The Carnitine Palmitoyl-Transferase 2 Cascade Hypothesis for Alzheimer's Disease.

Despite decades of intense research, the precise etiology of Alzheimer's disease (AD) remains unclear. In this hypothesis, we present a new perspective on this matter by identifying carnitine palmitoyl transferase-2 (CPT2) as a central target in AD. CPT2 is an enzyme situated within the inner mitochondrial membrane, playing a crucial role in beta-oxidation of fatty acids. It exhibits high sensitivity to hydrogen peroxide. This sensitivity holds relevance for the etiology of AD, as all major risk factors for the disease share a commonality in producing an excess of hydrogen peroxide right at this very mitochondrial membrane. We will explain the high sensitivity of CPT2 to hydrogen peroxide and elucidate how the resulting inhibition of CPT2 can lead to the characteristic phenotype of AD, thus clarifying its central role in the disease's etiology. This insight holds promise for the development of therapies for AD which can be implemented immediately.

Mast cells in neuroinflammation and brain disorders.

It is well recognized that neuroinflammation is involved in the pathogenesis of various neurodegenerative diseases. Microglia and astrocytes are major pathogenic components within this process and known to respond to proinflammatory mediators released from immune cells such as mast cells. Mast cells reside in the brain and are an important source of inflammatory molecules. Mast cell interactions with glial cells and neurons result in the release of mediators such as cytokines, proteases and reactive oxygen species. During neuroinflammation, excessive levels of these mediators can influence neurogenesis, neurodegeneration and blood-brain barrier (BBB) permeability. Mast cells are considered first responders and are able to initiate and magnify immune responses in the brain. Their possible role in neurodegenerative disorders such as multiple sclerosis, Alzheimer's disease and autism has gained increasing interest. We discuss the possible involvement of mast cells and their mediators in neurogenesis, neurodegeneration and BBB permeability and their role in neuronal disorders such as cerebral ischemia, traumatic brain injury, neuropathic pain, multiple sclerosis, Alzheimer's disease, migraine, autism, and depression.

New drug-strategies to tackle viral-host interactions for the treatment of influenza virus infections.

The influenza virus (IV) is a highly contagious virus causing seasonal global outbreaks affecting annually up to 20% of the world's population and leading to 250,000-500,000 deaths worldwide. Current vaccines have variable effectiveness, and, in particular during a pandemic outbreak, they are probably not available in the amounts needed to protect the world population. Therefore we need effective small molecule drugs to combat an IV infection and that can be produced, in case of pandemic, rapidly and in large quantities. Unfortunately, natural occurring IV becomes more and more resistant to current anti-IV drugs. And thus, there is an urgent need for development of alternative agents with new mechanisms of action. This review provides an overview of the pharmacology and effectiveness of new anti-IV agents, focusing on inhibition mechanisms directed against virus-host interactions.

A study of time- and sex-dependent effects of vortioxetine on rat sexual behavior: Possible roles of direct receptor modulation.

Treatment-related sexual dysfunction is a common side effect of antidepressants and contributes to patient non-compliance or treatment cessation. However, the multimodal antidepressant, vortioxetine, demonstrates low sexual side effects in depressed patients. To investigate the mechanisms involved, sexual behavior was assessed in male and female rats after acute, and repeated (7 and 14 days) treatment with vortioxetine, flesinoxan (a 5-HT1A receptor agonist), CP-94253 (a 5-HT1B receptor agonist), or ondansetron (a 5-HT3 receptor antagonist). These selective ligands were chosen to simulate vortioxetine's direct modulation of these receptors. Paroxetine was also included in the male study. Acute and repeated treatment with vortioxetine at doses corresponding to clinical levels (based on serotonin transporter occupancy) had minimal effects on sexual behavior in male and female rats. High dose vortioxetine plus flesinoxan (to mimic predicted clinical levels of 5-HT1A receptor occupancy by vortioxetine) facilitated male rat sexual behavior (acutely) while inhibiting female rat proceptive behavior (both acutely and after 14 days treatment). The selective serotonin reuptake inhibitor, paroxetine, inhibited male sexual behavior after repeated administration (7 and 14 days). Flesinoxan alone facilitated male sexual behavior acutely while inhibiting female rat proceptive behavior after repeated administration (7 and 14 days). CP-94253 inhibited sexual behavior in both male and female rats after repeated administration. Ondansetron had no effect on sexual behavior. These findings underline the complex serotonergic regulation of sexual behavior and indicate that the low sexual side effects of vortioxetine found in clinical studies are likely associated with its direct modulation of serotonin receptors.

