Striatal and Thalamic Auditory Response During Deep Brain Stimulation for Essential Tremor: Implications for Psychosis.

INTRODUCTION: The P50, a positive auditory-evoked potential occurring 50 msec after an auditory click, has been characterized extensively with electroencephalography (EEG) to detect aberrant auditory electrophysiology in disorders like schizophrenia (SZ) where 61-74% have an auditory gating deficit. The P50 response occurs in primary auditory cortex and several thalamocortical regions. In rodents, the gated P50 response has been identified in the reticular thalamic nucleus (RT)-a deep brain structure traversed during deep brain stimulation (DBS) targeting of the ventral intermediate nucleus (VIM) of the thalamus to treat essential tremor (ET) allowing for interspecies comparison. The goal was to utilize the unique opportunity provided by DBS surgery for ET to map the P50 response in multiple deep brain structures in order to determine the utility of intraoperative P50 detection for facilitating DBS targeting of auditory responsive subterritories. MATERIALS AND METHODS: We developed a method to assess P50 response intraoperatively with local field potentials (LFP) using microelectrode recording during routine clinical electrophysiologic mapping for awake DBS surgery in seven ET patients. Recording sites were mapped into a common stereotactic space. RESULTS: Forty significant P50 responses of 155 recordings mapped to the ventral thalamus, RT and CN head/body interface at similar rates of 22.7-26.7%. P50 response exhibited anatomic specificity based on distinct positions of centroids of positive and negative responses within brain regions and the fact that P50 response was not identified in the recordings from either the internal capsule or the dorsal thalamus. CONCLUSIONS: Detection of P50 response intraoperatively may guide DBS targeting RT and subterritories within CN head/body interface-DBS targets with the potential to treat psychosis and shown to modulate schizophrenia-like aberrancies in mouse models.

Genetic knockout of the α7 nicotinic acetylcholine receptor gene alters hippocampal long-term potentiation in a background strain-dependent manner.

Reduced α7 nicotinic acetylcholine receptor (nAChR) function is linked to impaired hippocampal-dependent sensory processing and learning and memory in schizophrenia. While knockout of the Chrna7 gene encoding the α7nAChR on a C57/Bl6 background results in changes in cognitive measures, prior studies found little impact on hippocampal synaptic plasticity in these mice. However, schizophrenia is a multi-genic disorder where complex interactions between specific genetic mutations and overall genetic background may play a prominent role in determining phenotypic penetrance. Thus, we compared the consequences of knocking out the α7nAChR on synaptic plasticity in C57/Bl6 and C3H mice, which differ in their basal α7nAChR expression levels. Homozygous α7 deletion in C3H mice, which normally express higher α7nAChR levels, resulted in impaired long-term potentiation (LTP) at hippocampal CA1 synapses, while C3H α7 heterozygous mice maintained robust LTP. In contrast, homozygous α7 deletion in C57 mice, which normally express lower α7nAChR levels, did not alter LTP, as had been previously reported for this strain. Thus, the threshold of Chrna7 expression required for LTP may be different in the two strains. Measurements of auditory gating, a hippocampal-dependent behavioral paradigm used to identify schizophrenia-associated sensory processing deficits, was abnormal in C3H α7 knockout mice confirming that auditory gating also requires α7nAChR expression. Our studies highlight the importance of genetic background on the regulation of synaptic plasticity and could be relevant for understanding genetic and cognitive heterogeneity in human studies of α7nAChR dysfunction in mental disorders.

Effects of a ketogenic diet on auditory gating in DBA/2 mice: A proof-of-concept study.

Although the ketogenic diet has shown promise in a pilot study and case report in schizophrenia, its effects in animal models of hypothesized disease mechanisms are unknown. This study examined effects of treatment with the ketogenic diet on hippocampal P20/N40 gating in DBA/2 mice, a translational endophenotype that mirrors inhibitory deficits in P50 sensory gating in schizophrenia patients. As expected, the diet increased blood ketone levels. Animals with the highest ketone levels showed the lowest P20/N40 gating ratios. These preliminary results suggest that the ketogenic diet may effectively target sensory gating deficits and is a promising area for additional research in schizophrenia.

Increasing pro-survival factors within whole brain tissue of Sprague Dawley rats via intracerebral administration of modified valproic acid.

