Persistent Anxiety-like Behavior Research Articles

Inhibiting the JNK Signaling Pathway Attenuates Hypersensitivity and Anxiety-Like Behavior in a Rat Model of Non-specific Chronic Low Back Pain.

Low back pain (LBP) has become a leading cause of disability worldwide. Astrocyte activation in the spinal cord plays an important role in the maintenance of latent sensitization of dorsal horn neurons in LBP. However, the role of spinal c-Jun N-terminal kinase (JNK) in astrocytes in modulating pain behavior of LBP model rats and its neurobiological mechanism have not been elucidated. Here, we investigate the role of the JNK signaling pathway on hypersensitivity and anxiety-like behavior caused by repetitive nerve growth factor (NGF) injections in male non-specific LBP model rats. LBP was produced by two injections (day 0, day 5) of NGF into multifidus muscle of the low backs of rats. We observed prolonged mechanical and thermal hypersensitivity in the low backs or hindpaws. Persistent anxiety-like behavior was observed, together with astrocyte, p-JNK, and neuronal activation and upregulated expression of monocyte chemoattractant protein-1 (MCP-1), and chemokine (C-X-C motif) ligand 1 (CXCL1) proteins in the spinal L2 segment. Second, the JNK inhibitor SP600125 was intrathecally administrated in rats from day 10 to day 12. It attenuated mechanical and thermal hypersensitivity of the low back or hindpaws and anxiety-like behavior. Meanwhile, SP600125 decreased astrocyte and neuronal activation and the expression of MCP-1 and CXCL1 proteins. These results showed that hypersensitivity and anxiety-like behavior induced by NGF in LBP rats could be attenuated by the JNK inhibitor, together with downregulation of spinal astrocyte activation, neuron activation, and inflammatory cytokines. Our results indicate that intervening with the spinal JNK signaling pathway presents an effective therapeutic approach to alleviating LBP.

Chronic intermittent ethanol exposure during adolescence produces sex- and age-dependent changes in anxiety and cognition without changes in microglia reactivity late in life.

Binge-like ethanol exposure during adolescence has been shown to produce long lasting effects in animal models including anxiety-like behavior that can last into young adulthood and impairments in cognition that can last throughout most of the lifespan. However, little research has investigated if binge-like ethanol exposure during adolescence produces persistent anxiety-like behavior and concomitantly impairs cognition late in life. Furthermore, few studies have investigated such behavioral effects in both female and male rats over the lifespan. Finally, it is yet to be determined if binge-like ethanol exposure during adolescence alters microglia activation in relevant brain regions late in life. In the present study female and male adolescent rats were exposed to either 3.0 or 5.0 g/kg ethanol, or water control, in a chronic intermittent pattern before being tested in the elevated plus maze and open field task over the next ∼18 months. Animals were then trained in a spatial reference task via the Morris water maze before having their behavioral flexibility tested. Finally, brains were removed, sectioned and presumptive microglia activation determined using autoradiography for [3H]PK11195 binding. Males, but not females, displayed an anxiety-like phenotype initially following the chronic intermittent ethanol exposure paradigm which resolved in adulthood. Further, males but not females had altered spatial reference learning and impaired behavioral flexibility late in life. Conversely, [3H]PK11195 binding was significantly elevated in females compared to males late in life and the level of microglia activation interacted as a function of sex and brain regions, but there was no long-term outcome related to adolescent alcohol exposure. These data further confirm that binge-like ethanol exposure during adolescence produces alterations in behavior that can last throughout the lifespan. In addition, the data suggest that microglia activation late in life is not exacerbated by prior binge-like ethanol exposure during adolescence but the expression is sex- and brain region-dependent across the lifespan.

Life-threatening, high-intensity trauma- and context-dependent anxiety in zebrafish and its modulation by epinephrine

