Exploring the neuroprotective effects of modafinil in a marmoset Parkinson model with immunohistochemistry, magnetic resonance imaging and spectroscopy

Psychostimulants as cognitive enhancers – the evidence for the use and abuse of smart drugs

While modafinil is licensed to treat narcolepsy as a psychostimulant, there is widespread use as a “smart drug” in the young to help study and interest in older populations as a cognitive enhancer. This review considers both the evidence for benefit and potential for harm. If it is as effective as it seems, should we all be using it? Should Neurologists recommend it, and should we worry if our patients are taking it? In this review the evidence base behind psychostimulants, in particular modafinil as a cognitive enhancer, is discussed.

Analgesic and anti-inflammatory effects of modafinil in a mouse model of neuropathic pain: A role for nitrergic and serotonergic pathways

OBJECTIVES

To evaluate the effects of modafinil on neuropathic pain induced by sciatic nerve cuffing in mice, and possible contribution of nitrergic/inflammatory and serotonergic systems.

METHODS

Neuropathic pain was induced by applying a polyethylene cuff around the left sciatic nerve. Seven days later, mice received modafinil (50, 100, and 200 mg/kg; intraperitoneal [i.p.]) and morphine (10 mg/kg, i.p.) as control. Mice also received pretreatments of the nonselective nitric oxide (NO) synthase (NOS) inhibitor L-NAME, the selective neuronal NOS inhibitor 7-nitroindazole, the selective inducible NOS inhibitor aminoguanidine, and the selective serotonin reuptake inhibitor citalopram before modafinil (100 mg/kg). von Frey test was used to evaluate mechanical allodynia. Additionally, sciatic nerves were collected for histopathological analysis. Tissue levels of NO metabolites, tumor necrosis factor (TNF)-α, and interleukin (IL)-6 were assessed.

RESULTS

Animals whose sciatic nerves were cuffed had a significantly (P<0.001) decreased paw withdrawal threshold (PWT) compared with the sham-operated group. Modafinil (100 mg/kg) and morphine significantly reversed PWT (P<0.001). Pretreatments with L-NAME, 7-nitroindazole, aminoguanidine, and citalopram in different groups markedly reversed analgesic effects of modafinil. Tissue homogenates of Cuffed sciatic nerves showed significantly higher levels of NO metabolites, TNF-α and IL-6 (P<0.001). Modafinil lowered NO metabolites, TNF-α, and IL-6 levels (P<0.001). Histopathology illustrated marked axonal degeneration and shrinkage in the cuffed sciatic nerve, which were improved in the modafinil-treated group.

CONCLUSIONS

Modafinil exerts analgesic and neuroprotective effects in cuff-induced neuropathic mice via possible involvement of the nitrergic/inflammatory and serotonergic systems.

HDAC superfamily promoters acetylation is differentially regulated by modafinil and methamphetamine in the mouse medial prefrontal cortex

Dysregulation of histone deacetylases (HDAC) has been proposed as a potential contributor to aberrant transcriptional profiles that can lead to changes in cognitive functions. It is known that METH negatively impacts the prefrontal cortex (PFC) leading to cognitive decline and addiction whereas modafinil enhances cognition and has a low abuse liability. We investigated if modafinil (90 mg/kg) and methamphetmine (METH) (1 mg/kg) may differentially influence the acetylation status of histones 3 and 4 (H3ac and H4ac) at proximal promoters of class I, II, III, and IV HDACs. We found that METH produced broader acetylation effects in comparison with modafinil in the medial PFC. For single dose, METH affected H4ac by increasing its acetylation at class I Hdac1 and class IIb Hdac10, decreasing it at class IIa Hdac4 and Hdac5. Modafinil increased H3ac and decreased H4ac of Hdac7. For mRNA, single-dose METH increased Hdac4 and modafinil increased Hdac7 expression. For repeated treatments (4 d after daily injections over 7 d), we found specific effects only for METH. We found that METH increased H4ac in class IIa Hdac4 and Hdac5 and decreased H3/H4ac at class I Hdac1, Hdac2, and Hdac8. At the mRNA level, repeated METH increased Hdac4 and decreased Hdac2. Class III and IV HDACs were only responsive to repeated treatments, where METH affected the H3/H4ac status of Sirt2, Sirt3, Sirt7, and Hdac11. Our results suggest that HDAC targets linked to the effects of modafinil and METH may be related to the cognitive-enhancing vs cognitive-impairing effects of these psychostimulants.

Cortico-Amygdala-Striatal Activation by Modafinil/Flecainide Combination

Background

Modafinil, a nonamphetaminic wake-promoting compound, is prescribed as first line therapy in narcolepsy, an invalidating disorder characterized by excessive daytime sleepiness and cataplexy. Although its mode of action remains incompletely known, recent studies indicated that modafinil modulates astroglial connexin-based gap junctional communication as administration of a low dose of flecainide, an astroglial connexin inhibitor, enhanced the wake-promoting and procognitive activity of modafinil in rodents and healthy volunteers. The aim of this study is to investigate changes in glucose cerebral metabolism in rodents, induced by the combination of modafinil+flecainide low dose (called THN102).

Methods

The impact of THN102 on brain glucose metabolism was noninvasively investigated using 18F-2-fluoro-2-deoxy-D-glucose Positron Emission Tomography imaging in Sprague-Dawley male rats. Animals were injected with vehicle, flecainide, modafinil, or THN102 and further injected with 18F-2-fluoro-2-deoxy-D-glucose followed by 60-minute Positron Emission Tomography acquisition. 18F-2-fluoro-2-deoxy-D-glucose Positron Emission Tomography images were coregistered to a rat brain template and normalized from the total brain Positron Emission Tomography signal. Voxel-to-voxel analysis was performed using SPM8 software. Comparison of brain glucose metabolism between groups was then performed.

Results

THN102 significantly increased regional brain glucose metabolism as it resulted in large clusters of 18F-2-fluoro-2-deoxy-D-glucose uptake localized in the cortex, striatum, and amygdala compared with control or drugs administered alone. These regions, highly involved in the regulation of sleep-wake cycle, emotions, and cognitive functions were hence quantitatively modulated by THN102.

