methylazoxymethanol and Microcephaly

Aberrant proteolytical processing of the amyloid precursor protein (APP) gives rise to beta-amyloid peptides, which form deposits characteristic for the brains of Alzheimer's disease patients. From in vitro studies, protein kinase C (PKC) is known for almost 20 years to be involved the secretory pathway of APP processing, resulting in the reduced generation of beta-amyloid peptides. However, the toxicity of activators of PKC, such as phorbol esters, has prevented to test the hypothesis of an inverse regulation of secretory APP processing and beta-amyloid generation in vivo. Here we present an animal model which allows to reveal the function of PKC in the proteolytical processing of APP in vivo. Studies by Johnstone and Coyle from the early 1980s have shown that treatment of pregnant rats with methylazoxymethanol acetate (MAM) results in the induction of neocortical microencephalopathy of the offsprings. Later on, the constitutive overactivation of PKC isoforms was described in affected brain structures of these animals. This led to the idea to study the APP processing under conditions of overactivated PKC in the brains of such animals in vivo. However, in mice and rats one can follow the generation of secretory APP products but the detection of rodent beta-amyloid peptides is delicate. Therefore, we adapted the MAM model to guinea pigs, which have a human beta-amyloid sequence, and investigated the relation between secretory APP processing and beta-amyloid generation in vivo. In the brains of microencephalic guinea pigs we observed increased levels of secretory APP fragments but no change in the concentration of beta-amyloid peptides. Our results indicate that both pathways of APP processing are differentially controlled under these experimental conditions in vivo.

Topics: Amyloid beta-Protein Precursor; Amyloid Precursor Protein Secretases; Animals; Aspartic Acid Endopeptidases; Brain; Brain Diseases; Disease Models, Animal; Endopeptidases; Enzyme Activation; Female; Guinea Pigs; Isoenzymes; Methylazoxymethanol Acetate; Microcephaly; Mutation; Peptide Hydrolases; Pregnancy; Protein Kinase C; Protein Processing, Post-Translational

The amygdala plays a crucial role in anxiety-related behavior and various neuropsychiatric disorders. The offspring of dams, administered methylazoxymethanol acetate (MAM) intraperitoneally at gestational day 15, exhibit micrencephaly and anxiety-related behavior, such as hyperactivity in rearing and crossing behavior, alongside a distinct Fos expression profile in the basolateral (BLA) and central amygdala. However, the histochemical underpinnings of these changes remain to be elucidated. To determine the histochemical alterations in MAM-induced model rats, we performed Nissl staining, immunohistochemistry for parvalbumin (PV) or calbindin (Calb), and immunohistochemistry for PV in conjunction with in situ hybridization for glutamate decarboxylase (GAD). We compared immunoreactivity in the BLA between normal and MAM-induced model rats and observed a significant decrease in the number of PV-positive neurons in MAM-induced model rats; however, no significant differences in the number of Nissl- and Calb-positive neurons were observed. We did not detect any significant between-group differences with regards to the effects of environmental enrichment on the number of PV-positive neurons in the BLA. Double-labeling for GAD and PV revealed that many PV-positive neurons colocalized with digoxigenin-GAD65/67 signals. In addition, GAD/PV double-positive neurons and the total number of GAD-positive neurons in the BLA were lower in the MAM-induced model rats. These results indicate that histochemical alterations observed in the BLA of the MAM-induced model rats may attribute to an aberrant GABAergic inhibitory system.

Topics: Animals; Basolateral Nuclear Complex; Carcinogens; Female; GABAergic Neurons; Interneurons; Male; Methylazoxymethanol Acetate; Microcephaly; Parvalbumins; Pregnancy; Rats; Rats, Sprague-Dawley

