Inhibition of auditory evoked potentials and prepulse inhibition of startle in DBA/2J and DBA/2Hsd inbred mouse substrains

Cortico-cortical connectivity behind acoustic information transfer to mouse orbitofrontal cortex is sensitive to neuromodulation and displays local sensory gating: relevance in disorders with auditory hallucinations?

BACKGROUND

Auditory hallucinations (which occur when the distinction between thoughts and perceptions is blurred) are common in psychotic disorders. The orbitofrontal cortex (OFC) may be implicated, because it receives multiple inputs, including sound and affective value via the amygdala, orchestrating complex emotional responses. We aimed to elucidate the circuit and neuromodulatory mechanisms that underlie the processing of emotionally salient auditory stimuli in the OFC — mechanisms that may be involved in auditory hallucinations.

METHODS

We identified the cortico-cortical connectivity conveying auditory information to the mouse OFC; its sensitivity to neuromodulators involved in psychosis and postpartum depression, such as dopamine and neurosteroids; and its sensitivity to sensory gating (defective in dysexecutive syndromes).

RESULTS

Retrograde tracers in OFC revealed input cells in all auditory cortices. Acoustic responses were abolished by pharmacological and chemogenetic inactivation of the above-identified pathway. Acoustic responses in the OFC were reduced by local dopaminergic agonists and neurosteroids. Noticeably, apomorphine action lasted longer in the OFC than in auditory areas, and its effect was modality-specific (augmentation for visual responses), whereas neurosteroid action was sex-specific. Finally, acoustic responses in the OFC reverberated to the auditory association cortex via feedback connections and displayed sensory gating, a phenomenon of local origin, given that it was not detectable in input auditory cortices.

LIMITATIONS

Although our findings were for mice, connectivity and sensitivity to neuromodulation are conserved across mammals.

CONCLUSION

The corticocortical loop from the auditory association cortex to the OFC is dramatically sensitive to dopamine and neurosteroids. This suggests a clinically testable circuit behind auditory hallucinations. The function of OFC input–output circuits can be studied in mice with targeted and clinically relevant mutations related to their response to emotionally salient sounds.

Macrophage-derived GPNMB accelerates skin healing

Healing is a vital response important for the re-establishment of the skin integrity following injury. Delayed or aberrant dermal wound healing leads to morbidity in patients. The development of therapies to improve dermal healing would be useful. Currently, the design of efficient treatments is stalled by the lack of detailed knowledge about the cellular and molecular mechanisms involved in wound healing. Recently, using state-of-the-art technologies, it was revealed that macrophages signal via GPNMB to mesenchymal stem cells, accelerating skin healing. Strikingly, transplantation of macrophages expressing GPNMB improves skin healing in GPNMB-mutant mice. Additionally, topical treatment with recombinant GPNMB restored mesenchymal stem cells recruitment and accelerated wound closure in the diabetic skin. From a drug development perspective, this GPNMB is a new candidate for skin healing.

Protocadherin 10 alters γ oscillations, amino acid levels, and their coupling; baclofen partially restores these oscillatory deficits

Approximately one in 45 children have been diagnosed with Autism Spectrum Disorder (ASD), which is characterized by social/communication impairments. Recent studies have linked a subset of familial ASD to mutations in the Protocadherin 10 (Pcdh10) gene. Additionally, Pcdh10's expression pattern, as well as its known role within protein networks, implicates the gene in ASD. Subsequently, the neurobiology of mice heterozygous for Pcdh10 (Pcdh10^+/-) has been investigated as a proxy for ASD. Male Pcdh10^+/- mice have demonstrated sex-specific deficits in social behavior, recapitulating the gender bias observed in ASD. Furthermore, in vitro slice preparations of these Pcdh10^+/- mice demonstrate selective decreases to high frequency electrophysiological responses, mimicking clinical observations. The direct in vivo ramifications of such decreased in vitro high frequency responses are unclear. As such, Pcdh10^+/- mice and their wild-type (WT) littermates underwent in vivo electrocorticography (ECoG), as well as ex vivo amino acid concentration quantification using High Performance Liquid Chromatography (HPLC). Similar to the previously observed reductions to in vitro high frequency electrophysiological responses in Pcdh10^+/- mice, male Pcdh10^+/- mice exhibited reduced gamma-band (30-80Hz), but not lower frequency (10 and 20Hz), auditory steady state responses (ASSR). In addition, male Pcdh10^+/- mice exhibited decreased signal-to-noise-ratio (SNR) for high gamma-band (60-100Hz) activity. These gamma-band perturbations for both ASSR and SNR were not observed in females. Administration of a GABA_B agonist remediated these electrophysiological alterations among male Pcdh10^+/-mice. Pcdh10^+/- mice demonstrated increased concentrations of GABA and glutamine. Of note, a correlation of auditory gamma-band responses with underlying GABA concentrations was observed in WT mice. This correlation was not present in Pcdh10^+/- mice. This study demonstrates the role of Pcdh10 in the regulation of excitatory-inhibitory balance as a function of GABA in ASD.

Sensory processing in autism spectrum disorders and Fragile X syndrome-From the clinic to animal models

Brains are constantly flooded with sensory information that needs to be filtered at the pre-attentional level and integrated into endogenous activity in order to allow for detection of salient information and an appropriate behavioral response. People with Autism Spectrum Disorder (ASD) or Fragile X Syndrome (FXS) are often over- or under-reactive to stimulation, leading to a wide range of behavioral symptoms. This altered sensitivity may be caused by disrupted sensory processing, signal integration and/or gating, and is often being neglected. Here, we review translational experimental approaches that are used to investigate sensory processing in humans with ASD and FXS, and in relevant rodent models. This includes electroencephalographic measurement of event related potentials, neural oscillations and mismatch negativity, as well as habituation and pre-pulse inhibition of startle. We outline robust evidence of disrupted sensory processing in individuals with ASD and FXS, and in respective animal models, focusing on the auditory sensory domain. Animal models provide an excellent opportunity to examine common mechanisms of sensory pathophysiology in order to develop therapeutics.

Developmental vitamin D deficiency and schizophrenia: the role of animal models

Schizophrenia is a debilitating neuropsychiatric disorder that affects 1% of the US population. Based on twin and genome-wide association studies, it is clear that both genetics and environmental factors increase the risk for developing schizophrenia. Moreover, there is evidence that conditions in utero, either alone or in concert with genetic factors, may alter neurodevelopment and lead to an increased risk for schizophrenia. There has been progress in identifying genetic loci and environmental exposures that increase risk, but there are still considerable gaps in our knowledge. Furthermore, very little is known about the specific neurodevelopmental mechanisms upon which genetics and the environment act to increase disposition to developing schizophrenia in adulthood. Vitamin D deficiency during the perinatal period has been hypothesized to increase risk for schizophrenia in humans. The developmental vitamin D (DVD) deficiency hypothesis of schizophrenia arises from the observation that disease risk is increased in individuals who are born in winter or spring, live further from the equator or live in urban vs. rural settings. These environments result in less exposure to sunlight, thereby reducing the initial steps in the production of vitamin D. Rodent models have been developed to characterize the behavioral and developmental effects of DVD deficiency. This review focuses on these animal models and discusses the current knowledge of the role of DVD deficiency in altering behavior and neurobiology relevant to schizophrenia.

nAChR dysfunction as a common substrate for schizophrenia and comorbid nicotine addiction: Current trends and perspectives

INTRODUCTION

The prevalence of tobacco use in the population with schizophrenia is enormously high. Moreover, nicotine dependence is found to be associated with symptom severity and poor outcome in patients with schizophrenia. The neurobiological mechanisms that explain schizophrenia-nicotine dependence comorbidity are not known. This study systematically reviews the evidence highlighting the contribution of nicotinic acetylcholine receptors (nAChRs) to nicotine abuse in schizophrenia.

METHODS

Electronic data bases (Medline, Google Scholar, and Web of Science) were searched using the selected key words that match the aims set forth for this review. A total of 276 articles were used for the qualitative synthesis of this review.