Conclusion

Data presented here provide the first evidence of a regional brain activation induced by THN102, currently being tested in a phase II clinical trial in narcoleptic patients.

Modafinil alleviates levodopa-induced excessive nighttime sleepiness and restores monoaminergic systems in a nocturnal animal model of Parkinson's disease

Treatment with dopaminergic agents result excessive daytime sleepiness (EDS) and some studies have shown the benefit of using modafinil for treating excessive daytime sleepiness of Parkinson's disease (PD) patient. We investigated whether modafinil have ameliorative properties against levodopa induced excessive nighttime sleepiness (ENS) in MPTP-treated murine nocturnal PD model. Our EEG analyses of whole day recordings revealed that modafinil reduce ENS of this nocturnal PD models with levodopa medications. Therefore, we investigated whether, modafinil post-treatment followed by MPTP shows any effect on monoamine contents of brain and found to robustly increased noradrenaline (NA) concentration of MPTP treated mice. Modafinil post-treatment, in neurorestorative context (5 days post-lesion) led to increased striatal dopamine (DA) concentrations of MPTP-treated mice. Here, we first confirmed that modafinil ameliorates levodopa induced excessive sleepiness and restores monoaminergic systems. The arousal and anti-parkinsonian effects displayed by modafinil indicate that in combination with dopaminergic agents, modafinil co-administration may be worthwhile in trying to suppress the excessive daytime sleepiness and progressive dopaminergic neuron loss in PD.

Glutamine/glutamate (Glx) concentration in prefrontal cortex predicts reversal learning performance in the marmoset

This study used Magnetic Resonance Spectroscopy (MRS) to identify potential neurometabolitic markers of cognitive performance in male (n = 7) and female (n = 8) middle-aged (∼5 years old) common marmosets (Callithrix jacchus). Anesthetized marmosets were scanned with a 4.7 T/40 cm horizontal magnet equipped with 450 mT/m magnetic field gradients and a 20 G/cm magnetic field gradient insert, within 3 months of completing the CANTAB serial Reversal Learning task. Neurometabolite concentrations of N-Acetyl Asparate, Myo-Inositol, Choline, Phosphocreatine + creatine, Glutamate and Glutamine were acquired from a 3 mm³ voxel positioned in the Prefrontal Cortex (PFC). Males acquired the reversals (but not simple discriminations) faster than the females. Higher PFC Glx (glutamate + glutamine) concentration was associated with faster acquisition of the reversals. Interestingly, the correlation between cognitive performance and Glx was significant in males, but not in females. These results suggest that MRS is a useful tool to identify biochemical markers of cognitive performance in the healthy nonhuman primate brain and that biological sex modulates the relationship between neurochemical composition and cognition.

Modafinil Improves Catalepsy in a Rat 6-Hydroxydopamine Model of Parkinson's Disease; Possible Involvement of Dopaminergic Neurotransmission

Purpose: Modafinil is a vigilance-enhancing drug licensed for narcolepsy. The use of modafinil leads to various neuromodulatory effects with very low abuse potential. A body of evidence suggested that modafinil may have anti-parkinsonian effects. This study was designed to evaluate whether modafinil could improve motor dysfunction in the 6-hydroxydopamine (6-OHDA)-induced rat model of Parkinson’s disease.

Methods: Male Wistar rats (180-220 g, n= 98) were used in this study. Parkinsonism was induced by injection of 6-hydroxydopamine (10 μg/2μl in 0.2 % ascorbic acid-saline) into the right striatum. Parkinsonian rats received intraperitoneal (ip) injections of modafinil (50, 75, and 100 mg/kg) and catalepsy-like immobility was assessed by the bar test (BT). Furthermore, involvement of dopamine D₁ and D₂ receptors in modafinil’s anti-parkinsonian effects was studied. For this purpose, parkinsonian animals were pretreated with SCH23390 and raclopride (the dopamine D₁ and D₂ receptor anatgonists, respectively) or SCH23390 + raclopride, and then assessed by the BT.

Results: Modafinil (100 mg/kg) showed anti-cataleptic effects in the BT. Notably, the effect of modafinil in the BT was reversed in parkinsonian rats pretreated with raclopride (1.25 mg/kg) and/or SCH23390 + raclopride (0.75 and 1.25 mg/kg, respectively), but not in those pretreated with SCH23390 (0.75 mg/kg).

Conclusion: Acute administration of modafinil improves 6-OHDA-induced motor impairment possibly through activation of dopamine D₂ receptors.

Modafinil attenuates inflammation via inhibiting Akt/NF-κB pathway in apoE-deficient mouse model of atherosclerosis

Modafinil, an FDA approved wakefulness drug prescribed to narcolepsy patients, has recently been shown to have anti-inflammatory effects and provides protection against neuroinflammation. It is unknown if modafinil can also protect against atherosclerosis, pathogenesis of which implicates inflammation. Using an apoE-deficient mouse model, we tried to elucidate the effects of modafinil treatment on the development of atherosclerosis. We tested serum levels of cytokines. We isolated mouse bone marrow-derived macrophages (BMDMs), detected effect of modafinil on the viability and proliferation of BMDMs, and on oxidized low-density lipoprotein-induced IL-6 and TNF-α, and supernatant level of IFN-γ as well as NF-κB activity in BMDMs. Modafinil inhibited the development of atherosclerosis in apoE^-/- mice. Modafinil suppressed the secretion of pro-inflammatory cytokines IL-6, TNF and IFN-γ, and promoted secretion of anti-inflammatory cytokines IL-4 and IL-10. Modafinil inhibited viability and proliferation of macrophages by negatively regulating levels of pro-inflammatory cytokines, p-Akt, p-IKBα and NF-κB activity in macrophages. Modafinil mitigates inflammation in apoE^-/- atherosclerosis mice via inhibiting NF-κB activity in macrophages, and could potentially serve as a therapeutic agent for atherosclerosis.

