A 13-week subchronic toxicity study of hexyl acetate in SD rats.

Hexyl acetate (CAS No. 142-92-7) is a naturally occurring ester compound that has a fruity odor. Despite its frequent use as a nature-identical flavoring agent, there are limited repeated dose toxicity data for hexyl acetate. Here we performed a 13-week subchronic toxicity study of hexyl acetate in male and female Crl:CD(SD) rats under GLP regulations. Hexyl acetate was given orally by gavage at doses of 0, 100, 300, or 1,000 mg/kg/day using corn oil as the vehicle. No significant toxicological changes in general condition, body weights, food intake, ophthalmology, hematology, organ weights, and histopathological findings were observed in any groups. Urinalysis revealed occult blood in two male animals treated with 1,000 mg/kg/day hexyl acetate, and one showed red blood cells in the urine sediment. Furthermore, blood biochemistry showed a significant increase in inorganic phosphorus levels in males treated with 1,000 mg/kg/day hexyl acetate. These results indicated that the no-observed-adverse-effect level (NOAEL) of hexyl acetate was 300 mg/kg/day for males and more than 1,000 mg/kg/day for females.

Induction of a thoracolumbar supernumerary rib in rat developmental toxicity studies: A short discussion on the critical window.

Thoracolumbar supernumerary ribs (TSRs) are classified as less severe skeletal anomalies in rat developmental toxicity studies, although their incidence is relatively high in rodent studies. To investigate the characteristics of the critical window for chemically-induced TSR, in this study, rats were administered 5-fluorocytocine (5-FC) or sodium salicylate (SAL) at one of three time periods on gestational day (GD) 9, early morning (7:00 am), midday (12:00 pm to 1:00 pm), or late afternoon (4:00 pm or 7:00 pm). The incidence of TSR and other anomalies were assessed in GD20 fetuses. A single treatment with both chemicals on GD9-induced TSR, with the incidence highest when administered at 7:00 Am, decreasing gradually when administered later. This trajectory was clearer in rats treated with 5-FC than with SAL. The critical period of TSR induction is shorter in rats administered 5-FC than SAL. The characteristics of the critical window may cause variability in the incidence of TSR observed in developmental toxicity studies.

Historical control data on developmental toxicity studies in rats.

Historical control data from prenatal developmental toxicity studies in rats have been used to evaluate whether toxicology outcomes were induced by exposure to a chemical or were within the range of spontaneous variation. These data are also important for monitoring animal characteristics. As a follow-up to historical control data from 1998 to 2010, this study analyzed control data from prenatal developmental studies performed in rats from 2011 to 2015. Data were collected from studies performed by 24 Japanese laboratories, including 15 pharmaceutical and chemical companies and nine contract research organizations, in Sprague-Dawley and two-sub-strains of Wistar Hannover rats. The data included maternal reproductive findings at terminal cesarean section and fetal findings, including incidences of spontaneous external, visceral, and skeletal anomalies. No noticeable differences in maternal reproductive data were observed among laboratories. The inter-laboratory variations in the incidences of fetal anomalies seemed to be due to differences in the selection of observation parameters, observation criteria, and classification of the findings, as well as to differences in terminology of fetal alterations. These historical control data may be helpful for adequate interpretation of experimental results and for evaluating the reproductive and developmental toxicities of various chemicals.

Prenatal sodium arsenite affects early development of serotonergic neurons in the fetal rat brain.

Prenatal arsenite exposure has been associated with developmental disorders in children, including reduced IQ and language abnormalities. Animal experiments have also shown that exposure to arsenite during development induced developmental neurotoxicity after birth. However, the evidence is not enough, and the mechanism is poorly understood, especially on the exposure during early brain development. This study assessed effects of sodium (meta) arsenite shortly after exposure on early developing fetal rat brains. Pregnant rats were administered 50 mg/L arsenite in their drinking water or 20 mg/kg arsenite orally using a gastric tube, on gestational days (GD) 9-15. Fetal brains were examined on GD16. Pregnant rats administered 20 mg/kg arsenite showed reductions in maternal body weight gain and food consumption during treatment, but not with 50 mg/L arsenite. Arsenite did not affect fetal development, as determined by body weight, mortality and brain size. Arsenite also did not induce excessive cell death or affect neural cell division in any region of the fetal neuroepithelium. Thyrosine hydroxylase immunohistochemistry revealed no difference in the distribution of catecholaminergic neurons between fetuses of arsenite treated and control rats. However, reductions in the number of serotonin positive cells in the fetal median and dorsal raphe nuclei were observed following maternal treatment with 20mg/kg arsenite. Image analysis showed that the serotonin positive areas decreased in all fetal mid- and hind-brain areas without altering distribution patterns. Maternal stress induced by arsenite toxicity did not alter fetal development. These results suggest that arsenite-induced neurodevelopmental toxicity involves defects in the early development of the serotonin nervous system.

Study for collecting background data on Wistar Hannover [Crl:WI(Han)] rats in embryo-fetal development studies--comparative data to Sprague Dawley rats.

