Direct enhancement of hippocampal dopamine or serotonin levels as a pharmacodynamic measure of combined antidepressant-anticonvulsant action

Sex and age differences in social and cognitive function in offspring exposed to late gestational hypoxia

BACKGROUND

Gestational sleep apnea is a hypoxic sleep disorder that affects 8-26% of pregnancies and increases the risk for central nervous system dysfunction in offspring. Specifically, there are sex differences in the sensitivity of the fetal hippocampus to hypoxic insults, and hippocampal impairments are associated with social dysfunction, repetitive behaviors, anxiety, and cognitive impairment. Yet, it is unclear whether gestational sleep apnea impacts these hippocampal-associated functions and if sex and age modify these effects. To examine the relationship between gestational sleep apnea and hippocampal-associated behaviors, we used chronic intermittent hypoxia (CIH) to model late gestational sleep apnea in pregnant rats. We hypothesized that late gestational CIH would produce sex- and age-specific social, anxiety-like, repetitive, and cognitive impairments in offspring.

METHODS

Timed pregnant Long-Evans rats were exposed to CIH or room air normoxia from GD 15-19. Behavioral testing of offspring occurred during either puberty or young adulthood. To examine gestational hypoxia-induced behavioral phenotypes, we quantified hippocampal-associated behaviors (social function, repetitive behaviors, anxiety-like behaviors, and spatial memory and learning), hippocampal neuronal activity (glutamatergic NMDA receptors, dopamine transporter, monoamine oxidase-A, early growth response protein 1, and doublecortin), and circulating hormones in offspring.

RESULTS

Late gestational CIH induced sex- and age-specific differences in social, repetitive, and memory functions in offspring. In female pubertal offspring, CIH impaired social function, increased repetitive behaviors, and elevated circulating corticosterone levels but did not impact memory. In contrast, CIH transiently induced spatial memory dysfunction in pubertal male offspring but did not impact social or repetitive functions. Long-term effects of gestational CIH on social behaviors were only observed in female offspring, wherein CIH induced social disengagement and suppression of circulating corticosterone levels in young adulthood. No effects of gestational CIH were observed in anxiety-like behaviors, hippocampal neuronal activity, or circulating testosterone and estradiol levels, regardless of sex or age of offspring.

CONCLUSIONS

Our results indicate that hypoxia-associated pregnancy complications during late gestation can increase the risk for behavioral and physiological outcomes in offspring, such as social dysfunction, repetitive behaviors, and cognitive impairment, that are dependent on sex and age.

Persistent extrasynaptic hyperdopaminergia in the mouse hippocampus induces plasticity and recognition memory deficits reversed by the atypical antipsychotic sulpiride

Evidence suggests that subcortical hyperdopaminergia alters cognitive function in schizophrenia and antipsychotic drugs (APD) fail at rescuing cognitive deficits in patients. In a previous study, we showed that blocking D2 dopamine receptors (D2R), a core action of APD, led to profound reshaping of mesohippocampal fibers, deficits in synaptic transmission and impairments in learning and memory in the mouse hippocampus (HP). However, it is currently unknown how excessive dopamine affects HP-related cognitive functions, and how APD would impact HP functions in such a state. After verifying the presence of DAT-positive neuronal projections in the ventral (temporal), but not in the dorsal (septal), part of the HP, GBR12935, a blocker of dopamine transporter (DAT), was infused in the CA1 of adult C57Bl/6 mice to produce local hyperdopaminergia. Chronic GBR12935 infusion in temporal CA1 induced a mild learning impairment in the Morris Water Maze and abolished long-term recognition memory in novel-object (NORT) and object-place recognition tasks (OPRT). Deficits were accompanied by a significant decrease in DAT+ mesohippocampal fibers. Intrahippocampal or systemic treatment with sulpiride during GBR infusions improved the NORT deficit but not that of OPRT. In vitro application of GBR on hippocampal slices abolished long-term depression (LTD) of fEPSP in temporal CA1. LTD was rescued by co-application with sulpiride. In conclusion, chronic DAT blockade in temporal CA1 profoundly altered mesohippocampal modulation of hippocampal functions. Contrary to previous observations in normodopaminergic mice, antagonising D2Rs was beneficial for cognitive functions in the context of hippocampal hyperdopaminergia.

Sex and age differences in social and cognitive function in offspring exposed to late gestational hypoxia

Background

Gestational sleep apnea affects 8-26% of pregnancies and can increase the risk for autism spectrum disorder (ASD) in offspring. ASD is a neurodevelopmental disorder associated with social dysfunction, repetitive behaviors, anxiety, and cognitive impairment. To examine the relationship between gestational sleep apnea and ASD-associated behaviors, we used a chronic intermittent hypoxia (CIH) protocol between gestational days (GD) 15-19 in pregnant rats to model late gestational sleep apnea. We hypothesized that late gestational CIH would produce sex- and age-specific social, mood, and cognitive impairments in offspring.

Methods

Timed pregnant Long-Evans rats were exposed to CIH or room air normoxia from GD 15-19. Behavioral testing of offspring occurred during either puberty or young adulthood. To examine ASD-associated phenotypes, we quantified ASD-associated behaviors (social function, repetitive behaviors, anxiety-like behaviors, and spatial memory and learning), hippocampal activity (glutamatergic NMDA receptors, dopamine transporter, monoamine oxidase-A, EGR-1, and doublecortin), and circulating hormones in offspring.

Results

Late gestational CIH induced sex- and age-specific differences in social, repetitive and memory functions in offspring. These effects were mostly transient and present during puberty. In female pubertal offspring, CIH impaired social function, increased repetitive behaviors, and increased circulating corticosterone levels, but did not impact memory. In contrast, CIH transiently induced spatial memory dysfunction in pubertal male offspring but did not impact social or repetitive functions. Long-term effects of gestational CIH were only observed in female offspring, wherein CIH induced social disengagement and suppression of circulating corticosterone levels in young adulthood. No effects of gestational CIH were observed on anxiety-like behaviors, hippocampal activity, circulating testosterone levels, or circulating estradiol levels, regardless of sex or age of offspring.

Conclusions

Our results indicate that hypoxia-associated pregnancy complications during late gestation can increase the risk for ASD-associated behavioral and physiological outcomes, such as pubertal social dysfunction, corticosterone dysregulation, and memory impairments.

The Role of the Dopamine System in Post-Stroke Mood Disorders in Newborn Rats

Post-stroke mood disorders (PSMD) affect disease prognosis in adults. Adult rodent models underlie the importance of the dopamine (DA) system in PSMD pathophysiology. There are no studies on PSMD after neonatal stroke. We induced neonatal stroke in 7-day-old (P7) rats by temporal left middle cerebral artery occlusion (MCAO). Performance in the tail suspension test (TST) at P14 and the forced swimming test (FST) and open field test (OFT) at P37 were studied to assess PSMD. DA neuron density in the ventral tegmental area, brain DA concentration and DA transporter (DAT) expression as well as D2 receptor (D2R) expression and G-protein functional coupling were also studied. MCAO animals revealed depressive-like symptoms at P14 associated with decreased DA concentration and reduced DA neuron population and DAT expression. At P37, MCAO rats showed hyperactive behavior associated with increased DA concentration, normalization of DA neuron density and decreased DAT expression. MCAO did not modify D2R expression but reduced D2R functionality at P37. MCAO-induced depressive-like symptoms were reversed by the DA reuptake inhibitor GBR-12909. In conclusion, MCAO in newborn rats induced depressive-like symptoms and hyperactive behavior in the medium and long term, respectively, that were associated with alterations in the DA system.