Magnetic resonance imaging and tensor-based morphometry in the MPTP non-human primate model of Parkinson's disease

Parkinson’s disease (PD) is the second most common neurodegenerative disorder producing a variety of motor and cognitive deficits with the causes remaining largely unknown. The gradual loss of the nigrostriatal pathway is currently considered the pivotal pathological event. To better understand the progression of PD and improve treatment management, defining the disease on a structural basis and expanding brain analysis to extra-nigral structures is indispensable. The anatomical complexity and the presence of neuromelanin, make the use of non-human primates an essential element in developing putative imaging biomarkers of PD. To this end, ex vivo T₂-weighted magnetic resonance images were acquired from control and 1-methyl-4 phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated marmosets. Volume measurements of the caudate, putamen, and substantia nigra indicated significant atrophy and cortical thinning. Tensor-based morphometry provided a more extensive and hypothesis free assessment of widespread changes caused by the toxin insult to the brain, especially highlighting regional cortical atrophy. The results highlight the importance of developing imaging biomarkers of PD in non-human primate models considering their distinct neuroanatomy. It is essential to further develop these biomarkers in vivo to provide non-invasive tools to detect pre-symptomatic PD and to monitor potential disease altering therapeutics.

Common marmoset (Callithrix jacchus) as a primate model for behavioral neuroscience studies

BACKGROUND

The common marmoset (Callithrix jacchus) has been proposed as a suitable bridge between rodents and larger primates. They have been used in several types of research including auditory, vocal, visual, pharmacological and genetics studies. However, marmosets have not been used as much for behavioral studies.

NEW METHOD

Here we present data from training 12 adult marmosets for behavioral neuroscience studies. We discuss the husbandry, food preferences, handling, acclimation to laboratory environments and neurosurgical techniques. In this paper, we also present a custom built "scoop" and a monkey chair suitable for training of these animals.

RESULTS

The animals were trained for three tasks: 4 target center-out reaching task, reaching tasks that involved controlling robot actions, and touch screen task. All animals learned the center-out reaching task within 1-2 weeks whereas learning reaching tasks controlling robot actions task took several months of behavioral training where the monkeys learned to associate robot actions with food rewards.

COMPARISON TO EXISTING METHOD

We propose the marmoset as a novel model for behavioral neuroscience research as an alternate for larger primate models. This is due to the ease of handling, quick reproduction, available neuroanatomy, sensorimotor system similar to larger primates and humans, and a lissencephalic brain that can enable implantation of microelectrode arrays relatively easier at various cortical locations compared to larger primates.

CONCLUSION

All animals were able to learn behavioral tasks well and we present the marmosets as an alternate model for simple behavioral neuroscience tasks.

Neurometabolic profiles of the substantia nigra and striatum of MPTP-intoxicated common marmosets: An in vivo proton MRS study at 9.4 T

Given the strong coupling between the substantia nigra (SN) and striatum (STR) in the early stage of Parkinson's disease (PD), yet only a few studies reported to date that have simultaneously investigated the neurochemistry of these two brain regions in vivo, we performed longitudinal metabolic profiling in the SN and STR of 1-methyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated common marmoset monkey models of PD (n = 10) by using proton MRS (¹ H-MRS) at 9.4 T. T₂ relaxometry was also performed in the SN by using MRI. Data were classified into control, MPTP_2weeks, and MPTP_6-10 weeks groups according to the treatment duration. In the SN, T₂ of the MPTP_6-10 weeks group was lower than that of the control group (44.33 ± 1.75 versus 47.21 ± 2.47 ms, p < 0.05). The N-acetylaspartate to total creatine ratio (NAA/tCr) and γ-aminobutyric acid to tCr ratio (GABA/tCr) of the MPTP_6-10 weeks group were lower than those of the control group (0.41 ± 0.04 versus 0.54 ± 0.08 (p < 0.01) and 0.19 ± 0.03 versus 0.30 ± 0.09 (p < 0.05), respectively). The glutathione to tCr ratio (GSH/tCr) was correlated with T₂ for the MPTP_6-10 weeks group (r = 0.83, p = 0.04). In the STR, however, GABA/tCr of the MPTP_6-10 weeks group was higher than that of the control group (0.25 ± 0.10 versus 0.16 ± 0.05, p < 0.05). These findings may be an in vivo depiction of the altered basal ganglion circuit in PD brain resulting from the degeneration of nigral dopaminergic neurons and disruption of nigrostriatal dopaminergic projections. Given the important role of non-human primates in translational studies, our findings provide better understanding of the complicated evolution of PD.

Longitudinal study of the substantia nigra in Parkinson disease: A high-field (1) H-MR spectroscopy imaging study

INTRODUCTION

The value of biomarkers in early diagnosis and development of therapeutics in Parkinson's disease (PD) is well established.

METHODS

We used proton magnetic resonance spectroscopy in a prospective, longitudinal study of 23 patients with early PD, naïve to dopaminergic therapy, and six age-matched healthy controls to examine the temporal changes in metabolic profile of substantia nigra over a period of 3 months.

RESULTS

N-acetyl aspartate to creatine ratio at month 3 was compared with baseline values in the PD and control groups, as well as the side-to-side difference of the ratio at baseline. By month 3, n-acetyl aspartate to creatine ratio had decreased by 4.4% in patients with PD (P = 0.024), without a concomitant change in healthy controls. The side-to-side asymmetry was significantly higher in the PD group (16.7%) vs. healthy controls (1.6%, P = 0.0024).

CONCLUSION

Estimation of change in the n-acetyl aspartate to creatine ratio appears to be a fast, quantifiable, and reliable marker of dopaminergic neuronal viability in PD.

