Squirrel Monkeys Research Articles

Reinforcing and adverse observable effects of nicotine and minor tobacco alkaloids in squirrel monkeys

The most prevalent psychoactive chemical in tobacco smoke is nicotine, which has been shown to maintain tobacco consumption as well as cause acute adverse effects at high doses, like nausea and emesis. Recent studies in laboratory animals have suggested that many non-nicotine constituents of tobacco smoke (e.g., minor tobacco alkaloids) may also contribute to tobacco’s overall reinforcing and adverse effects. Here, we used intravenous (IV) self-administration (n = 3) and observation (n = 4) procedures in squirrel monkeys to, respectively, compare the reinforcing and adverse observable effects of nicotine and three prominent minor tobacco alkaloids, nornicotine, anatabine, and myosmine. In self-administration studies, male squirrel monkeys were trained to respond under a second-order fixed-interval schedule of reinforcement and dose-effects functions for nicotine and each of the minor tobacco alkaloids nornicotine, anatabine, and mysomine were determined. Observation studies were conducted in a different group of male squirrel monkeys to quantify the ability of nicotine, nornicotine, anatabine, and mysomine to produce adverse overt effects, including hypersalivation, emesis, and tremors. Results show that nicotine and to a lesser extent nornicotine were readily self-administered, whereas anatabine and myosmine were not. In observation studies, all minor tobacco alkaloids produced adverse observable effects that were either comparable or more pronounced than nicotine. Collectively, the present results showing that nicotine and the minor tobacco alkaloids nornicotine, anatabine, and myosmine produce differential reinforcing and acute adverse observable effects in monkeys provides further evidence that these constituents may differently contribute to the psychopharmacological and adverse effects of tobacco consumption.

Trade-offs shaping transmission of sylvatic dengue and Zika viruses in monkey hosts

Mosquito-borne dengue (DENV) and Zika (ZIKV) viruses originated in Old World sylvatic (forest) cycles involving monkeys and canopy-living Aedes mosquitoes. Both viruses spilled over into human transmission and were translocated to the Americas, opening a path for spillback into Neotropical sylvatic cycles. Studies of the trade-offs that shape within-host dynamics and transmission of these viruses are lacking, hampering efforts to predict spillover and spillback. We infected a native, Asian host species (cynomolgus macaque) and a novel, American host species (squirrel monkey) with sylvatic strains of DENV-2 or ZIKV via mosquito bite. We then monitored aspects of viral replication (viremia), innate and adaptive immune response (natural killer (NK) cells and neutralizing antibodies, respectively), and transmission to mosquitoes. In both hosts, ZIKV reached high titers that translated into high transmission to mosquitoes; in contrast DENV-2 replicated to low levels and, unexpectedly, transmission occurred only when serum viremia was below or near the limit of detection. Our data reveal evidence of an immunologically-mediated trade-off between duration and magnitude of virus replication, as higher peak ZIKV titers are associated with shorter durations of viremia, and higher NK cell levels are associated with lower peak ZIKV titers and lower anti-DENV-2 antibody levels. Furthermore, patterns of transmission of each virus from a Neotropical monkey suggest that ZIKV has greater potential than DENV-2 to establish a sylvatic transmission cycle in the Americas.

Identification of Specific Cell Surface Markers on Immune Cells of Squirrel Monkeys (Saimiri sciureus).

Nonhuman primates are an important experimental model for the development of targeted biological therapeutics because of their immunological closeness to humans. However, there are very few antibody reagents relevant for delineating the different immune cell subsets based on nonhuman primate antigens directly or with cross-reactivity to those in humans. Here, we report specific expression of HLA-DR, PD-1, and CD123 on different circulating immune cell subsets in the peripheral blood that included T cells (CD3+), T cells subsets (CD4+ and CD8+), B cells (CD20+), natural killer (NK) cells (CD3-CD16+), and natural killer T cells (CD3+CD16+) along with different monocyte subsets in squirrel monkey (Saimiri sciureus). We established cross-reactivity of commercial mouse antihuman monoclonal antibodies (mAbs), with these various immune cell surface markers. These findings should aid further future comprehensive understanding of the immune parameters and identification of new biomarkers to significantly improve SQM as a model for biomedical studies.

