B.K. Nelson

Behavioral and neurochemical alterations in the offspring of rats after maternal or paternal inhalation exposure to the industrial solvent 2-methoxyethanol

The industrial solvent 2-methoxyethanol (2ME) has antifertility effects in male rats at 300 ppm and is teratogenic in rats and rabbits at 50 ppm. The present research investigated if exposure of paternal or maternal animals to 25 ppm 2ME, the current U.S. permissible occupational exposure limit, would produce detectable effects in the offspring. Eighteen male young-adult Sprague-Dawley rats were exposed to 25 ppm 2ME 7 hr/day, 7 days/week for 6 weeks; they were then mated with untreated females which were allowed to deliver and rear their young. In addition, groups of 15 pregnant rats were exposed 7 hr/day on gestation days 7-13 or 14-20 and allowed to deliver and rear their young. At birth, litters were culled to 4 females and 4 males for behavioral testing of neuromotor function, activity, and simple learning ability on days 10 through 90. In addition, brains from newborn and 21-day-old offspring were analyzed for neurochemical deviations from controls. No effects on paternal or maternal animals, nor on the number or weight of live offspring, were noted. Behavioral testing revealed significant differences from controls only in avoidance conditioning of offspring of mothers exposed on days 7-13. In contrast, neurochemical deviations were observed in brains from 21-day-old offspring from the paternally exposed group as well as from both maternally exposed groups; changes were numerous in the brainstem and cerebrum but were fewer in the cerebellum and midbrain. Thus it appears that both paternal and maternal inhalation of 25 ppm 2ME produces some effect which is reflected in neurochemical deviations in the offspring.

Neurochemical, but not behavioral deviations in the offspring of rats following prenatal or paternal inhalation exposure to ethanol

In addition to its widespread social use, ethanol is used extensively as an industrial solvent. Inhalation exposures to ethanol which produce narcosis in maternal rats are not teratogenic. The present study sought to extend the previous research by including offspring from paternal exposures, and testing for behavioral disorders in the offspring following maternal or paternal exposures. Groups of 18 male (approximately 450 g) and 15 female (200-300 g) Sprague-Dawley rats were exposed 7 hours/day for six weeks or throughout gestation to 16000, 10000, or 0 ppm ethanol by inhalation and then mated with untreated rats. Litters were culled to 4 males and 4 females, and were fostered within 16 hours after birth to untreated dams which had delivered their litters within 48 hours previously. Offspring from paternally or maternally exposed animals performed as well as controls on days 10-90 in tests of neuromotor coordination (ascent on a wire mesh screen, rotorod), activity levels (open field, modified-automated open field, and running wheel), and learning ability (avoidance conditioning and operant conditioning). In addition, brains of 10 21-day-old pups were analyzed for neurochemical differences from controls in concentrations of protein and the neurotransmitters acetylcholine, dopamine, norepinephrine, 5-hydroxytryptamine, substance P, Met-enkephalin, and beta-endorphin. Levels of acetylcholine, dopamine, substance P, and beta-endorphin were essentially unchanged in the offspring of rats exposed to ethanol. Complex, but significant changes in levels of norepinephrine occurred only in paternally exposed offspring. 5-Hydroxytryptamine levels were reduced in the cerebrum, and Met-enkephalin levels were increased in all brain regions of offspring from both maternally and paternally exposed rats.

Lack of selective developmental toxicity of three butanol isomers administered by inhalation to rats

