Brain changes in rats induced by prenatal injection of methylazoxymethanol

A Possible Link Between Pyriproxyfen and Microcephaly

The Zika virus has been the primary suspect in the large increase in incidence of microcephaly in 2015-6 in Brazil. While evidence for Zika being the cause of some of the cases is strong, its role as the primary cause of the large number of cases in Brazil has not been confirmed. Recently, the disparity between the incidences in different geographic locations has led to questions about the virus's role. Here we consider the alternative possibility that the use of the insecticide pyriproxyfen for control of mosquito populations in Brazilian drinking water is the primary cause. Pyriproxifen is a juvenile hormone analog which has been shown to correspond in mammals to a number of fat soluble regulatory molecules including retinoic acid, a metabolite of vitamin A, with which it has cross-reactivity and whose application during development has been shown to cause microcephaly. Methoprene, another juvenile hormone analog that was approved as an insecticide based upon tests performed in the 1970s, has metabolites that bind to the mammalian retinoid X receptor, and has been shown to cause developmental disorders in mammals. Isotretinoin is another example of a retinoid causing microcephaly in human babies via maternal exposure and activation of the retinoid X receptor in developing fetuses. Moreover, tests of pyriproxyfen by the manufacturer, Sumitomo, widely quoted as giving no evidence for developmental toxicity, actually found some evidence for such an effect, including low brain mass and arhinencephaly-incomplete formation of the anterior cerebral hemispheres-in exposed rat pups. Finally, the pyriproxyfen use in Brazil is unprecedented-it has never before been applied to a water supply on such a scale. Claims that it is not being used in Recife, the epicenter of microcephaly cases, do not distinguish the metropolitan area of Recife, where it is widely used, and the municipality, and have not been adequately confirmed. Given this combination of information about molecular mechanisms and toxicological evidence, we strongly recommend that the use of pyriproxyfen in Brazil be suspended until the potential causal link to microcephaly is investigated further.

Expanding the test set: Chemicals with potential to disrupt mammalian brain development

High-throughput test methods including molecular, cellular, and alternative species-based assays that examine critical events of normal brain development are being developed for detection of developmental neurotoxicants. As new assays are developed, a "training set" of chemicals is used to evaluate the relevance of individual assays for specific endpoints. Different training sets are necessary for each assay that would comprise a developmental neurotoxicity test battery. In contrast, evaluation of the predictive ability of a comprehensive test battery requires a set of chemicals that have been shown to alter brain development after in vivo exposure ("test set"). Because only a small number of substances have been well documented to alter human neurodevelopment, we have proposed an expanded test set that includes chemicals demonstrated to adversely affect neurodevelopment in animals. To compile a list of potential developmental neurotoxicants, a literature review of compounds that have been examined for effects on the developing nervous system was conducted. The search was limited to mammalian studies published in the peer-reviewed literature and regulatory studies submitted to the U.S. EPA. The definition of developmental neurotoxicity encompassed changes in behavior, brain morphology, and neurochemistry after gestational or lactational exposure. Reports that indicated developmental neurotoxicity was observed only at doses that resulted in significant maternal toxicity or were lethal to the fetus or offspring were not considered. As a basic indication of reproducibility, we only included a chemical if data on its developmental neurotoxicity were available from more than one laboratory (defined as studies originating from laboratories with a different senior investigator). Evidence from human studies was included when available. Approximately 100 developmental neurotoxicity test set chemicals were identified, with 22% having evidence in humans.

