Long-term safety and tolerability of lacosamide monotherapy in patients with epilepsy: Results from a multicenter, open-label trial.

The primary objective of this trial (SP1042; NCT02582866) was to assess long-term safety and tolerability of lacosamide monotherapy (200-600 mg/day) in adults with focal (partial-onset) seizures or generalized tonic-clonic seizures (without clear focal origin). This Phase III, long-term, open-label, multicenter, follow-up trial enrolled patients with epilepsy who were taking lacosamide in, and completed, the previous double-blind trial (SP0994; NCT01465997). Primary safety outcomes were treatment-emergent adverse events (TEAEs), discontinuations due to TEAEs, and serious TEAEs. One hundred and six patients were enrolled and received lacosamide: 84 (79.2%) completed the trial and 22 (20.8%) discontinued. The median duration of exposure was 854.0 days, with a median modal dose of 200 mg/day. Ninety-six (90.6%), 64 (60.4%), and 44 (41.5%) patients had ≥12, ≥24, and ≥36 months of lacosamide exposure, respectively. At least one TEAE was reported by 61 (57.5%) patients. The most common (≥4%) TEAEs were headache (10 [9.4%]), nasopharyngitis (eight [7.5%]), and back pain (five [4.7%]). One (0.9%) patient discontinued due to a TEAE (sudden unexpected death in epilepsy; not considered drug-related), 14 (13.2%) patients reported serious TEAEs, and seven (6.6%) patients reported TEAEs that were considered drug-related. Overall, long-term lacosamide monotherapy was generally well tolerated up to 600 mg/day, with no new safety signals identified.

Effects of lacosamide and carbamazepine on lipids in a randomized trial.

OBJECTIVE: The effects of anticonvulsants on lipids are the subject of considerable concern and investigation, but there are almost no data on this issue from randomized trials. We evaluated serum lipid profiles in adults with newly diagnosed epilepsy, following randomization to lacosamide (LCM) or carbamazepine (CBZ) monotherapy. METHODS: We analyzed data from a Phase 3, international, randomized, double-blind trial of LCM vs CBZ for the initial treatment of focal epilepsy. Serum lipid profiles in patients not taking lipid-lowering agents and providing blood samples under fasting conditions before treatment, and following 3 or 12 months of treatment with LCM or CBZ at various doses were analyzed. RESULTS: At 12 months, 271 patients satisfied the inclusion criteria for the analysis. No change was observed in LCM-treated patients for total cholesterol, cholesterol fractions, or triglycerides. CBZ-treated patients showed an increase of 21.1 mg/dL in total cholesterol, 12.6 mg/dL in low-density lipoprotein (LDL) cholesterol, 12.5 mg/dL in non-high density lipoprotein (non-HDL) cholesterol, and 8.5 mg/dL in HDL cholesterol; triglycerides remained unchanged. The proportion of patients with elevated total cholesterol levels (above the upper limit of the reference range) did not change in the LCM treatment group (37.0% at Baseline; 34.8% at 12 months), but increased from 30.8% (at Baseline) to 49.6% (at 12 months) in the CBZ treatment group. SIGNIFICANCE: This study provides Class II evidence that CBZ elevates serum lipids, whereas LCM has no effect on lipids. It supports LCM as an appropriate choice for new-onset focal epilepsy.

Efficacy and safety of adjunctive lacosamide in the treatment of primary generalised tonic-clonic seizures: a double-blind, randomised, placebo-controlled trial.

