Translational value of startle modulations

Multidimensional behavioral profiles associated with resilience and susceptibility after inescapable stress

Clinical depression is characterized by multiple concurrent symptoms, manifesting as a complex heterogeneous condition. Although some well-established classical behavioral assessments are widespread in rodent models, it remains uncertain whether rats also display stress-induced depression-related phenotypes in a multidimensional manner, i.e., simultaneous alterations in multiple behavioral tests. Here, we investigated multivariate patterns and profiles of depression-related behavioral traits in male Wistar rats subjected to inescapable footshocks (IS) or no-shocks (NS), followed by a comprehensive battery of behavioral tests and ethological characterization. We observed generalized stronger intra-test but weaker inter-test correlations. However, feature clustering of behavioral measures successfully delineated variables linked to resilience and susceptibility to stress. Accordingly, a noteworthy covariation pattern emerged, characterized by increased open field locomotion, reduced time in the elevated plus maze open arms, lower sucrose preference, and increased shuttle box escape failures that consistently differentiated IS from NS. Surprisingly there is little contribution from forced swim. In addition, individual clustering revealed a diversity of behavioral profiles, naturally separating NS and IS, including subpopulations entirely characterized by resilience or susceptibility. In conclusion, our study elucidates intricate relationships among classical depression-related behavioral measures, highlighting multidimensional individual variability. Our work emphasizes the importance of a multivariate framework for behavioral assessment in animal models to understand stress-related neuropsychiatric disorders.

Pharmacological modulation of conditioned fear in the fear-potentiated startle test: a systematic review and meta-analysis of animal studies

RATIONALE AND OBJECTIVES

Fear conditioning is an important aspect in the pathophysiology of anxiety disorders. The fear-potentiated startle test is based on classical fear conditioning and over the years, a broad range of drugs have been tested in this test. Synthesis of the available data may further our understanding of the neurotransmitter systems that are involved in the expression of conditioned fear.

METHODS

Following a comprehensive search in Medline and Embase, we included 68 research articles that reported on 103 drugs, covering 56 different drug classes. The systematic review was limited to studies using acute, systemic drug administration in naive animals.

RESULTS

Qualitative data synthesis showed that most clinically active anxiolytics, but not serotonin-reuptake inhibitors, reduced cued fear. Anxiogenic drugs increased fear potentiation in 35% of the experiments, reduced fear potentiation in 29% of the experiments, and were without effect in 29% of the experiments. Meta-analyses could be performed for five drug classes and showed that benzodiazepines, buspirone, 5-HT1A agonists, 5-HT1A antagonists, and mGluR2,3 agonists reduced cued conditioned fear. The non-cued baseline startle response, which may reflect contextual anxiety, was only significantly reduced by benzodiazepines and 5-HT1A antagonists. No associations were found between drug effects and methodological characteristics, except for strain.

CONCLUSIONS

The fear-potentiated startle test appears to have moderate to high predictive validity and may serve as a valuable tool for the development of novel anxiolytics. Given the limited available data, the generally low study quality and high heterogeneity additional studies are warranted to corroborate the findings of this review.

Posttraumatic stress symptoms in healthcare workers during the COVID-19 pandemic: A four-wave longitudinal study

BACKGROUND

Posttraumatic stress symptoms of healthcare workers have become a significant public concern in the healthcare system that have long COVID-19. It is less known how the pandemic impacts the HCWs' PTSS longitudinally and long-term risk factors for it.

METHODS

Four consecutive surveys were conducted among healthcare workers in China from 2019 to 2023 COVID-19 outbreaks. Multilevel mixed-effect models were used to examine longitudinal changes and risk factors. Network analysis was utilized to explore network centrality changes in PTSS symptoms.

RESULTS

HCWs' PTSS symptoms were increased over time during the COVID-19 pandemic. Being female, being nurse, working in the emergency department, working longer hours, less frequently going back home and having COVID-19 infection are risk factors of PTSS for HCWs; unmarried is the protective factor. Significant interaction between symptom changes and profession exists. PTSS networks showed that Avoidance of thoughts, Emotional-cue activity, Exaggerated startle response and Hypervigilance were the central symptoms during four waves. The global strength of the PTSS network grows over time, and nodal strength of Avoidance of thoughts, Loss of interest and Negative beliefs increased by COVID-19.

CONCLUSION

The pandemic's impacts on healthcare workers vary by professions. PTSS symptoms exacerbate, reinforce each other, and persists with recurring waves.

Chronic unilateral inhibition of GABA synthesis in the amygdala increases specificity of conditioned fear in a discriminative fear conditioning paradigm in rats

Neural activity in the amygdala is critical for fear learning. In anxiety disorder patients, bilateral hyperactivity of the amygdala can be observed. This hyperactivation is often associated with the facilitation of fear learning and/or over-generalization of conditioned fear. In contrast, hypoactivity of the amygdala, e.g. by pharmacological interventions, attenuates or blocks fear learning. To date, little is known about how neural excitability of the amygdala affects specificity or generalization of fear. Therefore, the present study utilized chronic inhibition of GABA synthesis in the amygdala to increase excitability and investigated the effect on the specificity of fear learning. In rats, unilateral cannulas aiming at the amygdala were implanted. The cannulas were connected to subcutaneously implanted osmotic mini pumps that delivered either the GABA synthesis inhibitor L-allylglycine or its inactive enantiomer D-allylglycine. Following one week of chronic GABA synthesis manipulation, the rats were submitted to a discriminative fear conditioning protocol. In addition, anxiety-like behavior in the light-dark box was measured. Our data show that chronic unilateral L-AG infusions into the amygdala improve the specificity of learned fear, support safety learning, and reduce fear generalization and anxiety. This data demonstrates that moderately increased amygdala excitability can be beneficial for the specificity of fear learning and highlights the potential application for therapeutic interventions.

Neurotoxicity and endocrine disruption caused by polystyrene nanoparticles in zebrafish embryo

Nanoplastics (NP) are present in aquatic and terrestrial ecosystems. Humans can be exposed to them through contaminated water, food, air, or personal care products. Mechanisms of NP toxicity are largely unknown and the Zebrafish embryo poses an ideal model to investigate them due to its high homology with humans. Our objective in the present study was to combine a battery of behavioral assays with the study of endocrine related gene expression, to further explore potential NP neurotoxic effects on animal behavior. Polystyrene nanoplastics (PSNP) were used to evaluate NP toxicity. Our neurobehavioral profiles include a tail coiling assay, a light/dark activity assay, two thigmotaxis anxiety assays (auditory and visual stimuli), and a startle response - habituation assay in response to auditory stimuli. Results show PSNP accumulated in eyes, neuromasts, brain, and digestive system organs. PSNP inhibited acetylcholinesterase and altered endocrine-related gene expression profiles both in the thyroid and glucocorticoid axes. At the whole organism level, we observed altered behaviors such as increased activity and anxiety at lower doses and lethargy at a higher dose, which could be due to a variety of complex mechanisms ranging from sensory organ and central nervous system effects to others such as hormonal imbalances. In addition, we present a hypothetical adverse outcome pathway related to these effects. In conclusion, this study provides new understanding into NP toxic effects on zebrafish embryo, emphasizing a critical role of endocrine disruption in observed neurotoxic behavioral effects, and improving our understanding of their potential health risks to human populations.

