Longitudinal positron emission tomography and postmortem analysis reveals widespread neuroinflammation in SARS-CoV-2 infected rhesus macaques

BACKGROUND

Coronavirus disease 2019 (COVID-19) patients initially develop respiratory symptoms, but they may also suffer from neurological symptoms. People with long-lasting effects after acute infections with severe respiratory syndrome coronavirus 2 (SARS-CoV-2), i.e., post-COVID syndrome or long COVID, may experience a variety of neurological manifestations. Although we do not fully understand how SARS-CoV-2 affects the brain, neuroinflammation likely plays a role.

METHODS

To investigate neuroinflammatory processes longitudinally after SARS-CoV-2 infection, four experimentally SARS-CoV-2 infected rhesus macaques were monitored for 7 weeks with 18-kDa translocator protein (TSPO) positron emission tomography (PET) using [¹⁸F]DPA714, together with computed tomography (CT). The baseline scan was compared to weekly PET-CTs obtained post-infection (pi). Brain tissue was collected following euthanasia (50 days pi) to correlate the PET signal with TSPO expression, and glial and endothelial cell markers. Expression of these markers was compared to brain tissue from uninfected animals of comparable age, allowing the examination of the contribution of these cells to the neuroinflammatory response following SARS-CoV-2 infection.

RESULTS

TSPO PET revealed an increased tracer uptake throughout the brain of all infected animals already from the first scan obtained post-infection (day 2), which increased to approximately twofold until day 30 pi. Postmortem immunohistochemical analysis of the hippocampus and pons showed TSPO expression in cells expressing ionized calcium-binding adaptor molecule 1 (IBA1), glial fibrillary acidic protein (GFAP), and collagen IV. In the hippocampus of SARS-CoV-2 infected animals the TSPO⁺ area and number of TSPO⁺ cells were significantly increased compared to control animals. This increase was not cell type specific, since both the number of IBA1⁺TSPO⁺ and GFAP⁺TSPO⁺ cells was increased, as well as the TSPO⁺ area within collagen IV⁺ blood vessels.

CONCLUSIONS

This study manifests [¹⁸F]DPA714 as a powerful radiotracer to visualize SARS-CoV-2 induced neuroinflammation. The increased uptake of [¹⁸F]DPA714 over time implies an active neuroinflammatory response following SARS-CoV-2 infection. This inflammatory signal coincides with an increased number of TSPO expressing cells, including glial and endothelial cells, suggesting neuroinflammation and vascular dysregulation. These results demonstrate the long-term neuroinflammatory response following a mild SARS-CoV-2 infection, which potentially precedes long-lasting neurological symptoms.

Brain Inflammation and Intracellular α-Synuclein Aggregates in Macaques after SARS-CoV-2 Infection

SARS-CoV-2 causes acute respiratory disease, but many patients also experience neurological complications. Neuropathological changes with pronounced neuroinflammation have been described in individuals after lethal COVID-19, as well as in the CSF of hospitalized patients with neurological complications. To assess whether neuropathological changes can occur after a SARS-CoV-2 infection, leading to mild-to-moderate disease, we investigated the brains of four rhesus and four cynomolgus macaques after pulmonary disease and without overt clinical symptoms. Postmortem analysis demonstrated the infiltration of T-cells and activated microglia in the parenchyma of all infected animals, even in the absence of viral antigen or RNA. Moreover, intracellular α-synuclein aggregates were found in the brains of both macaque species. The heterogeneity of these manifestations in the brains indicates the virus’ neuropathological potential and should be considered a warning for long-term health risks, following SARS-CoV-2 infection.