OBJECTIVE: To evaluate efficacy and safety of lacosamide (up to 12 mg/kg/day or 400 mg/day) as adjunctive treatment for uncontrolled primary generalised tonic-clonic seizures (PGTCS) in patients (≥4 years) with idiopathic generalised epilepsy (IGE). METHODS: Phase 3, double-blind, randomised, placebo-controlled trial (SP0982; NCT02408523) in patients with IGE and PGTCS taking 1-3 concomitant antiepileptic drugs. Primary outcome was time to second PGTCS during 24-week treatment. RESULTS: 242 patients were randomised and received ≥1 dose of trial medication (lacosamide/placebo: n=121/n=121). Patients (mean age: 27.7 years; 58.7% female) had a history of generalised-onset seizures (tonic-clonic 99.6%; myoclonic 38.8%; absence 37.2%). Median treatment duration with lacosamide/placebo was 143/65 days. Risk of developing a second PGTCS during 24-week treatment was significantly lower with lacosamide than placebo (Kaplan-Meier survival estimates 55.27%/33.37%; HR 0.540, 95% CI 0.377 to 0.774; p<0.001; n=118/n=121). Median time to second PGTCS could not be estimated for lacosamide (>50% of patients did not experience a second PGTCS) and was 77.0 days for placebo. Kaplan-Meier estimated freedom from PGTCS at end of the 24-week treatment period (day 166) for lacosamide/placebo was 31.3%/17.2% (difference 14.1%; p=0.011). More patients on lacosamide than placebo had ≥50% (68.1%/46.3%) or ≥75% (57.1%/36.4%) reduction from baseline in PGTCS frequency/28 days, or observed freedom from PGTCS during treatment (27.5%/13.2%) (n=119/n=121). 96/121 (79.3%) patients on lacosamide had treatment-emergent adverse events (placebo 79/121 (65.3%)), most commonly dizziness (23.1%), somnolence (16.5%), headache (14.0%). No patients died during the trial. CONCLUSIONS: Lacosamide was efficacious and generally safe as adjunctive treatment for uncontrolled PGTCS in patients with IGE.

Lacosamide in patients with epilepsy of cerebrovascular etiology.

OBJECTIVES: To assess tolerability and efficacy of lacosamide in adults with cerebrovascular epilepsy etiology (CVEE). MATERIALS AND METHODS: Exploratory post hoc analyses of a double-blind, initial monotherapy trial of lacosamide vs carbamazepine-controlled release (carbamazepine-CR) (SP0993; NCT01243177); a double-blind conversion to lacosamide monotherapy trial (SP0902; NCT00520741); and an observational study of adjunctive lacosamide added to one antiepileptic drug (SP0973 VITOBA; NCT01098162). Patients with CVEE were identified based on epilepsy etiology recorded at baseline. RESULTS: In the initial monotherapy trial, 61 patients had CVEE (lacosamide: 27; carbamazepine-CR: 34). 20 (74.1%) patients on lacosamide (27 [79.4%] on carbamazepine-CR) reported treatment-emergent adverse events (TEAEs), most commonly (≥10%) headache, dizziness, and fatigue (carbamazepine-CR: headache, dizziness). A numerically higher proportion of patients on lacosamide than carbamazepine-CR completed 6 months (22 [81.5%]; 20 [58.8%]) and 12 months (18 [66.7%]; 17 [50.0%]) treatment without seizure at last evaluated dose. In the conversion to monotherapy trial, 26/30 (86.7%) patients with CVEE reported TEAEs, most commonly (≥4 patients) dizziness, convulsion, fatigue, headache, somnolence, and cognitive disorder. During lacosamide monotherapy, 17 (56.7%) patients were 50% responders and six (20.0%) were seizure-free. In the observational study, 36/83 (43.4%) patients with CVEE reported TEAEs, most commonly (≥5%) fatigue and dizziness. Effectiveness was assessed for 75 patients. During the last 3 months, 60 (80%) were 50% responders and 42 (56.0%) were seizure-free. CONCLUSIONS: These exploratory post hoc analyses suggested lacosamide was generally well tolerated and effective in patients with CVEE, with data from the initial monotherapy trial suggesting numerically better efficacy than carbamazepine-CR.

Long-term safety and efficacy of lacosamide and controlled-release carbamazepine monotherapy in patients with newly diagnosed epilepsy.