The 5-HT1A/1B-receptor agonist eltoprazine increases both catecholamine release in the prefrontal cortex and dopamine release in the nucleus accumbens and decreases motivation for reward and "waiting" impulsivity, but increases "stopping" impulsivity.

The 5-HT1A/1B-receptor agonist eltoprazine has a behavioral drug signature that resembles that of a variety of psychostimulant drugs, despite the differences in receptor binding profile. These psychostimulants are effective in treating impulsivity disorders, most likely because they increase norepinephrine (NE) and dopamine (DA) levels in the prefrontal cortex. Both amphetamine and methylphenidate, however, also increase dopamine levels in the nucleus accumbens (NAc), which has a significant role in motivation, pleasure, and reward. How eltoprazine affects monoamine release in the medial prefrontal cortex (mPFC), the orbitofrontal cortex (OFC), and the NAc is unknown. It is also unknown whether eltoprazine affects different forms of impulsivity and brain reward mechanisms. Therefore, in the present study, we investigate the effects of eltoprazine in rats in the following sequence: 1) the activity of the monoaminergic systems using in vivo microdialysis, 2) motivation for reward measured using the intracranial self-stimulation (ICSS) procedure, and finally, 3) "waiting" impulsivity in the delay-aversion task, and the "stopping" impulsivity in the stop-signal task. The microdialysis studies clearly showed that eltoprazine increased DA and NE release in both the mPFC and OFC, but only increased DA concentration in the NAc. In contrast, eltoprazine decreased 5-HT release in the mPFC and NAc (undetectable in the OFC). Remarkably, eltoprazine decreased impulsive choice, but increased impulsive action. Furthermore, brain stimulation was less rewarding following eltoprazine treatment. These results further support the long-standing hypothesis that "waiting" and "stopping" impulsivity are regulated by distinct neural circuits, because 5-HT1A/1B-receptor activation decreases impulsive choice, but increases impulsive action.

Vilazodone does not inhibit sexual behavior in male rats in contrast to paroxetine: A role for 5-HT1A receptors?

Vilazodone (VLZ) is a selective serotonin reuptake inhibitor (SSRI) and 5-HT1A receptor partial agonist approved for the treatment of major depressive disorder in adults. In preclinical studies, VLZ had significantly lower sexual side effects than SSRIs and reduced serotonin transporter (SERT) levels in forebrain regions. In the current study, once-daily paroxetine (PAR, 10 mg/kg), VLZ (10 mg/kg), PAR + buspirone (BUS, 3 mg/kg; a 5-HT1A partial agonist), or vehicle (VEH) was administered to male rats for 2 weeks then switched for 7 days (eg, PAR switched to VLZ, PAR + BUS, or VEH). Sexual behavior (eg, ejaculation frequency and latency) was evaluated 1-hr postdose on days 1, 7, 14, and 21. After 2 weeks, treatment with PAR but not VLZ resulted in a significant decrease in sexual behavior. In a 30-min test, the range of ejaculation frequency was 3.08-3.5 with VLZ and 1.00-1.92 with PAR (P < 0.05 vs VEH). After switching from PAR to VEH, PAR + BUS, or VEH, sexual behaviors were normalized to control levels. In contrast, the switch from VLZ to PAR resulted in reduced sexual behaviors. This preclinical study showed that unlike PAR, an SSRI with no 5-HT1A receptor activity, initial treatment with VLZ did not result in sexual side effects at therapeutically relevant doses. Results in male rats switched from PAR to VLZ or PAR + BUS strongly suggest that activation of 5-HT1A receptors may mitigate the sexual side effects associated with conventional SSRIs.

Differential effects of vilazodone versus citalopram and paroxetine on sexual behaviors and serotonin transporter and receptors in male rats.