Trauma-related psychopathology transpires in some individuals after exposure to a life-threatening event. While aberrant adrenergic processes may contribute to this, a clear understanding of how said processes influence trauma-related conditions, remain inadequate. Here, we aimed to develop and describe a novel zebrafish (Danio rerio) model of life-threatening trauma-induced anxiety that may be representative of trauma related anxiety, and to evaluate the impact of stress-paired epinephrine (EPI) exposure in the model system. Four groups of zebrafish were each exposed to different and unique stress-related paradigms, i.e., i) a sham (trauma free), ii) high-intensity trauma (triple hit; THIT), iii) high-intensity trauma in the presence of EPI exposure (EHIT), and iv) EPI exposure on its own, all applied in the presence of a color context. Novel tank anxiety was subsequently assessed at 1, 4, 7 and 14 days after the traumatic event. The present results demonstrate that 1) through day 14, THIT or EPI exposure alone induced persistent anxiety-like behavior, 2) EHIT blunted the delayed anxiety-like sequalae associated with severe trauma, 3) exposure to a trauma-paired color context prior to anxiety testing bolstered the subsequent anxiety-like behavior of THIT, but not EHIT -exposed fish, and 4) despite this, THIT- and EPI-exposed fish showed a lesser degree of contextual avoidance behavior compared to sham- or EHIT-exposed fish. These results indicate that the stressors induced long-lasting anxiety-like behavior reminiscent of post trauma anxiety, while EPI displays complex interactions with the stressor, including a buffering effect to subsequent exposure of a trauma-paired cue.

Prenatal ethanol exposure leads to persistent anxiety-like behavior during adulthood indicated by reduced horizontal and vertical exploratory behaviors.

Fetal alcohol spectrum disorders (FASD) caused by prenatal ethanol exposure (PE) consist of many cognitive/behavioral deficits. Studies have reported that PE leads to impairments of learning and memory, attention, executive function, and anxiety. Open field (OF) is a common behavioral model which offers comprehensive ethological information. Here, we analyzed multiple parameters of OF to examine anxiety behavior and habituation after PE. Pregnant Sprague Dawley rats were gavaged twice/day with 0 or 3 g/kg/treatment ethanol (15% w/v) during gestational day (GD) 8-20, mimicking second-trimester heavy PE in humans. The control and PE adult offspring were subjected to OF task in different ambient light levels with or without acute stress. Prenatal ethanol exposure did not influence the overall locomotor activities or habituation in the OF. In lower ambient light, no PE effects could be detected. In higher ambient light, female PE rats showed less activities in the center zone, indicative of increased anxiety. Males show lower activities in the center zone only after acute stress. Rats spent <2% of the time in the center zone compared to >75% of the time in the corner zone where they engaged in frequent rearing activities (vertical exploration; exploratory rearing). Prenatal ethanol exposure led to lower rearing activities in the corner in both males and females. Acute stress masks the PE effects in males but not in females. The results support that heavy PE leads to persistent anxiety-like behavior during adulthood in both sexes. This conclusion is supported by using multiple parameters of exploratory behavior in the OF, including the rearing activities in the corner to reach reliable quantification of anxiety-like behavior.

Short- and Long-Term Effects of Suboptimal Selenium Intake and Developmental Lead Exposure on Behavior and Hippocampal Glutamate Receptors in a Rat Model.

Selenium (Se) is an essential trace element required for normal development as well as to counteract the adverse effects of environmental stressors. Conditions of low Se intake are present in some European countries. Our aim was to investigate the short- and long-term effects of early-life low Se supply on behavior and synaptic plasticity with a focus on the hippocampus, considering both suboptimal Se intake per se and its interaction with developmental exposure to lead (Pb). We established an animal model of Se restriction and low Pb exposure; female rats fed with an optimal (0.15 mg/kg) or suboptimal (0.04 mg/kg) Se diet were exposed from one month pre-mating until the end of lactation to 12.5 µg/mL Pb via drinking water. In rat offspring, the assessment of motor, emotional, and cognitive endpoints at different life stages were complemented by the evaluation of the expression and synaptic distribution of NMDA and AMPA receptor subunits at post-natal day (PND) 23 and 70 in the hippocampus. Suboptimal Se intake delayed the achievement of developmental milestones and induced early and long-term alterations in motor and emotional abilities. Behavioral alterations were mirrored by a drop in the expression of the majority of NMDA and AMPA receptor subunits analyzed at PND 23. The suboptimal Se status co-occurring with Pb exposure induced a transient body weight increase and persistent anxiety-like behavior. From the molecular point of view, we observed hippocampal alterations in NMDA (Glun2B and GluN1) and AMPA receptor subunit trafficking to the post-synapse in male rats only. Our study provides evidence of potential Se interactions with Pb in the developing brain.