Universal automated classification of the acoustic startle reflex using machine learning

The startle reflex (SR), a robust, motor response elicited by an intense auditory, visual, or somatosensory stimulus has been widely used as a tool to assess psychophysiology in humans and animals for almost a century in diverse fields such as schizophrenia, bipolar disorder, hearing loss, and tinnitus. Previously, SR waveforms have been ignored, or assessed with basic statistical techniques and/or simple template matching paradigms. This has led to considerable variability in SR studies from different laboratories, and species. In an effort to standardize SR assessment methods, we developed a machine learning algorithm and workflow to automatically classify SR waveforms in virtually any animal model including mice, rats, guinea pigs, and gerbils obtained with various paradigms and modalities from several laboratories. The universal features common to SR waveforms of various species and paradigms are examined and discussed in the context of each animal model. The procedure describes common results using the SR across species and how to fully implement the open-source R implementation. Since SR is widely used to investigate toxicological or pharmaceutical efficacy, a detailed and universal SR waveform classification protocol should be developed to aid in standardizing SR assessment procedures across different laboratories and species. This machine learning-based method will improve data reliability and translatability between labs that use the startle reflex paradigm.

Orexin deficiency affects sensorimotor gating and its amphetamine-induced impairment

The orexin neuropeptides have an important role in the regulation of the sleep/wake cycle and foraging, as well as in reward processing and emotions. Furthermore, recent research implicates the orexin system in different behavioral endophenotypes of neuropsychiatric diseases such as social avoidance and cognitive flexibility. Utilizing orexin-deficient mice, the present study tested the hypothesis that orexin is involved in two further mouse behavioral endophenotypes of neuropsychiatric disorders, i.e., sensorimotor gating and amphetamine sensitivity. The data revealed that orexin-deficient mice expressed a deficit in sensorimotor gating, measured by prepulse inhibition of the startle response. Amphetamine treatment impaired prepulse inhibition in wildtype and heterozygous orexin-deficient mice, but had no effects in homozygous orexin-deficient mice. Furthermore, locomotor activity and center time in the open field was not affected by orexin deficiency but was similarly increased or decreased, respectively, by amphetamine treatment in all genotypes. These data indicate that the orexin system modulates prepulse inhibition and is involved in mediating amphetamine's effect on prepulse inhibition. Future studies should investigate whether pharmacological manipulations of the orexin system can be used to treat neuropsychiatric diseases associated with deficits in sensorimotor gating, such as schizophrenia or attention deficit hyperactivity disorder.

Role of GluA4 in the acoustic and tactile startle responses

The primary startle response (SR) is an innate reaction evoked by sudden and intense acoustic, tactile or visual stimuli. In rodents and humans the SR involves reflexive contractions of the face, neck and limb muscles. The acoustic startle response (ASR) pathway consists of auditory nerve fibers (AN), cochlear root neurons (CRNs) and giant neurons of the caudal pontine reticular nucleus (PnC), which synapse on cranial and spinal motor neurons. The tactile startle response (TSR) is transmitted by primary sensory neurons to the principal sensory (Pr5) and spinal (Sp5) trigeminal nuclei. The ventral part of Pr5 projects directly to the PnC neurons. The SR requires rapid transmission of sensory information to initiate a fast motor response. Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPAR) are necessary to transmit auditory information to the PnC neurons and elicit the SR. AMPARs containing the glutamate AMPAR subunit 4 (GluA4) have fast kinetics, which makes them ideal candidates to transmit the SR signal. This study examined the role of GluA4 within the primary SR pathway by using GluA4 knockout (GluA4-KO) mice. Deletion of GluA4 considerably decreased the amplitude and probability of successful ASR and TSR, indicating that the presence of this subunit is critical at a common station within the startle pathway. We conclude that deletion of GluA4 affects the transmission of sensory signals from acoustic and tactile pathways to the motor component of the startle reflex. Therefore, GluA4 is required for the full response and for reliable elicitation of the startle response.

Postural freezing relates to startle potentiation in a human fear-conditioning paradigm

Freezing to impending threat is a core defensive response. It has been studied primarily using fear conditioning in non-human animals, thwarting advances in translational human anxiety research that has used other indices, such as skin conductance responses. Here we examine postural freezing as a human conditioning index for translational anxiety research. We employed a mixed cued/contextual fear-conditioning paradigm where one context signals the occurrence of the US upon the presentation of the CS, and another context signals that the CS is not followed by the US. Critically, during the following generalization phase, the CS is presented in a third and novel context. We show that human freezing is highly sensitive to fear conditioning, generalizes to ambiguous contexts, and amplifies with threat imminence. Intriguingly, stronger parasympathetically driven freezing under threat, but not sympathetically mediated skin conductance, predicts subsequent startle magnitude. These results demonstrate that humans show fear-conditioned animal-like freezing responses, known to aid in active preparation for unexpected attack, and that freezing captures real-life anxiety expression. Conditioned freezing offers a promising new, non-invasive, and continuous, readout for human fear conditioning, paving the way for future translational studies into human fear and anxiety.

BDNF haploinsufficiency induces behavioral endophenotypes of schizophrenia in male mice that are rescued by enriched environment

Brain-derived neurotrophic factor (BDNF) is implicated in a number of processes that are crucial for healthy functioning of the brain. Schizophrenia is associated with low BDNF levels in the brain and blood, however, not much is known about BDNF's role in the different symptoms of schizophrenia. Here, we used BDNF-haploinsufficient (BDNF^+/-) mice to investigate the role of BDNF in different mouse behavioral endophenotypes of schizophrenia. Furthermore, we assessed if an enriched environment can prevent the observed changes. In this study, male mature adult wild-type and BDNF^+/- mice were tested in mouse paradigms for cognitive flexibility (attentional set shifting), sensorimotor gating (prepulse inhibition), and associative emotional learning (safety and fear conditioning). Before these tests, half of the mice had a 2-month exposure to an enriched environment, including running wheels. After the tests, BDNF brain levels were quantified. BDNF^+/- mice had general deficits in the attentional set-shifting task, increased startle magnitudes, and prepulse inhibition deficits. Contextual fear learning was not affected but safety learning was absent. Enriched environment housing completely prevented the observed behavioral deficits in BDNF^+/- mice. Notably, the behavioral performance of the mice was negatively correlated with BDNF protein levels. These novel findings strongly suggest that decreased BDNF levels are associated with several behavioral endophenotypes of schizophrenia. Furthermore, an enriched environment increases BDNF protein to wild-type levels and is thereby able to rescue these behavioral endophenotypes.

