The purpose of this protocol is to guide researchers in performing a palpation-guided technique of intra-articular knee injection in guinea pigs and assessment using micro-computed tomography. Dunkin-Hartley guinea pigs are robust models for osteoarthritis research as they spontaneously develop osteoarthritis in their knees. Intra-articular drug delivery is a common method to study the effects of an investigational drug in vivo. In humans, therapeutic agents administered via intra-articular injection can offer pain relief and delay further progression of osteoarthritis. As with any species, the introduction of a needle into a joint space has the potential to cause injury, which can result in pain, lameness, or infection. Such adverse events can compromise animal welfare, confound study results, and necessitate additional animals to achieve study objectives. As such, it is imperative to develop proper injection techniques to prevent complications, especially in longitudinal studies that require multiple, repeated intra-articular injections. Using the presented methodology, five guinea pigs received bilateral knee injections under general anesthesia. Seven days after injection, animals were humanely euthanized for analysis of osteoarthritis severity. No adverse events occurred following anesthesia or knee injections, including limping, pain, or infection. X-ray micro-computed tomography analysis of the knee can detect pathologic changes associated with osteoarthritis. Micro-computed tomography data indicates osteoarthritis is more severe in older animals, as indicated by increased bone mineral density and trabecular thickness with age. These results are consistent with histologic changes and Modified Mankin scores, an established and widely used scoring system to assess arthritis severity in these same animals. This protocol can be utilized to refine intra-articular injections in guinea pigs.

S-adenosylmethionine (SAM) is the main methyl group donor and has antioxidant potential. In this study, preventive and regressive potential of SAM were investigated in high fat/high cholesterol (HFHC) diet-induced non-alcoholic fatty liver disease (NAFLD) in guinea pigs. They were injected with SAM (50 mg/kg, i.p.) for 6 weeks along with HFHC diet or 4 weeks after HFHC diet. Serum transaminase activities, total cholesterol (TC), triglyceride (TG), cytochrome p450-2E1 (CYP2E1) and hydroxyproline (Hyp) levels, prooxidative and antioxidative parameters, protein expressions of α-smooth muscle actin (α-SMA) and transforming growth factor-β1 (TGF-β1) together with histopathological changes were examined in the liver. SAM treatment diminished HFHC diet-induced increases in serum transaminase activities and hepatic TC, TG, CYP2E1, Hyp, α-SMA and TGF-β1 expressions and ameliorated prooxidant-antioxidant balance. Histopathological scores for hepatic steatosis, inflammation, and fibrosis were decreased by SAM treatment. Increases in TC, diene conjugate levels, and lipid vacuoles within the tunica media of the aorta were reduced in HFHC-fed animals treated with SAM. These protective effects were also detected in the regression period of HFHC-guinea pigs due to SAM. In conclusion, SAM treatment was found to be effective in prevention and regression of HFHC-induced hepatic and aortic lesions together with decreases in oxidative stress in guinea pigs with NAFLD.

The ciliary muscle constitutes a crucial element in refractive regulation. Investigating the pathophysiological mechanisms within the ciliary muscle during excessive contraction holds significance in treating ciliary muscle dysfunction. A guinea pig model of excessive contraction of the ciliary muscle induced by drops pilocarpine was employed, alongside the primary ciliary muscle cells was employed in in vitro experiments. The results of the ophthalmic examination showed that pilocarpine did not significantly change refraction and axial length during the experiment, but had adverse effects on the regulatory power of the ciliary muscle. The current data reveal notable alterations in the expression profiles of hypoxia inducible factor 1 (HIF-1α), ATP2A2, P53, α-SMA, Caspase-3, and BAX within the ciliary muscle of animals subjected to pilocarpine exposure, alongside corresponding changes observed in cultured cells treated with pilocarpine. Augmented levels of ROS were detected in both tissue specimens and cells, culminating in a significant increase in cell apoptosis in in vivo and in vitro experiments. Further examination revealed that pilocarpine induced an increase in intracellular Ca2+ levels and disrupted MMP, as evidenced by mitochondrial swelling and diminished cristae density compared to control conditions, concomitant with a noteworthy decline in antioxidant enzyme activity. However, subsequent blockade of Ca2+ channels in cells resulted in downregulation of HIF-1α, ATP2A2, P53, α-SMA, Caspase-3, and BAX expression, alongside ameliorated mitochondrial function and morphology. The inhibition of Ca2+ channels presents a viable approach to mitigate ciliary cells damage and sustain proper ciliary muscle function by curtailing the mitochondrial damage induced by excessive contractions.

