Prepulse inhibition predicts spatial working memory performance in the inbred Roman high- and low-avoidance rats and in genetically heterogeneous NIH-HS rats: relevance for studying pre-attentive and cognitive anomalies in schizophrenia

Stressing out! Effects of acute stress on prepulse inhibition and working memory

Prepulse inhibition (PPI) of the startle reflex serves as a pre-cognitive marker of sensorimotor gating, and its deficit may predict cognitive impairments. Startle reflex is modulated by many factors. Among them, stress has been a topic of interest, but its effects on both pre-cognitive and cognitive variables continue to yield divergent results. This study aims to analyze the effect of acute stress on PPI of the startle reflex and cognitive function (working memory, attention, inhibition, and verbal fluency). Participants were exposed to the MAST stress induction protocol or a stress-neutral task: stress group (n = 54) or control group (n = 54). Following stress induction, participants' startle responses were recorded, and cognition was assessed. The results revealed that participants in the stress group exhibited greater startle magnitude, lower PPI, and lower scores in working memory tests compared with the control group. Additionally, a correlation was found between working memory and PPI across all the participants, independent of stress group. These findings support the notion that after stress, both greater startle magnitude and diminished PPI could play an adaptive role by allowing for increased processing of stimuli potentially dangerous and stress-related. Similarly, our results lend support to the hypothesis that lower PPI may be predictive of cognitive impairment. Considering the impact of stress on both pre-cognitive (PPI) and cognitive (working memory) variables, we discuss the possibility that the effect of stress on PPI occurs through motivational priming and emphasize the relevance of considering stress in both basic and translational science.

Schizophrenia-relevant social, attentional and cognitive traits in female RHA vs. RLA rats: Effects of neonatal handling

The Roman high- (RHA) and low-avoidance (RLA) rats were bidirectionally selected and bred for, respectively, their rapid vs. extremely poor acquisition in the two-way active avoidance task. Consistent between-strain neurobehavioural differences have been found in anxiety- and stress-linked traits, as well as in schizophrenia-related phenotypes. RLAs display enhanced anxious- and stress-related phenotypes, whereas RHA rats show impulsivity, hyperactivity and attention/cognition-related impairments. Many of these typical behavioural phenotypes have been reported to be positively modulated by environmental treatments such as neonatal handling (NH). However, most studies on the Roman rat strains have been carried out in males. Thus, the present study for the first time focused on the joint evaluation of differences in novel object exploration (NOE), social interaction (SI), prepulse inhibition of the startle response (PPI), and cognitive performance and flexibility in various spatial tasks (using the Morris water maze, MWM) in females of both Roman rat strains. We also aimed at evaluating the long-lasting effects of NH treatment on the RHA vs. RLA profiles in these tests/tasks. Results show that anxiety-related behavior, as measured by the NOE test and self-grooming in the SI test, was increased in RLA rats, and dramatically reduced by NH. In the SI test RLA rats displayed diminished social interaction, which was rescued by NH. RHA females exhibited a deficit of PPI, which was not affected by NH. Spatial tasks in the MWM showed impairments of working memory, reference learning/memory and spatial reversal learning (i.e., cognitive flexibility) in RHA females. Spatial reference learning and cognitive flexibility (i.e., reversal task) showed some improvement in rats (mainly in RHAs) that had received NH during the first three weeks of life. With the exception of the SI test, the pattern of differences between female RHA vs. RLA profiles was overall consistent with what has previously been found in males of both strains, and NH treatment was able to enduringly improve some emotion-related and (spatial) cognitive outcomes in both strains.

Novel RXFP3 negative allosteric modulator RLX-33 reduces alcohol self-administration in rats

There is much interest in identifying novel pharmacotherapeutic targets that improve clinical outcomes for the treatment of alcohol use disorder (AUD). One promising target for therapeutic intervention is the relaxin family peptide 3 (RXFP3) receptor, a cognate receptor for neuropeptide relaxin-3, which has previously been implicated in regulating alcohol drinking behavior. Recently, we developed the first small-molecule RXFP3-selective negative allosteric modulator (NAM) RLX-33. Therefore, the goal of the present work was to characterize the impact of this novel NAM on affective-related behaviors and alcohol self-administration in rats. First, the effects of RLX-33 were tested on alcohol and sucrose self-administration in Wistar and alcohol-preferring P rats to determine the dose-response profile and specificity for alcohol. Then, we assessed the effects of systemic RLX-33 injection in Wistar rats in a battery of behavioral assays (open-field test, elevated zero maze, acoustic startle response test, and prepulse inhibition) and tested for alcohol clearance. We found that the lowest effective dose (5 mg/kg) reduced alcohol self-administration in both male and female Wistar rats, while in alcohol-preferring P rats, this effect was restricted to males, and there were no effects on sucrose self-administration or general locomotor activity. The characterization of affective and metabolic effects in Wistar rats generally found few locomotor, affective, or alcohol clearance changes, particularly at the 5 mg/kg dose. Overall, these findings are promising and suggest that RXFP3 NAM has potential as a pharmacological target for treating AUD.

c-Fos expression after neonatal handling in social brain regions: Distinctive profile of RHA-rat schizophrenia model on a social preference test

Neonatal handling (NH) is an environmental manipulation that induces long-lasting changes in behavioural, neuroendocrine, and neuroanatomical processes in rodents. We have previously reported that NH treatment increases social interaction preference in an animal model of schizophrenia-relevant features, the Roman high-avoidance (RHA) rats. The present study was aimed at evaluating whether the increase of social behaviour/preference due to NH treatment in RHA rats is associated with differences in c-Fos expression levels in some of the brain areas that integrate the "social brain". To this aim, we evaluated the performance of adult male rats from both Roman rat strains (RHA vs. RLA -Roman low-avoidance- rats), either untreated (control) or treated with NH (administered during the first 21 days of life) in a social interaction task. For the analyses of c-Fos activation untreated and NH-treated animals were divided into three different experimental conditions: undisturbed home cage controls (HC); rats exposed to the testing set-up context (CTX); and rats exposed to a social interaction (SI) test. It was found that, compared with their RLA counterparts, NH treatment increased social behaviour in RHA rats, and also specifically enhanced c-Fos expression in RHA rats tested for SI in some brain areas related to social behaviour, i.e. the infralimbic cortex (IL) and the medial posterodorsal amygdala (MePD) regions.

Atypical antipsychotics attenuate MK801-induced social withdrawal and hyperlocomotion in the RHA rat model of schizophrenia-relevant features

RATIONALE

The administration of NMDA receptor (NMDAR) antagonists constitutes a widely used model that produce both positive (e.g., hyperactivity) and negative (e.g., social withdrawal) symptoms relevant for schizophrenia in rodents. These effects can be reversed with the administration of atypical (second and third generation) antipsychotics.