Intranasal oxytocin compensates for estrus cycle-specific reduction of conditioned safety memory in rats: Implications for psychiatric disorders

Stress and anxiety disorder patients frequently fail to benefit from psychotherapies which often consist of inhibitory fear learning paradigms. One option to improve the therapy outcome is medication-enhanced psychotherapy. Research in humans and laboratory rodents has demonstrated that oxytocin (OT) reduces fear and facilitates fear extinction. However, the role of OT in conditioned safety learning, an understudied but highly suitable type of inhibitory fear learning, remains to be investigated. The present study aimed at investigating the effect of intranasal OT on conditioned safety. To test this, Sprague Dawley rats (♂n = 57; ♀n = 72) were safety conditioned. The effects of pre-training or pre-testing intranasal OT on conditioned safety and contextual fear, both measured by the acoustic startle response, and on corticosterone plasma levels were assessed. Furthermore, the involvement of the estrous cycle was analyzed. The present data show that intranasal OT administration before the acquisition or recall sessions enhanced conditioned safety memory in female rats while OT had no effects in male rats. Further analysis of the estrus cycle revealed that vehicle-treated female rats in the metestrus showed reduced safety memory which was compensated by OT-treatment. Moreover, all vehicle-treated rats, regardless of sex, expressed robust contextual fear following conditioning. Intranasal OT-treated rats showed a decrease in contextual fear, along with reduced plasma corticosterone levels. The present data demonstrate that intranasal OT has the capacity to compensate deficits in safety learning, along with a reduction in contextual fear and corticosterone levels. Therefore, add-on treatment with intranasal OT could optimize the therapy of anxiety disorders.

Effects of JL13, a pyridobenzoxazepine compound, in dopaminergic and glutamatergic models of antipsychotic activity

The pyridobenzoxazepine compound, 5-(4-methylpiperazin-1-yl)-8-chloro-pyrido[2,3-b][1,5]benzoxazepine (JL13), has been developed as a potential antipsychotic drug. We tested the hypothesis that JL13 is efficacious in both dopaminergic and glutamatergic animal models of schizophrenia. We investigated JL13 for its efficacy to prevent cocaine- and ketamine-induced hyperlocomotion and MK-801-induced deficits in prepulse inhibition (PPI) of the startle reflex. Male Swiss mice received injections of JL13 (0.1-10 mg/kg) and were tested in the open field for basal locomotion. In separate experiments, the animals received injections of JL13 (0.1-3 mg/kg) followed by cocaine (10 mg/kg), ketamine (60 mg/kg), or MK-801 (0.5 mg/kg) and were tested in the open field for hyperlocomotion. In addition, it was also tested if JL13 prevented MK-801-induced disruption of PPI. Only the highest dose of JL13 impaired spontaneous locomotion, suggesting its favorable profile regarding motor side effects. At doses that did not impair basal motor activity, JL13 prevented cocaine-, ketamine-, and MK-801-induced hyperlocomotion. Moreover, JL13 prevented MK-801-induced disruption of PPI. Extending previous findings, this study shows that JL13 exerts antipsychotic-like activity in both dopaminergic and glutamatergic models. This compound has a favorable pharmacological profile, similar to second-generation antipsychotics.

Autoantibodies against NMDA receptor 1 modify rather than cause encephalitis

The etiology and pathogenesis of "anti-N-methyl-D-aspartate-receptor (NMDAR) encephalitis" and the role of autoantibodies (AB) in this condition are still obscure. While NMDAR1-AB exert NMDAR-antagonistic properties by receptor internalization, no firm evidence exists to date that NMDAR1-AB by themselves induce brain inflammation/encephalitis. NMDAR1-AB of all immunoglobulin classes are highly frequent across mammals with multiple possible inducers and boosters. We hypothesized that "NMDAR encephalitis" results from any primary brain inflammation coinciding with the presence of NMDAR1-AB, which may shape the encephalitis phenotype. Thus, we tested whether following immunization with a "cocktail" of 4 NMDAR1 peptides, induction of a spatially and temporally defined sterile encephalitis by diphtheria toxin-mediated ablation of pyramidal neurons ("DTA" mice) would modify/aggravate the ensuing phenotype. In addition, we tried to replicate a recent report claiming that immunizing just against the NMDAR1-N368/G369 region induced brain inflammation. Mice after DTA induction revealed a syndrome comprising hyperactivity, hippocampal learning/memory deficits, prefrontal cortical network dysfunction, lasting blood brain-barrier impairment, brain inflammation, mainly in hippocampal and cortical regions with pyramidal neuronal death, microgliosis, astrogliosis, modest immune cell infiltration, regional atrophy, and relative increases in parvalbumin-positive interneurons. The presence of NMDAR1-AB enhanced the hyperactivity (psychosis-like) phenotype, whereas all other readouts were identical to control-immunized DTA mice. Non-DTA mice with or without NMDAR1-AB were free of any encephalitic signs. Replication of the reported NMDAR1-N368/G369-immunizing protocol in two large independent cohorts of wild-type mice completely failed. To conclude, while NMDAR1-AB can contribute to the behavioral phenotype of an underlying encephalitis, induction of an encephalitis by NMDAR1-AB themselves remains to be proven.

Animal models built for women's brain health: Progress and potential

Women and men have different levels of risk for a variety of brain disorders. Despite this well-known epidemiological finding, preclinical work utilizing animal models has historically only included male animals. The policies of funders to require consideration of sex as a biological variable has shifted the momentum to include female animals in preclinical neuroscience and to report findings by sex. However, there are many biological questions related to brain health that go beyond sex differences and are indeed specific to women. Here, the focus is on why animal models should be utilized in the pursuit of understanding women's brain health, a brief overview of what they have provided thus far, and why they still hold tremendous promise. This review concludes with a set of suggestions for how to begin to pursue translational animal models in a way that facilitates rapid success and harnesses the most powerful aspects of animal models.

Quantifying the Acoustic Startle Response in Mice Using Standard Digital Video

The startle response is an unconditional reflex, characterized by the rapid contraction of facial and skeletal muscles, to a sudden and intense startling stimulus. It is an especially useful tool in translational research for its consistency across species, simple neural circuitry, and sensitivity to a variety of experimental manipulations. The rodent acoustic startle response is commonly used to study fundamental properties of the central nervous system, including habituation, sensitization, classical conditioning, fear and anxiety, sensorimotor gating, and drug effects. The rodent startle response is typically assessed in stabilimeter chambers, and while these systems are excellent at measuring startle, they are designed only for this sole purpose. In the present study, we used the VideoFreeze system-a widely used tool for studying Pavlovian fear conditioning-to assess the acoustic startle response in freely moving mice. We validated the use of this system to quantify startle response amplitude and prepulse inhibition of startle. This is the first demonstration to date of using standard video in the automated assessment of the acoustic startle response in rodents. We believe that researchers already using the VideoFreeze system will benefit from the additional ability to assess startle without the purchase of new equipment.