RATIONALE: Sexual side effects are commonly associated with selective serotonin reuptake inhibitor (SSRI) treatment. Some evidence suggest that activation of 5-HT1A receptors attenuates SSRI-induced sexual dysfunction. OBJECTIVE: This study in male rats compared the effects of vilazodone, an antidepressant with SSRI and 5-HT1A receptor partial agonist activity, with other prototypical SSRIs (citalopram and paroxetine) on sexual behaviors and 5-HT receptors (5-HT1A and 5-HT2A) and transporter (5-HTT) levels in select forebrain regions of the limbic system using quantitative autoradiography. METHODS: Rats received vilazodone (1, 3, and 10 mg/kg), citalopram (10 and 30 mg/kg), or paroxetine (10 mg/kg) treatment for 14 days. Sexual behaviors (frequency and latency of mounts, intromissions, and ejaculations) were measured in the presence of an estrous female rat on days 1 (acute), 7 (subchronic), and 14 (chronic). RESULTS: Vilazodone-treated rats exhibited no sexual dysfunction compared with controls; in contrast, the citalopram- and paroxetine-treated rats exhibited impaired copulatory and ejaculatory behaviors after subchronic and chronic treatments. Chronic vilazodone treatment markedly decreased 5-HT1A receptor levels in cortical and hippocampal regions, while the SSRIs increased levels of this receptor in similar regions. All chronic treatments reduced 5-HTT levels across the forebrain; however, the magnitude of the decrease was considerably smaller for vilazodone than for the SSRIs. CONCLUSIONS: The current studies showed that chronic treatment with vilazodone, in contrast to citalopram and paroxetine, was not associated with diminished sexual behaviors in male rats, which may be related to the differential effects of vilazodone on 5-HT1A receptor and 5-HTT levels relative to conventional SSRIs.

The many different faces of major depression: it is time for personalized medicine.

First line antidepressants are the so-called SSRIs (selective serotonin reuptake inhibitors), e.g. fluvoxamine, fluoxetine, sertraline, paroxetine and escitalopram. Unfortunately, these drugs mostly do not provide full symptom relief and have a slow onset of action. Therefore other antidepressants are also being prescribed that inhibit the reuptake of norepinephrine (e.g. reboxetine, desipramine) or the reuptake of both serotonin (5-HT) and norepinephrine (e.g. venlafaxine, duloxetine, milnacipran). Nevertheless, many patients encounter residual symptoms such as impaired pleasure, impaired motivation, and lack of energy. It is hypothesized that an impaired brain reward system may underlie these residual symptoms. In agreement, there is some evidence that reuptake inhibitors of both norepinephrine and dopamine (e.g. methylphenidate, bupropion, nomifensine) affect these residual symptoms. In the pipeline are new drugs that block all three monoamine transporters for the reuptake of 5-HT, norepinephrine and dopamine, the so-called triple reuptake inhibitors (TRI). The working mechanisms of the above-mentioned antidepressants are discussed, and it is speculated whether depressed patients with different symptoms, sometimes even opposite ones due to atypical or melancholic features, can be matched with the different drug treatments available. In other words, is personalized medicine for major depression an option in the near future?

Food restriction does not relieve PTSD-like anxiety.

We used the inescapable foot shock paradigm (IFS) in rats as an animal model for post-traumatic stress disorder (PTSD). Previously we showed that exercise reversed the enhanced stress sensitivity induced by IFS. From literature it is known that food restriction has antidepressant and anxiolytic effects. Since both treatments influence energy expenditure, we questioned whether food restriction reduces anxiety in the IFS model via a comparable, NPY dependent mechanism as enrichment. Anxiety of IFS-exposed animals was measured as change in locomotion and freezing after sudden silence in an open field test, before and after two weeks of food restriction. In addition a forced swim test (FST) was performed. Next, using qPCR, the expression of neuropeptide Y (NPY) and the neuropeptide Y1 receptor (Y1 receptor) was measured in the amygdala. Food restriction increased locomotion and decreased freezing behavior both in control and IFS animals. These effects were small. IFS-induced anxiety was not abolished after two weeks of food restriction. IFS did not influence immobility or the duration of swimming in the FST of animals fed ad libitum. However, food restriction increased swimming and decreased the duration of immobility in IFS-exposed animals. Y1 receptor expression in the basolateral amygdala decreased after both IFS and food restriction. Although food restriction seems to induce a general anxiolytic effect, it does not operate via enhanced Y1 receptor expression and has no effect on the more pathogenic anxiety induced by IFS.