RESULTS

Substantial evidence from preclinical and clinical studies indicated that dysregulation of α7 and β2-subunit containing nAChRs account for the cognitive and affective symptoms of schizophrenia and nicotine use may represent a strategy to remediate these symptoms. Additionally, recent meta-analyses proposed that early tobacco use may itself increase the risk of developing schizophrenia. Genetic studies demonstrating that nAChR dysfunction that may act as a shared vulnerability factor for comorbid tobacco dependence and schizophrenia were found to support this view. The development of nAChR modulators was considered an effective therapeutic strategy to ameliorate psychiatric symptoms and to promote smoking cessation in schizophrenia patients.

CONCLUSIONS

The relationship between schizophrenia and smoking is complex. While the debate for the self-medication versus addiction vulnerability hypothesis continues, it is widely accepted that a dysfunction in the central nAChRs represent a common substrate for various symptoms of schizophrenia and comorbid nicotine dependence.

Modulation of mGlu2 Receptors, but Not PDE10A Inhibition Normalizes Pharmacologically-Induced Deviance in Auditory Evoked Potentials and Oscillations in Conscious Rats

Improvement of cognitive impairments represents a high medical need in the development of new antipsychotics. Aberrant EEG gamma oscillations and reductions in the P1/N1 complex peak amplitude of the auditory evoked potential (AEP) are neurophysiological biomarkers for schizophrenia that indicate disruption in sensory information processing. Inhibition of phosphodiesterase (i.e. PDE10A) and activation of metabotropic glutamate receptor (mGluR2) signaling are believed to provide antipsychotic efficacy in schizophrenia, but it is unclear whether this occurs with cognition-enhancing potential. The present study used the auditory paired click paradigm in passive awake Sprague Dawley rats to 1) model disruption of AEP waveforms and oscillations as observed in schizophrenia by peripheral administration of amphetamine and the N-methyl-D-aspartate (NMDA) antagonist phencyclidine (PCP); 2) confirm the potential of the antipsychotics risperidone and olanzapine to attenuate these disruptions; 3) evaluate the potential of mGluR2 agonist LY404039 and PDE10 inhibitor PQ-10 to improve AEP deficits in both the amphetamine and PCP models. PCP and amphetamine disrupted auditory information processing to the first click, associated with suppression of the P1/N1 complex peak amplitude, and increased cortical gamma oscillations. Risperidone and olanzapine normalized PCP and amphetamine-induced abnormalities in AEP waveforms and aberrant gamma/alpha oscillations, respectively. LY404039 increased P1/N1 complex peak amplitudes and potently attenuated the disruptive effects of both PCP and amphetamine on AEPs amplitudes and oscillations. However, PQ-10 failed to show such effect in either models. These outcomes indicate that modulation of the mGluR2 results in effective restoration of abnormalities in AEP components in two widely used animal models of psychosis, whereas PDE10A inhibition does not.

Pyramidal cell selective ablation of N-methyl-D-aspartate receptor 1 causes increase in cellular and network excitability

BACKGROUND

Neuronal activity at gamma frequency is impaired in schizophrenia (SZ) and is considered critical for cognitive performance. Such impairments are thought to be due to reduced N-methyl-D-aspartate receptor (NMDAR)-mediated inhibition from parvalbumin interneurons, rather than a direct role of impaired NMDAR signaling on pyramidal neurons. However, recent studies suggest a direct role of pyramidal neurons in regulating gamma oscillations. In particular, a computational model has been proposed in which phasic currents from pyramidal cells could drive synchronized feedback inhibition from interneurons. As such, impairments in pyramidal neuron activity could lead to abnormal gamma oscillations. However, this computational model has not been tested experimentally and the molecular mechanisms underlying pyramidal neuron dysfunction in SZ remain unclear.

METHODS

In the present study, we tested the hypothesis that SZ-related phenotypes could arise from reduced NMDAR signaling in pyramidal neurons using forebrain pyramidal neuron specific NMDA receptor 1 knockout mice.

RESULTS

The mice displayed increased baseline gamma power, as well as sociocognitive impairments. These phenotypes were associated with increased pyramidal cell excitability due to changes in inherent membrane properties. Interestingly, mutant mice showed decreased expression of GIRK2 channels, which has been linked to increased neuronal excitability.

CONCLUSIONS

Our data demonstrate for the first time that NMDAR hypofunction in pyramidal cells is sufficient to cause electrophysiological, molecular, neuropathological, and behavioral changes related to SZ.

Auditory event-related signals in mouse ERG recordings

PURPOSE

In murine disease models, particularly in cases when retinal electrical activity is reduced, an event-related component becomes apparent that does not change with the stimulus intensity in electroretinogram (ERG) recordings. In this work, we show that this electric component is evoked by the sound of the flash discharge rather than the light flash itself.

METHODS

Wild-type mice (C57BL/6), mice with rod function only (Cnga3 (-/-)), mice lacking any photoreceptor function (Cnga3 (-/-) rho (-/-)), and mice with no auditory function (Cdh23 (vAlb/vAlb) ) were examined with Xenon flash ERG systems. An acoustic noise generator was used to mask discharge sounds.

RESULTS

ERG recording modalities were identified where usually no discernible response can be elicited. These include photopic conditions in Cnga3 (-/-) mice, photopic conditions together with very low stimulus intensities in C57BL/6 mice, and both scotopic and photopic conditions in Cnga3 (-/-) rho (-/-) mice. However, in all of these cases, small signals, featuring an initial a-wave like deflection at about 20 ms and a subsequent b-wave like deflection peaking at about 40 ms after the flash, were detected. In contrast, such signals could not be detected in deaf Cdh23 (vAlb/vAlb) mice. Furthermore, masking the Xenon discharge sound by continuous acoustic noise led to a loss of the event-related signals in a reversible manner.

CONCLUSIONS

We could identify an auditory event-related component, presumably resembling auditory evoked potentials, as a major source of ERG signals of non-visual origin in mice. This finding may be of particular importance for the analysis and interpretation of ERG data in mice with reduced visual responses.

Electroencephalographic and early communicative abnormalities in Brattleboro rats

Reductions in the levels of the neuropeptide vasopressin (VP) and its receptors have been associated with schizophrenia. VP is also critical for appropriate social behaviors in humans as well as rodents. One of the prominent symptoms of schizophrenia is asociality and these symptoms may develop prodromally. A reduction in event-related potential (ERP) peak amplitudes is an endophenotype of schizophrenia. In this study, we use the Brattleboro (BRAT) rat to assess the role of VP deficiency in vocal communication during early development and on auditory ERPs during adulthood. BRAT rats had similar vocal communication to wild-type littermate controls during postnatal days 2 and 5 but the time between vocalizations was increased and the power of the vocalizations was reduced beginning at postnatal day 9. During adulthood, BRAT rats had deficits in auditory ERPs including reduced N40 amplitude and reduced low and high gamma intertrial coherence. These results suggest that the role of VP on vocal communication is an age-dependent process. Additionally, the deficits in ERPs indicate an impairment of auditory information processing related to the reduction in VP. Therefore, manipulation of the VP system could provide a novel mechanism for treatment for negative symptoms of schizophrenia.

Electroencephalographic changes following direct current deep brain stimulation of auditory cortex: a new model for investigating neuromodulation

BACKGROUND

Although deep brain (DBS) and transcranial direct current stimulation (tDCS) are used as investigative tools and therapies for a variety of neurological and psychiatric conditions, their mechanisms of action remain poorly understood. Therefore, there is a need for new animal models of neuromodulation.

OBJECTIVE

To introduce and validate a direct current DBS (DC-DBS) model that will use the anatomic precision of intracranial electrodes, as used in DBS, to apply direct current, as used in tDCS, over primary auditory cortex (A1) and induce electroencephalographic (EEG) changes.

METHODS

Twenty-four mice were assigned to 1 of 2 stimulation groups or a sham group and were implanted with electrodes in A1. Stimulation groups underwent DC-DBS stimulation for 20 minutes at 20 μA. Auditory EEG was recorded before stimulation and at 1 hour, 1 week, and 2 weeks poststimulation. EEG was analyzed for changes in N1 (N100 in humans, N40 in mice) amplitude and latency as well as delta and theta power.

