The potential of emamectin benzoate (EB) to cause developmental neurotoxicity in Sprague-Dawley rats was assessed using a study design by the US EPA. Dosages of 0 (deionized water), 0.1, 0.6, or 3.6 mg/kg/day were administered at 5 ml/kg by oral gavage from gestational day (GD) 6 to lactational day (LD) 20 to groups of 25 mated females each. Between GD 17 and 20 the high dose was reduced to 2.5 mg/kg/day because of pup tremors observed at this dose level in a concurrent two-generation study. Females were allowed to deliver and the young were evaluated for survival, growth, development, behavior, and histological changes to brain, spinal cord, peripheral nerve, and skeletal muscle. Behavioral assessment of the offspring consisted of open field motor activity, auditory startle habituation, and passive avoidance tests; each was conducted on weanling and adult animals (one animal/sex/litter). Histopathological examination of the CNS and PNS was conducted on one animal/sex/litter on postnatal days (PND) 11 and 60. There were significant increases in average F0 maternal body weight gains during gestation in the 0.6 and 3.6/2.5 mg/kg/day groups, but no other effects were observed in pregnant females of these or the low-dose groups during the study. Beginning on PND 6, tremors were observed in high-dose pups, and this was followed by hindlimb splay in all high-dose pups by PND 15-26. Both of these physical signs disappeared by PND 34 (i.e., 10-11 days after weaning). There were no compound-related deaths in F1 offspring. Beginning on PND 11, progressive decreases in preweaning average weights were observed in the high-dose group (to 42% below control in females on PND 21). Average weight gain during the postweaning period was significantly decreased in the 3.6/2.5 mg/kg/day group. There were EB-related effects in behavioral tests only in the high-dose group. A significant increase in PND 13 average horizontal motor activity was due to stereotypical movements. Average horizontal activity was decreased on PND 17 and in adult females, but there was no effects on PND 21. Average peak auditory startle response amplitude was decreased on PND 22 and in adults. There were no EB-related effects in the passive avoidance test, relative brain weights, or in the histological examination (including morphometry) of the nervous system. These results demonstrate that the high-dose EB exposure during gestation and lactation to rats produced evidence of neurotoxicity in the F1 offspring, and a clear No Observed Adverse Effect Level (NOAEL) for developmental neurotoxicity of EB was determined to be 0.6 mg/kg/day.

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PubMedDate not supplied

Chromosomal abnormalities and gene amplification in renal cancers induced in rats by nickel subsulfide.

Nickel subsulfide (alpha Ni3S2) was administered to male Fischer-344 rats by unilateral intrarenal (i.r.) injection (20 mg per rat) to establish the time-course of alpha Ni3S2-induced erythrocytosis and to identify chromosomal abnormalities and molecular genetic aberrations in ensuing renal cancers. Blood hematocrit values were increased in alpha Ni3S2-treated rats during two to 36 weeks post-injection, attained a maximum of 77 percent (SD +/- 5) at 16 weeks (vs 51 +/- 3 percent in vehicle controls), and returned to baseline at 40 weeks. Within 21 months, malignant neoplasms (five sarcomas, one carcinoma) occurred in the injected kidneys of 6/28 alpha Ni3S2-treated rats (vs 0/13 controls). Cytogenetic analyses of direct preparations or primary cell cultures showed prominent chromosomal aberrations in three neoplasms, with rearranged marker chromosomes, polyploidy, and in one case an homogeneously staining region (HSR). Assays for gene amplification were performed with probes for murine erythropoietin (EPO) gene and H-ras, c-fos, c-myc, and N-myc oncogenes, using deoxyribonucleic acid (DNA) samples isolated from injected kidneys and renal neoplasms, as well as from the contralateral, non-injected kidneys. No consistent pattern was found; in one sarcoma, N-myc was amplified six-fold and c-fos was amplified two-fold; in another sarcoma, H-ras, c-fos, and EPO were amplified two-fold. This study shows that (a) karyotypes of 3/6 renal neoplasms of alpha Ni3S2-treated rats contained prominent marker chromosomes, (b) oncogene amplification was noted in 2/6 renal neoplasms, and (c) the EPO gene was not consistently amplified in DNA from the injected kidneys of alpha Ni3S2-treated rats during the initiation of erythrocytosis, or in subsequent renal neoplasms.

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