The effect of maternal hyperthermia on the development of the brain in the guinea pig

Hyperthermia in utero due to maternal influenza is an environmental risk factor for schizophrenia

A hypothesis is presented that the association between maternal influenza and other causes of fever during the second trimester of pregnancy and the subsequent development of schizophrenia in the child is due to the damage caused by hyperthermia to the developing amygdalohippocampal complex and associated structures in the fetal brain. Hyperthermia is a known cause of congenital defects of the central nervous system and other organs after sufficiently severe exposures during early organogenesis. The pathogenic mechanisms include death of actively dividing neuroblasts, disruption of cell migration and arborization and vascular damage. In experimental studies, hyperthermia during later stages of central nervous system development also caused damage to the developing brainstem that was associated with functional defects. This damage usually results in hypoplasia of the parts undergoing active development at the time of exposure. Recent studies have shown no evidence of direct invasion of the fetus by the influenza virus. Factors that might interact with hyperthermia include familial liability to schizophrenia, season of birth, maternal nutrition, severe stress and medications used to alleviate the symptoms of fevers. The time of the development of the fetal amygdalohippocampal complex and the changes found in its structure and associated areas of the brain are compatible with the known effects of hyperthermia.

Review: Hyperthermia and fever during pregnancy

An episode of hyperthermia is not uncommon during pregnancy. The consequences depend on the extent of temperature elevation, its duration, and the stage of development when it occurs. Mild exposures during the preimplantation period and more severe exposures during embryonic and fetal development often result in prenatal death and abortion. Hyperthermia also causes a wide range of structural and functional defects. The central nervous system (CNS) is most at risk probably because it cannot compensate for the loss of prospective neurons by additional divisions by the surviving neuroblasts and it remains at risk at stages throughout pre- and postnatal life. In experimental animals the most common defects are of the neural tube, microphthalmia, cataract, and micrencephaly, with associated functional and behavioral problems. Defects of craniofacial development including clefts, the axial and appendicular skeleton, the body wall, teeth, and heart are also commonly found. Nearly all these defects have been found in human epidemiological studies following maternal fever or hyperthermia during pregnancy. Suggested future human studies include problems of CNS function after exposure to influenza and fever, including mental retardation, schizophrenia, autism, and cerebral palsy.

Heat stress induced histopathology and pathophysiology of the central nervous system

The number of reports on the effects of heat stress is still increasing on account of the temperature is one of the most encountered stressful factors on the different biological systems. Because the heat stress (HS) considered a model of thermal injury to the central nervous system (CNS), the purpose of this review was to assess the histopathological changes of HS on CNS. Also, this review emphasized that the heat stress may retard partially the degree of the postnatal neurogenesis and growth of CNS. Taken together, owing to one of the most important functions of heat shock protein is to protect the organisms from the deleterious effects of temperature, thus, it can be hypothesized that the formation of heat shock proteins may be related to the deleterious effect of HS. On the other hands, the alterations of neurotransmitters in the central nervous system might be involved in the physiological and biochemical responses that occur during heat stress. The hypothalamic monoaminergic systems play an important role in the thermoregulation through regulate the heat production and heat dissipation. In addition, the disturbance in the biochemical variables due to the high temperature may be the cause of the histopathological changes and the partial retardation in CNS and the reverse is true. Thus, further studies need to be done to emphasize this concept.

Teratogenic effect of hyperthermia during early organogenesis period in mice

Pregnant Swiss albino mice were subjected to 41, 42, or 43 degrees C temperature for 10 minutes on day 6.5 of gestation. Another group of animals treated at 37 degrees C was used as control. All animals were killed on the 18th day of gestation and fetuses were examined for prenatal mortality, growth retardation, and microphthalmia incidence. Results indicated a dose dependent increase in the mortality rates with a 42% death in the 43 degrees C group. Treatment with the higher temperatures (42 and 43 degrees C) resulted in a significant increase in the number of growth retarded fetuses and in the incidence of microphthalmia. Reduction in head length and decrease in brain weight were observed in the group exposed to 43 degrees C, particularly in the growth retarded fetuses. However, the percent brain weight(g)-body weight(g) ratio did not show any significant difference from the control values.

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.

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.

Hyperthermia as a teratogen: a review of experimental studies and their clinical significance

Although hyperthermia is teratogenic in birds, all the common laboratory animals, farm animals, and primates and satisfies defined criteria as a teratogen, its study as a human teratogen has been neglected. Homeothermic animals, including humans, can experience body temperature elevations induced by febrile infections, heavy exercise and hot environments which exceed the thresholds (1.5-2.5 degrees C elevation) which are known to cause a syndrome of embryonic resorptions, abortions, and malformations in experimental animals. Hyperthermia is particularly damaging to the central nervous system, and if a threshold exposure occurs at the appropriate stages of embryonic development, exencephaly, anencephaly, encephalocoele, micrencephaly, microphthalmia, neurogenic talipes, and arthrogryposis can be produced in a high proportion of exposed embryos, the incidence and type of defect depending on the species and strain within species, the stage of development, and the severity of hyperthermic exposure. Other defects which can be induced experimentally include exomphalos, hypoplasia of toes and teeth, renal agenesis, vertebral anomalies, maxillary hypoplasia, facial clefting, cataract, coloboma, and heart and vascular defects. Proliferating cells are particularly sensitive to temperature elevations, resulting in arrest of mitotic activity and immediate death of cells in mitosis with threshold elevations (1.5-2.5 degrees C) and delayed death of cells probably in S phase with higher elevations (3.5 degrees C). In general, lower temperature elevations (2.5 degrees C) require longer durations of elevation to cause defects than a simple spike at a higher elevation (4.5 degrees C). The death of cells is largely confined to the brain and in the day 21 guinea pig embryo to the alar regions of the brain. Cell death probably accounts for most of the defects in the central nervous system, but microvascular disturbances leading to leakage, oedema and haemorrhage, placental necrosis, and infarction are other known effects of hyperthermia; and these are probably involved in the pathogenesis of many defects of the heart, limbs, kidneys, and body wall. Recent experiments have demonstrated protection of rat embryos in culture against a known teratogenic exposure by a brief nonteratogenic exposure given at least 15 min earlier. This protection is associated with the synthesis of heat-shock proteins, and temporary arrest of the cell proliferative cycle. Hyperthermia appears to be capable of causing congenital defects in all species and may act alone or synergistically with other agents.(ABSTRACT TRUNCATED AT 400 WORDS)