Distributed representation in the song system of oscines: evolutionary implications and functional consequences.

This paper reviews the organizational principles and implications that have emerged from the analysis of HVc, a forebrain nucleus that is a major site of sensory, motor, and sensorimotor integration in the song control system of oscine passerine birds (songbirds). Anatomical, physiological, and behavioral data support the conclusion that HVc exists within a hierarchically organized system with parallel pathways that converge onto HVc. The organization of HVc is distributed and redundant, and its outputs exhibit broad divergence. A similar pattern of connectivity exists for neostriatum adjacent to HVc. This and other data support the hypothesis that the song system arose from an elaboration or duplication of pathways generally present in all birds. Spontaneous and auditory response activity is strongly correlated throughout HVc, with auditory responses exhibiting strong temporal modulation in a synchronized fashion throughout the nucleus. This suggests that the auditory representation of song is encoded in the synchronized temporal patterns of activation, and that the predominant selectivity for the individual's own song that is observed for HVc neurons results from interactions of auditory input with central pattern generators for song. Most, or all HVc neurons are recruited during singing. The auditory response and motor recruitment properties of individual HVc neurons have no simple relationship, and the spontaneous activity in HVc may build up in the seconds preceding a song. To the extent HVc participates in perceptual phenomena associated with song, production and perception are not tightly linked in adults but may be linked by shared developmental processes during periods of sensorimotor learning.

Reproductive and developmental toxicity of N,N-diethyl-m-toluamide in rats.

N,N-Diethyl-m-toluamide (mDET, DEET) is widely used as a topical insect repellent. It is the active ingredient in many consumer formulations, which usually contain 10-25% mDET in an alcohol base. More concentrated consumer products are also available, including some that are pure technical grade mDET. Persons living or employed in mosquito-infested areas may have very high seasonal exposures to mDET. Because contradictory reports had been published on the reproductive and developmental toxicity of mDET, a series of studies was conducted in male and female Sprague-Dawley rats. All treatments were administered by daily subcutaneous injections of undiluted mDET. A dose finding study was done using 12 time-mated females per group treated on Gestational Days (GD) 6-15 with 0.50, 0.62, 0.78, 0.92, or 1.2 ml mDET/kg/day. No females survived 10 days of mDET dosing with 1.2 ml/kg/day. Deaths occurred in all other groups except the low dose (0.50 ml/kg/day). Pregnant females treated on GD 6-15 with 0 or 0.30 ml/kg/day were used for the teratology study. Half of each group was euthanized on GD 20: the second half was singly housed in nesting boxes and allowed to deliver litters. Live pups were counted and weighed soon after birth on Postnatal Day (PD) 0 and again on PD 3, 9, and 14. Proven fertile males were treated 5 days/week for 9 weeks with 0, 0.30, 0.73, 1.15, or 1.80 ml mDET/kg/day for a male dose-finding study. Each group consisted of 20 males. No males survived the 1.80 ml/kg/day. Deaths occurred in all remaining dose groups except the 0.30 ml/kg/day and control group. Immediately following the final treatment of the male dose study, 11 males were randomly selected from the 0.30 and 0.73 ml/kg/day groups. They were cohabited for 7 days with 4 females per male during post-treatment Weeks 1 and 2. Half of the females were euthanized 12-14 days after the last day of cohabitation for a dominant lethal study; the remaining females were singly housed in nesting boxes and allowed to deliver litters. Live pups were counted and weighted on PD 0 and 3. There was no evidence of reproductive or developmental toxicity in any of these assays, but there were signs of neurotoxicity in treated adult male and female rats, which may relate to reports of neurotoxicity in humans heavily exposed to mDET-containing insect repellents.

Overview of reproductive and developmental toxicity studies of 1,3-butadiene in rodents.