Estrogen‐Mediated Mechanisms of Social Stress Susceptibility within the Central Amygdala

Social stress is the most common form of stress humans experience and is a risk factor for anxiety disorders. Women are 2‐3 times more likely to suffer from stress‐related anxiety disorders than men, but this heightened susceptibility is limited to the timeframe between the onset of puberty and menopause, suggesting a role for ovarian hormones. While the underlying neural mechanisms of stress susceptibility are unclear, many anxiety‐like behaviors in rodents including burying, startle responses and avoidance of elevated open spaces are regulated in part by corticotropin releasing factor (CRF) in the stress‐sensitive central nucleus of the amygdala (CeA). Recent evidence also highlights a critical role for estrogen (E) in regulating social stress susceptibility in female rats, and the CeA expresses estrogen receptor‐β (ER‐β). Although a large body of literature suggests that E may signal through ER‐β to reduce anxiety‐like behaviors during non‐stressful conditions, we hypothesize that in the context of social stress, E exacerbates anxiety‐like behaviors through increased expression of CRF in the CeA of female rats. This study examines the role for ER‐β in CeA in regulating stress susceptibility in female rats via region‐specific pharmacological blockade of ER‐β using PHTPP, an ER‐β antagonist. Following recovery from surgical implantation of indwelling bilateral CeA cannulae, adult female Sprague‐Dawley rats were injected with vehicle or PHTPP (0 or 10 µM; 0.5 µL over 1 min). One hour later, rats were subjected to control handling or witnessing an aggressive social defeat encounter between two male rats (WS, 15min/day x 5 days). WS and control rats were video‐recorded on days 1 and 5, and burying, freezing and rearing behaviors were quantified. Following 2 days of undisturbed rest in the absence of drug, all rats underwent a battery of tests to assess anxiety‐like behaviors including elevated plus maze (EPM), acoustic startle (ASR), and marble burying (MB). Each test was separated by 24 hours, and brain and blood were collected 2 days after MB. This study demonstrated that WS‐induced burying behavior was reduced by intra‐CeA PHTPP on days 1 and 5 of WS. There was no effect of WS nor PHTPP on freezing or rearing behavior during WS/control. The anxiogenic effects of WS are persistent as indicated by an enhanced ASR, increased MB and reduced open arm exploration during EPM among vehicle‐treated witnesses. PHTPP administration during WS attenuated these persistent anxiety‐like behaviors after WS exposure. Interestingly, PHTPP had opposing effects in WS and control rats such that PHTPP‐treated controls exhibited increased anxiety‐like behaviors indicated by increased marble burying and EPM closed arm time compared to vehicle‐treated controls. Brain tissue is currently being analyzed to determine the mechanism by which ER‐β regulates stress susceptibility, including measurement of CRF in the CeA and its projection regions. The findings from this study highlight a paradoxical role for E in regulating anxiety‐like behaviors, and further, identify that under conditions of social stress, E, acting through ER‐β, promotes stress susceptibility in female rats. Understanding the specific role for E in heightened stress susceptibility in females will help us to determine the physiological mechanisms underlying exaggerated social stress susceptibility among women.

202 A CTS Team Approach to Immune Signatures of PTSD Susceptibility

OBJECTIVES/GOALS: Post-traumatic stress disorder (PTSD) develops in a subset of individuals (15-25%) exposed to trauma. We report our preliminary findings investigating underlying peripheral immune responses related to risk and resilience to PTSD. METHODS/STUDY POPULATION: Sprague-Dawley rats (half male) were exposed to predator scent stress in the form of the fox pheromone 2,5-dihydro-2,4,5-trimethylthiazoline (TMT) once for 10 minutes. Seven days later, rats were assessed for persistent anxiety-like behavior using the acoustic startle response task (ASR) and elevated plus maze (EPM). Tail blood was collected for later inflammation analysis at three time points: 1) prior to experiment start, 2) after TMT exposure, and 3) after ASR and EPM. Using a with-in subjects design, our experiment elucidates the connection between PTSD-like symptoms and baseline immune function, inflammatory stress responses, and chronic inflammatory state after stress exposure. RESULTS/ANTICIPATED RESULTS: In comparison to healthy controls, humans with PTSD show elevated blood levels of inflammatory markers. Human studies also show a relationship between baseline immune dysfunction and later PTSD development. In agreement with this literature, we anticipate PTSD-like rats will have increased blood levels of inflammation markers at all three time points compared to resilient and control rats. These findings will back-translate human findings in support of the predator scent stress preclinical model of PTSD. DISCUSSION/SIGNIFICANCE: Our findings will elucidate the temporal aspects of proinflammatory markers and PTSD development. This study will indicate if baseline peripheral immune dysfunction, inflammatory response immediately after stress exposure, and/or chronic inflammatory state predicts ptsd-like behavior in rats.

Developmental Lead Exposure in Rats Causes Sex-Dependent Changes in Neurobiological and Anxiety-Like Behaviors that Are Improved by Taurine Co-treatment.

