Haloperidol differentially modulates prepulse inhibition and p50 suppression in healthy humans stratified for low and high gating levels

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.

Low prepulse inhibition predicts lower social interaction, impaired spatial working memory, reference memory and cognitive flexibility in genetically heterogeneous rats

The "Genetically Heterogeneous National Institutes of Health (NIHHS)" stock rat (hereafter HS) shows a wide phenotypic variation, as a result of having been derived from eight inbred rat strains. Thus, these rats may be a conceivable parallel model of a healthy human sample. In order to evaluate whether HS rats have face validity as an animal model of schizophrenia-relevant features, it should be demonstrated that they present behavioural traits that may model negative and cognitive symptoms of the disorder. Previous studies on HS rats have shown that prepulse inhibition (PPI, a measure of sensorimotor gating processes), which is impaired in schizophrenic patients, is correlated with their working memory performance. In this study, we evaluated whether low PPI in the HS stock rat predicts impairments of spatial working memory (SWM), spatial reference memory and cognitive flexibility in the Morris water maze (MWM) test, and we evaluated HS rats for social interaction (SI) in a social investigation task. HS rats were stratified into 2 different groups according to their PPI scores, i.e. low- and high-PPI. In the SI task, low-PPI rats showed decreased social behaviour compared to high-PPI rats. In addition, relative to high-PPI HS rats, the low-PPI group displayed poorer SWM performance, impaired cognitive flexibility (in a reversal task) and worsened long-term spatial memory. Such differential behaviours in social and cognitive paradigms provide evidence on the face validity of low-PPI HS rats as a model of negative-like and cognitive schizophrenia-relevant traits.

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.

Comparative Analysis of Dopaminergic and Cholinergic Mechanisms of Sensory and Sensorimotor Gating in Healthy Individuals and in Patients With Schizophrenia

Sensory and sensorimotor gating provide the early processing of information under conditions of rapid presentation of multiple stimuli. Gating deficiency is observed in various psychopathologies, in particular, in schizophrenia. However, there is also a significant proportion of people in the general population with low filtration rates who do not show any noticeable cognitive decline. The review article presents a comparative analysis of existing data on the peculiarities of cholinergic and dopaminergic mechanisms associated with lowering gating in healthy individuals and in patients with schizophrenia. The differences in gating mechanisms in cohorts of healthy individuals and those with schizophrenia are discussed.

Effects of methylphenidate on sensory and sensorimotor gating of initially psychostimulant-naïve adult ADHD patients

Deficient information processing in ADHD theoretically results in sensory overload, which in turn may underlie its symptoms. If this sensory overload is caused by deficient filtering of environmental stimuli, then one would expect finding deficits in P50 gating and prepulse inhibition of the startle reflex (PPI). Previous reports on these measures in ADHD have shown inconsistent findings, which may have been caused by either medication use or comorbidity (e.g. ASD). The primary aim of this study was therefore to explore P50 suppression and PPI in adult, psychostimulant-naïve patients with ADHD without major comorbidity, and to examine the effects of 6 weeks treatment with methylphenidate (MPH) on these measures. A total of 42 initially psychostimulant-naive, adult ADHD patients without major comorbidity and 42 matched healthy controls, were assessed for their P50 gating, PPI, and habituation/sensitization abilities at baseline and after 6 weeks of treatment with methylphenidate. Although six weeks of treatment with MPH significantly reduced symptomatology as well as improved daily life functioning in our patients, it neither significantly affected PPI, P50 suppression nor sensitization, but habituation unexpectedly decreased. The absence of PPI and P50 suppression deficits in our patients in the psychostimulant-naïve state indicates no gating deficits. In turn, this suggests that the difficulties to inhibit distraction of attention by irrelevant stimuli that many patients with (adult) ADHD report, have a different origin than the theoretical causes of sensory overload frequently reported in studies on patients with schizophrenia.

Deep brain stimulation and sensorimotor gating in tourette syndrome and obsessive-compulsive disorder

Recent translational data suggest that deep brain stimulation (DBS) of the cortico-striato-thalamo-cortical (CSTC) loops improves sensorimotor gating in psychiatric disorders that show deficient prepulse inhibition (PPI), a robust operational measure of sensorimotor gating. To our knowledge we are the first to investigate this effect in patients with Tourette syndrome (TS). We measured PPI of the acoustic startle reflex in patients with TS (N = 10) or Obsessive-Compulsive Disorder (OCD) (N = 8) treated with DBS of the centromedian and ventro-oral internal thalamic nucleus and the anterior limb of internal capsule-nucleus accumbens area respectively, and aged- and gender-matched healthy controls (HC). PPI of the DBS groups was measured in randomized order in the ON and OFF stimulation condition. Statistical analysis revealed no significant difference in PPI (%) of patients with TS between ON (M = 20.5, SD = 14.9) and OFF (M = 25.2, SD = 29.7) condition. There were significantly reduced PPI levels in patients with TS in the ON condition compared to HC (M = 49.2, SD = 10.7), but no significant difference in PPI between TS in the OFF condition and HC. Furthermore, we found no significant stimulation or group effect for OCD and HC (OCD ON: M = 57.0, SD = 8.3; OCD OFF: 67.8, SD = 19.6; HC: M = 63.0, SD = 24.3). Our study has a number of limitations. Sample sizes are small due to the restricted patient collective. The study was not controlled for use of psychoactive medication or nicotine. Furthermore, we were not able to assess presurgical PPI measurements. In conclusion, we were able to show that PPI is impaired in patients with TS. This finding is in line with recent translational work. With respect to the OCD cohort we were not able to replicate our previously published data. A disability in sensorimotor gating plays a pivotal role in many psychiatric disorders therefore more research should be conducted to disentangle the potential and limitations of modulating sensorimotor gating via brain stimulation techniques.

Prepulse inhibition of the acoustic startle reflex and P50 gating in aging and alzheimer's disease

Inhibition plays a crucial role in many functional domains, such as cognition, emotion, and actions. Studies on cognitive aging demonstrate changes in inhibitory mechanisms are age- and pathology-related. Prepulse inhibition (PPI) is the suppression of an acoustic startle reflex (ASR) to an intense stimulus when a weak prepulse stimulus precedes the startle stimulus. A reduction of PPI is thought to reflect dysfunction of sensorimotor gating which normally suppresses excessive behavioral responses to disruptive stimuli. Both human and rodent studies show age-dependent alterations of PPI of the ASR that are further compromised in Alzheimer's disease (AD). The auditory P50 gating, an index of repetition suppression, also is characterized as a putative electrophysiological biomarker of prodromal AD. This review provides the latest evidence of age- and AD-associated impairment of sensorimotor gating based upon both human and rodent studies, as well as the AD-related disruption of P50 gating in humans. It begins with a concise review of neural networks underlying PPI regulation. Then, evidence of age- and AD-related dysfunction of both PPI and P50 gating is discussed. The attentional/ emotional aspects of sensorimotor gating and the neurotransmitter mechanisms underpinning PPI and P50 gating are also reviewed. The review ends with conclusions and research directions.

Auditory Sensory Gating and the Big Five Personality Factors

Abstract. Sensory gating allows an individual to filter out irrelevant sensory information from the environment, potentially freeing attentional resources for more complex tasks. Some work has demonstrated a relationship between auditory sensory gating and cognitive skills such as executive function, although the functional significance is not well understood. The relationship between sensory gating and personality dimensions has not been adequately explored. Participants completed a paired-tone sensory gating event-related potential (ERP) paradigm and the Big Five Inventory to assess personality characteristics. Participants with more robust P50 sensory gating reported a significantly greater degree of conscientiousness; conscientiousness (but not the other Big Five factors) predicted sensory gating ability. Longer ERP latencies were associated with participants being more conscientious (P50 component), more agreeable, and less neurotic (N100 component). A better understanding of the behavioral correlates of sensory gating will help elucidate the functional consequences of reduced sensory gating both in typical adults and clinical groups.