RESULTS

DC-DBS led to significant EEG changes (all P values < .05). Among the stimulated animals, there were durable reductions in delta and theta power. There were no differences within the sham group, and neither N40 latencies nor amplitudes changed across time.

CONCLUSION

Our results show DC-DBS-induced reductions in slow-wave activity consistent with recent tDCS studies. We propose that this model will provide a means to explore basic mechanisms of neuromodulation and could facilitate future application of DC-DBS in humans.

Mice with reduced NMDA receptor expression: more consistent with autism than schizophrenia?

Reduced NMDA-receptor (NMDAR) function has been implicated in the pathophysiology of neuropsychiatric disease, most strongly in schizophrenia but also recently in autism spectrum disorders (ASD). To determine the direct contribution of NMDAR dysfunction to disease phenotypes, a mouse model with constitutively reduced expression of the obligatory NR1 subunit has been developed and extensively investigated. Adult NR1(neo-/-) mice show multiple abnormal behaviors, including reduced social interactions, locomotor hyperactivity, self-injury, deficits in prepulse inhibition (PPI) and sensory hypersensitivity, among others. Whereas such phenotypes have largely been interpreted in the context of schizophrenia, these behavioral abnormalities are rather non-specific and are frequently present across models of diseases characterized by negative symptom domains. This study investigated auditory electrophysiological and behavioral paradigms relevant to autism, to determine whether NMDAR hypofunction may be more consistent with adult ASD-like phenotypes. Indeed, transgenic mice showed behavioral deficits relevant to all core ASD symptoms, including decreased social interactions, altered ultrasonic vocalizations and increased repetitive behaviors. NMDAR disruption recapitulated clinical endophenotypes including reduced PPI, auditory-evoked response N1 latency delay and reduced gamma synchrony. Auditory electrophysiological abnormalities more closely resembled those seen in clinical studies of autism than schizophrenia. These results suggest that NMDAR hypofunction may be associated with a continuum of neuropsychiatric diseases, including schizophrenia and autism. Neural synchrony abnormalities suggest an imbalance of glutamatergic and GABAergic coupling and may provide a target, along with behavioral phenotypes, for preclinical screening of novel therapeutics.

Generating embryonic stem cells from the inbred mouse strain DBA/2J, a model of glaucoma and other complex diseases

Mouse embryonic stem (ES) cells are derived from the inner cell mass of blastocyst stage embryos and are used primarily for the creation of genetically engineered strains through gene targeting. While some inbred strains of mice are permissive to the derivation of embryonic stem cell lines and are therefore easily engineered, others are nonpermissive or recalcitrant. Genetic engineering of recalcitrant strain backgrounds requires gene targeting in a permissive background followed by extensive backcrossing of the engineered allele into the desired strain background. The inbred mouse strain DBA/2J is a recalcitrant strain that is used as a model of many human diseases, including glaucoma, deafness and schizophrenia. Here, we describe the generation of germ-line competent ES cell lines derived from DBA/2J mice. We also demonstrate the utility of DBA/2J ES cells with the creation of conditional knockout allele for Endothelin-2 (Edn2) directly on the DBA/2J strain background.

Nicotine receptor subtype-specific effects on auditory evoked oscillations and potentials

Background

Individuals with schizophrenia show increased smoking rates which may be due to a beneficial effect of nicotine on cognition and information processing. Decreased amplitude of the P50 and N100 auditory event-related potentials (ERPs) is observed in patients. Both measures show normalization following administration of nicotine. Recent studies identified an association between deficits in auditory evoked gamma oscillations and impaired information processing in schizophrenia, and there is evidence that nicotine normalizes gamma oscillations. Although the role of nicotine receptor subtypes in augmentation of ERPs has received some attention, less is known about how these receptor subtypes regulate the effect of nicotine on evoked gamma activity.

Methodology/Principal Findings

We examined the effects of nicotine, the α7 nicotine receptor antagonist methyllycaconitine (MLA) the α4β4/α4β2 nicotine receptor antagonist dihydro-beta-erythroidine (DHβE), and the α4β2 agonist AZD3480 on P20 and N40 amplitude as well as baseline and event-related gamma oscillations in mice, using electrodes in hippocampal CA3. Nicotine increased P20 amplitude, while DHβE blocked nicotine-induced enhancements in P20 amplitude. Conversely, MLA did not alter P20 amplitude either when presented alone or with nicotine. Administration of the α4β2 specific agonist AZD3480 did not alter any aspect of P20 response, suggesting that DHβE blocks the effects of nicotine through a non-α4β2 receptor specific mechanism. Nicotine and AZD3480 reduced N40 amplitude, which was blocked by both DHβE and MLA. Finally, nicotine significantly increased event-related gamma, as did AZD3480, while DHβE but not MLA blocked the effect of nicotine on event-related gamma.

Conclusions/Significance

These results support findings showing that nicotine-induced augmentation of P20 amplitude occurs via a DHβE sensitive mechanism, but suggests that this does not occur through activation of α4β2 receptors. Event-related gamma is strongly influenced by activation of α4β2, but not α7, receptor subtypes, while disruption of N40 amplitude requires the activation of multiple receptor subtypes.

GABAB-mediated rescue of altered excitatory-inhibitory balance, gamma synchrony and behavioral deficits following constitutive NMDAR-hypofunction

Reduced N-methyl-D-aspartate-receptor (NMDAR) signaling has been associated with schizophrenia, autism and intellectual disability. NMDAR-hypofunction is thought to contribute to social, cognitive and gamma (30-80 Hz) oscillatory abnormalities, phenotypes common to these disorders. However, circuit-level mechanisms underlying such deficits remain unclear. This study investigated the relationship between gamma synchrony, excitatory-inhibitory (E/I) signaling, and behavioral phenotypes in NMDA-NR1(neo-/-) mice, which have constitutively reduced expression of the obligate NR1 subunit to model disrupted developmental NMDAR function. Constitutive NMDAR-hypofunction caused a loss of E/I balance, with an increase in intrinsic pyramidal cell excitability and a selective disruption of parvalbumin-expressing interneurons. Disrupted E/I coupling was associated with deficits in auditory-evoked gamma signal-to-noise ratio (SNR). Gamma-band abnormalities predicted deficits in spatial working memory and social preference, linking cellular changes in E/I signaling to target behaviors. The GABA(B)-receptor agonist baclofen improved E/I balance, gamma-SNR and broadly reversed behavioral deficits. These data demonstrate a clinically relevant, highly translatable neural-activity-based biomarker for preclinical screening and therapeutic development across a broad range of disorders that share common endophenotypes and disrupted NMDA-receptor signaling.

MeCP2+/- mouse model of RTT reproduces auditory phenotypes associated with Rett syndrome and replicate select EEG endophenotypes of autism spectrum disorder

Impairments in cortical sensory processing have been demonstrated in Rett syndrome (RTT) and Autism Spectrum Disorders (ASD) and are thought to contribute to high-order phenotypic deficits. However, underlying pathophysiological mechanisms for these abnormalities are unknown. This study investigated auditory sensory processing in a mouse model of RTT with a heterozygous loss of MeCP2 function. Cortical abnormalities in a number of neuropsychiatric disorders, including ASD are reflected in auditory evoked potentials and fields measured by EEG and MEG. One of these abnormalities, increased latency of cortically sourced components, is associated with language and developmental delay in autism. Additionally, gamma-band abnormalities have recently been identified as an endophenotype of idiopathic autism. Both of these cortical abnormalities are potential clinical endpoints for assessing treatment. While ascribing similar mechanisms of idiopathic ASD to Rett syndrome (RTT) has been controversial, we sought to determine if mouse models of RTT replicate these intermediate phenotypes. Mice heterozygous for the null mutations of the gene MeCP2, were implanted for EEG. In response to auditory stimulation, these mice recapitulated specific latency differences as well as select gamma and beta band abnormalities associated with ASD. MeCP2 disruption is the predominant cause of RTT, and reductions in MeCP2 expression predominate in ASD. This work further suggests a common cortical pathophysiology for RTT and ASD, and indicates that the MeCP2+/- model may be useful for preclinical development targeting specific cortical processing abnormalities in RTT with potential relevance to ASD.