PXg: Comprehensive Identification of Noncanonical MHC-I–Associated Peptides From De Novo Peptide Sequencing Using RNA-Seq Reads

Discovering noncanonical peptides has been a common application of proteogenomics. Recent studies suggest that certain noncanonical peptides, known as noncanonical major histocompatibility complex-I (MHC-I)-associated peptides (ncMAPs), that bind to MHC-I may make good immunotherapeutic targets. De novo peptide sequencing is a great way to find ncMAPs since it can detect peptide sequences from their tandem mass spectra without using any sequence databases. However, this strategy has not been widely applied for ncMAP identification because there is not a good way to estimate its false-positive rates. In order to completely and accurately identify immunopeptides using de novo peptide sequencing, we describe a unique pipeline called proteomics X genomics. In contrast to current pipelines, it makes use of genomic data, RNA-Seq abundance and sequencing quality, in addition to proteomic features to increase the sensitivity and specificity of peptide identification. We show that the peptide-spectrum match quality and genetic traits have a clear relationship, showing that they can be utilized to evaluate peptide-spectrum matches. From 10 samples, we found 24,449 canonical MHC-I–associated peptides and 956 ncMAPs by using a target-decoy competition. Three hundred eighty-seven ncMAPs and 1611 canonical MHC-I–associated peptides were new identifications that had not yet been published. We discovered 11 ncMAPs produced from a squirrel monkey retrovirus in human cell lines in addition to the two ncMAPs originating from a complementarity determining region 3 in an antibody thanks to the unrestricted search space assumed by de novo sequencing. These entirely new identifications show that proteomics X genomics can make the most of de novo peptide sequencing’s advantages and its potential use in the search for new immunotherapeutic targets.

Diversity and prevalence of zoonotic infections at the animal-human interface of primate trafficking in Peru.

Wildlife trafficking creates favorable scenarios for intra- and inter-specific interactions that can lead to parasite spread and disease emergence. Among the fauna affected by this activity, primates are relevant due to their potential to acquire and share zoonoses - infections caused by parasites that can spread between humans and other animals. Though it is known that most primate parasites can affect multiple hosts and that many are zoonotic, comparative studies across different contexts for animal-human interactions are scarce. We conducted a multi-parasite screening targeting the detection of zoonotic infections in wild-caught monkeys in nine Peruvian cities across three contexts: captivity (zoos and rescue centers, n = 187); pet (households, n = 69); and trade (trafficked or recently confiscated, n = 132). We detected 32 parasite taxa including mycobacteria, simian foamyvirus, bacteria, helminths, and protozoa. Monkeys in the trade context had the highest prevalence of hemoparasites (including Plasmodium malariae/brasilianum, Trypanosoma cruzi, and microfilaria) and enteric helminths and protozoa were less common in pet monkeys. However, parasite communities showed overall low variation between the three contexts. Parasite richness (PR) was best explained by host genus and the city where the animal was sampled. Squirrel (genus Saimiri) and wooly (genus Lagothrix) monkeys had the highest PR, which was ~2.2 times the PR found in tufted capuchins (genus Sapajus) and tamarins (genus Saguinus/Leontocebus) in a multivariable model adjusted for context, sex, and age. Our findings illustrate that the threats of wildlife trafficking to One Health encompass exposure to multiple zoonotic parasites well-known to cause disease in humans, monkeys, and other species. We demonstrate these threats continue beyond the markets where wildlife is initially sold; monkeys trafficked for the pet market remain a reservoir for and contribute to the translocation of zoonotic parasites to households and other captive facilities where contact with humans is frequent. Our results have practical applications for the healthcare of rescued monkeys and call for urgent action against wildlife trafficking and ownership of monkeys as pets.