Serotonergic therapy in epilepsy

PURPOSE OF REVIEW

The serotonergic system is implicated in multiple aspects of epilepsy, including seizure susceptibility, sudden unexpected death in epilepsy (SUDEP), and comorbid depression. Despite the complexity of serotonin's effects on various neuronal networks, ongoing research provides considerable insight into the role of serotonin in human epilepsy. This review explores the potential roles of serotonergic therapies to improve clinical outcomes in epilepsy.

RECENT FINDINGS

In recent decades, research has markedly increased our knowledge of the diverse effects of serotonin on brain function. Animal models of epilepsy have identified the influence of serotonin on seizure threshold in specific brain regions, serotoninergic augmentation's protective effects on terminal apnea and mortality in SUDEP, and mechanisms underlying behavioral improvement in some models of comorbid depression. Human clinical studies are largely consistent with animal data but the translation into definitive treatment decisions has moved less rapidly.

SUMMARY

Evidence for serotonergic therapy is promising for improvement in seizure control and prevention of SUDEP. For some epilepsies, such as Dravet syndrome, basic research on serotonin receptor agonists has translated into a positive clinical trial for fenfluramine. The cumulative results of safety and efficacy studies support the routine use of SSRIs for comorbid depression in epilepsy.

Post-weaning Social Isolated Flinders Sensitive Line Rats Display Bio-Behavioural Manifestations Resistant to Fluoxetine: A Model of Treatment-Resistant Depression

Treatment-resistant depression (TRD) complicates the management of major depression (MD). The underlying biology of TRD involves interplay between genetic propensity and chronic and/or early life adversity. By combining a genetic animal model of MD and post-weaning social isolation rearing (SIR), we sought to produce an animal that displays more severe depressive- and social anxiety-like manifestations resistant to standard antidepressant treatment. Flinders Sensitive Line (FSL) pups were social or isolation reared from weaning [postnatal day (PND) 21], receiving fluoxetine (FLX) from PND 63 (10 mg/kg × 14 days), and compared to Sprague Dawley (SD) controls. Depressive-, anxiety-like, and social behaviour were assessed from PND 72 in the forced swim test (FST) and social interaction test (SIT). Post-mortem cortico-hippocampal norepinephrine (NE), serotonin (5-HT), and dopamine (DA), as well as plasma interleukin 6 (IL-6), tumour necrosis factor alpha (TNF-α), corticosterone (CORT), and dopamine-beta-hydroxylase (DBH) levels were assayed. FSL rats displayed significant cortico-hippocampal monoamine disturbances, and depressive- and social anxiety-like behaviour, the latter two reversed by FLX. SIR-exposed FSL rats exhibited significant immobility in the FST and social impairment which were, respectively, worsened by or resistant to FLX. In SIR-exposed FSL rats, FLX significantly raised depleted NE and 5-HT, significantly decreased DBH and caused a large effect size increase in DA and decrease in CORT and TNF-α. Concluding, SIR-exposed FSL rats display depressive- and social anxiety-like symptoms that are resistant to, or worsened by, FLX, with reduced plasma DBH and suppressed cortico-hippocampal 5-HT, NE and DA, all variably altered by FLX. Exposure of a genetic animal model of MD to post-weaning SIR results in a more intractable depressive-like phenotype as well as changes in TRD-related biomarkers, that are resistant to traditional antidepressant treatment. Given the relative absence of validated animal models of TRD, these findings are especially promising and warrant study, especially further predictive validation.

GPCR-Based Dopamine Sensors-A Detailed Guide to Inform Sensor Choice for In vivo Imaging

Understanding how dopamine (DA) encodes behavior depends on technologies that can reliably monitor DA release in freely-behaving animals. Recently, red and green genetically encoded sensors for DA (dLight, GRAB-DA) were developed and now provide the ability to track release dynamics at a subsecond resolution, with submicromolar affinity and high molecular specificity. Combined with rapid developments in in vivo imaging, these sensors have the potential to transform the field of DA sensing and DA-based drug discovery. When implementing these tools in the laboratory, it is important to consider there is not a 'one-size-fits-all' sensor. Sensor properties, most importantly their affinity and dynamic range, must be carefully chosen to match local DA levels. Molecular specificity, sensor kinetics, spectral properties, brightness, sensor scaffold and pharmacology can further influence sensor choice depending on the experimental question. In this review, we use DA as an example; we briefly summarize old and new techniques to monitor DA release, including DA biosensors. We then outline a map of DA heterogeneity across the brain and provide a guide for optimal sensor choice and implementation based on local DA levels and other experimental parameters. Altogether this review should act as a tool to guide DA sensor choice for end-users.

Effect of catechol-O-methyltransferase Val(108/158)Met polymorphism on antidepressant efficacy of fluvoxamine

Rationale

The catechol-O-methyltransferase (COMT) enzyme inactivates catecholamines, and the COMT Val(108/158)Met polymorphism (rs4680) influences the enzyme activity. Recent clinical studies found a significant effect of rs4680 on antidepressant response to fluoxetine and paroxetine, but several other studies were negative. No study considered drug plasma levels as possible nuisance covariate.

Objectives

We studied the effect of rs4680 on response to fluvoxamine antidepressant monotherapy.

Patients and methods

Forty-one consecutively admitted inpatients affected by a major depressive episode in course of major depressive disorder were administered fluvoxamine for 6 weeks. Changes in severity of depression were assessed with weekly Hamilton Depression ratings and analyzed with repeated measures ANOVA in the context of General Linear Model, with rs4680 and fluvoxamine plasma levels as factors.

Results

rs4680 significantly interacted with time in affecting antidepressant response to fluvoxamine, with outcome being inversely proportional to the enzyme activity: better effects in Met-carriers, worse effects in Val/Val homozygotes. The effect became significant at the fourth week of treatment, and influence final response rates. Fluvoxamine plasma levels had marginal effects on outcome.

Conclusions

This is the first study that reports a positive effect of rs4680 on response to fluvoxamine, and the third independent report of its influence on response to selective 5-HT reuptake inhibitors (SSRIs). Our findings support the hypothesis that factors affecting catecholaminergic neurotransmission might contribute to shape the individual response to antidepressants irrespective of their primary molecular target.

Long-Term Treatment with Fluvoxamine Decreases Nonmotor Symptoms and Dopamine Depletion in a Postnatal Stress Rat Model of Parkinson's Disease

Nonmotor symptoms (NMS) such as anxiety, depression, and cognitive deficits are frequently observed in Parkinson's disease (PD) and precede the onset of motor symptoms by years. We have recently explored the short-term effects of Fluvoxamine, a selective serotonin reuptake inhibitor (SSRI) on dopaminergic neurons in a parkinsonian rat model. Here, we report the long-term effects of Fluvoxamine, on early-life stress-induced changes in the brain and behavior. We specifically evaluated the effects of Fluvoxamine on brain mechanisms that contribute to NMS associated with PD in a unilateral 6-hydroxydopamine-lesioned rat model. A 14-day early postnatal maternal separation protocol was applied to model early-life stress followed by unilateral intracerebral infusion of 6-hydroxydopamine (6-OHDA) to model aspects of parkinsonism in rats. The anxiolytic, antidepressant, and cognitive effects of Fluvoxamine were confirmed using the elevated plus-maze (EPM) test, sucrose preference test (SPT), and Morris water maze (MWM) test. Further to that, our results showed that animals exposed to early-life stress displayed increased plasma corticosterone and malondialdehyde (MDA) levels which were attenuated by Fluvoxamine treatment. A 6-OHDA lesion effect was evidenced by impairment in the limb-use asymmetry test as well as decreased dopamine (DA) and serotonin levels in the striatum, prefrontal cortex, and hippocampus. These effects were surprisingly attenuated by Fluvoxamine treatment in all treated rats. This study is the first to suggest that early and long-term treatment of neuropsychological diseases with Fluvoxamine may decrease the vulnerability of dopaminergic neurons that degenerate in the course of PD.