NMDA antagonists recreate signal-to-noise ratio and timing perturbations present in schizophrenia

RATIONALE

There is increasing evidence that functional deficits in schizophrenia may be driven by a reduction in the signal-to-noise ratio (SNR) and consistent timing of neural signals. This study examined the extent to which exposure to the NMDA receptor antagonists ketamine and MK801, frequently used pharmacological models of schizophrenia, recreate deficits in electrophysiological markers of disturbed brain circuits that are thought to underlie the illness. Furthermore, this study characterizes the specificity of these differences across the frequency spectrum so as to help identify the nature of selective circuit abnormalities that mediate each oscillatory response as relevant to schizophrenia.

DESIGN

Mouse EEG was recorded during exposure to repeated auditory stimuli after injection of either vehicle or drug. The dose-response relationship for each electrophysiological measure was determined for ketamine and MK-801. Time-frequency analyses were performed to assess baseline, total, and evoked power and intertrial coherence (ITC) at low (5-10 Hz) and high (35-80 Hz)-frequencies.

RESULTS

High frequency evoked and total power was decreased by MK-801 and ketamine in a dose-dependent fashion. High frequency baseline power was increased by MK-801 and ketamine in a dose-dependent fashion. Similar to evoked power, high frequency inter-trial coherence was dose-dependently decreased by both drugs. Low frequency ITC was only decreased by ketamine.

CONCLUSIONS

Both ketamine and MK-801 cause alterations in high-frequency baseline (noise), total (signal), and evoked (signal) power resulting in a loss of high frequency SNR that is thought to primarily reflect local circuit activity. These changes indicate an inappropriate increase in baseline activity, which can also be interpreted as non-task related activity. Ketamine induced a loss of intertrial coherence at low frequencies, indicating a loss of consistency in low-frequency circuit mechanisms. As a proportion of baseline power, both drugs had a relative shift from low to high frequencies, reflecting a change in the balance of brain activity from coordination of global regions to a pattern of discoordinated, autonomous local activity. These changes are consistent with a pattern of fragmented regional brain activity seen in schizophrenia.

Dysbindin-1 mutant mice implicate reduced fast-phasic inhibition as a final common disease mechanism in schizophrenia

DTNBP1 (dystrobrevin binding protein 1) is a leading candidate susceptibility gene in schizophrenia and is associated with working memory capacity in normal subjects. In schizophrenia, the encoded protein dystrobrevin-binding protein 1 (dysbindin-1) is often reduced in excitatory cortical limbic synapses. We found that reduced dysbindin-1 in mice yielded deficits in auditory-evoked response adaptation, prepulse inhibition of startle, and evoked γ-activity, similar to patterns in schizophrenia. In contrast to the role of dysbindin-1 in glutamatergic transmission, γ-band abnormalities in schizophrenia are most often attributed to disrupted inhibition and reductions in parvalbumin-positive interneuron (PV cell) activity. To determine the mechanism underlying electrophysiological deficits related to reduced dysbindin-1 and the potential role of PV cells, we examined PV cell immunoreactivity and measured changes in net circuit activity using voltage-sensitive dye imaging. The dominant circuit impact of reduced dysbindin-1 was impaired inhibition, and PV cell immunoreactivity was reduced. Thus, this model provides a link between a validated candidate gene and an auditory endophenotypes. Furthermore, these data implicate reduced fast-phasic inhibition as a common underlying mechanism of schizophrenia-associated intermediate phenotypes.

Validating γ oscillations and delayed auditory responses as translational biomarkers of autism

BACKGROUND

Difficulty modeling complex behavioral phenotypes in rodents (e.g., language) has hindered pathophysiological investigation and treatment development for autism spectrum disorders. Recent human neuroimaging studies, however, have identified functional biomarkers that can be more directly related to the abnormal neural dynamics of autism spectrum disorders. This study assessed the translational potential of auditory evoked-response endophenotypes of autism in parallel mouse and human studies of autism.

METHODS

Whole-cortex magnetoencephalography was recorded in 17 typically developing and 25 autistic children during auditory pure-tone presentation. Superior temporal gyrus activity was analyzed in time and frequency domains. Auditory evoked potentials were recorded in mice prenatally exposed to valproic acid (VPA) and analyzed with analogous methods.

RESULTS

The VPA-exposed mice demonstrated selective behavioral alterations related to autism, including reduced social interactions and ultrasonic vocalizations, increased repetitive self-grooming, and prepulse inhibition deficits. Autistic subjects and VPA-exposed mice showed a similar 10% latency delay in the N1/M100 evoked response and a reduction in γ frequency (30-50 Hz) phase-locking factor. Electrophysiological measures were associated with mouse behavioral deficits. In mice, γ phase-locking factor was correlated with expression of the autism risk gene neuroligin-3 and neural deficits were modulated by the mGluR5-receptor antagonist MPEP.

CONCLUSIONS

Results demonstrate a novel preclinical approach toward mechanistic understanding and treatment development for autism.

Ketamine Modulates Theta and Gamma Oscillations

Ketamine, an N-methyl-d-aspartate (NMDA) receptor glutamatergic antagonist, has been studied as a model of schizophrenia when applied in subanesthetic doses. In EEG studies, ketamine affects sensory gating and alters the oscillatory characteristics of neuronal signals in a complex manner. We investigated the effects of ketamine on in vivo recordings from the CA3 region of mouse hippocampus referenced to the ipsilateral frontal sinus using a paired-click auditory gating paradigm. One issue of particular interest was elucidating the effect of ketamine on background network activity, poststimulus evoked and induced activity. We find that ketamine attenuates the theta frequency band in both background activity and in poststimulus evoked activity. Ketamine also disrupts a late, poststimulus theta power reduction seen in control recordings. In the gamma frequency range, ketamine enhances both background and evoked power, but decreases relative induced power. These findings support a role for NMDA receptors in mediating the balance between theta and gamma responses to sensory stimuli, with possible implications for dysfunction in schizophrenia.

Sleep, activity, temperature and arousal responses of mice deficient for muscarinic receptor M2 or M4

AIMS

The type 2 muscarinic receptor (M2R) differs from the other G-protein-coupled muscarinic receptor (type 4, or M4R) in tissue distribution and physiologic effects. We studied the impact of these receptors on sleep and arousal by using M2R and M4R knock-out (KO) mice.

MAIN METHODS

M2R and M4R KO and genetically intact mice were compared in terms of normal patterns of sleep, responses to sleep loss, infectious challenge and acoustic startle, and acoustic prepulse inhibition of startle (PPI).

KEY FINDINGS

Under basal conditions, M2R and M4R KO mice do not differ from the background strain or each other in the amount or diurnal pattern of sleep, locomotor activity, and body temperature. After enforced sleep loss, M2R KO mice, in contrast to the other two strains, show no rebound in slow-wave sleep (SWS) time, although their SWS is consolidated, and they show a greater rebound in time spent in REMS (rapid-eye-movement sleep) and REMS consolidation. During influenza infection, M2R KO mice, as compared with the other strains, show marked hypothermia and a less robust increase in SWS. During Candida albicans infection, M2R KO mice show a greater increase in SWS and a greater inflammatory response than do the other strains. M2R KO mice also show greater acoustic startle amplitude than does the background strain, although PPI was not different across the 3 strains over a range of stimulus intensities.

SIGNIFICANCE

Taken together, these findings support different roles for M2R and M4R in the modulation of sleep and arousal during homeostatic challenge.