Quantitative assessment of grasping strength in platyrrhine monkeys.

Despite the longstanding importance of grasping adaptations in theories of primate evolution, quantitative data on primate grasping strength remain rare. We present the results of two studies testing the prediction that callitrichines-given their comparative retreat from a small-branch environment and specialization for movement and foraging on tree trunks and large boughs-should be characterized by weaker grasping forces and underdeveloped digital flexor muscles relative to other platyrrhines. First, we directly measured manual grasping strength in marmosets (Callithrix jacchus) and squirrel monkeys (Saimiri boliviensis), using a custom-constructed force transducer. Second, we reanalyzed existing datasets on the fiber architecture of forearm and leg muscles in 12 platyrrhine species, quantifying digital flexor muscle physiological cross-sectional area (i.e., PCSA, a morphometric proxy of muscle strength) relative to the summed PCSA across all forearm or leg muscles. Callithrix was characterized by lower mean and maximum grasping forces than Saimiri, and callitrichines as a clade were found to have relatively underdeveloped manual digital flexor muscle PCSA. However, relative pedal digital flexor PCSA did not significantly differ between callitrichines and other platyrrhines. We found partial support for the hypothesis that variation in predominant substrate usage explains variation in empirical measurements of and morphological correlates of grasping strength in platyrrhines. Future research should extend the work presented here by (1) collecting morphological and empirical metrics of grasping strength in additional primate taxa and (2) extending performance testing to include empirical measures of primate pedal grasping forces as well.

MEDICAL-SURGICAL MANAGEMENT OF INTESTINAL INFECTION BY PROSTHENORCHIS ELEGANS IN NONHUMAN PRIMATES FROM COSTA RICA.

Parasitism is one of the most important diseases in nonhuman primates (NHP). Parasitism by Prosthenorchis elegans can be a threat to health and conservation of NHP in Costa Rica. Surgical management of intestinal acanthocephalan infection in two squirrel monkeys (Saimiri oerstedii) and one white-faced monkey (Cebus imitator) is described as an alternative to the lack of pharmacologic control options when there is a high burden of parasites present. A complete physical evaluation, including medical ultrasound techniques, allow for diagnosis of the parasite and its lesions. When animals present with a high burden of parasites, surgical management has shown to promote good health outcomes and increase the probability of survival.

Photoacoustic imaging of squirrel monkey cortical responses induced by peripheral mechanical stimulation.

Non-human primates (NHPs) are crucial models for studies of neuronal activity. Emerging photoacoustic imaging modalities offer excellent tools for studying NHP brains with high sensitivity and high spatial resolution. In this research, a photoacoustic microscopy (PAM) device was used to provide a label-free quantitative characterization of cerebral hemodynamic changes due to peripheral mechanical stimulation. A 5 × 5 mm area within the somatosensory cortex region of an adult squirrel monkey was imaged. A deep, fully connected neural network was characterized and applied to the PAM images of the cortex to enhance the vessel structures after mechanical stimulation on the forelimb digits. The quality of the PAM images was improved significantly with a neural network while preserving the hemodynamic responses. The functional responses to the mechanical stimulation were characterized based on the improved PAM images. This study demonstrates capability of PAM combined with machine learning for functional imaging of the NHP brain.