In vivo metabotropic glutamate receptor 5 availability-associated functional connectivity alterations in drug-naïve young adults with major depression

There has been increasing interest in glutamatergic neurotransmission as a putative underlying mechanism of depressive disorders. We performed [¹¹C]ABP688 positron emission tomography (PET) and resting-state functional magnetic resonance imaging (rs-fMRI) in drug-naïve young adult patients with major depression to examine alterations in metabotropic glutamate receptor-5 (mGluR5) availability, and to investigate their functional significance relating to neural systems-level changes in major depression. Sixteen psychotropic drug-naïve patients with major depression without comorbidity (median age: 22.8 years) and fifteen matched healthy controls underwent [¹¹C]ABP688 PET imaging and 3-T MRI. For mGluR5 availability, we quantified [¹¹C]ABP688 binding potential (BP_ND) using the simplified reference tissue model. Seed-based functional connectivity analysis was performed using rs-fMRI data with regions derived from quantitative [¹¹C]ABP688 PET analysis as seeds. In region-of-interest (ROI)-based and voxel-based analyses, the [¹¹C]ABP688 BP_ND was significantly lower in patients than in controls in the prefrontal cortex ROI and in voxel clusters within the prefrontal, temporal, and parietal cortices, and supramarginal gyrus. The [¹¹C]ABP688 BP_ND seed-based functional connectivity analysis showed significantly less negative connectivity from the inferior parietal cortex seed to the fusiform gyrus and inferior occipital cortex in patients than in controls. The correlation patterns between [¹¹C]ABP688 BP_ND and functional connectivity strength (β) for the superior prefrontal cortex seed were opposite in the depression and control groups. In conclusion, using a novel approach combining [¹¹C]ABP688 PET and rs-fMRI analyses, our study provides a first evidence of lower mGluR5 availability and related functional connectivity alterations in drug-naïve young adults with major depression without comorbidity.

Serotonin abnormalities in Dravet syndrome mice before and after the age of seizure onset

Dravet syndrome (DS) is a genetic form of severe epilepsy often associated with mutation of the SCN1A gene encoding the voltage gated sodium channel Nav1.1. Typically refractive to conventional therapy, serotonin neurotransmission may be an innovative target for treatment. To further understand the role of serotonin in this disorder, in this study we examined the state of the endogenous serotonin system in an Scn1a^+/- mouse model of DS. Examined at an age before seizures appear, we found the hypothermic effect of 5-HT_1A receptor agonist administration was attenuated. HPLC analysis of brain monoamine content revealed modestly reduced serotonin levels in tissue samples of the midbrain that included the dorsal raphe nucleus but no changes elsewhere in the brain. The reduced sensitivity to 5-HT_1A agonist administration seen at young ages reversed after the age of seizure development when mice showed an exaggerated hypothermic response. Likewise, adult DS mice showed a pronounced hypersensitivity to a 5-HT_2A/2C agonist. As adults however monoamine levels were not detectably altered. Thus there are alterations in the endogenous serotonin system that both precede and follow the appearance of seizure in DS mice, most strikingly in the response to agonist administration.

Inhibitor of Striatal-Enriched Protein Tyrosine Phosphatase, 8-(Trifluoromethyl)-1,2,3,4,5-Benzopentathiepin-6-Amine hydrochloride (TC-2153), Produces Antidepressant-Like Effect and Decreases Functional Activity and Protein Level of 5-HT2A Receptor in the Brain

The serotoninergic 5-HT_2A receptor is involved in the mechanism of depression and antidepressant drugs action. Earlier we showed that striatal-enriched protein tyrosine phosphatase (STEP) inhibitor - 8-(trifluoromethyl)-1,2,3,4,5-benzopentathiepin-6-amine hydrochloride (TC-2153) affects both the brain serotoninergic system and the brain-derived neurotropic factor that are known to be involved in the psychopathology of depression. In the present study we investigated the effects of chronic TC-2153 administration on behavior in the standard battery of tests as well as the effects of acute and chronic TC-2153 treatment on the brain 5-HT_2A receptors in mice. We obtained a prominent antidepressant-like effect of chronic TC-2153 treatment in the forced swim test without any adverse side effects on locomotor activity, anxiety, exploration, motor skill and obsessive-compulsive-like behavior. Moreover, both acute and chronic TC-2153 administration inhibited the functional activity of 5-HT_2A receptors estimated by the number of 2,5-dimethoxy-4-iodoamphetamine (DOI, agonist of 5-HT_2A receptors)-induced head-twitches. TC-2153 treatment also attenuated the DOI-induced c-fos expression in cortical and hippocampal neurons and reduced the 5-HT_2A receptor protein level in the hippocampus and frontal cortex, but not in the striatum. Taken together, our combined data demonstrate that the antidepressant effect of STEP inhibitor TC-2153 could be mediated by its inhibitory properties towards the 5-HT_2A receptor-mediated signaling.

The Impact and Mechanism of Methylated Metabotropic Glutamate Receptors 1 and 5 in the Hippocampus on Depression-Like Behavior in Prenatal Stress Offspring Rats

An increasing number of epidemiological investigations and animal models research suggest that prenatal stress (PS) could cause depression-like behavior in the offspring, which is sex specific. However, the underlying mechanisms remain to be elucidated. This study is to investigate the promoter methylation of metabotropic glutamate receptor 1 (mGluR1) and metabotropic Glutamate Receptor 5 (mGluR5) gene modification on PS induced depression-like behavior in offspring rats (OR). PS models were established, with or without 5-aza-2′-deoxycytidine (5-azaD, decitabine) treatment. Animal behavior was assessed by the sucrose preference test (SPT), forced swimming test (FST), and open field test (OFT). The mRNA and protein expression levels of mGluR1 and mGluR5 in the hippocampus of offspring were detected with quantitative real-time PCR and Western blot analysis, respectively. The promoter methylation in the hippocampus of mGluR1 and mGluR5 OR were also analyzed. SPT showed significantly reduced sucrose preference in PS induced OR. FST showed significantly prolonged immobility time in PS induced OR. OFT showed significantly reduced central residence time in PS induced OR and no significantly influence in rearing as well as in frequency of micturition. Moreover, the mRNA, protein expression levels, and gene promoter methylation level of mGluR1 and mGluR5 in the hippocampus were significantly increased in the PS induced male OR, while no significantly influence in the PS induced female OR. Furthermore, the PS induced effects in male OR could be reversed by the microinjection of 5-azaD. In conclusion, our results showed that the promoter methylation of mGluR1 and mGluR5 gene modification is only involved in PS induced depression-like behavior in male OR in a sex-specific manner. These findings might contribute to the understanding of the disease pathogenesis and clinical treatment in future.

Outside the box: Medications worth considering when traditional antiepileptic drugs have failed

PURPOSE

Review and discuss medications efficacious for seizure control, despite primary indications for other diseases, as treatment options in patients who have failed therapy with traditional antiepileptic drugs (AEDs).