Monoamine reuptake inhibitors in Parkinson's disease

The motor manifestations of Parkinson's disease (PD) are secondary to a dopamine deficiency in the striatum. However, the degenerative process in PD is not limited to the dopaminergic system and also affects serotonergic and noradrenergic neurons. Because they can increase monoamine levels throughout the brain, monoamine reuptake inhibitors (MAUIs) represent potential therapeutic agents in PD. However, they are seldom used in clinical practice other than as antidepressants and wake-promoting agents. This review article summarises all of the available literature on use of 50 MAUIs in PD. The compounds are divided according to their relative potency for each of the monoamine transporters. Despite wide discrepancy in the methodology of the studies reviewed, the following conclusions can be drawn: (1) selective serotonin transporter (SERT), selective noradrenaline transporter (NET), and dual SERT/NET inhibitors are effective against PD depression; (2) selective dopamine transporter (DAT) and dual DAT/NET inhibitors exert an anti-Parkinsonian effect when administered as monotherapy but do not enhance the anti-Parkinsonian actions of L-3,4-dihydroxyphenylalanine (L-DOPA); (3) dual DAT/SERT inhibitors might enhance the anti-Parkinsonian actions of L-DOPA without worsening dyskinesia; (4) triple DAT/NET/SERT inhibitors might exert an anti-Parkinsonian action as monotherapy and might enhance the anti-Parkinsonian effects of L-DOPA, though at the expense of worsening dyskinesia.

Modafinil effects on behavior and oxidative damage parameters in brain of wistar rats

The effects of modafinil (MD) on behavioral and oxidative damage to protein and lipid in the brain of rats were evaluated. Wistar rats were given a single administration by gavage of water or MD (75, 150, or 300 mg/kg). Behavioral parameters were evaluated in open-field apparatus 1, 2, and 3 h after drug administration. Thiobarbituric acid reactive substances (TBARS) and protein carbonyl formation were measured in the brain. MD increased locomotor activity at the highest dose 1 and 3 h after administration. MD administration at the dose of 300 mg/kg increased visits to the center of open-field 1 h after administration; however, 3 h after administration, all administered doses of MD increased visits to the open-field center. MD 300 mg/kg increased lipid damage in the amygdala, hippocampus, and striatum. Besides, MD increased protein damage in the prefrontal cortex, amygdala, and hippocampus; however, this effect varies depending on the dose administered. In contrast, the administration of MD 75 and 300 mg/kg decreased the protein damage in the striatum. This study demonstrated that the MD administration induces behavioral changes, which was depending on the dose used. In addition, the effects of MD on oxidative damage parameters seemed to be in specific brain region and doses.

Short- and long-term treatment with modafinil differentially affects adult hippocampal neurogenesis

The generation of new neurons in the dentate gyrus of the adult brain has been demonstrated in many species including humans and is suggested to have functional relevance for learning and memory. The wake promoting drug modafinil has popularly been categorized as a so-called neuroenhancer due to its positive effects on cognition. We here show that short- and long-term treatment with modafinil differentially effects hippocampal neurogenesis. We used different thymidine analogs (5-bromo-2-deoxyuridine (BrdU), chlorodeoxyuridine (CldU), iododeoxyuridine (IdU)) and labeling protocols to investigate distinct regulative events during hippocampal neurogenesis, namely cell proliferation and survival. Eight-week-old mice that were treated with modafinil (64mg/kg, i.p.) every 24h for 4days show increased proliferation in the dentate gyrus indicated by BrdU-labeling and more newborn granule cells 3weeks after treatment. Short-term treatment for 4days also enhanced the number of postmitotic calretinin-expressing progenitor cells that were labeled with BrdU 1week prior to treatment indicating an increased survival of new born immature granule cells. Interestingly, long-term treatment for 14days resulted in an increased number of newborn Prox1(+) granule cells, but we could not detect an additive effect of the prolonged treatment on proliferation and survival of newborn cells. Moreover, daily administration for 14days did not influence the number of proliferating cells in the dentate gyrus. Together, modafinil has an acute impact on precursor cell proliferation as well as survival but loses this ability during longer treatment durations.

Differential effects of modafinil on memory in naïve and memory-impaired rats

Modafinil is a wake-promoting drug and has been approved for the treatment of excessive daytime sleepiness in narcolepsy and obstructive sleep apnea. Modafinil was shown to improve learning and memory in rodents, and to reverse memory deficits induced by sleep deprivation or stress. However, depending on the memory paradigm used, modafinil might also impair memory. We aimed to investigate the effects of modafinil on memory consolidation and retrieval for object recognition and inhibitory avoidance in naïve adult rats. We also investigated whether acute or chronic administration of modafinil would reverse memory deficits induced by iron overload, a model of memory impairment related to neurodegenerative disorders. Adult naïve rats received modafinil (0.0, 0.75, 7.5 or 75 mg/kg) either immediately after training or 1 h prior to testing in object recognition or inhibitory avoidance. Iron-treated rats received modafinil immediately after training in object recognition. In order to investigate the effects of chronic modafinil, iron-treated rats received daily injections of modafinil for 17 days, and 24 h later they were trained in object recognition or inhibitory avoidance. Acute modafinil does not affect memory consolidation or retrieval in naive rats. A single injection of modafinil at the highest dose was able to recover recognition memory in iron-treated rats. Chronic modafinil completely recovered iron-induced recognition memory and emotional memory deficits. Additional preclinical and clinical studies are necessary in order to support the applicability of modafinil in recovering memory impairment associated with neurodegenerative disorders.