Combining CDP-choline and galantamine: Effects of a selective α7 nicotinic acetylcholine receptor agonist strategy on P50 sensory gating of speech sounds in healthy volunteers

BACKGROUND

Schizophrenia (SCZ) patients and relatives have deficits in early cortical sensory gating (SG) typically measured by suppression of electroencephalography-derived P50 event-related potentials (ERPs) in a conditioning-testing (S₁-S₂) paradigm. Associated with alpha 7 nicotinic acetylcholine receptor (α7 nAChR) dysfunction and shown to be improved with nicotine and α7 nAChR agonists, SG has recently been shown to be improved in low P50 suppressing SCZ patients following acute CDP-choline treatment.

AIMS

This pilot study in healthy humans assessed the SG effects of an α7 nAChR strategy combining CDP-choline with galantamine, a positive allosteric modulator (PAM) of nAChRs, aimed at increasing and prolonging nicotinic receptor activity.

METHODS

The combined effect of CDP-choline (500 mg) and galantamine (16 mg) on speech P50 gating indices rP50 (S₂/S₁) and dP50 (S₁-S₂) was examined in 30 healthy participants stratified into low and high baseline P50 suppressors in a randomized, double-blind, placebo-controlled and counterbalanced design.

RESULTS

In low suppressors, CDP-choline/galantamine (vs. placebo) improved rP50 and dP50 gating, and reduced S₂P50 amplitudes. No P50 gating effects were observed in high suppressors; however, CDP-choline/galantamine (vs. placebo) increased their S₂P50 amplitudes.

CONCLUSION

Findings from this pilot study with CDP-choline/galantamine in a healthy, SCZ-like surrogate deficient gating sample are consistent with the association of α7 nAChR mechanisms in SG impairment in SCZ and support further research trials with CDP-choline and galantamine targeting sensory processes.

Combining CDP-choline and galantamine, an optimized α7 nicotinic strategy, to ameliorate sensory gating to speech stimuli in schizophrenia

Neural α7 nicotinic acetylcholine receptor (nAChR) expression and functioning deficits have been extensively associated with cognitive and early sensory gating (SG) impairments in schizophrenia (SCZ) patients and their relatives. SG, the suppression of irrelevant and redundant stimuli, is measured in a conditioning-testing (S₁-S₂) paradigm eliciting electroencephalography-derived P50 event-related potentials (ERPs), the S₂ amplitudes of which are typically suppressed relative to S₁. Despite extensive reports of nicotine-related improvements and several decades of research, an efficient nicotinic treatment has yet to be approved for SCZ. Following reports of SG improvements in low P50 suppressing SCZ patients and healthy participants with the α7 agonist, CDP-choline, this pilot study examined the combined modulatory effect of CDP-choline (500 mg) and galantamine (16 mg), a nAChR positive allosteric modulator and acetylcholinesterase inhibitor, on SG to speech stimuli in twenty-four SCZ patients in a randomized, double-blind and placebo-controlled design. As expected, in low P50 suppressors CDP-choline/galantamine (vs. Placebo) improved rP50 and dP50 scores by increasing inhibitory mechanisms as reflected by S₂P50 amplitude reductions. Results also suggest a moderating role for auditory verbal hallucinations in treatment response. These preliminary findings provide supportive evidence for the involvement of α7 nAChR activity in speech gating in SCZ and support additional trials, examining different dose combinations and repeated doses of this optimized and personalized targeted α7 cholinergic treatment for SG dysfunction in subgroups of SCZ patients.

Neonatal corticosterone mitigates autoimmune neuropsychiatric disorders associated with streptococcus in mice

Increased glucocorticoid concentrations have been shown to favor resilience towards autoimmune phenomena. Here, we addressed whether experimentally induced elevations in circulating glucocorticoids mitigate the abnormalities exhibited by an experimental model of Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcus (PANDAS). This is a pathogenic hypothesis linking repeated exposures to Group-A-beta-hemolytic streptococcus (GAS), autoantibodies targeting selected brain nuclei and neurobehavioral abnormalities. To persistently elevate glucocorticoid concentrations, we supplemented lactating SJL/J mice with corticosterone (CORT; 80 mg/L) in the drinking water. Starting in adolescence (postnatal day 28), developing offspring were exposed to four injections - at bi-weekly intervals - of a GAS homogenate and tested for behavioral, immunological, neurochemical and molecular alterations. GAS mice showed increased perseverative behavior, impaired sensorimotor gating, reduced reactivity to a serotonergic agonist and inflammatory infiltrates in the anterior diencephalon. Neonatal CORT persistently increased circulating glucocorticoids concentrations and counteracted these alterations. Additionally, neonatal CORT increased peripheral and CNS concentrations of the anti-inflammatory cytokine IL-9. Further, upstream regulator analysis of differentially expressed genes in the striatum showed that the regulatory effect of estradiol is inhibited in GAS-treated mice and activated in GAS-treated mice exposed to CORT. These data support the hypothesis that elevations in glucocorticoids may promote central immunomodulatory processes.

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.

Lower limb flexor reflex: Comparisons between drug-induced akathisia and restless legs syndrome

BACKGROUND AND OBJECTIVE

Akathisia is characterized by restlessness and crawling sensations similar to restless legs syndrome (RLS). Long latency flexor reflex (LLFR) which has helped to advance RLS pathophysiology has never been investigated in akathisia. Due to the clinical commonalities of akathisia and RLS, we investigated the behavior of LLFR in patients with akathisia aiming to understand pathophysiology of akathisia.

PATIENTS AND METHODS

Seven patients with neuroleptic-induced akathisia, 12 drug-naïve patients with primary RLS and 17 healthy subjects were prospectively enrolled in the study. LLFR was recorded from unilateral tibialis anterior (TA) and long head of biceps femoris (BF) muscles after stimulating the sole by trains of electrical stimuli. We measured amplitude, latency, duration, presence of response and compared between three groups.

RESULTS

One-way ANOVA showed mean durations of early and late responses recorded over TA were the longest in akathisia group compared to both RLS group and healthy subjects (p=0.012). The spatial spread of LLFR in akathisia patients was comparable to those of healthy subjects whereas presence of response on BF was significantly less in akathisia than RLS group.

CONCLUSIONS

Our findings indicate increased excitability of LLFR pathway in akathisia group. These findings are probably due to lack of inhibition originated in regions other than those known to downregulate in RLS.

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.

Individual difference in prepulse inhibition does not predict spatial learning and memory performance in C57BL/6 mice

The startle reflex to an intense acoustic pulse stimulus is attenuated if the pulse stimulus is shortly preceded by a weak non-startling prepulse stimulus. This attenuation of the startle reflex represents a form of pre-attentional sensory gating known as prepulse inhibition (PPI). Although PPI does not require learning, its expression is regulated by higher cognitive processes. PPI deficits have been detected in several psychiatric conditions including schizophrenia where they co-exist with cognitive deficits. A potential link between PPI expression and cognitive performance has therefore been suggested such that poor PPI may predict, or may be mechanistically linked to, overt cognitive impairments. A positive relationship between PPI and strategy formation, planning efficiency, and execution speed has been observed in healthy humans. However, parallel studies in healthy animals are rare. It thus remains unclear what cognitive domains may be associated with, or orthogonal to, sensory gating in the form of PPI in healthy animals. The present study evaluated a potential link between the magnitude of PPI and spatial memory performance by comparing two subgroups of animals differing substantially in baseline PPI expression (low-PPI vs high-PPI) within a homogenous cohort of 100 male adult C57BL/6 mice. Assessment of spatial reference memory in the Morris water maze and spatial recognition memory in the Y-maze failed to reveal any difference between low-PPI and high-PPI subjects. These negative findings contrast with our previous reports that individual difference in PPI correlated with sustained attention and working memory performance in C57BL/6 mice.