Animal models

Epilepsy accounts for a significant portion of the dis-ease burden worldwide. Research in this field is fundamental and mandatory. Animal models have played, and still play, a substantial role in understanding the patho-physiology and treatment of human epilepsies. A large number and variety of approaches are available, and they have been applied to many animals. In this chapter the in vitro and in vivo animal models are discussed,with major emphasis on the in vivo studies. Models have used phylogenetically different animals - from worms to monkeys. Our attention has been dedicated mainly to rodents.In clinical practice, developmental aspects of epilepsy often differ from those in adults. Animal models have often helped to clarify these differences. In this chapter, developmental aspects have been emphasized.Electrical stimulation and chemical-induced models of seizures have been described first, as they represent the oldest and most common models. Among these models, kindling raised great interest, especially for the study of the epileptogenesis. Acquired focal models mimic seizures and occasionally epilepsies secondary to abnormal cortical development, hypoxia, trauma, and hemorrhage.Better knowledge of epileptic syndromes will help to create new animal models. To date, absence epilepsy is one of the most common and (often) benign forms of epilepsy. There are several models, including acute pharmacological models (PTZ, penicillin, THIP, GBL) and chronic models (GAERS, WAG/Rij). Although atypical absence seizures are less benign, thus needing more investigation, only two models are so far available (AY-9944,MAM-AY). Infantile spasms are an early childhood encephalopathy that is usually associated with a poor out-come. The investigation of this syndrome in animal models is recent and fascinating. Different approaches have been used including genetic (Down syndrome,ARX mutation) and acquired (multiple hit, TTX, CRH,betamethasone-NMDA) models.An entire section has been dedicated to genetic models, from the older models obtained with spontaneous mutations (GEPRs) to the new engineered knockout, knocking, and transgenic models. Some of these models have been created based on recently recognized patho-genesis such as benign familial neonatal epilepsy, early infantile encephalopathy with suppression bursts, severe myoclonic epilepsy of infancy, the tuberous sclerosis model, and the progressive myoclonic epilepsy. The contribution of animal models to epilepsy re-search is unquestionable. The development of further strategies is necessary to find novel strategies to cure epileptic patients, and optimistically to allow scientists first and clinicians subsequently to prevent epilepsy and its consequences.

Undertaking positive control studies as part of developmental neurotoxicity testing: a report from the ILSI Research Foundation/Risk Science Institute expert working group on neurodevelopmental endpoints

Developmental neurotoxicity testing involves functional and neurohistological assessments in offspring during and following maternal and/or neonatal exposure. Data from positive control studies are an integral component in developmental neurotoxicity risk assessments. Positive control data are crucial for evaluating a laboratory's capability to detect chemical-induced changes in measured endpoints. Positive control data are also valuable in a weight-of-evidence approach to help determine the biological significance of results and provide confidence in negative results from developmental neurotoxicity (DNT) studies. This review is a practical guide for the selection and use of positive control agents in developmental neurotoxicology. The advantages and disadvantages of various positive control agents are discussed for the endpoints in developmental neurotoxicity studies. Design issues specific to positive control studies in developmental neurotoxicity are considered and recommendations on how to interpret and report positive control data are made. Positive control studies should be conducted as an integral component of the incorporation and use of developmental neurotoxicity testing methods in laboratories that generate data used in risk decisions.

Effects of prenatal methylazoxymethanol acetate (MAM) treatment in rats on water maze performance

Prenatal methylazoxymethanol acetate (MAM) treatment has been shown to induce morphological abnormalities in cortical areas of the offspring. Based on the neuroanatomical and behavioural abnormalities, this treatment has been suggested as a useful animal model for schizophrenia. In a previous study (Jongen-Relo AL, Leng A, Luber M, Pothuizen HHJ, Weber L, Feldon J. The prenatal methylazoxymethanol acetate treatment: a neurodevelopmental animal model for schizophrenia? Behav Brain Res 2004;149:159-81) we have studied MAM-treated animals in a series of behavioural tests related to schizophrenia, such as latent inhibition and pre-pulse inhibition of the acoustic startle response to establish the validity of prenatal MAM treatment (20mg/kg i.p. on gestational days 9-15; MAM 9-MAM 15). We found that, apart from a marginal effect of increased activity in the open field, the MAM treatment on gestational day 15 was behaviourally ineffective. Here, we extended our previous study to a water maze experiment conducted in the same batch of animals as presented previously (MAM 12-MAM 15). MAM-treated animals showed similar water maze performance compared with control animals during the acquisition phase and the probe tests. However, during the reversal phase, MAM 15 animals showed impaired acquisition of the new platform location. This might indicate some cognitive deficits in MAM 15 animals in terms of working memory or behavioural flexibility. However, in combination with the lack of behavioural abnormalities of MAM 12-MAM 15 animals in several other tests related to schizophrenia in the previously reported study, the use of MAM treatment (MAM 12-MAM 15) as a valid model for schizophrenia still remains debatable.