Sperm proteome and sperm parameters of captive Amazon squirrel monkeys (Saimiri collinsi Osgood, 1916) during the non-fatted and fatted condition

The aims of this work were (1) to characterize the proteome profile of Saimiri collinsi (Amazon squirrel monkey) sperm, and (2) to evaluate if there are meaningful differences in sperm quality and sperm protein landscape during the non-fatted and fatted conditions of the animals. Semen of adult males (n=4) was collected by electroejaculation and diluted in ACP-118® extender. Sperm concentration, motility, vigor, plasma membrane integrity and functionality, and sperm morphology were evaluated. Sperm proteome was characterized by mass spectrometry. The non-fatted and fatted conditions were defined according to the fattening index. There were increases in seminal volume, pH, and sperm motility of S. collinisi during the fatted in comparison with the non-fatted condition (p < 0.05). Animals in the fatted condition had greater body mass (909 ± 23.98 g) in comparison with the non-fatted condition (818.8 ± 5.97 g, p = 0.0001). There were 1161 proteins identified in the sperm of the monkeys. Thirty-seven proteins were upregulated (p < 0.05) in non-fatted condition (such as coiled-coil domain-containing protein 105, protein kinase C alpha type isoform X1, pyruvate dehydrogenase protein X component – mitochondrial and heat shock 70 kDa protein 1-like) and they were involved in cellular and metabolic processes, catalytic activity and binding. Twenty-eight sperm proteins proteins were upregulated (p < 0.05) in fatted condition (such as Cytochrome b-c1 complex subunit 2, mitochondrial; calcium-binding mitochondrial carrier protein SCaMC-1-like; heat shock 70 kDa protein 13, and izumo sperm-egg fusion protein 1), participating in cellular processes, metabolic processes, and localization, binding, catalytic activity, ATP-dependent activity, and transport activity. Functional annotations of sperm proteins upregulated in non-fatted condition were described as hydrogen ion transport, chaperone, cilium, flagellum, and cell projection. In in fatted conditions, such annotations were described as fertilization, spermatogenesis and transport, chaperone, and motor protein. The present study brings an unprecedent contribution to our understanding about the reproductive biology of adult Saimiri collinsi. It also provides support for conservation and development of assisted reproductive technologies for Neotropical primates.

Insights into Novel Therapies and the Pathogenesis of Alzheimer's disease, and the Possible Role of COVID-19

The Wisniewski laboratory has helped develop novel biomarkers and therapeutic approaches to AD, particular immunotherapeutic approaches that affect both the adaptive and innate immune systems. We have developed a means to stimulate innate immunity to ameliorate AD pathology, which we have tested in aged squirrel monkeys, and now are conducting a phase I clinical trial. We have also developed both active and passive immunization that specifically targets the dominant β-sheet secondary structure of multiple toxic oligomers concurrently (including both Aβ and tau oligomers). Recently we have also documented the neurological manifestations of SARS-CoV-2 infection (in particular cognitive dysfunction) and associated biomarkers of neurodegeneration and neuroinflammation. We have also developed an unbiased proteomic methodology that produces robust data utilizing archival formalin, fixed paraffin embedded human tissue, using this method to perform the most extensive proteomic analysis of amyloid plaques and the phosphorylated tau interaction, as well as to characterize the amyloid proteome of distinct subtypes of AD including rapidly progressive AD and AD in Down syndrome. These studies have helped enhance the understanding of the pathogenesis of AD, and also with the development of novel therapies.

Model-based parcellation of diffusion MRI of injured spinal cord predicts hand use impairment and recovery in squirrel monkeys

A mathematical model-based parcellation of magnetic resonance diffusion tensor images (DTI) has been developed to quantify progressive changes in three types of tissues – grey (GM), white matter (WM), and damaged spinal cord tissue, along with behavioral assessments over a 6 month period following targeted spinal cord injuries (SCI) in monkeys. Sigmoid Gompertz function based fittings of DTI metrics provide early indicators that correlate with, and predict, recovery of hand grasping behavior. Our three tissue pool model provided unbiased, data-driven segmentation of spinal cord images and identified DTI metrics that can serve as reliable biomarkers of severity of spinal cord injuries and predictors of behavioral outcomes.

