Maternal hyperthermia as a cause of "idiopathic" mental retardation

[Importance of the clinical genetics evaluation on hydrocephalus]

The aim of this study was to characterize the possibility of genetic etiology in a group of individuals with congenital hydrocephalus in which the etiology was indeterminate and to confirm that earlier diagnosed. The casuistry was composed by 16 individuals with congenital hydrocephalus. Investigation protocol included anamnesis, familial investigation, physical examination, computerized tomography or magnetic resonance image of head, vertebral column X-ray, karyotype and dysmorphological study. Results were analyzed in two groups. In Group I (3M:9F) was composed by hydrocephalus associated with unspecific signs. Group II (7 males) had findings of epectrum of L1 disease. Genetic counseling could be offered in 11 cases. These results demonstrate the great etiological heterogeneity of congenital hydrocephalus and reinforce the importance of dysmphology evaluation as an important complementary investigation.

Prenatal infection and risk for schizophrenia: IL-1beta, IL-6, and TNFalpha inhibit cortical neuron dendrite development

Prenatal exposure to infection increases risk for schizophrenia, and we have hypothesized that inflammatory cytokines, generated in response to maternal infection, alter neuron development and increase risk for schizophrenia. We sought to study the effect of cytokines generated in response to infection-interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNFalpha), and interleukin-6 (IL-6)-on the dendritic development of cortical neurons. Primary mixed neuronal cultures were obtained from E18 rats and exposed to 0, 100, or 1000 units (U)/ml of IL-1beta, TNFalpha, IL-6, or IL-1beta+TNFalpha for 44 h. MAP-2-positive neurons were randomly identified for each condition and the number of primary dendrites, nodes, and total dendrite length was determined. We found that 100 U of TNFalpha significantly reduced the number of nodes (27%, p=0.02) and total dendritic length (14%, p=0.04), but did not affect overall neuron survival. A measure of 100 U IL-1beta+TNFalpha significantly reduced the number of primary dendrites (17%, p=0.006), nodes (32%, p=0.001), and total dendritic length (30%, p<0.0001), although it did not affect overall neuron survival. At 1000 U, each cytokine significantly reduced the number of primary dendrites (14-24%), nodes (28-37%), as well as total dendritic length (25-30%); neuron survival was reduced by 14-21%. These results indicate that inflammatory cytokines can significantly reduce dendrite development and complexity of developing cortical neurons, consistent with the neuropathology of schizophrenia. These findings also support the hypothesis that cytokines play a key mechanistic role in the link between prenatal exposure to infection and risk for schizophrenia.

The induction of neural tube defects by maternal hyperthermia: a comparison of the guinea-pig and human

In our recent studies on the effects of maternal hyperthermia on the embryonic guinea-pig, we have demonstrated two 'teratogenic windows' at embryonic days 13 and 21 (E13 and E21). E13 encompasses the period of the closure of the neural groove and anterior neuropore, and E21 the commencement of the cortical plate. The approximate equivalent developmental times in the human are E23-E25 and E49-E56 respectively. In the guinea-pig, maternal hyperthermia at E13 results in a high incidence of neural tube defects (NTD), many open, and associated with other defects such as microphthalmia, and scoliosis or kyphosis. The NTD were most common in the developing hindbrain and all demonstrated considerable infoldings of neural tissue, rosettes of neuroepithelial cells, outpocketings of neural tissue and large cystic cavities beneath the defect. In human examples from the Kyoto Human Embryo Collection, 16 had verified hyperthermic insults at E23-E25 and all had NTD which showed similar deformities to the guinea-pig. Most embryos with such gross defects are aborted in the early fetal period in both species.