Ketamine treatment upon memory retrieval reduces fear memory in marmoset monkeys

Emotionally arousing experiences are retained very well as seen in posttraumatic stress disorder (PTSD). Various lines of evidence indicate that reactivation of these memories renders them labile which offers a potential time-window for intervention. We tested in non-human primates whether ketamine, administered during fear memory reactivation, affected passive (inhibitory) avoidance learning. For the consolidation of contextual emotional memory, the unescapable foot-shock paradigm in a passive avoidance task with two compartments (dark vs illuminated) was used. After entering the dark compartment, marmoset monkeys received four random foot-shocks (1 mA, 4 s) within 15-min. This stressful exposure increased the saliva cortisol and heart rate and impaired REM-sleep (p<0.05). One week later the monkeys were re-exposed to the stressful situation for the reconsolidation of the fearful experience. During the re-exposure the monkeys were treated with ketamine (0.5 mg/kg) or saline. In week 3, the monkeys were placed in the experimental setting to test their memory for the fearful experience. In contrast to the vehicle-treated monkeys, who avoided the dark compartment, the ketamine-treated monkeys entered the dark compartment that was previously associated with the fearful experience (p<0.05). Post-mortem analysis of the hippocampus showed that ketamine-treated animals exhibited less doublecortin positive neurons and BrdU-labeled cells in the dentate gyrus. This study reveals that a single low dose of ketamine, administered upon fear retrieval in monkeys, reduce contextual fear memory and attenuate neurogenesis in the hippocampus. These are important findings for considering ketamine as a potential candidate to target traumatic memories in PTSD.

How the COVID-19 pandemic highlights the necessity of animal research

Recently, a petition was offered to the European Commission calling for an immediate ban on animal testing. Although a Europe-wide moratorium on the use of animals in science is not yet possible, there has been a push by the non-scientific community and politicians for a rapid transition to animal-free innovations. Although there are benefits for both animal welfare and researchers, advances on alternative methods have not progressed enough to be able to replace animal research in the foreseeable future. This trend has led first and foremost to a substantial increase in the administrative burden and hurdles required to make timely advances in research and treatments for human and animal diseases. The current COVID-19 pandemic clearly highlights how much we actually rely on animal research. COVID-19 affects several organs and systems, and the various animal-free alternatives currently available do not come close to this complexity. In this Essay, we therefore argue that the use of animals is essential for the advancement of human and veterinary health.

Involvement of the Red Nucleus in the Compensation of Parkinsonism may Explain why Primates can develop Stable Parkinson's Disease

Neurological compensatory mechanisms help our brain to adjust to neurodegeneration as in Parkinson's disease. It is suggested that the compensation of the damaged striato-thalamo-cortical circuit is focused on the intact thalamo-rubro-cerebellar pathway as seen during presymptomatic Parkinson, paradoxical movement and sensorimotor rhythm (SMR). Indeed, the size of the red nucleus, connecting the cerebellum with the cerebral cortex, is larger in Parkinson's disease patients suggesting an increased activation of this brain area. Therefore, the red nucleus was examined in MPTP-induced parkinsonian marmoset monkeys during the presymptomatic stage and after SMR activation by neurofeedback training. We found a reverse significant correlation between the early expression of parkinsonian signs and the size of the parvocellular part of the red nucleus, which is predominantly present in human and non-human primates. In quadrupedal animals it consists mainly of the magnocellular part. Furthermore, SMR activation, that mitigated parkinsonian signs, further increased the size of the red nucleus in the marmoset monkey. This plasticity of the brain helps to compensate for dysfunctional movement control and can be a promising target for compensatory treatment with neurofeedback technology, vibrotactile stimulation or DBS in order to improve the quality of life for Parkinson's disease patients.

Sensorimotor rhythm neurofeedback as adjunct therapy for Parkinson's disease

Neurofeedback may enhance compensatory brain mechanisms. EEG‐based sensorimotor rhythm neurofeedback training was suggested to be beneficial in Parkinson's disease. In a placebo‐controlled study in parkinsonian nonhuman primates we here show that sensorimotor rhythm neurofeedback training reduces MPTP‐induced parkinsonian symptoms and both ON and OFF scores during classical L‐DOPA treatment. Our findings encourage further development of sensorimotor rhythm neurofeedback training as adjunct therapy for Parkinson's disease which might help reduce L‐DOPA‐induced side effects.