Morphological and metabolic changes in the nigro-striatal pathway of synthetic proteasome inhibitor (PSI)-treated rats: a MRI and MRS study

Systemic administration of a Synthetic Proteasome Inhibitor (PSI) in rats has been described as able to provide a model of Parkinson's disease (PD), characterized by behavioral and biochemical modifications, including loss of dopaminergic neurons in the substantia nigra (SN), as assessed by post-mortem studies. With the present study we aimed to assess in-vivo by Magnetic Resonance (MR) possible morphological and metabolic changes in the nigro-striatal pathway of PSI-treated rats. 10 animals were subcutaneously injected with PSI 6.0 mg/kg dissolved in DMSO 100%. Injections were made thrice weekly over the course of two weeks. 5 more animals injected with DMSO 100% with the same protocol served as controls. The animals underwent MR sessions before and at four weeks after the end of treatment with either PSI or vehicle. MR Imaging was performed to measure SN volume and Proton MR Spectroscopy ((1)H-MRS) was performed to measure metabolites changes at the striatum. Animals were also assessed for motor function at baseline and at 4 and 6 weeks after treatment. Dopamine and dopamine metabolite levels were measured in the striata at 6 weeks after treatment. PSI-treated animals showed volumetric reduction of the SN (p<0.02) at 4 weeks after treatment as compared to baseline. Immunofluorescence analysis confirmed MRI changes in SN showing a reduction of tyrosine hydroxylase expression as compared to neuron-specific enolase expression. A reduction of N-acetyl-aspartate/total creatine ratio (p = 0.05) and an increase of glutamate-glutamine-γ amminobutirrate/total creatine were found at spectroscopy (p = 0.03). At 6 weeks after treatment, PSI-treated rats also showed motor dysfunction compared to baseline (p = 0.02), accompanied by dopamine level reduction in the striatum (p = 0.02). Treatment with PSI produced morphological and metabolic modifications of the nigro-striatal pathway, accompanied by motor dysfunction. MR demonstrated to be a powerful mean to assess in-vivo the nigro-striatal pathway morphology and metabolism in the PSI-based PD animal model.

PET analysis of dopaminergic neurodegeneration in relation to immobility in the MPTP-treated common marmoset, a model for Parkinson's disease

Background

Positron Emission Tomography (PET) measurement was applied to the brain of the common marmoset, a small primate species, treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The marmoset shows prominent Parkinson’s disease (PD) signs due to dopaminergic neural degeneration. Recently, the transgenic marmoset (TG) carrying human PD genes is developing. For phenotypic evaluations of TG, non-invasive PET measurement is considered to be substantially significant. As a reference control for TG, the brain of the MPTP-marmoset as an established and valid model was scanned by PET. Behavioral analysis was also performed by recording locomotion of the MPTP-marmoset, as an objective measure of PD signs.

Methodology/Principal Findings

Marmosets received several MPTP regimens (single MPTP regimen: 2 mg/kg, s.c., per day for 3 consecutive days) were used for PET measurement and behavioral observation. To measure immobility as a central PD sign, locomotion of marmosets in their individual living cages were recorded daily by infrared sensors. Daily locomotion counts decreased drastically after MPTP regimens and remained diminished for several months or more. PET scan of the brain, using [¹¹C]PE2I as a ligand of the dopamine (DA) transporter, was performed once several months after the last MPTP regimen. The mean binding potential (BP_ND) in the striatum (putamen and caudate) of the MPTP-marmoset group was significantly lower than that of the MPTP-free control group (n = 5 for each group). In the MPTP-marmosets, the decrease of BP_ND in the striatum closely correlated with the decrease in locomotion counts (r = 0.98 in putamen and 0.91 in caudate).

Conclusion/Significance

The present characterization of neural degeneration using non-invasive PET imaging and of behavioral manifestation in the MPTP marmoset mimics typical PD characteristics and can be useful in evaluating the phenotype of TG marmosets being developed.

Modafinil abrogates methamphetamine-induced neuroinflammation and apoptotic effects in the mouse striatum

Methamphetamine is a drug of abuse that can cause neurotoxic damage in humans and animals. Modafinil, a wake-promoting compound approved for the treatment of sleeping disorders, is being prescribed off label for the treatment of methamphetamine dependence. The aim of the present study was to investigate if modafinil could counteract methamphetamine-induced neuroinflammatory processes, which occur in conjunction with degeneration of dopaminergic terminals in the mouse striatum. We evaluated the effect of a toxic methamphetamine binge in female C57BL/6 mice (4 × 5 mg/kg, i.p., 2 h apart) and modafinil co-administration (2 × 90 mg/kg, i.p., 1 h before the first and fourth methamphetamine injections) on glial cells (microglia and astroglia). We also evaluated the striatal expression of the pro-apoptotic BAX and anti-apoptotic Bcl-2 proteins, which are known to mediate methamphetamine-induced apoptotic effects. Modafinil by itself did not cause reactive gliosis and counteracted methamphetamine-induced microglial and astroglial activation. Modafinil also counteracted the decrease in tyrosine hydroxylase and dopamine transporter levels and prevented methamphetamine-induced increases in the pro-apoptotic BAX and decreases in the anti-apoptotic Bcl-2 protein expression. Our results indicate that modafinil can interfere with methamphetamine actions and provide protection against dopamine toxicity, cell death, and neuroinflammation in the mouse striatum.

Simple synthesis of modafinil derivatives and their anti-inflammatory activity

Simple synthesis of modafinil derivatives and their biological activity are described. The key synthetic strategies involve substitution and coupling reactions. We determined the anti-inflammatory effects of modafinil derivatives in cultured BV2 cells by measuring the inhibition of nitrite production and expression of iNOS and COX-2 after LPS stimulation. It was found that for sulfide analogues introduction of aliphatic groups on the amide part (compounds 11a–d) resulted in lower anti-inflammatory activity compared with cyclic or aromatic moieties (compounds 11e–k). However, for the sulfoxide analogues, introduction of aliphatic moieties (compounds 12a–d) showed higher anti-inflammatory activity than cyclic or aromatic fragments (compounds 12e–k) in BV-2 microglia cells.

Chronic modafinil effects on drug-seeking following methamphetamine self-administration in rats

Acute administration of the cognitive enhancing drug, modafinil (Provigil®), reduces methamphetamine (Meth) seeking following withdrawal from daily self-administration. However, the more clinically relevant effects of modafinil on Meth-seeking after chronic treatment have not been explored. Here, we determined the impact of modafinil on Meth-seeking after chronic daily treatment during extinction or abstinence following Meth self-administration. Rats self-administered intravenous Meth during daily 2-h sessions for 14 d, followed by extinction sessions or abstinence. During this period, rats received daily injections of vehicle, 30, or 100 mg/kg modafinil and were then tested for Meth-seeking via cue, Meth-primed, and context-induced reinstatement at early and late withdrawal time-points. We found that chronic modafinil attenuated relapse to a Meth-paired context, decreased conditioned cue-induced and Meth-primed reinstatement, and resulted in enduring reductions in Meth-seeking even after discontinuation of treatment. Additionally, we determined that only a very high dose of modafinil (300 mg/kg) during maintenance of self-administration had an impact on Meth intake. These results validate and extend clinical and preclinical findings that modafinil may be a viable treatment option for Meth addiction.