Chronic inhibition of GABA synthesis in the infralimbic cortex facilitates conditioned safety memory and reduces contextual fear

Accurate discrimination between danger and safety cues is essential for survival. Recent findings in humans indicate that patients suffering from anxiety disorders cannot reliably use safety cues in order to inhibit fear responses. However, the neuroanatomical pathways of conditioned safety are still unclear. Aim of the present study was to investigate whether chronic inhibition of GABA synthesis in the infralimbic (IL) cortex, a critical region for fear inhibition, would lead to enhanced conditioned safety memory. Male Sprague Dawley rats were equipped with osmotic mini-pumps attached to an infusion cannula aimed at the IL. Mini-pumps were either filled with the glutamate decarboxylase (GAD) inhibitor L-allylglycine (L-AG) or the inactive enantiomer D-allylglycine (D-AG). Previous studies demonstrated that chronic infusions of L-AG lead to lower GABA levels and overall enhanced neural activity. The effect of IL disinhibition on conditioned safety was investigated utilizing the acoustic startle response. Chronic disinhibition of the IL facilitated conditioned safety memory, along with reduced contextual fear and lower corticosterone levels. The present findings suggest that the IL is a key brain region for conditioned safety memory. Because anxiety disorder patients are often not capable to use safety cues to inhibit unnecessary fear responses, the present findings are of clinical relevance and could potentially contribute to therapy optimization.

Making translation work: Harmonizing cross-species methodology in the behavioural neuroscience of Pavlovian fear conditioning

Translational neuroscience bridges insights from specific mechanisms in rodents to complex functions in humans and is key to advance our general understanding of central nervous function. A prime example of translational research is the study of cross-species mechanisms that underlie responding to learned threats, by employing Pavlovian fear conditioning protocols in rodents and humans. Hitherto, evidence for (and critique of) these cross-species comparisons in fear conditioning research was based on theoretical viewpoints. Here, we provide a perspective to substantiate these theoretical concepts with empirical considerations of cross-species methodology. This meta-research perspective is expected to foster cross-species comparability and reproducibility to ultimately facilitate successful transfer of results from basic science into clinical applications.

Sensorimotor Gating in Cocaine-Related Disorder with Comorbid Schizophrenia or Antisocial Personality Disorder

Objective: Schizophrenia, cocaine-related disorder, antisocial personality disorder, and psychopathy share biological bases, but few studies discriminate between these disorders by means of prepulse inhibition. This work studies the phenotype of patients with cocaine-related disorders who are vulnerable to presenting a dual diagnosis of schizophrenia or antisocial personality disorder, by evaluating their prepulse inhibition, impulsivity and psychopathy personality traits. Methods: The sample (n = 38) was divided into three groups: (1) cocaine-related disorder (8 individuals diagnosed with cocaine-related disorder who did not present any other mental disorder), (2) cocaine-related disorder and schizophrenia (n = 14), and (3) cocaine-related disorder and antisocial personality disorder (n = 16). Results: The prepulse inhibition in the two groups with dual diagnosis was lower than that in the cocaine-related disorder group, F(2, 35) = 6.52, p = .004, while there was no significant differences between the two dual-diagnosis groups. Psychopathy was evaluated with the revised Hare Psychopathy Checklist and showed no correlation with the prepulse inhibition. Secondary psychopathy (impulsivity and poor behavior control), as evaluated with Levenson Self-Report Psychopathy Scale, was related to the prepulse inhibition. Two discriminating functions were obtained that allowed prediction of patient inclusion in the groups using the prepulse inhibition and the revised Hare Psychopathy Checklist with a success rate of 81.6% (cocaine-related disorder = 62.5%; cocaine-related disorder and schizophrenia = 78.6%; cocaine-related disorder and antisocial personality disorder = 93.8%). These results are discussed in regard to the neurobiological implications of prepulse inhibition in dual diagnosis. Conclusions: The results suggest that the prepulse inhibition is a promising dual-diagnosis vulnerability marker in individuals with cocaine addiction, because prepulse inhibition deficits are related both to schizophrenia and antisocial personality disorder. In addition, prepulse inhibition, which is considered a good endophenotype for studies on the genetic and neurobiological basis of cocaine-related disorder and schizophrenia, could be used in the same way in studies on antisocial personality disorder.

Deficiency of the immunoproteasome subunit β5i/LMP7 supports the anxiogenic effects of mild stress and facilitates cued fear memory in mice

Proteolysis as mediated by one of the major cellular protein degradation pathways, the ubiquitin-proteasome system (UPS), plays an essential role in learning and memory formation. However, the functional relevance of immunoproteasomes in the healthy brain and especially their impact on normal brain function including processes of learning and memory has not been investigated so far. In the present study, we analyzed the phenotypic effects of an impaired immunoproteasome formation using a β5i/LMP7-deficient mouse model in different behavioral paradigms focusing on locomotor activity, exploratory behavior, innate anxiety, startle response, prepulse inhibition, as well as fear and safety conditioning. Overall, our results demonstrate no strong effects of constitutive β5i/LMP7-deficiency on gross locomotor abilities and anxiety-related behavior in general. However, β5i/LMP7-deficient mice expressed more anxiety after mild stress and increased cued fear after fear conditioning. These findings indicate that the basal proper formation of immunoproteasomes and/or at least the expression of β5i/LMP7 in healthy mice seem to be involved in the regulation of anxiety and cued fear levels.

Circuit activity underlying a distinct modulator of prepulse inhibition

Prepulse inhibition (PPI), the diminished eye blink response to a startling pulse induced by a prepulse, is regulated by brainstem, and modulated by cerebral, processes. Attentional modulation by the prepulse (AMP), a potential biomarker of psychotic disorders, differs from other modulatory processes because it only occurs if the interval between the prepulse and pulse exceeds 100 ms (>PP100). Videotaped eye blinks were measured during fMRI scanning in 15 healthy subjects hearing 64 pulse alone, 64 PP60 and 64 PP120 trials in a rapid event-related design. Because attentional influences on PPI vary spontaneously, we posited AMP could be isolated by comparing eye blink and Blood Oxygen Level Dependent covariation during the two PP trial types. Behavioral regressor coefficients reflecting significant covariation covered the insula and auditory cortices during PP120 but not PP60 trials. Clusters within the right anterior insula and auditory cortex were specific to AMP. Functional connections (FCs) between cerebral ROIs implicated in PPI were stronger during PP120 trials. The four FCs that were individually stronger during PP120 trials involved the right insula or auditory cortex and three were not present during PP60 trials. Converging evidence indicates the right insula is the hub of a network underlying AMP.