METHODS

Literature searches were conducted utilizing PubMed and MEDLINE databases employing combinations of search terms including, but not limited to, "epilepsy", "refractory", "seizure", and the following medications: acetazolamide, amantadine, bumetanide, imipramine, lidocaine, verapamil, and various stimulants.

RESULTS

Data from relevant case studies, retrospective reviews, and available clinical trials were gathered, analyzed, and reported. Experience with acetazolamide, amantadine, bumetanide, imipramine, lidocaine, verapamil, and various stimulants show promise for cases of refractory epilepsy in both adults and children. Many medications lack large scale, randomized clinical trials, but the available data is informative when choosing treatment for patients that have failed traditional epilepsy therapies.

CONCLUSIONS

All neurologists have encountered a patient that failed nearly every AED, diet, and surgical option. For these patients, we often seek fortuitous discoveries within small series and case reports, hoping to find a treatment that might help the patient. In the present review, we describe medications for which antiepileptic effect has been ascribed after they were introduced for other indications.

mGlu1 receptor as a drug target for treatment of substance use disorders: time to gather stones together?

Modulation of the mGlu1 receptor was repeatedly shown to inhibit various phenomena associated with exposure to abused drugs. Efficacy in preclinical models was observed with both positive and negative allosteric modulators (PAMs and NAMs, respectively) using essentially non-overlapping sets of experimental methods. Taken together, these data indicate that the mGlu1 receptor certainly plays a significant role in the plasticity triggered by the exposure to abused drugs and is involved in the maintenance of drug-seeking and drug-taking behaviors. Understanding whether modulation of the mGlu1 receptor activity can also affect drug-seeking and drug-taking in humans could have a significant impact on the future development of medications in this field. We argue that the mGlu1 receptor NAMs have a significant value as potential tools for human experimental pharmacology that could help to validate methods used in preclinical research. Compared with the PAMs, the mGlu1 receptor NAMs appear to be better candidates for this role due to the following: (1) a number of highly potent, selective, and chemically diverse mGlu1 receptor NAMs to choose from; (2) availability of high-quality PET ligands to monitor target exposure; and (3) a rich pharmacological profile with a number of effects that can complement anti-addictive action (e.g., anxiolytic/antidepressant) and may also serve as additional pharmacodynamic readouts during the preclinical-to-clinical translation. We believe that the mGlu1 receptor NAMs have a significant value as potential tools for human experimental pharmacology that could help to validate methods used in preclinical research.

Evidence in support of using a neurochemistry approach to identify therapy for both epilepsy and associated depression

The present study aimed to develop a neurochemistry-based single or adjuvant therapy approach for comprehensive management of epilepsy and associated depression employing pentylenetetrazole-kindled animals. Kindling was induced in two-month-old male Swiss albino mice by administering a subconvulsant pentylenetetrazole dose (35mg/kg, i.p.) at an interval of 48±2h. These kindled animals were treated with saline and sodium valproate (300mg/kg/day, i.p.) for 15days. Except for the naïve group, all other groups were challenged with pentylenetetrazole (35mg/kg, i.p.) on days 5, 10, and 15 to evaluate the seizure severity. Depression was evaluated in all experimental groups after normalization of locomotor activity, using tail suspension and forced swim test on days 1, 5, 10, and 15. Four hours after behavioral evaluations on day 15, all animals were euthanized to collect their serum and discrete brain parts. Corticosterone levels were estimated in all the experimental groups as a marker of a dysregulated hypothalamus pituitary adrenal axis. Neurochemical alterations (norepinephrine, dopamine, tryptophan, kynurenine, serotonin, glutamate, GABA, and total nitrate levels) were also estimated in the cortical and hippocampal areas of the mouse brain. Results revealed that saline-treated kindled animals were associated with significant depression and altered neurochemical milieu in comparison with naïve animals. Chronic valproate treatment in kindled animals significantly reduced seizure severity score bud did not ameliorate associated depression or completely restore altered biochemical and neurochemical milieu. Based on the observation of neurochemical changes in all the groups, we propose that restoration of altered neurochemical milieu, elevated indoleamine 2,3-dioxygenase enzyme activity, and corticosterone levels using pharmacological tools with/out valproic acid may be explored for management of both epilepsy and comorbid depression.

Pharmacokinetic/pharmacodynamic considerations for epilepsy - depression comorbidities

INTRODUCTION

Epilepsy may be frequently associated with psychiatric disorders and its co-existence with depression usually results in the reduced quality of life of patients with epilepsy. Also, the efficacy of antiepileptic treatment in depressed patients with epilepsy may be significantly reduced.

AREAS COVERED

Results of experimental studies indicate that antidepressants co-administered with antiepileptic drugs may either increase their anticonvulsant activity, remain neutral or decrease the protective action of antiepileptic drugs in models of seizures. Apart from purely pharmacodynamic interactions, pharmacokinetic mechanisms have been proven to contribute to the final outcome. We report on clinical data regarding the pharmacokinetic interactions of enzyme-inducing antiepileptic drugs with various antidepressants, whose plasma concentration may be significantly reduced. On the other hand, antidepressants (especially selective serotonin reuptake inhibitors) may influence the metabolism of antiepileptics, in many cases resulting in the elevation of plasma concentration of antiepileptic drugs.

EXPERT OPINION

The preclinical data may provide valuable clues on how to combine these two groups of drugs - antidepressant drugs neutral or potentiating the anticonvulsant action of antiepileptics are recommended in this regard. Avoidance of antidepressants clearly decreasing the convulsive threshold or decreasing the anticonvulsant efficacy of antiepileptic drugs (f.e. bupropion or mianserin) in patients with epilepsy is recommended.

Adjuvant indoleamine 2,3-dioxygenase enzyme inhibition for comprehensive management of epilepsy and comorbid depression

Epilepsy is one of the major neurological disorders frequently associated with psychiatric disorders such as depression. Alteration of tryptophan metabolism towards kynurenine pathway may be one of the plausible reasons for association of depression in epilepsy. Hence, this study was envisaged to evaluate the dose dependent inhibition of indoleamine 2,3-dioxygenase (IDO) enzyme (responsible for shifting tryptophan metabolism) employing minocycline with valproic acid for comprehensive management of epilepsy and comorbid depression. Kindling was induced in male swiss albino mice by administration of pentylenetetrazole subconvulsive dose (35mg/kg, i.p.) at an interval of 48±2h. Kindled animals were treated with saline, valproate (300mg/kg/day i.p.), valproate in combination with different doses of minocycline (10mg/kg; 20mg/kg; 40mg/kg)/day i.p. and minocycline per se (40mg/kg/day i.p.) for 15 days. Except naïve, all the groups were challenged with pentylenetetrazole (35mg/kg i.p.) on day 5, 10, and 15 to evaluate the seizure severity score. Depression was evaluated in all experimental groups using tail suspension and forced swim test on days 1, 5, 10 and 15, 2h after pentylenetetrazole challenge. Results suggested that saline treated kindled animals were significantly associated with depression. Chronic valproate treatment significantly reduced seizure severity score but unable to ameliorate the associated depression. Minocycline supplementation with valproic acid dose dependently ameliorated depression associated with epilepsy. Neurochemical and biochemical findings also supported the behavioural findings of the study. Thus, our results suggested that supplementation of IDO enzyme inhibitors with valproic acid could be explored further for comprehensive management of epilepsy and associated depression.