Dose-Dependent Changes in Auditory Sensory Gating in the Prefrontal Cortex of the Cynomolgus Monkey

BACKGROUND Sensory gating, often described as the ability to filter out irrelevant information that is repeated in close temporal proximity, is essential for the selection, processing, and storage of more salient information. This study aimed to test the effect of sensory gating under anesthesia in the prefrontal cortex (PFC) of monkeys following injection of bromocriptine, haloperidol, and phencyclidine (PCP). MATERIAL AND METHODS We used an auditory evoked potential that can be elicited by sound to examine sensory gating during treatment with haloperidol, bromocriptine, and PCP in the PFC in the cynomolgus monkey. Scalp electrodes were located in the bilateral PFC and bilateral temporal, bilateral parietal, and occipital lobes. Administration of bromocriptine (0.313 mg/kg, 0.625 mg/kg, and 1.25 mg/kg), haloperidol (0.001 mg/kg, 0.01 mg/kg, and 0.05 mg/kg), and the N-methyl-D-aspartic acid receptor antagonist PCP (0.3 mg/kg) influenced sensory gating. RESULTS We demonstrated the following: (1) Administration of mid-dose bromocriptine disrupted sensory gating (N100) in the right temporal lobe, while neither low-dose nor high-dose bromocriptine impaired gating. (2) Low-dose haloperidol impaired gating in the right prefrontal cortex. Mid-dose haloperidol disrupted sensory gating in left occipital lobe. High-dose haloperidol had no obvious effect on sensory gating. (3) Gating was impaired by PCP in the left parietal lobe. CONCLUSIONS Our studies showed that information processing was regulated by the dopaminergic system, which might play an important role in the PFC. The dopaminergic system influenced sensory gating in a dose- and region-dependent pattern, which might modulate the different stages that receive further processing due to novel information.

Comparing Pharmacological Modulation of Sensory Gating in Healthy Humans and Rats: The Effects of Reboxetine and Haloperidol

Sensory gating is the brain's ability to filter out irrelevant information before it reaches high levels of conscious processing. In the current study we aimed to investigate the involvement of the noradrenergic and dopaminergic neurotransmitter systems in sensory gating. Furthermore, we investigated cross-species reliability by comparing effects in both healthy humans and rats, while keeping all experimental conditions as similar as possible between the species. The design of the human experiment (n=21) was a double-blind, placebo-controlled, cross-over study where sensory gating was assessed following a dose of either reboxetine (8 mg), haloperidol (2 mg), their combination or placebo at four separate visits. Similarly in the animal experiment sensory gating was assessed in rats, (n=22) following a dose of reboxetine (2 mg/kg), haloperidol (0.08 mg/kg), their combination or placebo. The sensory gating paradigms in both experiments were identical. In humans, we found significantly reduced P50 suppression following separate administration of reboxetine or haloperidol, while their combined administration did not reach statistical significance compared with placebo. In the rats, we found a similar significant reduction of sensory gating (N40) following treatment with haloperidol and the combination of haloperidol and reboxetine, but not with separate reboxetine treatment, compared with placebo. Our study indicates that even when experimental conditions are kept as similar as possible, direct human to rat cross-species translation of pharmacological effects on sensory gating is challenging, which calls for more focussed research in this important translational area.

Cortical electroconvulsive stimulation alleviates breeding-induced prepulse inhibition deficit in rats

In patients with medical-refractory schizophrenia electroconvulsive therapy (ECT), i.e., the induction of therapeutic seizures via cortical surface electrodes, is effectively used. Electroconvulsive stimulation (ECS) in rodents simulates ECT in humans and is applied to investigate the mechanisms underlying this treatment. Experimentally-induced reduced prepulse inhibition (PPI) of the acoustic startle response (ASR), i.e., the reduction of the startle response to an intense acoustic stimulus when this stimulus is shortly preceded by a weaker not-startling stimulus, serves as an endophenotype for neuropsychiatric disorders that are accompanied by disturbed sensorimotor gating, such as schizophrenia. Here we used rats selectively bred for high and low PPI to evaluate whether bifrontal cortical ECS would affect PPI. For this purpose, cortical screw electrodes were stereotactically implanted above the frontal cortex. After recovery ECS was applied for five consecutive days with stimuli of 1 ms pulse-width, 100 pulses/s, 1 s duration, ranging from 5.5 mA to 10 mA. PPI of ASR was measured one day before ECS, and on days 1, 7, and 14 after the last ECS. In rats with breeding-induced low PPI ECS increased PPI one week after stimulation. In contrast, ECS decreased PPI in rats with high PPI on the first day after stimulation. The reaction to the startle impulse was reduced by ECS without difference between groups. This work provides evidence that rats with breeding-induced high or low PPI could be used to further investigate the underlying mechanisms of ECT in neuropsychiatric disorders with disturbed sensorimotor gating like schizophrenia.

Mice repeatedly exposed to Group-A β-Haemolytic Streptococcus show perseverative behaviors, impaired sensorimotor gating, and immune activation in rostral diencephalon

Repeated exposure to Group-A β-Haemolytic Streptococcus (GAS) may constitute a vulnerability factor in the onset and course of pediatric motor disturbances. GAS infections/colonization can stimulate the production of antibodies, which may cross the blood brain barrier, target selected brain areas (e.g. basal ganglia), and exacerbate motor alterations. Here, we exposed developing SJL male mice to four injections with a GAS homogenate and evaluated the following domains: motor coordination; general locomotion; repetitive behaviors; perseverative responses; and sensorimotor gating (pre-pulse inhibition, PPI). To demonstrate that behavioral changes were associated with immune-mediated brain alterations, we analyzed, in selected brain areas, the presence of infiltrates and microglial activation (immunohistochemistry), monoamines (HPLC), and brain metabolites (in vivo Magnetic Resonance Spectroscopy). GAS-exposed mice showed increased repetitive and perseverative behaviors, impaired PPI, and reduced concentrations of serotonin in prefrontal cortex, a brain area linked to the behavioral domains investigated, wherein they also showed remarkable elevations in lactate. Active inflammatory processes were substantiated by the observation of infiltrates and microglial activation in the white matter of the anterior diencephalon. These data support the hypothesis that repeated GAS exposure may elicit inflammatory responses in brain areas involved in motor control and perseverative behavior, and result in phenotypic abnormalities.

The separate and combined effects of monoamine oxidase inhibition and nicotine on P50 sensory gating

INTRODUCTION

The cognitive effects of nicotine in humans remain a topic of great interest, due to the continued prevalence of cigarette smoking in society as well as the hypothesis that cognitively impaired populations such as schizophrenia patients use nicotine as a means of self-medicating against deficits of sensory gating. However, chronic smoking can predispose individuals to robust monoamine oxidase (MAO) inhibition, and thus far, the effect of MAO inhibition on human sensory gating is unknown.

METHODS

In this study, we investigated the effects of both nicotine (6-mg gum) and pharmacologically induced MAO-A inhibition via moclobemide (75 mg) on P50 event-related potential-indexed sensory gating in a sample of 24 healthy non-smoking males.

RESULTS

Ratio score (rP50) measured gating revealed significant improvement in auditory stimulus suppression after combined nicotine and MAO-A inhibition compared to placebo and to the nicotine-alone condition. This nicotine + MAO-A inhibition-induced efficient gating was consistent regardless of participants' baseline (placebo) gating efficiency, despite the observation that nicotine in the absence of MAO-A inhibition exhibited a detrimental effect on gating in participants with high baseline suppression ratios.