Neural tissue exposure to valproic acid (VPA) increases several pro-survival phospho-proteins that can be used as biomarkers for indicating a beneficial drug response (pAkt(Ser473), pGSK3ß(Ser9), pErk1/2(Thr202/Tyr204)). Unfortunately, targeting VPA to neural tissue is a problem due to severe asymmetrical distribution, wherein the drug tends to remain in peripheral blood rather than localizing within the brain. Intracerebral delivery of an amide-linked VPA-PEG conjugate could address these issues by enhancing retention and promoting cerebro-global increases in pro-survival phospho-proteins. It is necessary to assay for the retained bioactivity of a PEGylated valproic acid molecule, along with locating an intracranial cannula placement that optimizes the increase of a known downstream biomarker for chronic VPA exposure. Here we show an acute injection of VPA-PEG conjugate within brain tissue increased virtually all of the assayed phospho-proteins, including well-known pro-survival factors. In contrast, an acute injection of VPA expectedly decreased signaling throughout the hour. Needle penetration into whole brain tissue is the intentional cause of trauma in this procedure. The trauma to brain tissue was observed to overcome known phospho-protein increases for unmodified VPA in the injected solution, while VPA-PEG conjugate appeared to induce significant increases in pro-survival phospho-proteins, despite the procedural trauma.

The antiepileptic drug levetiracetam improves auditory gating in DBA/2 mice.

Schizophrenia is associated with deficits in P50 gating. This deficit is preclinically modeled in the DBA/2 mouse by depth recordings in the hippocampus. Neurobiologically, the deficit may be due to dysfunction in inhibitory circuitry. It follows that anti-epileptic drugs which impact this circuitry, such as levetiracetam (LEV), may improve gating. To that end, the goal of this study was to evaluate the ability of LEV to normalize sensory gating in the DBA/2 mouse. Gating of the murine analog of the P50, the P20-N40, was evaluated from in vivo hippocampal recordings in 39 male DBA/2 mice. Gating effects were evaluated using four doses of LEV (3, 10, 30, and 100 mg/kg). The 10 mg/kg dose improved P20-N40 gating (P = 0.016). No other doses significantly affected gating. Low-dose LEV may improve P20-N40 gating in the DBA/2 mouse model of schizophrenia. Low-doses of LEV may improve P20-N40 gating in the DBA/2 mouse model of schizophrenia and warrant further investigation in the illness.

Maximizing the effect of an α7 nicotinic receptor PAM in a mouse model of schizophrenia-like sensory inhibition deficits.

Positive allosteric modulators (PAMs) for the α7 nicotinic receptor hold promise for the treatment of sensory inhibition deficits observed in schizophrenia patients. Studies of these compounds in the DBA/2 mouse, which models the schizophrenia-related deficit in sensory inhibition, have shown PAMs to be effective in improving the deficit. However, the first published clinical trial of a PAM for both sensory inhibition deficits and related cognitive difficulties failed, casting a shadow on this therapeutic approach. The present study used both DBA/2 mice, and C3H Chrna7 heterozygote mice to assess the ability of the α7 PAM, PNU-120596, to improve sensory inhibition. Both of these strains of mice have reduced hippocampal α7 nicotinic receptor numbers and deficient sensory inhibition similar to schizophrenia patients. Low doses of PNU-120596 (1 or 3.33mg/kg) were effective in the DBA/2 mouse but not the C3H Chrna7 heterozygote mouse. Moderate doses of the selective α7 nicotinic receptor agonist, choline chloride (10 or 33mg/kg), were also ineffective in improving sensory inhibition in the C3H Chrna7 heterozygote mouse. However, combining the lowest doses of both PNU-120596 and choline chloride in this mouse model did improve sensory inhibition. We propose here that the difference in efficacy of PNU-120596 between the 2 mouse strains is driven by differences in hippocampal α7 nicotinic receptor numbers, such that C3H Chrna7 heterozygote mice require additional direct stimulation of the α7 receptors. These data may have implications for further clinical testing of putative α7 nicotinic receptor PAMs.

The interaction between maternal immune activation and alpha 7 nicotinic acetylcholine receptor in regulating behaviors in the offspring.