A series of studies to further evaluate the developmental and reproductive toxicity of inhaled 1,3-butadiene was sponsored by the National Toxicology Program. Pregnant Sprague-Dawley rats (24-28/group) and Swiss (CD-1) mice (18-22/group) were exposed to atmospheric concentrations of 0, 40, 200, or 1000 ppm 1,3-butadiene for 6 hr/day on days 6 through 15 of gestation (dg) and killed on dg 18 (mice) or dg 20 (rats). Subsequently, the uterine contents were evaluated; individual fetal body weights were recorded; and external, visceral, and skeletal examinations were performed. In rats, maternal toxicity was observed in the 1000-ppm group in the form of reduced extragestational weight gain and, during the first week of treatment, decreased body weight gain. Under these conditions, there was no evidence of developmental toxicity in rats. In contrast, results of the mouse developmental toxicity study indicated that the fetus may be more susceptible than the dam to inhaled 1,3-butadiene. Maternal toxicity was observed in mice at the 200- and 1000-ppm 1,3-butadiene exposure levels, whereas 40 ppm and higher concentrations of 1,3-butadiene caused significant exposure-related reductions in the mean body weights of male fetuses. Mean body weights of female fetuses were also reduced at the 200- and 1000-ppm exposure levels. No increased incidence of malformations was observed in either study. Other studies addressing male reproductive and mutagenesis end points were performed with B6C3F1 mice (sperm-head morphology) and Swiss (CD-1) mice (dominant lethal study).(ABSTRACT TRUNCATED AT 250 WORDS)

Relative potency of four ethylene glycol ethers for induction of paw malformations in the CD-1 mouse.

Time-mated CD-1 mice were orally dosed on gestation day 11 (plug = 0) with distilled water (control) or one of four glycol ethers at a dose of 4 mmol/kg: ethylene glycol monomethyl ether (EGME, 304 mg/kg), ethylene glycol dimethyl ether (EGdiME, 361 mg/kg), diethylene glycol dimethyl ether (diEGdiME, 537 mg/kg), triethylene glycol dimethyl ether (triEGdiME, 713 mg/kg). Fetuses were collected on gestation day 18, weighed, and examined for gross external malformations. Fetuses were cleared and stained to examine paws. There were no signs of treatment-related maternal toxicity, and intrauterine survival was unaffected by glycol ether treatments. Fetal body weights were significantly reduced only in litters treated with EGdiME. There was no treatment-related pattern of gross external malformations other than paw defects. Only triEGdiME failed to produce a significant incidence of malformations. Paw defects were present in 87.5% of EGME-treated litters (68.5% of fetuses), 86.7% of EGdiME-treated litters (33.8% of fetuses), and 77.8% of diEGdiME-treated litters (39.7% of fetuses). Hindpaw defects predominated over forepaw, and syndactyly was the most common malformation. The incidences of oligodactyly and short digits were also significantly increased. The similarity of malformations produced by these methyl-substituted glycol ethers is proposed to be attributable to in vivo conversion to a common teratogen, methoxyacetic acid.

Workshop on the Chernoff/Kavlock preliminary developmental toxicity test.

The Chernoff/Kavlock assay, proposed as a preliminary screen for teratogenic potential, was the subject of a 2-day workshop sponsored by the National Institute for Occupational Safety and Health. Data from three large testing programs were presented, representing tests of 165 chemicals, of which 33 were tested at least twice. Applications of the test in industrial laboratories and product development, hazard identification, and risk assessment were discussed. Workshop participants recognized the assay as one of several valid ways to preliminarily evaluate chemicals with unknown developmental toxicity. Other preliminary tests were also discussed in terms of their relationship to this test, which was seen as having the advantage of providing information on neonatal viability. Other techniques, particularly an abbreviated conventional teratology study, were also recognized as appropriate screens. The preferred test in a particular laboratory will be dependent upon the particular skills and objectives of that laboratory. Standardized protocols were suggested, but flexibility in experimental design was considered necessary, and many variations on the basic test could be appropriate. This preliminary test has been used most often as a single-dose test in mice, but might provide more generally useful data if conducted in rats using two dose levels. Workshop participants viewed the test as highly reliable in correctly identifying developmentally toxic chemicals and suggested that a negative finding in a properly conducted Chernoff/Kavlock test could be a sufficient basis for regulatory agencies to determine that conventional teratology tests in the same species are not warranted.