CONCLUSION

Nicotine and monoamine oxidase-inhibiting agents in tobacco smoke appear to exert a synergistic effect on sensory gating, which may contribute to the elevated dependence rates seen in populations with cognitive deficits such as schizophrenia.

Dopaminergic activity and behaviour in SOCS2 transgenic mice: Revealing a potential drug target for schizophrenia

Alterations in immune function have been implicated in the aetiopathogenesis of schizophrenia. Specifically, the induction of inflammatory cytokines, which are important immunological factors in infection or inflammation, may be critical factors altering the normal course of brain development and increasing schizophrenia risk. Suppressor of cytokine signalling 2 (SOCS2) can negatively regulate the signalling of cytokines. The present study aimed to determine the behavioural phenotype of transgenic mice over-expressing SOCS2 (SOCS2 Tg) in paradigms of relevance to schizophrenia. Both male and female SOCS2 Tg mice displayed reduced locomotor hyperactivity after the administration of the dopamine releaser, amphetamine, compared to wildtype controls (WT). However, only male SOCS2 Tg mice showed enhanced prepulse inhibition compared to WT. Dopamine D2 receptors mRNA expression was reduced and dopamine transporter mRNA expression was increased in the nucleus accumbens of female, but not male, SOCS2 Tg mice, compared to WT. The role of hyperdopaminergia has long been implicated in the aetiology of schizophrenia. This study shows that over-expression of SOCS2 reduces the psychostimulant effects of amphetamine, enhances PPI, and alters mesolimbic dopaminergic activity. SOCS2 may provide a novel target in the development of treatments for schizophrenia.

Neurological soft signs and prepulse inhibition of the startle reflex in psychosis: A pilot study

OBJECTIVE

Prepulse inhibition (PPI) of the startle reflex deficit and neurological soft signs (NSS) are two markers of vulnerability to psychosis. This study investigated the possibility of a PPI-NSS relation due to a putative common biological substrate, hypothesizing that patients with higher NSS scores also show higher PPI deficits. Moreover, we examined the possibility of an association of PPI deficits and NSS with negative symptoms.

METHODS

Fifteen subjects with psychosis and fifteen healthy controls underwent PPI and NSS evaluations.

RESULTS

Patients did not exhibit higher PPI deficits but only higher NSS rates (p < 0.01), as compared with healthy controls. Higher NSS rates were not associated with PPI deficits, and NSS sensory integration signs correlated positively with negative symptoms (p < 0.01).

CONCLUSION

Our study supported the hypothesis that NSS are trait markers whereas PPI deficits state markers and that their putative common biological substrate is not sufficient to determinate an association between them. The study hypothesis, however, needs further investigation.

CDP-choline: effects of the procholine supplement on sensory gating and executive function in healthy volunteers stratified for low, medium and high P50 suppression

Diminished auditory sensory gating and associated neurocognitive deficits in schizophrenia have been linked to altered expression and function of the alpha-7 nicotinic acetycholinergic receptor (α7 nAChR), the targeting of which may have treatment potential. Choline is a selective α7 nAChR agonist and the aim of this study was to determine whether cytidine 5'-diphosphocholine (CDP-choline), or citicoline, a dietary source of choline, increases sensory gating and cognition in healthy volunteers stratified for gating level. In a randomized, placebo-controlled, double-blind design involving acute administration of low, moderate doses (500 mg, 1000 mg) of CDP-choline, 24 healthy volunteers were assessed for auditory gating as indexed by suppression of the P50 event-related potential (ERP) in a paired-stimulus (S1, S2) paradigm, and for executive function as measured by the Groton Maze Learning Task (GMLT) of the CogState Schizophrenia Battery. CDP-choline improved gating (1000 mg) and suppression of the S2 P50 response (500 mg, 1000 mg), with the effects being selective for individuals with low gating (suppression) levels. Tentative support was also shown for increased GMLT performance (500 mg) in low suppressors. These preliminary findings with CDP-choline in a healthy, schizophrenia-like surrogate sample are consistent with a α7 nAChR mechanism and support further trials with choline as a pro-cognitive strategy.

Effects of dopamine D2/D3 blockade on human sensory and sensorimotor gating in initially antipsychotic-naive, first-episode schizophrenia patients

It has been suggested that psychophysiological measures of sensory and sensorimotor gating, P50 gating and prepulse inhibition of the startle reflex (PPI), underlie core features of schizophrenia and are linked to dopaminergic pathways in the striatum and prefrontal cortex. In the present study, the effects of a potent D2/D3 receptor antagonist, amisulpride, were investigated on PPI and P50 gating in a large sample of antipsychotic-naive, first-episode patients with schizophrenia. A total of 52 initially antipsychotic-naive, first-episode schizophrenia patients were assessed for their P50 gating, PPI, and habituation/sensitization abilities at baseline and after 2 and 6 weeks of treatment with flexible doses of amisulpride. In addition, 47 matched healthy controls were assessed at baseline and after 6 weeks. At baseline, the patients showed significantly reduced PPI, yet normal levels of P50 gating, habituation, and sensitization. Treatment with amisulpride showed no effects on these measures, either at 2 or 6 weeks of follow-up. This is the first study investigating the effects of monotherapy with a relatively selective dopamine D2/D3 receptor antagonist (amisulpride) on sensory and sensorimotor gating deficits in a longitudinal study of a large group of initially antipsychotic-naive, first-episode patients with schizophrenia. Our finding that amisulpride effectively reduced symptom severity in our patients without reducing their PPI deficits indicates that increased activity of dopamine D2 receptors may be involved in symptomatology of patients with schizophrenia, but not in their sensorimotor gating deficits.

How do high- and low-frequency repetitive transcranial magnetic stimulations modulate the temporal cortex

Few studies have examined the impact of repetitive transcranial magnetic stimulation (rTMS) on the cortical excitability of nonmotor cortices; current treatments often target the temporal or prefrontal cortex. We used auditory evoked potentials recorded in 24 healthy subjects to evaluate the neuromodulatory effects of low- and high-frequency rTMS in the temporal lobe. Both auditory evoked potential P50 amplitude, a marker of cortical excitability, and P50 ratio, a marker of sensory gating known to be impaired in patients with auditory verbal hallucinations, were compared before and after rTMS. We observed a similar effect after both stimulation frequencies, with a decrease in P50 amplitude and no significant effect on P50 ratio. Low- and high-frequency rTMS applied to the temporal lobe seemed to exert the same cortical neuromodulation effect, while auditory sensory gating may not be modulated by temporal rTMS.

Influence of aripiprazole, risperidone, and amisulpride on sensory and sensorimotor gating in healthy 'low and high gating' humans and relation to psychometry

Despite advances in the treatment of schizophrenia spectrum disorders with atypical antipsychotics (AAPs), there is still need for compounds with improved efficacy/side-effect ratios. Evidence from challenge studies suggests that the assessment of gating functions in humans and rodents with naturally low-gating levels might be a useful model to screen for novel compounds with antipsychotic properties. To further evaluate and extend this translational approach, three AAPs were examined. Compounds without antipsychotic properties served as negative control treatments. In a placebo-controlled, within-subject design, healthy males received either single doses of aripiprazole and risperidone (n=28), amisulpride and lorazepam (n=30), or modafinil and valproate (n=30), and placebo. Prepulse inhibiton (PPI) and P50 suppression were assessed. Clinically associated symptoms were evaluated using the SCL-90-R. Aripiprazole, risperidone, and amisulpride increased P50 suppression in low P50 gaters. Lorazepam, modafinil, and valproate did not influence P50 suppression in low gaters. Furthermore, low P50 gaters scored significantly higher on the SCL-90-R than high P50 gaters. Aripiprazole increased PPI in low PPI gaters, whereas modafinil and lorazepam attenuated PPI in both groups. Risperidone, amisulpride, and valproate did not influence PPI. P50 suppression in low gaters appears to be an antipsychotic-sensitive neurophysiologic marker. This conclusion is supported by the association of low P50 suppression and higher clinically associated scores. Furthermore, PPI might be sensitive for atypical mechanisms of antipsychotic medication. The translational model investigating differential effects of AAPs on gating in healthy subjects with naturally low gating can be beneficial for phase II/III development plans by providing additional information for critical decision making.