Mutation of human chromosome 15q13.3 increases the risk for autism and schizophrenia. One of the noteworthy genes in 15q13.3 is CHRNA7, which encodes the nicotinic acetylcholine receptor alpha 7 subunit (α7nAChR) associated with schizophrenia in clinical studies and rodent models. This study investigates the role of α7nAChR in maternal immune activation (MIA) mice model, a murine model of environmental risk factor for autism and schizophrenia. We provided choline, a selective α7nAChR agonist among its several developmental roles, in the diet of C57BL/6N wild-type dams throughout the gestation and lactation period and induced MIA at mid-gestation. The adult offspring behavior and gene expression profile in the maternal-placental-fetal axis at mid-gestation were investigated. We found that choline supplementation prevented several MIA-induced behavioral abnormalities in the wild-type offspring. Pro-inflammatory cytokine interleukin-6 (Il6) and Chrna7 gene expression in the wild-type fetal brain were elevated by poly(I:C) injection and were suppressed by gestational choline supplementation. We further investigated the gene expression level of Il6 in Chrna7 mutant mice. We found that the basal level of Il6 was higher in Chrna7 mutant fetal brain, which suggests that α7nAChR may serve an anti-inflammatory role in the fetal brain during development. Lastly, we induced MIA in Chrna7(+/-) offspring. The Chrna7(+/-) offspring were more vulnerable to MIA, with increased behavioral abnormalities. Our study shows that α7nAChR modulates inflammatory response affecting the fetal brain and demonstrates its effects on offspring behavior development after MIA.

Erratum: The antiepileptic drug levetiracetam improves auditory gating in DBA/2 mice.

[This corrects the article DOI: 10.1038/npjschz.2015.2.][This corrects the article DOI: 10.1038/npjschz.2015.2.].

Dietary choline supplementation to dams during pregnancy and lactation mitigates the effects of in utero stress exposure on adult anxiety-related behaviors.

Brain cholinergic dysfunction is associated with neuropsychiatric illnesses such as depression, anxiety, and schizophrenia. Maternal stress exposure is associated with these same illnesses in adult offspring, yet the relationship between prenatal stress and brain cholinergic function is largely unexplored. Thus, using a rodent model, the current study implemented an intervention aimed at buffering the potential effects of prenatal stress on the developing brain cholinergic system. Specifically, control and stressed dams were fed choline-supplemented or control chow during pregnancy and lactation, and the anxiety-related behaviors of adult offspring were assessed in the open field, elevated zero maze and social interaction tests. In the open field test, choline supplementation significantly increased center investigation in both stressed and nonstressed female offspring, suggesting that choline-supplementation decreases female anxiety-related behavior irrespective of prenatal stress exposure. In the elevated zero maze, prenatal stress increased anxiety-related behaviors of female offspring fed a control diet (normal choline levels). However, prenatal stress failed to increase anxiety-related behaviors in female offspring receiving supplemental choline during gestation and lactation, suggesting that dietary choline supplementation ameliorated the effects of prenatal stress on anxiety-related behaviors. For male rats, neither prenatal stress nor diet impacted anxiety-related behaviors in the open field or elevated zero maze. In contrast, perinatal choline supplementation mitigated prenatal stress-induced social behavioral deficits in males, whereas neither prenatal stress nor choline supplementation influenced female social behaviors. Taken together, these data suggest that perinatal choline supplementation ameliorates the sex-specific effects of prenatal stress.

Acute administration of Δ9 tetrahydrocannabinol does not prevent enhancement of sensory gating by clozapine in DBA/2 mice.

Despite high rates of marijuana abuse in schizophrenia, the physiological interactions between tetrahydrocannabinol (THC) and antipsychotic medications are poorly understood. A well-characterized feature of schizophrenia is poor gating of the P50 auditory-evoked potential. This feature has been translationally modeled by the DBA/2 mouse, which exhibits poor suppression of the P20-N40 AEP, the rodent analog of the human P50. Previous work has demonstrated that this deficit is reversed by the antipsychotic clozapine. It is unknown, however, if this effect is altered by THC administration. Using a conditioning-testing paradigm with paired auditory stimuli, the effects of clozapine and dronabinol (a pharmaceutical THC formulation) on inhibitory P20-N40 AEP processing were assessed from in vivo hippocampal CA3 recordings in anesthetized DBA/2 mice. The effects of clozapine (0.33 mg/kg) and dronabinol (10 mg/kg) were assessed alone and in combination (0.33, 1 or 1.83 mg/kg clozapine with 10mg/kg dronabinol). Improved P20-N40 AEP gating was observed after acute administration of 0.33 mg/kg clozapine. Co-injection of 0.33 mg/kg clozapine and 10 mg/kg THC, however, did not improve gating relative to baseline. This effect was overcome by higher doses of clozapine (1 and 1.83 mg/kg), as these doses improved gating relative to baseline in the presence of 10 mg/kg THC. 10 mg/kg THC alone did not affect gating. In conclusion, THC does not prevent improvement of P20-N40 gating by clozapine.

