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During the Zika virus (ZIKV) outbreak and after evidence of its sexual transmission was obtained, concerns arose about the impact of the adverse effects of ZIKV infection on human fertility. In this study, we evaluated the clinical-laboratory aspects and testicular histopathological patterns of pubertal squirrel monkeys (Saimiri collinsi) infected with ZIKV, analyzing the effects at different stages of infection. The susceptibility of S. collinsi to ZIKV infection was confirmed by laboratory tests, which detected viremia (mean 1.63 × 106 RNA copies/µL) and IgM antibody induction. Reduced fecal testosterone levels, severe testicular atrophy and prolonged orchitis were observed throughout the experiment by ultrasound. At 21 dpi, testicular damage associated with ZIKV was confirmed by histopathological and immunohistochemical (IHC) analyses. Tubular retraction, the degeneration and necrosis of somatic and germ cells in the seminiferous tubules, the proliferation of interstitial cells and an inflammatory infiltrate were observed. ZIKV antigen was identified in the same cells where tissue injuries were observed. In conclusion, squirrel monkeys were found to be susceptible to the Asian variant of ZIKV, and this model enabled the identification of multifocal lesions in the seminiferous tubules of the infected group evaluated. These findings may suggest an impact of ZIKV infection on male fertility.

The Spix's Saddleback Tamarin, Leontocebus fuscicollis is widely distributed across the Amazon region, but is endangered. This species is serving an important role in biomedical research in captivity. However, reference values for hematological and biochemical parameters are required for the proper characterization of the species. It was therefore the objective of our research to establish these parameters taking into consideration sex and body mass differences in healthy adult Spix's saddleback tamarins. Collecting 2 mL of blood from each individual, 20 animals were examined (7 males, 13 females), and hematological and biochemical parameters were determined using commercial kits. Of the sixteen variables measured, only red blood cell (RBC), hemoglobin (Hb) and hematocrit (Ht) values were significantly higher in males (7.12 ± 0.98 106/mm, 14.98 ± 1.25 g/dL and 48.71 ± 4.91%, respectively), while red cell distribution width (RDW) was higher in females (14.58 ± 1.89%). Of the biochemical parameters measured, only gamma-glutamyl transferase (GGT) enzyme showed higher activity in females (8.08 ± 4.87 U/L), and a high glucose concentration range was observed (102.0 to 521.0 mg/dL) for both sexes. These parameters established with reference ranges for healthy adults provide a reliable reference source for the interpretation of laboratory housed saddleback tamarin.

Dengue virus (DENV) of the Flaviviridae family is a single positive-stranded RNA virus that is transmitted by Aedes aegypti and Aedes albopictus mosquitoes. The objective of this study was to investigate the use of chloroquine (CLQ) as an antiviral drug against dengue virus in monkeys. To analyze the action of the drug in vivo, nonhuman primates groups (Aotus azarai infulatus) were inoculated with a subcutaneous injection of a virulent strain of DENV-2, treated and untreated CLQ. Blood hematological, viremia, and serum biochemical values were obtained from 16 DENV-2-inoculated, treated and untreated; four received only CLQ and one mock-infected Aotus monkeys. Monkey serum samples (day 0–10 post-inoculation) were assayed by reverse transcription polymerase chain reaction and Cytometric Bead Array for determination of viremia and inflammatory cytokines, respectively. Additionally, body temperature and activity levels were determined. In the present work, CLQ was effective on replication of DENV-2 in Aotus monkeys; a time viremia reduction was observed compared with the controls. The concentration of tumor necrosis factor alpha and interferon gamma in the serum of the animals had a statistically significant reduction in the groups treated with CLQ after infection compared with the controls. A significant decrease in systemic levels of the liver enzyme aspartate aminotransferase (AST) was also observed in the animals treated with CLQ after infection compared with the controls. These results suggest that CLQ interferes in DENV-2 replication in Aotus monkeys.

Diffusion MRI provides multiple quantitative descriptors of neural tissue derived from distinct physical and biophysical models, each probing different aspects of cerebral microstructure. While these metrics are often interpreted independently, their joint statistical structure may encode information about latent biophysical properties that constrain and organize brain microarchitecture. Here, we investigate whether stable patterns of multimodal diffusion MRI covariation reveal underlying biophysical diffusion properties of cerebral microstructure in the squirrel monkey (Saimiri sciureus). Using a high-resolution multimodal diffusion MRI dataset acquired at 11.7T (400 μm isotropic resolution) from 15 adult subjects, we analyzed tensor-based metrics alongside advanced multicompartment and axonal models, including NODDI and ActiveAx. Voxelwise and region-level correlation analyses were performed across multiple spatial scales to examine the structure, redundancy, and stability of relationships among diffusion-derived maps. We show that metrics originating from conceptually distinct models consistently organize into a low-dimensional structure characterized by stable clusters of covariation, robust to changes in parcellation and spatial aggregation. These patterns cannot be explained by trivial metric redundancy alone, but instead suggest convergence toward a reduced set of effective biophysical degrees of freedom governing diffusion behavior in neural tissue, including axonal organization, neurite density, orientation dispersion, and isotropic diffusion components. We interpret these covariation structures as manifestations of latent biophysical diffusion properties, emergent tissue states that are not directly observable through any single metric but become apparent through their structured relationships. From a systems neuroscience perspective, the stability of these latent dimensions supports the view that adult cerebral microstructure reflects the steady-state outcome of neurodevelopmental dynamics operating under biophysical constraints. Rather than providing a regional atlas, this work proposes a conceptual framework for interpreting multimodal diffusion MRI as a projection of an underlying low-dimensional biophysical state space organizing cerebral microstructure in primate brains.Competing Interest StatementThe authors have declared no competing interest.Footnotes* http://saimiri.bcblab.com/Funder Information DeclaredNational Council for Scientific and Technological Development (CNPq), Chamada CNPq 25/2021 - Bolsas no País