Social context influences sensorimotor gating in female African cichlid fish Astatotilapia burtoni

Disruption in prepulse inhibition (PPI), a sensorimotor gating phenomenon found in many species, has been associated with various psychiatric disorders in humans. Social defeat has been identified as a mediator of naturally evoked reductions of PPI in African cichlid fish Astatotilapia burtoni where males reversibly alter social status and their sensorimotor gating abilities. Here we investigated A. burtoni females, which establish a male-like social hierarchy with dominant (DOM) and subordinate (SUB) individuals when housed in communities without males. We asked if DOM and SUB females demonstrate socially induced PPI differences comparable to their male DOM and SUB counterparts. Results suggest that social defeat reduced PPI in SUB females as compared to DOM females (p = 0.033) and mixed-sex community female controls (p = 0.017). However, socially defeated females in same-sex communities remained proactive when engaging in antagonistic behaviors, which appears beneficial in avoiding substantial reductions in PPI as seen in reactive, socially defeated males. In open field swimming tests, SUB females exhibited increased anxiety-related behavior (thigmotaxis) as compared to females from mixed-sex communities (COM). Taken together, our results emphasize social defeat is a reliable modulator of PPI independent of sex, and anxiety related to social defeat might be a factor in mediating PPI plasticity.

Rhodiola rosea root extract has antipsychotic-like effects in rodent models of sensorimotor gating

ETHNOPHARMACOLOGICAL RELEVANCE: The plant arctic root (Rhodiola rosea, L.) is growing in northern regions of Europe, Asia and North America. Extracts of R. rosea are used in traditional medicine for various conditions related to nervous system function. According to scientific studies from the last decades, the plant might have potential for use in the treatment of memory impairments, stress and depression, but reports concerning other neuropsychiatric disorders are scarce.

AIM OF THE STUDY

In this context, our study aimed to examine potential antipsychotic-like effects of R. rosea root extract.

MATERIALS AND METHODS

We tested the effects of R. rosea root extract on prepulse inhibition in rats and mice. Prepulse inhibition is an established operational measure of sensorimotor gating, which is impaired in schizophrenia and other psychotic disorders.

RESULTS

R. rosea root extract increased prepulse inhibition in rats and mice. Interestingly, the R. rosea extract had stronger effects in those individual animals that had low baseline levels of prepulse inhibition. Therefore, we performed further experiments in which we pharmacologically induced a prepulse inhibition deficit by two different psychostimulants, either the dopamine D2 receptor agonist apomorphine or the NMDA receptor antagonist dizocilpine (MK-801). Pre-treatment with the R. rosea extract significantly restored both, apomorphine- and dizocilpine-induced prepulse inhibition deficits.

CONCLUSIONS

The present study demonstrates that R. rosea extract robustly reverses prepulse inhibition deficits in rodents. This suggests antipsychotic-like effects of R. rosea extract. Future studies should focus on the pharmacological mechanisms underlying these effects.

The Impact of Stressor Exposure and Glucocorticoids on Anxiety and Fear

Anxiety disorders and trauma- and stressor-related disorders, such as posttraumatic stress disorder (PTSD), are common and are associated with significant economic and social burdens. Although trauma and stressor exposure are recognized as a risk factors for development of anxiety disorders and trauma or stressor exposure is recognized as essential for diagnosis of PTSD, the mechanisms through which trauma and stressor exposure lead to these disorders are not well characterized. An improved understanding of the mechanisms through which trauma or stressor exposure leads to development and persistence of anxiety disorders or PTSD may result in novel therapeutic approaches for the treatment of these disorders. Here, we review the current state-of-the-art theories, with respect to mechanisms through which stressor exposure leads to acute or chronic exaggeration of avoidance or anxiety-like defensive behavioral responses and fear, endophenotypes in both anxiety disorders and trauma- and stressor-related psychiatric disorders. In this chapter, we will explore physiological responses and neural circuits involved in the development of acute and chronic exaggeration of anxiety-like defensive behavioral responses and fear states, focusing on the role of the hypothalamic-pituitary-adrenal (HPA) axis and glucocorticoid hormones.

Anxiety-dependent modulation of motor responses to pain expectancy

The relationship between pain expectancy and motor system plays a crucial role in the human defensive system. Here, we took advantage of the inhibitory modulation of the motor pathway to the muscle of the hand receiving painful stimuli, by recording motor-evoked potentials (MEPs) to Transcranial Magnetic Stimulation (TMS). We employed a classical conditioning paradigm in which neutral (visual and auditory) stimuli were conditioned by pairing either painful or not-painful stimuli (electric shocks) in separated groups. Only the Pain Group showed clear motor responses: i.e. a significant decrease in MEPs amplitude, with respect to the neutral condition, not only in conditioning stimuli, when actual shocks were paired with neutral stimuli, but also in conditioned stimuli, when shocks were only expected. Significant differences between the two groups suggest that the MEPs decrease is specific for pain expectancy and does not pertain to anticipation in general. Furthermore, in the Pain Group, a significant negative correlation between physiological responses to conditioned stimuli and the participants’ anxiety traits was found: the lower the MEPs amplitude, the higher the participants’ anxiety scores. The present findings suggest that, in order for defensive motor responses to occur, actual pain is not necessary; rather, anxiety-dependent pain expectancy can be sufficient.

Associative Learning of Stimuli Paired and Unpaired With Reinforcement: Evaluating Evidence From Maggots, Flies, Bees, and Rats

Finding rewards and avoiding punishments are powerful goals of behavior. To maximize reward and minimize punishment, it is beneficial to learn about the stimuli that predict their occurrence, and decades of research have provided insight into the brain processes underlying such associative reinforcement learning. In addition, it is well known in experimental psychology, yet often unacknowledged in neighboring scientific disciplines, that subjects also learn about the stimuli that predict the absence of reinforcement. Here we evaluate evidence for both these learning processes. We focus on two study cases that both provide a baseline level of behavior against which the effects of associative learning can be assessed. Firstly, we report pertinent evidence from Drosophila larvae. A re-analysis of the literature reveals that through paired presentations of an odor A and a sugar reward (A+) the animals learn that the reward can be found where the odor is, and therefore show an above-baseline preference for the odor. In contrast, through unpaired training (A/+) the animals learn that the reward can be found precisely where the odor is not, and accordingly these larvae show a below-baseline preference for it (the same is the case, with inverted signs, for learning through taste punishment). In addition, we present previously unpublished data demonstrating that also during a two-odor, differential conditioning protocol (A+/B) both these learning processes take place in larvae, i.e., learning about both the rewarded stimulus A and the non-rewarded stimulus B (again, this is likewise the case for differential conditioning with taste punishment). Secondly, after briefly discussing published evidence from adult Drosophila, honeybees, and rats, we report an unpublished data set showing that relative to baseline behavior after truly random presentations of a visual stimulus A and punishment, rats exhibit memories of opposite valence upon paired and unpaired training. Collectively, the evidence conforms to classical findings in experimental psychology and suggests that across species animals associatively learn both through paired and through unpaired presentations of stimuli with reinforcement – with opposite valence. While the brain mechanisms of unpaired learning for the most part still need to be uncovered, the immediate implication is that using unpaired procedures as a mnemonically neutral control for associative reinforcement learning may be leading analyses astray.