Modafinil effects on cognition and emotion in schizophrenia and its neurochemical modulation in the brain

Modafinil is a central nervous system wake promoting agent used for the treatment of excessive daytime sleeping. Its vigilance promoting properties and low abuse potential has intrigued the scientific community and has led to use it as a cognitive enhancer, before its neural functions were understood. Here, we review the effects of modafinil in human cognition and emotion and its specific actions on symptoms in patients with schizophrenia and whether these are consistently effective throughout the literature. We also performed a systematic review on the effects of modafinil on neurotransmitter signalling in different areas of the brain in order to better understand the neuromechanisms of its cognitive and emotional enhancing properties. A review of its effects in schizophrenia suggests that modafinil facilitates cognitive functions, with pro-mnemonic effects and problem solving improvements. Emotional processing also appears to be enhanced by the drug, although to date there are only a limited number of studies. The systematic review on the neurochemical modulation of the modafinil suggests that its mnemonic enhancing properties might be the result of glutamatergic and dopaminergic increased neuronal activation in the hippocampus and in the prefrontal cortex respectively. Other neurotransmitters were also activated by modafinil in various limbic brain areas, suggesting that the drug acts on these brain regions to influence emotional responses. These reviews seek to delineate the neuronal mechanisms by which modafinil affects cognitive and emotional function. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Modafinil inhibits K(Ca)3.1 currents and muscle contraction via a cAMP-dependent mechanism

Modafinil has been used as a psychostimulant for the treatment of narcolepsy. However, its primary mechanism of action remains elusive. Therefore, we examined the effects of modafinil on K(Ca)3.1 channels and vascular smooth muscle contraction. K(Ca)3.1 currents and channel activity were measured using a voltage-clamp technique and inside-out patches in mouse embryonic fibroblast cell line, NIH-3T3 fibroblasts. Intracellular adenosine 3',5'-cyclic monophosphate (cAMP) concentration was measured, and the phosphorylation of K(Ca)3.1 channel protein was examined using western blotting in NIH-3T3 fibroblasts and/or primary cultured mouse aortic smooth muscle cells (SMCs). Muscle contractions were recorded from mouse aorta and rat pulmonary artery by using a myograph developed in-house. Modafinil was found to inhibit K(Ca)3.1 currents in a concentration-dependent manner, and the half-maximal inhibition (IC(50)) of modafinil for the current inhibition was 6.8 ± 0.7 nM. The protein kinase A (PKA) activator forskolin also inhibited K(Ca)3.1 currents. The inhibitory effects of modafinil and forskolin on K(Ca)3.1 currents were blocked by the PKA inhibitors PKI(14-22) or H-89. In addition, modafinil relaxed blood vessels (mouse aorta and rat pulmonary artery) in a concentration-dependent manner. Modafinil increased cAMP concentrations in NIH-3T3 fibroblasts or primary cultured mouse aortic SMCs and phosphorylated K(Ca)3.1 channel protein in NIH-3T3 fibroblasts. However, open probability and single-channel current amplitudes of K(Ca)3.1 channels were not changed by modafinil. From these results, we conclude that modafinil inhibits K(Ca)3.1 channels and vascular smooth muscle contraction by cAMP-dependent phosphorylation, suggesting that modafinil can be used as a cAMP-dependent K(Ca)3.1 channel blocker and vasodilator.

Convenient synthesis and biological evaluation of modafinil derivatives: benzhydrylsulfanyl and benzhydrylsulfinyl [1,2,3]triazol-4-yl-methyl esters

Simple synthesis and biological activities of modafinil derivatives are described. The key reactions include condensation of acid and propargyl alcohol, subsequent 1,3-dipolar cycloaddition reaction of alkynes and (3-azido-propyl)cyclohexane or (4-azido-butyl)benzene in the presence of sodium ascorbate and CuSO₄·5H₂O in excellent yield. They were then evaluated for the suppression of LPS-induced NO generation in vitro. It was found that all compounds showed moderate effects for suppression of LPS-induced NO generation.

In vivo monitoring of recovery from neurodegeneration in conditional transgenic SCA1 mice

Reliable and objective markers of neuronal function and pathology that can directly assess the effects of neuroprotective treatments in the brain are urgently needed for clinical trials in neurodegenerative diseases. Here we assessed the sensitivity of high field proton magnetic resonance spectroscopy ((1)H MRS) to monitor reversal of neurodegeneration by taking advantage of a well characterized conditional mouse model of spinocerebellar ataxia type 1 (SCA1), where the cerebellar pathology and ataxic phenotype are reversible by doxycycline administration. Transgene expression was suppressed by feeding the mice with chow that contains doxycycline from 6 to 12 weeks of age in an early stage group and from 12 to 24 weeks in a mid-stage group. Cerebellar neurochemical profiles of treated and untreated conditional mice were measured at 9.4 tesla (T) before and after treatment and compared to those of wild type (WT) controls, as well as to histology measures (molecular layer thickness in the primary fissure and a global pathological severity score). Concentrations of N-acetylaspartate (NAA) and myo-inositol in the treated mice trended toward normalization to WT levels in both the early and mid-stage groups. The NAA-to-myo-inositol ratio was significantly different between the treated vs. untreated SCA1 mice and demonstrated partial reversal to WT values both at early and mid-stage, consistent with the histological measures. Taurine and total creatine levels were completely normalized in early and mid-stage treatment groups, respectively. The MRS markers were a more sensitive measure of treatment response than the histological measures from the same volume-of-interest in the early stage group. NAA, myo-inositol and taurine levels were significantly correlated with the histology measures in data combined from all groups. These data demonstrate that MRS markers reliably detect rescue from neuronal pathology and imply that the neurochemical levels measured by MRS accurately reflect treatment efficacy. Therefore this study presents an important step in validating MRS biomarkers as potential surrogate markers to evaluate therapeutics in pre-clinical and clinical trials in SCA1.