Long-term improvements in sensory inhibition with gestational choline supplementation linked to α7 nicotinic receptors through studies in Chrna7 null mutation mice.

Perinatal choline supplementation has produced several benefits in rodent models, from improved learning and memory to protection from the behavioral effects of fetal alcohol exposure. We have shown that supplemented choline through gestation and lactation produces long-term improvement in deficient sensory inhibition in DBA/2 mice which models a similar deficit in schizophrenia patients. The present study extends that research by feeding normal or supplemented choline diets to DBA/2 mice carrying the null mutation for the α7 nicotinic receptor gene (Chrna7). DBA/2 mice heterozygotic for Chrna7 were bred together. Dams were placed on supplemented (5 gm/kg diet) or normal (1.1 gm/kg diet) choline at mating and remained on the specific diet until offspring weaning. Thereafter, offspring were fed standard rodent chow. Adult offspring were assessed for sensory inhibition. Brains were obtained to ascertain hippocampal α7 nicotinic receptor levels. Choline-supplemented mice heterozygotic or null-mutant for Chrna7 failed to show improvement in sensory inhibition. Only wildtype choline-supplemented mice showed improvement with the effect solely through a decrease in test amplitude. This supports the hypothesis that gestational-choline supplementation is acting through the α7 nicotinic receptor to improve sensory inhibition. Although there was a significant gene-dose-related change in hippocampal α7 receptor numbers, binding studies did not reveal any choline-dose-related change in binding in any hippocampal region, the interaction being driven by a significant genotype main effect (wildtype>heterozygote>null mutant). These data parallel a human study wherein the offspring of pregnant women receiving choline supplementation during gestation, showed better sensory inhibition than offspring of women on placebo.

Cotinine impacts sensory processing in DBA/2 mice through changes in the conditioning amplitude.

Cotinine, a major metabolite of nicotine, has produced improved learning and memory in rodents and non-human primates and corrects apomorphine-induced loss of pre-pulse startle inhibition in rats. The present study assessed cotinine, both acute and chronic (7-day), in the sensory inhibition paradigm in DBA/2 mice. These mice spontaneously show a deficit in hippocampal sensory inhibition, as assessed by the P20-N40 EEG paradigm, which models the deficit observed in schizophrenia patients. Anesthetized DBA/2 mice were recorded in the CA3 region of hippocampus for inhibition of paired, identical auditory stimuli, then administered cotinine (0.33, 0.1, 0.33, 1.0 or 3.3 mg/kg SQ) and recorded for 90 min. At doses of 0.1, 0.33 and 1.0 mg/kg, there were significant increases in conditioning amplitude, with no changes in test amplitude or TC ratio. Blockade of α4ß2 nicotinic receptors with central administration of DHΒE blocked the increase in the conditioning amplitude induced by the 1.0 mg/kg dose of cotinine, as did blockade of α7 nicotinic receptors with α-bungarotoxin. Daily injections of 0.33, 1.0 or 3.3 mg/kg for 7 days produced similar increases in the conditioning amplitude on the 7th day, but only at the 0.33 and 3.3 mg/kg doses. Determination of the "carry over" effect of the previous 6 daily doses of cotinine, prior to the 7th dose, showed that there was a significant increase in the conditioning amplitude as compared to the baseline data for mice receiving the equivalent acute dose. There were no significant effects on test amplitude or TC ratio for any of the chronic doses. These data suggest that cotinine modulates the conditioning amplitude in the sensory inhibition paradigm through the α4ß2 nicotinic receptor and possibly also through the α7 nicotinic receptor, as well. However the data do not suggest that cotinine is a potential therapeutic for the treatment of sensory inhibition deficits in schizophrenia.