Evaluation of 60 chemicals in a preliminary developmental toxicity test.

The number of chemicals in commerce which have not been evaluated for potential developmental toxicity is large. Because of the time and expense required by conventional developmental toxicity tests, an abbreviated assay is needed that will preliminarily evaluate otherwise untested chemicals to help prioritize them for conventional testing. A proposed short-term in vivo assay has been used in a series of studies in which a total of 60 chemicals were tested. Some were independently tested two or four times each. In this preliminary test, pregnant mice were dosed during mid-pregnancy and were then allowed to deliver litters. Litter size, birth weight, and neonatal growth and survival to postnatal day 3 were recorded as indices of potential developmental toxicity. Results in this assay and conventional mouse teratology tests were generally concordant. Conventional data were available for 14 chemicals (ten teratogens, one fetotoxin, three nonteratogens), of which 11 (nine teratogens, one fetotoxin, one nonteratogen) produced evidence of developmental toxicity. This included conventional data for three chemicals (ethylene glycol, diethylene glycol dimethyl ether, and triethylene glycol dimethyl ether) that were untested before the present study. As high priority candidates for conventional testing on the basis of results here, all were subsequently studied in a standard teratology assay and were confirmed to be teratogenic in mice. Additionally, one of them (ethylene glycol) plus a fourth high priority candidate for conventional study (diethylene glycol monomethyl ether) were subsequently tested in rats and were found to be teratogenic in that species.

Recommendations for the statistical analysis of Chernoff/Kavlock test data.

The statistical analyses of the data related to the teratogenic testing of 60 compounds utilizing the Chernoff/Kavlock test are the basis of this paper. The hypotheses chosen to be tested and the statistical tests utilized to test those hypotheses are discussed. The topics explored are the use of comparisonwise error rate versus experimentwise error rate, the use of nonparametric tests versus more "conventional" parametric tests and the use of "historical data" in assessing and interpreting group difference.

A recommended protocol for the Chernoff/Kavlock preliminary developmental toxicity test and a proposed method for assigning priority scores based on results of that test.

Recommendations are made for a standard protocol for the Chernoff/Kavlock preliminary developmental toxicity test, and a weighted scoring system is proposed to provide a numerical prioritization. Protocol recommendations include use of pregnant animals for dose-finding studies and, in the testing phase, treatment on gestation days 6-15 at an overtly maternally toxic dose. This treatment period corresponds to the usual timing of a teratology test and provides an improved data base in the event a conventional test is deemed appropriate. Five indices of potential developmental toxicity are: the proportion of pregnant survivors at term that produces a viable litter (at least one liveborn pup), average litter size and pup weight at birth, and average neonatal survival and body weight gain to 3 days of age. Neither systematic examinations of pups (living or dead) for malformations nor counts of dead pups are considered productive. In the proposed method for point scores, each of the five indices is assigned a point value that varies according to broad classes of maternal toxicity. The maximum total point value is 22. When there is no statistically significant difference between treated and control groups, the assigned value is subtracted from 22. If there is a statistically significant treatment effect, or if statistics cannot be applied, then no points are subtracted. The points remaining after all five indices are considered constitute the priority score, which may range from 0 (low) to 22 (high priority).

Calcium homeostasis in pregnant rats treated with ethylene glycol monomethyl ether (EGME).