The prenatal methylazoxymethanol acetate treatment: a neurodevelopmental animal model for schizophrenia?

The prenatal methylazoxymethanol acetate (MAM) treatment has been proposed as a suitable model for the neurodevelopmental aspects of schizophrenia since the morphological abnormalities it induces in the brain are subtle and in line with most reports of neuropathology in schizophrenic brains. However, the functional aspects of this treatment have not been investigated with behavioural paradigms that are relevant for the psychopathology of the symptoms of schizophrenia. In the present study, we investigated the validity of the prenatal MAM treatment as a developmental model for schizophrenia with a prepulse inhibition of the acoustic startle reflex, latent inhibition, locomotor activity, and cognition and emotionality with freezing in fear conditioning paradigms. We have conducted two studies: in Study I, MAM was injected from E09 to E12, and in Study II MAM was administered at later stages in the embryonic development, from E12 to E15. Morphologically, the prenatal MAM treatment induced mild to severe reduction in brain weights and in the entorhinal cortex, prefrontal cortex and striatum volumes, the severity of the effects depending on the timing of administration. However, despite the morphological abnormalities induced by the MAM treatments, no behavioural deficits were observed in the MAM-treated animals when compared to Controls in prepulse inhibition, latent inhibition with the two-way active avoidance, and in the freezing paradigms. Therefore, due to the consistent lack of treatment effect observed in the present investigation, we conclude that the prenatal MAM treatment has no validity as a behavioural model for schizophrenia.

Postnatal behavior in hatano high- and low-avoidance rats following prenatal exposure to low-dose methylazoxymethanol

The hypothesis that genetic factors influence behavioral effects was tested in rats exposed prenatally to methylazoxymethanol (MAM). We examined whether baseline behavior is an important factor influencing behavioral effects, and whether a behaviorally selected strain was useful for study of neurobehavioral teratology. Pregnant high- and low-avoidance animals (HAAs and LAAs) of the Hatano strain, selectively bred for high and low shuttlebox avoidance responses, respectively, were given an IP injection of a low dose of MAM (15 mg/kg) on day 14 of gestation. The offspring of these animals were subjected to behavioral tests for locomotor activity (running-wheel and open-field tests) and learning ability (Biel maze and shuttlebox avoidance tests). There were no significant effects of MAM on running-wheel activity or shuttlebox avoidance learning, whereas the number of errors in the Biel maze was increased in the MAM offspring of both strains. Interestingly, open-field activity of the MAM offspring was markedly decreased in LAAs but not in HAAs. Therefore, an additional experiment was performed to determine plasma levels of ACTH and corticosterone following open-field exposure. When compared to control offspring of the respective strains, plasma levels of ACTH and corticosterone were not altered by prenatal MAM treatment in LAAs. Instead, the MAM offspring in HAAs exhibited decreased ACTH levels in absence of behavioral alterations. These results demonstrated that prenatal exposure to low doses of MAM may alter postnatal behavior and endocrine response of the offspring, although to a differing degree in HAAs and LAAs. Our observations suggested that behaviorally selected strains are sensitive to neurobehavioral teratogens such as MAM.