OBJECTIVE: A large-scale, double-blind trial (SP0993; NCT01243177) demonstrated that lacosamide was noninferior to controlled-release carbamazepine (carbamazepine-CR) in terms of efficacy, and well tolerated as first-line monotherapy in patients (≥16 years of age) with newly diagnosed epilepsy. We report primary safety outcomes from the double-blind extension of the noninferiority trial (SP0994; NCT01465997) and post hoc analyses of pooled long-term safety and efficacy data from both trials. METHODS: Patients were randomized 1:1 to lacosamide or carbamazepine-CR. Doses were escalated (lacosamide: 200/400/600 mg/d; carbamazepine-CR: 400/800/1200 mg/d) based on seizure control. Eligible patients continued randomized treatment in the extension. Primary outcomes of the extension were treatment-emergent adverse events (TEAEs), serious TEAEs, and discontinuations due to TEAEs. Post hoc analyses of data from combined trials included 12- and 24-month seizure freedom and TEAEs by number of comorbid conditions. RESULTS: A total of 886 patients were treated in the initial trial and 548 in the extension; 211 of 279 patients (75.6%) on lacosamide and 180/269 (66.9%) on carbamazepine-CR completed the extension. In the extension, 181 patients (64.9%) on lacosamide and 182 (67.7%) on carbamazepine-CR reported TEAEs; in both groups, nasopharyngitis, headache, and dizziness were most common. Serious TEAEs were reported by 32 patients (11.5%) on lacosamide and 22 (8.2%) on carbamazepine-CR; 12 (4.3%) and 21 (7.8%) discontinued due to TEAEs. In the combined trials (median exposure: lacosamide 630 days; carbamazepine-CR 589 days), Kaplan-Meier estimated proportions of patients with 12- and 24-month seizure freedom from first dose were 50.8% (95% confidence interval 46.2%-55.4%) and 47.0% (42.2%-51.7%) on lacosamide, and 54.9% (50.3%-59.6%) and 50.9% (46.0%-55.7%) on carbamazepine-CR. Incidences of drug-related TEAEs and discontinuations due to TEAEs increased by number of comorbid conditions and were lower in patients on lacosamide. SIGNIFICANCE: Long-term (median ~2 years) lacosamide monotherapy was efficacious and generally well tolerated in adults with newly diagnosed epilepsy. Seizure freedom rates were similar with lacosamide and carbamazepine-CR.

Nalmefene, Given as Needed, in the Routine Treatment of Patients with Alcohol Dependence: An Interventional, Open-Label Study in Primary Care.

AIMS: This 12-week, open-label, primary care study (NCT02195817) evaluated the efficacy and safety of nalmefene, taken as needed, to reduce alcohol consumption in adults with a diagnosis of alcohol dependence and drinking at least at high drinking risk levels (DRL, > 60 g/day for men, > 40 g/day for women). METHODS: Following the Screening Visit, patients recorded their daily alcohol consumption for 2 weeks. Patients were then categorised by their self-reported drinking levels; those who maintained at least a high DRL in the 2-week period were included in Cohort-A, and those who reduced their alcohol consumption below high DRL were included in Cohort-B. Cohort-A received simple psychosocial interventions and were supplied with nalmefene 18 mg to be taken on days when they perceived a risk of drinking alcohol. Patients in Cohort-B received a simple psychosocial intervention and were treated per normal practice. RESULTS: Of the 378 enrolled patients, 330 were included in Cohort-A and 48 in Cohort-B. For patients in Cohort-A, the mean change from screening to Week-12 in the number of heavy drinking days/month was -13.1 days/month (95% CI -14.4 to -11.9, p < 0.0001). Overall, 55% of patients reduced their DRL by ≥2 risk levels and 44% of patients reduced to a low DRL. The most common adverse events were nausea (18.3%) and dizziness (17.7%). Patients in Cohort-B maintained their lower level alcohol consumption at the 12-week follow-up. CONCLUSIONS: Patients with alcohol dependence treated in primary care with nalmefene, taken as needed, in conjunction with simple psychosocial support, significantly reduced their alcohol consumption. Treatment was well tolerated.

Nalmefene Reduces Reward Anticipation in Alcohol Dependence: An Experimental Functional Magnetic Resonance Imaging Study.