This study aimed to investigate the effects of the intravenous administration of lidocaine in the auditory cortex after the systemic administration of salicylate. Healthy male albino Hartley guinea pigs were divided into two groups. The control group received only lidocaine, whereas the experimental group received lidocaine after checking for the effects of salicylate. Extracellular recordings of spikes in the primary auditory cortex and dorsocaudal areas in healthy albino Hartley guinea pigs were continuously documented (pre- and post-lidocaine, pre- and post-salicylate, and post-salicylate after adding lidocaine to post-salicylate). We recorded 160 single units in the primary auditory cortex from five guinea pigs and 155 single units in the dorsocaudal area from another five guinea pigs to confirm the effects of lidocaine on untreated animals. No significant change was detected in either the threshold or Q10dB value after lidocaine administration in the primary auditory cortex and dorsocaudal areas. Spontaneous firing activity significantly decreased after lidocaine administration in the primary auditory cortex and dorsocaudal areas. Next, we recorded 160 single units in the primary auditory cortex from five guinea pigs and 137 single units in the dorsocaudal area from another five guinea pigs to determine the effects of lidocaine on salicylate-treated animals. The threshold was significantly elevated after salicylate administration; however, no additional change was detected after adding lidocaine to the primary auditory cortex and dorsocaudal areas. Regarding the Q10dB value, lidocaine negated the significant changes induced by salicylate in the primary auditory cortex and dorsocaudal areas. Moreover, lidocaine negated the significant changes in spontaneous firing activities induced by salicylate in the primary auditory cortex and dorsocaudal areas. In conclusion, changes in the Q10dB value and spontaneous firing activities induced by salicylate administration are abolished by lidocaine administration, suggesting that these changes are related to the presence of tinnitus.

Culling of guinea pigs can provide a large number of animals per year for meat production, but little information is available in the scientific literature on the carcass characteristics and non-carcass components of these animals. The objective of this study was to evaluate the carcass and non-carcass characteristics of cull guinea pigs in comparison to their fattening counterparts. Forty-eight fattening (3 months-age, 24 females and 24 males) and forty-eight cull (14 months-age, 24 females and 24 males) guinea pigs were slaughtered and carcass yield, linear measurements, tissular composition, and non-carcass components were evaluated. In general, cull guinea pigs had higher carcass, tissue, and non-carcass component weights. Cull male and both female guinea pig groups had similar carcass yields. Cull animals had higher carcass and hind leg lengths, lumbar and thoracic circumferences, and carcass compactness than their young counterparts. However, a sex effect was found for leg compactness depending on whether they were fattened or cull. Tissue percentages values were similar between fattening and culling animals of the same sex. However, females had a higher percentage of fat tissue than males. Fattening females had the best muscle to bone ratio, followed by cull males. The non-carcass elements were more represented in fattening animals than in culls, probably due to an allometric growth of the viscera in relation to the rest of the body. In commercial and cooking terms, this information is valuable for producers and researchers who need to understand the factors that influence carcass characteristics of guinea pigs.

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OBJECTIVE: Electroanatomical adaptations during the neonatal to adult phase have not been comprehensively studied in preclinical animal models. To explore the impact of age as a biological variable on cardiac electrophysiology, we employed neonatal and adult guinea pigs, which are a recognized animal model for developmental research.
RESULTS: Electrocardiogram recordings were collected in vivo from anaesthetized animals. A Langendorff-perfusion system was employed for the optical assessment of action potentials and calcium transients. Optical data sets were analysed using Kairosight 3.0 software. The allometric relationship between heart weight and body weight diminishes with age, it is strongest at the neonatal stage (R2 = 0.84) and abolished in older adults (R2 = 1E-06). Neonatal hearts exhibit circular activation, while adults show prototypical elliptical shapes. Neonatal conduction velocity (40.6 ± 4.0 cm/s) is slower than adults (younger: 61.6 ± 9.3 cm/s; older: 53.6 ± 9.2 cm/s). Neonatal hearts have a longer action potential duration (APD) and exhibit regional heterogeneity (left apex; APD30: 68.6 ± 5.6 ms, left basal; APD30: 62.8 ± 3.6), which was absent in adults. With dynamic pacing, neonatal hearts exhibit a flatter APD restitution slope (APD70: 0.29 ± 0.04) compared with older adults (0.49 ± 0.04). Similar restitution characteristics are observed with extrasystolic pacing, with a flatter slope in neonates (APD70: 0.54 ± 0.1) compared with adults (younger: 0.85 ± 0.4; older: 0.95 ± 0.7). Neonatal hearts display unidirectional excitation-contraction coupling, while adults exhibit bidirectionality.
CONCLUSIONS: Postnatal development is characterized by transient changes in electroanatomical properties. Age-specific patterns can influence cardiac physiology, pathology, and therapies for cardiovascular diseases. Understanding heart development is crucial to evaluating therapeutic eligibility, safety, and efficacy.