In order to elucidate the regeneration properties of serotonergic fibers in the hippocampus of methylazoxymethanol acetate (MAM)-induced micrencephalic rats (MAM rats), we examined serotonergic regeneration in the hippocampus following neonatal intracisternal 5,7-dihydroxytryptamine (5,7-DHT) injection. Prenatal exposure to MAM resulted in the formation of hippocampal heterotopia in the dorsal hippocampus. Immunohistochemical and neurochemical analyses revealed hyperinnervation of serotonergic fibers in the hippocampus of MAM rats. After neonatal 5,7-DHT injection, most serotonergic fibers in the hippocampus of 2-week-old MAM rats had degenerated, while a small number of serotonergic fibers in the stratum lacunosum-moleculare (SLM) of the hippocampus and in the hilus adjacent to the granular cell layer of the dentate gyrus (DG) had not. Regenerating serotonergic fibers from the SLM first extended terminals into the hippocampal heterotopia, then fibers from the hilus reinnervated the DG and some fibers extended to the heterotopia. These findings suggest that the hippocampal heterotopia exerts trophic target effects for regenerating serotonergic fibers in the developmental period in micrencephalic rats.

Topics: 5,6-Dihydroxytryptamine; Age Factors; Analysis of Variance; Animals; Chromatography, High Pressure Liquid; Creatinine; Female; Hippocampus; Immunohistochemistry; Male; Methylazoxymethanol Acetate; Microcephaly; Nerve Fibers, Unmyelinated; Nerve Regeneration; Neurons; Periventricular Nodular Heterotopia; Pregnancy; Prenatal Exposure Delayed Effects; Rats; Rats, Sprague-Dawley; Serotonin

Fixed-ratio discrimination (FRD) training session-accuracy curves were constructed using first-order, nonlinear regression and probit analyses to determine maximal (asymptotic) accuracy and the number of sessions required to reach half-maximal accuracy. Increased FRD difficulty (reductions in the differences between the 2 fixed-ratio values to be discriminated) and a training parameter change each increased the number of sessions required to reach half-maximal accuracy and decreased maximal FRD accuracy (i.e., session-accuracy curves were shifted down and to the right) regardless of analysis procedure. These findings indicate that the above manipulations induced mixed competitive-noncompetitive inhibition of the rate of FRD learning. Microencephalic rats were more sensitive to increases in FRD difficulty, whereas control rats were more sensitive to the training parameter change.

Topics: Animals; Behavior, Animal; Discrimination Learning; Female; Kinetics; Methylazoxymethanol Acetate; Microcephaly; Pregnancy; Prenatal Exposure Delayed Effects; Rats; Rats, Sprague-Dawley; Reinforcement Schedule; Task Performance and Analysis; Teratogens

Prenatal exposure of pregnant rats to methylazoxymethanol acetate (MAM) induces microencephaly in the offspring. In the present study of these microencephalic rats (MAM rats) we used quantitative autoradiography to investigate [3H] paroxetine binding sites, which are a selective marker of serotonin (5-HT) transporters (5-HTT). The binding in the accumbens, cortex, hippocampus, and dorsolateral thalamus was significantly increased in MAM rats, compared to the control rats, while there was a significant decrease in the dorsal raphe nucleus of the MAM rats. The levels of 5-HTT mRNA in the dorsal raphe nuclei were analyzed by in situ hybridization, which revealed a significant decrease in 5-HTT mRNA-positive neurons in the MAM rats compared to the control rats. The results imply serotonergic hyperinnervation in the cerebral hemispheres of MAM rats, while a target-dependent secondary degeneration of 5-HT neurons might be induced in the dorsal raphe nuclei of MAM rats.

Topics: Animals; Autoradiography; Binding Sites; Brain; Carrier Proteins; Cerebellum; Cerebral Cortex; Female; Hippocampus; Membrane Glycoproteins; Membrane Transport Proteins; Methylazoxymethanol Acetate; Microcephaly; Nerve Tissue Proteins; Neurons; Nucleus Accumbens; Paroxetine; Pregnancy; Prenatal Exposure Delayed Effects; Raphe Nuclei; Rats; Rats, Wistar; RNA, Messenger; Serotonin; Serotonin Plasma Membrane Transport Proteins; Thalamus