BACKGROUND: Nalmefene is a µ and δ opioid receptor antagonist, κ opioid receptor partial agonist that has recently been approved in Europe for treating alcohol dependence. It offers a treatment approach for alcohol-dependent individuals with "high-risk drinking levels" to reduce their alcohol consumption. However, the neurobiological mechanism underpinning its effects on alcohol consumption remains to be determined. Using a randomized, double-blind, placebo-controlled, within-subject crossover design we aimed to determine the effect of a single dose of nalmefene on striatal blood oxygen level-dependent (BOLD) signal change during anticipation of monetary reward using the monetary incentive delay task following alcohol challenge. METHODS: Twenty-two currently heavy-drinking, non-treatment-seeking alcohol-dependent males were recruited. The effect of single dose nalmefene (18 mg) on changes in a priori defined striatal region of interest BOLD signal change during reward anticipation compared with placebo was investigated using functional magnetic resonance imaging. Both conditions were performed under intravenous alcohol administration (6% vol/vol infusion to achieve a target level of 80 mg/dL). RESULTS: Datasets from 18 participants were available and showed that in the presence of the alcohol infusion, nalmefene significantly reduced the BOLD response in the striatal region of interest compared with placebo. Nalmefene did not alter brain perfusion. CONCLUSIONS: Nalmefene blunts BOLD response in the mesolimbic system during anticipation of monetary reward and an alcohol infusion. This is consistent with nalmefene's actions on opioid receptors, which modulate the mesolimbic dopaminergic system, and provides a neurobiological basis for its efficacy.

Distinct Effects of Nalmefene on Dopamine Uptake Rates and Kappa Opioid Receptor Activity in the Nucleus Accumbens Following Chronic Intermittent Ethanol Exposure.

The development of pharmacotherapeutics that reduce relapse to alcohol drinking in patients with alcohol dependence is of considerable research interest. Preclinical data support a role for nucleus accumbens (NAc) κ opioid receptors (KOR) in chronic intermittent ethanol (CIE) exposure-induced increases in ethanol intake. Nalmefene, a high-affinity KOR partial agonist, reduces drinking in at-risk patients and relapse drinking in rodents, potentially due to its effects on NAc KORs. However, the effects of nalmefene on accumbal dopamine transmission and KOR function are poorly understood. We investigated the effects of nalmefene on dopamine transmission and KORs using fast scan cyclic voltammetry in NAc brain slices from male C57BL/6J mice following five weeks of CIE or air exposure. Nalmefene concentration-dependently reduced dopamine release similarly in air and CIE groups, suggesting that dynorphin tone may not be present in brain slices. Further, nalmefene attenuated dopamine uptake rates to a greater extent in brain slices from CIE-exposed mice, suggesting that dopamine transporter-KOR interactions may be fundamentally altered following CIE. Additionally, nalmefene reversed the dopamine-decreasing effects of a maximal concentration of a KOR agonist selectively in brain slices of CIE-exposed mice. It is possible that nalmefene may attenuate withdrawal-induced increases in ethanol consumption by modulation of dopamine transmission through KORs.

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

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

Discovery and development of 11C-Lu AE92686 as a radioligand for PET imaging of phosphodiesterase10A in the brain.

UNLABELLED: Phosphodiesterase 10A (PDE10A) plays a key role in the regulation of brain striatal signaling, and several pharmaceutical companies currently investigate PDE10A inhibitors in clinical trials for various central nervous system diseases. A PDE10A PET ligand may provide evidence that a clinical drug candidate reaches and binds to the target. Here we describe the successful discovery and initial validation of the novel radiolabeled PDE10A ligand 5,8-dimethyl-2-[2-((1-(11)C-methyl)-4-phenyl-1H-imidazol-2-yl)-ethyl]-[1,2,4]triazolo[1,5-a]pyridine ((11)C-Lu AE92686) and its tritiated analog (3)H-Lu AE92686. METHODS: Initial in vitro experiments suggested Lu AE92686 as a promising radioligand, and the corresponding tritiated and (11)C-labeled compounds were synthesized. (3)H-Lu AE92686 was evaluated as a ligand for in vivo occupancy studies in mice and rats, and (11)C-Lu AE92686 was evaluated as a PET tracer candidate in cynomolgus monkeys and in humans. RESULTS: (11)C-Lu AE92686 displayed high specificity and selectivity for PDE10A-expressing regions in the brain of cynomolgus monkeys and humans. Similar results were found in rodents using (3)H-Lu AE92686. The binding of (11)C-Lu AE92686 and (3)H-Lu AE92686 to striatum was completely and dose-dependently blocked by the structurally different PDE10A inhibitor 2-[4-(1-methyl-4-pyridin-4-yl-1H-pyrazol-3-yl)-phenoxymethyl]-quinoline (MP-10) in rodents and in monkeys. In all species, specific binding of the radioligand was seen in the striatum but not in the cerebellum, supporting the use of the cerebellum as a reference region. The binding potentials (BPND) of (11)C-Lu AE92686 in the striatum of both cynomolgus monkeys and humans were evaluated by the simplified reference tissue model with the cerebellum as the reference tissue, and BPND was found to be high and reproducible-that is, BPNDs were 6.5 ± 0.3 (n = 3) and 7.5 ± 1.0 (n = 12) in monkeys and humans, respectively. CONCLUSION: Rodent, monkey, and human tests of labeled Lu AE92686 suggest that (11)C-Lu AE92686 has great potential as a human PET tracer for the PDE10A enzyme.

