Ninth Day Of Gestation Research Articles

Sertraline associated with gold nanoparticles reduce cellular toxicity and induce sex-specific responses in behavior and neuroinflammation biomarkers in a mouse model of anxiety

This study aimed to evaluate the effects of sertraline associated with gold nanoparticles (AuNPs) in vitro cell viability and in vivo behavior and inflammatory biomarkers in a mouse model of anxiety. Sertraline associated with AuNPs were synthesized and characterized. For the in vitro study, NIH3T3 and HT-22 cells were treated with different doses of sertraline, AuNPs, and sertraline + AuNPs and their viability was evaluated using the MTT assay. For the in vivo study, pregnant Swiss mice were administered a single dose of lipopolysaccharide (LPS) on the ninth day of gestation. The female and male offspring were divided into five treatment groups on PND 60 and administered chronic treatment for 28 days. The animals were subjected to behavioral testing and were subsequently euthanized. Their brains were collected and analyzed for inflammatory biomarkers. Sertraline associated with AuNPs exhibited significant changes in surface characteristics and increased diameters. Different doses of sertraline + AuNPs showed higher cell viability in NIH3T3 and HT-22 cells compared with sertraline alone. The offspring of LPS-treated dams exhibited anxiety-like behavior and neuroinflammatory biomarker changes during adulthood, which were ameliorated via sertraline + AuNPs treatment. The treatment response was sex-dependent and brain region–specific. These results suggest that AuNPs, which demonstrate potential to bind to other molecules, low toxicity, and reduced inflammation, can be synergistically used with sertraline to improve drug efficacy and safety by decreasing neuroinflammation and sertraline toxicity.

Effect of ethanol consumption during pregnancy and lactation on bone histomorphometry and invitro osteogenic differentiation of bone marrow mesenchymal stem cells in maternal rats.

This study aimed to evaluate the effect of maternal ethanol consumption during gestation and lactation on bone mass and osteogenic differentiation of mesenchymal stem cells of the bone marrow (BMMSCs) in rats. Thirteen adult Wistar rats were used. The rats were mated, and after confirmation of gestation, (day 0) they were distributed in two groups: the control group and the ethanol-treated group. From the ninth day of gestation, the rats of the ethanol and control groups were administered 40% alcoholic solution (4g ethanol/kg) and distilled water, respectively, daily via gavage until the thirtieth day of lactation. The BMMSCs were extracted from the right femurs and tibiae and cultured using an osteogenic medium for 7, 14, and 21 days. The conversion of MTT to formazan crystals, alkaline phosphatase activity, and percentages of cells per field were analyzed. The number of mineralized nodules per field was examined, and quantification of the gene transcripts for osteopontin, osteocalcin, and BMP-2 was evaluated on day 21 by real-time RT-PCR. Morphometric evaluations of the percentage of trabecular bone and cortical thickness in the left femur and tibia were performed. The means were compared by the Student's t-test, and the differences were considered significant if p<0.05. The BMMSCs of the rats that consumed ethanol during gestation and lactation, when subjected to osteogenic differentiation invitro, demonstrated higher conversion of MTT to formazan, higher alkaline phosphatase activity, a higher percentage of cells per field, higher expression of BMP-2, and higher synthesis of mineralized nodules when compared to those of control rat cells. However, there was no significant difference in the percentage of trabecular bone or cortical thickness between both groups. Hence, the consumption of ethanol during pregnancy and lactation did not alter the trabecular and cortical bone tissues of the femur and tibia compared with that of pregnant and lactating control rats that did not consume alcohol, despite BMMSCs showing higher osteogenic differentiation under invitro conditions.

P.1.e.004 Sex-hormone fluctuation triggers subclinical depressive symptoms and affects immune cell numbers in peripheral blood in healthy women

The aim of the present study was to determine the influence of thyroid hormones on the anxiety of male Wistar rats. Dysthyroidism was induced by adding 20 mg of methimazole (100 ml) to their drinking water or by adding 0.3 mg of l-thyroxine (100 ml) to their drinking water from the ninth day of gestation. After weaning, the drugs were administered to young rats until the end of the experiment. Anxious behavior was measured using the elevated plus maze and social interaction tests when the animals were 85 days old. Chronic methimazole administration produced a significant anxiolytic pattern in both tests. In the plus maze test, the methimazole-treated animals entered and remained more time in the open arms than the control animals. In the social interaction test, they spent more time in bodily contact, and did this more frequently than those in the control group did. Results from this experiment suggest that chronic thyroid deficiency produces an anxiolytic-like effect in both tests.