FR discrimination training effects in SHR and microencephalic rats

Fixed-ratio (FR) discrimination learning in adult male spontaneously hypertensive rats (SHR), methylazoxymethanol-induced microencephalic Sprague-Dawley (MAM), and Sprague-Dawley control rats was examined. SHR and MAM rats had little problem learning incrementally more difficult FR discriminations (FR1 vs. FR16, FR4 vs. FR16, and FR8 vs. FR16) that resulted in parallel increases in errors in all animals, and displayed only modest learning deficits during a subsequent FR4 vs. FR16 position reversal. When training involved nonincremental changes in difficulty (FR8 vs. FR16, FR4 vs. FR16, FR8 vs. FR16, FR12 vs. FR16, and FR14 vs. FR16), SHR and MAM rats evidenced relatively large learning deficits during the initial FR8 vs. FR16 discrimination but had no difficulty with the last two discriminations. Furthermore, training selectively and significantly elevated hippocampal weight in MAM rats. These findings: a) question prior suggestions that MAM and SHR model separate human developmental disabilities; b) indicate that manifestation of learning deficits in even markedly brain-damaged organisms depends on initial task difficulty and can be overcome by experience; and c) are the first indicating that training-induced antagonism of prenatally induced hippocampal hypoplasia and its consequences is possible.

Selective in vitro blockade of neuroepithelial cells proliferation by methylazoxymethanol, a molecule capable of inducing long lasting functional impairments

In order to characterize the antiproliferative effect of methylazoxymethanol neuroepithelial cells derived from the rat striata primordia at embryonic day 14 have been exposed to graded doses of this compound. It was found that methylazoxymethanol application to striatal neuroblasts elicits a blockade of cell proliferation at a dose which does not interfere with cell survival. By using synchronized cells and short term exposures to this compound, we found that the antiproliferative effect of methylazoxymethanol is strikingly correlated to the number of cells actively dividing in culture, thus indicating that the cells targeted by methylazoxymethanol must be in an active mitotic phase. To test for the selectivity of action of Methylazoxymethanol for dividing neuroblasts either cultures composed of mature proliferating astrocytes or muscle cells have been subjected to the same treatment. It has been observed that astrocytes proliferation was not affected by the dose of methylazoxymethanol shown to be effective on neuroepithelial cells. Finally we demonstrated that methylazoxymethanol is able only transiently to interfere with smooth muscle cell division, further supporting its selectivity of action within the developing CNS.

The impaired long-term potentiation in the CA1 field of the hippocampus of cognitive deficient microencephalic rats is restored by D-serine

Rat embryos exposed on gestational day 15 to methyl-azoxymethanol acetate develop a microencephaly characterized primarily by a hypoplasia of the neocortex and CA fields of the hippocampus that in adulthood is associated with disturbances in learning. In brain slices prepared from microencephalic rats, we have examined the field excitatory postsynaptic potentials and population spike in the CA1 field of the hippocampus evoked by stimulation of the stratum radiatum. These parameters did not differ from those obtained in slices from control rats. High frequency stimulation of the stratum radiatum afferent fibres, which readily induced long-term potentiation of the field excitatory postsynaptic potentials and population spike in the CA1 field of the hippocampus of control rats, failed to induce long-term potentiation in that of microencephalic rats. High frequency stimulation of the perforant path readily elicited long-term potentiation in the dentate gyrus of both control and microencephalic rats. Picrotoxin had no apparent effect on field excitatory postsynaptic potentials and population spike in the CA1 field of the microencephalic rats, indicating that little GABAergic inhibition was present in slices from these rats. D-2-Amino-phosphonovalerate suppressed the field potentials in slices from microencephalic rats by more than 50%, suggesting that N-methyl-D-aspartate receptors contributed markedly to the synaptic responses evoked by single stimuli. D-Serine, but not picrotoxin, restored long-term potentiation in the CA1 field of the microencephalic rats. The D-serine effect was prevented by pretreating the slices with either 7-chloro-kynurenate or D-2-amino-phosphonovalerate. The failure to induce long-term potentiation, if also found in vivo, may be among the factors related to the learning deficits displayed by these rats.