OBJECTIVES

In this study we combined the NMDAR-antagonist model with the Roman High-Avoidance (RHA) strain, a psychogenetically selected model of schizophrenia-relevant features. We also studied whether some atypical antipsychotic drugs (clozapine, ziprasidone, and aripiprazole) would be able to attenuate or reverse the behavioural alterations induced by MK801 and whether such effects might be dependent on the rat strain.

METHODS

MK801 dose-response study was conducted in RHA and Roman Low-Avoidance (RLA) male rats. After that, the 0.15 mg/kg MK801 dose was selected to carry out pharmacological studies versus atypical antipsychotics.

RESULTS

In the first experiment we establish that MK801 (dizocilpine), a NMDAR antagonist, produces dose-related hyperactivity and social withdrawal, which are more marked in RHA than RLA rats. The administration of the atypical antipsychotics clozapine (2.5 mg/kg) or ziprasidone (2.5 mg/kg) partially reversed or attenuated some of the social behaviour deficits and hyperactivity induced by the administration of MK801. Aripiprazole (3 mg/kg), a third-generation antipsychotic, reversed or attenuated the social preference deficit, the hyperactivity and the impairment of social latency induced by MK801.

CONCLUSIONS

These results seem to be in line with previous studies with the NMDAR-antagonist model and add face (MK801-induced social withdrawal and hyperactivity) and predictive (attenuation of MK801-induced effects by atypical antipsychotics) validity to the RHA rat strain as a model of schizophrenia-relevant features.

A maturational shift in the frontal cortex synaptic transcriptional landscape underlies schizophrenia-relevant behavioural traits: A congenital rat model

Disruption of brain development early in life may underlie the neurobiology behind schizophrenia. We have reported more immature synaptic spines in the frontal cortex (FC) of adult Roman High-Avoidance (RHA-I) rats, a behavioural model displaying schizophrenia-like traits. Here, we performed a whole transcriptome analysis in the FC of 4 months old male RHA-I (n=8) and its counterpart, the Roman Low-Avoidance (RLA-I) (n=8). We identified 203 significant genes with overrepresentation of genes involved in synaptic function. Next, we performed a gene set enrichment analysis (GSEA) for genes co-expressed during neurodevelopment. Gene networks were obtained by weighted gene co-expression network analysis (WGCNA) of a transcriptomic dataset containing human FC during lifespan (n=269). Out of thirty-one functional gene networks, six were significantly enriched in the RHA-I. These were differentially regulated during infancy and enriched in biological ontologies related to myelination, synaptic function, and immune response. We validated differential gene expression in a new cohort of adolescent (<=2 months old) and young-adult (>=3 months old) RHA-I and RLA-I rats. The results confirmed overexpression of Gsn, Nt5cd1, Ppp1r1b, and Slc9a3r1 in young-adult RHA-I, while Cables1, a regulator of Cdk5 phosphorylation in actin regulation and involved in synaptic plasticity and maturation, was significantly downregulated in adolescent RHA-I. This age-related expression change was also observed for presynaptic components Snap25 and Snap29. Our results show a different maturational expression profile of synaptic components in the RHA-I strain, supporting a shift in FC maturation underlying schizophrenia-like behavioural traits and adding construct validity to this strain as a neurodevelopmental model.

Narrative Review of the Complex Interaction between Pain and Trauma in Children: A Focus on Biological Memory, Preclinical Data, and Epigenetic Processes

The incidence and collective impact of early adverse experiences, trauma, and pain continue to increase. This underscores the urgent need for translational efforts between clinical and preclinical research to better understand the underlying mechanisms and develop effective therapeutic approaches. As our understanding of these issues improves from studies in children and adolescents, we can create more precise preclinical models and ultimately translate our findings back to clinical practice. A multidisciplinary approach is essential for addressing the complex and wide-ranging effects of these experiences on individuals and society. This narrative review aims to (1) define pain and trauma experiences in childhood and adolescents, (2) discuss the relationship between pain and trauma, (3) consider the role of biological memory, (4) decipher the relationship between pain and trauma using preclinical data, and (5) examine the role of the environment by introducing the importance of epigenetic processes. The ultimate scope is to better understand the wide-ranging effects of trauma, abuse, and chronic pain on children and adolescents, how they occur, and how to prevent or mitigate their effects and develop effective treatment strategies that address both the underlying causes and the associated physiological and psychological effects.

Age-related changes in prepulse inhibition of the startle response

Introduction

Acoustic prepulse inhibition of the startle response (PPI) is a phenomenon characterized by the reduction in the startle reflex caused by the presence of weak and brief stimulus before an intense and sudden stimulus (pulse). These phenomena can be observed in several species, but in humans it is commonly measured by the eyeblink using electromyography. PPI works as an operational measure of sensorimotor gating, which is the ability to suppress motor responses for sensory stimulus. Healthy aging is marked by several changes in neural processing, like inhibitory functioning decline. In this line, PPI measure can be a potential biomarker for changes related to the aging process.

Methods

In this research we aim to investigate if PPI is reduced with aging and if this reduction would be associated with cognitive functioning of older adults. To this aim, we compared PPI levels of older adults (over 60 years old) with PPI levels of young adults (from 18 to 28 years old).

Results

With that, we found, significantly lower PPI level (F[1,25] = 7.44 p = 0.01) and lower startle amplitude startle amplitude: (U = 26.000 p = 0.001) in older adults than in young adults. However, we did not find differences in levels of habituation (T = -1.1 p = 0.28) and correlation between PPI and cognition within the sample of healthy older adults.

Discussion

Our results demonstrate that aging is a factor that affects PPI and that it does not seem to predict cognition, however, future studies should explore the potential of using PPI for monitoring cognitive changes associated with techniques such as cognitive training.

Neurobehavioral Profiles of Six Genetically-based Rat Models of Schizophrenia- related Symptoms

Schizophrenia is a chronic and severe mental disorder with high heterogeneity in its symptoms clusters. The effectiveness of drug treatments for the disorder is far from satisfactory. It is widely accepted that research with valid animal models is essential if we aim at understanding its genetic/ neurobiological mechanisms and finding more effective treatments. The present article presents an overview of six genetically-based (selectively-bred) rat models/strains, which exhibit neurobehavioral schizophrenia-relevant features, i.e., the Apomorphine-susceptible (APO-SUS) rats, the Low-prepulse inhibition rats, the Brattleboro (BRAT) rats, the Spontaneously Hypertensive rats (SHR), the Wisket rats and the Roman High-Avoidance (RHA) rats. Strikingly, all the strains display impairments in prepulse inhibition of the startle response (PPI), which remarkably, in most cases are associated with novelty-induced hyperlocomotion, deficits of social behavior, impairment of latent inhibition and cognitive flexibility, or signs of impaired prefrontal cortex (PFC) function. However, only three of the strains share PPI deficits and dopaminergic (DAergic) psychostimulant-induced hyperlocomotion (together with prefrontal cortex dysfunction in two models, the APO-SUS and RHA), which points out that alterations of the mesolimbic DAergic circuit are a schizophrenia-linked trait that not all models reproduce, but it characterizes some strains that can be valid models of schizophrenia-relevant features and drug-addiction vulnerability (and thus, dual diagnosis). We conclude by putting the research based on these genetically-selected rat models in the context of the Research Domain Criteria (RDoC) framework, suggesting that RDoC-oriented research programs using selectively-bred strains might help to accelerate progress in the various aspects of the schizophrenia-related research agenda.