Chronic ketamine impairs fear conditioning and produces long-lasting reductions in auditory evoked potentials

Ketamine is an NMDA receptor antagonist with a variety of uses, ranging from recreational drug to pediatric anesthetic and chronic pain reliever. Despite its value in the clinical setting, little is known about the immediate and long-lasting effects of repeated ketamine treatment. We assessed the effects of chronic administration of a subanesthetic dose of ketamine on contextual fear conditioning, detection of pitch deviants and auditory gating. After four, but not two, weeks of daily ketamine injections, mice exhibited decreased freezing in the fear conditioning paradigm. Gating of the P80 component of auditory evoked potentials was also significantly altered by treatment condition, as ketamine caused a significant decrease in S1 amplitude. Additionally, P20 latency was significantly increased as a result of ketamine treatment. Though no interactions were found involving test week, stimulus and treatment condition, these results suggest that repeated ketamine administration impairs fear memory and has lasting effects on encoding of sensory stimuli.

Neuregulin 1 transgenic mice display reduced mismatch negativity, contextual fear conditioning and social interactions

INTRODUCTION

Neuregulin-1 (NRG1) is one of susceptibility genes for schizophrenia and plays critical roles in glutamatergic, dopaminergic and GABAergic signaling. Using mutant mice heterozygous for Nrg1 (Nrg1(+/-)) we studied the effects of Nrg1 signaling on behavioral and electrophysiological measures relevant to schizophrenia.

EXPERIMENTAL PROCEDURE

Behavior of Nrg1(+/-) mice and their wild type littermates was evaluated using pre-pulse inhibition, contextual fear conditioning, novel object recognition, locomotor, and social choice paradigms. Event-related potentials (ERPs) were recorded to assess auditory gating and novel stimulus detection.

RESULTS

Gating of ERPs was unaffected in Nrg1(+/-) mice, but mismatch negativity in response to novel stimuli was attenuated. The Nrg1(+/-) mice exhibited behavioral deficits in contextual fear conditioning and social interactions, while locomotor activity, pre-pulse inhibition and novel object recognition were not impaired.

SUMMARY

Nrg1(+/-) mice had impairments in a subset of behavioral and electrophysiological tasks relevant to the negative/cognitive symptom domains of schizophrenia that are thought to be influenced by glutamatergic and dopaminergic neurotransmission. These mice are a valuable tool for studying endophenotypes of schizophrenia, but highlight that single genes cannot account for the complex pathophysiology of the disorder.

Novel environment and GABA agonists alter event-related potentials in N-methyl-D-aspartate NR1 hypomorphic and wild-type mice

Clinical and experimental data suggest dysregulation of N-methyl-d-aspartate receptor (NMDAR)-mediated glutamatergic pathways in schizophrenia. The interaction between NMDAR-mediated abnormalities and the response to novel environment has not been studied. Mice expressing 5 to 10% of normal N-methyl-d-aspartate receptor subunit 1 (NR1) subunits [NR1(neo)(-/-)] were compared with wild-type littermates for positive deflection at 20 ms (P20) and negative deflection at 40 ms (N40) auditory event-related potentials (ERPs). Groups were tested for habituation within and across five testing sessions, with novel environment tested during a sixth session. Subsequently, we examined the effects of a GABA(A) positive allosteric modulator (chlordiazepoxide) and a GABA(B) receptor agonist (baclofen) as potential interventions to normalize aberrant responses. There was a reduction in P20, but not N40 amplitude within each habituation day. Although there was no amplitude or gating change across habituation days, there was a reduction in P20 and N40 amplitude and gating in the novel environment. There was no difference between genotypes for N40. Only NR1(neo)(-/-) mice had reduced P20 in the novel environment. Chlordiazepoxide increased N40 amplitude in wild-type mice, whereas baclofen increased P20 amplitude in NR1(neo)(-/-) mice. As noted in previous publications, the pattern of ERPs in NR1(neo)(-/-) mice does not recapitulate abnormalities in schizophrenia. In addition, reduced NR1 expression does not influence N40 habituation but does affect P20 in a novel environment. Thus, the pattern of P50 (positive deflection at 50 ms) but not N100 (negative deflection at 100 ms) in human studies may relate to subjects' reactions to unfamiliar environments. In addition, NR1 reduction decreased GABA(A) receptor-mediated effects on ERPs while causing increased GABA(B) receptor-mediated effects. Future studies will examine changes in GABA receptor subunits after reductions in NR1 expression.

N-methyl-d-aspartic acid receptor antagonist-induced frequency oscillations in mice recreate pattern of electrophysiological deficits in schizophrenia

INTRODUCTION

Electrophysiological responses to auditory stimuli have provided a useful means of elucidating mechanisms and evaluating treatments in psychiatric disorders. Deficits in gating during paired-click tasks and lack of mismatch negativity following deviant stimuli have been well characterized in patients with schizophrenia. Recently, analyses of basal, induced, and evoked frequency oscillations have gained support as additional measures of cognitive processing in patients and animal models. The purpose of this study is to examine frequency oscillations in mice across the theta (4-7.5 Hz) and gamma (31-61 Hz) bands in the context of N-methyl-d-aspartic acid receptor (NMDAR) hypofunction and dopaminergic hyperactivity, both of which are thought to serve as pharmacological models of schizophrenia.

EXPERIMENTAL PROCEDURES

Electroencephalograms (EEG) were recorded from mice in five treatment groups that consisted of haloperidol, risperidone, amphetamine, ketamine, or ketamine plus haloperidol during an auditory task. Basal, induced and evoked powers in both frequencies were calculated.

RESULTS

Ketamine increased basal power in the gamma band and decreased the evoked power in the theta band. The increase in basal gamma was not blocked by treatment with a conventional antipsychotic. No other treatment group was able to fully reproduce this pattern in the mice.

CONCLUSIONS

Ketamine-induced alterations in EEG power spectra are consistent with abnormalities in the theta and gamma frequency ranges reported in patients with schizophrenia. Our findings support the hypothesis that NMDAR hypofunction contributes to the deficits in schizophrenia and that the dopaminergic pathways alone may not account for these changes.

A novel electrophysiological model of chemotherapy-induced cognitive impairments in mice

PURPOSE

Chemotherapeutic agents are known to produce persistent cognitive deficits in cancer patients. However, little progress has been made in developing animal models to explore underlying mechanisms and potential therapeutic interventions. We report an electrophysiological model of chemotherapy-induced cognitive deficits using a sensory gating paradigm, to correspond with performance in two behavioral tasks.

EXPERIMENTAL DESIGN

Mice received four weekly injections of methotrexate and 5-fluorouracil. Whole-brain event-related potentials (ERPs) were recorded throughout using a paired-click paradigm. Mice underwent contextual fear conditioning (CFC) and novel-object recognition testing (NOR).

RESULTS

Chemotherapy-treated animals showed significantly impaired gating 5 weeks after drug treatments began, as measured by the ratio of the first positive peak in the ERP (P1) minus the first negative peak (N1) between first and second auditory stimuli. There was no effect of drug on the amplitude of P1-N1 or latency of P1. The drug-treated animals also showed significantly increased freezing during fear conditioning and increased exploration without memory impairment during novel object recognition.

CONCLUSIONS

Chemotherapy causes decreased ability to gate incoming auditory stimuli, which may underlie associated cognitive impairments. These gating deficits were associated with a hyperactive response to fear conditioning and reduced adaptation to novel objects, suggesting an additional component of emotional dysregulation. However, amplitudes and latencies of ERP components were unaffected, as was NOR performance, highlighting the subtle nature of these deficits.