Experimental hypothyroidism during pregnancy affects nociception and locomotor performance of offspring in rats

Thyroid hormones (THs) play a crucial role in the development of several organic systems. An adequate support of maternal THs may be required to ensure a normal nociceptive function of offspring into adulthood. We investigated the impact of experimental gestational hypothyroidism (EGH) on nociceptive threshold and motor performance in the offspring at different post-natal days (PND) in both male and female rats. EGH was induced by the administration of 0.02% methimazole (MMI) in the drinking water from the ninth day of gestation until birth. The offspring from MMI-treated dams (OMTDs) or from water-treated dams (OWTDs) were assessed for thermal and mechanical nociception using the tail-flick test and von Frey filaments, respectively. Both rota-rod and grip strength were used to assess motor function. OMTD had reduced thermal (p<0.05) but not mechanical threshold at all studied ages (60 and 120 PND). Sixty-day-old OMTD presented reduced latency to the tail-flick test (p=0.01). Grip strength in 120-day-old OMTD was reduced (p<0.01). However, only male OMTD presented a lower locomotor performance on the rota-rod test when analysed on the 60th PND (p<0.01). EGH promotes hypersensitivity to noxious thermal but not mechanical stimulus. Moreover, motor force is similarly reduced in male and female OMTDs, whereas motor performance is reduced only in mature male OMTD, suggesting the presence of a protective factor in females.

Nonexploratory movement and behavioral alterations in a thalidomide or valproic acid-induced autism model rat

Autism is a behaviorally characterized disorder with impairments in social interactions, as well as stereotyped, repetitive patterns of behaviors and interests. Exposure of rat fetuses to thalidomide (THAL) or valproic acid (VPA) on the ninth day of gestation has been reported as a useful model for human autism. We have shown that early serotonergic neural development is disrupted in these rats. In the current study, we used a radial maze and open field experimental paradigm to investigate whether these rats present behavioral and/or learning aberrations. THAL (500mg/kg), VPA (800mg/kg), or vehicle was administered orally to E9 pregnant rats at 7-10 weeks of age. Although the mean number of correct and incorrect arm choices in the initial eight arm choices did not differ between control and teratogen-exposed groups, achievement of learning (seven or eight consecutive correct choices for 3 consecutive days for individual rats) seemed to be impaired in teratogen-exposed groups. Interestingly, average time to explore the maze task was shorter in the teratogen-exposed groups, indicating that correct choice might be due to mere coincidence (i.e., nonexploratory movement). Unexpectedly, no significant differences were observed in social interaction in these rats. These results indicate that prenatal exposure to THAL and VPA might alter behavior in a manner that is, in part, consistent with human autism.

Pregnancy outcome in ethanol-treated mice with folic acid supplementation in saccharose

Maternal folic acid deficiency is the most important metabolic factor in the etiology of neural tube defects (NTD) and is reduced by ethanol, which is extensively consumed by young women. The objective of the study was to determine whether folic acid supplementation in dietary saccharose is efficient in the prevention NTD induced by ethanol in fetuses of Swiss mice. Pregnant mice were divided into four groups of six animals each: control (C), ethanol (E), deficient-supplemented (DS), and deficient-supplemented + ethanol (DSE). Groups C and E received commercial mouse chow (containing 3 mg/kg folic acid) throughout the experiment, while groups DS and DSE received a folic acid-free diet with the addition of saccharose supplemented with folic acid (2 mg/kg folic acid) in water. Group E and DSE animals received ethanol (4 g/kg) administered intraperitoneally from the seventh to the ninth gestational day (gd) and were euthanized on the 18th gd, while groups C and DS received saline. Congenital anomalies were observed in groups E and DSE. The fetal weight and length of the animals in group E were lower than in groups C and DS and, in group DSE, were lower than in groups C and DS. The placental diameter of group E was smaller than that of group C, and the placental weight of group C animals was lower than that of groups E, DSE, and DS. The study demonstrated that dietary supplementation with folate in saccharose is an accessible means of consumption that could be further diffused but in an increased dose than recommended to reduce the teratogenic effects of ethanol.