Age‐associated biomarker profiles in a non‐human primate model of sporadic CAA

AbstractBackgroundAdvancements of novel therapeutic interventions for Alzheimer’s disease (AD) have been hindered by a lack of animal models in preclinical research that naturally recapitulate the pathologic features of disease with age. Our prior work demonstrated the utility of squirrel monkeys (SQMs), a non‐human primate (NHP) model of sporadic AD pathology with abundant cerebral amyloid angiopathy (CAA), as an opportune species to assess the potential therapeutic outcomes and safety profile of our novel immunomodulatory approach using TLR9 agonist CpG‐ODN. Here we provide the first longitudinal and cross‐sectional study on aging and disease pathogenesis in SQMs by characterizing blood/CSF biomarker signatures of AD/CAA pathology.MethodSIMOA, ELISA, and Luminex platform immunoassays were utilized to investigate age‐associated profiles of plasma and CSF biomarkers involved in neurodegeneration (NfL, GFAP), brain and peripheral inflammation/glia activation (YKL‐40/CHI3L1, sTREM2), and cerebrovascular dysfunction/BBB integrity (albumin index, bFGF, VCAM‐1, MMPs).ResultCross‐sectional analysis revealed statistically significant differences in plasma NfL and GFAP levels between age groups ranging from 6 to 23 years old (NfL: one‐way ANOVA, f(6,84)) = 6.395, p&lt;0.0001; GFAP: one‐way ANOVA, f(6,84)) = 8.111, p&lt;0.0001). Preliminary assessments revealed significantly higher plasma YKL‐40/CHI3L1 and MMP1 levels, while VCAM‐1, bFGF, and MMP2 levels were significantly lower in the geriatric SQMs when compared to the young group. CSF analyses demonstrated significantly higher YKL‐40/CHI3L1 and bFGF levels, and an elevated albumin index among the geriatric cohort when compared to young monkeys. Moreover, a longitudinal follow‐up of a separate SQM cohort over three years (19‐22 years old) revealed a significant increase in plasma sTREM2 levels; neurogranin levels appeared to increase, but differences were not significant (p = 0.0625, Wilcoxon signed‐rank test). Further characterizations of fluid biomarker trajectories and their relationships with age‐associated changes in cognition and neuroimaging markers are forthcoming.ConclusionSQMs present a valuable opportunity to evaluate biomarker signatures associated with aging and the development of cerebrovascular amyloid pathology. The use of this advantageous model is important to enhance the translational potential of novel therapeutics for human benefit.

Evaluation of biomarker, behavioral, and immunostimulatory profiles following treatment with Class C CpG ODN in a non‐human primate model of sporadic CAA

AbstractBackgroundInnate immunomodulation has shown potential to be an effective therapeutic approach in ameliorating pathological features of Alzheimer’s Disease (AD). Our recently published study showed a reduction in cognitive deficits and AD‐related pathology in a squirrel monkey model (SQM) of sporadic cerebral amyloid angiopathy (CAA) following treatment with TLR9 agonist, Class B CpG ODN. Subsequently, we commenced a chronic treatment study evaluating the efficacy and safety of Class C CpG ODN in geriatric SQMs. Here, we further explore the efficacy of Class C CpG ODN by evaluating fluid biomarkers and implementing automated cognitive tests. Moreover, we assess the immunostimulatory profiles induced by Class B and Class C CpG ODNs using RNA‐Seq genome‐wide transcriptome analysis of SQM PBMCs.MethodGeriatric SQMs received monthly injections of CpG ODN‐C or saline (VEH) over three years. Fluid biomarkers for cerebrovascular dysfunction, neurodegeneration, and neuroinflammation were assessed by Luminex and SIMOA. Touchscreen‐based Automated Cognitive Testing System (ACTS) was applied among socially living SQMs to assess behavioral changes. RNA‐Seq analyses were performed using PBMCs isolated 24hrs following CpG ODN‐B and ‐C administrations in a separate cohort of elderly SQMs.ResultOur initial experiments confirmed the utility of SQMs for investigating plasma age‐associated neurodegeneration biomarkers, including NfL, GFAP, and neurogranin. Preliminary evaluation of cerebrovascular dysfunction‐related plasma biomarkers, such as MMPs, albumin index, bFGF, and VCAM, revealed no differences between our treatment groups at earlier time points. Although not significant, higher levels of plasma sTREM2 and YKL‐40 were observed in VEH monkeys compared to CpG ODN‐treated group. Concluding assessments will be performed in plasma collected at the end of the treatment period. Characterization of additional plasma/CSF biomarkers related to AD/neurodegeneration is underway. ACTS‐based two‐choice discrimination learning task revealed that CpG ODN‐treated group performed with a greater correct response rate than the VEH group. As expected, RNA‐Seq analyses of SQM PBMCs revealed significantly altered pathways, including Th1/Th2, TLR signaling, phagocytosis, chemokine signaling, interferon signaling, and senescence pathways, in addition to pathways involved in infiltration, activation, and recruitment of various immune cells.ConclusionThe study highlights the potential of the SQM model for future translational research on CAA/AD and for advancing innovative therapeutic interventions.