Methylazoxymethanol (MAM), an aglycone of cycasin extracted from Cycad seed, is reported to induce microencephaly in rats after prenatal or postnatal administration. Forty postnatal day (PND) 1 rats derived from 8 timed-pregnant rats were used to evaluate the effect of a single subcutaneous injection of MAM on PND 1 on cell proliferation in rat brain. All dams were fed NIH-31 diet. In the MAM-treated group, each pup received a single injection of MAM at 10 mg/kg body weight. In the control group, pups were injected with saline solution. Body weight of pups was recorded on PNDs 1, 7, 14, 21, 28, and 60. One male pup in each litter was removed for sacrifice by decapitation on PNDs 7, 14, 21, 28, and 60. The brain was removed and dissected to obtain the brain stem, caudate nucleus, cerebellum, frontal cortex, hippocampus, hypothalamus, and olfactory bulb. The percentage (%) of S-phase cells in the cell cycle for each region was measured as index of cell proliferation. A significant (p<0. 05) reduction in body weight was detected on PND 7. The % S-phase cells in cerebellum on PND 7 and olfactory bulb on PND 14 initially increased and then later decreased. There were significant decreases in the % S-phase cells in both cerebellum and caudate nucleus on PND 21 and olfactory bulb on PND 28. No significant changes were found in other brain regions in cell proliferation activity between the control and MAM-treated groups. The % of S-phase cells in cerebellum decreased 65% on PND 60 but lacked statistical significance due to small number of animals used in each group. The results indicated that a single injection of MAM at 10 mg/kg/body weight on PND 1 inhibited cell proliferation in the cerebellum in a manner that could lead to microencephaly.

Topics: Aging; Animals; Animals, Newborn; Brain; Carcinogens; Cell Cycle; Cell Division; Flow Cytometry; Male; Methylazoxymethanol Acetate; Microcephaly; Rats; Rats, Sprague-Dawley

Postnatal changes in the fiber distribution and release of 5-HT in the somatosensory cortex (Sm) of methylazoxymethanol acetate (MAM)-induced microencephalic rats were studied. A transient accumulation of serotonergic fibers was observed in the Sm of the control and MAM rats in the first 2 weeks following birth. However, the density of serotonergic fibers was higher in the MAM rats than in the controls, and the distribution pattern of serotonergic fibers was more extensive in the MAM rats. The microdialysis indicated a high basal level and a delayed K+ -evoked 5-HT release in the Sm of MAM rats on postnatal day 10. The present results suggest morphological and functional alterations of serotonergic fibers in the Sm of MAM rats during the critical period of cortical formation.

Topics: Abnormalities, Drug-Induced; Aging; Animals; Female; Immunohistochemistry; Male; Methylazoxymethanol Acetate; Microcephaly; Microdialysis; Rats; Rats, Sprague-Dawley; Serotonin; Somatosensory Cortex; Teratogens

The postnatal development of serotonin (5HT)-immunoreactive axons was studied in the visual cortex of the cerebrum in both normal and microcephalic rats during early postnatal and young adult stages. Severe microcephaly in rat offspring was induced by prenatal exposure to methylazoxymethanol acetate (MAM), an anti-mitotic agent, on day 15 of gestation. From postnatal day 1 (PND 1) to PND 5, fine and short 5HT fibers were irregularly dispersed throughout the occipital cortex in both the control and MAM-treated rats (MAM-rats). A conspicuous aggregation of dot-like 5HT terminals was found in controls, but not in MAM-rats, in a shallow layer of the dorsomedial region of the occipital cortical plate. On PND 7, such an aggregation of 5HT terminals was found in both groups. The density of the aggregation increased up to PND 9, but then decreased gradually, finally becoming unrecognizable at around PND 15 in both groups. MAM-rats, however, always showed hyperaggregation of 5HT terminals when compared with controls on the same PND. The density of 5HT fibers gradually increased, and finally made up a network-like formation at PND 28 in both groups, its pattern was essentially identical to the abnormal distribution of 5HT fibers during the later stage. As a result, the network-like formation of 5HT fibers in the MAM-rats at PND 28 was markedly twisted and somewhat hyperdense. In Nissl-stained preparations from PND 9 to 15, the 5HT terminal aggregation in the control rats was precisely confined to the newly forming layer IV of the visual cortex. In the MAM-rats, on the other hand, the aggregation of 5HT terminals was not associated with a specific cortical layer because of a disarranged cytoarchitecture of the microcephaly.