Deviance-elicited Changes in Event-related Potentials are Attenuated by Ketamine in Mice

Background: People with schizophrenia exhibit reduced ability to detect change in the auditory environment, which has been linked to abnormalities in N-methyl-D-aspartate (NMDA) receptor-mediated glutamate neurotransmission. This ability to detect changes in stimulus qualities can be measured with electroencephalography using auditory event-related potentials (ERPs). For example, reductions in the N100 and mismatch negativity (MMN), in response to pitch deviance, have been proposed as endophenotypes of schizophrenia. This study examines a novel rodent model of impaired pitch deviance detection in mice using the NMDA receptor antagonist ketamine. Methods: ERPs were recorded from unanesthetized mice during a pitch deviance paradigm prior to and following ketamine administration. First, N40 amplitude was evaluated using stimuli between 4 and 10 kHz to assess the amplitude of responses across the frequency range used. The amplitude and latency of the N40 were analyzed following standard (7 kHz) and deviant (5–9 kHz) stimuli. Additionally, we examined which portions of the ERP are selectively altered by pitch deviance to define possible regions for the mouse MMN. Results: Mice displayed increased N40 amplitude that was followed by a later negative component between 50 and 75 msec in response to deviant stimuli. Both the increased N40 and the late N40 negativity were attenuated by ketamine. Ketamine increased N40 latency for both standard and deviant stimuli alike. Conclusions: The mouse N40 and a subsequent temporal region have deviance response properties similar to the human N100 and, possibly, MMN. Deviance responses were abolished by ketamine, suggesting that ketamine-induced changes in mice mimic deviance detection deficits in schizophrenia.

Antipsychotic-like properties of phosphodiesterase 4 inhibitors: evaluation of 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone (RO-20-1724) with auditory event-related potentials and prepulse inhibition of startle

Antipsychotic medications function through antagonism of D2 dopamine receptors. Blockade of D2 receptors causes an increase in intracellular cAMP, a ubiquitous second messenger. Inhibition of phosphodiesterase (PDE) activity, a family of enzymes that degrade cyclic nucleotides, causes the same effect. The conceptual linkage between dopamine D2 receptors and PDE activity via cAMP suggests a possible therapeutic potential for PDE inhibitors in schizophrenia. The limited number of studies in support of this hypothesis used rolipram, a specific inhibitor of the PDE4 family. In this study, we investigated the impact of 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone (RO-20-1724), another PDE4-specific inhibitor, on auditory event-related potentials (ERPs), prepulse inhibition (PPI) of the startle reflex, and locomotor activity in mice. The ability to reverse amphetamine-induced alterations in ERPs and PPI was used as a model for psychosis. ERPs after RO-20-1724 revealed increased amplitude for the P20 and N40 ERP components. RO-20-1724 reversed the disruptive effect of amphetamines on ERPs and restored gating at a dose that did not impair locomotor activity. However, RO-20-1724 failed to reverse a amphetamine-induced decrease of PPI. Inconsistent results between these two psychosis models suggest that pure sensory processing, as measured with auditory ERPs, may be more sensitive to the effects of intracellular cAMP than sensorimotor effects as assessed with PPI. It remains unclear whether antipsychotic-like properties are a common feature of PDE4 inhibition, or if they are restricted to the pharmacological profile of rolipram. Future studies should examine how PDE4 subtype specificity might contribute to differences between rolipram and RO-20-1724 in sensorimotor gating.

Variables affecting prepulse inhibition of the startle reflex and the response to antipsychotics in DBA/2NCrl mice

RATIONALE

DBA/2 mice demonstrate poor prepulse inhibition (PPI) as is also observed in schizophrenic patients, and their PPI is improved by antipsychotics. Thus, the DBA/2 mouse is increasingly used for testing of novel antipsychotics in PPI; however, the strain has not been fully characterized for relevant variables affecting compound testing.

OBJECTIVES

The objectives of this study were to compare four DBA/2 substrains, evaluate light- and dark-phase testing on startle, PPI, and drug-induced improvement in PPI in DBA/2NCrl mice, test chamber lighting on startle and PPI in DBA/2NCrl mice and to evaluate vehicles on baseline PPI in DBA/2NCrl mice.

RESULTS

DBA/2NCrl and DBA/2J mice were acceptable for PPI testing, while DBA/2NHsd mice had diminished startle reflexes. Startle responses to the prepulses alone were observed in 46% of the DBA/2NTac mice. PPI and startle did not show diurnal variations or variations due to chamber lighting. Olanzapine and aripiprazole showed better drug-induced improvements in PPI during the light phase. The vehicle 25% (2-hydroxypropyl)-beta-cyclodextrin variably improved PPI, an effect not observed with other vehicles.

CONCLUSIONS

DBA/2NHsd and DBA/2NTac mice were unacceptable for PPI experiments. The finding of responses to the prepulses alone by DBA/2NTac mice further indicates the advisability of routinely monitoring responses to prepulses alone. Unlike rats, DBA/2NCrl mice did not have greater startle amplitudes during the dark phase. Compound efficacy was better during the light phase because of poorer PPI in the vehicle group. Some vehicles may have unacceptable effects on PPI in DBA/2NCrl mice and may not be appropriate for studies evaluating novel compounds.

Quiet mutations in inbred strains of mice

The year 2009 is the 100th anniversary of the founding of the first inbred strain of mouse, called DBA. During the last 100 years, inbred strains have proved their value for biomedical research and the number of such strains has mushroomed to over 450, each with different genotypic and phenotypic characteristics and useful for the study of disease and normal function. However, although inbred strains are stable, they are not fixed entities and researchers need to be aware of the phenomena of new mutations and of genetic drift, which occur within all mouse colonies. If the mutations are what we term in this review 'quiet mutations', then they might result in rather unexpected and sometimes tremendously valuable results. Here, we discuss these phenomena and look at how new genomic technologies might help us to detect 'quiet mutations' and use them to our advantage.

Effects of nicotine vary across two auditory evoked potentials in the mouse

BACKGROUND

Schizophrenia patients display sensory processing deficits, reduced alpha7-nicotine receptor expression, and increased incidence of smoking, prompting investigation of nicotine receptor agonists as possible treatments. We evaluated the effects of acute and chronic nicotine, using an animal model that incorporates genetic variation for sensory processing and nicotine sensitivity.

METHODS

C57BL/6J and DBA/2Hsd mice received 2 weeks of 4.2 mg/kg chronic nicotine or saline. Auditory evoked potentials were recorded before and after acute nicotine injection of 1.05 mg/kg on day 14, with a paired-click paradigm (S1/S2). Amplitude and gating of the P20 and N40 were compared between conditions.

RESULTS

Acute nicotine increased the amplitude and gating of the P20 and decreased the amplitude and gating of the N40 across all groups, primarily by acting on S1. Chronic nicotine attenuated the effects of acute nicotine on the N40.

CONCLUSIONS

Our data support the notion that the mouse P20 shares pharmacological response properties with the human P50. In addition, findings suggest that nicotine might increase the initial sensory response (S1), with a resulting improvement in gating of some components.

Mecamylamine blocks nicotine-induced enhancement of the P20 auditory event-related potential and evoked gamma

Cigarette smoking is significantly more prevalent in individuals with schizophrenia than in non-affected populations. Certain neurocognitive deficits and disruptions common in schizophrenia may be altered by smoking, leading to the hypothesis that schizophrenics engage in smoking behavior to alleviate specific neurocognitive symptoms of the disorder. Additionally, research suggests that individuals with schizophrenia have altered auditory event-related potentials (ERPs) and abnormalities in evoked gamma oscillations which are both indices of sensory information processing. This study was conducted to examine the effect of acute administration of nicotine and the non-specific nicotinic antagonist mecamylamine on the P20 and N40 components of the ERP and evoked gamma oscillations in mice. Acute nicotine (1 mg/kg) significantly increased P20 amplitude, an effect that was blocked by pretreatment with mecamylamine (2 mg/kg). Additionally, acute nicotine increased the normal burst of evoked gamma following an auditory stimulus. The increase in evoked gamma was also blocked by mecamylamine pretreatment. Although acute nicotine decreased amplitude of the N40 component, this decrease was not attenuated by mecamylamine. These results replicate findings that nicotine may enhance early sensory information processing through the nicotinic acetylcholinergic receptor system in an established model (ERPs) and extend these findings in an emerging, novel model (evoked gamma oscillations) of sensory information processing. The results also support the hypothesis that nicotine may be beneficial to individuals with deficits in neurocognitive functions, such as those suffering from schizophrenia.