Sonic hedgehog and bone morphogenetic protein 4 expressions in the hindgut region of murine embryo with anorectal malformations

Purpose The aim of this study was to determine the possible role of the retinoid-mediated signaling pathway in the pathogenesis of anorectal malformations (ARM). The authors investigated whether all-trans retinoic acid (ATRA) affects the expression pattern of Sonic hedgehog (Shh) and Bone morphogenetic protein 4 (BMP4), which play important roles in anorectal morphogenesis in vertebrates. Methods Pregnant ICR strain mice were fed 100 mg/kg of ATRA on the ninth gestational day (E9). Embryos with or without administration of ATRA were obtained from the uteri between E12 and E16 and were fixed immediately in a 4% paraformaldehyde solution. Frozen sections were evaluated for concentric layers around the endodermal epithelium by H&E and immunohistochemistry using antibodies created specifically to act against Shh and BMP4. Results More than 95% of the embryos administered ATRA had ARM; rectoprostatic urethral fistula, rectocloacal fistula, and short tail were the most frequent anomalies in the mouse embryos. On E14, normal mouse embryos had normal rectum and anus in which the epithelium of the anorectum was positive for Shh, and the mesenchyme was positive for BMP4. In the ARM embryos, however, the epithelium of the anorectum was negative for Shh, and the mesenchyme was also negative for BMP4. Conclusions In normal hindgut development, Shh from the epithelium induces BMP4 expression in the mesenchyme, which differentiates into the lamina propria and the submucosa. In ARM embryos, expressions of Shh and BMP4 could not be found in those regions of the hindgut. Therefore, these findings indicate that Shh and BMP4, which appear to play a crucial role in organogenesis of the hindgut, were disturbed in the cell signaling pathway between the epithelium and the mesenchyme layers.

Laternal nicotine exposure increases nicotine preference in periadolescent male but not female C57B1/6J mice.

Maternal cigarette smoking is a risk factor for adolescent smoking. One possible explanation for increased smoking by human adolescents after maternal nicotine exposure is that exposure increases nicotine preference. However, it is difficult to separate the biological and social causes of smoking behavior in humans. This experiment examined the relationship between maternal nicotine exposure and nicotine preference in periadolescent offspring using a mouse model of oral nicotine consumption. Pregnant females were provided saccharin-flavored water containing 50 microg/ml nicotine (n = 4) or no nicotine (n = 5) from the ninth day of gestation through weaning on postnatal day (PD) 21. Offspring from these females were tested for nicotine preference during periadolescence (PDs 35-42) by providing access to both saccharin-only and nicotine solutions (50 microg/ml) 24 hr a day in the home cage in a two-bottle choice test. Male mice exposed maternally to nicotine (n = 9) exhibited an increased nicotine preference in adolescence compared to non-nicotine exposed controls (n = 12). Maternal nicotine exposure did not alter nicotine preference by periadolescent female mice. Nicotine consumption was confirmed by serum cotinine measurement. These data are consistent with human epidemiological reports that maternal nicotine exposure is associated with increased risk of cigarette smoking. Differential outcomes for males and females suggest that different processes underlie sex differences in nicotine consumption following maternal nicotine exposure.

Effects of chronic dysthyroidism on activity and exploration

The aim of the present study was to determine the influence of thyroid function on the activity and exploratory behaviour of male Wistar rats. Dysthyroidism was induced by adding drugs to their drinking water from the ninth day of gestation. This method is not as stressful as daily thyroxine injections or thyroidectomy, and therefore did not affect the analysed behavioural patterns. After weaning, the drugs were administered to the young rats until the end of the experiment. Activity and exploration were measured using the Boissier test, a light–darkness test and an open-field test when they were 77 days old. In order to verify that the animals' motor capacity had not been impaired, a psychomotor battery was used. Chronic hyperthyroidism produced a significant increase in activity, but did not affect exploration. On the other hand, hypothyroidism did not affect activity, but did increase exploration. This increase in exploration was observed in activity-independent behavioural parameters, such as head dipping and glancing.

Effects of dysthyroidism in plus maze and social interaction tests

The aim of the present study was to determine the influence of thyroid hormones on the anxiety of male Wistar rats. Dysthyroidism was induced by adding 20 mg of methimazole (100 ml) to their drinking water or by adding 0.3 mg of l-thyroxine (100 ml) to their drinking water from the ninth day of gestation. After weaning, the drugs were administered to young rats until the end of the experiment. Anxious behavior was measured using the elevated plus maze and social interaction tests when the animals were 85 days old. Chronic methimazole administration produced a significant anxiolytic pattern in both tests. In the plus maze test, the methimazole-treated animals entered and remained more time in the open arms than the control animals. In the social interaction test, they spent more time in bodily contact, and did this more frequently than those in the control group did. Results from this experiment suggest that chronic thyroid deficiency produces an anxiolytic-like effect in both tests.