Attenuated methamphetamine induced neurotoxicity by modafinil administration in mice

Methamphetamine (METH) is a highly addictive drug that might induce neurotoxicity. Clinical trials have reported that modafinil, a wake-promoting agent used to treat sleep disorders, may have some efficacy for the treatment of psychostimulant addiction. In this study we tested possible neuroprotective effects of modafinil after toxic METH administration in mice. We evaluated the effect of modafinil (two injections of either 90 or 180 mg/kg) and METH binge (3 × 7 mg/kg i.p. injections, 3-h apart) coadministration on DA striatal content, TH immunoreactivity in striatal areas and spontaneous locomotor activity. We also investigated acute locomotor activity and stereotypy profile in mice treated with a single METH dose (2 and 7 mg/kg) pretreated with modafinil (90 and 180 mg/kg). We found that mice treated with a METH binge showed a marked decrease in DA and dopaminergic metabolites as well as lower levels of TH immunoreactivity in the dorsal striatum. Pretreatment with modafinil (both 90 and 180 mg/kg) attenuated these effects but did not prevent METH induced decrease in locomotion. We also found that groups that received the combination of both modafinil and single dose METH showed a decrease in total distance traveled in an open field compared with METH groups. We observed an increment in the time mice expended doing stereotypic movements (continuous sniffing) in the group that received the combination of both METH and modafinil (i.e., decreasing locomotion). Our results suggest a possible protective role of modafinil against METH acute striatal toxicity.

Evolution of extra-nigral damage predicts behavioural deficits in a rat proteasome inhibitor model of Parkinson's disease

Establishing the neurological basis of behavioural dysfunction is key to provide a better understanding of Parkinson's disease (PD) and facilitate development of effective novel therapies. For this, the relationships between longitudinal structural brain changes associated with motor behaviour were determined in a rat model of PD and validated by post-mortem immunohistochemistry. Rats bearing a nigrostriatal lesion induced by infusion of the proteasome inhibitor lactacystin into the left-medial forebrain bundle and saline-injected controls underwent magnetic resonance imaging (MRI) at baseline (prior to surgery) and 1, 3 and 5 weeks post-surgery with concomitant motor assessments consisting of forelimb grip strength, accelerating rotarod, and apormorphine-induced rotation. Lactacystin-injected rats developed early motor deficits alongside decreased ipsilateral cortical volumes, specifically thinning of the primary motor (M1) and somatosensory cortices and lateral ventricle hypertrophy (as determined by manual segmentation and deformation-based morphometry). Although sustained, motor dysfunction and nigrostriatal damage were maximal by 1 week post-surgery. Additional volume decreases in the ipsilateral ventral midbrain; corpus striatum and thalamus were only evident by week 3 and 5. Whilst cortical MRI volume changes best predicted the degree of motor impairment, post-mortem tyrosine hydroxylase immunoreactivity in the striatum was a better predictor of motor behaviour overall, with the notable exception of performance in the accelerating rotarod, in which, M1 cortical thickness remained the best predictor. These results highlight the importance of identifying extra-nigral regions of damage that impact on behavioural dysfunction from damage to the nigrostriatal system.

The marmoset as a model of aging and age-related diseases

The common marmoset (Callithrix jacchus) is poised to become a standard nonhuman primate aging model. With an average lifespan of 5 to 7 years and a maximum lifespan of 16½ years, marmosets are the shortest-lived anthropoid primates. They display age-related changes in pathologies that mirror those seen in humans, such as cancer, amyloidosis, diabetes, and chronic renal disease. They also display predictable age-related differences in lean mass, calf circumference, circulating albumin, hemoglobin, and hematocrit. Features of spontaneous sensory and neurodegenerative change--for example, reduced neurogenesis, ß-amyloid deposition in the cerebral cortex, loss of calbindin D(28k) binding, and evidence of presbycusis--appear between the ages of 7 and 10 years. Variation among colonies in the age at which neurodegenerative change occurs suggests the interesting possibility that marmosets could be specifically managed to produce earlier versus later occurrence of degenerative conditions associated with differing rates of damage accumulation. In addition to the established value of the marmoset as a model of age-related neurodegenerative change, this primate can serve as a model of the integrated effects of aging and obesity on metabolic dysfunction, as it displays evidence of such dysfunction associated with high body weight as early as 6 to 8 years of age.

Assessment of metabolic changes in the striatum of a MPTP-intoxicated canine model: in vivo ¹H-MRS study of an animal model for Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the progressive loss of the dopaminergic neurons in the substantia nigra pars compacta, which projects to the striatum. We induced a selective loss of nigrostriatal dopamine neurons, by infusing the mitochondrial complex 1 inhibitor 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine (MPTP) into adult beagle dogs (N=5). Single voxel ¹H water suppressed magnetic resonance spectroscopy (¹H-MRS) at 3 T was used to assess the metabolic changes in the striatum of canine before and after MPTP intoxication. The metabolite spectra obtained from the striatum (voxel size: 2 cm³) showed a lower N-acetyl aspartate to total creatine (creatine+phosphocreatine) ratio after MPTP intoxication. There were no significant differences in other metabolite ratios such as glutamate+glutamine, choline-containing compounds (glycerophosphocholine+phophorylcholine and myo-inositol). Our findings indicated that ¹H-MRS is a sensitive, noninvasive measure of neural toxicity and biochemical alterations of the striatum in a canine model of PD, and further studies are needed to confirm brain metabolic changes in association with progression of MPTP-intoxication.