What rodent models of deep brain stimulation can teach us about the neural circuit regulation of prepulse inhibition in neuropsychiatric disorders

Deep brain stimulation (DBS) is routinely used for treatment of movement disorders and it is also under investigation for neuropsychiatric disorders with deficient sensorimotor gating, such as schizophrenia, Tourette's syndrome and obsessive compulsive disorder. Electrical stimulation induces excitation and inhibition both at the stimulation site and at projection sites, thus modulating synchrony and oscillatory behavior of neuronal networks. We first provide background information on DBS in neuropsychiatric disorders accompanied by deficient sensorimotor gating. We then introduce prepulse inhibition (PPI) as a measure for sensorimotor gating in these disorders. Thereafter, we report on the use of DBS in rat models with deficient PPI induced by pharmacologic, genetic and neurodevelopmental manipulation. These models offer the opportunity to define the neuronal circuit regulation that is of relevance to PPI and its deficits in neuropsychiatric disorders with disturbed sensorimotor gating. Finally, we report on the use of the PPI paradigm in human patients operated for DBS on/off stimulation, which may further elucidate the neuronal network involved in regulation of PPI.

Adolescent Exposure to the Synthetic Cannabinoid WIN 55212-2 Modifies Cocaine Withdrawal Symptoms in Adult Mice

Chronic cannabinoid consumption is an increasingly common behavior among teenagers and has been shown to cause long-lasting neurobehavioral alterations. Besides, it has been demonstrated that cocaine addiction in adulthood is highly correlated with cannabis abuse during adolescence. Cocaine consumption and subsequent abstinence from it can cause psychiatric symptoms, such as psychosis, cognitive impairment, anxiety, and depression. The aim of the present research was to study the consequences of adolescent exposure to cannabis on the psychiatric-like effects promoted by cocaine withdrawal in adult mice. We pre-treated juvenile mice with the cannabinoid CB1 receptor agonist WIN 55212-2 (WIN) and then subjected them to a chronic cocaine treatment during adulthood. Following these treatments, animals were tested under cocaine withdrawal in the following paradigms: pre-pulse inhibition, object recognition, elevated plus maze, and tail suspension. The long-term psychotic-like actions induced by WIN were not modified after cocaine cessation. Moreover, the memory impairments induced by cocaine withdrawal were not altered by previous adolescent WIN intake. However, WIN pre-treatment prevented the anxiogenic effects observed after cocaine abstinence, and led to greater depressive-like symptoms following cocaine removal in adulthood. This study is the first to show the long-lasting behavioral consequences of juvenile exposure to WIN on cocaine withdrawal in adult mice.

Analyzing the experiences of adolescent control rats: Effects of the absence of physical or social stimulation on anxiety-like behaviour are dependent on the test

The present study was designed to systematically assess the control experience routinely used in our laboratory as part of studies on predator odour stress. Specifically, we examined effects of the physical and social components of this control experience on measures of anxiety-like behaviour in adolescent rats. Adolescent animals are at increased susceptibility to environmental perturbations and have been used for such studies much less often. Long-Evans rats of both sexes were subjected to physical stimulation (Exposed or Unexposed) and social stimulation (Single-Housed or Pair-Housed), resulting in four groups. Exposed rats received six 30-min exposures to an enclosed arena containing an unscented piece of cat collar occurring between adolescence and early adulthood, while Unexposed remained in the home cage. Groups of Exposed and Unexposed animals were housed singly (Single-Housed) from early adolescence to early adulthood or Pair-Housed during this time. Experimental procedures began in adolescence and involved repeated assessment of startle amplitude (measure of anxiety-like behaviour) and prepulse inhibition (PPI; a measure of sensorimotor gating) to gauge the short-term impact of social and/or physical stimulation. All animals were re-paired in adulthood prior to a final startle/PPI session to assess if isolation limited to adolescence could impose long-term effects that were not reversible. We also measured anxiety-like behaviour in adulthood using an extended open field test (EOFT; addition of novel objects to the open field on later days), and the elevated plus maze task (EPM), as well as a sucrose preference test (SPT) to measure anhedonia. An absence of social or physical stimulation resulted in increased startle amplitude and some measures of anxiety-like behaviour in the EOFT, but a reduction in such anxiety-like behaviour in the EPM task. These results suggest common neural substrates for the physical and social experiences. Performance in the SPT was unaltered by any experimental treatments. Sensorimotor gating, as measured by PPI, was increased in the absence of physical stimulation with no short-term effect of isolation, or of re-pairing. These results indicate the importance of considering individual components of the rearing environment of rats, while showing the need to use multiple assays of anxiety-like behaviour.

Adolescent but not adult ethanol binge drinking modulates cocaine withdrawal symptoms in mice

Background

Ethanol (EtOH) binge drinking is an increasingly common behavior among teenagers that induces long-lasting neurobehavioral alterations in adulthood. An early history of EtOH abuse during adolescence is highly correlated with cocaine addiction in adulthood. Abstinence of cocaine abuse can cause psychiatric symptoms, such as anxiety, psychosis, depression, and cognitive impairments. This study assessed the consequences of adolescent exposure to EtOH on the behavioral alterations promoted by cocaine withdrawal in adulthood.

Methods

We pretreated juvenile (34–47 days old) or adult (68–81 days old) mice with EtOH (1.25 g/kg) following a binge-drinking pattern. Then, after a three-week period without drug delivery, they were subjected to a chronic cocaine treatment in adulthood and tested under cocaine withdrawal by the ensuing paradigms: open field, elevated plus maze, prepulse inhibition, tail suspension test, and object recognition. Another set of mice were treated with the same EtOH binge-drinking procedure during adolescence and were tested immediately afterwards under the same behavioral paradigms.

Results

Adolescent EtOH pretreatment undermined the anxiogenic effects observed after cocaine abstinence, reduced prepulse inhibition, and increased immobility scores in the tail suspension test following cocaine withdrawal. Moreover, the memory deficits evoked by these substances when given separately were enhanced in cocaine-withdrawn mice exposed to EtOH during adolescence. EtOH binge drinking during adolescence also induced anxiety, depressive symptoms, and memory impairments when measured immediately afterwards. In contrast, neither EtOH nor cocaine alone or in combination altered any of these behaviors when given in adulthood.

Conclusions

EtOH binge drinking induces short- and long-term behavioral alterations and modulates cocaine withdrawal symptoms when given in adolescent mice.

Don't fear 'fear conditioning': Methodological considerations for the design and analysis of studies on human fear acquisition, extinction, and return of fear

The so-called 'replicability crisis' has sparked methodological discussions in many areas of science in general, and in psychology in particular. This has led to recent endeavours to promote the transparency, rigour, and ultimately, replicability of research. Originating from this zeitgeist, the challenge to discuss critical issues on terminology, design, methods, and analysis considerations in fear conditioning research is taken up by this work, which involved representatives from fourteen of the major human fear conditioning laboratories in Europe. This compendium is intended to provide a basis for the development of a common procedural and terminology framework for the field of human fear conditioning. Whenever possible, we give general recommendations. When this is not feasible, we provide evidence-based guidance for methodological decisions on study design, outcome measures, and analyses. Importantly, this work is also intended to raise awareness and initiate discussions on crucial questions with respect to data collection, processing, statistical analyses, the impact of subtle procedural changes, and data reporting specifically tailored to the research on fear conditioning.