Development of the pelvic floor muscles of murine embryos with anorectal malformations

Background/Purpose: Recent biological studies have elucidated the molecular mechanism of muscle development, in which various regulatory molecules play key roles during embryogenesis. To determine possible myogenic abnormalities in anorectal malformations (ARM), the authors investigated the pelvic muscle development in murine embryos affected with ARM. Methods: ARM embryos were induced by all-trans retinoic acid (ATRA) on the ninth gestational day (E9.0). Embryonal specimens were obtained from the uteri between E10.5 and E16.0, and the frozen sections were prepared for immunohistochemistry using antibodies specific for MyoD, myogenin, and PGP9.5 molecules. Results: In ARM embryos, the neural tube was irregularly branched and formed an anomalous mass in the sacral region. Embryonal caudal somites differentiated into myogenic cells to form proper myotubes in the pelvis corresponding to the developmental stages between E12.5 and E15.0 both in affected embryos and the controls. Conclusions: In ARM embryos, an impaired anatomic framework of the pelvis was caused by neural maldevelopment, whereas muscle development proceeded physiologically. These results support the hypothesis that pelvic floor muscles may function in ARM children, in whom neural abnormalities such as meningomyelocele or tethered spinal cord have been ruled out, if the surgical correction is appropriately completed. J Pediatr Surg 37:224-227. Copyright © 2002 by W.B. Saunders Company.

Impaired distribution of retinoic acid receptors in the hindgut-tailgut region of murine embryos with anorectal malformations

Background/Purpose: Retinoid-mediated signal transduction plays a crucial role in the organogenesis of various organs. To investigate the pathogenesis of anorectal malformations (ARM), the authors studied the distribution pattern of retinoic acid receptors (RARs) in ARM murine embryos induced by overdose of all-trans retinoic acid (ATRA). Methods: Pregnant mice were gavage-fed 100 mg/kg of ATRA on the ninth gestational day (E9.0). Embryos were obtained between E11.0 and E14.0 and were fixed immediately in a 4% paraformaldehyde solution. Frozen sections were prepared for immunohistochemistry using antibodies specifically raised against RAR-alpha, RAR-beta, and RAR-gamma. Results: Over 98% of the embryos administered ATRA had ARM; rectoprostatic urethral and rectocloacal fistulas were the most frequent anomalies. The immunoreactivity of RAR-alpha was found equally in the epithelium of hindgut-tailgut in normal embryos on E11.5. However, it was absent in the hindgut in the treated embryos. The immunoreactivities of RAR-beta and RAR-gamma showed no difference in the distal hindgut. Conclusions: Impaired distribution of RAR-alpha in the hindgut-tailgut on E11.5 resulted in the incomplete partitioning of the cloaca and the rectourethral or rectocloacal fistula on E14.0. These results suggest that overdose of ATRA affects the distal hindgut development by directly disrupting the retinoid-mediated signalling pathway. J Pediatr Surg 36:377-380. Copyright © 2001 by W.B. Saunders Company.

Development of anorectal malformations using etretinate

Purpose: To investigate the pathogenesis of anorectal malformations (ARM), the authors studied cell proliferation and programmed cell death (apoptosis) patterns in murine embryos that develop ARM as a result of administering an overdose of etretinate, a long-acting vitamin A analogue (retinoid). Methods: Pregnant mice were fed 60 mg/kg of etretinate on the ninth gestational day (E9). Embryos were obtained between E9.5 and E13, and prepared for histological study. Cell proliferation was examined using proliferative cell-specific nuclear antigen (PCNA) expression. Apoptosis was identified by detecting in situ DNA fragmentation using the TdT-mediated dUTP-digoxigenin nick end-labeling (TUNEL) method. Results: Over 95% of etretinate-treated embryos had ARM including rectoprostatic urethral or rectocloacal fistula. In the histological study, ARM embryos showed defective cell proliferation in the cloacal membrane and excessive apoptosis in the dorsocaudal region on E11, which resulted in a lack of apoptosis in the anal orifice and a short tail on E12, respectively. Cells forming the urorectal septum showed the same pattern of cell proliferation and apoptosis both in ARM embryos and the controls. These results suggest that impairments of embryonal cellular dynamics in the cloacal membrane and dorsocaudal region induce some types of ARM.