Individual and Familial Susceptibility to MPTP in a Common Marmoset Model for Parkinson's Disease

INTRODUCTION

Insight into susceptibility mechanisms underlying Parkinson's disease (PD) would aid the understanding of disease etiology, enable target finding and benefit the development of more refined disease-modifying strategies.

METHODS

We used intermittent low-dose MPTP (0.5 mg/kg/week) injections in marmosets and measured multiple behavioral and neurochemical parameters. Genetically diverse monkeys from different breeding families were selected to investigate inter- and intrafamily differences in susceptibility to MPTP treatment.

RESULTS

We show that such differences exist in clinical signs, in particular nonmotor PD-related behaviors, and that they are accompanied by differences in neurotransmitter levels. In line with the contribution of a genetic component, different susceptibility phenotypes could be traced back through genealogy to individuals of the different families.

CONCLUSION

Our findings show that low-dose MPTP treatment in marmosets represents a clinically relevant PD model, with a window of opportunity to examine the onset of the disease, allowing the detection of individual variability in disease susceptibility, which may be of relevance for the diagnosis and treatment of PD in humans.

Progression and recovery of Parkinsonism in a chronic progressive MPTP-induction model in the marmoset without persistent molecular and cellular damage

Chronic exposure to low-dose 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in marmoset monkeys was used to model the prodromal stage of Parkinson's disease (PD), and to investigate mechanisms underlying disease progression and recovery. Marmosets were subcutaneously injected with MPTP for a period of 12weeks, 0.5mg/kg once per week, and clinical signs of Parkinsonism, motor- and non-motor behaviors were recorded before, during and after exposure. In addition, postmortem immunohistochemistry and proteomics analysis were performed. MPTP-induced parkinsonian clinical symptoms increased in severity during exposure, and recovered after MPTP administration was ended. Postmortem analyses, after the recovery period, revealed no alteration of the number and sizes of tyrosine hydroxylase (TH)-positive dopamine (DA) neurons in the substantia nigra. Also levels of TH in putamen and caudate nucleus were unaltered, no differences were observed in DA, serotonin or nor-adrenalin levels in the caudate nucleus, and proteomics analysis revealed no global changes in protein expression in these brain areas between treatment groups. Our findings indicate that parkinsonian symptoms can occur without detectable damage at the cellular or molecular level. Moreover, we show that parkinsonian symptoms may be reversible when diagnosed and treated early.

Muscle contractile properties as an explanation of the higher mean power output in marmosets than humans during jumping

The muscle mass-specific mean power output (PMMS,mean) during push-off in jumping in marmosets (Callithrix jacchus) is more than twice that in humans. In the present study it was tested whether this is attributable to differences in muscle contractile properties. In biopsies of marmoset m. vastus lateralis (VL) and m. gastrocnemius medialis (GM) (N=4), fibre-type distribution was assessed using fluorescent immunohistochemistry. In single fibres from four marmoset and nine human VL biopsies, the force-velocity characteristics were determined. Marmoset VL contained almost exclusively fast muscle fibres (>99.0%), of which 63% were type IIB and 37% were hybrid fibres, fibres containing multiple myosin heavy chains. GM contained 9% type I fibres, 44% type IIB and 47% hybrid muscle fibres. The proportions of fast muscle fibres in marmoset VL and GM were substantially larger than those reported in the corresponding human muscles. The curvature of the force-velocity relationships of marmoset type IIB and hybrid fibres was substantially flatter than that of human type I, IIA, IIX and hybrid fibres, resulting in substantially higher muscle fibre mass-specific peak power (PFMS,peak). Muscle mass-specific peak power output (PMMS,peak) values of marmoset whole VL and GM, estimated from their fibre-type distributions and force-velocity characteristics, were more than twice the estimates for the corresponding human muscles. As the relative difference in estimated PMMS,peak between marmosets and humans is similar to that of PMMS,mean during push-off in jumping, it is likely that the difference in in vivo mechanical output between humans and marmosets is attributable to differences in muscle contractile properties.