Test-retest reliability of prepulse inhibition (PPI) and PPI correlation with working memory

OBJECTIVE

Sensorimotor gating is experimentally operationalized by the prepulse inhibition (PPI) of the startle response (SR). Previous studies suggest high test-retest reliability of PPI and potential correlation with working memory (WM). Here, we aimed to validate and extend the test-retest reliability of PPI in healthy humans and its correlation with WM performance.

METHODS

We applied an acoustic startle PPI paradigm with four different prepulse intensities (64, 68, 72 and 76 dB) and two different WM tasks [n-back, change detection task (CDT)] in a group of 26 healthy adults (final sample size n = 23). To assess test-retest reliability, we performed all tests on two separate days ~27 days (range: 21-32 days) apart.

RESULTS

We were able to confirm high test-retest reliability of the PPI with a mean intraclass correlation (ICC) of > 0.80 and significant positive correlation of PPI with n-back but not with CDT performance. Detailed analysis showed that PPI across all prepulse intensities significantly correlated with both the 2-back and 0-back conditions, suggesting regulation by cross-conditional processes (e.g. attention). However, when removing the 0-back component from the 2-back data, we found a specific and significant correlation with WM for the 76-dB PPI condition.

CONCLUSION

With the present study, we were able to confirm the high test-retest reliability of the PPI in humans and could validate and expand on its correlation with WM performance.

Quetiapine Ameliorates MIA-Induced Impairment of Sensorimotor Gating: Focus on Neuron-Microglia Communication and the Inflammatory Response in the Frontal Cortex of Adult Offspring of Wistar Rats

The maternal immune activation produced by the systemic administration of lipopolysaccharide (LPS) in rats provides valuable insights into the basis of behavioural schizophrenia-like disturbances and biochemical changes in the brains of the offspring, such as microglial activation. Regarding therapy, antipsychotics continually constitute the cornerstone of schizophrenia treatment. To their various efficacy and side effects, as well as not fully recognised mechanisms of action, further characteristics have been suggested, including an anti-inflammatory action via the impact on neuron–microglia axes responsible for inhibition of microglial activation. Therefore, in the present study, we sought to determine whether chronic treatment with chlorpromazine, quetiapine or aripiprazole could influence schizophrenia-like behavioural disturbances at the level of sensorimotor gating in male offspring prenatally exposed to LPS. Simultaneously, we wanted to explore if the chosen antipsychotics display a positive impact on the neuroimmunological parameters in the brains of these adult animals with a special focus on the ligand-receptor axes controlling neuron–microglia communication as well as pro- and anti-inflammatory factors related to the microglial activity. The results of our research revealed the beneficial effect of quetiapine on deficits in sensorimotor gating observed in prenatally LPS-exposed offspring. In terms of axes controlling neuron–microglia communication and markers of microglial reactivity, we observed a subtle impact of quetiapine on hippocampal Cx3cl1 and Cx3cr1 levels, as well as cortical Cd68 expression. Hence, further research is required to fully define and explain the involvement of quetiapine and other antipsychotics in Cx3cl1-Cx3cr1 and/or Cd200-Cd200r axes modulation and inflammatory processes in the LPS-based model of schizophrenia-like disturbances.

Effects of personality on assessments of anxiety and cognition

Individual variation in responses to commonly used tests of anxiety and spatial memory is often reported. While this variation is frequently considered to be 'noise', evidence suggests that it is, at least partially, related to consistent individual differences in behavioral responses (i.e., personality). The same tests used to assess anxiety are often used to profile personality traits, but personality differences are rarely considered when testing treatment differences in anxiety. Focusing on the rat literature, we describe fundamental principles involved in anxiety and spatial memory tests and we discuss how personality differences and housing conditions can influence behavioral responses in these tests. We propose that an opportunity exists to increase stress resiliency in environmentally sensitive individuals by providing environmental enrichment. We conclude by discussing different approaches to incorporating personality measures into the design and analysis of future studies; given the potential that variation masks research outcomes, we suggest that a strategy which considers the individual and its housing can contribute to improving research reproducibility.

Different maturation patterns for sensorimotor gating and startle habituation deficits in male and female RHA vs RLA rats

Neurodevelopmental anomalies are thought to play a crucial role in the emergence of schizophrenia. The Roman high-avoidance (RHA) rats exhibit impaired prepulse inhibition (PPI), as well as other behavioral and cognitive singularities related to schizophrenia syndromes compared to the Roman low-avoidance (RLA) rats. In the present study, we aimed at elucidating whether PPI deficits in the RHA rats take place during prepubescence, adolescence, or adulthood. Thus, we evaluated the levels of PPI of both strains and both sexes during these three developmental phases. Additionally, we also investigated the onset of startle habituation deficits in the same groups. The results showed that male RHA rats exhibit a clear-cut PPI reduction compared to their RLA counterparts in adulthood. In female RHA rats, we observed lower levels of PPI since adolescence and through adulthood. We also found no differences between PPI percentages among the three ages in RHA male rats. Contrarily, in male RLA rats, PPI levels were increased in adults compared to their adolescent and prepubescent counterparts. Finally, a deficit in startle habituation was observed in adulthood of both male and female RHA rats, although in the latter case the disturbance in startle habituation was more profound. These results further the description of the maturational trajectory of cognitive markers relevant to schizophrenia prodrome and they add face validity to the RHA rats as a model of schizophrenia-relevant phenotypes.

Social preference in Roman rats: age and sex variations relevance for modeling negative schizophrenia-like features

Social withdrawal is one of the most relevant negative symptoms of schizophrenia. Animal models that mimic schizophrenia's symptoms, in general, and negative symptoms, in particular, are difficult to develop because of the high complexity of symptoms and neurochemical disturbances that schizophrenia patients display throughout their lives. In recent years we have shown that Roman High- Avoidance (RHA) rats exhibit some phenotypes that are thought to represent positive symptoms, cognitive/attentional symptoms, as well as some negative symptoms of the disease. In the present study, we aimed at elucidating whether the social interaction (SI) deficits exhibited by adult male RHA rats, compared to their Roman Low-Avoidance (RLA) counterparts, are also present during adolescence, as well as whether there are between-strain differences in adolescent and adult female rats. The results of the present study show that adult male RHA rats exhibited a deficit in social preference compared to their RLA counterparts. Such a deficit was not observed in adolescent RHA rats or female rats of any age. The results also show that the adult male rats of both strains had significant decreases in social preference compared to the adolescent male rats. Additionally, we also show that female adult RHA rats have greater social preference than their male counterparts. These results seem to be in line with previous rodent and human studies and add face validity to the RHA rats as a model of schizophrenia.