Topics: Animals; Female; Immunohistochemistry; Male; Methylazoxymethanol Acetate; Microcephaly; Nerve Fibers; Neuronal Plasticity; Pregnancy; Rats; Rats, Wistar; Serotonin; Teratogens; Visual Cortex

Methylazoxymethanol (MAM)-induced cortical hypoplasia resulted in a 20% decrease in the Bmax of 5-HT2A receptors in the frontal cortex with no change in the Bmax of 5-HT1A receptors. Chronic treatment with amitriptyline did not further decrease the Bmax of 5-HT2A receptors in the MAM-lesioned cortex, suggesting that the persistent down-regulation of cortical 5-HT2A receptors in MAM-lesioned rats was induced by serotonergic hyperinnervation.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Alkylating Agents; Amitriptyline; Animals; Antidepressive Agents, Tricyclic; Behavior, Animal; Cerebral Cortex; Female; Ketanserin; Kinetics; Male; Methylazoxymethanol Acetate; Microcephaly; Pregnancy; Rats; Rats, Wistar; Receptors, Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists

Exposure of fetal rats to X-irradiation at a dose of 1.5 Gy on gestational day 15 results in severe microcephaly. In these X-irradiated rats with microcephaly, a possible alteration of local circuits in the somatosensory cortex was examined using a fluorescent dye, DiI. The dye was placed at the superficial part of the transversely sectioned somatosensory cortex just beneath the pial surface of both the control and X-irradiated rats on postnatal day 11. In the controls, DiI-labeled fibers showed a layer-dependent distribution in the somatosensory cortex, whereas in the X-irradiated rats, this layer-dependent distribution of DiI-labeled fibers was distorted. Furthermore, the fasciculus observed beneath cortical layer VI (white matter), which was made of DiI-labeled axons originating from the cortical neurons, was well developed in the controls. On the other hand, in the X-irradiated rats, the fasciculus made of DiI-labeled fibers was split, reduced in number, and irregularly distributed. These observation suggest that prenatal exposure of fetal rats to X-irradiation may affect the development of local circuits in the cerebral cortex, and may also damage the axonal projection of cortical neurons to the thalamus.

Topics: Abnormalities, Radiation-Induced; Animals; Cerebral Cortex; Female; Male; Maternal Exposure; Methylamines; Methylazoxymethanol Acetate; Microcephaly; Nerve Fibers; Neurons; Pregnancy; Prenatal Exposure Delayed Effects; Rats; Rats, Wistar; Somatosensory Cortex; Teratogens

A single injection of 20 mg/kg methylazoxymethanol acetate (MAM) on gestational day 14 in Brown Norway rats produced micrencephalic offspring (whole brain approximately equal to 65% of control). Despite the micrencephaly, MAM-induced alterations in behavior assessed here were relatively mild. The MAM-treated rats exhibited increased activity under darkened conditions in a complex maze and marginally increased activity after a challenge of methamphetamine. Open field activity, running wheel activity, and emergence behavior using a light/dark apparatus were not significantly affected. Compared with a similar study of Sprague-Dawley micrencephalics [Ferguson S.A., Racey F.D., Paule M.G. and Holson R.R. (1993) Behavioral effects of methyloxymethanol-induced microencephaly. Behav. Neurosci. 107, 1-101], frontal cortex and striatum weights were more reduced in Brown Norway micrencephalics. The MAM-induced behavioral alterations in the Brown Norway strain may have appeared attenuated compared to alterations shown by MAM-treated Sprague-Dawley rats due to differences in baseline between these two strains. Compared to control Sprague-Dawley rats in the previous study, control Brown Norway rats were more active in the open field and running wheels, but less active in the complex maze, exhibiting little to no learning. Emergence tests indicated increased dark preference in Brown Norway rats. Baseline behavior (increased activity and light shyness) of control Brown Norway rats was similar to that of MAM-treated Sprague-Dawley rats; a potential confound in the detection of behavioral effects of a compound. These findings emphasize the effects that strain selection may have on the outcome and interpretation of toxicological/teratological studies.