Alpha4beta2 nicotinic receptor stimulation contributes to the effects of nicotine in the DBA/2 mouse model of sensory gating

RATIONALE

Nicotine improves the deficiencies of sensory gating function in schizophrenic patients and in dilute brown non-Agouti (DBA/2) mice. This effect of nicotine has been attributed to activation of the alpha7 nicotinic acetylcholine receptor (nAChR) subtype.

OBJECTIVE

The aim of this study was to determine whether the activation of another nAChR subtype, the central nervous system (CNS) prominent alpha4beta2 receptor, also contributes to the effects of nicotine on sensory gating in DBA/2 mice.

METHODS

Unanesthetized DBA/2 mice were treated either with nicotine, the alpha4beta2 antagonist dihydro-beta-erythroidine, the noncompetitive nAChR antagonist mecamylamine, or a combination of an antagonist and nicotine. Thereafter, gating was assessed by recording hippocampal evoked potentials (EP), which were elicited by pairs of auditory clicks. The EP response to the second click, or test amplitude (TAMP), was divided by the EP response to the first click, or condition amplitude (CAMP), to derive gating T:C ratios.

RESULTS

Nicotine significantly (p<0.05) lowered T:C ratios by 42%, while significantly increasing CAMP by 55%. After a pretreatment with dihydro-beta-erythroidine, nicotine still significantly lowered T:C ratios by 28%; however, the nicotine-induced increase of CAMP was blocked. Mecamylamine blocked the effect of nicotine on both T:C ratios and CAMP.

CONCLUSIONS

Activation of alpha4beta2 receptors by nicotine increases CAMP. However, under conditions where alpha4beta2 receptors are blocked, nicotine still lowers T:C ratios and may improve sensory gating, possibly through the activation of other nAChR subtypes such as alpha7. These effects of nicotine on auditory EPs may be indicative of a profile that would improve information processing in schizophrenia and other CNS diseases.

Mice expressing constitutively active Gsalpha exhibit stimulus encoding deficits similar to those observed in schizophrenia patients

People with schizophrenia display sensory encoding deficits across a broad range of electrophysiological and behavioral measures, suggesting fundamental impairments in the ability to transduce the external environment into coherent neural representations. This inability to create basic components of complex stimuli interferes with a high fidelity representation of the world and likely contributes to cognitive deficits. The current study evaluates the effects of constitutive forebrain activation of the G(s)alpha G-protein subunit on auditory threshold and gain using acoustic brainstem responses and cortically generated N40 event-related potentials to assess the role of cyclic AMP signaling in sensory encoding. Additionally, we examine the ability of pharmacological treatments that mimic (amphetamine) or ameliorate (haloperidol) positive symptoms of schizophrenia to test the hypothesis that the encoding deficits observed in G(s)alpha transgenic mice can be normalized with treatment. We find that G(s)alpha transgenic mice have decreased amplitude of cortically generated N40 but normal acoustic brainstem response amplitude, consistent with forebrain transgene expression and a schizophrenia endophenotype. Transgenic mice also display decreased stimulus intensity response (gain) in both acoustic brainstem response and N40, indicating corticofugal influence on regions that lack transgene expression. N40 deficits in transgenic animals were ameliorated with low dose haloperidol and reversed with higher dose, suggesting dopamine D2 receptor-linked Gi activity contributes to the impairment. Consistent with this hypothesis, we recreated the G(s)alpha transgenic deficit in wild type animals using the indirect dopamine agonist amphetamine. This transgenic model of sensory encoding deficits provides a foundation for identifying biochemical contributions to sensory processing impairments associated with schizophrenia.

Corticosterone modulates auditory gating in mouse

Previous studies suggest that circulating glucocorticoids may influence the encoding and processing of sensory stimuli. The current study investigated this hypothesis by measuring the generation (amplitude), gating (recovery cycle), and sensitivity (intensity function) of auditory evoked responses in C57BL/6 mice treated with chronic corticosterone (0, 1, 5, 15, or 30 mg/kg/day for 14 days). We found that low-dose corticosterone (5 but not 1 mg/kg/day) enhanced the amplitude and improved gating of evoked potentials without affecting the intensity function. In comparison, higher doses (15 and 30 mg/kg/day) decreased the amplitude and impaired gating of evoked potentials, also without altering the stimulus intensity function. At all doses, lower amplitudes of evoked potentials were significantly correlated with higher circulating corticosterone levels. These data highlight the need to consider serum glucocorticoid levels when assessing human disease states associated with aberrations of information processing such as schizophrenia and depression.

Strain-dependent behavioral alterations induced by peripheral interleukin-1 challenge in neonatal mice

Interleukin-1 (IL-1) is implicated in the pathogenesis of various psychiatric diseases. Peripheral administration of IL-1alpha to neonatal rats induces cognitive and behavioral abnormalities and, therefore, the IL-1alpha-treated animals might serve as a schizophrenia model. The present study assessed genetic influences on IL-1alpha-triggered behavioral impairments, using four different strains of neonatal mice, C3H/He, DBA/2, C57BL/6, and ddY. Neonatal treatments with IL-1alpha differentially altered adult behavioral/cognitive traits in a strain-dependent manner. IL-1alpha treatment decreased prepulse inhibition in DBA/2 and C57BL/6 mice but not in C3H/He and ddY. The treatment increased locomotor activity and startle responses in DBA/2 mice and, conversely, decreased startle responses in C3H/He mice. Behavioral alterations were most remarkable in DBA/2 mice but undetectable in ddY mice. The magnitudes of IL-1alpha actions differed between the brain and periphery and were influenced by mouse genetic background. The IL-1-triggered acute signaling, Ikappa-B degradation, was significant in the frontal cortex of DBA/2 mice and in the hypothalamus of C3H/He mice. An increase in brain p38 MAP kinase phosphorylation was also most marked in the DBA/2 strain. In contrast, subchronic influences of IL-1alpha injections failed to illustrate the strain-dependent behavioral alterations. The peripheral effects of IL-1alpha did not match the strain-dependency of the behavioral alterations, either. Acceleration of tooth eruption and eyelid opening as well as attenuation of weight gain was most marked in C3H/He mice and the induction of serum amyloid protein was the largest in ddY mice. Thus, the peripheral effects of IL-1alpha in DBA/2 mice were relatively inferior to those in the other strains. The present animal study suggests that, in early postnatal development, circulating IL-1alpha trigger brain cytokine signaling and produce distinct influences on later neurobehavioral traits, both depending on genetic background.

Neurotransmission- and cellular stress-related gene expression associated with prepulse inhibition in mice

Prepulse inhibition (PPI) is a cross-species measure of sensorimotor gating. PPI deficits have been associated with a number of neuropsychiatric disorders, including schizophrenia. Differential PPI has been demonstrated also across various inbred mouse strains; however, the molecular mechanisms underlying these differences in sensorimotor gating remain unclear. Here, we sought to identify gene expression in the medial prefrontal cortex (mPFC) of mice associated with PPI using a laser microdissection and microarray analysis-based approach. C57BL/6 mouse substrains were used for the study as they have dramatically different PPI. Transcriptional analysis of closely related substrains was predicted to reduce the detection of genetic variation incidental to the phenotype. Microarray analysis comparing the mPFC of C57BL/6J to C57BL/6NHsd mice revealed neurotransmission- and cellular stress-related transcriptional responses associated with lower PPI. Down-regulation of metabotropic glutamate receptor 5, phospholipase C, and inositol monophosphatase 1 gene expression suggest altered phosphoinositide signaling, while decreased expression of a gamma-amino-butyric acid (GABA)A receptor subunit implies changes in GABAergic signaling. Genes involved in neuronal excitation and protection were also differentially expressed, including up-regulation of five immediate early genes and anti-apoptotic/survival factors as Bcl2-associated athanogene 3 and brain-derived neurotrophic factor. These data support previous findings of genetic influences on PPI, and provide novel insights into the molecular mechanisms regulating sensorimotor gating.