Daytime sleepiness in elderly Parkinson's disease patients and treatment with the psychostimulant modafinil: A preliminary study

BACKGROUND

Patients with Parkinson's disease (PD) or Parkinsonian syndromes often report excessive daytime sleepiness (EDS). The aim of this study was to evaluate the effects of the psychostimulant modafinil on elderly, institutionalized, severely impaired PD patients with EDS.

METHOD

A three-week open study on ten institutionalized PD patients scoring >10 points on the Epworth Sleepiness Scale (ESS) with modafinil eventually on 100 mg twice a day. Patients were assessed at the start, week 1, and week 3 with ESS, Clinical Global Impression (CGI) scale severity of PD and appetite.

RESULTS

Reduction of ESS score and PD severity over time were found as well as a significant increase in appetite and reduction in CGI score.

CONCLUSION

Modafinil 100 mg twice a day was safe and modestly effective for the treatment of EDS in elderly, institutionalized PD patients. Sustaining wakefulness throughout all stages of PD is crucial for participating in life, maintaining social life, and improving quality of life.

Non-invasive evaluation of nigrostriatal neuropathology in a proteasome inhibitor rodent model of Parkinson's disease

Background

Predominantly, magnetic resonance imaging (MRI) studies in animal models of Parkinson's disease (PD) have focused on alterations in T₂ water ¹H relaxation or ¹H MR spectroscopy (MRS), whilst potential morphological changes and their relationship to histological or behavioural outcomes have not been appropriately addressed. Therefore, in this study we have utilised MRI to scan in vivo brains from rodents bearing a nigrostriatal lesion induced by intranigral injection of the proteasome inhibitor lactacystin.

Results

Lactacystin induced parkinsonian-like behaviour, characterised by impaired contralateral forelimb grip strength and increased contralateral circling in response to apomorphine. T₂-weighted MRI, 3-weeks post-lesion, revealed significant morphological changes in PD-relevant brain areas, including the striatum and ventral midbrain in addition to a decrease in T₂ water ¹H relaxation in the substantia nigra (SN), but not the striatum. Post-mortem histological analyses revealed extensive dopaminergic neuronal degeneration and α-synuclein aggregation in the SN. However, extensive neuronal loss could also be observed in extra-nigral areas, suggesting non-specific toxicity of lactacystin. Iron accumulation could also be observed throughout the midbrain reflecting changes in T₂. Importantly, morphological, but not T₂ relaxivity changes, were significantly associated with both behavioural and histological outcomes in this model.

Conclusions

A pattern of morphological changes in lactacystin-lesioned animals has been identified, as well as alterations in nigral T₂ relaxivity. The significant relationship of morphological changes with behavioural and histological outcomes in this model raises the possibility that these may be useful non-invasive surrogate markers of nigrostriatal degeneration in vivo.

Propagation and characterisation of dendritic cells from G-CSF mobilised peripheral blood monocytes and stem cells in common marmoset monkeys

The common marmoset is a small New World Primate that has been used as an immunological model for a number of human diseases. Dendritic cells (DC) have not been extensively characterised in this species and in particular protocols to derive DC from living donors without the need for animal sacrifice are presently lacking. This study establishes new protocols to generate substantial numbers of marmoset DC for use in cell therapy studies. Recombinant human G-CSF was used to mobilise peripheral blood monocytes and CD34(+) stem cells in sufficient numbers for large scale in-vitro DC propagation using cytokine conditioning including IL-4, GM-CSF, FLT3-L, stem cell factor and thrombopoietin. Marmoset DC exhibited morphology similar to human DC, were capable of antigen uptake and presentation and had moderate allo-stimulatory ability. Monocyte-derived DC had a maturation-resistant immature phenotype, whereas haematopoietic precursor-derived DC were semi-mature in phenotype and function. This study confirms the feasibility of the marmoset as a unique small primate model in which to pursue DC-based immunotherapy strategies.

Intrauterine hyperexposure to dexamethasone of the common marmoset monkey revealed normal cerebral metabolite concentrations in adulthood as assessed by quantitative proton magnetic resonance spectroscopy in vivo

BACKGROUND

Animal models of human brain disorders often have to rely on non-human primates because of their immunological, physiological, and cognitive similarities to humans.

METHODS

Localized proton magnetic resonance spectroscopy was performed to assess cerebral metabolite profiles of male common marmoset monkeys in vivo and to determine putative alterations of adult brain metabolism in response to intrauterine hyperexposure to the synthetic glucocorticoid hormone dexamethasone.

RESULTS

Excellent spectral quality allowed for absolute quantification of the concentrations of major metabolites in predominantly white matter, gray matter, and thalamus. Marmoset monkeys intrauterinely hyperexposed to dexamethasone revealed normal neurochemical profiles at adulthood.

CONCLUSIONS

Prenatally applied dexamethasone does not lead to persistent metabolic alterations affecting adult brain integrity.

In vivo imaging markers of neurodegeneration of the substantia nigra

Non invasive detection and monitoring of substantia nigra degeneration is a long sought aim for neuroscientists, clinicians and pharmaceutical companies with an interest in Parkinson's disease (PD). Functional imaging techniques are established tools to assess the extent of striatal dopaminergic denervation that indirectly reflects nigral degeneration. They allow characterization of the dopaminergic denervation during the premotor phase of PD and have clinical value to establish the diagnosis in parkinsonism, but have proven to be unsatisfactory as surrogate markers in recent treatment trials. There is strong research interest in developing new imaging tests for nigral degeneration using a variety of structural brain imaging techniques. Nigral hyperechogenicity assessed by transcranial sonography emerges as a robust and low cost test to diagnose PD. Additionally, various advanced magnetic resonance imaging contrasts and high field magnetic resonance spectroscopy show promising sensitivity to nigral pathology in PD. Qualification of these emerging imaging tests against defined biomarker criteria is a complex and challenging task ahead. More systematic validation studies analogous to clinical trials are needed to meet the expectations and criteria defined by regulatory bodies before imaging biomarkers can be used as surrogate endpoints for neuroprotective or restorative trials.