to shocks in control rats modified behavior in the EPM. However, a brief session of shocks in previously IMO-exposed rats dramatically increased anxiety in the EPM. HPA and freezing responses to shocks were similar in control and previous IMO groups. Therefore, a single exposure to IMO appears to induce long-lasting HPA and behavioral sensitization to mild superimposed stressors, although the two responses are likely to be at least partially independent. Long-term effects of IMO on the susceptibility to stress-induced endocrine and emotional disturbances may be relevant to the characterization of animal models of post-traumatic stress.