Neurobehavioral and neurodevelopmental profiles of a heuristic genetic model of differential schizophrenia- and addiction-relevant features: The RHA vs. RLA rats

The Roman High- (RHA) and Low-(RLA) avoidance rat lines/strains were generated through bidirectional selective breeding for rapid (RHA) vs. extremely poor (RLA) two-way active avoidance acquisition. Compared with RLAs and other rat strains/stocks, RHAs are characterized by increased impulsivity, deficits in social behavior, novelty-induced hyper-locomotion, impaired attentional/cognitive abilities, vulnerability to psychostimulant sensitization and drug addiction. RHA rats also exhibit decreased function of the prefrontal cortex (PFC) and hippocampus, increased functional activity of the mesolimbic dopamine system and a dramatic deficit of central metabotropic glutamate-2 (mGlu2) receptors (due to a stop codon mutation at cysteine 407 in Grm2 -cys407*-), along with increased density of 5-HT2A receptors in the PFC, alterations of several synaptic markers and increased density of pyramidal "thin" (immature) dendrític spines in the PFC. These characteristics suggest an immature brain of RHA rats, and are reminiscent of schizophrenia features like hypofrontality and disruption of the excitation/inhibition cortical balance. RHA rats represent a promising heuristic model of neurodevelopmental schizophrenia-relevant features and comorbidity with drug addiction vulnerability.

Oxytocin attenuates schizophrenia-like reduced sensorimotor gating in outbred and inbred rats in line with strain differences in CD38 gene expression

Prepulse inhibition (PPI) of the startle response is a measure of sensorimotor gating that is impaired in many clinical conditions, including schizophrenia. The inbred Roman high-avoidance (RHA) rats, compared to their low-avoidance (RLA) counterparts, show distinct schizophrenia-like phenotypes, such as spontaneous deficits in PPI accompanied by decreased medial prefrontal cortex (mPFC) activity and volume. Schizophrenia-like deficits are usually attenuated by antipsychotic drugs, but these drugs often produce severe side effects. In order to reduce these side effects, the neuropeptide oxytocin has been proposed as an alternative natural antipsychotic for schizophrenia. Here, we examined the effects of peripheral oxytocin administration (saline, 0.04, and 0.2 mg/kg) on PPI in the RHA vs. RLA rats, as well as in the outbred heterogeneous stock (HS) rats. Our results showed that oxytocin increased PPI in the HS rats and attenuated PPI deficits in the RHA rats, but it did not significantly affect PPI in the RLAs. To explore whether these divergent effects were associated with differences in oxytocinergic mechanisms, we analyzed gene expression of the oxytocin receptor (OXTR) and the regulator of oxytocin release (CD38) in the mPFC of the Roman rats. Consistent with the differential oxytocin effects on PPI (RHA > RLA), constitutive CD38 expression was reduced in the RHA rats compared to the RLAs, while oxytocin administration increased OXTR expression in both strains. Overall, the present work reveals that oxytocin administration shows antipsychotic-like effects on PPI in outbred and inbred rats, and it suggests that these effects may be related to basal differences in oxytocin-mediated mechanisms in the mPFC.

Decreased social interaction in the RHA rat model of schizophrenia-relevant features: Modulation by neonatal handling

The Roman-Low (RLA) and High-Avoidance (RHA) rat strains have been bidirectionally selected and bred, respectively, for extremely poor vs. rapid acquisition of the two-way active avoidance task. Over 50 years of selective breeding have led to two strains displaying many differential specific phenotypes. While RLAs display anxious-related behaviours, RHA rats show impulsivity, and schizophrenia-like positive and cognitive symptoms or phenotypes. Neonatal handling (NH) is an environmental treatment with long-lasting anxiolytic-like and anti-stress effects. NH also reduces symptoms related to schizophrenia, such as pre-pulse inhibition (PPI) impairment and latent inhibition (LI) deficits, and improves spatial working memory and cognitive flexibility. The present work was aimed at exploring whether RHAs also display negative schizophrenia-like symptoms (or phenotypes), such as lowered preference for social interaction (i.e. asociality), and whether NH would reduce these deficits. To this aim, we evaluated naïve inbred RHA and RLA rats in a social interaction (SI) test after either long- or short-term habituation to the testing set up (studies 1-2). In Study 3 we tested untreated and NH-treated RHA and RLA rats in novel object exploration (NOE) and SI tests. Compared with RHAs, RLA rats displayed increased anxiety-related behaviours in the NOE (i.e. higher behavioural inhibition, lesser exploration of the novel object) and SI (i.e. higher levels of self-grooming) tests which were dramatically reduced by NH treatment, thus supporting the long-lasting anxiolytic-like effect of NH. Remarkably, RHA rats showed decreased social preference in the SI test compared with RLAs, evidencing that RHAs would present a relative asociality, which is thought to model some negative symptomatology (i.e. social withdrawal) of schizophrenia. NH increased absolute levels of social behaviour in both strains, but with a more marked effect in RHA rats, especially in the first 5 min of the SI test. Thus, it is hypothesized that, apart from its effects on anxiety-related behaviours, NH might have long-lasting positive effects on behavioural and neurobiological processes that are impaired in schizophrenia.

Increased thin-spine density in frontal cortex pyramidal neurons in a genetic rat model of schizophrenia-relevant features

The cellular mechanisms altered during brain wiring leading to cognitive disturbances in neurodevelopmental disorders remain unknown. We have previously reported altered cortical expression of neurodevelopmentally regulated synaptic markers in a genetic animal model of schizophrenia-relevant behavioral features, the Roman-High Avoidance rat strain (RHA-I). To further explore this phenotype, we looked at dendritic spines in cortical pyramidal neurons, as changes in spine density and morphology are one of the main processes taking place during adolescence. An HSV-viral vector carrying green fluorescent protein (GFP) was injected into the frontal cortex (FC) of a group of 11 RHA-I and 12 Roman-Low Avoidance (RLA-I) male rats. GFP labeled dendrites from pyramidal cells were 3D reconstructed and number and types of spines quantified. We observed an increased spine density in the RHA-I, corresponding to a larger fraction of immature thin spines, with no differences in stubby and mushroom spines. Glia cells, parvalbumin (PV) and somatostatin (SST) interneurons and surrounding perineuronal net (PNN) density are known to participate in FC and pyramidal neuron dendritic spine maturation. We determined by stereological-based quantification a significantly higher number of GFAP-positive astrocytes in the FC of the RHA-I strain, with no difference in microglia (Iba1-positive cells). The number of inhibitory PV, SST interneurons or PNN density, on the contrary, was unchanged. Results support our belief that the RHA-I strain presents a more immature FC, with some structural features like those observed during adolescence, adding construct validity to this strain as a genetic behavioral model of neurodevelopmental disorders.