Topics: Animals; Behavior, Animal; Body Weight; Brain; Female; Male; Maze Learning; Methamphetamine; Methylazoxymethanol Acetate; Microcephaly; Organ Size; Rats; Rats, Inbred BN; Rats, Sprague-Dawley; Species Specificity; Teratogens

Methylazoxymethanol (MAM)-induced cerebral hypoplasia resulted in a significant increase in concentrations of 5-hydroxytryptamine (5-HT, serotonin) and norepinephrine in the frontal cortex, suggesting that these monoaminergic neurons were compressed due to smaller brain volumes. The serotonergic and noradrenergic presynaptic autoreceptors in rat brain are thought to be 5-HT1B receptors and alpha 2-adrenoceptors, respectively. If so, prenatal MAM treatment should increase the density of 5-HT1B and adrenaline alpha 2 receptors in the brain via the compression of noradrenergic and serotonergic axon terminals in the brains of rats with MAM-induced microencephaly. However, neither the densities nor the affinities of 5-HT1B and adrenaline alpha 2 receptors were changed in the MAM rats, suggesting that these presynaptic autoreceptors comprise only a small percentage of the total receptor population. Most 5-HT1B and adrenaline alpha 2 receptors were localized post-synaptically.

Topics: Alkylating Agents; Animals; Autoreceptors; Biogenic Monoamines; Brain; Female; Methylazoxymethanol Acetate; Microcephaly; Pregnancy; Prenatal Exposure Delayed Effects; Rats; Rats, Wistar; Receptor, Serotonin, 5-HT1B; Receptors, Adrenergic, alpha-2; Receptors, Serotonin

Neuroleptic and anticonvulsant drugs are used to reduce the occurrence of aberrant behaviors, seizures, or both in individuals with mental retardation. However, their use may disrupt the learning of desired skills, and the extent to which anatomical (e.g., microencephaly) or biochemical abnormalities or both in such individuals alter the effects of drugs on learning is not known. In this study, the effects of neuroleptics and anticonvulsants on learning and performance in a repeated acquisition task in methylazoxymethanol-induced microencephalic and saline control rats were assessed. Thioridazine was more potent in microencephalic rats than in control rats in increasing errors and decreasing response rates. Clozapine was equally potent in both microencephalic and control rats in increasing errors and decreasing response rates. The effect of carbamazepine was biphasic in both rat groups: Low doses decreased errors and increased response rates, whereas higher doses did the opposite.

Topics: Animals; Anticonvulsants; Antipsychotic Agents; Brain; Clozapine; Conditioning, Operant; Female; Learning; Methylazoxymethanol Acetate; Microcephaly; Organ Size; Pregnancy; Rats; Rats, Sprague-Dawley; Teratogens; Thioridazine

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.

Topics: Animals; Brain; Discrimination Learning; Female; Food; Hippocampus; Hypertension; Male; Methylazoxymethanol Acetate; Microcephaly; Organ Size; Pregnancy; Rats; Rats, Inbred SHR; Rats, Sprague-Dawley; Reinforcement Schedule; Teratogens

Micrencephalic Sprague-Dawley rats were produced by an injection of 20 mg/kg methylazoxymethanol acetate on gestational Day 14. Brain weights of the offspring were 70% of controls while weights of frontal cortex and hippocampus were approximately 58% (Ferguson, Racey, Paule, & Holson, 1993). Operant performance was measured with particular emphasis on assessment of time estimation. The temporal response differentiation (TRD) and the progressive ratio (PR) tasks, previously used in the NCTR operant test battery for monkeys, were chosen for evaluation. The TRD schedule is notably different from other temporal tasks in that it requires subjects to initiate and maintain a lever press for 10-14 s. The PR task was included as a measure of motivation to work for food reinforces. Micrencephalics acquired and performed both tasks comparably to controls. During extinction, however, micrencephalics exhibited an increased TRD lever hold duration. This suggests an atypical response perservation, that is, perseverating the previously correct response. Previously, frontal cortical alterations were suggested to contribute heavily to micrencephalic-induced behavioral alterations (Ferguson et al., 1993). This study provides further evidence that response perseveration, a hallmark of frontal cortical lesions, is expressed in micrencephalic rats.