Clonidine normalizes levels of P50 gating in patients with schizophrenia on stable medication

BACKGROUND

Sensory gating deficits are among the core features of schizophrenia. Recently, we reported significantly increased sensorimotor gating following additional administration of single dosages of clonidine to the treatment of stably medicated patients with schizophrenia who, in spite of their medication, showed gating deficits. In the current study, we investigated whether this result is generalizable to filtering of sensory information as a whole, by examining clonidine's effect on P50 suppression in the same group of patients.

METHODS

In a double-blind, placebo-controlled, randomized yet balanced cross-over design, 20 male schizophrenia patients on stable medication were assessed in a psychophysiological test battery, including a sensory gating paradigm on 5 occasions: once after oral administration of placebo and after single doses of 25, 50, 75, and 150 µg of clonidine. Their results were compared with 20 age-matched healthy male volunteers, who received no treatment.

RESULTS

Patients showed significantly reduced levels of P50 suppression in the placebo session compared with controls. All dosages of clonidine significantly diminished these deficits to such levels that they no longer differed significantly from the healthy controls (except the highest dose).

CONCLUSIONS

This is the first study to show that even a single low dose of clonidine administered to stably medicated patients with schizophrenia not only significantly increases their levels of P50 suppression but also normalizes them. The results indicate that α2-noradrenergic agonists are capable of normalizing levels of P50 gating, which has a potentially high clinical relevance for the medical treatment of schizophrenia.

Modulation of auditory deviance detection by acute nicotine is baseline and deviant dependent in healthy nonsmokers: a mismatch negativity study

OBJECTIVE

Cognitive enhancement resulting from nicotinic acetylcholine receptor stimulation may be evidenced by increased efficiency of the auditory-frontal cortex network of auditory discrimination, which is impaired in schizophrenia, a cognitive disorder associated with excessive tobacco use. Investigating automatic (preattentive) detection of acoustic change with the mismatch negativity (MMN) brain event-related potential in response to nicotine in individuals with varying baseline levels of auditory discrimination may provide useful insight into the cholinergic regulation of this neural network and its potential amelioration with novel nicotinic agents.

METHODS

Sixty healthy, non-smoking male volunteers were presented with an 'optimal' multi-feature MMN paradigm in a randomized, placebo controlled double-blind design with 6 mg of nicotine gum.

RESULTS

Participants with low, medium, and high baseline amplitudes responded differently to nicotine (vs. placebo), and nicotine response was feature specific. Whereas MMN in individuals with high amplitudes was diminished by nicotine, MMN increased in those with low amplitudes. Nicotine effects were not shown in medium amplitude participants.

CONCLUSIONS

These findings provide preliminary support for the role of nicotinic neurotransmission in sensory memory processing of auditory change and suggest that nicotinic receptor modulation can both enhance and diminish change detection, depending on baseline MMN and its eliciting stimulus feature.

Varenicline disrupts prepulse inhibition only in high-inhibitory rats

Varenicline, a widely used smoking cessation drug, has partial agonistic activity at α4β2 nicotinic receptors, and full agonistic activity at α7 nicotinic receptors. Thus it may interact with cognitive processes and may alleviate some of the cognitive disturbances observed in psychotic illnesses such as schizophrenia. We aimed to test the effects of varenicline on sensorimotor gating functioning, which is crucial for normal cognitive processes, especially for the integration of sensory and cognitive information processing and the execution of appropriate motor responses. Prepulse inhibition (PPI) of the acoustic startle reflex was used to test the sensorimotor gating functioning. First, the effects of varenicline and nicotine on rats having high or low baseline PPI levels were evaluated; then, varenicline was applied prior to apomorphine (0.5 mg/kg), and MK-801 (0.15 mg/kg), which are used as comparative models of PPI disruption. Varenicline (0.5-3 mg/kg) did not change PPI when given alone in naïve animals. When rats were selected according to their baseline PPI values, varenicline (1 mg/kg) significantly decreased PPI in high-inhibitory (HI) but not in low-inhibitory (LI) rats. Nicotine (1 mg/kg; tartrate salt) produced a similar activity in LI and HI groups. In combination experiments, varenicline did not reverse either apomorphine or the MK-801-induced disruption of PPI. These results demonstrate that the effects of both varenicline and nicotine on sensorimotor gating are influenced by the baseline PPI levels. Moreover, varenicline has no effect on apomorphine or the MK-801-induced disruption of PPI.

Transcription factor 4 (TCF4) and schizophrenia: integrating the animal and the human perspective

Schizophrenia is a genetically complex disease considered to have a neurodevelopmental pathogenesis and defined by a broad spectrum of positive and negative symptoms as well as cognitive deficits. Recently, large genome-wide association studies have identified common alleles slightly increasing the risk for schizophrenia. Among the few schizophrenia-risk genes that have been consistently replicated is the basic Helix-Loop-Helix (bHLH) transcription factor 4 (TCF4). Haploinsufficiency of the TCF4 (formatting follows IUPAC nomenclature: TCF4 protein/protein function, Tcf4 rodent gene cDNA mRNA, TCF4 human gene cDNA mRNA) gene causes the Pitt-Hopkins syndrome-a neurodevelopmental disease characterized by severe mental retardation. Accordingly, Tcf4 null-mutant mice display developmental brain defects. TCF4-associated risk alleles are located in putative coding and non-coding regions of the gene. Hence, subtle changes at the level of gene expression might be relevant for the etiopathology of schizophrenia. Behavioural phenotypes obtained with a mouse model of slightly increased gene dosage and electrophysiological investigations with human risk-allele carriers revealed an overlapping spectrum of schizophrenia-relevant endophenotypes. Most prominently, early information processing and higher cognitive functions appear to be associated with TCF4 risk genotypes. Moreover, a recent human study unravelled gene × environment interactions between TCF4 risk alleles and smoking behaviour that were specifically associated with disrupted early information processing. Taken together, TCF4 is considered as an integrator ('hub') of several bHLH networks controlling critical steps of various developmental, and, possibly, plasticity-related transcriptional programs in the CNS and changes of TCF4 expression also appear to affect brain networks important for information processing. Consequently, these findings support the neurodevelopmental hypothesis of schizophrenia and provide a basis for identifying the underlying molecular mechanisms.

Effects of melatonin on prepulse inhibition, habituation and sensitization of the human startle reflex in healthy volunteers

Prepulse inhibition of the startle reflex (PPI) is an operational measure of sensorimotor gating, which is demonstrated to be impaired in patients with schizophrenia. In addition, a disruption of the circadian rhythm together with blunted melatonin secretion is regularly found in patients with schizophrenia and it is theorized that these may contribute to their attentional deficits. The aim of this study was to assess the effects of acute melatonin on healthy human sensorimotor gating. Twenty-one healthy male volunteers were administered melatonin or placebo after which their levels of PPI were assessed. Melatonin significantly reduced startle magnitude and ratings of alertness, but did not influence PPI, nor sensitization and habituation. However, when taking baseline scores in consideration, melatonin significantly increased PPI in low scoring individuals while significantly decreasing it in high scoring individuals in low intensity prepulse trialtypes only. In addition, subjective ratings of alertness correlated with PPI. The results suggest that melatonin has only minor influences on sensorimotor gating, habituation and sensitization of the startle reflex of healthy males. The data do indicate a relationship between alertness and PPI. Further research examining the effects of melatonin on these processes in patients with schizophrenia is warranted.