Lead (Pb2+) is a developmental neurotoxicant that causes alterations in the brain's excitation-to-inhibition (E/I) balance by disrupting the development of the GABAergic systems. These GABAergic disruptions have persistent neurobiological and neurobehavioral structure-function relationships that can be examined using animal models of Pb2+ exposure. Further, taurine, a GABA-AR agonist, has been shown to offer neuroprotection against neurodevelopmental Pb2+ exposure and senescence. The present study evaluated the effects of Pb2+ exposure (i.e., at 150 ppm and 1,000 ppm doses) on Long Evans hooded rats during the perinatal period of development on locomotor activity in the open field (OF) and anxiety-like behaviors in the elevated plus maze (EPM). This was followed by an examination of brain mass using an encephalization quotient (EQ) and isotropic fractionation (ITF) of total cells and the number of neurons and non-neuronal cells in the prefrontal cortex, hippocampus, and diencephalon. The results suggest that neurodevelopmental Pb2+ exposure caused persistent anxiety-like behaviors in both the OF and EPM with associated changes in EQ, but not ITF-determined cell density. Further, taurine treatment was observed to compensate for Pb2+ exposure in the behavioral assessments although precise neurobiological mechanisms remain unknown. Thus, more work is required to evaluate the role of taurine and other anxiolytic compounds in the alleviation of neurotoxicant-induced neurobehavioral syndromes and their associated neurobiological correlates.

Mice display learning and behavioral deficits after a 30-day spaceflight on Bion-M1 satellite

Profound effects of spaceflight on the physiology of humans and non-human animals are well-documented but incompletely explored. Current goals to undertake interplanetary missions increase the urgency to learn more about adaptation to prolonged spaceflight and readaptation to Earth-normal conditions, especially with the inclusion of radiation exposures greater than those confronted in traditional, orbital flights. The 30-day-long Bion M-1 biosatellite flight was conducted at a relatively high orbit, exposing the mice to greater doses of radiation in addition to microgravity, a combination of factors relevant to Mars missions. Results of the present studies with mice provide insights into the consequences on brain function of long-duration spaceflight. After landing, mice showed profound deficits in vestibular responses during aerial drop tests. Spaceflown mice displayed reduced grip strength, rotarod performance, and voluntary wheel running, each, which improved gradually but incompletely over the 7-days of post-flight testing. Continuous monitoring in the animals’ home cage activity, in combination with open-field and other tests of motor performance, revealed indices of altered affect, expressed as hyperactivity, potentiated thigmotaxis, and avoidance of open areas which, together, presented a syndrome of persistent anxiety-like behavior. A learned, operant response acquired before spaceflight was retained, whereas the acquisition of a new task was impaired after the flight. We integrate these observations with other results from Bion-M1’s program, identifying deficits in musculoskeletal and cardiovascular systems, as well as in the brain and spinal cord, including altered gene expression patterns and the accompanying neurochemical changes that could underlie our behavioral findings.

Delayed behavioral and genomic responses to acute combined stress in zebrafish, potentially relevant to PTSD and other stress-related disorders: Focus on neuroglia, neuroinflammation, apoptosis and epigenetic modulation

Stress is a common trigger of stress-related illnesses, such as anxiety, phobias, depression and post-traumatic stress disorder (PTSD). Various animal models successfully reproduce core behaviors of these clinical conditions. Here, we develop a novel zebrafish model of stress (potentially relevant to human stress-related disorders), based on delayed persistent behavioral, endocrine and genomic responses to an acute severe ‘combined’ stressor. Specifically, one week after adult zebrafish were exposed to a complex combined 90-min stress, we assessed their behaviors in the novel tank and the light-dark box tests, as well as whole-body cortisol and brain gene expression, focusing on genomic biomarkers of microglia, astrocytes, neuroinflammation, apoptosis and epigenetic modulation. Overall, stressed fish displayed persistent anxiety-like behavior, elevated whole-body cortisol, as well as upregulated brain mRNA expression of genes encoding the glucocorticoid receptor, neurotrophin BDNF and its receptors (TrkB and P75), CD11b (a general microglial biomarker), COX-2 (an M1-microglial biomarker), CD206 (an M2-microglial biomarker), GFAP (a general astrocytal biomarker), C3 (an A1-astrocytal biomarker), S100α10 (an A2-astrocytal biomarker), as well as pro-inflammatory cytokines IL-6, IL-1β, IFN-γ and TNF-α. Stress exposure also persistently upregulated the brain expression of several key apoptotic (Bax, Caspase-3, Bcl-2) and epigenetic genes (DNMT3a, DNMT3b, HAT1, HDAC4) in these fish. Collectively, the present model not only successfully recapitulates lasting behavioral and endocrine symptoms of clinical stress-related disorders, but also implicates changes in neuroglia, neuroinflammation, apoptosis and epigenetic modulation in long-term effects of stress pathogenesis in vivo.