Life-Course Contribution of Prenatal Stress in Regulating the Neural Modulation Network Underlying the Prepulse Inhibition of the Acoustic Startle Reflex in Male Alzheimer's Disease Mice

The prepulse inhibition (PPI) of the acoustic startle reflex (ASR), as an index of sensorimotor gating, is one of the most extensively used paradigms in the field of neuropsychiatric disorders. Few studies have examined how prenatal stress (PS) regulates the sensorimotor gating during the lifespan and how PS modifies the development of amyloid-beta (Aβ) pathology in brain areas underlying the PPI formation. We followed alternations in corticosterone levels, learning and memory, and the PPI of the ASR measures in APPNL-G-F/NL-G-F offspring of dams exposed to gestational noise stress. In-depth quantifications of the Aβ plaque accumulation were also performed at 6 months. The results indicated an age-dependent deterioration of sensorimotor gating, long-lasting PS-induced abnormalities in PPI magnitudes, as well as deficits in spatial memory. The PS also resulted in a higher Aβ aggregation predominantly in brain areas associated with the PPI modulation network. The findings suggest the contribution of a PS-induced hypothalamic-pituitary-adrenal (HPA) axis hyperactivity in regulating the PPI modulation substrates leading to the abnormal development of the neural protection system in response to disruptive stimuli. The long-lasting HPA axis dysregulation appears to be the major underlying mechanism in precipitating the Aβ deposition, especially in brain areas contributed to the PPI modulation network.

Differential expression of synaptic markers regulated during neurodevelopment in a rat model of schizophrenia-like behavior

Schizophrenia is considered a neurodevelopmental disorder. Recent reports relate synaptic alterations with disease etiology. The inbred Roman High- (RHA-I) and Low- (RLA-I) Avoidance rat strains are a congenital neurobehavioral model, with the RHA-I displaying schizophrenia-related behaviors and serotonin 2A (5-HT2A) and metabotropic glutamate 2 (mGlu2) receptor alterations in the prefrontal cortex (PFC). We performed a comprehensive characterization of the RHA-I/RLA-I rats by real-time qPCR and Western blotting for 5-HT1A, 5-HT2A, mGlu2, dopamine 1 and dopamine 2 receptors (DRD1 and DRD2), AMPA receptor subunits Gria1, Gria2 and NMDA receptor subunits Grin1, Grin2a and Grin2b, as well as pre- and post-synaptic components in PFC and hippocampus (HIP). Besides corroborating decreased mGlu2 (Grm2) expression, we found increased mRNA levels for Snap25, Synaptophysin (Syp), Homer1 and Neuregulin-1 (Nrg1) in the PFC of the RHA-I and decreased expression of Vamp1, and Snapin in the HIP. We also showed alterations in Vamp1, Grin2b, Syp, Snap25 and Nrg1 at protein levels. mRNA levels of Brain Derived Neurotrophic Factor (BDNF) were increased in the PFC of the RHA-I rats, with no differences in the HIP, while BDNF protein levels were decreased in PFC and increased in HIP. To investigate the temporal dynamics of these synaptic markers during neurodevelopment, we made use of the open source BrainCloud™ dataset, and found that SYP, GRIN2B, NRG1, HOMER1, DRD1 and BDNF expression is upregulated in PFC during childhood and adolescence, suggesting a more immature neurobiological endophenotype in the RHA-I strain.

Schizophrenia-like reduced sensorimotor gating in intact inbred and outbred rats is associated with decreased medial prefrontal cortex activity and volume

Prepulse inhibition (PPI) of startle response is a measure of sensorimotor gating that is impaired in schizophrenia and in many other clinical conditions. Rat models using pharmacological or surgical strategies reveal that PPI is modulated by the cortico-striatal-pallido-thalamic (CSPT) circuit. Here, we explore whether spontaneous variation in PPI in intact inbred and outbred rats is associated with functional and structural differences in the CSPT circuit. Inbred Roman High-(RHA) and Low-avoidance (RLA) and outbred heterogeneous stock (HS) rats were assessed for PPI, brain activity, and brain volume. Brain activity was assessed by c-Fos expression and brain volume by magnetic resonance imaging. Relevant structures of the CSPT circuit were evaluated, such as the medial prefrontal cortex (mPFC), cingulate cortex, hippocampus (HPC), amygdala, nucleus accumbens (NAc), and dorsal striatum. RHA showed lower PPI than RLA rats, while HS rats were stratified by their PPI levels in three groups. Reduced PPI was accompanied by decreased mPFC activity in Roman and HS rats and increased NAc shell activity in HS rats. Low PPI was also associated with decreased mPFC and HPC volumes in Roman and HS rats. This study reports a consistent relationship between decreased function and volume of the mPFC and spontaneous low-PPI levels in inbred and outbred intact rats. Moreover, our findings suggest that, apart from a hypoactive and smaller mPFC, a hyperactive NAc and smaller HPC may underlie reduced PPI levels. Our results support the notion that sensorimotor gating is modulated by forebrain structures and highlight the importance of the mPFC in its regulation.

Dissociation between schizophrenia-relevant behavioral profiles and volumetric brain measures after long-lasting social isolation in Roman rats

Social isolation rearing of rodents is an environmental manipulation known to induce or potentiate psychotic-like symptoms and attentional and cognitive impairments relevant for schizophrenia. When subjected to a 28-week isolation rearing treatment, the Roman high-avoidance (RHA-I) rats display the common behavioral social isolation syndrome, with prepulse inhibition (PPI) deficits, hyperactivity, increased anxiety responses and learning/memory impairments when compared to their low-avoidance (RLA-I) counterparts. These results add face validity to the RHA-I rats as an animal model for schizophrenia-relevant behavioral and cognitive profiles and confirm previous results. The aim here was to further investigate the neuroanatomical effects of the isolation rearing, estimated through volume differences in medial prefrontal cortex (mPFC), dorsal striatum (dSt) and hippocampus (HPC). Results showed a global increase in volume in the mPFC in the isolated rats of both strains, as well as strain effects (RLA > RHA) in the three brain regions. These unexpected but robust results, might have unveiled some kind of compensatory mechanisms due to the particularly long-lasting isolation rearing period, much longer than those commonly used in the literature (which usually range from 4 to 12 weeks).

A Genetic Model of Impulsivity, Vulnerability to Drug Abuse and Schizophrenia-Relevant Symptoms With Translational Potential: The Roman High- vs. Low-Avoidance Rats

The bidirectional selective breeding of Roman high- (RHA) and low-avoidance (RLA) rats for respectively rapid vs. poor acquisition of active avoidant behavior has generated two lines/strains that differ markedly in terms of emotional reactivity, with RHA rats being less fearful than their RLA counterparts. Many other behavioral traits have been segregated along the selection procedure; thus, compared with their RLA counterparts, RHA rats behave as proactive copers in the face of aversive conditions, display a robust sensation/novelty seeking (SNS) profile, and show high impulsivity and an innate preference for natural and drug rewards. Impulsivity is a multifaceted behavioral trait and is generally defined as a tendency to express actions that are poorly conceived, premature, highly risky or inappropriate to the situation, that frequently lead to unpleasant consequences. High levels of impulsivity are associated with several neuropsychiatric conditions including attention-deficit hyperactivity disorder, obsessive-compulsive disorder, schizophrenia, and drug addiction. Herein, we review the behavioral and neurochemical differences between RHA and RLA rats and survey evidence that RHA rats represent a valid genetic model, with face, construct, and predictive validity, to investigate the neural underpinnings of behavioral disinhibition, novelty seeking, impulsivity, vulnerability to drug addiction as well as deficits in attentional processes, cognitive impairments and other schizophrenia-relevant traits.

