Computed Tomography as a Method for Age Determination of Carnivora and Odontocetes with Validation from Individuals with Known Age.

Traditional methods for age determination of wildlife include either slicing thin sections off or grinding a tooth, both of which are laborious and invasive. Especially when it comes to ancient and valuable museum samples of rare or extinct species, non-invasive methods are preferable. In this study, X-ray micro-computed tomography (µ-CT) was verified as an alternative non-invasive method for age determination of three species within the order of Carnivora and suborders Odontoceti. Teeth from 13 red foxes (Vulpes vulpes), 2 American mink (Neogale vison), and 2 harbor porpoises (Phocoena phocoena) of known age were studied using µ-CT. The number of visible dental growth layers in the µ-CT were highly correlated with true age for all three species (R2 = 96%, p < 0.001). In addition, the Bland-Altman plot showed high agreement between the age of individuals and visible dental layers represented in 2D slices of the 3D µ-CT images. The true age of individuals was on average 0.3 (±0.6 SD) years higher than the age interpreted by the µ-CT image, and there was a 95% agreement between the true age and the age interpreted from visible dental layers in the µ-CT.

A self-unfolding proximity enabling device for oral delivery of macromolecules.

Oral delivery of macromolecules remains highly challenging due to their rapid degradation in the gastrointestinal tract and poor absorption across the tight junctions of the epithelium. In the last decade, researchers have investigated several medical devices to overcome these challenges using various approaches, some of which involve piercing through the intestine using micro and macro needles. We have developed a new generation of medical devices called self-unfolding proximity enabling devices, which makes it possible to orally deliver macromolecules without perforating the intestine. These devices protect macromolecules from the harsh conditions in the stomach and release their active pharmaceutical ingredients in the vicinity of the intestinal epithelium. One device version is a self-unfolding foil that we have used to deliver insulin and nisin to rats and pigs respectively. In our study, this device has shown a great potential for delivering peptides, with a significant increase in the absorption of solid dosage of insulin by ∼12 times and nisin by ∼4 times in rats and pigs, respectively. With the ability to load solid dosage forms, our devices can facilitate enhanced absorption of minimally invasive oral macromolecule formulations.

Special Challenges in PET Imaging of Ectothermic Vertebrates.

The bulk of biomedical positron emission tomography (PET)-scanning experiments are performed on mammals (ie, rodents, pigs, and dogs), and the technique is only infrequently applied to answer research questions in ectothermic vertebrates such as fish, amphibians, and reptiles. Nevertheless, many unique and interesting physiological characteristics in these ectothermic vertebrates could be addressed in detail through PET. The low metabolic rate of ectothermic animals, however, may compromise the validity of physiological and biochemical parameters derived from the images created by PET and other scanning modalities. Here, we review some of the considerations that should be taken into account when PET scanning fish, amphibians, and reptiles. We present specific results from our own experiments, many of which remain previously unpublished, and we draw on examples from the literature. We conclude that knowledge on the natural history and physiology of the species studied and an understanding of the limitations of the PET scanning techniques are necessary to avoid the design of faulty experiments and erroneous conclusions.

The Self-Stranding Behavior of a Killer Whale (Orcinus orca) in Inner Danish Waters and Considerations concerning Human Interference in Live Strandings.

The rescue attempts of stranded whales and euthanasia considerations must include condition assessments of the individual involved, but this is challenged by our insufficient knowledge about the health statuses of these whales. Here, we describe three separate strandings of a young male killer whale (Orcinus orca) in shallow Danish waters during 2021-2022. During the first two stranding events, the whale exhibited remarkable behavior and, after refloating attempts and several kilometers of swimming, it returned to shallow water. This suggests that it actively chose to be in this shallow water, perhaps to ensure free airways and respiration. During the last stranding, it stayed in shallow water for 30 days, during which, euthanasia was considered due to its seemingly worsened condition, including a collapsed dorsal fin. However, suddenly, the whale swam away and, a year later, he was seen alive, confirming that euthanasia would have been the wrong decision. This case raises an important question as to when and under what circumstances active human interventions, such as refloating attempts, should be launched and when euthanasia should be carried out. Every stranding is unique and decisions should be based on thorough considerations of the animal's health and the chance of a successful rescue.

Combined In Vivo Microdialysis and PET Studies to Validate [11C]Yohimbine Binding as a Marker of Noradrenaline Release.