Auditory sensory processing deficits in sensory gating and mismatch negativity-like responses in the social isolation rat model of schizophrenia.

Patients with schizophrenia exhibit disturbances in information processing. These disturbances can be investigated with different paradigms of auditory event related potentials (ERP), such as sensory gating in a double click paradigm (P50 suppression) and the mismatch negativity (MMN) component in an auditory oddball paradigm. The aim of the current study was to test if rats subjected to social isolation, which is believed to induce some changes that mimic features of schizophrenia, displays alterations in sensory gating and MMN-like response. Male Lister-Hooded rats were separated into two groups; one group socially isolated (SI) for 8 weeks and one group housed (GH). Both groups were then tested in a double click sensory gating paradigm and an auditory oddball paradigm (MMN-like) paradigm. It was observed that the SI animals showed reduced sensory gating of the cortical N1 amplitude. Furthermore, the SI animals showed significant reduction in cortical MMN-like response compared with the GH animals. No deficits in sensory gating or MMN-like response were observed in the hippocampus (CA3) of the SI animals compared with GH animals. In conclusion, the change in sensory gating of the N1 amplitude supports previous findings in SI rats and the reduced MMN-like response is similar to the deficits of MMN seen in patients with schizophrenia. Since reduced auditory MMN amplitude is believed to be more selectively associated with schizophrenia than other measures of sensory gating deficits, the current study supports the face validity of the SI reared rat model for schizophrenia.

Identification of a new series of non-peptidic NK3 receptor antagonists.

The identification and structure-activity relationships of 2-aminomethyl-1-aryl cyclopropane carboxamides as novel NK(3) receptor antagonists are reported. The compound series was optimized to give analogues with low nanomolar binding to the NK(3) receptor and brain exposure, leading to activity in vivo in the senktide-induced hypoactivity model in gerbils.

Pharmacological characterization of social isolation-induced hyperactivity.

RATIONALE: Social isolation (SI) of rats directly after weaning is a non-pharmacological, non-lesion animal model based on the neurodevelopmental hypothesis of schizophrenia. The model causes several neurobiological and behavioral alterations consistent with observations in schizophrenia. OBJECTIVES: In the present study, we evaluated if isolated rats display both a pre-pulse inhibition (PPI) deficit and hyperactivity. Furthermore, the sensitivity of SI hyperactivity to antipsychotic was evaluated. METHODS: Rats were socially isolated or group-housed for 12 weeks starting on postnatal day 25. In one batch of animals, the PPI and hyperactivity response were repeatedly compared. Furthermore, we investigated the robustness of the SI-induced hyperactivity by testing close to 50 batches of socially isolated or group-housed rats and tested the sensitivity of the assay to first- and second-generation antipsychotics, haloperidol, olanzapine, and risperidone, as well as the group II selective metabotrobic glutamate receptor agonist (LY404039). RESULTS: Socially isolated rats showed a minor PPI deficit and a robust increase in hyperactivity compared with controls. Furthermore, SI-induced hyperactivity was selectively reversed by all antipsychotics, as well as the potential new antipsychotic, LY404039. CONCLUSION: SI-induced hyperactivity was more pronounced and robust, as compared with SI-induced PPI deficits. Furthermore, SI-induced hyperactivity might be predictive for antipsychotic efficacy, as current treatment was effective in the model. Finally, using LY404039, a compound in development against schizophrenia, we have shown that the hyperactivity assay is sensitive to potential novel mechanisms of action. Thus, SI-induced hyperactivity might be a robust and novel in vivo screening assay of antipsychotic efficacy.