Topics: Animals; Behavior, Animal; Brain; Conditioning, Operant; Frontal Lobe; Methylazoxymethanol Acetate; Microcephaly; Rats; Rats, Sprague-Dawley; Task Performance and Analysis

Behavioral testings in methylazoxymethanol (MAM)-induced microcephalic rats were conducted. Pregnant Sprague-Dawley rats were treated intraperitoneally with 0, 20 or 40 mg/kg of MAM once a day on day 14 of gestation and were allowed to delivery. Male pups from each litter were examined for open field test at 6 weeks of age and shuttle-box avoidance test at 7 weeks or more of age. In the open field activity of pups, the counts of ambulation and locomoting distance in 40 mg/kg group have increased significantly as compared with those in control group. In the shuttle-box avoidance test, the avoidance response rate was dose-dependently high in the session of the 1st day. As to the interaction between the avoidance response rate and sequence of sessions, however, the avoidance response rate in 40 mg/kg group was significantly low. Rate of the rats with errors and number of response during the intertrial interval was significantly high in 40 mg/kg group. Thus, we could demonstrate functional disturbance in the memory retaining ability in utero MAM-exposed rats.

Topics: Abnormalities, Drug-Induced; Animals; Avoidance Learning; Dose-Response Relationship, Drug; Female; Male; Memory; Methylazoxymethanol Acetate; Microcephaly; Pregnancy; Prenatal Exposure Delayed Effects; Rats; Rats, Sprague-Dawley

Micrencephalic neonatal pups were obtained from pregnant Crj:CD (SD) rats once treated with 5 mg/kg of N-methyl-N-nitrosourea (MNU) or 40 mg/kg of methylazoxymethanol (MAM) on day 12, 13, 14 or 15 of gestation (vaginal plug = day 0). They were reared by their own mothers and were subjected to various neurobehavioral tests during the suckling period, days 0 to 22 after birth. The brain weights in the MNU- and MAM-treated pups on postnatal day 22 were significantly less than those in the control pups. These micrencephalic pups were retarded in neurobehavioral ontogeny. By several tests, each of them showed an impaired performance such as paired limb movement, clumsy locomotion or hyperreflexive reaction. These behavioral disorders appeared different according to the day of treatment, without any substantial difference between the test compounds, MNU and MAM. The findings suggest that the different neurobehavioral characteristics in the micrencephalic pups may reflect their different brain disorders induced by the test compounds given on the different period of the treatment.

Topics: Animals; Behavior, Animal; Body Weight; Brain; Female; Locomotion; Male; Methylazoxymethanol Acetate; Methylnitrosourea; Microcephaly; Organ Size; Pregnancy; Prenatal Exposure Delayed Effects; Rats; Rats, Inbred Strains; Rodent Diseases; Swimming

The effect of methylazoxymethanol (MAM), administered on the 15th gestational day, on the density and pattern of muscarinic cholinergic receptors in some brain areas was assessed using combined radioreceptor binding and autoradiographic techniques. The effect of 15 days' treatment with acetyl-L-carnitine on the same parameter was also assessed. The density of muscarinic cholinergic receptors was found to be increased in the brain of MAM-microencephalic rats. Acetyl-L-carnitine administration caused a significant reduction in the density of receptors under study. A possible role of acetyl-L-carnitine in restoring central cholinergic neurotransmission is discussed.

Topics: Acetylcarnitine; Animals; Autoradiography; Azo Compounds; Brain Chemistry; Carnitine; Cerebral Cortex; Male; Methylazoxymethanol Acetate; Microcephaly; Quinuclidinyl Benzilate; Rats; Rats, Inbred Strains; Receptors, Muscarinic; Staining and Labeling; Sympathetic Nervous System; Synaptic Transmission

The effects of methylazoxymethanol acetate (MAM) administered on the 15th gestational day, and of acetyl-L-carnitine treatment, on rat brain total and ribosomal RNA levels, were studied. In the brain of MAM-treated rats both total and ribosomal RNA concentrations were significantly reduced. Acetyl-L-carnitine treatment restored total and ribosomal RNA levels. The frontal cortex and the hippocampus were the brain areas most sensitive to acetyl-L-carnitine administration. Histochemical demonstration of tissue stores of nucleic acids showed that the loss of RNA induced by MAM occurs primarily within the cytoplasm of nerve cells in various telencephalic areas. Neuronal cytoplasmatic RNA is also sensitive to acetyl-L-carnitine treatment.