Eat the fruit earlier: Sakis (Pithecia chrysocephala) show enhanced temporal fruit resource access compared with squirrel monkeys (Saimiri sciureus) in an urban forest fragment in Brazil.

Fruit availability experienced by different primate species is likely to vary due to species-specific fruit use, even within the same habitat and timeframe. Pitheciines, primates of the subfamily Pitheciinae, particularly favor the seeds of unripe fruits. Researchers consider this dietary characteristic an adaptation to increase access to fruit resources. However, the relative advantages of pitheciines over sympatric non-pitheciine non-seed-eating primates regarding species-specific fruit availability is not well studied. In a 26-ha forest within the city of Manaus, Amazonian Brazil, we assessed the wild-food feeding behavior of free-ranging groups of golden-faced sakis (Pithecia chrysocephala) and sympatric common squirrel monkeys (Saimiri sciureus). We hypothesized that sakis would have greater and more consistent access to wild fruit due to (1) a wider variety of fruit species in their diet, and (2) longer consumption periods per fruit species. We recorded the plant species, part (pulp or seed), and developmental stage (ripe or unripe) of wild fruit consumed by both species. We also conducted monthly fruit censuses of 1000 trees and vines to estimate overall wild fruit abundance. As an indicator of fruit availability, we calculated the proportion of available fruiting trees and vines for each primate species separately based on their observed diet. Throughout the year, the proportion of available trees and vines was significantly higher and more temporally stable for sakis than for squirrel monkeys. This was because sakis used shared fruit species longer than squirrel monkeys by consuming both ripe and unripe fruit. Although sakis had a broader fruit repertoire than squirrel monkeys, it did not contribute to the higher fruit availability. Thus, the fruit feeding system of sakis identifies aspects of a niche that is less restricted in the timing of fruit consumption, which led to a relative advantage in fruit availability.

In vitro and in vivo immune assessments of genetically-engineered pig skin grafts in New World (squirrel) monkeys.

Half a million patients in the USA alone require treatment for burns annually. Following an extensive burn, it may not be possible to provide sufficient autografts in a single setting. Genetic manipulations (GM) of pigs offer the possibility of reducing primate humoral and cellular rejection of pig skin xenografts and thus extending graft survival. We compared the survival of skin grafts from pigs with 9-GM with that of autografts and allografts in squirrel monkeys. Monitoring for rejection was by (1) macroscopic examination, (2) histopathological examination of skin biopsies, and (3) measurement of anti-monkey and anti-pig IgM and IgG antibodies. Autografts (n = 5) survived throughout the 28 days of follow-up without histopathological features of rejection. Median survival of allografts (n = 6) was 14 days and of pig xenografts (n = 12) 21 days. Allotransplantation was associated with an increase in anti-monkey IgM, but the anticipated subsequent rise in IgG had not yet occurred at the time of euthanasia. Pig grafts were associated with increases in anti-pig IgM and IgG. In all cases, histopathologic features of rejection were similar. 9-GM pig skin xenografts survive at least as long as monkey skin allografts (and trended to survive longer), suggesting that they are a realistic clinical option for the temporary treatment of burns. Although monkeys with pig skin grafts developed anti-pig IgM and IgG antibodies, these did not cross-react with monkey antigens, indicating that a primary 9-GM pig skin graft would not be detrimental to a subsequent monkey skin allograft.