Tropisetron improves deficient inhibitory auditory processing in DBA/2 mice: role of alpha 7 nicotinic acetylcholine receptors

RATIONALE

Deficient inhibitory processing of the P50 auditory evoked potential is a pathophysiological feature of schizophrenia. Several lines of evidence suggest that alpha 7 nicotinic receptors play a critical role in this phenomenon. Similar to schizophrenic patients, DBA/2 mice spontaneously exhibit a deficit in inhibitory processing of the P20-N40 auditory evoked potential, which is thought to be a rodent analog of the human P50 auditory evoked potential.

OBJECTIVE

The present study was undertaken to examine whether tropisetron, a partial agonist at alpha 7 nicotinic receptors and an antagonist at 5-hydroxytryptamine-3 receptors, improves this deficit in DBA/2 mice.

RESULTS

Administration of tropisetron (1 mg/kg i.p.) significantly improved the deficient inhibitory processing of the P20-N40 auditory evoked potential in DBA/2 mice. Coadministration of methyllycaconitine (MLA; 3 mg/kg i.p.), a partially selective antagonist at alpha 7 nicotinic receptors, significantly blocked the normalizing effect of tropisetron. Furthermore, MLA alone did not alter the deficient inhibitory processing of the P20-N40 auditory evoked potential in DBA/2 mice.

CONCLUSIONS

The data suggest that tropisetron improves the deficient inhibitory processing of the P20-N40 auditory evoked potential in DBA/2 mice by effects on alpha 7 and perhaps alpha 4 beta 2 nicotinic receptors. Tropisetron may be useful for the treatment of deficient inhibitory processing in schizophrenia.

Ketamine produces lasting disruptions in encoding of sensory stimuli

The current study analyzed the acute, chronic, and lasting effects of ketamine administration in four inbred mouse strains (C3H/HeHsd, C57BL/6Hsd, FVB/Hsd, and DBA/2Hsd) to evaluate vulnerability to ketamine as a drug of abuse and as a model of schizophrenia. Serum half-life of ketamine was similar between all strains (approximately 13 min). Also, the ratio of brain-to-serum ketamine levels was 3:1. Examination of multiple phases of auditory processing using auditory-evoked potentials (AEPs) following acute ketamine (0, 5, and 20 mg/kg) treatment revealed C3H/HeHsd mice to be most vulnerable to ketamine-induced alterations in AEPs, whereas FVB/Hsd mice exhibited the least electrophysiological sensitivity to ketamine. Overall, the precortical P1-evoked potential component increased in amplitude and latency, whereas the cortically generated N1 and P2 components decreased in amplitude and latency following acute ketamine across all strains. Brain catecholamine analyses indicated that ketamine decreased hippocampus epinephrine levels in C3H/HeHsd but elevated hippocampus epinephrine levels in FVB/Hsd, suggesting one potential mechanism for AEP vulnerability to ketamine. Based on results of the acute study, the immediate and lasting effects of chronic low-dose ketamine on AEPs were examined among C3H/HeHsd (sensitive) and FVB/Hsd (insensitive) mice. We observed a decrement of the N1 amplitude that persisted at least 1 week after the last exposure to ketamine across both strains. This lasting deficit in information processing occurred in the absence of acute changes among the FVB/Hsd mice. Implications for both ketamine abuse and N-methyl-D-aspartate hypofunction models of schizophrenia are discussed.

Neural cell adhesion molecule-null mice are not deficient in prepulse inhibition of the startle response

Mice constitutively deficient in the neural cell adhesion molecule have morphological changes in the brain, which are hallmarks of schizophrenia. Schizophrenic patients are impaired in sensorimotor processing indicated by a deficit in prepulse inhibition of the acoustic startle response. Here we tested whether prepulse inhibition and prepulse facilitation are changed in neural cell adhesion molecule-deficient mice compared with their wild-type littermates. Neither prepulse inhibition nor prepulse facilitation (which occurred only at the lowest prepulse intensity used and was weak) was altered. This result is discussed in the light of the 'two-hit' hypothesis of schizophrenia, suggesting that in neural cell adhesion molecule-deficient mice, a prepulse inhibition deficit may become apparent only after treatment with a 'second hit' (such as increased stress).

Phosphodiesterase inhibitors: a novel mechanism for receptor-independent antipsychotic medications

OVERVIEW

All current antipsychotic medications work by binding to Gi-coupled dopamine (DA) D2 receptors. Such medications are thought to affect cellular function primarily by decreasing DA-mediated regulation of intracellular cyclic adenosine monophosphate (cAMP).However, several studies indicate that cAMP signal transduction abnormalities in schizophrenia may not be limited to D2-containing cells. The current study examines the potential of using non-receptor-based agents that modify intracellular signal transduction as potential antipsychotic medications.

METHODS

The indirect DA agonist amphetamine has been used to model the auditory sensory processing deficits in schizophrenia. Such pharmacologically induced abnormalities are reversed by current antipsychotic treatments. This study examines the ability of the phosphodiesterase-4 inhibitor, rolipram, to reverse amphetamine-induced abnormalities in auditory-evoked potentials that are characteristic of schizophrenia.

RESULTS

Rolipram reverses amphetamine-induced reductions in auditory-evoked potentials.

CONCLUSION

This finding could lead to novel approaches to receptor-independent treatments for schizophrenia.

Monoamine reuptake inhibition and nicotine receptor antagonism reduce amplitude and gating of auditory evoked potentials

BACKGROUND

Sensory encoding deficits have been extensively studied as endophenotypic markers of schizophrenia using auditory evoked potentials. In order to increase understanding of the neurochemical basis of such deficits, we utilized an animal model to test whether monoamine reuptake inhibition and nicotine receptor antagonism reduce the amplitude and gating of the P20 and N40 auditory components.

METHODS

C57BL/6J mice received 12 days of chronic vehicle, bupropion, haloperidol or bupropion plus haloperidol. Auditory evoked potentials were then recorded in alert mice to measure the amplitude and gating of evoked components during a paired click paradigm similar to tasks used to measure the P50 and N100 auditory potentials in schizophrenia. Evoked potentials were recorded prior to and following acute nicotine.

RESULTS

Bupropion reduced the amplitude and gating of the N40 evoked potential in mice, similar to the P50 and N100 endophenotypes associated with sensory encoding deficits in schizophrenia. This deficit was fully reversed only by the combination of haloperidol and nicotine, suggesting that dopamine reuptake inhibition and nicotine antagonism both contribute to the observed phenotype. Furthermore, nicotine increased P20 amplitude across all groups supporting a role for nicotine agonists in pre-attentive sensory encoding deficits.

CONCLUSIONS

We propose that the combination of monoamine inhibition and nicotine receptor antagonism may serve as a useful model for preclinical screening of pharmaceutical compounds aimed at treating sensory encoding deficits in schizophrenia.

Sensorimotor gating deficits in transgenic mice expressing a constitutively active form of Gs alpha

Schizophrenia is a complex disorder characterized by wide-ranging cognitive impairments, including deficits in learning as well as sensory gating. The causes of schizophrenia are unknown, but alterations in intracellular G-protein signaling pathways are among the molecular changes documented in patients with schizophrenia. Using the CaMKIIalpha promoter to drive expression in neurons within the forebrain, we have developed transgenic mice that express a constitutively active form of G(s)alpha (G(s)alpha(*)), the G protein that couples receptors such as the D(1) and D(5) dopamine receptors to adenylyl cyclase. We have also generated mice in which the CaMKIIalpha promoter drives expression of a dominant-negative form of protein kinase A, R(AB). Here, we examine startle responses and prepulse inhibition of the startle reflex (PPI) in these G(s)alpha(*) and R(AB) transgenic mice. G(s)alpha(*) transgenic mice exhibited selective deficits in PPI, without exhibiting alterations in the startle response, whereas no deficit in startle or PPI was found in the R(AB) transgenic mice. Thus, overstimulation of the cAMP/PKA pathway disrupts PPI, but the cAMP/PKA pathway may not be essential for sensorimotor gating. G(s)alpha(*) transgenic mice may provide an animal model of certain endophenotypes of schizophrenia, because of the similarities between them and patients with schizophrenia in G-protein function, hippocampus-dependent learning, and sensorimotor gating.