The olfactory bulbectomy model in mice and rat: one story or two tails?

Olfactory bulbectomy (OBX), the surgical removal of the olfactory bulbs, lead, both in mice and rats, to a specific set of behavioral changes in social behavior, cognitive function and activity. The latter is often used as a readout measure to predict antidepressant effects of new compounds. More recently, the model is used to study neurodegeneration and the associated cognitive decline. Although most of the OBX-induced behavioral and neurochemical changes seen in mice and rats are very similar, there are also some remarkable differences. For instance, OBX has different effects on BDNF and the 5-HT2c receptor of these two species. These species differ also in how they respond to certain treatments after OBX. In this review we describe these species-specific differences and discuss what they may mean in terms of translational value.

Dorsomedial Prefrontal Cortex Mediates the Impact of Serotonin Transporter Linked Polymorphic Region Genotype on Anticipatory Threat Reactions.

BACKGROUND: Excessive anticipatory reactions to potential future adversity are observed across a range of anxiety disorders, but the neurogenetic mechanisms driving interindividual differences are largely unknown. We aimed to discover and validate a gene-brain-behavior pathway by linking presumed genetic risk for anxiety-related psychopathology, key neural activity involved in anxious anticipation, and resulting aversive emotional states. METHODS: The functional neuroanatomy of aversive anticipation was probed through functional magnetic resonance imaging in two independent samples of healthy subjects (n = 99 and n = 69), and we studied the influence of genetic variance in the serotonin transporter linked polymorphic region (5-HTTLPR). Skin conductance and startle data served as objective psychophysiological indices of the intensity of individuals' anticipatory responses to potential threat. RESULTS: Threat cues signaling risk of future electrical shock activated the dorsomedial prefrontal cortex (dmPFC), anterior insula, bed nucleus of the stria terminalis, thalamus, and midbrain consistently across both samples. Threat-related dmPFC activation was enhanced in 5-HTTLPR short allele carriers in sample 1 and this effect was validated in sample 2. Critically, we show that this region mediates the increase in anticipatory psychophysiological reactions in short allele carriers indexed by skin conductance (experiment 1) and startle reactions (experiment 2). CONCLUSIONS: The converging results from these experiments demonstrate that innate 5-HTTLPR linked variation in dmPFC activity predicts psychophysiological responsivity to pending threats. Our results reveal a neurogenetic pathway mediating interindividual variability in anticipatory responses to threat and yield a novel mechanistic account for previously reported associations between genetic variability in serotonin transporter function and stress-related psychopathology.

From non-pharmacological treatments for post-traumatic stress disorder to novel therapeutic targets.

The development of new pharmacological therapies starts with target discovery. Finding new therapeutic targets for anxiety disorders is a difficult process. Most of the currently described drugs for post-traumatic stress disorder (PTSD) are based on the inhibition of serotonin reuptake. The mechanism of action of selective serotonin reuptake inhibitors was already described in 1977 (Benkert et al., 1977). Now, almost 40 years later, we still rely on the same mechanism of action and more effective pharmacological therapies, based on other working mechanisms, are not on the market yet. Finding new molecular switches that upon modulation cure or alleviate the disorder is hampered by a lack of valid animal models. Many of the characteristics of psychiatric disorders are typically human and hence animal models feature only part of the underlying pathology. In this review we define a set of criteria for animal models of PTSD. First, we describe the symptomatology and pathology of PTSD and the current pharmacological and non-pharmacological treatment options. Next, we compare three often-used animal models and analyze how these models comply with the set of criteria. Finally, we discuss how resolving the underlying mechanisms of effective non-pharmacological treatments (environmental enrichment, re-exposure) may aid therapeutic target discovery.

Neuroprotective and cognitive enhancing effects of a multi-targeted food intervention in an animal model of neurodegeneration and depression.