Intermittent versus continuous central administration of clozapine in DBA/2 mice, improvement in sensory inhibition deficits.

Deficient sensory inhibition, the failure to inhibit responses to repeated stimuli, is a hallmark of schizophrenia, and is thought to be related to difficulties with attention and working memory. Sensory inhibition is assessed by comparing the auditory-evoked EEG responses to 2 closely-spaced identical stimuli. Normal individuals show suppressed response to the second stimulus while schizophrenia patients have responses of similar magnitude to both stimuli. This deficit has been linked to polymorphisms in the promoter for the α7 nicotinic receptor gene, resulting in reduced numbers of receptors on hippocampal interneurons. This deficit is modeled in DBA/2 mice which also show a polymorphism in the promoter for the α7 nicotinic receptor gene and reduced numbers of hippocampal α7 receptors. Systemic administration of clozapine, the most efficacious antipsychotic medication, improves sensory inhibition deficits in both schizophrenia patients and DBA/2 mice. We have previously shown that acute intracerebroventricular (ICV) injections of clozapine induced similar improvement in sensory inhibition in DBA/2 mice. Here we demonstrate the efficacy of chronic ICV clozapine administration in improving sensory inhibition in DBA2 mice. Mice received ICV vehicle, 3, 7.5, 15 or 30 µg of clozapine, either continuously or as a once-per-day injection. Mice were recorded on the 7th day of drug delivery. Both approaches produced improved sensory inhibition, but the daily bolus injection was effective at a lower dose (3 µg/day) than the continuous delivery (15 µg/day). The bolus injections also showed significant improvement up to 36 h post injection thus suggesting that this approach may be more efficacious.

The effects of prenatal stress on alpha4 beta2 and alpha7 hippocampal nicotinic acetylcholine receptor levels in adult offspring.

Prenatal stress in humans is associated with psychiatric problems in offspring such as anxiety, depression, and schizophrenia. These same illnesses are also associated with neuronal nicotinic acetylcholine receptor (nAChR) dysfunction. Despite the known associations between prenatal stress exposure and offspring mental illness, and between mental illness and nAChR dysfunction, it is not known whether prenatal stress exposure impacts neuronal nAChRs. Thus, we tested the hypothesis that maternal stress alters the development of hippocampal alpha4 beta2 (α4ß2∗) and alpha7 (α7∗) nicotinic receptor levels in adult offspring. Female Sprague-Dawley rats experienced unpredictable variable stressors two to three times daily during the last week of gestation. At weaning (21 days) the offspring of prenatally stressed (PS) and nonstressed (NS) dams were assigned to same-sex PS or NS groups. In young adulthood (56 days), the brains of offspring were collected and adjacent sections processed for quantitative autoradiography using [125I]-epibatidine (α4ß2* nicotinic receptor-selective) and [125I]-α-bungarotoxin (α-BTX; α7* nicotinic receptor-selective) ligands. We found that PS significantly increased hippocampal α4ß2* nAChRs of males and females in all subfields analyzed. In contrast, only females showed a trend toward PS-induced increases in α7* nAChRs in the dentate gyrus. Interestingly, NS females displayed a significant left-biased lateralization of α7* nAChRs in the laconosum moleculare of area CA1, whereas PS females did not, suggesting that PS interfered with normal lateralization patterns of α7* nAChRs during development. Taken together, our results suggest that PS impacts the development of hippocampal nAChRs, which may be an important link between PS exposure and risk for neuropsychiatric illness.

Short-term treatment with tolfenamic acid improves cognitive functions in Alzheimer's disease mice.

Tolfenamic acid lowers the levels of the amyloid precursor protein (APP) and amyloid beta (Aß) when administered to C57BL/6 mice by lowering their transcriptional regulator specificity protein 1 (SP1). To determine whether changes upstream in the amyloidogenic pathway that forms Aß plaques would improve cognitive outcomes, we administered tolfenamic acid for 34 days to hemizygous R1.40 transgenic mice. After the characterization of cognitive deficits in these mice, assessment of spatial learning and memory functions revealed that treatment with tolfenamic acid attenuated long-term memory and working memory deficits, determined using Morris water maze and the Y-maze. These improvements occurred within a shorter period of exposure than that seen with clinically approved drugs. Cognitive enhancement was accompanied by reduction in the levels of the SP1 protein (but not messenger RNA [mRNA]), followed by lowering both the mRNA and the protein levels of APP and subsequent Aß levels. These findings provide evidence that tolfenamic acid can disrupt the pathologic processes associated with Alzheimer's disease (AD) and are relevant to its scheduled biomarker study in AD patients.