Mechanical output in jumps of marmosets (Callithrix jacchus)

In this study we determined the mechanical output of common marmosets (Callithrix jacchus) during jumping. Vertical ground reaction forces were measured in 18 animals while they jumped from an instrumented crossbar to a crossbar located 70 cm higher. From the vertical force time histories, we calculated the rate of change of mechanical energy of the centre of mass (dE/dt). The mean value of dE/dt during the push-off amounted to 51.8±6.2 W kg(-1) body mass, and the peak value to 116.4±17.6 W kg(-1) body mass. We used these values in combination with masses of leg muscles, determined in two specimens, to estimate mean and peak values of dE/dt of 430 and 970 W kg(-1) muscle, respectively. These values are higher than values reported in the literature for jumps of humans and bonobos, but smaller than those of jumps of bushbabies. Surprisingly, the mean value of dE/dt of 430 W kg(-1) muscle was close to the maximal power output of 516 W kg(-1) muscle reported in the literature for isokinetic contractions of rat medial gastrocnemius, one of the fastest mammalian muscles. Further study of the force-velocity relationship of muscle tissue of small primates is indicated.

Oral treatment with the NADPH oxidase antagonist apocynin mitigates clinical and pathological features of parkinsonism in the MPTP marmoset model

This study evaluates the therapeutic efficacy of the NADPH oxidase inhibitor apocynin, isolated as principal bioactive component from the medicinal plant Picrorhiza kurroa, in a marmoset MPTP model of Parkinson's disease (PD). The methoxy-substituted catechol apocynin has a similar structure as homovanillic acid (HVA), a metabolite of dopamine (DA). Apocynin acquires its selective inhibitory capacity of the reactive oxygen species generating NADPH oxidase via metabolic activation by myeloperoxidase (MPO). As MPO is upregulated in activated brain microglia cells of PD patients and in MPTP animal models, the conditions for metabolic activation of apocynin and inhibition of microglia NADPH oxidase are in place. Marmoset monkeys received oral apocynin (100 mg/kg; p.o.) (n = 5) or Gum Arabica (controls; n = 5) three times daily until the end of the study, starting 1 week before PD induction with MPTP (1 mg/kg s.c. for 8 days). Parkinsonian symptoms, motor function, home-cage activity and body weight were monitored to assess the disease development and severity. Post-mortem numbers of the tyrosine hydroxylase expressing DA neurons in the substantia nigra were counted. During the MPTP injections, apocynin limited the body weight loss and relieved parkinsonian symptoms compared to controls (Linear regression, P < 0.05) indicating a reduction of disease progression. During the last test week, apocynin also improved the hand-eye coordination performance compared with vehicle treatment (resp. 39.3 ± 4.5 % and 17.7 ± 6.7 %; P = 0.048) and improved the home cage activity with 32 % (P = 0.029), indicating anti-Parkinson efficacy. Apocynin also increased the number of surviving DA neurons in MPTP-treated marmosets with 8.5 % (P = 0.059), indicating a tendency towards a neuroprotective efficacy. In conclusion, compensation for the loss of DA and its metabolite HVA by apocynin mitigates the PD progression and limits the parkinsonian signs and motor-function deterioration.

Neuroprotective effects of riluzole in early phase Parkinson's disease on clinically relevant parameters in the marmoset MPTP model