This study aimed to develop and evaluate a guinea pig model for glaucoma, comparing resultant eyeball enlargement with an existing myopia model. Thirty guinea pigs underwent intracameral injection of magnetic microspheres to induce chronic ocular hypertension (COH). Intraocular pressure (IOP) was systematically monitored, revealing a successful induction of COH in 73.33% of the guinea pigs. The mean IOP increased from a baseline of 18.04 ± 1.33 mmHg, reaching a peak at week 3 (36.31 ± 6.13 mmHg) and remaining elevated for at least 7 weeks. All data are presented as mean ± standard deviation of the mean. Subsequently, detailed assessments were conducted to validate the established glaucoma model. Immunofluorescent staining demonstrated a significant decrease in the density of retinal ganglion cells (RGC) in the glaucoma group. Optic disc excavation and notable thinning of the lamina cribrosa (LC) were observed. The quantity of optic nerve ax·ons in glaucoma group gradually decreased from baseline (44553 ± 3608/mm2) to week 4 (28687 ± 2071/mm2) and week 8 (17977 ± 3697/mm2). Moreover, regarding the global enlargement of eyeballs, both the transverse and longitudinal axis in glaucomatous eyes were found to be significantly larger than that in myopic eyes, particularly in the anterior chamber depth (1.758 ± 0.113 mm vs. 1.151 ± 0.046 mm). These findings indicate distinct patterns of structural changes associated with glaucoma and myopia in the guinea pig model. This guinea pig model holds promise for future research aimed at exploring biomechanical mechanisms, therapeutic interventions, and advancing our understanding of the relationship between glaucoma and myopia.

Favipiravir is a ribonucleoside analogue that has been explored as a therapeutic for the treatment of Ebola Virus Disease (EVD). Promising data from rodent models has informed nonhuman primate trials, as well as evaluation in patients during the 2013-2016 West African EVD outbreak of favipiravir treatment. However, mixed results from these studies hindered regulatory approval of favipiravir for the indication of EVD. This study examined the influence of route of administration, duration of treatment, and treatment schedule of favipiravir in immune competent mouse and guinea pig models using rodent-adapted Zaire ebolavirus (EBOV). A dose of 300 mg/kg/day of favipiravir with an 8-day treatment was found to be fully effective at preventing lethal EVD-like disease in BALB/c mice regardless of route of administration (oral, intraperitoneal, or subcutaneous) or whether it was provided as a once-daily dose or a twice-daily split dose. Preclinical data generated in guinea pigs demonstrates that an 8-day treatment of 300 mg/kg/day of favipiravir reduces mortality following EBOV challenge regardless of route of treatment or duration of treatments for 8, 11, or 15 days. This work supports the future translational development of favipiravir as an EVD therapeutic.

Herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2) are two of the most prevalent human viruses worldwide. They are known to cause a variety of diseases including genital herpes, meningitis, encephalitis, cold sores and herpes stromal keratitis. The seropositive rate for HSV-1 is around 90%, whereas for HSV-2 it remains around 20-25% for the general adult population. The infections caused by these viruses remain difficult to study because a large proportion of infected individuals are asymptomatic. Furthermore, given the neurotropic characteristics of the virus, studies aimed at understanding the complex pathogenesis in humans is difficult. As a result, animal models have been developed to understand several characteristics of HSV biology, pathogenesis, disease and host responses to infection. These models are also commonly used as the first evaluation of new drugs and vaccines. There are several well-established animal models to study infection with HSV, including mice, guinea pigs and rabbits. Variables within the animal models depend on the species of animal, route of infection, viral strain, dosage, etc. This review aims at summarizing the most commonly used animal models to study HSV pathogenesis and therapies.