The industrial solvent ethylene glycol monomethyl ether (EGME) is a known teratogen that has been reported to alter calcium metabolism in guinea pigs during chronic exposure. Because of the tremendous demand of reproduction on maternal calcium stores, the effects of EGME on calcium and vitamin D metabolism during gestation were examined. Timed pregnant rats were treated by gavage with 0, 50, or 100 mg/kg EGME in 10 ml/kg distilled water on Days 9-15 of gestation (sperm = Day 1) and examined on Days 16 and 21. Virgin rats were treated for 7 days with 0 or 100 mg/kg EGME and examined 5 days later. EGME exposure did not affect body or kidney weight in virgin or pregnant rats, but liver weight was reduced in near-term pregnant rats treated with 100 mg/kg EGME. EGME (50 mg/kg) reduced litter size and fetal body weight and caused a significant number of live fetuses to have visceral abnormalities. EGME (100 mg/kg) caused all fetuses to be resorbed. In nonpregnant rats, 100 mg/kg did not affect serum 1,25-dihydroxyvitamin D (1,25(OH)2D3), 25-hydroxyvitamin D, ionic calcium, total calcium, or parathyroid hormone. EGME appeared to have a dose-dependent effect on calcium and vitamin D metabolism during gestation. On Day 21 of gestation, total calcium and ionic calcium were increased and 1,25(OH)2D3 was reduced in rats treated with EGME compared with nontreated controls. However, significant alterations in calcium homeostasis were evident only in dams that completely resorbed their litters. The changes in calcium and vitamin D metabolism during gestation appear to be secondary to the EGME-induced loss of litters.

Reproductive toxicology of inhaled styrene oxide in rats and rabbits.

Experiments were performed to evaluate reproductive and developmental toxicology in rats and rabbits exposed to styrene oxide by inhalation. Female rats were exposed to 100 or 300 ppm styrene oxide or to filtered air for 7 h/day, 5 days/week for 3 weeks. Extensive mortality occurred in rats that received prolonged exposure to 100 ppm styrene oxide while 300 ppm was rapidly lethal. As a result exposures were terminated in this latter group and the group was eliminated from further study. The rats of the 0 and 100 ppm groups were then mated and exposed to 0 or 100 ppm styrene oxide daily through 18 days of gestation (dg). Female rabbits were artificially inseminated and exposed for 7 h daily to 0, 15, or 50 ppm styrene oxide through 24 dg. Both of these lower concentrations used for exposure of the rabbits produced mortality of does. The rats were killed at 20 dg and the rabbits at 30 dg. Pregnant animals were examined for toxic changes including altered tissue weights and histopathologic effects. Litters were evaluated using several measures of embryotoxicity, and live fetuses were examined for external, visceral, and skeletal malformations. Exposure during gestation appeared to increase preimplantation loss in rats, and tended to increase the incidence of resorptions in rabbits. In both species, fetal weights and crown-rump lengths were reduced by gestational exposure. The incidences of ossification defects of the sternebrae aned occipital bones were increased by gestational exposure of rats to styrene oxide. These results indicate that inhalation exposures at these concentrations produce reproductive and development toxicity, as well as maternal toxicity.

Developmental toxicity of diethylene glycol monomethyl ether (diEGME).

Diethylene glycol monomethyl ether (diEGME) was one of 15 glycols tested in CD-1 mice using a short-term in vivo reproductive toxicity assay (Chernoff/Kavlock test). Because results were strongly suggestive of potential reproductive toxicity, a teratology study was conducted in Sprague-Dawley rats. Time-mated females were orally dosed on Days 7-16 of gestation with diEGME in distilled water. Doses of 0, 1000, 1495, 2235, 3345, and 5175 mg/kg/day were used in a preliminary dose-finding study. At 5175 mg/kg/day, two of nine rats died, five of five litters were totally resorbed, and maternal extra gestational body weight gain was reduced. At 3345 mg/kg/day, six of nine litters were resorbed but there were no deaths and extra gestational body weight gain was not affected. Visceral and skeletal examinations revealed a dose-related increase in malformations, primarily of the ribs and cardiovascular system. Subsequently, pregnant rats were similarly dosed with 0, 720, or 2165 mg/kg/day. Neither dose was maternally toxic, but fetal body weights and the number of live implantations were significantly reduced at 2165 mg/kg/day. Rib malformations were seen in 9.1% (control), 42.9% (720 mg/kg/day, p less than 0.05), and 80.0% (2165 mg/kg/day, p less than 0.001) of litters. Cardiovascular malformations occurred in 0.0, 4.8, and 71.4% (p less than 0.001) of litters. Diethylene glycol monomethyl ether thus was teratogenic in rats at all doses tested, producing a dose-dependent series of malformations similar to those produced by other members of the glycol ether family.