Deficits of perceived spatial separation-induced prepulse inhibition in patients with bipolar disorder compared to healthy controls

OBJECTIVE

This study aimed to assess sensorimotor gating deficits in patients with bipolar disorder (BD) using a modified perceived spatial separation-induced prepulse inhibition (PSS-PPI) paradigm. The relationships between PSS-PPI, demographic and clinical characteristics, and cognitive functioning were also analyzed.

METHODS

In this cross-sectional study, 30 patients with BD were compared to 33 healthy controls (HC) with respect to prepulse inhibition measures of PSS-PPI using a 120 ms lead interval. The Young Mania Rating Scale, Hamilton Depression Scale, and Hamilton Anxiety Scale were used to assess manic, depressive, and anxiety symptoms. Cognition was evaluated using the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and the Stroop color-word test.

RESULTS

Compared with HC, patients with BD had a lower PSS-PPI level. PSS-PPI showed medium effect size (ES) between patients with BD and HC (ES = 0.65). Among patients with BD, PSS-PPI was positively correlated with the language domain of RBANS and negatively correlated with double word time and color interference time. There were no differences in PSS-PPI levels between patients with and without psychotic symptoms or between those euthymic patients or depressive patients with BD.

CONCLUSIONS

Patients with BD show a sensorimotor gating deficit as measured by perceived spatial separation-induced PPI of the startle response, which was more sensitive compared to the classic PPI paradigm. Euthymic bipolar patients and depressive bipolar patients show similar PPI level. PPI deficit in patients with BD is related to cognition, but not with demographic and clinical characteristics.

Rats selectively bred for showing divergent behavioral traits in response to stress or novelty or spontaneous yawning with a divergent frequency show similar changes in sexual behavior: the role of dopamine

Sexual behavior plays a fundamental role for reproduction in mammals and other animal species. It is characterized by an anticipatory and a consummatory phase, and several copulatory parameters have been identified in each phase, mainly in rats. Sexual behavior varies significantly across rats even when they are of the same strain and reared under identical conditions. This review shows that rats of the same strain selectively bred for showing a divergent behavioral trait when exposed to stress or novelty (i.e. Roman high and low avoidance rats, bred for their different avoidance response to the shuttle box, and high and low novelty exploration responders rats, bred for their different exploratory response to a novel environment) or a spontaneous behavior with divergent frequency (i.e. low and high yawning frequency rats, bred for their divergent yawning frequency) show similar differences in sexual behavior, mainly in copulatory pattern, but also in sexual motivation. As shown by behavioral pharmacology and intracerebral microdialysis experiments carried out mainly in Roman rats, these sexual differences may be due to a more robust dopaminergic tone present in the mesocorticolimbic dopaminergic system of one of the two sub-lines (e.g. high avoidance, high novelty exploration, and low yawning rat sub-lines). Thus, differences in genotype and/or in prenatal/postnatal environment lead not only to individual differences in temperament and environmental/emotional reactivity but also in sexual behavior. Because of the highly conserved mechanisms controlling reproduction in mammals, this may occur not only in rats but also in humans.

Comparative Analysis of Gene Expression Profiles Involved in Calcium Signaling Pathways Using the NLVH Animal Model of Schizophrenia

In this study, we evaluated the expression profile changes of genes that intervene in the calcium signaling pathway, in young and adult Wistar rats, using the animal model of neonatal lesion in ventral hippocampus (NLVH) (a recognized animal model for schizophrenia) and compared to the group of control animals (Sham). Through microarray technology, gene expression profiles were obtained from the three brain areas (nucleus accumbens, prefrontal cortex, and hippocampus) of young male Wistar rats (45 days) and adults (90 days) whether or not subjected to NLVH. The calcium signaling pathway reported a greater number of differentially expressed genes with z-score two values, > 2 (over-expression) and < - 2 (under-expression), in the three evaluated areas. The comparative analyses of this approach were performed in juvenile and adult rats with ventral hippocampal lesion in neonate rats (NLVH). NLVH influenced change expressions in various genes involved in Ca²⁺ homeostasis, including Cacna1d, Atp2a2, Adcy2, Ppp3cb, and Ptk2b. The expression of Adcy2, Ppp3cb, and Ptk2b genes changed in both age groups; therefore, the study of gene expression profiles between juvenile and adult rats may help to understand the molecular mechanisms of schizophrenia.

Roman high and low avoidance rats differ in their response to chronic olanzapine treatment at the level of body weight regulation, glucose homeostasis, and cortico-mesolimbic gene expression

Olanzapine, an antipsychotic agent mainly used for treating schizophrenia, is frequently associated with body weight gain and diabetes mellitus. Nonetheless, studies have shown that not every individual is equally susceptible to olanzapine's weight-gaining effect. Therefore, Roman high and low avoidance rat strains were examined on their responsiveness to olanzapine treatment. The Roman high avoidance rat shares many behavioral and physiological characteristics with human schizophrenia, such as increased central dopaminergic sensitivity, whereas the Roman low avoidance rat has been shown to be prone to diet-induced obesity and insulin resistance. The data revealed that only the Roman high avoidance rats are susceptible to olanzapine-induced weight gain and attenuated glucose tolerance. Here it is suggested that the specific olanzapine-induced weight gain in Roman high avoidance rats could be related to augmented dopaminergic sensitivity at baseline through increased expression of prefrontal cortex dopamine receptor D1 mRNA and nucleus accumbens dopamine receptor D2 mRNA expression. Regression analyses revealed that olanzapine-induced weight gain in the Roman high avoidance rat is above all related to increased prolactin levels, whereas changes in glucose homeostasis is best explained by differences in central dopaminergic receptor expressions between strains and treatment. Our data indicates that individual differences in dopaminergic receptor expression in the cortico-mesolimbic system are related to susceptibility to olanzapine-induced weight gain.