Meclizine enhancement of sensorimotor gating in healthy male subjects with high startle responses and low prepulse inhibition

Histamine H1 receptor systems have been shown in animal studies to have important roles in the reversal of sensorimotor gating deficits, as measured by prepulse inhibition (PPI). H1-antagonist treatment attenuates the PPI impairments caused by either blockade of NMDA glutamate receptors or facilitation of dopamine transmission. The current experiment brought the investigation of H1 effects on sensorimotor gating to human studies. The effects of the histamine H1 antagonist meclizine on the startle response and PPI were investigated in healthy male subjects with high baseline startle responses and low PPI levels. Meclizine was administered to participants (n=24) using a within-subjects design with each participant receiving 0, 12.5, and 25 mg of meclizine in a counterbalanced order. Startle response, PPI, heart rate response, galvanic skin response, and changes in self-report ratings of alertness levels and affective states (arousal and valence) were assessed. When compared with the control (placebo) condition, the two doses of meclizine analyzed (12.5 and 25 mg) produced significant increases in PPI without affecting the magnitude of the startle response or other physiological variables. Meclizine also caused a significant increase in overall self-reported arousal levels, which was not correlated with the observed increase in PPI. These results are in agreement with previous reports in the animal literature and suggest that H1 antagonists may have beneficial effects in the treatment of subjects with compromised sensorimotor gating and enhanced motor responses to sensory stimuli.

SSR504734 enhances basal expression of prepulse inhibition but exacerbates the disruption of prepulse inhibition by apomorphine

RATIONALE

Inhibition of glycine transporter 1 (GlyT1) elevates extracellular glycine and can thus increase N-methyl-D-aspartate receptor (NMDAR) excitability in the brain. The potent GlyT1 inhibitor, SSR504734, has also been shown to potentiate the behavioral effects of direct and indirect dopamine agonists. Thus, an acute systemic dose of SSR504734 was sufficient to exacerbate the motor-stimulant effect of the dopamine releaser amphetamine in C57BL/6 mice, even though SSR504734 alone exerted no significant effect on motor activity.

OBJECTIVES

Here, we explore if SSR504734 might modulate dopamine-dependent sensory gating in the paradigm of prepulse inhibition (PPI) of the acoustic startle reflex.

METHODS

Experiment 1 characterized the effect of SSR504734 (10 and 30 mg/kg i.p.) on PPI expression when administered alone. Experiments 2 and 3 investigated the impact of SSR504734 when administered in conjunction with the dopamine receptor agonist, apomorphine (1 and 2 mg/kg s.c.), which is known to reliably disrupt PPI.

RESULTS

When administered alone, acute SSR504734 enhanced PPI only at 30 mg/kg--a dose that has been shown to improve cognitive functions including working memory, which has been linked to enhanced NMDAR function resulting from the elevation of extracellular glycine. However, this effect did not allow SSR504734 to antagonize the PPI-disruptive effect of apomorphine. At the lower dose of 10 mg/kg--that was insufficient to enhance PPI when administered alone--SSR504734 even exacerbated the deleterious effect of apomorphine on PPI.

CONCLUSIONS

The therapeutic potential of GlyT1 inhibition against distinct behavioral/cognitive deficiency might require different magnitudes of GlyT1 inhibition.

Baseline dependency of nicotine's sensory gating actions: similarities and differences in low, medium and high P50 suppressors

Reduced suppression of the P50 auditory event-related potential in schizophrenia patients relative to normal controls is indicative of a sensory gating deficit and is one of the most robust findings reported for functional brain abnormalities in this disorder. However, there is considerable gating variability in patients and controls and there is little understanding as to how inter-individual differences moderate gating responses to drugs and nicotinic agonists in particular, which have shown potential to reverse gating deficits. In this study the effects of acutely administered nicotine (gum, 6 mg) on sensory gating in a paired (S₁-S₂) auditory stimulus paradigm were investigated in 57 healthy, non-smoking volunteers stratified as low (n = 19), medium (n = 19) and high (n = 19) P50 suppressors on the basis of three separate baseline derived gating indices, P50 ratios, P50 difference scores, and gating difference waveforms. Relative to placebo, nicotine consistently improved gating in low suppressors as stratified with all three gating indices, exerted no effects in medium suppressors and reduced gating in high suppressors. Analysis of individual stimulus (S₂, S₂) amplitudes showed distinctly different mechanisms of action underlying nicotine effects in individuals with low and high baseline suppression. The results parallel similar findings of baseline-dependency in the gating effects of several antipsychotic drugs in healthy volunteers and support the use of group segmentation as a translational model in novel cognitive drug development for schizophrenia.

Prepulse inhibition in HIV-associated neurocognitive disorders

Sensorimotor inhibition, or the ability to filter out excessive or irrelevant information, theoretically supports a variety of higher-level cognitive functions. Impaired inhibition may be associated with increased impulsive and risky behavior in everyday life. Individuals infected with HIV frequently show impairment on tests of neurocognitive function, but sensorimotor inhibition in this population has not been studied and may be a contributor to the profile of HIV-associated neurocognitive disorders (HAND). Thirty-seven HIV-infected individuals (15 with HAND) and 48 non-infected comparison subjects were assessed for prepulse inhibition (PPI), an eyeblink startle paradigm measuring sensorimotor gating. Although HIV status alone was not associated with PPI deficits, HIV-positive participants meeting criteria for HAND showed impaired PPI compared to cognitively intact HIV-positive subjects. In HIV-positive subjects, PPI was correlated with working memory but was not associated with antiretroviral therapy or illness factors. In conclusion, sensorimotor disinhibition in HIV accompanies deficits in higher-order cognitive functions, although the causal direction of this relationship requires investigation. Subsequent research on the role of sensorimotor gating on decision-making and risk behaviors in HIV may be indicated.

Relationship between nicotine dependence and the endophenotype-related trait of cognitive function but not acoustic startle reponses in Japanese patients with schizophrenia

OBJECTIVES

We investigated whether nicotine dependence affects these endophenotypes in Japanese schizophrenia patients and whether alpha4 and beta2 subunits of neuronal nicotinic acetylcholine receptor genes (alpha4 subunit of the nAChR gene (CHRNA4)/beta2 subunit of the nAChR gene (CHRNB2)) were associated with nicotine dependence in patients (n = 100) and healthy controls (n = 107).

METHODS

First, in patients, we evaluated cognitive function, using the Brief Assessment of Cognition in Schizophrenia, and acoustic startle responses. Second, we evaluated the severity of nicotine dependence, using the Tobacco Dependence Screener, the Fagerström Test for Nicotine Dependence, and the Brinkman index in current smokers in both groups. Third, we evaluated the relationship between acoustic startle responses, cognitive function, and severity of nicotine dependence. Finally, using 12 tagging single-nucleotide polymorphisms in each the CHRNA4/CHRNB2, we used multiple linear regression analysis to examine the association between nicotine dependence measures and each selected single-nucleotide polymorphism.

RESULTS

The presence and severity of nicotine dependence were associated with verbal memory and executive function in schizophrenia patients. However, nicotine dependence was not correlated with any acoustic startle response. In addition, rs755203 and rs1044397 in CHRNA4 were associated with nicotine dependence in healthy controls.

CONCLUSIONS

Nicotine dependence might influence the level of verbal memory and executive function in schizophrenia patients. In addition, rs755203 and rs1044397 in CHRNA4 might play a role in the pathophysiology of nicotine dependence in healthy controls in the Japanese population.

Kami-ondam-tang, a traditional herbal prescription, attenuates the prepulse inhibition deficits and cognitive impairments induced by MK-801 in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Kami-ondam-tang (KODT) has been used to treat neuropsychiatric disorders, including neurosis and insomnia, in traditional herbal medicine. However, the mechanisms of this drug have not been well characterized in the treatment of schizophrenia-like behaviors.