Metabotropic Glutamate Receptors 7 within the Nucleus Accumbens are Involved in Relief Learning in Rats

Relief learning is an appetitive association of a formally neutral cue with relief induced by the offset of an aversive stimulus. Since the nucleus accumbens mediates relief learning and accumbal metabotropic glutamate receptors 7 (mGluR7) modulate appetitive-like processes, we hypothesized that accumbal mGluR7 may be involved in the modulation of relief learning. Therefore, we injected the allosteric mGluR7 agonist AMN082 into the nucleus accumbens and tested the effects of these injections on acquisition and expression of relief memory, as well as on the reactivity to electric stimuli. AMN082 injections blocked acquisition but not expression of relief memory. In addition, accumbal AMN082 injections strongly reduced the locomotor reactivity to electric stimuli indicating antinociceptive effects. These antinociceptive effects might be causal for the blockade of relief learning after AMN082 injections. Taken together, the present study indicates that functional activation of accumbal mGluR7 has antinociceptive effects that interfere with relief learning.

Ontogeny of sensorimotor gating and short-term memory processing throughout the adolescent period in rats

Adolescence and puberty are highly susceptible developmental periods during which the neuronal organization and maturation of the brain is completed. The endocannabinoid (eCB) system, which is well known to modulate cognitive processing, undergoes profound and transient developmental changes during adolescence. With the present study we were aiming to examine the ontogeny of cognitive skills throughout adolescence in male rats and clarify the potential modulatory role of CB1 receptor signalling. Cognitive skills were assessed repeatedly every 10th day in rats throughout adolescence. All animals were tested for object recognition memory and prepulse inhibition of the acoustic startle reflex. Although cognitive performance in short-term memory as well as sensorimotor gating abilities were decreased during puberty compared to adulthood, both tasks were found to show different developmental trajectories throughout adolescence. A low dose of the CB1 receptor antagonist/inverse agonist SR141716 was found to improve recognition memory specifically in pubertal animals while not affecting behavioral performance at other ages tested. The present findings demonstrate that the developmental trajectory of cognitive abilities does not occur linearly for all cognitive processes and is strongly influenced by pubertal maturation. Developmental alterations within the eCB system at puberty onset may be involved in these changes in cognitive processing.

L-type Ca2+ channels in mood, cognition and addiction: integrating human and rodent studies with a focus on behavioural endophenotypes

Brain Cav 1.2 and Cav 1.3 L-type Ca2+ channels play key physiological roles in various neuronal processes that contribute to brain function. Genetic studies have recently identified CACNA1C as a candidate risk gene for bipolar disorder (BD), schizophrenia (SCZ), major depressive disorder (MDD) and autism spectrum disorder (ASD), and CACNA1D for BD and ASD, suggesting a contribution of Cav 1.2 and Cav 1.3 Ca2+ signalling to the pathophysiology of neuropsychiatric disorders. Once considered sole clinical entities, it is now clear that BD, SCZ, MDD and ASD share common phenotypic features, most likely due to overlapping neurocircuitry and common molecular mechanisms. A major future challenge lies in translating the human genetic findings to pathological mechanisms that are translatable back to the patient. One approach for tackling such a daunting scientific endeavour for complex behaviour-based neuropsychiatric disorders is to examine intermediate biological phenotypes in the context of endophenotypes within distinct behavioural domains. This will better allow us to integrate findings from genes to behaviour across species, and improve the chances of translating preclinical findings to clinical practice.

Cortical network dysfunction caused by a subtle defect of myelination

Subtle white matter abnormalities have emerged as a hallmark of brain alterations in magnetic resonance imaging or upon autopsy of mentally ill subjects. However, it is unknown whether such reduction of white matter and myelin contributes to any disease‐relevant phenotype or simply constitutes an epiphenomenon, possibly even treatment‐related. Here, we have re‐analyzed Mbp heterozygous mice, the unaffected parental strain of shiverer, a classical neurological mutant. Between 2 and 20 months of age, Mbp^+/‐ versus Mbp^+/+ littermates were deeply phenotyped by combining extensive behavioral/cognitive testing with MRI, 1H‐MR spectroscopy, electron microscopy, and molecular techniques. Surprisingly, Mbp‐dependent myelination was significantly reduced in the prefrontal cortex. We also noticed a mild but progressive hypomyelination of the prefrontal corpus callosum and low‐grade inflammation. While most behavioral functions were preserved, Mbp^+/‐ mice exhibited defects of sensorimotor gating, as evidenced by reduced prepulse‐inhibition, and a late‐onset catatonia phenotype. Thus, subtle but primary abnormalities of CNS myelin can be the cause of a persistent cortical network dysfunction including catatonia, features typical of neuropsychiatric conditions. GLIA 2016;64:2025–2040

High levels of impulsivity in rats are not accompanied by sensorimotor gating deficits and locomotor hyperactivity

High levels of impulsivity have been linked to a number of psychiatric disorders, including attention-deficit/hyperactivity disorder, drug abuse and schizophrenia. Additionally, schizophrenia patients commonly show deficits in another rather preattentive form of response inhibition, called sensorimotor gating. Given that higher-order functions, such as impulse control, are protected by early and preattentive processes, disturbed gating mechanisms may hamper more complex cognitive-executive functions. In the present study, we therefore tested whether high levels of impulsivity are accompanied by impaired sensorimotor gating in rats. High (HI) and low impulsive (LI) rats were identified based on the number of premature responses in the 5-choice serial reaction time task. Here, LI rats showed higher numbers of omission errors which may suggest attentional deficits while HI rats completed significantly less trials which could indicate a decrease in motivation. However, HI and LI rats did not differ in terms of impulsive decision-making in a delay-based decision-making T-maze task, prepulse inhibition of the acoustic startle response (a measure of sensorimotor gating mechanisms) or locomotor activity levels. Overall, our data indicate that high motor impulsivity is not a suitable predictor of deficient sensorimotor gating and is further not necessarily associated with attentional deficits and/or locomotor hyperactivity in rats.

Relief learning is dependent on NMDA receptor activation in the nucleus accumbens

BACKGROUND AND PURPOSE

Recently, we demonstrated that the nucleus accumbens (NAC) is required for the acquisition and expression of relief memory. The purpose of this study was to investigate the role of NMDA receptors within the NAC in relief learning.

EXPERIMENTAL APPROACH

The NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (AP-5) was injected into the NAC. The effects of these injections on the acquisition and expression of relief memory, as well as on the reactivity to aversive electric stimuli, were tested.

KEY RESULTS

Intra-accumbal AP-5 injections blocked the acquisition but not the expression of relief memory. Furthermore, reactivity to aversive electric stimuli was not affected by the AP-5 injections.

CONCLUSION AND IMPLICATION

The present data indicate that NMDA-dependent plasticity within the NAC is crucial for the acquisition of relief memory.