Loss-of-function mutation in Mirta22/Emc10 rescues specific schizophrenia-related phenotypes in a mouse model of the 22q11.2 deletion

Identification of protective loss-of-function (LoF) mutations holds great promise for devising novel therapeutic interventions, although it faces challenges due to the scarcity of protective LoF alleles in the human genome. Exploiting the detailed mechanistic characterization of animal models of validated disease mutations offers an alternative. Here, we provide insights into protective-variant biology based on our characterization of a model of the 22q11.2 deletion, a strong genetic risk factor for schizophrenia (SCZ). Postnatal brain up-regulation of Mirta22/Emc10, an inhibitor of neuronal maturation, represents the major transcriptional effect of the 22q11.2-associated microRNA dysregulation. Here, we demonstrate that mice in which the Df(16)A deficiency is combined with a LoF Mirta22 allele show rescue of key SCZ-related deficits, namely prepulse inhibition decrease, working memory impairment, and social memory deficits, as well as synaptic and structural plasticity abnormalities in the prefrontal cortex. Additional analysis of homozygous Mirta22 knockout mice, in which no alteration is observed in the above-mentioned SCZ-related phenotypes, highlights the deleterious effects of Mirta22 up-regulation. Our results support a causal link between dysregulation of a miRNA target and SCZ-related deficits and provide key insights into beneficial LoF mutations and potential new treatments.

Dopamine, Noradrenaline and Differences in Sexual Behavior between Roman High and Low Avoidance Male Rats: A Microdialysis Study in the Medial Prefrontal Cortex

Roman High- (RHA) and Low-Avoidance (RLA) outbred rats, which differ for a respectively rapid vs. poor acquisition of the active avoidance response in the shuttle-box, display differences in sexual activity when put in the presence of a sexually receptive female rat. Indeed RHA rats show higher levels of sexual motivation and copulatory performance than RLA rats, which persist also after repeated sexual activity. These differences have been correlated to a higher tone of the mesolimbic dopaminergic system of RHA rats vs. RLA rats, revealed by the higher increase of dopamine found in the dialysate obtained from the nucleus accumbens of RHA than RLA rats during sexual activity. This work shows that extracellular dopamine and noradrenaline (NA) also, increase in the dialysate from the medial prefrontal cortex (mPFC) of male RHA and RLA rats put in the presence of an inaccessible female rat and more markedly during direct sexual interaction. Such increases in dopamine (and its main metabolite 3,4-dihydroxyphenylacetic acid, DOPAC) and NA were found in both sexually naïve and experienced animals, but they were higher: (i) in RHA than in RLA rats; and (ii) in sexually experienced RHA and RLA rats than in their naïve counterparts. Finally, the differences in dopamine and NA in the mPFC occurred concomitantly to those in sexual activity, as RHA rats displayed higher levels of sexual motivation and copulatory performance than RLA rats in both the sexually naïve and experienced conditions. These results suggest that a higher dopaminergic tone also occurs in the mPFC, together with an increased noradrenergic tone, which may be involved in the different copulatory patterns found in RHA and RLA rats, as suggested for the mesolimbic dopaminergic system.

Deficits of perceived spatial separation induced prepulse inhibition in patients with schizophrenia: relationships to symptoms and neurocognition

BACKGROUND

Prepulse inhibition (PPI) and attention were impaired, which may cause psychotic symptoms and (or) hinder the cognitive functions in schizophrenia. However, due to the measurement methods of PPI, findings about the relationship between PPI and clinical symptoms, cognitive performances have been equivocal.

METHODS

Seventy-five schizophrenia patients (SZ) and 50 healthy controls (HC) were assessed in a modified acoustic PPI paradigm, named perceived spatial separation-induced PPI (PSS-PPI), compared to perceived spatial co-location PPI (PSC-PPI) with inter-stimulus interval (ISI) of 120 ms. Repeatable Battery for the Assessment of Neuropsychological Status and the Stroop Color-Word Test were administered to all subjects.

RESULTS

Significant decrease in the modified PPI was found in the patients as compared to the controls, and effect sizes (Cohen'd) for patients vs. HCs % PPI levels achieved a significant level (PSC-PPI d = 0.84, PSS-PPI d = 1.27). A logistic regression model based on PSS-PPI significantly represented the diagnostic grouping (χ²₌ 29.3; p < 0 .001), with 85.2% area under ROC curve in predicting group membership. In addition, patients exhibited deficits in neurocognition. Among patients of "non-remission", after controlling for gender, age, education, duration, recurrence times, onset age, cigarettes per day and chlorpromazine equivalent dosage, PSS-PPI levels were associated with positive and negative symptoms, PANSS total and thought disorder (P1, P6, P7, N5, N7, G9). In multiple linear regression analyses, male and higher attention scores contributed to better PSC-PPI and PSS-PPI in controls group, while larger amount of smoke and longer word-color interfere time contributed to poor PSS-PPI. In patients' group, higher education and attention scores contributed to better PSS-PPI, while repeated relapse contributed to poor PSS-PPI.

CONCLUSIONS

The acoustic perceived spatial separation-induced PPIs may bring to light the psychopathological symptoms, especially for thought disorder, and the mechanism(s) of the novel PPI paradigm was associated with attention function.

Differences in 5-HT2A and mGlu2 Receptor Expression Levels and Repressive Epigenetic Modifications at the 5-HT2A Promoter Region in the Roman Low- (RLA-I) and High- (RHA-I) Avoidance Rat Strains

The serotonin 2A (5-HT_2A) and metabotropic glutamate 2 (mGlu2) receptors regulate each other and are associated with schizophrenia. The Roman high- (RHA-I) and the Roman low- (RLA-I) avoidance rat strains present well-differentiated behavioral profiles, with the RHA-I strain emerging as a putative genetic rat model of schizophrenia-related features. The RHA-I strain shows increased 5-HT_2A and decreased mGlu2 receptor binding levels in prefrontal cortex (PFC). Here, we looked for differences in gene expression and transcriptional regulation of these receptors. The striatum (STR) was included in the analysis. 5-HT_2A, 5-HT_1A, and mGlu2 mRNA and [³H]ketanserin binding levels were measured in brain homogenates. As expected, 5-HT_2A binding was significantly increased in PFC in the RHA-I rats, while no difference in binding was observed in STR. Surprisingly, 5-HT_2A gene expression was unchanged in PFC but significantly decreased in STR. mGlu2 receptor gene expression was significantly decreased in both PFC and STR. No differences were observed for the 5-HT_1A receptor. Chromatin immunoprecipitation assay revealed increased trimethylation of histone 3 at lysine 27 (H3K27me3) at the promoter region of the HTR2A gene in the STR. We further looked at the Akt/GSK3 signaling pathway, a downstream point of convergence of the serotonin and glutamate system, and found increased phosphorylation levels of GSK3β at tyrosine 216 and increased β-catenin levels in the PFC of the RHA-I rats. These results reveal region-specific regulation of the 5-HT_2A receptor in the RHA-I rats probably due to absence of mGlu2 receptor that may result in differential regulation of downstream pathways.

Differential effects of antipsychotic and propsychotic drugs on prepulse inhibition and locomotor activity in Roman high- (RHA) and low-avoidance (RLA) rats

RATIONALE

Animal models with predictive and construct validity are necessary for developing novel and efficient therapeutics for psychiatric disorders.