The effects of pre-natal exposure to methylazoxymethanol acetate on microglia

The effects of exposure to a cytotoxic agent, methylazoxymethanol acetate (MAM Ac), on the distribution, density and quantitative morphology of microglia in the rat forebrain have been examined with the aid of a peroxidase-conjugated lectin derived from Griffonia simplicifolia. Following exposure to MAM Ac (25 mg/kg maternal body weight) on embryonic day 13 (E13), round microglia were concentrated around the areas of induced cell death at the outer margins of the ventricular germinal zone, particularly in the striatopallidal angle and dorsal thalamus. By E19, there were no detectable differences in microglia distribution between experimental and control animals. The increase in number of microglial cells in the neocortex and caudatoputamen on exposure to MAM Ac lasted for only 4 to 6 days. Subsequently, the number of microglia dropped below control values in both regions. The density of microglia in these areas was similar in control and experimental animals from 6 days after exposure. The proportion of microglia relative to all other cells was also similar at post-natal day 17 (P17) in both experimental and control animals. These results suggest that the distribution and final size of the microglial population is determined by the microenvironment and not by the extent of cell death which may have acted as the initial stimulus to microglial invasion.

Neuropharmacological study of aged MAM-treated rats

After evaluation of activity in an open field, norepinephrine (NE), serotonin (5HT), 5-hydroxyindolacetic acid (5HIAA), homovanillic acid (HVA), and choline acetyltransferase (CAT) were investigated in cortex of 26-month-old rats poisoned with methylazoxymethanol (MAM) as compared to control rats of the same age. NE and 5HT concentrations showed a marked increase, but levels were normal when expressed as total content, just as in MAM-exposed young adults. Concentrations of 5HIAA were also increased but to a lesser extent than 5 HT. Aged MAM rats did not show any modification of spontaneous activity although hyperactivity is characteristic of young adults exposed to MAM. Together with this behavioral observation, a significant decrease in total HVA content was measured. Because HVA levels seem correlated with activity in MAM-exposed rats, we speculate that the behavioral abnormality recovers in old age. Total CAT activity was also reduced. These results indicate that the neurochemical pattern of young adult MAM-poisoned rats is conserved in aged rats except for some changes in the dopaminergic and cholinergic systems.

Excitatory amino acid receptors in brains of rats with methylazoxymethanol-induced microencephaly

We used methylazoxymethanol-acetate (MAM), a potent alkylating agent, to produce microencephaly in offspring by injecting it into pregnant rats on day 15 of gestation. Binding activities of central excitatory amino acid receptors were examined in Triton-treated membranes prepared from brains of adult offspring with MAM-induced microencephaly (MAM rats). MAM rats exhibited approximately 40-50% reductions of the wet weights of the cerebral cortex, hippocampus and striatum compared to those in controls. In the cortex and hippocampus of MAM-rats, total bindings of [3H]glutamate (Glu) (which is sensitive to N-methyl-D-aspartate (NMDA) receptor), and strychnine-insensitive [3H]glycine (Gly) and (+)-5-[3H]methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imi ne (MK-801; a noncompetitive antagonist of NMDA receptor), were reduced to approximately 40% of those in controls. Similarly, in both regions of MAM rats, total bindings of [3H]kainate and DL-alpha-amino-3-[3H]hydroxy-5-methylisoxazole-4-propionic acid (an agonist of quisqualate receptors), were reduced to approximately 35-50% of those in controls. However, total bindings of these radioligands in the striatum of MAM rats were more than 65% of those in controls, despite the significant loss of striatum mass. However, specific bindings of radioligands in the striatum of MAM rats were elevated by more than 60% of those in controls, and Scatchard analysis revealed that elevations of [3H]Glu, [3H]Gly and [3H]MK-801 bindings were due to a significant increase in the densities of binding sites, with their affinities remaining unaltered. Spatial recognition ability examined by an 8-armed radial maze task was markedly impaired compared to those in controls. These results suggest that the proliferation of neurons bearing excitatory amino acid receptors (EAA) in the striatum is less affected by MAM treatment on day 15 of gestation than that in the cortex and hippocampus in spite of drastic weight loss in these brain regions. The significant reduction of EAA receptors in the cortex and hippocampus may be involved in the impairment of spatial memory observed in MAM-treated rats.