Retinoic Acid Regulates Thymosin β Levels in Rat Neuroblastoma Cells

A small acidic polypeptide, termed thymosin beta 10, has been identified and is present in the nervous system of the rat by the ninth day of gestation. Thymosin beta 10 levels rise during the remaining days of life in utero, and then decline to nearly undetectable values between the second and fourth week post partum. The present study investigates the possible developmental signals and mechanisms that might regulate the expression of thymosin beta 10 during neuroembryogenesis. Many cell lines derived from tumors of the central nervous system express thymosin beta 10, as well as its homologue gene product, thymosin beta 4. Because some of these cell lines respond to exogenously applied agents by increasing their apparent state of differentiation, we have determined whether thymosin beta 10 levels are coordinately modulated. In several neuroblastomas, including the B103 and B104 lines, retinoic acid elicits a time- and dose-dependent increase in the content of thymosin beta 10, but not that of thymosin beta 4. The increase in thymosin beta 10 polypeptide is associated with a marked increase in the specific mRNA encoding this molecule. The mRNA for thymosin beta 4 is unaffected by retinoic acid. This is in contrast with the situation in vivo, where the expression of both genes decreases after birth. Other agents that influence the morphology of B104 cells, such as phorbol esters and dibutyryl cyclic AMP, have no influence on beta-thymosin levels. A range of steroids, which like retinoids act upon nuclear receptors, was also inactive. The stimulatory action of retinoic acid is detectable within 4 h, and thymosin beta 10 peptide levels continue to rise for at least 4 days. The influence of the isoprenoid is fully reversible and exhibits structural specificity. We believe that this culture system is mimicking the early rising phase of thymosin beta 10 levels in brain and that endogenous retinoids may be candidate physiological regulators of this gene.

Differentiation, Maturation, and Proliferation of Macrophages in the Mouse Yolk Sac: A Light-Microscopic, Enzyme-Cytochemical, Immunohistochemical, and Ultrastructural Study

Primitive macrophages first appear in the blood islands of the mouse yolk sac on the ninth day of gestation. After the tenth day of fetal life, these cells differentiate into fetal macrophages and become mature, with the development of intracellular organelles. They appear in the mesenchymal layer and further immigrate into the extraembryonic coelom. The fetal macrophages do not show any cytochemical peroxidase or 5'-nucleotidase activity, and they possess a marked proliferative capacity. Promonocytes or monocytes that have an incomplete ultrastructure emerge in the blood islands of the yolk sac a day after the occurrence of the fetal macrophages. These events suggest that fetal macrophages differentiate from primitive macrophages before the development of promonocytes or monocytes in the mouse yolk sac; they actively proliferate and are colonized into the embryonic tissues. These results also indicate that the ontogeny of the monocyte/macrophage is different in the early embryo compared with its later developmental stages.

A possible role for protein dissociation in the functioning of embryonic haemoglobins.

ABSTRACT During early mammalian development the changing demands for oxygen in embryonic tissues are met, in part, by the synthesis of a series of embryonic haemoglobins. At the earliest stages of development three embryonic haemoglobins are synthesized in both humans and mice (Melderis, Steinheider &amp; Ostertag, 1974; Shimizu &amp; Watanabe, 1978; Brotherton, Chui, Gauldie &amp; Patterson, 1979; Purdie, Wells &amp; Brittain, 1983; Brittain &amp; Wells, 1983). The proportions of each haemoglobin present in the mouse red blood cells vary significantly from the ninth day of gestation until parturition (Purdie et al. 1983). Although studies have been made on this developmental system of gene switching and haemoglobin composition (Brotherton et al. 1979) very few studies have been made on the functional characteristics of these embryonic haemoglobins, mainly because of the limited amount of material available (Bauer et al. 1975 ; Brittain &amp; Wells, 1983 ; Purdie et al. 1983). The oxygen binding curves for whole blood from the earliest embryos show anomalous binding patterns (Wells &amp; Brittain, 1981; Purdie et al. 1983; Brittain &amp; Wells, 1983). The high oxygen affinity component present in the red blood cells of early embryonic mice has been correlated with the presence of embryonic haemoglobin El, which has a subunit structure χ2ϵ2 (Melderis et al. 1974). This haemoglobin species El shows very low cooperativity in both its equilibrium and kinetic functions (Purdie et al. 1983; Brittain, Sutherland &amp; Greenwood, 1986). Recent investigations have indicated that the functioning of this haemoglobin is not related to any unusual redox balance within the embryonic red blood cell (Brittain &amp; Tottle, 1986) and thus the occurrence of an essentially non-cooperative haemoglobin with a tetrameric subunit structure has posed something of a paradox. This study presents data on the dimerization of mouse embryonic haemoglobin El over a range of conditions and, together with numerical simulations of oxygen binding curves, illustrates how, within the early embryonic red blood cell, high oxygen affinity and sensitivity to pH may be obtained by protein dimerization.