Endocannabinoid modulating drugs improve anxiety but not the expression of conditioned fear in a rodent model of post-traumatic stress disorder

The endocannabinoid (eCB) system is a potential target for the treatment of symptoms of post-traumatic stress disorder (PTSD). Similar to clinical PTSD, approximately 25–30% of rats that undergo cued fear conditioning exhibit impaired extinction learning. In addition to extinction-resistant fear, these “weak extinction” (WE) rats show persistent anxiety-like behaviors. The goal of the present study was to test the hypothesis that behavioural differences between WE animals and those presenting normal extinction patterns (strong extinction; SE) could be mediated by the eCB system. Rats undergoing fear conditioning/extinction and fear recall sessions were initially segregated in weak and strong-extinction groups. Two weeks later, animals underwent a fear recall session followed by a novelty-suppressed feeding (NSF) test. In acute experiments, WE rats were injected with either the fatty acid amide hydrolase (FAAH) inhibitor URB597 or the CB1 agonist WIN55,212-2 1 h prior to long-term recall and NSF testing. SE animals were injected with the inverse CB1 receptor agonist AM251. In chronic experiments, WE and SE rats were given daily injections of URB597 or AM251 between short and long-term recall sessions. We found that acute administration of WIN55,212-2 but not URB597 reduced anxiety-like behaviour in WE rats. In contrast, AM251 was anxiogenic in SE animals. Neither treatment was effective in altering freezing expression during fear recall. The chronic administration of AM251 to SE or URB597 to WE did not alter fear or anxiety-like behaviour or changed the expression of FAAH and CB1. Together, these results suggest that systemic manipulations of the eCB system may alter anxiety-like behaviour but not the behavioural expression of an extinction-resistant associative fear memory.

Acute inhalation of combustion smoke triggers neuroinflammation and persistent anxiety-like behavior in the mouse

Context: Acute inhalation of combustion smoke triggers neurologic sequelae in survivors. Due to the challenges posed by heterogeneity of smoke exposures in humans, mechanistic links between acute smoke inhalation and neuropathologic sequelae have not been systematically investigated.Methods: Here, using mouse model of acute inhalation of combustion smoke, we studied longitudinal neurobehavioral manifestations of smoke exposures and molecular/cellular changes in the mouse brain.Results: Immunohistochemical analyses at eight months post-smoke, revealed hippocampal astrogliosis and microgliosis accompanied by reduced myelination. Elevated expression of proinflammatory cytokines was also detected. Longitudinal testing in different neurobehavioral paradigms in the course of post-smoke recovery, revealed lasting anxiety-like behavior. The examined paradigms included the open field exploration/anxiety testing at two, four and six months post-smoke, which detected decreases in total distance traveled and time spent in the central arena in the smoke-exposed compared to sham-control mice, suggestive of dampened exploratory activity and increased anxiety-like behavior. In agreement with reduced open field activity, cued fear conditioning test revealed increased freezing in response to conditioned auditory stimulus in mice after acute smoke inhalation. Similarly, elevated plus maze testing demonstrated lesser presence in open arms of the maze, consistent with anxiety-like behavior, for the post-smoke exposure mice.Conclusions: Taken together, our data demonstrate for the first time persistent neurobehavioral manifestations of acute inhalation of combustion smoke and provide new insights into long-term progression of events initiated by disrupted brain oxygenation that might contribute to lasting adverse sequelae in survivors of smoke inhalation injuries.

Novel rodent model of breast cancer survival with persistent anxiety-like behavior and inflammation