The present study evaluates neuroprotection in a marmoset MPTP (1-methyl-1,2,3,6-tetrahydropyridine) model representing early Parkinson's disease (PD). The anti-glutamatergic compound riluzole is used as a model compound for neuroprotection. The compound is one of the few protective compounds used in the clinic for a neurodegenerative disorder. Marmoset monkeys were randomized into three groups of six: 1) an MPTP group receiving a total MPTP dose of 7 mg/kg (4 injections over two weeks, s.c.) 2) a riluzole group receiving besides MPTP, a twice daily dose of riluzole (10 mg/kg, p.o.), starting one week before MPTP and continuing for one week after the final MPTP injection and 3) a control group receiving saline instead of MPTP and riluzole. The marmosets' Parkinsonian symptoms were scored daily and their activity level, hand-eye coordination, jumping behavior, axial turning and night sleep parameters were tested and recorded weekly. At three weeks following the last MPTP challenge, brains were dissected and dopamine levels in the striatum and the tyrosine hydroxylase (TH) expressing dopamine (DA) neurons in the substantia nigra (SN) were compared. MPTP affected all behavioral parameters and sleep architecture and induced a relatively mild (50%) decline of DA neurons in the substantia nigra (SN). Riluzole relieved the Parkinsonian signs, and improved the hand-eye coordination as well as turning ability. Moreover, riluzole prevented the impact of MPTP on sleep architecture and rapid eye movement behavioral disorder (RBD). Riluzole also increased the number of surviving DA neurons in MPTP-treated marmosets to 75%. However, riluzole did not prevent the MPTP-induced impairments on locomotor activity and jumping activity. In conclusion, reduction of excitotoxicity by riluzole appeared to be effective in reducing progressive neurodegeneration and relieved several clinically relevant PD symptoms in an animal model representing the early phase of PD.

REM sleep behavior disorder in the marmoset MPTP model of early Parkinson disease

STUDY OBJECTIVES

Sleep problems are a common phenomenon in most neurological and psychiatric diseases. In Parkinson disease (PD), for instance, sleep problems may be the most common and burdensome non-motor symptoms in addition to the well-described classical motor symptoms. Since sleep disturbances generally become apparent in the disease before motor symptoms emerge, they may represent early diagnostic tools and a means to investigate early mechanisms in PD onset. The sleep disturbance, REM sleep behavior disorder (RBD), precedes PD in one-third of patients. We therefore investigated sleep changes in marmoset monkeys treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP), the non-human primate model for idiopathic PD.

DESIGN

Mild parkinsonism was induced in 5 marmoset monkeys (3M/2F) over a 2-week period of subchronic MPTP treatment. Electroencephalograms (EEGs) and electromyograms (EMGs) were recorded weekly. Motor activity and hand-eye coordination were also measured weekly, and any signs of parkinsonism were noted each day. Sleep parameters, motor activity, and performance data before and after MPTP treatment were compared between MPTP-treated marmosets and 4 control marmosets (1M/3F).

RESULTS

MPTP increased the number of sleep epochs with high-amplitude EMG bouts during REM sleep relative to control animals (mean ± SEM percentage of REM 58.2 ± 9.3 vs. 29.6 ± 7.7; P < 0.05). Of all sleep parameters measured, RBD-like measures discriminated best between MPTP-treated and control animals. On the other hand, functional motor behavior, as measured by hand-eye coordination, was not affected by MPTP treatment (correct trials MPTP: 23.40 ± 3.56 vs. control: 36.13 ± 5.88 correct trials; P = 0.32).

CONCLUSIONS

This REM sleep-specific change, in the absence of profound changes in wake motor behaviors, suggests that the MPTP marmoset model of PD could be used for further studies into the mechanisms and treatment of RBD and other sleep disorders in premotor symptom PD.

The MPTP marmoset model of parkinsonism: a multi-purpose non-human primate model for neurodegenerative diseases

Aging societies face an increasing prevalence of neurodegenerative disorders for which no cure exists. The paucity of relevant animal models that faithfully reproduce clinical and pathogenic features of neurodegenerative diseases is a major cause for the lack of effective therapies. Clinically distinct disorders, such as Alzheimer's and Parkinson's disease, are driven by overlapping pathogenic mechanisms that converge onto vulnerable neurons to ultimately cause abnormal clinical outcomes. These similarities, particularly in the early phases of neurodegeneration, might help identify appropriate animal model systems for studying of cell pathology. While reviewing some of the cellular mechanisms of disease progression, we discuss the MPTP-induced model of Parkinsonism in marmoset monkeys as a model system for construct, face and predictive validity in neurodegenerative studies.