Electrocardiographic study of rat fetuses exposed to ethylene glycol monomethyl ether (EGME).

The widely used industrial solvent ethylene glycol monomethyl ether (EGME) is teratogenic to rats and mice, inducing a variety of heart and major vessel abnormalities. In the present study, electrocardiography was used to evaluate heart function in day 20 rat (Sprague-Dawley) fetuses from mothers treated on gestation days 7-13 (sperm = day 1) with 0, 25, or 50 mg/kg EGME by gavage in 10 ml/kg water. The increased incidence of fetuses with cardiovascular malformations (primarily right ductus arteriosus and ventricular septal defect) and abnormal electrocardiograms (EKG) was dose dependent. The most prevalent EKG abnormality was a prolonged QRS wave. Mean QRS intervals were not significantly increased by EGME exposure, but there were significantly more litters in the 50-mg/kg EGME group that had one or more fetuses with QRS complexes of 40 msec or longer. The enhanced duration and the appearance of the aberrant QRS's suggested the presence of an intraventricular conduction delay in these fetuses. Heart rate and other EKG characteristics such as the P wave or P-R and Q-T intervals were not significantly affected by exposure to EGME. There did not appear to be an association between abnormal EKG's and fetal heart dysmorphology.

Developmental toxicity of nine selected compounds following prenatal exposure in the mouse: naphthalene, p-nitrophenol, sodium selenite, dimethyl phthalate, ethylenethiourea, and four glycol ether derivatives.

Ethylene glycol dimethyl ether (EGdiME), diethylene glycol dimethyl ether (diEGdiME), triethylene glycol dimethyl ether (triEGdiME), diethylene glycol diethyl ether (diEGdiEE), ethylenethiourea (ETU), sodium selenite (SS), dimethyl phthalate (DMP), naphthalene (NAP), or p-nitrophenol (PNP) were administered by gavage for eight consecutive days to female CD-1 mice. Weight loss was insensitive as an index of sublethal adult toxicity and was inadequate for determining a maximum tolerated dose. LD50 values indicate that SS, NAP, and PNP were more toxic (8.4, 353.6, and 625.7 mg/kg, respectively) than the polyglycol ethers, ETU, and DMP (LD50 values ranged from 2525.8 to 6281.9 mg/kg). Each of the compounds was administered on d 7 through 14 to pregnant animals at a single dose estimated to be at or just below the threshold of adult lethality. In such a reproductive study, each of the compounds could be categorized on the basis of the pattern of maternal lethality and fetotoxicity which it produced. The number of dams with complete resorptions was significantly increased after administration of ETU, and no mice in the EGdiME-, diEGdiME-, or triEGdiME-treated groups delivered any viable offspring. Maternal lethality was significant in the EGdiME, triEGdiME, PNP, and NAP groups. There was a slight reduction in the average number of live pups per litter in the diEGdiEE- and PNP-treated groups and a significant reduction in the NAP group. The number dead per litter was increased with diEGdiEE. SS and DMP had no effect on maternal or fetal survival at the doses administered. Individual pup weight at d 1 postpartum was only significantly reduced by diEGdiEE, and no gross congenital abnormalities were detected in neonates from any treatment group. These results provide guidelines for the subsequent toxicity testing of these chemicals.

Developmental effects after inhalation exposure of gravid rabbits and rats to ethylene glycol monoethyl ether.

