Incidences and Range of Spontaneous Microscopic Lesions in the Eye of Sprague-Dawley Rats and Han Wistar Rats Used in Toxicity Studies

Abstract

The incidence and range of spontaneous microscopic lesions were determined in the eyes of male and female control Sprague-Dawley and Han Wistar rats. Data were collected retrospectively from 1411, 817, 970, 658, and 3999 rats from control groups of 4-, 13-, 26-, 52-, and 104-week studies, respectively, carried out between 1997 and 2019. Microscopic lesions of the eye were rare in 4- and 13-week studies, uncommon in 26- and 52-week studies, and were of relatively higher incidence in 104-week studies. Neoplastic lesions were sporadic and were only observed in 104-week studies. In Sprague-Dawley rats, the most common lesions (>1% in 104-week studies) were retinal degeneration, retinal rosettes/folds, and lenticular degeneration. The Han Wistar rats presented a range of ocular lesions similar to the Sprague-Dawley rats. However, retinal degeneration occurred with an earlier onset and at higher incidences, ranging from >5% in 26-week studies up to 45.72% in 104-week studies. In both strains, females exhibited higher incidences and severities of retinal degeneration. It is hoped that reference to the incidences reported here will facilitate the differentiation of spontaneous lesions from test article–induced lesions in toxicology studies in these strains of rat.

Historical Control Background Incidence of Spontaneous Neoplastic Lesions of Sprague-Dawley Rats in 104-Week Toxicity Studies

“…Some of the ocular tumors noted in the current data evaluated included malignant amelanotic melanoma, Harderian gland adenoma, and malignant schwannoma, the incidence of which was very low and is similar to the results observed in a previous study. 7 In these current data, amelanotic melanoma was noted in the eye in females, while Harderian gland adenoma and schwannoma were noted in males at 0.1% incidence (Table 11; Figure 20).…”

“…Some of the ocular tumors noted in the current data evaluated included malignant amelanotic melanoma, Harderian gland adenoma, and malignant schwannoma, the incidence of which was very low and is similar to the results observed in a previous study. 7…”

Rift Valley Fever Virus Infects the Posterior Segment of the Eye and Induces Inflammation in a Rat Model of Ocular Disease

“…Evaluation of the adaptive immune response in the eye may prove difficult due to the high lethality from RVFV infection in rats, but follow-up studies would be useful to determine its contribution to long-term ocular pathology. We noted high immune cell counts observed in some uninfected animals, which may be due to the development of spontaneous retinal lesions that can occasionally occur in Sprague Dawley rats ( 33 ). We were unable to complete in depth analysis of retinal function and health through fundus imaging or electroretinogram due to a lack of both accessibility and sensitivity of this equipment in the ABSL-3.…”

Introduction of gloved hand to cage induces 22-kHz ultrasonic vocalizations in male albino rats

“…This brings up the question 'why other animals did not respond with 22-kHz USVs to the same stimuli?' Is this due to the possible inherited retinal dystrophy or deficit as reported, especially in female rats [17,26]? To increase our understanding of the mechanism of the hand-induced USVs, we first checked the retinal function of all 22-kHz responders and all (SD) and subset (WH) non-responder animals to the photopic test stimuli, using the full-field flash ERG technique.…”

“…Rodents collect external/environmental information via their sensory systems, such as visual, hearing, smell, taste, and touch/pain. In albino rats, spontaneous retinal degeneration has been reported [17]. The purpose of the present study was to test whether the introduction of a gloved human hand in the cage could evoke USVs in naïve albino rats with or without normal visual function.…”