A less stressful animal model: a conditioned avoidance behaviour task for guineapigs

In the conventional shuttle box, animals are trained to avoid electric foot-shocks. As a consequence of these stress-inducing foot-shocks the animals become anxious and are difficult to train. The aim of the present study was to avoid the stress-inducing foot-shocks and to develop a fast and reliable conditioned avoidance behaviour task for guineapigs. We examined whether narrowband noises at four different sound levels above hearing threshold could be used as conditioned stimulus (CS). The unconditioned stimulus (UCS) was a stream of air, which was used instead of the conventionally used electric foot-shocks. The animals were initially trained with a CS of 78 dB sound pressure level (SPL). In this initial training, guineapigs learned to detect a narrowband noise of 78 dB SPL. Interestingly, during the first additional training session in which three other sound levels were applied, guineapigs did not immediately generalize the learned response at 78 dB SPL to lower sound levels of 58 and 68 dB SPL. However, in this session a noise level of 88 dB SPL led immediately to a high level of responses. The response latency decreased with increasing sound level, from approximately 7 s at 58 dB SPL to approximately 3 s at 88 dB SPL. The escape latency during the UCS was approximately 0.6 s. The present results demonstrate that after reducing the level of stress guineapigs can acquire a response in only a few sessions and furthermore, although the guineapigs were less anxious, training at sound levels of 78 and 88 dB SPL was influenced by an aversive reaction by the guineapig. The results indicate that this aversive reaction of the guineapig is crucial for the training.

Therapeutic effects of Delta9-THC and modafinil in a marmoset Parkinson model

Current therapies for Parkinson's disease (PD) like l-dopa and dopamine (DA) agonists have declined efficacy after long term use. Therefore, research towards supplementary or alternative medication is needed. The implementation in PD can be expedited by application of compounds already used in the clinic. In this study the therapeutic effects of the psychoactive compounds Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and modafinil were tested in the 1-methyl-1,2,3,6-tetrahydropyridine (MPTP)-marmoset model for PD. The anti-parkinson effects of Delta(9)-THC (4 mg/kg) and modafinil (100 mg/kg) in parkinsonian marmosets were assessed with two behavioral rating scales covering parkinsonian symptoms and involuntary movements and two test systems assessing the locomotor activity and hand-eye coordination. Delta(9)-THC improved activity and hand-eye coordination, but induced compound-related side-effects. Modafinil improved activity and observed parkinsonian symptoms but not hand-eye coordination. It can be concluded that both compounds have therapeutic values and could supplement existing therapies for PD.

Efficacy of caffeine and modafinil in counteracting sleep deprivation in the marmoset monkey

BACKGROUND AND PURPOSE

The effects of sleep deprivation are a burden in our 24-h society. The use of wake-promoting compounds could improve the performance in situations where sleep cannot be allowed. In this study, the efficacy of the wake-promoting compounds, modafinil and caffeine, in counteracting the effects of 24-h sleep deprivation in the marmoset monkey were tested. As caffeine is habitually used, the efficacy of both compounds after short- and long-term use was investigated.

MATERIALS AND METHODS

After a normal active day, the animals were kept awake and received wake-promoting compounds during the whole night. Three times during the sleep-deprived night, putative fatigue was assessed with an activity test and the vigilance and ability to execute a task was assessed with a hand-eye coordination (HEC) task.

RESULTS

Both compounds were able to counteract to some extent the decline in performance. Modafinil was able to keep the activity at baseline performance, but performance on the HEC task was not improved. Caffeine was able to keep performance in the HEC task at a level just below daytime level but was not able to keep activity at daytime levels during the last part of the night. Caffeine and modafinil administration for 2 weeks showed a comparable effect on activity as acute use. The performance on the HEC task was similar after chronic caffeine and improved after chronic modafinil.

CONCLUSION

It is therefore concluded that modafinil and caffeine were both able to postpone or prevent the decline in vigilance and psychomotor performance and increase in fatigue induced by sleep deprivation.