As part of an ongoing study of the developmental toxicology of industrial alcohols, this report presents the results of the teratology assessments of 1-butanol, 2-butanol, and t-butanol administered by inhalation to rats. Groups of approximately 15 Sprague-Dawley rats were exposed at 8000, 6000, 3500, or 0 ppm 1-butanol, 7000, 5000, 3500, or 0 ppm 2-butanol, or 5000, 3500, 2000, or 0 ppm t-butanol for 7 hr/day on Gestation Days 1-19 (sperm = 0). In each case, the highest concentration was selected to produce maternal toxicity. Dams were sacrificed on Gestation Day 20, and fetuses were individually weighed, tagged, and examined for external malformations. One-half of the fetuses were stained and examined for skeletal abnormalities, and the other half were examined for visceral defects using the Wilson technique. For each butanol isomer examined, the highest concentration (and the intermediate in some cases) was maternally toxic, as manifest by reduced weight gain and feed intake. Even at a maternally toxic dose, and in spite of a dose-dependent reduction in fetal weights for each isomer, the only teratogenicity observed was a slight increase in skeletal malformations (primarily rudimentary cervical ribs), seen with the highest concentration of 1-butanol. Thus, although teratogenicity was observed at 8000 ppm 1-butanol, and developmental toxicity was observed with each of the butyl alcohol isomers studied, concentrations 50 times the current permissible exposure limits for these three butanol isomers do not produce teratogenicity in rats.

Review of experimental male-mediated behavioral and neurochemical disorders

Paternal exposures to exogenous agents have been reported to produce a variety of developmental defects in the offspring. In experimental animals, these effects include decreased litter size and weight, increased stillbirth and neonatal death, birth defects, tumors, and functional/behavioral abnormalities-some of these effects being transmitted to the second and third generations. This article reviews the exogenous agents that have reportedly caused behavioral or neurochemical alterations in offspring of experimental animals following paternal exposures, including advanced age, alcohols, cyclophosphamide, ethylene dibromide, lead, opiates, and a few miscellaneous chemicals. Based upon the consistency of effects in several of these agents in a variety of studies in experimental animals, the conclusion is that paternal exposures may contribute to the incidence of neurobehavioral disorders in humans.

Developmental toxicology evaluation of 1-pentanol, 1-hexanol, and 2-ethyl-1-hexanol administered by inhalation to rats

As part of a large study evaluating the developmental toxicology of industrial alcohols, groups of approximately 15 Sprague-Dawley rats were exposed for 7 h/day on gestation days 1–19 to one of three alcohols at the highest concentrations we could generate as a vapor. Since these concentrations were not sufficiently high to be toxic to the maternal rats, lower levels were not included. These concentrations were 14,000, 3500, and 850 mg/m3 1-pentanol, 1-hexanol, and 2-ethyl-1-hexanol, respectively. Dams were weighed daily for the first week of exposure and weekly thereafter and were sacrificed on day 20. Fetuses were serially removed, blotted dry, examined for external malformations, sexed, weighed, fixed, and examined for visceral or skeletal defects. Pentanol reduced maternal feed intake and weight gain, but there were no significant decreases in fetal weights. Resorptions were slightly increased in the group exposed to 1-hexanol, and 2-ethyl-1-hexanol reduced maternal feed intake, but neither hexanol derivative produced malformations. Obviously, teratogenicity by other routes of exposure cannot be ruled out, particularly in view of the low volatility of these alcohols. However, the present studies indicate that inhalation of pentanol, hexanol, or 2-ethyl-1-hexanol at the stated concentrations can produce limited maternal toxicity, but none was teratogenic to rats.

Interactions of radiofrequency radiation on 2-methoxyethanol teratogenicity in rats.

Concurrent exposures to chemical and physical agents occur in the workplace; exposed workers include those involved with the microelectronics industry, plastic sealers and electrosurgical units. Previous animal research indicates that hyperthermia induced by an elevation in ambient temperature can potentiate the toxicity and teratogenicity of some chemical agents. We previously demonstrated that combined exposure to radiofrequency (r.f.; 10 MHz) radiation, which also induces hyperthermia and is teratogenic to exposed animals, and the industrial solvent 2‐methoxyethanol (2ME) produces enhanced teratogenicity in rats. A subsequent study replicated and extended that research by investigating the interactive dose‐related teratogenicity of r.f. radiation (sham exposure or maintaining colonic temperatures at 42.0°C for 0, 10, 20 or 30 min by r.f. radiation absorption) and 2ME (0, 75, 100, 125 or 150 mg/kg) on gestation days 9 or 13 of rats. The purpose of the present research is to determine the effects of r.f. radiation (sufficient to maintain colonic temperatures at 42.0°C for 10 min) on a range of doses of 2ME (0, 20, 40, 60, 80, 100, 120 and 140 mg kg−1) administered on gestation day 13 of rats. Focusing on characterizing the dose–response pattern of interactions, this research seeks to determine the lowest interactive effect level. Day 20 fetuses were examined for external and skeletal malformations. The results are consistent with previous observations. Dose‐related developmental toxicity was observed for 2ME both in the presence and absence of r.f. radiation. However, concurrent RF radiation exposure changed the shape of the dose–effect curve of 2ME. These data indicate that combined exposure effects should be considered when developing exposure guidelines and intervention strategies. © 1997 by John Wiley & Sons, Ltd.