Socially isolated rats exhibit changes in dopamine homeostasis pertinent to schizophrenia.

Post-weaning social isolation of rats produces an array of behavioral and neurochemical changes indicative of altered dopamine function. It has therefore been suggested that post-weaning social isolation mimics some aspects of schizophrenia. Here we replicate and extent these findings to include an investigation of prefrontal cortical dopamine dynamics using in vivo microdialysis. Social isolation for 12 weeks after weaning caused increased locomotor activity in response to novelty and amphetamine challenge. In vivo microdialysis experiments revealed that while social isolation did not change basal dopamine levels in the nucleus accumbens, it did cause a significant reduction of basal dopamine release in the prefrontal cortex. In addition, social isolation lead to a significantly larger dopamine response to an amphetamine challenge, in both the nucleus accumbens and the prefrontal cortex compared to group housed controls. Taken together, these results indicate that post-weaning social isolation alters dopaminergic function with changes resembling subcortical hyperdopaminergia and prefrontal hypodopaminergia similar to what has been observed in schizophrenic patients.

Novel NK(3) receptor antagonists for the treatment of schizophrenia and other CNS indications.

The cloning of the three tachykinin receptors in the late 1980s formed the basis of intense preclinical research efforts into the systems relating to the tachykinin receptors, as well as compound screening campaigns. Remarkably, orally active non-peptide antagonists were successfully identified for all three of the tachykinin receptors, providing tools for further evaluation of the pharmacology of these receptor systems. The NK3 receptor (mammalian tachykinin receptor 3), which exhibited a discrete expression pattern and the modulatory regulation of various transmitter systems in the CNS, has attracted significant interest. Preclinical studies demonstrated that the NK3 receptor might be a promising target for CNS disorders, and clinical trials with non-peptide NK3 receptor antagonists have been performed for indications such as schizophrenia, major depressive disorder, panic attacks and Parkinson's disease. In particular, the positive results of the schizophrenia meta-trial with osanetant increased the focus on the NK3 receptor system and its clinical potential. Consequently, a significant number of patents covering non-peptide antagonists for the NK3 receptor have been published during the past decade. This review describes the most recent NK3 receptor antagonists (published from 2004 to 2009), which are classified into seven unique templates.

Increased dopaminergic activity in socially isolated rats: an electrophysiological study.

The development of animal models mimicking symptoms associated with schizophrenia has been a critical step in understanding the neurobiological mechanisms underlying the disease. Long-term social isolation from weaning in rodents, a model based on the neurodevelopmental hypothesis of schizophrenia, has been suggested to mimic some of the deficits seen in schizophrenic patients. We confirm in the present study that socially isolated rats display an increase in both spontaneous and d-amphetamine-induced locomotor activity, as well as deficits in sensorimotor gating as assessed in a pre-pulse inhibition paradigm. In addition, in vivo electrophysiological studies revealed changes in dopaminergic cell firing activity in the ventral tegmental area of isolated rats when compared to group-housed controls. These alterations include an increase in the number of spontaneously active dopaminergic neurons, and a change of firing activity towards a more irregular and bursting firing pattern. Taken together, our findings suggest that the behavioral phenotype induced by social isolation may be driven by an overactive dopamine system.

Stereological brain volume changes in post-weaned socially isolated rats.

Rearing rats in isolation after weaning is an environmental manipulation that leads to behavioural and neurochemical alterations that resemble what is seen in schizophrenia. The model is neurodevelopmental in origin and has been used as an animal model of schizophrenia. However, only a few studies have evaluated the neuroanatomical changes in this animal model in comparison to changes seen in schizophrenia. In this study, we applied stereological volume estimates to evaluate the total brain, the ventricular system, and the pyramidal and granular cell layers of the hippocampus in male and female Lister Hooded rats isolated from postnatal day 25 for 15 weeks. We observed the expected gender differences in total brain volume with males having larger brains than females. Further, we found that isolated males had significantly smaller brains than group-housed controls and larger lateral ventricles than controls. However, this was not seen in female rats. Isolated males had a significant smaller hippocampus, dentate gyrus and CA2/3 where isolated females had a significant smaller CA1 compared to controls. Thus, our results indicate that long-term isolation of male rats leads to neuroanatomical changes corresponding to those seen in schizophrenia.