Pattern formation of the otic placode and morphogenesis of the otocyst

The early embryonic development of the inner ear anlage, from the otic placode stage to formation of the otocyst, was documented in CBA/CBA mice by scanning electron microscopy. The otic placode is identified at the eight- to ten-somite stage, as revealed by the surface morphology of the developing ectoderm. The cells in the otic depression are considerably smaller than those of the adjacent ectodermal surface. Rapid invagination of the otic anlage occurs during the ninth gestational day (approximately eight to 20 somites). In most specimens from the tenth gestational day, the otic vesicle has closed toward the ectodermal surface. The surface of the otocyst on the 13th gestational day shows considerable specialization, with regional differences of the surface structure.

Anesthetics as teratogens: nitrous oxide is fetotoxic, xenon is not.

Exposure of pregnant rats to the anesthetic nitrous oxide on the ninth day of gestation causes fetal resorption, skeletal anomalies, and macroscopic lesions including encephalocele, anophthalmia, microphthalmia, and gastroschisis. The inert gas xenon, which has anesthetic properties similar to those of nitrous oxide, does not cause teratogenic effects under the same experimental conditions.

Effect of Increased Maternal Hemoglobin Oxygen Affinity on Fetal Growth in the Rat

A disparity between fetal and maternal hemoglobin oxygen affinities (i.e., P50fetal<P50meternal) is believed to be important in facilitating oxygen transfer from maternal to fetal circulation. However, human females with high oxygen affinity mutant hemoglobins (P50meternal<P50fetal) have successfully borne children, calling into question the importance of the usual maternal/fetal P50 gradient. We have investigated the effect of artificially increased maternal hemoglobin oxygen affinity on fetal growth in the rat. Pregnant rats were exchange transfused with homologous blood on the ninth day of gestation, the experimental group receiving donor blood having P50 ≃ 15.0 mm Hg achieved by prior incubation with sodium cyanate. This changed mean maternal P50 from 41.1 to 24.6 mm Hg; the normal prenatal rat has P50 = 24.7 mm Hg due to low erythrocyte 2,3-DPG content. Parameters reflecting the adequacy of fetal oxygenation were examined on the 20th and 21st days of gestation and at term (22 days). Fetuses from the experimental group were significantly smaller on the 21st day (p < 0.001) and at term (p < 0.01), and this was accompanied by placental hypertrophy. There was no significant difference in fetal weight on the 20th day of gestation unless a second exchange transfusion was performed to further lower maternal P50. There was a trend towards erythrocytosis in the experimental group fetuses. We conclude that a narrowing of the P50 difference between mother and fetus has adverse effects on fetal wellbeing in the rat.

MALFORMATIONS OF THE CENTRAL NERVOUS SYSTEM INDUCED BY NEUROTROPIC DRUGS IN MOUSE EMBRYOS.

Out of a sample of fifteen neurotropic drugs consisting of seven antidepressants and anti-psychotics, two antianxiety drugs, one anticonvulsant, three opiates and two synthetic analgesics, twelve were found to be teratogenic for mouse embryos, causing malformations of the central nervous system. After single injections of the teratogenic dose administered at the very beginning of the ninth day of gestation, four days later, i.e. in 13-day-old embryos, the induced defects appeared to make up a recurring syndrome of malformations which consists of several abnormalities present in various frequencies either individually or in combination in the same embryos. These malformations are: exencephaly, craniorachischisis, cervical and thoraco-lumbar myeloschisis, hydrocephalic dilatation of the fourth brain ventricle, Z-shaped kinking of the spinal cord and lumbar hydromyelia. In addition, after administration of some of the drugs, branchyury or anury with or without lumbar myeloaplasia were recorded. In general the results reported here seem to suggest that because of their possible affinity neurotropic drugs are potentially teratogenic for the embryonic central nervous system if applied at the time of the neural tube closure although it is known that there are drugs in this group which do not cause any malformations of the central nervous system and that many non-neurotropic agents do cause such malformations. Secondly, the results seem to suggest also that the position of the malformations along the cerebro-spinal axis may be depending to some extent on the pharmacological properties of the drugs tested. These conjectures are treated here as entirely provisional pending further investigations.