Development of neurons and synapses in ochratoxin A-induced microcephalic mice: a quantitative assessment of somatosensory cortex

Ochratoxin A (a mycotoxin) is known to cause cell death in the developing brain of embryos 1-2 days after treatment. Microcephaly was observed with high frequency in mice by prenatal treatment with ochratoxin A. Using a stereological method, the numerical densities of neurons and synapses were investigated in the somatosensory cortex of 6-week-old microcephalic mice. The numerical density of neurons in ochratoxin A-treated mice represented a 39% increase compared to the control mice, but there was no difference in the numerical density of synapses. The somatosensory cortices of control mice had about 13,000 synapses per neuron, whereas ochratoxin A-treated mice had about 9,400 synapses per neuron. The deficits in synapse-to-neuron ratios seen in ochratoxin A-induced microcephalic brain seemed to result from a reduced dendritic growth.

Changes in secondary structure of DNA of rat embryos following treatment with diethylnitrosamine and methylazoxymethanol acetate in vivo

Diethylnitrosamine (DEN) and methylazoxymethanol acetate (MAM) are not transplacental carcinogenic but embryotoxic to Wistar rats when administered by i.p. injection on day 12 of gestation. MAM, a weak teratogen to rats during this period, induced a dose dependent increase in the number of resorptions to 15% and 40% of the litters following doses of 15 and 25 mg/kg bw, respectively. Rats similarly treated with 70, 150, and 180 mg DEN/kg bw resulted in increases in total DNA mass of day 13 embryos by 31%, 45% and 52%, respectively, compared to the saline treated controls. Twenty percent reduction in total DNA amount was detected following 25 mg MAM/kg bw. Benzoylated DEAE-cellulose (BD-cellulose) chromatography fractionates DNA on the basis of secondary structure by stepwise elution of double-stranded DNA with 1.0M NaCl solution (SE-DNA) followed by elution of DNA containing single-stranded regions with caffeine solution (CE-DNA). Day 13 embryonic DNA was monitored by in vivo labelling with [methyl-3H]-thymidine (3H-TdR) on days 6 and 7 of gestation. Significant increases in percentages of caffeine-eluted DNA (%CE-DNA) compared to control values were detected 24 h after treatment of day 12 embryos with 70, 150, and 180 mg DEN/kg bw. Such increases were not observed after MAM. Incorporation of [methyl-14C]-thymidine (14C-TdR) into embryonic DNA demonstrated the effects of treatment with these compounds on DNA synthesis in vivo. When compared to saline controls, DEN induced significant increases in 14C-TdR incorporation into embryo DNA, 1 h prior to analysis, but the increases were not proportional to the doses administered. Similar analysis of MAM treated samples showed no significant changes to %CE-DNA values. The relative %CE-DNA is expressed as the ratio of the percentage of caffeine-eluted 14C-labelled DNA to %CE-DNA (i.e., %CE-14C-DNA:%CE-3H-DNA). In the majority of control embryos the 14C-specific activity of CE-DNA was higher than the 14C-specific activity of SE-DNA. No significant change to relative %CE-DNA values of embryos to those of the controls was observed 24 h after treatment of day 12 gestation rats with single doses of DEN and MAM. The results of this study support the hypothesis that initiation mechanisms of teratogenesis and transplacental carcinogenesis are different. The pertinence of %CE-DNA and relative %CE-DNA values to teratogenesis and transplacental carcinogenesis is also discussed.