The noradrenaline system attracts attention for its role in mood disorders and neurodegenerative diseases but the lack of well-validated methods impairs our understanding when assessing its function and release in vivo. This study combines simultaneous positron emission tomography (PET) and microdialysis to explore if [11C]yohimbine, a selective antagonist radioligand of the α2 adrenoceptors, may be used to assess in vivo changes in synaptic noradrenaline during acute pharmacological challenges. Anesthetised Göttingen minipigs were positioned in a head holder in a PET/CT device. Microdialysis probes were placed in the thalamus, striatum and cortex and dialysis samples were collected every 10 min. Three 90 min [11C]yohimbine scans were acquired: at baseline and at two timepoints after the administration of amphetamine (1-10 mg/kg), a non-specific releaser of dopamine and noradrenaline, or nisoxetine (1 mg/kg), a specific noradrenaline transporter inhibitor. [11C]yohimbine volumes of distribution (VT) were obtained using the Logan kinetic model. Both challenges induced a significant decrease in yohimbine VT, with time courses reflecting their different mechanisms of action. Dialysis samples revealed a significant increase in noradrenaline extracellular concentrations after challenge and an inverse correlation with changes in yohimbine VT. These data suggest that [11C]yohimbine can be used to evaluate acute variations in synaptic noradrenaline concentrations after pharmacological challenges.

The Effectiveness of Virtual Fencing of Bull Calves in a Holistic Grazing System.

Large grazers are essential for nature conservation. In order to prevent grazers from moving to unintended areas, it may be necessary to keep them inside enclosures. Physical fences present a number of problems, such as fragmenting the landscape. Virtual fencing, however, is a possible replacement for physical fencing, making it possible to enclose grazers without physical boundaries. Virtual fencing systems utilise collars with GPS technology to track animals and deliver auditory warnings and electric impulses to keep animals within predefined boundaries. This study examines how effective the virtual fencing system Nofence© is at enclosing calves in a holistically managed setting. Holistic management is a rotational grazing technique where an enclosure is grazed in small strips at a time. It is investigated whether the calves become habituated to the virtual fence and whether there is a correlation between the number of warnings received by every two calves in order to explore potential herd behaviour. Finally, this study examines which calves interact the most with the virtual fence by investigating the relationship between physical activity and number of interactions. Seventeen calves were fitted with a GPS collar from the company Nofence© and placed in a holistically managed enclosure. Data were gathered from 4 July to 30 September 2022. The study found that virtual fence was able to contain calves inside the designated enclosure, and over time the calves received notably fewer electrical impulses compared to auditory warnings. The results of Pearson's correlation between auditory warnings received by two random calves were inconclusive, but the use of a sliding window analysis should be further explored. Lastly, the most physically active animals were the ones who received the most auditory warnings, but they did not receive more impulses. No significant correlation was found between the number of electric impulses received and the physical activity of the animals.

Facing Danger: Exploring Personality and Reactions of European Hedgehogs (Erinaceus europaeus) towards Robotic Lawn Mowers.

The populations of European hedgehog (Erinaceus europaeus) are in decline, and it is essential that research identifies and mitigates the factors causing this. Hedgehogs are increasingly sharing habitats with humans, being exposed to a range of dangers in our backyards. Previous research has documented that some models of robotic lawn mowers can cause harm to hedgehogs. This study explored the personality and behaviour of 50 live hedgehogs when facing an approaching, disarmed robotic lawn mower. By combining a novel arena and novel object test, we found that 27 hedgehogs could be categorised as "shy" and 23 as "bold", independently of sex and age. The encounter tests with a robotic lawn mower showed that the hedgehogs positioned themselves in seven different ways. Personality did not affect their reactions. Adult hedgehogs tended to react in a shyer manner, and the hedgehogs, generally, acted less boldly during their second encounter with the robotic lawn mower. Additionally, our results show that bold individuals reacted in a more unpredictable way, being more behaviourally unstable compared to the shy individuals. This knowledge will be applied in the design of a standardised hedgehog safety test, eventually serving to produce and approve hedgehog-friendly robotic lawn mowers.

Testing the Impact of Robotic Lawn Mowers on European Hedgehogs (Erinaceus europaeus) and Designing a Safety Test.