The effects of ethylene glycol monoethyl ether (EGEE) were determined on development in utero. Pregnant New Zealand White rabbits were exposed to air or 160 or 617 ppm EGEE for 7 hr/day from 1 to 18 days of gestation (dg). Virgin Wistar rats were exposed to 150 or 649 ppm EGEE or air 5 days/week for the 3 weeks immediately preceding their breeding. Sperm-positive rats were subsequently exposed to air or 202 or 767 ppm EGEE for 7 hr/day from 1 to 19 dg. Group sizes were 29 to 38 per concentration for both species. Pregestational exposure of rats had no effect on mating success, and there was no effect of EGEE exposure on establishment of pregnancy in either species. Rabbits exposed to the both concentrations had decreased food intake and depressed weight gain. Exposure-related mortality occurred in the 617 ppm EGEE group of rabbits. The only toxic sign seen in rats was reduced weight gain after exposure to 767 ppm EGEE. Exposure induced high embryomortality at maternal toxic concentrations in rats and rabbits, while lower levels induced fetal growth retardation in rats but not in rabbits. Gestational exposure increased the incidence of anomalies and variations; these were primarily of soft tissues in rabbits and of skeleton in rats. Thus, significant evidence of terata, fetal growth retardation and embryomortality were induced in rabbits and rats at levels that were below or similar to those that induced maternal manifestation of toxicity. These data implicate EGEE as a teratogen.

Results of testing fifteen glycol ethers in a short-term in vivo reproductive toxicity assay.

Fifteen glycol ethers were investigated for their potential to cause adverse reproductive toxic effects using an in vivo mouse screening bioassay. Pregnant mice were orally dosed once per day on days 7 through 14 of gestation at concentrations causing 0 to 41% maternal mortality. Reproductive endpoints included pup survival in utero (percent of live litters/pregnant survivors), pup perinatal and postnatal survival (number of live pups per litter, number of dead pups per litter, and pup survival to 2.5 days of age), and pup body weight statistics (weight at birth and weight at 2.5 days of age). The study was conducted in two phases: a dose range-finding phase using nonpregnant female mice, and a definitive reproductive phase using time-mated mice. The range-finding phase sought to identify, for each chemical, the maternal LD10 as the target dose. However, based upon reproductive phase results, such an exact dose was impractical to achieve. Thus, a range from the LD5 to the LD20 was considered a sufficient challenge dose that would not affect results due to high mortality, i.e., greater than the LD20. Glycol ethers were assigned to groups having different priorities for further testing based upon whether a sufficient challenge dose was administered and the degree of effects recorded for each chemical.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental toxicity of four glycol ethers applied cutaneously to rats.

Previous NIOSH studies demonstrated the embryo- and fetotoxicity and teratogenicity of ethylene glycol monoethyl ether (EGEE) applied to the shaved skin of pregnant rats. In the present study ethylene glycol monoethyl ether acetate (EGEEA), ethylene glycol monobutyl ether (EGBE), and diethylene glycol monoethyl ether (diEGEE) were tested in the same experimental model, using distilled water as the negative control and EGEE as a positive control. Water or undiluted glycols were applied four times daily on days 7 to 16 of gestation to the shaved interscapular skin with an automatic pipetter. Volumes of EGEE (0.25 mL), EGEEA (0.35 mL), and diEGEE (0.35 mL) were approximately equimolar (2.6 mmole per treatment). EGBE at 0.35 mL four times daily (approximately 2.7 mmole per treatment) killed 10 of 11 treated rats, and was subsequently tested at 0.12 mL (0.9 mmole) per treatment. EGEE- and EGEEA-treated rats showed a reduction in body weight relative to water controls that was associated with completely resorbed litters and significantly fewer live fetuses per litter. Fetal body weights were also significantly reduced in those groups. Visceral malformations and skeletal variations were significantly increased in EGEE and EGEEA groups over the negative control group. No embryotoxic, fetotoxic, or teratogenic effects were detected in the EGBE- or diEGEE-treated litters.