The purpose of the present study was to collect the background data on Wistar Hannover [Crl:WI(Han)] (hereafter Wistar Han) rats in embryo-fetal development studies from the 6 safety research facilities of pharmaceutical companies and contract research organizations. In each facility, 20 or 22 female rats were dosed with vehicle solution during the organogenesis period. As a result, no abnormalities in clinical signs and necropsy findings in dams were found. Body weights and food consumption in dams were lower than those in Sprague Dawley (SD) rats. The number of corpora lutea (13.3 vs. 16.0 in SD) and implantations (11.8 vs. 14.7) were fewer, and fetal body weights (3.66 vs. 3.70) and placental weights (0.42 vs. 0.45) tended to be lower than those in SD rats. Regarding the fetal abnormalities, the incidence of several findings such as the persistent left umbilical artery (10.4% vs. 1.1%) and cervical (5.2% vs. 0.4%), full (7.4% vs. 0.9%) or short supernumerary (64.5% vs. 9.9%) and wavy ribs (6.6% vs. 0.3%) was higher than that in SD rats. Our present study showed that they maintained a sufficient number of live fetuses and the difference in the fetal sex ratio was not observed. In conclusion, Wistar Han rats were considered to be a suitable strain for embryo-fetal development toxicity study. Since the incidence of several abnormalities was higher than that in SD rats, it may be said that to accumulate background control data is important to evaluate the embryo-fetal development toxicity study using Wistar Han rats.

An antioxidant, N,N'-diphenyl-p-phenylenediamine (DPPD), affects labor and delivery in rats: a 28-day repeated dose test and reproduction/developmental toxicity test.

A 28-day repeated dose toxicity test and reproduction/developmental toxicity test for N,N'-diphenyl-p-phenylenediamine (DPPD) were conducted in [Crl:CD(SD)] SPF rats. Male and female rats were dosed with DPPD by gavage for 28 days at 0, 100, 300, or 1000 mg/kg bw/day or for a total of 42-46 days at 0, 8, 50, or 300 mg/kg bw/day. No significant adverse effects were observed in the repeated dose toxicity study up to 1000 mg/kg bw/day in both sexes. In the reproduction/developmental toxicity study, two females showed piloerection, hypothermia, and pale skin; one died and the other showed dystocia on day 23 of pregnancy at 300 mg/kg bw/day. Another female delivered only three live pups at 300 mg/kg bw/day. A significantly prolonged gestation period was observed at 50 and 300 mg/kg bw/day. The NOAELs of repeated dose toxicity and reproduction/developmental toxicity were considered to be 1000 and 8 mg/kg bw/day, respectively.

Abnormal brain function of the rat neonate in a prenatal 5-bromo-2'-deoxyuridine (BrdU)-induced developmental disorder model.

Neonatal brain function was investigated in a prenatal BrdU-induced developmental disorder model, which has been reported to exhibit behavioral abnormalities such as locomotor hyperactivity, impaired learning and memory, and lower anxiety in offspring. After 1h home cage deprivation we observed an increase in the number of c-Fos (neuronal activity marker) immunoreactive cells in several brain regions of the olfactory and stress-related areas in normal neonates at 11 days. Next, pregnant rats were exposed to 50mg/kg of BrdU from gestation days 9-15, and their offspring at 11 days were home-cage deprived. Compared to vehicle control, the number of c-Fos immunoreactive cells in BrdU group was found to be decreased in the piriform cortex and locus coeruleus, which are known to play an important role in neonatal learning and memory. We also analyzed Pearson product-moment correlation coefficient of the number of c-Fos immunoreactive cells, focusing on the piriform cortex and locus coeruleus versus numerous other brain areas (11 areas including amygdala). Numerous significant correlations were observed in the vehicle control group, however, correlations of the locus coeruleus disappeared in the BrdU group. By observing c-Fos immunoreactivity after home cage deprivation our study uncovers abnormal brain functions as early as postnatal day 11 in this disorder model. Based on these results, we propose a new histological approach for functional characterization of developmental disorder models.

Nasal instillation of nanoparticle-rich diesel exhaust particles slightly affects emotional behavior and learning capability in rats.

In the present study, in order to reveal novel adverse effects of ultrafine particles (UFP) on the central nervous system, the effects of nanoparticle-rich diesel exhaust particles (NRDEP; count mode diameter, 21.45 nm) on emotional behavior, learning capability and brain neurotransmitter levels were studied in rats by intranasal instillation (iNI). NRDEP (10 and 50 µg/rat) was instilled into 2-week old infant, male rats once a week for 4 weeks. Spontaneous motor activity measured was observed to be inverse to the dose level. In active avoidance tests using a shuttle box, NRDEP-treated animals showed a lower avoidance performance than control animals given air-instillation. The levels of dopamine and its metabolite (DOPAC) in the medial mammillary nucleus of the brain tended to be lower in the NRDEP-treated animals. From these results, although the effects of NRDEP by iNI on the emotionality and the brain neurotransmitter levels were not fully clear, the results obtained by avoidance testing suggested involvement of UFP in learning capability.