Serotonin7 receptors in the lateral habenular nucleus regulate depressive-like behaviors in the hemiparkinsonian rats

Preclinical studies indicate that serotonin7 (5-HT7) receptors may regulate depressive-like behaviors. Depression is a common symptom in Parkinson's disease (PD); however, its pathophysiology is unclear. Here we examined whether 5-HT7 receptors in the lateral habenular nucleus (LHb) involve in the regulation of PD-related depression. Unilateral 6-hydroxydopamine lesions of the substantia nigra pars compacta in rats induced depressive-like responses as measured by the sucrose preference and forced swim tests when compared to sham-operated rats. Intra-LHb injection of 5-HT7 receptor agonist AS19 (1, 2 and 4μg/rat) induced or increased the expression of depressive-like behaviors in sham-operated and the lesioned rats. Further, intra-LHb injection of 5-HT7 receptor antagonist SB269970 (1.5, 3 and 6μg/rat) produced antidepressant effects in the two groups of rats. However, the doses producing these effects in the lesioned rats were higher than those in sham-operated rats. Neurochemical results showed that intra-LHb injection of AS19 (4μg/rat) decreased dopamine and 5-HT levels in the medial prefrontal cortex, habenula and hippocampus in sham-operated and the lesioned rats; whereas SB269970 (6μg/rat) increased dopamine and 5-HT levels in these structures. In addition, noradrenaline levels in these structures were not changed after intra-LHb injection of AS19 or SB269970 in the two groups of rats. These findings suggest that activation or blockade of 5-HT7 receptors in the LHb may change the activity of LHb glutamate neurons, and then decreases or increases dopamine and 5-HT levels in the limbic and limbic-related brain regions, which are involved in the regulation of depressive-like behaviors.

Effect of endurance training on seizure susceptibility, behavioral changes and neuronal damage after kainate-induced status epilepticus in spontaneously hypertensive rats

The therapeutic efficacy of regular physical exercises in an animal model of epilepsy and depression comorbidity has been confirmed previously. In the present study, we examined the effects of endurance training on susceptibility to kainate (KA)-induced status epilepticus (SE), behavioral changes and neuronal damage in spontaneously hypertensive rats (SHRs). Male SHRs were randomly divided into two groups. One group was exercised on a treadmill with submaximal loading for four weeks and the other group was sedentary. Immediately after the training period, SE was evoked in half of the sedentary and trained rats by KA, while the other half of the two groups received saline. Basal systolic (SP), diastolic (DP) and mean arterial pressure (MAP) of all rats were measured at the beginning and at the end of the training period. Anxiety, memory and depression-like behaviour were evaluated a month after SE. The release of 5-HT in the hippocampus was measured using a liquid scintillation method and neuronal damage was analyzed by hematoxylin and eosin staining. SP and MAP of exercised SHRs decreased in comparison with the initial values. The increased resistance of SHRs to KA-induced SE was accompanied by an elongated latent seizure-free period, improved object recognition memory and antidepressant effect after the training program. While the anticonvulsant and positive behavioral effects of endurance training were accompanied by an increase of 5-HT release in the hippocampus, it did not exert neuroprotective activity. Our results indicate that prior exercise is an effective means to attenuate KA-induced seizures and comorbid behavioral changes in a model of hypertension and epilepsy suggesting a potential influence of hippocampal 5-HT on a comorbid depression. However, this beneficial impact does not prevent the development of epilepsy and concomitant brain damage.

Activation and blockade of serotonin7 receptors in the prelimbic cortex regulate depressive-like behaviors in a 6-hydroxydopamine-induced Parkinson's disease rat model

The role of serotonin7 (5-HT7) receptors in the regulation of depression is poorly understood, particularly in Parkinson's disease-associated depression. Here we examined whether 5-HT7 receptors in the prelimbic (PrL) sub-region of the ventral medial prefrontal cortex (mPFC) involve in the regulation of depressive-like behaviors in sham-operated rats and rats with unilateral 6-hydroxydopamine lesions of the medial forebrain bundle. The lesion induced depressive-like responses as measured by the sucrose preference and forced swim tests when compared to sham-operated rats. Intra-PrL injection of 5-HT7 receptor agonist AS19 (0.5, 1 and 2 μg/rat) increased sucrose consumption, and decreased immobility time in sham-operated and the lesioned rats, indicating the induction of antidepressant-like effects. Further, intra-PrL injection of 5-HT7 receptor antagonist SB269970 (1.5, 3 and 6 μg/rat) decreased sucrose consumption, and increased immobility time, indicating the induction of depressive-like responses. However, the doses producing these effects in the lesioned rats were higher than those in sham-operated rats. Neurochemical results showed that intra-PrL injection of AS19 (2 μg/rat) increased dopamine, 5-hydroxytryptamine (5-HT) and noradrenaline (NA) levels in the mPFC, habenula and ventral hippocampus (vHip) in sham-operated and the lesioned rats; whereas SB269970 (6 μg/rat) decreased 5-HT levels in the habenula and vHip, and the levels of NA in the mPFC, habenula and vHip in the two groups of rats. The results suggest that 5-HT7 receptors in the PrL play an important role in the regulation of these behaviors, which attribute to changes in monoamine levels in the limbic and limbic-related brain regions after activation and blockade of 5-HT7 receptors.

Effects of AT1 receptor antagonism on kainate-induced seizures and concomitant changes in hippocampal extracellular noradrenaline, serotonin, and dopamine levels in Wistar-Kyoto and spontaneously hypertensive rats

In the management of epilepsy, AT1 receptor antagonists have been suggested as an additional treatment strategy. A hyperactive brain angiotensin (Ang) II system and upregulated AT1 receptors are implicated in the cerebrovascular alterations in a genetic form of hypertension. Uncontrolled hypertension could also, in turn, be a risk factor for a seizure threshold decrease and development of epileptogenesis. The present study aimed to assess the effects of the selective AT1 receptor antagonist ZD7155 on kainic acid (KA)-induced status epilepticus (SE) development and accompanying changes in the hippocampal extracellular (EC) neurotransmitter levels of noradrenaline (NAD), serotonin (5-HT), and dopamine (DA) in spontaneously hypertensive rats (SHRs) and their parent strain Wistar-Kyoto (WKY) rats, since monoamines are well-known neurotransmitters involved in mechanisms of both epilepsy and hypertension. Status epilepticus was evoked in freely moving rats by a repetitive intraperitoneal (i.p.) administration of KA in subconvulsant doses. In the treatment group, ZD7155 (5mg/kg i.p.) was coadministered with the first KA injection. Spontaneously hypertensive rats exhibited higher susceptibility to SE than WKY rats, but the AT1 receptor antagonist did not alter the development of SE in SHRs or in WKY rats. In vivo microdialysis demonstrated significant KA-induced increases of the hippocampal NAD and DA levels in SHRs and of NAD, 5-HT, and DA in WKY rats. Although SHRs developed more severe seizures while receiving a lower dose of KA compared to WKY rats, AT1 receptor antagonism completely prevented all KA-induced increases of hippocampal monoamine levels in both rat strains without affecting seizure development per se. These results suggest a lack of direct relationship between KA-induced seizure susceptibility and adaptive changes of hippocampal NAD, 5-HT, and DA levels in the effects of ZD7155 in WKY rats and SHRs.