Previous research has established that some models of robotic lawn mowers are potentially harmful to hedgehogs. As the market for robotic lawn mowers is expanding rapidly and the populations of European hedgehogs (Erinaceus europaeus) are in decline, it is important to investigate this risk further to understand the potential threat which some robotic lawn mowers may pose to hedgehogs. We tested 19 models of robotic lawn mowers in collision with hedgehog cadavers to measure their effect on hedgehogs. Our results showed that some models of robotic lawn mowers may injure hedgehogs, whereas others are not harmful to them. Apart from one single incidence, all robotic lawn mowers had to physically touch the hedgehog carcasses to detect them. Larger hedgehog cadavers were less likely to be "injured", with height being the most influential measure of size. The firmness of the tested hedgehog cadavers (frozen or thawed) did not influence the outcome of the collision tests. Neither the position of the hedgehog cadavers nor the selected technical features of the lawn mowers affected the probability of injury. Based on the results, we designed a standardised safety test to measure the effect of a specific model of robotic lawn mower on hedgehogs.

Heterochronic maturation of anatomical plugs for protecting the airway in rorqual whales (Balaenopteridae).

Recently, a unique mechanism for protecting the airway during lunge feeding was discovered in rorqual whales (Balaenopteridae). This mechanism is based on an oral plug structure in the soft palate with similarities in musculo-fatty composition to the nasal plugs protecting the respiratory tract of rorquals from water entry and barotrauma during diving. As a follow-up, we present here a developmental series on fetal, prenatal, juvenile and adult specimens across five species of rorquals, showing differential maturation of the nasal and oral respiratory protection plugs. Nasal plugs are fully formed to serve an immediate crucial function at birth. By contrast, the soft palate remains muscular until the onset of solid food intake, where a musculo-fatty oral plug is developed.

Cortisol in Manure from Cattle Enclosed with Nofence Virtual Fencing.

To increase the efficiency and geographic expansion of nature conservation, large grazers have recently been used, either in the form of wild hoof-bearing animals or as domesticated ruminants including cattle. Using physical fencing limits migrating wildlife, while virtual fences encourage the animals to stay in the desired area without physical restrictions on wild animals. However, virtual fences raise ethical questions regarding the electric impulses emitted by the collar and stress in the fenced animals. Here, we tested if keeping twelve Angus cows (Bos Taurus) in a virtual fencing (Nofence©) compromised their welfare. For this purpose, we collected manure samples from five cows every second day prior to and after the transition from traditional to virtual fencing over a period of 18 days. Cortisol concentrations were 20.6 ± 5.23 ng/g w/w (mean ± SD), ranging from 12 to 42 ng/g w/w across individuals and concentrations did not change over the study period. We, therefore, conclude that there is no evidence suggesting that the cows were stressed from the use for virtual fencing, thus making virtual fencing a reasonable alternative to traditional electric physical fencing of cows.

Skull and Neck Lesions in a Long-Finned Pilot Whale (Globicephala melas): A Result of Ship Collision?

Necropsy on an adult male pilot whale stranded in Denmark in an area with heavy boat traffic revealed internal lesions in the head and neck region, while the exterior did not show any visible lesions. We found multiple fractured bones, muscle trauma and extensive hemorrhage including a fractured occipital bone with several fragments and bone pieces deeply embedded into the cerebrum of the brain. The brain was literally smashed while the third and partially fourth cervical vertebrae were almost pulverized surrounded by large amounts of blood and muscle contusion. The whale was likely killed due to a ship collision, and this particular case substantiates the value of always performing full necropsies including incisions in head and neck regions on all stranded whales-especially in areas with heavy boat traffic. This case demonstrates the importance of veterinarians performing full necropsies of whales to rule out other causes of death. Otherwise, ship collisions may be an overlooked issue having implications for population health.

N-(4-[18F]fluorobenzyl)cholylglycine, a potential tracer for positron emission tomography of enterohepatic circulation and drug-induced inhibition of ileal bile acid transport. A proof-of-concept PET/CT study in pigs.