Expression of freezing and fear-potentiated startle during sustained fear in mice

Fear-potentiated acoustic startle paradigms have been used to investigate phasic and sustained components of conditioned fear in rats and humans. This study describes a novel training protocol to assess phasic and sustained fear in freely behaving C57BL/6J mice, using freezing and/or fear-potentiated startle as measures of fear, thereby, if needed, allowing in vivo application of various techniques, such as optogenetics, electrophysiology and pharmacological intervention, in freely behaving animals. An auditory Pavlovian fear conditioning paradigm, with pseudo-randomized conditioned-unconditioned stimulus presentations at various durations, is combined with repetitive brief auditory white noise burst presentations during fear memory retrieval 24 h after fear conditioning. Major findings are that (1) a motion sensitive platform built on mechano-electrical transducers enables measurement of startle responses in freely behaving mice, (2) absence or presence of startle stimuli during retrieval as well as unpredictability of a given threat determine phasic and sustained fear response profiles and (3) both freezing and startle responses indicate phasic and sustained components of behavioral fear, with sustained freezing reflecting unpredictability of conditioned stimulus (CS)/unconditioned stimulus (US) pairings. This paradigm and available genetically modified mouse lines will pave the way for investigation of the molecular and neural mechanisms relating to the transition from phasic to sustained fear.

Neuropharmacology of altered brain oscillations in schizophrenia

Impairments in spatial and temporal integration of brain network activity are a core feature of schizophrenia. Neural network oscillatory activity is considered to be fundamentally important in coordinating neural activity throughout the brain. Hence, exploration of brain oscillations has become an indispensible tool to study the neural basis of mental illnesses. However, most of the studies in schizophrenia include medicated patients. This implicates the question to what extent are changes in the electrophysiological parameters genuine illness effects, genuine drug effects or a mixture of both. We here provide a short overview of the neuropharmacology of brain oscillations with respect to schizophrenia. The core assumption of the so-called "pharmaco-EEG" approach is that drug effects on mental and cognitive functions are reflected in changes in quantitative EEG parameters. Hence, clinical efficacy of drugs might be predicted on the basis of the neuropharmacology of electrophysiological measures, such as brain oscillations. Vice versa, knowledge of drug effects on brain oscillations can be of essence in understanding schizophrenia. However, the current literature lacks systematic findings, because of at least two problems. First, the pharmacology of most antipsychotic drugs is complex including interactions with several transmitter receptors. Second, the neuropathology of schizophrenia still has no pathognomonic signature. Even though it is presently not possible to clearly dissociate drug- and illness effects in neural oscillations, this review emphasizes future studies to foster the understanding of this relationship in schizophrenia and other neuropsychiatric diseases.

The Mauthner-cell circuit of fish as a model system for startle plasticity

The Mauthner-cell (M-cell) system of teleost fish has a long history as an experimental model for addressing a wide range of neurobiological questions. Principles derived from studies on this system have contributed significantly to our understanding at multiple levels, from mechanisms of synaptic transmission and synaptic plasticity to the concepts of a decision neuron that initiates key aspects of the startle behavior. Here we will review recent work that focuses on the neurophysiological and neuropharmacological basis for modifications in the M-cell circuit. After summarizing the main excitatory and inhibitory inputs to the M-cell, we review experiments showing startle response modulation by temperature, social status, and sensory filtering. Although very different in nature, actions of these three sources of modulation converge in the M-cell network. Mechanisms of modulation include altering the excitability of the M-cell itself as well as changes in excitatory and inhibitor drive, highlighting the role of balanced excitation and inhibition for escape decisions. One of the most extensively studied forms of startle plasticity in vertebrates is prepulse inhibition (PPI), a sensorimotor gating phenomenon, which is impaired in several information processing disorders. Finally, we review recent work in the M-cell system which focuses on the cellular mechanisms of PPI and its modulation by serotonin and dopamine.

Relief learning is distinguished from safety learning by the requirement of the nucleus accumbens

Aversive events induce aversive memories (fear learning) and can also establish appetitive memories. This is the case for cues associated with the cessation of an aversive event (relief learning) or occurring in an explicitly unpaired fashion (safety learning). However, the neural basis of relief and safety learning is poorly understood. In particular, it is not clear whether relief learning and safety learning are neuronally distinct. In the present study, we ask whether the nucleus accumbens is required for the acquisition of relief- and/or safety memory. Temporary inactivation of the nucleus accumbens by local injections of the GABA-A receptor agonist muscimol during the learning session abolished relief learning whereas safety learning was not affected. Thus, the requirement for a functional nucleus accumbens distinguishes relief from safety learning, showing that these two forms of learning are neuronally distinct.

BDNF-dependent consolidation of fear memories in the perirhinal cortex

In the recent years the perirhinal cortex (PRh) has been identified as a crucial brain area in fear learning. Since the neurotrophin brain-derived neurotrophic factor (BDNF) is an important mediator of synaptic plasticity and also crucially involved in memory consolidation of several learning paradigms, we analyzed now whether fear conditioning influences the expression of BDNF protein in the PRh. Here we observed a specific increase of BDNF protein 120 min after fear conditioning training. In order to test whether this increase of BDNF protein level is also required for the consolidation of the fear memory, we locally applied the Trk receptor inhibitor k252a into the PRh during this time window in a second series of experiments. By interfering with Trk-signaling during this critical time window, the formation of a long-term fear memory was completely blocked, indicated by a complete lack of fear potentiated startle 1 day later. In conclusion the present study further emphasizes the important role of the PRh in cued fear learning and identified BDNF as an important mediator for fear memory consolidation in the PRh.

Prevention and reversal of ketamine-induced schizophrenia related behavior by minocycline in mice: Possible involvement of antioxidant and nitrergic pathways

It has been hypothesized that oxidative imbalance and alterations in nitrergic signaling play a role in the neurobiology of schizophrenia. Preliminary evidence suggests that adjunctive minocycline treatment is efficacious for cognitive and negative symptoms of schizophrenia. This study investigated the effects of minocycline in the prevention and reversal of ketamine-induced schizophrenia-like behaviors in mice. In the reversal protocol, animals received ketamine (20 mg/kg per day intraperitoneally or saline for 14 days, and minocycline (25 or 50 mg/kg daily), risperidone or vehicle treatment from days 8 to 14. In the prevention protocol, mice were pretreated with minocycline, risperidone or vehicle prior to ketamine. Behaviors related to positive (locomotor activity and prepulse inhibition of startle), negative (social interaction) and cognitive (Y maze) symptoms of schizophrenia were also assessed. Glutathione (GSH), thiobarbituric acid-reactive substances (TBARS) and nitrite levels were measured in the prefrontal cortex, hippocampus and striatum. Minocycline and risperidone prevented and reversed ketamine-induced alterations in behavioral paradigms, oxidative markers (i.e. ketamine-induced decrease and increase in GSH levels and TBARS content, respectively) as well as nitrite levels in the striatum. These data provide a rationale for evaluating minocycline as a novel psychotropic agent and suggest that its mechanism of action includes antioxidant and nitrergic systems.