Negative versus positive allosteric modulation of metabotropic glutamate receptors (mGluR5): indices for potential pro-cognitive drug properties based on EEG network oscillations and sleep-wake organization in rats

RATIONALE

Evidence is emerging that positive and negative modulation of the metabotropic glutamate (mGluR5) receptors has the potential for treating cognitive deficits and neuroprotection associated with psychiatric and neurodegenerative diseases, respectively. Sleep and synchronisation of disparate neuronal networks are critically involved in neuronal plasticity, and disturbance in vigilance states and cortical network connectivity contribute significantly to cognitive deficits described in schizophrenia and Alzheimer's disease. Here, we examined the circadian changes of mGluR5 density and the functional response to modulation of mGluR5 signaling.

METHODS

The current study carried out in Sprague-Dawley rats quantified the density of mGluR5 across the light-dark cycle with autoradiography. The central activity of mGluR5 negative allosteric modulators (2-methyl-6-(phenylethynyl)pyridine (MPEP) and [(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) and positive allosteric modulators (S-(4-fluoro-phenyl)-{3-[3-(4-fluoro-phenyl)-[1,2,4]oxadiazol-5-yl]-piperidin-1-yl}-methanone (ADX47273) and (7S)-3-tert-butyl-7-[3-(4-fluoro-phenyl)-1,2,4-oxadiazol-5-yl]-5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-a]pyridine (LSN2814617) was examined on sleep-wake architecture. The functional effect of mGluR5 modulation on cortical networks communication was described in freely moving animals.

RESULTS

The density of mGluR5 in the striatal, cortical, hippocampal and thalamic structures was unchanged across the light-dark cycle. Allosteric blockade of mGluR5 consistently consolidated deep sleep, enhanced sleep efficiency and elicited prominent functional coherent network activity in slow theta and gamma oscillations. However, allosteric activation of mGluR5 increased waking, decreased deep sleep and reduced functional network connectivity following the activation of slow alpha oscillatory activity.

CONCLUSION

This functional study differentiates the pharmacology of allosteric blockade of mGluR5 from that of allosteric activation and suggests that mGluR5 blockade enhances sleep and facilitates oscillatory network connectivity, both processes being known to have relevance in cognition processes.

Activation of serotonin(2C) receptors in the lateral habenular nucleus increases the expression of depression-related behaviors in the hemiparkinsonian rat

The roles of lateral habenular nucleus (LHb) glutamate neurons and serotonin2C (5-HT2C) receptors in depression are poorly understood, particularly in Parkinson's disease-associated depression. Here we assessed the importance of LHb glutamate neurons and 5-HT2C receptors for depressive-like behaviors in sham-operated rats and rats with unilateral 6-hydroxydopamine lesions of the substantia nigra. The lesion induced depressive-like responses compared to sham-operated rats. Intra-LHb injection of potent, selective 5-HT2C receptor agonist Ro60-0175 decreased sucrose consumption and increased immobility time in sham-operated rats, indicating the induction of depressive-like responses, and intra-LHb injection of Ro60-0175 further increased the expression of depressive-like behaviors in the lesioned rats. Activation of LHb 5-HT2C receptors by the local administration of Ro60-0175 increased the firing rate of EAAC1 (a neuronal glutamate transporter)-positive neurons and percentage of the neurons with burst-firing pattern in the two groups of rats. Compared to sham-operated rats, the duration of Ro60-0175 action on the firing rate of EAAC1-positive neurons was markedly prolonged in the lesioned rats. Intra-LHb injection of Ro60-0175 decreased dopamine, 5-HT and noradrenaline levels in the medial prefrontal cortex, habenula, hippocampus and amygdala in sham-operated and the lesioned rats. The lesion did not change the percentage of EAAC1/5-HT2C receptor co-expressing neurons in the LHb. These findings indicate that activation of 5-HT2C receptors in the LHb increases firing activity of LHb glutamate neurons and then decreases monoamine levels in several brain regions, which increase the expression of depressive-like behaviors. Further, our results also suggest that the lesion leads to hyperfunctionality of 5-HT2C receptors on glutamate neurons of the LHb.

The role of NMDA receptors in the pathophysiology and treatment of mood disorders

Mood disorders such as major depressive disorder and bipolar disorder are chronic and recurrent illnesses that cause significant disability and affect approximately 350 million people worldwide. Currently available biogenic amine treatments provide relief for many and yet fail to ameliorate symptoms for others, highlighting the need to diversify the search for new therapeutic strategies. Here we present recent evidence implicating the role of N-methyl-D-aspartate receptor (NMDAR) signaling in the pathophysiology of mood disorders. The possible role of NMDARs in mood disorders has been supported by evidence demonstrating that: (i) both BPD and MDD are characterized by altered levels of central excitatory neurotransmitters; (ii) NMDAR expression, distribution, and function are atypical in patients with mood disorders; (iii) NMDAR modulators show positive therapeutic effects in BPD and MDD patients; and (iv) conventional antidepressants/mood stabilizers can modulate NMDAR function. Taken together, this evidence suggests the NMDAR system holds considerable promise as a therapeutic target for developing next generation drugs that may provide more rapid onset relief of symptoms. Identifying the subcircuits involved in mood and elucidating the role of NMDARs subtypes in specific brain circuits would constitute an important step toward the development of more effective therapies with fewer side effects.

Effect of acute and chronic tianeptine on the action of classical antiepileptics in the mouse maximal electroshock model

BACKGROUND

The aim of the study was to analyze the influence of acute and chronic treatment with tianeptine, an antidepressant selectively accelerating presynaptic serotonin reuptake, on the protective activity of classical antiepileptic drugs in the maximal electroshock test in mice.

METHODS

Electroconvulsions were produced by means of an alternating current (50 Hz, 25 mA, 0.2 s) delivered via ear-clip electrodes. Motor impairment and long-term memory deficits in animals were quantified in the chimney test and in the passive-avoidance task, respectively. Brain concentrations of antiepileptic drugs were measured by fluorescence polarization immunoassay.

RESULTS

Acute and chronic treatment with tianeptine (25-50 mg/kg) did not affect the electroconvulsive threshold. Furthermore, tianeptine applied in both acute and chronic protocols enhanced the anticonvulsant action of valproate and carbamazepine, but not that of phenytoin. Neither acute nor chronic tianeptine changed the brain concentrations of valproate, carbamazepine or phenytoin. On the other hand, both single and chronic administration of tianeptine diminished the brain concentration of phenobarbital. In spite of this pharmacokinetic interaction, the antidepressant enhanced the antielectroshock action of phenobarbital. In terms of adverse effects, acute/chronic tianeptine (50 mg/kg) and its combinations with classic antiepileptic drugs did not impair motor performance or long-term memory in mice.

CONCLUSION

The obtained results justify the conclusion that tianeptine may be beneficial in the treatment of depressive disorders in the course of epilepsy.

Reduced levels of NR1 and NR2A with depression-like behavior in different brain regions in prenatally stressed juvenile offspring

Adolescence is a time of continued brain maturation, particularly in limbic and cortical regions, which undoubtedly plays a role in the physiological and emotional changes. Juvenile rats repeatedly exposed to prenatal stress (PS) exhibit behavioral features often observed in neuropsychiatric disorders including depression. However, to date the underlying neurological mechanisms are still unclear. In the current study, juvenile offspring rats whose mothers were exposed to PS were evaluated for depression-related behaviors in open field and sucrose preference test. NMDA receptor subunits NR1 and NR2A in the hippocampus, frontal cortex and striatum were assayed by western blotting. The results indicated that PS resulted in several behavioral anomalies in the OFT and sucrose preference test. Moreover, reduced levels of NMDA receptor subunits NR1 and NR2A in the hippocampus, and NR1 in prefrontal cortex and striatum of prenatally stressed juvenile offspring were found. Treatment with MK-801 to pregnant dams could prevent all those changes in the juvenile offspring. Collectivity, these data support the argument that PS to pregnant dams could induce depression-like behavior, which may be involved with abnormal expression of NR1 and NR2A in specific brain regions, and MK-801 may have antidepressant-like effects on the juvenile offspring.