Reproductive toxicity of the glycol ethers.

The glycol ethers are an important and widely used class of solvents. Recent studies have demonstrated that ethylene glycol monomethyl ether (EGME), ethylene glycol dimethyl ether (EGdiME), ethylene glycol monoethyl ether (EGEE), and ethylene glycol monoethyl ether acetate (EGEEA) are teratogenic. Other studies have demonstrated that testicular atrophy or infertility follow treatment of males with EGME, ethylene glycol monomethyl ether acetate (EGMEA), EGEE, EGEEA, diethylene glycol dimethyl ether (diEGdiME), and diethylene glycol monoethyl ether (diEGEE). Experimental data are reviewed and structure-activity relationships are speculated upon.

Evaluation of propylene oxide for mutagenic activity in 3 in vivo test systems.

Propylene oxide (CAS No. 75-56-9) was tested for mutagenic activity following vapor exposure using 3 in vivo test systems. Rat dominant lethal and mouse sperm-head morphology assays were conducted using males exposed to propylene oxide at 300 ppm in a dynamic exposure chamber for 7 h per day on 5 consecutive days. A sex-linked recessive lethal test in Drosophila melanogaster employed a 24-h static exposure to propylene oxide at 645 ppm. Male mice were killed 1, 3, 5, 7, and 9 weeks post-exposure for evaluation of sperm-head morphology. Propylene oxide exposure did not result in an increase in abnormal forms. Male rats were mated with 2 virgin females per week for 6 weeks following exposure. A statistically significant increase in preimplantation losses and a statistically significant reduction in the number of living implants in the first post-exposure week did not appear to be treatment related. A highly significant increase in sex-linked recessive lethal mutations was observed in two germ cell stages (mature sperm and developing spermatocytes). These results warrant continued caution in potential human exposure to propylene oxide.

Reproductive-toxicologic assessment of the epoxides ethylene oxide, propylene oxide, butylene oxide, and styrene oxide.

Ethylene oxide (CAS no 75-21-8), propylene oxide (CAS no 75-56-9), butylene oxide (CAS no 106-88-7), and styrene oxide (CAS no 96-09-3) were tested for teratogenic activity by inhalation exposure of rats and rabbits. Ethylene oxide and propylene oxide were tested at only one concentration in both species (150 ppm for ethylene oxide and 500 ppm for propylene oxide). Butylene oxide was tested at 250 and 1,000 ppm in both species, while styrene oxide was tested at 100 ppm in rats and 15 and 50 ppm in rabbits. For each of these four epoxides, the acute toxicity was similar for pregnant and nonpregnant rats. Styrene oxide was the most toxic in both species, and rabbits were more sensitive than rats. Rats exposed to propylene oxide for 7 h/d, 5 d/week for three weeks before breeding had a significant reduction in the number of corpora lutea. Fetal mortality was not increased, but significantly fewer mated rats were found pregnant following gestational exposure to styrene oxide, a finding suggesting preimplantation loss. In rabbits exposed to styrene oxide, the number of resorptions per litter was increased in concentration related manner, but differences were not statistically significant. Fetal examination revealed evidence of fetotoxicity with all four epoxides. There was no overt teratogenic activity, but a number of minor morphologic aberrations were detected.

Drosophila as a tool for the rapid assessment of chemicals for teratogenicity.

Drosophila melanogaster is being investigated for its potential to aid in identifying priority chemicals for teratologic study. The method encompasses treating larvae over the entire metamorphosis period, i.e., from the egg through three instar stages to pupa formation, by incorporating the test chemical into the medium. Adult flies are systematically examined under a binocular microscope for external morphological anomalies. Data from treated flies can be compared with those from concurrent control flies using standard statistical tests. Results from this developmental work reveal a dramatic and reproducible response of Drosophila to various chemical treatments. Validation studies, testing known teratogens and nonteratogens, are necessary before such a system can be incorporated into existing teratologic screening regimens.