AIM OF THE STUDY

We investigated whether schizophrenia-like behaviors induced by MK-801, a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, could be attenuated by KODT.

MATERIALS AND METHODS

Acute systemic administration of MK-801 was used to establish an animal model of schizophrenia. The effects of KODT on the MK-801-induced prepulse inhibition (PPI) deficits, hyperlocomotion, social withdrawal, and cognitive impairment were assessed. We also examined the changes in the expression levels of Akt and extracellular signal-regulated kinase (ERK) after the administration of KODT with MK-801 in the cortical and hippocampal tissues.

RESULTS

The acoustic startle response test showed that the acoustic startle enhancement and PPI deficits induced by MK-801 were attenuated by KODT. Moreover, KODT ameliorated social and objective recognition impairments that were induced by MK-801 in the social novelty preference test and the novel object recognition test. In addition, the upregulation of phosphorylated Akt or phosphorylated ERK expression induced by MK-801 was blocked by KODT in the cortex. However, MK-801-induced hyperlocomotion was not affected by KODT in the open field test.

CONCLUSION

These findings suggest that KODT attenuates MK-801-induced PPI disruption, social interaction deficits, and cognitive impairments, possibly, by regulating of cortical Akt and ERK signaling.

Effects of COMT genotype on sensory gating and its modulation by nicotine: Differences in low and high P50 suppressors

Elevated smoking rates seen in schizophrenia populations may be an attempt to correct neuropathologies associated with deficient nicotinic acetylcholine receptors and/or dopaminergic systems using exogenous nicotine. However, nicotine's effects on cognitive processing and sensory gating have been shown to be baseline-dependent. Evidence of a restorative effect on sensory gating deficits by nicotine-like agonists has been demonstrated, however, its underlying mechanisms in the context of dopamine dysregulation are unclear. Catechol-O-methyltransferase (COMT), a key dopamine regulator in the brain, contains a co-dominant allele in which a valine-to-methionine substitution causes variations in enzymatic activity leading to reduced synaptic dopamine levels in the Val/Val genotype. Using a randomized, double-blind, placebo-controlled design with 57 non-smokers, this study examined the effects of COMT genotype on sensory gating and its modulation by nicotine in low vs. high suppressors. The results were consistent with the hypothesis that increased dopamine resulting from nicotine stimulation or Met allelic activity would benefit gating in low suppressors and impair gating in high suppressors, and that this gating improvement with nicotine would be more evident in Val carriers who were low suppressors, while the gating impairment would be more evident in Met carriers who were high suppressors. These findings reaffirm the importance of baseline-dependency and suggest a subtle relationship between COMT genotype and baseline-stratified levels of sensory gating, which may help to explain the variability of cognitive abilities in schizophrenia populations.

P50 suppression and its neural generators in antipsychotic-naive first-episode schizophrenia before and after 6 months of quetiapine treatment

BACKGROUND

Numerous studies have demonstrated sensory gating deficits in schizophrenia. However, only a few longitudinal studies report on the effects of antipsychotic treatment on sensory gating deficits and their results are inconsistent. In the present study, P50 suppression and its neural generators were investigated in antipsychotic-naïve first-episode patients with schizophrenia before and after 6 months of treatment with quetiapine.

METHODS

Thirty-four antipsychotic-naïve first-episode schizophrenia patients and age and gender matched healthy controls were tested in an auditory sensory gating paradigm at baseline and after 6 months. During this period, the patients were treated with quetiapine, while controls received no treatment. Sixteen patients completed the study.

RESULTS

Patients showed significant reduced P50 suppression compared with controls at baseline but not at follow-up. Furthermore, a significant positive correlation between baseline P50 suppression and dose of quetiapine at follow-up was found. P50 suppression in patients receiving above median dosages of quetiapine increased significantly from baseline to follow-up. At baseline, a frontocentral source was significantly more active in patients than in controls at the time of the testing stimulus.

CONCLUSIONS

The present findings suggest that P50 suppression deficits are already present at an early stage of schizophrenia. Furthermore, particularly those patients with more severe gating deficits appeared to need higher dosages of quetiapine, although their clinical symptoms did not seem to indicate this. Quetiapine treatment significantly improved these gating deficits. Furthermore, a frontocentral source in the brain appeared to be involved in the deficient P50 gating of the patients.

Sensory and sensorimotor gating in adult attention-deficit/hyperactivity disorder (ADHD)

Even though there is an impaired perceptual capacity in attention-deficit/hyperactivity disorder (ADHD) patients, psychophysiological alterations, such as impaired gating as indexed by prepulse inhibition (PPI) or suppression of P50 auditory event-related potentials, have not been found in patients with ADHD. Hence, potential relationships of psychophysiological measures of gating to psychopathology and cognitive performance remain unclear. The present study investigates two distinct operational measures of gating as well as cognitive performance within adult ADHD patients in order to assess the relationship of these measures to psychopathology. PPI, P50 suppression, cognitive performance, and psychopathologic symptoms were assessed in 26 ADHD patients and 26 healthy control subjects. ADHD patients compared to healthy control subjects exhibited impaired P50 suppression, performed worse in cognitive tasks, and reported more psychopathological symptoms, but were normal in the test of PPI. Thus, P50 gating deficits are not specific to schizophrenia-spectrum disorders. These findings highlight the differences between P50 gating and PPI as measures of the gating construct. In keeping with the lack of correlations between these two putative operational measures of gating seen in both humans and animals, adult ADHD patients exhibit deficient P50 suppression and poor cognitive performance, despite exhibiting normal levels of PPI.

Baseline prepulse inhibition expression predicts the propensity of developing sensitization to the motor stimulant effects of amphetamine in C57BL/6 mice

RATIONALE

The startle reflex to a sudden intense acoustic pulse stimulus is attenuated if the pulse is shortly preceded by a weak prepulse stimulus. This represents a form of sensory gating, known as prepulse inhibition (PPI), observable across species. PPI is modulated by dopamine and readily disrupted by acute amphetamine. Prior repeated exposures to amphetamine also disrupt PPI even when the drug is not present during test, suggesting that a sensitized mesolimbic dopamine system-inducible even by a single exposure to amphetamine-might be responsible. However, this causative link has been challenged by inconsistent efficacy between different amphetamine pre-treatment regimes, which all robustly sensitize the behavioral response to amphetamine.

METHODS

Here, the presence of such a link in reverse was tested by comparing the propensity to develop amphetamine sensitization between high- and low-PPI expressing individuals identified within a homogeneous cohort of C57BL/6 mice. Comparison of dopamine content including its metabolites was performed separately in drug naïve mice by post-mortem HPLC.

RESULTS

Behavioral sensitization was substantially stronger in the low-PPI group compared with the high-PPI group, while the magnitude of their response to the first amphetamine challenge was similar. Dopamine content within the nucleus accumbens and medial prefrontal cortex was significantly higher in low-PPI relative to high-PPI mice.

CONCLUSION

Individuals with weak sensory gating characterized by low basal PPI expression may be more susceptible to the development of dopamine sensitization and therefore at greater risk of developing schizophrenia. Conversely, high baseline expression might predict a resistance to dopaminergic sensitization.