Developmental toxicity interactions of salicylic acid and radiofrequency radiation or 2-methoxyethanol in rats.

Radiofrequency (RF) radiation is used in a variety of workplaces where workers are concurrently exposed to chemicals. Combined exposure to RF radiation (10 MHz) and the industrial solvent, 2-methoxyethanol (2ME), produces enhanced teratogenicity in rats. The purpose of the present research was to determine if the synergistic effects noted for RF radiation and 2ME are generalizable to other chemicals. Since salicylic acid (SA) is widely used as an analgesic and is teratogenic in animals, SA was selected to address generalizability. Based on the literature and our pilot studies, 0, 250, or 350 mg/kg SA were administered by gavage on gestation Day 9 or 13 to rats. Concurrently rats given SA on Day 9 were exposed to RF radiation sufficient to maintain colonic temperature at 41 degrees C for 60 min (or sham). Those given SA on Day 13 were also given 0 or 100 mg/kg 2ME (gavage). Dams were sacrificed on gestation Day 20, and the fetuses were examined for external malformations. The data provide no evidence of synergistic interactions between RF radiation and salicylic acid (resorptions and malformations). Limited evidence of antagonism was observed between 2ME and salicylic acid (fetal weights). This investigation highlights the importance of additional research on interactions in developmental toxicology, and emphasizes the need to consider combined exposure effects when developing both physical agent and chemical agent exposure guidelines and intervention strategies.

Developmental Toxicology Assessment of 1-Octanol, 1-Nonanol, and 1-Decanol Administered by Inhalation to Rats

As part of a large study evaluating the developmental toxicology of industrial alcohols administered by inhalation, groups of approximately 15 pregnant female Sprague-Dawley rats were exposed for 7 h/day on gestation days 1-19 (sperm = 0) to one of three long-chain alcohols at the maximum concentrations that could be generated as a vapor. These concentrations were 400 mg/m3 1-octanol, 150 mg/m3 1-nonanol, and 100 mg/m3 1-decanol. Dams were weighed daily for the first week of exposure, and weekly thereafter. On gestation day 20, rats were sacrificed. Fetuses were serially removed, blotted dry, examined for external malformations, sexed, weighed, placed in appropriate fixatives, and subsequently examined for visceral or skeletal abnormalities. No treatment-related effects were observed in pregnant females, frequency of resorptions, fetal weights, or skeletal/visceral malformations. Thus, long-chain alcohols at these vapor concentrations appear not to be toxic as evidenced by these fetal and maternal parameters.

Selecting exposure parameters in developmental neurotoxicity assessments

Numerous factors must be considered in selecting exposure parameters for developmental neurotoxicity investigations. Whether employing a single dose during pregnancy, or continuous exposure from prepregnancy through early postnatal developmental periods, the following primary factors should be addressed: 1) Purpose of the study; 2) pharmacokinetics/pharmacodynamics; 3) biotransformation; 4) genotypic variables; 5) limiting factors, including the availability of test compounds for evaluation; and, 6) several general, miscellaneous factors. Whether a single, large dose of an exogenous agent is more toxic to the developing nervous system than a series of smaller doses depends upon the interaction of the physicochemical, pharmacokinetic, and pharmacodynamic properties of the agent with the genotypic features of the test organism.