Label-free autofluorescence and hyperspectral imaging of cerebral amyloid-β lesions in aged squirrel monkeys.

The observation of amyloid-β (Aβ) lesions using autofluorescence in transgenic mice and human Alzheimer disease patients has been reported frequently. However, no reports verify the autofluorescence of spontaneous Aβ amyloidosis in animals, to our knowledge. We validated the autofluorescence of Aβ lesions in spontaneous squirrel monkey cases under label-free conditions; lesions had intense blue-white autofluorescence in fluorescence microscopy using excitation light at 400-440 nm. Thioflavin S staining and immunohistochemistry of the same specimens revealed that this blue-white autofluorescence was derived from Aβ lesions. Hyperspectral analysis of these lesions revealed a characteristic spectrum with bimodal peaks at 440 and 460 nm, as reported for Aβ lesions in mice. Principal component analysis using hyperspectral data specifically separated the Aβ lesions from other autofluorescent substances, such as lipofuscin. A non-labeled and mechanistic detection of Aβ lesions by hyperspectral imaging could provide valuable insights for developing early diagnostic techniques.

228.7: In vitro and in vivo immune assessments of TKO pig skin grafts in New World (squirrel) monkeys

228.7: In vitro and in vivo immune assessments of TKO pig skin grafts in New World (squirrel) monkeys

Fatal neural angiostrongyliasis in the Bolivian squirrel monkey (Saimiri boliviensis boliviensis) leading to defining Angiostrongylus cantonensis risk map at a zoo in Australia

Neural angiostrongyliasis (NA) is a parasitic disease caused by Angiostrongylus cantonensis (rat lungworm). This study presents a case of NA in a captive Bolivian squirrel monkey from a zoo in western Sydney, Australia. The objective was to identify the A. cantonensis cox1 haplotype responsible for the infection and compare its mitochondrial DNA (mtDNA) to known Australian mtDNA. An epidemiological investigation was conducted to assess the risk of infection, focusing on the resident rat population in the zoo. Methods involved trapping rats and collecting rat faeces for Angiostrongylus detection, speciation, and cox1 haplotype confirmation. Various techniques were employed, including necropsy, morphological examination, and molecular methods such as ITS-2 qPCR, cox1 sequencing, and ITS-2 metabarcoding. Cluster analysis of rat faeces distribution and Angiostrongylus detection utilised an equal sampling effort (ESE) approach. Gastropods were collected throughout the study for Angiostrongylus surveillance using a hypersensitive qPCR assay. Results revealed significant clustering of rat faeces near exhibits with fresh food provision and absence of predators. Angiostrongylus-positive faeces were uniformly distributed across the zoo property. Mitochondrial DNA analysis confirmed the presence of the Ac13 haplotype of A. cantonensis in the monkey. Morphology, ITS-2 metabarcoding and partial cox1 sequencing detected only A. cantonensis, with the Ac13 cox1 haplotype predominating. A high prevalence of infection (64%, 9/14) was found in brown rats, with quantification of larvae indicating high shedding rates. Co-infections with both Ac13 and local SYD.1 A. cantonensis cox1 haplotypes were observed. Only three gastropods (all of which were Angiostrongylus-negative) were found in the survey. To minimise the risk of exposure for susceptible species, targeted rodent control was implemented in areas with higher exposure risk. A potential strategy (which requires further exploration) to consider for future zoo design was suggested. This study provides insights into the epidemiology and genetic diversity of A. cantonensis in Australia, emphasising the importance of control measures to prevent future outbreaks.