Deletion of striatal adenosine A(2A) receptor spares latent inhibition and prepulse inhibition but impairs active avoidance learning

Following early clinical leads, the adenosine A(2A)R receptor (A(2A)R) has continued to attract attention as a potential novel target for treating schizophrenia, especially against the negative and cognitive symptoms of the disease because of A(2A)R's unique modulatory action over glutamatergic in addition to dopaminergic signaling. Through (i) the antagonistic interaction with the dopamine D(2) receptor, and (ii) the regulation of glutamate release and N-methyl-d-aspartate receptor function, striatal A(2A)R is ideally positioned to fine-tune the dopamine-glutamate balance, the disturbance of which is implicated in the pathophysiology of schizophrenia. However, the precise function of striatal A(2A)Rs in the regulation of schizophrenia-relevant behavior is poorly understood. Here, we tested the impact of conditional striatum-specific A(2A)R knockout (st-A(2A)R-KO) on latent inhibition (LI) and prepulse inhibition (PPI) - behavior that is tightly regulated by striatal dopamine and glutamate. These are two common cross-species translational tests for the assessment of selective attention and sensorimotor gating deficits reported in schizophrenia patients; and enhanced performance in these tests is associated with antipsychotic drug action. We found that neither LI nor PPI was significantly affected in st-A(2A)R-KO mice, although a deficit in active avoidance learning was identified in these animals. The latter phenotype, however, was not replicated in another form of aversive conditioning - namely, conditioned taste aversion. Hence, the present study shows that neither learned inattention (as measured by LI) nor sensory gating (as indexed by PPI) requires the integrity of striatal A(2A)Rs - a finding that may undermine the hypothesized importance of A(2A)R in the genesis and/or treatment of schizophrenia.

Startle reactivity and prepulse inhibition of the acoustic startle response are modulated by catechol-O-methyl-transferase Val(158) Met polymorphism in adults with 22q11 deletion syndrome

22q11 deletion syndrome (22q11DS) is a genetic disorder caused by a microdeletion on chromosome 22, which includes the gene coding for catechol-O-methyl-transferase (COMT). High dopamine (DA) levels due to COMT haplo-insufficiency may be associated with the increased risk of developing schizophrenia in adults with 22q11DS. Reduced prepulse inhibition (PPI) of the acoustic startle response has been associated with schizophrenia and with disrupted DAergic transmission in the prefrontal cortex (PFC). COMT Val(158)Met polymorphism has been shown to influence PPI. We report the first study in adults with 22q11DS to examine PPI of the acoustic startle response and its modulation by COMT Val(158)Met polymorphism. Startle reactivity (SR) and PPI of the acoustic startle response were measured in 23 adults with 22q11DS and 21 healthy controls. 22q11DS subjects were genotyped for the functional COMT Val(158)Met polymorphism. 22q11DS Met hemizygotes showed reduced SR and PPI compared with 22q11DS Val hemizygotes. The effect of COMT Val(158)Met polymorphism on PPI was no longer significant when controlling for baseline SR. Met hemizygosity in 22q11DS is associated with reduced SR and influences PPI indirectly. Decreased PFC functioning following excessive PFC DA levels may be one of the mechanisms by which the Met genotype in 22q11DS disrupts SR.

The effect of acute exogenous melatonin on P50 suppression in healthy male volunteers stratified for low and high gating levels

Sensory gating is frequently found to be disturbed in patients with schizophrenia. In addition, a disruption of the circadian rhythm together with a low nocturnal melatonin output is regularly found in these patients. Since there is some evidence that a brief period of sleep normalizes sensory gating in schizophrenia patients, it is conceivable that their disrupted melatonin level may contribute to the deficits in P50 suppression. In this initial study, the effects of acutely administered melatonin on sensory gating in healthy subjects were investigated. In a double-blind placebo-controlled crossover design, 21 healthy male volunteers were administered melatonin (4 mg) or placebo, after which they were tested in a P50 suppression paradigm. In the group as a whole, melatonin did not affect P50 suppression. However, melatonin increased the P50 ratio in the individuals with high baseline suppression. In contrast to what was expected, melatonin reduced P50 suppression, albeit only in those individuals with high baseline suppression. The current study does not support a beneficial effect of acute exposure to exogenous melatonin on sensory gating. Future research should focus on melatonin's ability to restore basic sleep rhythms and its subsequent effects on sensory gating, in both healthy volunteers and patients with schizophrenia.

Cognitive and prepulse inhibition deficits in psychometrically high schizotypal subjects in the general population: relevance to schizophrenia research

Schizophrenia and schizotypal personality disorder share common clinical profiles, neurobiological and genetic substrates along with Prepulse Inhibition and cognitive deficits; among those, executive, attention, and memory dysfunctions are more consistent. Schizotypy is considered to be a non-specific "psychosis-proneness," and understanding the relationship between schizotypal traits and cognitive function in the general population is a promising approach for endophenotypic research in schizophrenia spectrum disorders. In this review, findings for executive function, attention, memory, and Prepulse Inhibition impairments in psychometrically defined schizotypal subjects have been summarized and compared to schizophrenia patients and their unaffected first-degree relatives. Cognitive flexibility, sustained attention, working memory, and Prepulse Inhibition impairments were consistently reported in high schizotypal subjects in accordance to schizophrenia patients. Genetic studies assessing the effects of various candidate gene polymorphisms in schizotypal traits and cognitive function are promising, further supporting a polygenic mode of inheritance. The implications of the findings, methodological issues, and suggestions for future research are discussed.

Adenosine augmentation ameliorates psychotic and cognitive endophenotypes of schizophrenia

An emerging theory of schizophrenia postulates that hypofunction of adenosine signaling may contribute to its pathophysiology. This study was designed to test the "adenosine hypothesis" of schizophrenia and to evaluate focal adenosine-based strategies for therapy. We found that augmentation of adenosine by pharmacologic inhibition of adenosine kinase (ADK), the key enzyme of adenosine clearance, exerted antipsychotic-like activity in mice. Further, overexpression of ADK in transgenic mice was associated with attentional impairments linked to schizophrenia. We observed that the striatal adenosine A2A receptor links adenosine tone and psychomotor response to amphetamine, an indicator of dopaminergic signaling. Finally, intrastriatal implants of engineered adenosine-releasing cells restored the locomotor response to amphetamine in mice overexpressing ADK, whereas the same grafts placed proximal to the hippocampus of transgenic mice reversed their working memory deficit. This functional double dissociation between striatal and hippocampal adenosine demonstrated in Adk transgenic mice highlights the independent contributions of these two interconnected brain regions in the pathophysiology of schizophrenia and thus provides the rationale for developing local adenosine augmentation therapies for the treatment of schizophrenia.

The effect of pregabalin on sensorimotor gating in 'low' gating humans and mice

Pregabalin, an anticonvulsant and anxiolytic compound that binds to α2-δ auxiliary subunit Types 1 and 2 of voltage-gated calcium channels, has been shown to reduce excitatory neurotransmission partially through modulation of glutamatergic signaling. Prepulse inhibition (PPI) of startle is an operational measure of sensorimotor gating impacted by disruption of the glutamatergic system and is reduced in schizophrenia patients. Dysregulation of the glutamatergic system has also been implicated in the pathophysiology of schizophrenia. Here we tested the hypothesis that pregabalin may ameliorate PPI in a model of deficient gating in humans and mice. In study 1, 14 healthy human subjects participated in a within subjects, cross-over study with placebo, 50 mg or 200 mg pregabalin treatment prior to undergoing a PPI task. In study 2, 24 C57BL/6 mice underwent a similar procedure with vehicle, 30 and 100 mg/kg dose treatments. In both studies, subjects were assigned to a "Low" or "High" gating group using a median split procedure based on their PPI performance during placebo/vehicle. Drug effects were then examined across these groups. In humans, pregabalin treatment significantly increased PPI performance in the "low gating" group. In mice, pregabalin treatment significantly increased PPI in the low gating group but reduced PPI in the high gating group. Across species, pregabalin treatment improves PPI in subjects with low gating. These data support further exploration of pregabalin as a potential treatment for disorders characterized by sensorimotor gating deficits and glutamatergic hypersignaling, such as schizophrenia.