Breast cancer survivors are an expanding population that is troubled by lasting mental health problems, including depression and anxiety. These issues reduce quality-of-life throughout survivorhood. Research indicates that tumor biology, cancer treatments, and stress contribute to these mood disturbances. Although the mechanisms underlying these various causes remain under investigation, neuroinflammation is a leading hypothesis. To date, rodent models of recurrence-free tumor survival for understanding mechanisms by which these behavioral issues persist after cancer are lacking. Here, we test the extent to which potential behavioral symptoms persist after mammary tumor removal in mice (i.e., establishment of a cancer survivor model), while also empirically testing the causal role of tumors in the development of neuroinflammatory-mediated affective-like behaviors. Complete surgical resection of a non-metastatic orthotopic, syngeneic mammary tumor reversed tumor-induced increases of circulating cytokines (IL-6, CXCL1, IL-10) and myeloid-derived cells and modulated neuroinflammatory gene expression (Cd11b, Cxcl1). Multiple anxiety-like behaviors and some central and peripheral immune markers persisted or progressed three weeks after tumor resection. Together, these data indicate that persistent behavioral changes into cancer survivorhood may be due, in part, to changes in immunity that remain even after successful tumor removal. This novel survivor paradigm represents an improvement in modeling prevalent cancer survivorship issues and studying the basic mechanisms by which cancer/cancer treatments influence the brain and behavior.

Chronic intermittent ethanol exposure produces persistent anxiety in adolescent and adult rats.

Ethanol (EtOH) dependence and tolerance in the adult are marked by increased function of NMDA receptors and decreased function of GABAA receptors, which coincide with altered receptor subunit expression in specific brain regions. Adolescents often use EtOH at levels greater than adults, yet the receptor subunit expression profiles following chronic intermittent EtOH (CIE) exposure in adolescents are not known. Persistent age-dependent changes in receptor subunit alterations coupled with withdrawal-related anxiety may help explain the increase in alcohol abuse following adolescent experimentation with the drug. Adolescent and adult rats received 10 intraperitoneal administrations of 4.0g/kg EtOH or saline every 48hours. At either 24hours or 12days after the final exposure, anxiety-like behavior was assessed on the elevated plus maze and tissue was collected. Western blotting was used to assess changes in selected NMDA and GABAA receptor subunits in whole cortex and bilateral hippocampus. CIE exposure yields a persistent increase in anxiety-like behavior in both age groups. However, selected NMDA and GABAA receptor subunits were not differentially altered by this CIE exposure paradigm in adolescents or adults. CIE exposure produced persistent anxiety-like behavior, which has important implications for alcohol cessation. Given the reported behavioral and neuropeptide expression changes in response to this dose of EtOH, it is important for future work to consider the circumstances under which these measures are altered by EtOH exposure.

Withdrawal from chronic amphetamine produces persistent anxiety-like behavior but temporally-limited reductions in monoamines and neurogenesis in the adult rat dentate gyrus

Acute amphetamine administration activates monoaminergic pathways and increases systemic corticosterone, both of which influence anxiety states and adult dentate gyrus neurogenesis. Chronic amphetamine increases anxiety states in rats when measured at 24 h and at 2 weeks of withdrawal. However, the effects of chronic amphetamine exposure and withdrawal on long term anxiety-like behavior and adult neurogenesis in the dentate gyrus are unknown. Adult male rats were administered amphetamine (2.5 mg/kg, ip.) daily for two weeks. Anxiety-like behaviors were increased markedly in amphetamine-treated rats following four weeks of withdrawal from amphetamine. Plasma corticosterone level was unaltered by amphetamine treatment or withdrawal. However, norepinephrine and serotonin concentrations were selectively reduced in the dentate gyrus 20 h following amphetamine treatment. This effect did not persist through the four week withdrawal period. In separate experiments, rats received bromodeoxyuridine to label cells in S-phase, prior to or immediately following amphetamine treatment. Newly generated cells were quantified to measure extent of progenitor cell proliferation and neurogenesis following treatment or withdrawal. Progenitor cell proliferation and neurogenesis were not significantly affected by amphetamine exposure when measured 20 h following the last amphetamine treatment. However, neurogenesis in the dentate gyrus was reduced after four weeks of withdrawal when compared to saline-pretreated rats. Overall, our findings indicate that withdrawal from chronic amphetamine leads to persistent anxiety-like behavior which may be maintained by reduced neurogenesis in the dentate gyrus at this protracted withdrawal time point. However, neurogenesis is unaffected at earlier withdrawal time points where anxiety states emerge, suggesting different mechanisms may underlie the emergence of anxiety states during amphetamine withdrawal.