INTRODUCTION: Enterohepatic circulation (EHC) of conjugated bile acids is an important physiological process crucial for bile acids to function as detergents and signal carriers. Perturbation of the EHC by disease or drugs may lead to serious and life-threatening liver and gastrointestinal disorders. In this proof-of-concept study in pigs, we investigate the potential of N-(4-[18F]fluorobenzyl)cholylglycine ([18F]FBCGly) as tracer for quantitative positron emission tomography (PET) of the EHC of conjugated bile acids. METHODS: The biodistribution of [18F]FBCGly was investigated by PET/CT in domestic pigs following intravenous and intraileal administration of the tracer. Hepatic kinetics were estimated from PET and blood data using a 2-tissue compartmental model and dual-input of [18F]FBCGly. The ileal uptake of [18F]FBCGly was investigated with co-injection of nifedipine and endogenous cholyltaurine. Dosimetry was estimated from the PET data using the Olinda 2.0 software. Blood, bile and urine samples were analyzed for possible fluorine-18 labelled metabolites of [18F]FBCGly. RESULTS: [18F]FBCGly was rapidly taken up by the liver and excreted into bile, and underwent EHC without being metabolized. Both nifedipine and endogenous cholyltaurine inhibited the ileal uptake of [18F]FBCGly. The flow-dependent hepatic uptake clearance was estimated to median 1.2 mL blood/min/mL liver tissue. The mean residence time of [18F]FBCGly in hepatocytes was 4.0 ± 1.1 min. Critical organs for [18F]FBCGly were the gallbladder wall (0.94 mGy/MBq) and the small intestine (0.50 mGy/MBq). The effective dose for [18F]FBCGly was 36 µSv/MBq. CONCLUSION: We have shown that [18F]FBCGly undergoes EHC in pigs without being metabolized and that its ileal uptake is inhibited by nifedipine and endogenous bile acids. Combined with our previous findings in rats, we believe that [18F]FBCGly has potential as PET tracer for assessment of EHC of conjugated bile acids under physiological conditions as well as conditions with perturbed hepatic and ileal bile acid transport.

Impact of aging on animal models of Parkinson's disease.

Aging is the biggest risk factor for developing Parkinson's disease (PD), the second most common neurodegenerative disorder. Several animal models have been developed to explore the pathophysiology underlying neurodegeneration and the initiation and spread of alpha-synuclein-related PD pathology, and to investigate biomarkers and therapeutic strategies. However, bench-to-bedside translation of preclinical findings remains suboptimal and successful disease-modifying treatments remain to be discovered. Despite aging being the main risk factor for developing idiopathic PD, most studies employ young animals in their experimental set-up, hereby ignoring age-related cellular and molecular mechanisms at play. Consequently, studies in young animals may not be an accurate reflection of human PD, limiting translational outcomes. Recently, it has been shown that aged animals in PD research demonstrate a higher susceptibility to developing pathology and neurodegeneration, and present with a more disseminated and accelerated disease course, compared to young animals. Here we review recent advances in the investigation of the role of aging in preclinical PD research, including challenges related to aged animal models that are limiting widespread use. Overall, current findings indicate that the use of aged animals may be required to account for age-related interactions in PD pathophysiology. Thus, although the use of older animals has disadvantages, a model that better represents clinical disease within the elderly would be more beneficial in the long run, as it will increase translational value and minimize the risk of therapies failing during clinical studies. Furthermore, we provide recommendations to manage the challenges related to aged animal models.

Lymph Nodes Draining Infections Investigated by PET and Immunohistochemistry in a Juvenile Porcine Model.

BACKGROUND: [18F]FDG and [11C]methionine accumulate in lymph nodes draining S. aureus -infected foci. The lymph nodes were characterized by weight, [11C]methionine- and [18F]FDG-positron emissions tomography (PET)/computed tomography (CT), and immunohistochemical (IHC)-staining. METHODS: 20 pigs inoculated with S. aureus into the right femoral artery were PET/CT-scanned with [18F]FDG, and nine of the pigs were additionally scanned with [11C]methionine. Mammary, medial iliac, and popliteal lymph nodes from the left and right hind limbs were weighed. IHC-staining for calculations of area fractions of Ki-67, L1, and IL-8 positive cells was done in mammary and popliteal lymph nodes from the nine pigs. RESULTS: The pigs developed one to six osteomyelitis foci. Some pigs developed contiguous infections of peri-osseous tissue and inoculation-site abscesses. Weights of mammary and medial iliac lymph nodes and their [18F]FDG maximum Standardized Uptake Values (SUVFDGmax) showed a significant increase in the inoculated limb compared to the left limb. Popliteal lymph node weight and their FDG uptake did not differ significantly between hind limbs. Area fractions of Ki-67 and IL-8 in the right mammary lymph nodes and SUVMetmax in the right popliteal lymph nodes were significantly increased compared with the left side. CONCLUSION: The PET-tracers [18F]FDG and [11C]methionine, and the IHC- markers Ki-67 and IL-8, but not L1, showed increased values in lymph nodes draining soft tissues infected with S. aureus. The increase in [11C]methionine may indicate a more acute lymph node response, whereas an increase in [18F]FDG may indicate a more chronic response.