OBJECTIVES

We have carried out a pharmacological characterization of the Roman high- (RHA-I) and low-avoidance (RLA-I) rat strains with different acutely administered propsychotic (DOI, MK-801) and antipsychotic drugs (haloperidol, clozapine), as well as apomorphine, on prepulse inhibition (PPI) of startle and locomotor activity (activity cages).

RESULTS

RHA-I rats display a consistent deficit of PPI compared with RLA-I rats. The typical antipsychotic haloperidol (dopamine D2 receptor antagonist) reversed the PPI deficit characteristic of RHA-I rats (in particular at 65 and 70 dB prepulse intensities) and reduced locomotion in both strains. The atypical antipsychotic clozapine (serotonin/dopamine receptor antagonist) did not affect PPI in either strain, but decreased locomotion in a dose-dependent manner in both rat strains. The mixed dopamine D1/D2 agonist, apomorphine, at the dose of 0.05 mg/kg, decreased PPI in RHA-I, but not RLA-I rats. The hallucinogen drug DOI (5-HT2A agonist; 0.1-1.0 mg/kg) disrupted PPI in RLA-I rats in a dose-dependent manner at the 70 dB prepulse intensity, while in RHA-I rats, only the 0.5 mg/kg dose impaired PPI at the 80 dB prepulse intensity. DOI slightly decreased locomotion in both strains. Finally, clozapine attenuated the PPI impairment induced by the NMDA receptor antagonist MK-801 only in RLA-I rats.

CONCLUSIONS

These results add experimental evidence to the view that RHA-I rats represent a model with predictive and construct validity of some dopamine and 5-HT2A receptor-related features of schizophrenia.

Serum Response Factor (SRF) Ablation Interferes with Acute Stress-Associated Immediate and Long-Term Coping Mechanisms

Stress experience modulates behavior, metabolism, and energy expenditure of organisms. One molecular hallmark of an acute stress response is a rapid induction of immediate early genes (IEGs) such as c-Fos and Egr family members. IEG transcription in neurons is mediated by the neuronal activity-driven gene regulator serum response factor (SRF). We show a first role of SRF in immediate and long-lasting acute restraint stress (AS) responses. For this, we employed a standardized mouse phenotyping protocol at the German Mouse Clinic (GMC) including behavioral, metabolic, and cardiologic tests as well as gene expression profiling to analyze the consequences of forebrain-specific SRF deletion in mice exposed to AS. Adult mice with an SRF deletion in glutamatergic neurons (Srf; ^{CaMKIIa-CreERT2} ) showed hyperactivity, decreased anxiety, and impaired working memory. In response to restraint AS, instant stress reactivity including locomotor behavior and corticosterone induction was impaired in Srf mutant mice. Interestingly, even several weeks after previous AS exposure, SRF-deficient mice showed long-lasting AS-associated changes including altered locomotion, metabolism, energy expenditure, and cardiovascular changes. This suggests a requirement of SRF for mediating long-term stress coping mechanisms in wild-type mice. SRF ablation decreased AS-mediated IEG induction and activity of the actin severing protein cofilin. In summary, our data suggest an SRF function in immediate AS reactions and long-term post-stress-associated coping mechanisms.

Prepulse inhibition in euthymic bipolar disorder patients in comparison with control subjects

OBJECTIVE

Deficient prepulse inhibition (PPI) of the startle response, indicating sensorimotor gating deficits, has been reported in schizophrenia and other neuropsychiatric disorders. This study aimed to assess sensorimotor gating deficits in patients with euthymic bipolar. Furthermore, we analysed the relationships between PPI and clinical and cognitive measures.

METHOD

Prepulse inhibition was measured in 64 patients with euthymic bipolar and in 64 control subjects matched for age, gender, education level and smoking status. Clinical characteristics and level of functioning were assessed in all participants using Hamilton Depression Rating Scale (HDRS), Young Mania Rating Scale (YMRS) and Functioning Assessment Short Test (FAST). Cognition was evaluated using the Measurement and Treatment Research to Improve Cognition in Schizophrenia Consensus Cognitive Battery (MCCB) and the Stroop test as an additional measure of executive function.

RESULTS

Compared with controls, patients with bipolar disorder exhibited PPI deficits at 60- and 120-millisecond prepulse-pulse intervals. Among patients with bipolar disorder, PPI was correlated with the social cognition domain of the MCCB. PPI was not significantly correlated with other clinical, functional and neurocognitive variables in either group.

CONCLUSIONS

Our data suggest that PPI deficit is a neurobiological marker in euthymic bipolar disorder, which is associated with social cognition but not with other clinical, functional or cognitive measures.

Divergent effects of isolation rearing on prepulse inhibition, activity, anxiety and hippocampal-dependent memory in Roman high- and low-avoidance rats: A putative model of schizophrenia-relevant features

Social isolation of rats induces a constellation of behavioral alterations known as "isolation syndrome" that are consistent with some of the positive and cognitive symptoms observed in schizophrenic patients. In the present study we have assessed whether isolation rearing of inbred Roman high-avoidance (RHA-I) and Roman low-avoidance (RLA-I) strains can lead to the appearance of some of the key features of the "isolation syndrome", such as prepulse inhibition (PPI) deficits, increased anxious behavior, hyperactivity and memory/learning impairments. Compared to RLA-I rats, the results show that isolation rearing (IR) in RHA-I rats has a more profound impact, as they exhibit isolation-induced PPI deficits, increased anxiety, hyperactivity and long-term reference memory deficits, while isolated RLA-I rats only exhibit deficits in a spatial working memory task. These results give further support to the validity of RHA-I rats as a genetically-based model of schizophrenia relevant-symptoms.

Association between prepulse inhibition of the startle response and latent inhibition of two-way avoidance acquisition: A study with heterogeneous NIH-HS rats

This study presents the first evaluation of the associations between responses in two paradigms related to schizophrenia in the genetically heterogeneous NIH-HS rat stock. NIH-HS rats are a stock of genetically heterogeneous animals that have been derived from eight different inbred strains. A rotational breeding schedule has been followed for more than eighty generations, leading to a high level of genetic recombination that makes the NIH-HS rats a unique tool for studying the genetic basis of (biological, behavioral, disease-related) complex traits. Previous work has dealt with the characterization of coping styles, cognitive and anxiety/fear-related profiles of NIH-HS rats. In the present study we have completed their characterization in two behavioral models, prepulse inhibition (PPI) and latent inhibition (LI) of the two-way active avoidance response, that appear to be related to schizophrenia or to schizophrenia-relevant symptoms. We have found that these rats display PPI for each of the four prepulse intensities tested, allowing their stratification in high, medium and low PPI subgroups. When testing these three subgroups for LI of two-way active avoidance acquisition it has been observed that the LowPPI and MediumPPI subgroups present impaired LI, which, along with the fact that the HighPPI group presents significant LI, allows us to hypothesize that responses in these two paradigms are somehow related and that selection of NIH-HS rats for Low vs HighPPI could make a promising animal model for the study of clusters of schizophrenia-relevant symptoms and their underlying neurobiological mechanisms.