Are vesicular neurotransmitter transporters potential treatment targets for temporal lobe epilepsy?

The vesicular neurotransmitter transporters (VNTs) are small proteins responsible for packing synaptic vesicles with neurotransmitters thereby determining the amount of neurotransmitter released per vesicle through fusion in both neurons and glial cells. Each transporter subtype was classically seen as a specific neuronal marker of the respective nerve cells containing that particular neurotransmitter or structurally related neurotransmitters. More recently, however, it has become apparent that common neurotransmitters can also act as co-transmitters, adding complexity to neurotransmitter release and suggesting intriguing roles for VNTs therein. We will first describe the current knowledge on vesicular glutamate transporters (VGLUT1/2/3), the vesicular excitatory amino acid transporter (VEAT), the vesicular nucleotide transporter (VNUT), vesicular monoamine transporters (VMAT1/2), the vesicular acetylcholine transporter (VAChT) and the vesicular γ-aminobutyric acid (GABA) transporter (VGAT) in the brain. We will focus on evidence regarding transgenic mice with disruptions in VNTs in different models of seizures and epilepsy. We will also describe the known alterations and reorganizations in the expression levels of these VNTs in rodent models for temporal lobe epilepsy (TLE) and in human tissue resected for epilepsy surgery. Finally, we will discuss perspectives on opportunities and challenges for VNTs as targets for possible future epilepsy therapies.

In vivo dialysis setup with a loop injection valve facilitates retrodialysis studies

INTRODUCTION

Retrodialysis, as used in neuropharmacological research, is a technique for in vivo delivery of neuroactive agents with concurrent monitoring of their effects on cellular activity with a separation between certain degree of spatial and temporal resolution. Typically, this is accomplished either by the use of a liquid-switch requiring multiple pumps, or by exchange of flow tubing requiring stopping and restarting dialysis. In the present study, we describe the use of a medium pressure injection valve for retrodialysis that overcomes these problems.

METHODS

The valve was configured with a loop to deliver 20μL of solution, and artificial CSF flow from the pump to the probe was established via this device. The application of this setup was evaluated in urethane anesthetized adult male C57BL/6J mice prepared with a CMA 11 probe implanted in the ventral hippocampus. By switching between the load and inject positions, the loop was filled with escitalopram solution (0.3μM) and delivered at a rate of 1μL/min at the probe for retrodialysis. Escitalopram (2mg/kg BW) was administered subcutaneously for microdialysis studies. During these treatments, dialysate fractions were collected for the determination of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA).

RESULTS

Irrespective of route of escitalopram administration, the pattern of dialysate 5-HT, and 5-HIAA response was comparable to that reported by other investigators. Accordingly, the in-line valve assembly did not compromise retrodialysis or microdialysis sampling. The manipulations to carry out retrodialysis using the valve setup are easy and simple.

DISCUSSION

An in-line injection valve is a promising adaptation for retrodialysis studies and can be incorporated as a standard part of in vivo dialysis instrumentation.

Altered expression of vesicular monoamine transporter 2 in epileptic patients and experimental rats

In the central nervous system (CNS), vesicular monoamine transporter 2 (VMAT2) transports cytoplasmic monoamines such as dopamine into synaptic vesicles for storage and subsequent exocytotic release. Recent studies have provided direct evidence for VMAT2-regulated monoamine neurotransmitter involvement in the neurophysiological activities of neurological disease. This study investigated the expression pattern of VMAT2 in patients with temporal lobe epilepsy (TLE) and in a rat model of epilepsy. We assessed the expression of VMAT2 in the temporal neocortex in 24 TLE patients using western blotting and quantitative real time PCR (qRT-PCR) analyses. These results showed that VMAT2 expression dynamically decreased in TLE patients when compared with the control subjects (n = 12). And that VMAT2 protein transiently increased in acute stages (1 day and 3 days) after epileptic seizures in pilocarpine-treated rats; however, it clearly decreased after spontaneous recurrent seizures (7 days, 21 days, and 60 days after seizures). In addition, double immunofluorescence and immunohistochemical labeling studies performed in patient and experimental animal tissue revealed that VMAT2 protein was mainly expressed in the cytoplasm and in the axons of neurons but not glial cells in the hippocampus and temporal lobe cortex. These data suggested that the abnormal expression of VMAT2 mRNA and protein in epileptic brain tissue may contribute to vulnerability toward epilepsy-related psychiatric disorders and cognitive impairment.

Lu AA21004, a novel multimodal antidepressant, produces regionally selective increases of multiple neurotransmitters--a rat microdialysis and electrophysiology study

The monoaminergic network, including serotonin (5-HT), norepinephrine (NE), and dopamine (DA) pathways, is highly interconnected and has a well-established role in mood disorders. Preclinical research suggests that 5-HT receptor subtypes, including 5-HT1A, 5-HT1B, 5-HT3, and 5-HT7 receptors as well as the 5-HT transporter (SERT), may have important roles in treating depression. This study evaluated the neuropharmacological profile of Lu AA21004, a novel multimodal antidepressant combining 5-HT3 and 5-HT7 receptor antagonism, 5-HT1B receptor partial agonism, 5-HT1A receptor agonism, and SERT inhibition in recombinant cell lines. Extracellular 5-HT, NE and DA levels were evaluated in the ventral hippocampus (vHC), medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) after acute and subchronic treatment with Lu AA21004 or escitalopram. The acute effects of LuAA21004 on NE and DA neuronal firing were also evaluated in the locus coeruleus (LC) and ventral tegmental area (VTA), respectively. Acute Lu AA21004 dose-dependently increased 5-HT in the vHC, mPFC and NAc. Maximal 5-HT levels in the vHC were higher than those in the mPFC. Furthermore, mPFC 5-HT levels were increased at low SERT occupancy levels. In the vHC and mPFC, but not the NAc, high Lu AA21004 doses increased NE and DA levels. Lu AA21004 slightly decreased LC NE neuronal firing and had no effect on VTA DA firing. Results are discussed in context of occupancy at 5-HT3, 5-HT1B and 5-HT1A receptors and SERT. In conclusion, Lu AA21004, acting via two pharmacological modalities, 5-HT receptor modulation and SERT inhibition, results in a brain region-dependent increase of multiple neurotransmitter concentrations.