Neuroprotective effects of modafinil in a marmoset Parkinson model: behavioral and neurochemical aspects

The vigilance-enhancing agent modafinil has neuroprotective properties: it prevents striatal ischemic injury, nigrostriatal pathway deterioration after partial transsection and intoxication with 1-methyl-1,2,3,6-tetrahydropyridine. The present study determines the protective effects of modafinil in the marmoset 1-methyl-1,2,3,6-tetrahydropyridine Parkinson model on behavior and on monoamine levels. Twelve marmoset monkeys were treated with a total dose of 6 mg/kg 1-methyl-1,2,3,6-tetrahydropyridine. Simultaneously, six animals received a daily oral dose of modafinil (100 mg/kg) and six animals received vehicle for 27 days. Behavior was observed daily and the locomotor activity, hand-eye coordination, small fast movements, anxiety-related behavior and startle response of the animals were tested twice a week for 3 weeks. Modafinil largely prevented the 1-methyl-1,2,3,6-tetrahydropyridine-induced change in observed behavior, locomotor activity, hand-eye coordination and small fast movements, whereas the vehicle could not prevent the devastating effects of 1-methyl-1,2,3,6-tetrahydropyridine. Dopamine levels in the striatum of the vehicle+1-methyl-1,2,3,6-tetrahydropyridine-treated animals were reduced to 5% of control levels, whereas the dopamine levels of the modafinil+1-methyl-1,2,3,6-tetrahydropyridine-treated animals were reduced to 41% of control levels. The present data suggest that modafinil prevents decrease of movement-related behavior and dopamine levels after 1-methyl-1,2,3,6-tetrahydropyridine intoxication and can be an efficaceous pharmacological intervention in the treatment of Parkinson's disease.

Behavioral effects of modafinil in marmoset monkeys

RATIONALE

Modafinil is increasingly used in sleep disturbances in general and in neurodegenerative diseases and is recently being used in healthy people for attention control. However, the application of modafinil is possibly not only restricted to alertness enhancing effects. More insight in this compound may lead to new applications. Not all behavioral aspects have been studied sufficiently; therefore, more detailed investigations on modafinil's positive and aversive behavioral effects are addressed in this paper.

OBJECTIVES

Determination of effects of modafinil in marmoset monkeys with observational methods and with behavioral tests measuring locomotor activity, hand-eye coordination, response to a threat situation and startle response.

MATERIALS AND METHODS

Two hours after oral administration of modafinil in doses of 50, 100, 150, and 225 mg/kg, animals were observed and tested in the behavioral test systems.

RESULTS

Locomotor activity was increased after 100 mg/kg modafinil in the Bungalow test and after 100, 150, and 225 mg/kg, as found in the movement parameters of the human threat test. Moreover, modafinil showed anxiolytic-like effects in the human threat test. No other side effects were observed, nor were the hand-eye coordination and startle response affected.

CONCLUSIONS

Besides psychostimulation, modafinil has no aversive effects in the doses used in the domains measured. The potential anxiolytic-like effects of modafinil may create new possibilities for the therapeutic use of modafinil.

Stress adversely affects efficacy of physostigmine–scopolamine pretreatment against soman in guinea pigs

During military operations, soldiers may be exposed to mixtures of chemicals and to physical, emotional and psychological stress factors, which all may influence efficacy of any treatment, including the nerve agent pretreatment regimen. The purpose of this study was therefore to investigate the influence of chronic intermittent, variable, unpredictable and uncontrollable stress conditions on the side effects and therapeutic efficacy of the combination of physostigmine (0.025 mg/kg/h) and scopolamine (0.018 mg/kg/h) as a pretreatment against 2 x LD50 soman intoxication in guinea pigs. Stress during pretreatment led to an increase of motor activity and an increase of power in the EEG delta2 frequency band. After chronic stress, exposure of pretreated animals to 2 x LD50 soman resulted in more severe intoxication symptoms, a more persistent effect on the startle response, and considerable more severe and persistent effects on the EEG power-spectrum, indicating irreversible brain damage.