Perinatal choline effects on neonatal pathophysiology related to later schizophrenia risk.

OBJECTIVE: Deficient cerebral inhibition is a pathophysiological brain deficit related to poor sensory gating and attention in schizophrenia and other disorders. Cerebral inhibition develops perinatally, influenced by genetic and in utero factors. Amniotic choline activates fetal α7-nicotinic acetylcholine receptors and facilitates development of cerebral inhibition. Increasing this activation may protect infants from future illness by promoting normal brain development. The authors investigated the effects of perinatal choline supplementation on the development of cerebral inhibition in human infants. METHOD: A randomized placebo-controlled clinical trial of dietary phosphatidylcholine supplementation was conducted with 100 healthy pregnant women, starting in the second trimester. Supplementation to twice normal dietary levels for mother or newborn continued through the third postnatal month. All women received dietary advice regardless of treatment. Infants' electrophysiological recordings of inhibition of the P50 component of the cerebral evoked response to paired sounds were analyzed. The criterion for inhibition was suppression of the amplitude of the second P50 response by at least half, compared with the first response. RESULTS: No adverse effects of choline were observed in maternal health and delivery, birth, or infant development. At the fifth postnatal week, the P50 response was suppressed in more choline-treated infants (76%) compared with placebo-treated infants (43%) (effect size=0.7). There was no difference at the 13th week. A CHRNA7 genotype associated with schizophrenia was correlated with diminished P50 inhibition in the placebo-treated infants, but not in the choline-treated infants. CONCLUSIONS: Neonatal developmental delay in inhibition is associated with attentional problems as the child matures. Perinatal choline activates timely development of cerebral inhibition, even in the presence of gene mutations that otherwise delay it.

Chronic central administration of valproic acid: Increased pro-survival phospho-proteins and growth cone associated proteins with no behavioral pathology.

Valproic acid (VPA) is the most widely prescribed antiepileptic drug due to its ability to treat a broad spectrum of seizure types. However, potential complications of this drug include anticonvulsant polytherapy metabolism, organ toxicity and teratogenicity which limit its use in a variety of epilepsy patients. Direct delivery of VPA intracerebroventricularly (ICV) could circumvent the toxic effects normally seen with the oral route of administration. An additional potential benefit would be significantly reduced dosing while achieving high brain concentrations. Epileptogenic tissue from patients with intractable seizures has shown significant cell death which may be mitigated by maximizing cerebral VPA exposure. Here we show ICV administration of VPA localized to the periventricular zone increased pro-survival phospho-proteins (pAkt(Ser473), pAkt(Thr308), pGSK3ß(Ser9), pErk1/2(Thr202/Tyr204)) and growth cone associated proteins (2G13p, GAP43) in a whole animal system. No significant changes in DCX, NeuN, synaptotagmin, and synaptophysin were detected. Assessment of possible behavioral alterations in rats receiving chronic central infusions of VPA was performed with the open field and elevated plus mazes. Neither paradigm revealed any detrimental effects of the drug infusion process.

Effects of the novel α7 nicotinic acetylcholine receptor agonist ABT-107 on sensory gating in DBA/2 mice: pharmacodynamic characterization.