Phosphodiesterase 10A inhibition modulates the sensitivity of the mesolimbic dopaminergic system to D-amphetamine: involvement of the D1-regulated feedback control of midbrain dopamine neurons.

Phosphodiesterase (PDE) 10A is highly expressed in medium spiny neurons of the striatum, at the confluence of the corticostriatal glutamatergic and the midbrain dopaminergic pathways, both believed to be involved in the physiopathology of schizophrenia. There is a growing body of evidence suggesting that targeting PDE10A may be beneficial for the treatment of positive symptoms in schizophrenia. The aim of the present study was to investigate how PDE10A inhibition modulates mesolimbic dopaminergic neurotransmission. We found that the selective PDE10A inhibitor, MP-10, blocked D-amphetamine-induced hyperactivity as well as D-amphetamine-induced dopamine efflux in the nucleus accumbens in a dose-dependent manner. We further investigated the mechanism by which PDE10A inhibition affects dopaminergic neurotransmission. We report that MP-10 potentiated the effect of a high but not a low dose of D-amphetamine on the mean firing rate of dopaminergic neurons recorded from the ventral tegmental area. Similarly, the effect of a high, but not a low dose of D-amphetamine, was completely reversed by the selective D(1) antagonist, SCH23390. These data suggest that the D(1)-regulated feedback control of midbrain dopamine neurons is a critical pathway involved in the modulation of the response of mesolimbic dopamine neurons to D-amphetamine by PDE10A inhibition.

Different function of pedunculopontine GABA and glutamate receptors in nucleus accumbens dopamine, pedunculopontine glutamate and operant discriminative behavior.

The nucleus accumbens, as the main input structure of the ventral basal ganglia loop, is described as a limbic-motor interface. Dopamine input to nucleus accumbens modulates processing of concurrent glutamate input from limbic structures carrying motor and motivational information. There is evidence that these dopamine/glutamate interactions are fundamentally involved in response selection processes. However, the pedunculopontine tegmental nucleus (PPTg) in the brainstem is connected with limbic structures as well as dopaminergic midbrain areas, which also project to the nucleus accumbens. Furthermore, behavioral studies implicate the PPTg in complex, motivated behavior. Thus, the PPTg might be involved in motivated behavior by influencing response selection processes in the nucleus accumbens. In this study we used in vivo microdialysis in freely moving rats in order to inhibit (100, 200, 300 and 400 microm baclofen) or stimulate [5, 12.5, 25 or 50 micromalpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA)] the PPTg in animals that are performing an operant discrimination task for food reward. The behavioral consequences were correlated with dopamine and glutamate levels in nucleus accumbens and PPTg, respectively. PPTg inhibition by local GABAB receptors impaired the response rate and accuracy of performance in the operant discrimination task. PPTg stimulation by local AMPA receptors exclusively impaired the response rate. Both treatments blocked the performance-driven dopamine signal in nucleus accumbens, whereas glutamate in PPTg was enhanced after AMPA administration only. The data indicate that the PPTg functionally participates in a network of subcortical and cortical structures, which is responsible for the execution of motivated behavior and response selection processes.

Noradrenaline transmission within the ventral bed nucleus of the stria terminalis is critical for fear behavior induced by trimethylthiazoline, a component of fox odor.

The bed nucleus of the stria terminalis (BNST) is involved in the mediation of fear behavior in rats. A previous study of our laboratory demonstrated that temporary inactivation of the BNST blocks fear behavior induced by exposure to trimethylthiazoline (TMT), a component of fox odor. The present study investigates whether noradrenaline release within the BNST is critical for TMT-induced fear behavior. First, we confirmed previous studies showing that the ventral BNST is the part of the BNST that receives the densest noradrenaline innervation. Second, using in vivo microdialysis, we showed that noradrenaline release within the BNST is strongly increased during TMT exposure, and that this increase can be blocked by local infusions of the alpha2-receptor blocker clonidine. Third, using intracerebral injections, we showed that clonidine injections into the ventral BNST, but not into neighboring brain sites, completely blocked TMT-induced potentiation of freezing behavior. The present data clearly show that the noradrenergic innervation of the ventral BNST is important for the full expression of behavioral signs of fear to the predator odor TMT.