Topics: Acetylcarnitine; Animals; Behavior, Animal; Brain Chemistry; Carnitine; Cerebral Cortex; Corpus Striatum; DNA; Hippocampus; Histocytochemistry; Male; Methylazoxymethanol Acetate; Microcephaly; Rats; Rats, Inbred Strains; RNA; RNA, Ribosomal; Staining and Labeling

The regional levels of several cell marker proteins in the brain and the ability of operant discrimination learning on a multiple fixed ratio (FR), fixed interval (FI) schedule were determined in rats with microencephaly induced by prenatal treatment with methylazoxymethanol (MAM), an antimitotic agent, on the 11 th to 13 th days (Group A) or on the 15 th day (Group B) of gestation. The cell marker proteins were determined with a sensitive enzyme immunoassay. Neuron-specific enolase (NSE; gamma gamma-enolase) had a significantly lowered level in the neocortex anterior in Group A. Non-neuronal enolase (NNE; alpha alpha-enolase) was significantly reduced in the superior colliculus, lateral geniculate body and optic nerve, but increased 1.5 fold in the retina in Group A. S-100b protein, a marker of astroglial cells, showed no significant change. As for the learning performance, the Group B animals showed an elevated behavioral activity and made evident discrimination between the FI and FR schedule. But Group A animals had prolonged FR components requiring responses to light on, and their spontaneous activity counts recorded by Automex showed an inhibition of behavior in light environments. These findings suggest a causative role of some developmental abnormality in the central visual system, indicated by the aberrant cell marker levels, in the disturbed learning ability of the Group A animals.

Topics: Abnormalities, Drug-Induced; Alkylating Agents; Animals; Azo Compounds; Brain; Brain Chemistry; Conditioning, Operant; Discrimination Learning; Female; Gestational Age; Locomotion; Methylazoxymethanol Acetate; Microcephaly; Organ Size; Phosphopyruvate Hydratase; Pregnancy; Rats; Rats, Inbred Strains; S100 Proteins

The effect of methylazoxymethanol (MAM) administration at the 15th gestational day on some behavioural and morpho-functional parameters of rat brain was investigated. The effect of a 13-15-day treatment of acetyl-L-carnitine on the same parameters was also assessed. MAM microencephalic rats showed a significant impairment in water-maze and pole-climbing tests. The histochemical reactivity of the enzyme NADH2-tetrazolium reductase (NADHR) at the level of frontal and occipital cortex, neostriatum and hippocampus was remarkably reduced. Also cholinacetyltransferase (ChAT) immunoreactivity within nerve cell bodies of the pontine tegmentum was decreased in MAM-treated animals. On the contrary, acetylcholinesterase (AChE) reactivity was increased in all the investigated brain areas with the sole exception of the neostriatum. Nissl reactivity was decreased in the cytoplasm of the pyramidal neurons of the frontal cortex and hippocampus, and slightly increased in the cytoplasm of pyramidal neurons of the occipital cortex of MAM microencephalic rats. Acetyl-L-carnitine treatment improved the behaviour of microencephalic rats in water-maze and pole-climbing tests. Moreover the substance stimulated NADHR reactivity in the cerebral cortex and hippocampus as well as ChAT immunoreactivity in the cytoplasm of neurons of the raphe pontine nuclei. Pharmacological treatment reduced AChE reactivity in the cerebral cortex and the hippocampus, and improved the pattern of Nissl reactivity within all brain areas examined.

Topics: Acetylcarnitine; Acetylcholinesterase; Animals; Behavior, Animal; Brain; Carnitine; Female; Histocytochemistry; Male; Methylazoxymethanol Acetate; Microcephaly; NADH Tetrazolium Reductase; Nissl Bodies; Pregnancy; Rats; Rats, Inbred Strains

The retinofugal projections of albino rats made micrencephalic by prenatal exposure to the cytotoxic teratogen methylazoxymethanol acetate (MAM Ac) have been examined. The only abnormality noted was an increased projection to the lateral posterior nucleus of the thalamus in rats exposed to MAM Ac on embryonic day 15. The relatively normal retinofugal projections were surprising in view of the extensive damage induced by prenatal exposure to this drug.

Topics: Abnormalities, Drug-Induced; Animals; Female; Geniculate Bodies; Methylazoxymethanol Acetate; Microcephaly; Pregnancy; Rats; Rats, Inbred Strains; Retina; Superior Colliculi; Thalamic Nuclei; Visual Pathways