Browsing by Author "Rizzoto, Guilherme"

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    Pathogenesis of Heat-Induced Infertility in Male Mammals
    (2020-09-04) Rizzoto, Guilherme; Kastelic, John P.; Caulkett, Nigel; Klein, Claudia; Thundathil, Jacob C.; McGowan, Michael R.; Easton, Paul A.
    Testicular temperature must be 3-5 ºC below body temperature for physiological spermatogenesis and testicular function. Therefore, increased testicular temperatures, either the entire body or just the testes, reduce sperm quality and fertility. Our understanding regarding the pathophysiology of testicular heat stress is unclear. There is a long-standing dogma that as testicular temperature increases, there is no change in blood flow, and the testes, which are regarded as physiologically functioning on the brink of hypoxia, undergo frank hypoxia. However, recent data challenged this dogma, indicating that temperature itself was the major pathological agent. Therefore, this thesis was developed to further investigate the subject. In a series of five studies, the overall aim was to investigate changes in testicular blood flow in response to testicular heat stress and its pathophysiology on testes and testicular function. In the first two studies, we investigated how heat stress and hypoxia affect testicular blood flow and metabolism in rams; both treatments increased testicular blood flow which supported metabolic needs, with no indications of hypoxia. The third study was a comparison of responses between Bos indicus and Bos taurus bulls to increased testicular temperature. Once again, testicular blood flow significantly increased, supporting metabolic needs, with no indications of hypoxia. These three studies provided new knowledge to debunk the previous dogma and to support the new understanding that temperature itself was the main pathological factor of testicular heat stress. In the last two studies, we investigated how heat stress modulates gene expression in bull and mouse testes. Heat stress caused modulation of gene P53 and components of the P53-dependent apoptotic pathway, also upregulation of genes associated with the antioxidant (GPX1) and chaperone systems (Hsp70) and downregulation of the StAR gene and reduced testosterone concentrations (impaired steroidogenesis). Collectively, these studies provided novel information regarding testicular vascular physiology under local heat stress and described several factors associated with its pathophysiology in the testes. Lastly, it is expected that these findings will serve as a strong base for new studies in this area, to elucidate in more detail, how heat stress affects reproduction in male mammals.
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    Wound inflammation post-orchiectomy affects the social dynamic of Nelore bulls
    (2023-07-15) Marcelino, Caique M.; Trindade, Pedro H. E.; García, Henry D. M.; Pupulim, Antonio G. R.; Martins, Cyntia L.; Rizzoto, Guilherme; Teixeira-Neto, Francisco; Macitelli, Fernanda; Kastelic, John P.; Ferreira, João C. P.
    Abstract Background Confinement of cattle imposes spatial restrictions and predisposes to aversive social encounters that can lead to contusions, wounds, pain, stress, fright, and reduced productivity. Although endogenous testosterone concentrations are linked to agonistic dominance behaviors in males, it is unknown whether decreased blood testosterone concentrations after castration alter social hierarchy rank in Nelore bulls. Therefore, in this study, we investigated the impact of the surgical would inflammation post-orchiectomy on social dynamics in a group of Nelore bulls (Bos indicus). Fourteen Nelore (Bos indicus) bulls were castrated and assessed pre- and post-surgically. Parameters evaluated were agonistic (mounting, headbutting, and fighting) and affiliative (head-play) behavior, plasma testosterone concentrations, average daily weight gain (ADG), and a score for severity of post-surgical infection. Exploratory statistics included social network analysis (SNA), hierarchy rank delta (Δ), and principal component analysis (PCA). Furthermore, statistical inferences included the Wilcoxon test, multiple logistic regression models, and Spearman's correlation. Results The social dynamic of Nelore bulls was modified after castration based on the findings of the SNA and the PCA. The moderate correlation between the postoperative inflammation level with the Δ, and the significant effect of this level in the logistic model post-castration were partially attributed to effects of pain on social relations. Conclusions Our findings suggest the severity of post-surgical inflammation, which has an association with pain intensity, was closely associated with changes in the social hierarchy.