The Effects of Chronic Naltrexone on Reinstatement of Opioid-Induced Drug-Seeking Behavior and Antinociception.

Opioid addiction is a chronic relapsing disorder in which drug-seeking behavior during abstinence can be provoked by exposure to a µ-opioid receptor (MOR) agonist or opioid-associated cues. Opioid self-administration behavior in laboratory subjects can be reinstated by priming with MOR agonists or agonist-related stimuli, providing a procedure suitable for relapse-related studies. The opioid antagonist naltrexone has been forwarded as a medication that can forestall relapse and, in an extended-release formulation, has demonstrated some treatment success. However, chronic naltrexone treatment has not been extensively investigated in nonhuman subjects and aspects of its pharmacology remain uncertain. For example, the relative effectiveness of naltrexone in reducing the priming strength of opioid agonists differing in efficacy is not well understood. Here, using intravenous self-administration and warm-water tail withdrawal procedures, we investigated changes in the direct reinforcing effects of oxycodone and in the priming strength and antinociceptive effects of opioid agonists in squirrel monkeys (n = 4) during chronic treatment with naltrexone (0.2 mg/kg/d). Results show that naltrexone produced: 1) a 10-fold rightward shift in the dose-response function for the reinforcing effects of oxycodone, and 2) in reinstatement and antinociception experiments, comparable rightward shifts in the dose-response functions for higher-efficacy MOR agonists (methadone, heroin, and oxycodone) but rightward and downward shifts in the dose-response functions for lower-efficacy MOR agonists (buprenorphine, nalbuphine, and butorphanol). These results suggest that, although chronic naltrexone should be effective in forestalling relapse following exposure to lower- and higher-efficacy agonists, the inability of lower-efficacy agonists to surmount naltrexone antagonism may complicate the prescription of opioids for pain. SIGNIFICANCE STATEMENT: Although naltrexone is commonly used in the treatment of opioid use disorder, its ability to reduce the priming strength of opioid agonists has not been extensively investigated. This study shows that chronic naltrexone treatment induces rightward shifts in the reinstatement and antinociceptive properties of higher efficacy opioid agonists, but rightward and downward shifts for lower efficacy opioid agonists, suggesting lower efficacy agonists may not be able to surmount naltrexone-induced antagonism of these two effects, and perhaps naltrexone offers greater protection against lower efficacy agonists.

Nasal vaccination of six squirrel monkeys (Saimiri sciureus): Improved immunization protocol against Toxoplasma gondii with a nanoparticle-born vaccine

Toxoplasma gondii is an intracellular protozoon found worldwide, which completes its life cycle between felids (its definitive host) and other warm-blooded animals. While the infection rarely leads to severe complications in humans, many animal species are very susceptible to this infection, for example the squirrel monkey (Saimiri sciureus) which is the subject of this study. Toxoplasmosis is lethal for 80% of cases in this species, and fatal outbreaks are frequently reported in zoological parks.No efficient treatment exists, but a new vaccine prepared with maltodextrin nanoparticles containing killed T. gondii antigens has been tested recently in French zoos. The animals were immunized through heterologous administrations, with two nasal doses at one-month interval, followed by nasal/subcutaneous boosts thereafter. No death has been reported since the beginning of this vaccination campaign, but we felt the protocol could be simplified.Here, an improved and less-invasive immunization protocol was evaluated on 6 Saimiri sciureus in the French zoo La Palmyre. It consisted of two nasal administrations at one-month interval, followed by a nasal boost at 6 months. A specific memory T-cell immunity was observed by ELISPOT after two administrations in all the animals, without humoral responses. The results suggest that 2 nasal administrations induce a protective immune response against T. gondii infection and might be sufficient to induce a strong Tcell memory, further improving immunity.