Nicotinic acetylcholine receptor (nAChR) agonists improve sensory gating deficits in animal models and schizophrenic patients. The aim of this study was to determine whether the novel and selective α7 nAChR full agonist 5-(6-[(3R)-1-azabicyclo[2.2.2]oct-3-yloxy]pyridazin-3-yl)-1H-indole (ABT-107) improves sensory gating deficits in DBA/2 mice. Sensory gating was measured by recording hippocampal-evoked potential P20-N40 waves and determining gating test/conditioning (T/C) ratios in a paired auditory stimulus paradigm. ABT-107 at 0.1 µmol/kg (average plasma concentration of 1.1 ng/ml) significantly improved sensory gating by lowering T/C ratios during a 30-min period after administration in unanesthetized DBA/2 mice. ABT-107 at 1.0 µmol/kg was ineffective at 30 min after administration when average plasma levels were 13.5 ng/ml. However, the 1.0 µmol/kg dose was effective 180 min after administration when plasma concentration had fallen to 1.9 ng/ml. ABT-107 (0.1 µmol/kg) also improved sensory gating in anesthetized DBA/2 mice pretreated with α7 nAChR-desensitizing doses of nicotine (6.2 µmol/kg) or ABT-107 (0.1 µmol/kg) itself. Moreover, repeated b.i.d. dosing of ABT-107 (0.1 µmol/kg) was as efficacious as a single dose. The acute efficacy of ABT-107 (0.1 µmol/kg) was blocked by the nAChR antagonist methyllycaconitine, but not by the α4ß2 nAChR antagonist dihydro-ß-erythroidine. These studies demonstrate that ABT-107 improves sensory gating through the activation of nAChRs, and efficacy is sustained under conditions of repeated dosing or with prior nAChR activation with nicotine.

Sensory and sensorimotor gating deficits after neonatal ventral hippocampal lesions in rats.

Neonatal ventral hippocampal lesions (NVHLs) in rats lead to reduced prepulse inhibition (PPI) of startle and other behavioral deficits in adulthood that model abnormalities in schizophrenia patients. A neurophysiological deficit in schizophrenia patients and their first-degree relatives is reduced gating of the P50 event-related potential (ERP). N40 ERP gating in rats may be a cross-species analog of P50 gating, and is disrupted in experimental manipulations related to schizophrenia. Here, we tested whether N40 gating as well as PPI is disrupted after NVHLs, using contemporaneous measures of these two conceptually related phenomena. Male rat pups received sham or ibotenic acid NVHLs on postnatal day 7. PPI was tested on days 35 and 56, after which rats were equipped with cortical surface electrodes for ERP measurements. One week later, PPI and N40 gating were measured in a single test, using paired S1-S2 clicks spaced 500 ms apart to elicit N40 gating. Compared to sham-lesioned rats, those with NVHLs exhibited PPI deficits on days 35 and 56. NVHL rats also exhibited reduced N40 gating and reduced PPI, when measured contemporaneously at day 65. Deficits in PPI and N40 gating appeared most pronounced in rats with larger lesions, focused within the ventral hippocampus. In this first report of contemporaneous measures of two important schizophrenia-related phenotypes in NVHL rats, NVHLs reproduce both sensory (N40) and sensorimotor (PPI) gating deficits exhibited in schizophrenia. In this study, lesion effects were detected prior to pubertal onset, and were sustained well into adulthood.

The smoking cessation drug varenicline improves deficient P20-N40 inhibition in DBA/2 mice.

Varenicline, an FDA approved smoking cessation pharmacotherapy, is an α4ß2* nicotinic acetylcholine receptor (nAChR) partial agonist and an α7* nAChR full agonist. Both subtypes of nAChR are involved in modulating auditory evoked responses in rodents. In DBA/2 mice, an inbred strain, auditory evoked responses to paired auditory stimuli fail to inhibit to the second stimulus. This mouse strain replicates the auditory evoked response inhibition deficit experienced by the majority of schizophrenia patients. In this current study, we examined the effects of five different doses of varenicline (0.06, 0.3, 0.6, 3 and 6mg/kg) on auditory evoked responses in anesthetized DBA/2 mice. We also administered α4ß2* and α7* nAChR selective antagonists prior to varenicline administration to determine which nAChR subtypes mediate the effects of varenicline. Four of the five doses of varenicline produced improvements in auditory evoked response inhibition deficits. Selective blockade of either the α4ß2* or α7* nAChR in competition with 0.6mg/kg varenicline prevented varenicline induced improvements. In competition with a higher dose of varenicline (3mg/kg) only blockade of the α4ß2* nAChR prevented varenicline induced improvement in auditory evoked response inhibition. These data indicate the importance of α4ß2* nAChRs and the potential involvement of the α7* subtype in varenicline's effects on auditory evoked responses in DBA/2 mice.