Rising neurodegenerative and depressive disease prevalence combined with the lack of effective pharmaceutical treatments and dangerous side effects, has created an urgent need for the development of effective therapies. Considering that these disorders are multifactorial in origin, treatments designed to interfere at different mechanistic levels may be more effective than the traditional single-targeted pharmacological concepts. To that end, an experimental diet composed of zinc, melatonin, curcumin, piperine, eicosapentaenoic acid (EPA, 20:5, n-3), docosahexaenoic acid (DHA, 22:6, n-3), uridine, and choline was formulated. This diet was tested on the olfactory bulbectomized rat (OBX), an established animal model of depression and cognitive decline. The ingredients of the diet have been individually shown to attenuate glutamate excitoxicity, exert potent anti-oxidant/anti-inflammatory properties, and improve synaptogenesis; processes that all have been implicated in neurodegenerative diseases and in the cognitive deficits following OBX in rodents. Dietary treatment started 2 weeks before OBX surgery, continuing for 6 weeks in total. The diet attenuated OBX-induced cognitive and behavioral deficits, except long-term spatial memory. Ameliorating effects of the diet extended to the control animals. Furthermore, the experimental diet reduced hippocampal atrophy and decreased the peripheral immune activation in the OBX rats. The ameliorating effects of the diet on the OBX-induced changes were comparable to those of the NMDA receptor antagonist, memantine, a drug used for the management of Alzheimer's disease. This proof-of-concept study suggests that a diet, which simultaneously targets multiple disease etiologies, can prevent/impede the development of a neurodegenerative and depressive disorders and the concomitant cognitive deficits.

Serotonin 1A receptors and sexual behavior in female rats: a review.

This review focuses on the role of serotonin and especially 5-HT1A receptors in female rat sexual behavior. In addition, the differences and/or similarities with male rats are discussed. Overall, in both males and females 5-HT1A receptors do not appear to be involved in sexual behavior under normal circumstances, but become very important under conditions of elevated serotonin levels. 5-HT1A receptor agonists facilitate sexual behavior in male rats, but inhibit female sexual activity. At first sight, this seems quite conflicting, but could be due to our definitions of different elements of sexual behavior. Three different phases can be distinguished in rats' sexual cycle, the introductory (precopulatory), the copulatory and the executive (ejaculatory) phases. Different mechanisms and brain regions are involved in these phases. If the appropriate phases of males and females are properly compared, the role of 5-HT1A receptors in rats might be more similar than assumed thus far.

Sexual side effects of serotonergic antidepressants: mediated by inhibition of serotonin on central dopamine release?

Antidepressant-induced sexual dysfunction adversely affects the quality of life of antidepressant users and reduces compliance with treatment. Animal models provide an instructive approach for examining potential sexual side effects of novel drugs. This review discusses the stability and reproducibility of our standardized test procedure that assesses the acute, subchronic and chronic effects of psychoactive compounds in a 30 minute mating test. In addition, we present an overview of the effects of several different (putative) antidepressants on male rat sexual behavior, as tested in our standardized test procedure. By comparing the effects of these mechanistically distinct antidepressants (paroxetine, venlafaxine, bupropion, buspirone, DOV 216,303 and S32006), this review discusses the putative mechanism underlying sexual side effects of antidepressants and their normalization. This review shows that sexual behavior is mainly inhibited by antidepressants that increase serotonin neurotransmission via blockade of serotonin transporters, while those that mainly increase the levels of dopamine and noradrenaline are devoid of sexual side effects. Those sexual disturbances cannot be normalized by simultaneously increasing noradrenaline neurotransmission, but are normalized by increasing both noradrenaline and dopamine neurotransmission. Therefore, it is hypothesized that the sexual side effects of selective serotonin reuptake inhibitors may be mediated by their inhibitory effects on dopamine signaling in sex brain circuits. Clinical development of novel antidepressants should therefore focus on compounds that simultaneously increase both serotonin and dopamine signaling.

Serotonin 1A receptors and sexual behavior in male rats: a review.

Serotonin plays an important role in male sexual behavior. Many studies have been performed on the pivotal role of 5-HT1A receptors in sexual behavior. Overall, 5-HT1A receptors do not appear to be involved under normal circumstances, but become very important under conditions of elevated serotonin levels in sexual behavior. 5-HT1A receptor agonists facilitate ejaculatory behavior in male rats, while inhibiting copulatory behavior. Three different phases can be distinguished in rats' sexual cycle, the introductory (precopulatory), the copulatory and the executive (ejaculatory) phases. Different mechanisms and brain regions are involved in these phases. The mechanisms, brain regions and the possible involvement of 5-HT and 5-HT1A receptors in the appropriate phases in male rat sexual behavior will be discussed in the current review.