Spontaneous partial recovery of striatal dopaminergic uptake despite nigral cell loss in asymptomatic MPTP-lesioned female minipigs.

The Göttingen minipig is a large animal with a gyrencephalic brain that expresses -complex behavior, making it an attractive model for Parkinson's disease research. Here, we investigate the temporal evolution of presynaptic dopaminergic function for 14 months after injections of 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) into the minipig using a multi-tracer longitudinal positron emission tomography (PET) design. We injected seven sedated minipigs with 1-2 mg/kg of MPTP, and two with saline, three times a week over four weeks. We monitored behavioral deficits using a validated motor scale and walking mat. Brains were imaged with (+)-⍺-[11C]-dihydrotetrabenazine ([11C]-DTBZ) and [18F]-dihydroxyphenylalanine ([18F]-FDOPA) PET at baseline and 1, 3, 10 and 14 months after MPTP injection, and immunohistochemistry was used to assess nigral cell loss. The minipigs showed mild bradykinesia and impaired coordination at early timepoints after MPTP. PET revealed decreases of striatal [11C]-DTBZ and [18F]-FDOPA uptake post-MPTP with partial spontaneous recovery of [18F]-FDOPA after 10 months. Postmortem analysis estimated an MPTP-induced nigral loss of 57% tyrosine hydroxylase+ and 43% Nissl-stained cells. Normal motor function despite substantial damage to the dopaminergic system is consistent with prodromal Parkinson's disease, and offers an opportunity for testing disease-modifying therapies. However, partial spontaneous recovery of dopamine terminal function must be taken into account in future studies.

Is Virtual Fencing an Effective Way of Enclosing Cattle? Personality, Herd Behaviour and Welfare.

In modern nature conservation and rewilding there is a need for controlling the movements of large grazers in extensively managed areas. The inflexibility of physical fencing can be a limitation in nature management, and the physical boundaries created by physical fencing can have detrimental effects on wildlife. Virtual fencing systems provide boundaries without physical structures. These systems utilise collars with GPS technology to track animals and deliver auditory or electric cues to encourage the animals to stay within the predefined boundaries. This study aims to assess the use of virtual fencing (Nofence©) to keep twelve Angus cows (Bos taurus) within a virtual enclosure without compromising their welfare. As such, the study examines inter-individual differences between the cows as well as their herd behaviour, when reacting and learning to respond appropriately to virtual fencing. Moreover, the activity of the cows was used as an indicator of welfare. The virtual fencing was successful in keeping the herd within the designated area. Moreover, the cattle learned to avoid the virtual border and respond to auditory cues, where the cows received significantly more auditory warning and electric impulses per week throughout the first 14 days than the remaining 125 days (p < 0.001). The cows were found to express both inter-individual differences (p < 0.001) and herd behaviour. The cattle did not express any significant changes in their activity upon receiving an electrical impulse from the collar. Thus, indicating that there were little to no acute welfare implications associated with the use of virtual fencing in this study. This study clearly supports the potential for virtual fencing as a viable alternative to physical electric fencing. However, it also shows that both individual differences in personality and herd structure should be considered when selecting individuals for virtual fencing.

Validation and optimisation of an automatic blood sampler for preclinical positron emission tomography research in domestic pigs.

In preclinical positron emission tomography animal studies, continuous blood sampling is used to measure the time course of the activity concentration in arterial blood. However, pigs have hypercoagulable blood that tends to clot inside plastic tubes. We tested several tube materials and lengths and the use of three-way connectors. We validated set-ups for automated blood sampling with and without blood recirculation that could run for 90 minutes without problematic clots and without any evidence of emboli formation during necropsy.

Preclinical Testing of Radiopharmaceuticals for the Detection and Characterization of Osteomyelitis: Experiences from a Porcine Model.