Mammalian stress proteins HSP70 and HSP28 coinduced by nicotine and either ethanol or heat

Cells exposed to a variety of stresses such as heat or ethanol respond by increasing their rate of synthesis of a set of proteins termed heat shock proteins (HSP). These proteins then appear to offer protection against the stressor and many other insults. The HSP also play important roles in unstressed cells. They are involved in the regulation of the cell cycle and during specific stages in the development of organisms. Exposure to stress during development (e.g., in pupal stages of insects or during gestation in mammals) leads to birth defects that are specific to the timing of the stress. It has been hypothesized that the ill-timed induction of HSP is responsible for this phenomenon. Epidemiological studies in humans have related teratogenic events to maternal exposures to hyperthermia or ethanol during pregnancy. The rate of alcohol-induced birth defects is greatly enhanced by smoking, suggesting a role for nicotine. Nicotine by itself, however, is said not to induce HSP. We hypothesized that nicotine may act as a coinducer (or facilitator) of stress responses. This possibility we tested on three levels: protection against heat (thermotolerance), induction of specific HSP, and binding of the heat shock transcription factor to the heat shock element. Each of these tests showed clearly that nicotine does indeed play such a role. This places nicotine in a novel position; to date, no other coinducers of stress responses have been reported. Our results may offer an explanation for the epidemiological data cited earlier.

Mammalian stress proteins HSP70 and HSP28 coinduced by nicotine and either ethanol or heat

Cells exposed to a variety of stresses such as heat or ethanol respond by increasing their rate of synthesis of a set of proteins termed heat shock proteins (HSP). These proteins then appear to offer protection against the stressor and many other insults. The HSP also play important roles in unstressed cells. They are involved in the regulation of the cell cycle and during specific stages in the development of organisms. Exposure to stress during development (e.g., in pupal stages of insects or during gestation in mammals) leads to birth defects that are specific to the timing of the stress. It has been hypothesized that the ill-timed induction of HSP is responsible for this phenomenon. Epidemiological studies in humans have related teratogenic events to maternal exposures to hyperthermia or ethanol during pregnancy. The rate of alcohol-induced birth defects is greatly enhanced by smoking, suggesting a role for nicotine. Nicotine by itself, however, is said not to induce HSP. We hypothesized that nicotine may act as a coinducer (or facilitator) of stress responses. This possibility we tested on three levels: protection against heat (thermotolerance), induction of specific HSP, and binding of the heat shock transcription factor to the heat shock element. Each of these tests showed clearly that nicotine does indeed play such a role. This places nicotine in a novel position; to date, no other coinducers of stress responses have been reported. Our results may offer an explanation for the epidemiological data cited earlier.

Interference with neural crest migration by maternal hyperthermia as a cause of embryonic death due to heart failure

Maternal hyperthermia has been demonstrated to be a teratogen in every animal species studied, and a minimum core temperature rise of 2.5 degrees C can produce a number of developmental defects. However, numerous embryos fail to survive to term. In the guinea-pig, heating the embryos prior to neural tube closure induces significant neural tube defects, but all embryos die within 20 days of heating. A number have aberrant cardiac development and many show spectacular pericardial effusions and congestion in the peripheral circulation. We suggest that maternal hyperthermia has interfered with neural crest migration which is a major component in the induction of these changes.

Quantitative study of the effects of maternal hyperthermia on cell death and proliferation in the guinea pig brain on day 21 of pregnancy

On embryonic day 21, pregnant guinea pigs were exposed to a 44 degrees C environment for 1 hour. As a result, all brain ventricular zone cells in M phase of the mitotic cycle when heat-shock occurred became immediately pyknotic and all cell division was stopped for 4-8 hr. The pyknotic cells were removed at a definable rate until mitosis resumed, after which removal occurred in an apparently random manner. Long delays in the return to mitosis were related to increased destruction of S-phase cells deep within the ventricular zone and largely confined to the alar lamina. Upon recovery, a rostrocaudal delay in mitosis was apparent, and the number of mitotic figures was increased compared with control numbers for 1 hr, after which they returned to control numbers. It was evident that up to 40% of the cells within the ventricular zone were destroyed following brief maternal heat stress.