Persistent anxiety-like behavior in marmosets following a recent predatory stress condition: Reversal by diazepam

Initial investigations indicated the use of the Marmoset Predator Confrontation Test (MPCT) as an experimental procedure to measure fear/anxiety-related behaviors in non-human primates. However, possible long-term habituation effects and re-use of experimental subjects need to be verified. This study, therefore, compared the behavioral response of experienced versus naïve adult black tufted-ear marmosets ( Callithrix penicillata) in the MPCT, with/without diazepam administrations. Subjects were tested in the figure-8 maze and confronted with a taxidermized wild-cat predator stimulus. After four initial 20-min maze habituation sessions, each subject was submitted to two randomly-assigned 20-min predator confrontation sessions: vehicle and 2 mg/kg of diazepam. Confrontation with the predator induced significant behavioral changes; i.e., proximic avoidance and tsik-tsik alarm call. Diazepam administration, concomitant to predator exposure, reversed the behavioral changes observed. In both the experienced and naïve marmosets a similar behavioral profile and response pattern to diazepam was detected, corroborating the important selective pressure that felines seem to have on marmoset behavioral ecology. Therefore, during a more naturalistic-like regimen — i.e., recurring intermittent predator encounters — the general response pattern remains highly consistent, regardless of prior experience. One may consider the re-use of marmoset subjects in the MPCT, particularly under these specific conditions (i.e. repeated 20-min confrontations, 72-h apart).

A contemporary view of MDMA

Several years of pre-clinical and clinical research specify that MDMA (a principal ingredient in the drug known as “ecstasy”) is neurotoxic to serotonergic nerve terminals, and these neurobiological changes have been predicted to account for neurocognitive deficits, depression, and anxiety seen in human users. In 2002, a high-profile scientific report presented evidence that acute MDMA exposure caused significant damage to dopamine neurons in nonhuman primates (Ricaurte et al. 2002). The finding received considerable media attention, and gave the public the impression that MDMA was far more hazardous than originally thought. Less than a year later, the authors conceded that they were unable to replicate or extend their findings, and this was attributed to the fact that methamphetamine, not MDMA, was used in the earlier experiment (Ricaurte et al. 2003). Critics heralded the mix-up as the tip of an iceberg of a larger scientific/government coalition with an agenda to push forward the War on Drugs. The battle cry went out that “the US research agency that supports research on drug abuse needs to ensure its independence from intense political pressure to prove that recreational drugs are harmful” (Nature 2003), and a claim was made that NIDA favors “studies that are liable to prove the toxicity of recreational drugs” (Knight 2003). As expected, this issue provided fodder for individuals and organizations that would like a major revamping of MDMA research efforts. As a result, a debate on the actual harms of MDMA use was ignited with questions on whether MDMA is neurotoxic at all (Morris 2003). In the following year, Rich De La Garza and Ron Cowan organized a mini-symposium for the annual meeting of the Society for Neuroscience with the intent of providing the essential facts of neurotoxicity and neurocognitive changes that result from MDMA exposure in humans and animals. The current special issue is one outcome of that presentation and the contributions include original investigations as well as reviews that provide a critical analysis of published data pointing out strengths and weaknesses of established findings and frequently used methodologies. The special issue begins with the elegant and comprehensive work of Baumann and colleagues who show that typical doses of MDMA causing long-term serotonin (5-HT) depletion in rats do not reliably increase markers of neurotoxic damage such as cell death, silver staining, or reactive gliosis. MDMA administration induces persistent anxiety-like behaviors in the absence of measurable 5-HT deficits. A review article by De La Garza and colleagues reveals that MDMA serves as a reinforcer in rats (as measured in intravenous self-administration assays), though the responses are not of similar frequency relative to those previously reported for other psychostimulants (e.g., cocaine). Kuhn and colleagues report sex-specific differences in locomotor effects produced by MDMA. Female rats exhibit greater behavioral activation than males after MDMA treatment initially and upon challenge after a 2-week recovery period. The mechanism by which MDMA increases locomotor activity more in females is attributed to Psychopharmacology (2007) 189:403–405 DOI 10.1007/s00213-006-0636-4

Anisomycin, a Protein Synthesis Inhibitor, Disrupts Traumatic Memory Consolidation and Attenuates Posttraumatic Stress Response in Rats

Paradoxical changes in memory represent a troublesome characteristic of posttraumatic stress disorder (PTSD). Exceptionally vivid intrusive memories of some aspects of the trauma are mingled with patchy amnesia regarding other important aspects. Molecular studies of the memory process suggest that the conversion from labile short-term memory into long-term fixed traces involves protein synthesis. This study assessed the effects of administration of anisomycin, a protein synthesis inhibitor, after initial exposure, after exposure to a cue associated with triggering experience, and after reexposure to the triggering trauma in an animal model of PTSD. Magnitude of changes in prevalence of anxiety-like behaviors on the elevated plus-maze and nonhabituated exaggerated startle reaction were compared in rats that were exposed to predator stress, with and without microinjection of anisomycin. Microinjection of anisomycin before and after stress exposure reduced anxiety-like and avoidant behavior, reduced the mean startle amplitude, and reversed the stress-induced habituation deficit 7 days later. The persistent anxiety-like behaviors that were seen after stress exposure do not appear to be sensitive to anisomycin after reexposure to a cue associated with the event or after reexposure to the index experience. Disruption of the process of traumatic memory consolidation may be useful for mitigating PTSD symptoms.