The development of new and better radioactive tracers capable of detecting and characterizing osteomyelitis is an ongoing process, mainly because available tracers lack selectivity towards osteomyelitis. An integrated part of developing new tracers is the performance of in vivo tests using appropriate animal models. The available animal models for osteomyelitis are also far from ideal. Therefore, developing improved animal osteomyelitis models is as important as developing new radioactive tracers. We recently published a review on radioactive tracers. In this review, we only present and discuss osteomyelitis models. Three ethical aspects (3R) are essential when exposing experimental animals to infections. Thus, we should perform experiments in vitro rather than in vivo (Replacement), use as few animals as possible (Reduction), and impose as little pain on the animal as possible (Refinement). The gain for humans should by far exceed the disadvantages for the individual experimental animal. To this end, the translational value of animal experiments is crucial. We therefore need a robust and well-characterized animal model to evaluate new osteomyelitis tracers to be sure that unpredicted variation in the animal model does not lead to a misinterpretation of the tracer behavior. In this review, we focus on how the development of radioactive tracers relies heavily on the selection of a reliable animal model, and we base the discussions on our own experience with a porcine model.

Radiotracers for Bone Marrow Infection Imaging.

INTRODUCTION: Radiotracers are widely used in medical imaging, using techniques of gamma-camera imaging (scintigraphy and SPECT) or positron emission tomography (PET). In bone marrow infection, there is no single routine test available that can detect infection with sufficiently high diagnostic accuracy. Here, we review radiotracers used for imaging of bone marrow infection, also known as osteomyelitis, with a focus on why these molecules are relevant for the task, based on their physiological uptake mechanisms. The review comprises [67Ga]Ga-citrate, radiolabelled leukocytes, radiolabelled nanocolloids (bone marrow) and radiolabelled phosphonates (bone structure), and [18F]FDG as established radiotracers for bone marrow infection imaging. Tracers that are under development or testing for this purpose include [68Ga]Ga-citrate, [18F]FDG, [18F]FDS and other non-glucose sugar analogues, [15O]water, [11C]methionine, [11C]donepezil, [99mTc]Tc-IL-8, [68Ga]Ga-Siglec-9, phage-display selected peptides, and the antimicrobial peptide [99mTc]Tc-UBI29-41 or [68Ga]Ga-NOTA-UBI29-41. CONCLUSION: Molecular radiotracers allow studies of physiological processes such as infection. None of the reviewed molecules are ideal for the imaging of infections, whether bone marrow or otherwise, but each can give information about a separate aspect such as physiology or biochemistry. Knowledge of uptake mechanisms, pitfalls, and challenges is useful in both the use and development of medically relevant radioactive tracers.

Ageing promotes pathological alpha-synuclein propagation and autonomic dysfunction in wild-type rats.

Neuronal aggregates of misfolded alpha-synuclein protein are found in the brain and periphery of patients with Parkinson's disease. Braak and colleagues have hypothesized that the initial formation of misfolded alpha-synuclein may start in the gut, and then spread to the brain via peripheral autonomic nerves hereby affecting several organs, including the heart and intestine. Age is considered the greatest risk factor for Parkinson's disease, but the effect of age on the formation of pathology and its propagation has not been studied in detail. We aimed to investigate whether propagation of alpha-synuclein pathology from the gut to the brain is more efficient in old versus young wild-type rats, upon gastrointestinal injection of aggregated alpha-synuclein. Our results demonstrate a robust age-dependent gut-to-brain and brain-to-gut spread of alpha-synuclein pathology along the sympathetic and parasympathetic nerves, resulting in age-dependent dysfunction of the heart and stomach, as observed in patients with Parkinson's disease. Moreover, alpha-synuclein pathology is more densely packed and resistant to enzymatic digestion in old rats, indicating an age-dependent maturation of alpha-synuclein aggregates. Our study is the first to provide a detailed investigation of alpha-synuclein pathology in several organs within one animal model, including the brain, skin, heart, intestine, spinal cord and autonomic ganglia. Taken together, our findings suggest that age is a crucial factor for alpha-synuclein aggregation and complete propagation to heart, stomach and skin, similar to patients. Given that age is the greatest risk factor for human Parkinson's disease, it seems likely that older experimental animals will yield the most relevant and reliable findings. These results have important implications for future research to optimize diagnostics and therapeutics in Parkinson's disease and other age-associated synucleinopathies. Increased emphasis should be placed on using aged animals in preclinical studies and to elucidate the nature of age-dependent interactions.