Human fear acquisition deficits in relation to genetic variants of the corticotropin releasing hormone receptor 1 and the serotonin transporter.

The ability to identify predictors of aversive events allows organisms to appropriately respond to these events, and failure to acquire these fear contingencies can lead to maladaptive contextual anxiety. Recently, preclinical studies demonstrated that the corticotropin-releasing factor and serotonin systems are interactively involved in adaptive fear acquisition. Here, 150 healthy medication-free human subjects completed a cue and context fear conditioning procedure in a virtual reality environment. Fear potentiation of the eyeblink startle reflex (FPS) was measured to assess both uninstructed fear acquisition and instructed fear expression. All participants were genotyped for polymorphisms located within regulatory regions of the corticotropin releasing hormone receptor 1 (CRHR1 - rs878886) and the serotonin transporter (5HTTLPR). These polymorphisms have previously been linked to panic disorder and anxious symptomology and personality, respectively. G-allele carriers of CRHR1 (rs878886) showed no acquisition of fear conditioned responses (FPS) to the threat cue in the uninstructed phase, whereas fear acquisition was present in C/C homozygotes. Moreover, carrying the risk alleles of both rs878886 (G-allele) and 5HTTLPR (short allele) was associated with increased FPS to the threat context during this phase. After explicit instructions regarding the threat contingency were given, the cue FPS and context FPS normalized in all genotype groups. The present results indicate that genetic variability in the corticotropin-releasing hormone receptor 1, especially in interaction with the 5HTTLPR, is involved in the acquisition of fear in humans. This translates prior animal findings to the human realm.

Minocycline restores spatial but not fear memory in olfactory bulbectomized rats.

We investigated the effects of minocycline, a microglia suppressant, on olfactory bulbectomized (OBX) rats, a model of cognitive and behavioral impairments arising from neurodegenerative processes. Previously, we demonstrated that the major OBX-induced behavioral and cognitive impairments develop between day 3 and 7 following bulbectomy. Here we show that the onset of these cognitive changes parallel in time with signs of microglia activation (increased mRNA levels of IL-1ß and CD68) in hippocampus. Next, rats were treated with minocycline (50mg/kg, i.p.) once daily for 4 weeks. OBX surgery was done at day 3 of drug treatment. Animals were tested in a battery of behavioral assays: open field, passive avoidance (fear learning and memory-acquired prior to OBX) and T-maze (spatial memory, conducted post bulbectomy). Minocycline normalized OBX-induced hyperactivity in the open field. Minocycline failed to prevent fear memory loss, but protected the OBX rats against hippocampal-dependent spatial memory deficit. Our findings suggest that treatment with minocycline may be effective in the early phase of a neurodegenerative disease.

Celecoxib delays cognitive decline in an animal model of neurodegeneration.

Cyclooxygenase-2 (COX-2) is thought to play a role in the pathogenesis of various neurodegenerative disorders. However, clinical trials with COX-2 inhibitors have yielded contradictory results. In the present study we investigated whether COX-2 plays a role in the behavioral and cognitive impairments seen in olfactory bulbectomized rats. These impairments arise from neurodegenerative processes. First, we determined the time course of the OBX-induced behavioral (hyperactivity) and cognitive changes (fear memory) and how these correlate with changes in COX-2 mRNA expression in hippocampus. This experiment showed that the major impairments in behavior and cognition developed between Days 3 and 14 after OBX surgery, which correlated with changes in mRNA levels of COX-2, which increased at Days 7 and 14 after surgery but not anymore at day 28. In a subsequent experiment, rats were treated, starting two days before surgery, with the COX-2 inhibitor celecoxib (10 mg/kg, dissolved in drinking water) for 4 weeks. OBX-induced hyperactivity in the open field was normalized after 2 weeks of celecoxib treatment, but not longer after 4 weeks. Celecoxib partly rescued fear learning and memory deficits without affecting spatial memory. The effects of celecoxib on fear memory lasted up to 1 week posttreatment, but disappeared thereafter. Our results show that COX-2 plays a limited role (both in magnitude and time) in the development of the OBX syndrome.