Effects of MPEP, a selective metabotropic glutamate mGlu5 ligand, on sleep and wakefulness in the rat

Metabotropic glutamate receptors (mGlu) have been implicated in the regulation of physiological and behavioral processes. Pharmacological evidence involves group I mGlu receptors in the regulation of emotional states and antagonism of these receptors has been proposed as a novel class of anxiolytic drugs having also antidepressant effects. Here, the effects of mGlu5 receptor selective modulation on sleep and wake states are explored. 32 male Wistar rats were implanted with electrodes for recording sleep and wake states. 2-Methyl-6-(phenylethynyl)pyridine hydrochloride (MPEP hydrochloride, 5, 10, and 20 mg/kg, i.p.), a potent, selective and systemically active mGlu5 receptor negative allosteric modulator, or vehicle was administered 1 h after the beginning of the light period. Sleep recordings were conducted for 3 h. MPEP (5, 10, and 20 mg/kg) significantly suppressed rapid eye movement (REM) sleep, decreasing the number of episodes and mean episode duration, and increased its latency. A reduction of light and deep slow wave sleep (SWS) latency was observed in the groups receiving 10 or 20 mg/kg, increasing latency to first wakefulness episode. 10 mg/kg of MPEP also increased non rapid eye movement sleep (NREM). The present results suggest that mGlu5 receptors might be involved in sleep regulation, more specifically in REM sleep, and drugs that block these receptors could potentially benefit the treatment of pathologies were REM sleep is enhanced.

In vivo brain microdialysis as a formulation-screening tool for a poorly soluble centrally acting drug

OBJECTIVE

Efficacy of a formulation of a poorly soluble centrally acting drug was evaluated by measuring dopamine responses using in vivo brain microdialysis.

METHODS

Co-crystals (1:1) of carbamazepine and nicotinamide (CBZ-NCT) were complexed with cyclodextrins (γ-CDs) using supercritical fluid processing. Phase solubility and intrinsic dissolution were studied. Pharmacodynamic studies were performed on rats divided into three groups getting either CBZ-NCT in CD (20 mg/kg CBZ), pure CBZ solution or vehicle. A guide cannula was implanted to attach the microdialysis probe. Dialysate samples were analyzed for dopamine levels, which were compared between groups.

RESULTS

The optimized CBZ formulation (5% w/w in γ-CD) with solubility - 10 mg/mL showed stepwise increase in dopamine response (maximum 250% of baseline) compared to neat CBZ or vehicle (p < 0.05). The pharmacokinetics of the drug required 30 min to elicit CNS response, which peaked at about 1.5-2 h.

CONCLUSION

Hence, brain microdialysis was successfully used to evaluate a dissolution rate enhancing formulation.

Seizure-induced 5-HT release and chronic impairment of serotonergic function in rats

We analyzed the dynamic concentration change of serotonin (5-HT) and its main metabolite 5-hydroxyindoleacetic acid (5-HIAA) within the epileptic hippocampus in rats. Seizure was induced by systemic injection of pilocarpine (320mg/kg, i.p.). Using electroencephalography (EEG) recordings, we found that primary seizure discharge was induced 30min after pilocarpine administration and that recurrent discharge peaked 14d after the onset of status epilepticus (SE). The extracellular fluid in the hippocampus was sampled by microdialysis from conscious animals at various time points before and after SE. The concentrations of 5-HT and 5-HIAA in the samples were measured by high-performance liquid chromatography and electrochemical detection (HPLC-ECD). Interestingly, 5-HT levels in the hippocampus were dramatically increased within the 30min following SE. This reversed to basal level by 4d after SE and continued to drop to 48% at 7d and 28% of basal level 14d after SE. Accordingly, a marked increase of 5-HIAA in the hippocampus appeared at 2d after SE, then gradually declined to levels below baseline. To identify serotonergic neurons in the raphe nuclei (a major source of 5-HT release in the brain), brain sections were immunostained for tryptophan hydroxylase (TPH). The number of TPH positive neurons and the intensity of TPH staining significantly decreased at 28d after SE. These data suggest that pilocarpine induces depletion of 5-HT in the hippocampus and significantly compromise serotonergic neurons in the raphe nuclei. The loss of serotonergic function may play a significant role in the pathophysiology of epilepsy.

Rhythm and blues: animal models of epilepsy and depression comorbidity

Clinical evidence shows a strong, bidirectional comorbidity between depression and epilepsy that is associated with decreased quality of life and responsivity to pharmacotherapies. At present, the neurobiological underpinnings of this comorbidity remain hazy. To complicate matters, anticonvulsant drugs can cause mood disturbances, while antidepressant drugs can lower seizure threshold, making it difficult to treat patients suffering from both depression and epilepsy. Animal models have been created to untangle the mechanisms behind the relationship between these disorders and to serve as screening tools for new therapies targeted to treat both simultaneously. These animal models are based on chemical interventions (e.g. pentylenetetrazol, kainic acid, pilocarpine), electrical stimulations (e.g. kindling, electroshock), and genetic/selective breeding paradigms (e.g. genetically epilepsy-prone rats (GEPRs), genetic absence epilepsy rat from Strasbourg (GAERS), WAG/Rij rats, swim lo-active rats (SwLo)). Studies on these animal models point to some potential mechanisms that could explain epilepsy and depression comorbidity, such as various components of the dopaminergic, noradrenergic, serotonergic, and GABAergic systems, as well as key brain regions, like the amygdala and hippocampus. These models have also been used to screen possible therapies. The purpose of the present review is to highlight the importance of animal models in research on comorbid epilepsy and depression and to explore the contributions of these models to our understanding of the mechanisms and potential treatments for these disorders.

mGlu2/3 and mGlu5 receptors: potential targets for novel antidepressants

Major depressive disorder is among the most prevalent forms of mental illness. All currently available antidepressant medications have stemmed from study of the mechanisms of serendipitously discovered drugs, and only 30-50% of patients exhibit remission and frequently at least 3-4 weeks are required for manifestation of significant therapeutic effects. To overcome these drawbacks, discovering novel neuronal mechanisms of pathophysiology of depression as well as more effective treatments are necessary. This review focuses on the metabotropic glutamate (mGlu) receptors and their potential for drug targets for the treatment of depression. In particular, accumulating evidence has indicated the potential importance and usefulness of agents acting on mGlu2/3 and mGlu5 receptors. Preclinical and clinical evidence of mGlu2/3 receptor ligands and mGlu5 receptor antagonists are described. Moreover, their potential in clinic will be discussed in the context of neuronal mechanisms of ketamine, an agent recently demonstrated a robust effect for patients with treatment-resistant depression. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.

Dopamine in the hippocampus is cleared by the norepinephrine transporter

Abnormal dopaminergic neurotransmission in the hippocampus may be involved in certain aspects of cognitive dysfunction. In the hippocampus, there is little, if any, expression of dopamine transporters (DAT), indicating that the mechanism for dopamine clearance differs from that in the striatum. Here, by means of in-vivo microdialysis in freely moving rats, we tested the hypothesis that the norepinephrine transporter (NET) is involved in dopamine clearance in the hippocampus. We found that systemic administration of the selective NET inhibitor reboxetine (3 mg/kg) and the psychostimulants amphetamine (0.5 mg/kg) and cocaine (10 mg/kg) increased hippocampal dopamine efflux. Local administration of reboxetine (300 μM) produced a large increase in hippocampal dopamine levels that could not be further enhanced by the addition of the NET/DAT inhibitor nomifensine (100 μM). Administration of the specific DAT inhibitor GBR12909 at a concentration (1 mM) that robustly increased dopamine in the nucleus accumbens had a comparably smaller effect in the hippocampus. In line with a minor role of DAT in the hippocampus, we detected very little DAT in this area using ligand binding with radiolabelled RTI-55. Moreover, in contrast to raclopride (100 μM), a dopamine D2-autoreceptor antagonist, local administration of the α2-adrenoceptor antagonist idazoxan (100 μM) increased hippocampal dopamine. Taken together, our data demonstrate an interaction between dopamine and norepinephrine systems in the hippocampus. It is proposed that this interaction originates from a shared uptake mechanism at the NET level.