3,4-Methylenedioxymethamphetamine (MDMA) neurotoxicity in rats: a reappraisal of past and present findings

Rationale3,4-Methylenedioxymethamphetamine (MDMA) is a widely abused illicit drug. In animals, high-dose administration of MDMA produces deficits in serotonin (5-HT) neurons (e.g., depletion of forebrain 5-HT) that have been interpreted as neurotoxicity. Whether such 5-HT deficits reflect neuronal damage is a matter of ongoing debate.ObjectiveThe present paper reviews four specific issues related to the hypothesis of MDMA neurotoxicity in rats: (1) the effects of MDMA on monoamine neurons, (2) the use of “interspecies scaling” to adjust MDMA doses across species, (3) the effects of MDMA on established markers of neuronal damage, and (4) functional impairments associated with MDMA-induced 5-HT depletions.ResultsMDMA is a substrate for monoamine transporters, and stimulated release of 5-HT, NE, and DA mediates effects of the drug. MDMA produces neurochemical, endocrine, and behavioral actions in rats and humans at equivalent doses (e.g., 1–2 mg/kg), suggesting that there is no reason to adjust doses between these species. Typical doses of MDMA causing long-term 5-HT depletions in rats (e.g., 10–20 mg/kg) do not reliably increase markers of neurotoxic damage such as cell death, silver staining, or reactive gliosis. MDMA-induced 5-HT depletions are accompanied by a number of functional consequences including reductions in evoked 5-HT release and changes in hormone secretion. Perhaps more importantly, administration of MDMA to rats induces persistent anxiety-like behaviors in the absence of measurable 5-HT deficits.ConclusionsMDMA-induced 5-HT depletions are not necessarily synonymous with neurotoxic damage. However, doses of MDMA which do not cause long-term 5-HT depletions can have protracted effects on behavior, suggesting even moderate doses of the drug may pose risks.

Accentuated Decrease in Social Interaction in Rats Subjected to Repeated Ethanol Withdrawals

Background Previous work has shown that repeated withdrawals from chronic ethanol exposure can kindle seizures in rodents. In this article, the effects of a three-cycle model of ethanol exposure and withdrawal on the social interaction test of anxiety are summarized. Methods Rats were exposed to ethanol (7% or 4.5%) diets over three periods of 5 days, with 2 days of withdrawal between cycles. Between 5 and 6 hr after the ethanol was removed, pairs of rats were placed in open field chambers for the assessment of social interaction behavior and locomotor activity. Results After the third cycle of ethanol (7%) presentation, both male and female rats exhibited lower social interaction behavior (more anxiety) and activity than after a single cycle. Rats exposed to a similar amount of ethanol but tested while ethanol was still available did not exhibit a reduction in social interaction. The decrease in social interaction was still present for up to 24 hr but had disappeared by 48 hr after ethanol was withdrawn. When rats were allowed 8 or 16 days to recover from the effects of the three-cycle protocol, a further exposure to 5 days of 7% ethanol diet resulted in a reduction in social interaction on withdrawal similar to that seen from the three-cycle protocol. In contrast, rats exposed continuously to 7% ethanol diet for 15 consecutive days exhibited higher levels of social interaction when maintained on control diet for 8 or 16 days and then reexposed to ethanol. Rats that were exposed to the three-cycle protocol and allowed 32 days to recover before being reexposed to ethanol still had a partial deficit in social interaction. Finally, animals subjected to repeated withdrawals from 4.5% ethanol exhibited a reduction in social interaction without a change in activity after the final withdrawal from ethanol, whereas rats exposed continuously to a 4.5% ethanol diet did not exhibit a reduction in social interaction or activity. Neither blood ethanol concentrations nor changes in body weight could account for these behavioral differences. Conclusion Repeated withdrawal from ethanol can lead to accentuated or more persistent anxiety-like behavior in rats, as indicated by a decrease in social interaction. The withdrawal-induced decrease in locomotor activity is not accentuated by repeated withdrawals. This model of repeated withdrawals from ethanol may prove useful in defining the neurochemical basis of this accentuation.