Developmental disturbance of rat cerebral cortex following prenatal low-dose gamma-irradiation: a quantitative study

Pregnant rats were exposed to a single whole-body gamma-irradiation on Day 15 of gestation at a dose of 0.27, 0.48, 1.00, or 1.46 Gy. They were allowed to give birth and the offspring were killed at 6 or 12 weeks of age for microscopic and electron microscopic examinations of the cerebrum. Their body weight, brain weight, cortical thickness, and numerical densities of whole cells and synapses in somatosensory cortex were examined. Growth of the dendritic arborization of layer V pyramidal cells was also examined quantitatively with Golgi-Cox specimens. A significant dose-related reduction in brain weight was found in all irradiated groups. Neither gross malformation nor abnormality of cortical architecture was observed in the groups exposed to 0.27 Gy. A significant change was found in thickness of cortex in the groups exposed to 0.48 Gy or more. Cell packing density increased significantly in the group exposed to 1.00 Gy. Significant reduction in the number of intersections of dendrites with the zonal boundaries were found in the groups exposed to 0.27 Gy or more. There was no difference in the numerical density of synapses in layer I between the control and irradiated groups. These results suggested that doses as low as 0.27 Gy could cause a morphologically discernible change in the mammalian cerebrum.

Increased uptake sites for serotonin and dopamine with decreased S2 serotonin receptors in microencephalic rat brain

Methylazoxymethanol (MAM)-induced cerebral hypoplasia resulted in a significant increase in densities of both serotonin uptake sites in frontal cortex and dopamine uptake sites in striatum, suggesting serotonergic and dopaminergic axons terminals were compressed in the smaller brain volumes. The density of S2 serotonin receptors in MAM-lesioned frontal cortex was decreased probably due to down-regulation, while densities of D1 and D2 dopamine receptors in striatum were identical between MAM-lesioned rats and control rats.

Neurochemical effects of prenatal treatment with ochratoxin A on fetal and adult mouse brain

Ochratoxin A (OA) is a mycotoxin produced by several storage fungi, such as Aspergillus ochraceus and several Penicillium species. OA (3 mg/kg) was given intraperitoneally to pregnant mice on day 11 of gestation (day 1 = day of insemination), and neurochemical changes in brains of their offspring were examined at fetal and adult stages. OA treatment produced retardation of intrauterine growth as well as microencephaly and reductions in total weight and DNA content of fetal brains. Specific activities of lysosomal enzymes in fetal brains began to increase by the 2nd day after treatment and to reach peak activities by the 3rd or 4th day after injection, indicative of cell death in the developing brains. Examination of brain regions of offspring three months after birth revealed that both tissue weight and DNA content were reduced to 80% of control in cerebral hemispheres (CHs; cerebral cortex and subjacent white matter, hippocampus, and amygdala) and to 90% of control in remainder of the brain (BGDM; basal ganglia, diencephalon, and mesencephalon). Total content of noradrenaline (NA), dopamine (DA) 5-hydroxytryptamine (5-HT) in treated CH showed about 15% reduction, although, expressed on a tissue weight basis, concentrations of these monoamines were increased by about 15%. Total DA content in BGDM was also reduced to 85% of controls, but total content of NA and 5-HT in BGDM and pons-medulla oblongata did not change. These results suggest that synaptogenesis of monoamine neurons in the cerebrum is impaired by prenatal treatment with OA, and that dopaminergic neurons show a slight selective vulnerability to the toxin.

Neocortical transplants in the micrencephalic rat brain: morphology and behavior

Normal fetal (E18) neocortical tissue transplanted into the hypoplastic posterior neocortex of infant (10 +/- 2-day-old) rats with transplacentally induced micrencephaly developed into very large, healthy, and permanent transplants. Although the cellular organization within the transplants rarely resembled that of normal rat neocortex, the transplants formed a broad area of interface with the host brain and established fiber connections with it. When tested at 2 months and 1-year-of-age, the presence of the transplant had no significant effect on the typically abnormal performance of micrencephalic rats on two tests of unspecific function, open field activity and maze learning. However, a small group of micrencephalic rats in whom the transplant tissue had failed to fill in the small brain lesions inescapably inflicted during surgery, showed greater behavioral deficits than the micrencephalic controls, suggesting that the transplant had corrected the lesion effect.