Effect of hypoxia on DNA fragmentation in different brain regions of the newborn piglet

Apoptotic Markers in the Midbrain of the Human Neonate After Perinatal Hypoxic/Ischemic Injury

Our previous postmortem studies on neonates with neuropathological injury of perinatal hypoxia/ischemia (PHI) showed a dramatic reduction of tyrosine hydroxylase expression (dopamine synthesis enzyme) in substantia nigra (SN) neurons, with reduction of their cellular size. In order to investigate if the above observations represent an early stage of SN degeneration, we immunohistochemically studied the expression of cleaved caspase-3 (CCP3), apoptosis inducing factor (AIF), and DNA fragmentation by using terminal deoxynucleotidyltransferase-mediated dUTP-biotin 3'-end-labeling (TUNEL) technique in the SN of 22 autopsied neonates (corrected age ranging from 34 to 46.5 gestational weeks), in relation to the severity/duration of PHI injury, as estimated by neuropathological criteria. No CCP3-immunoreactive neurons and a limited number of apoptotic TUNEL-positive neurons with pyknotic characteristics were found in the SN. Nuclear AIF staining was revealed only in few SN neurons, indicating the presence of early signs of AIF-mediated degeneration. By contrast, motor neurons of the oculomotor nucleus showed higher cytoplasmic AIF expression and nuclear translocation, possibly attributed to the combined effect of developmental processes and increased oxidative stress induced by antemortem and postmortem factors. Our study indicates the activation of AIF, but not CCP3, in the SN and oculomotor nucleus of the human neonate in the developmentally critical perinatal period.

Neuropathology of the Guillain-Mollaret Triangle (Dentato-Rubro-Olivary Network) in Sudden Unexplained Perinatal Death and SIDS

The present study was undertaken to evaluate the possible alterations of the triangle of Guillain and Mollaret (G-Mt), a neuronal brainstem/cerebellum network (from the dentate nucleus to red nucleus and inferior olivary nucleus) already known for its involvement in the pathogenesis of the palatal myoclonus, in sudden unexplained perinatal and infant death. In 44 cases of perinatal and infant death victims, aged from 26 gestational weeks to 10 months of life, we investigated, besides the histological morphology of the three nuclei, the c-fos and apoptotic expression, as well as the possible effects elicited by maternal cigarette smoking.

A significant increase of lesions (hypoplasia and/or increased c-fos and apoptotic neuronal immunopositivity) of the three nuclei was found in unexplained death victims, compared with age-matched controls. These alterations were related to maternal cigarette smoking habit.

We postulated that the G-Mt is an important network involved in the pathogenesis of a wide spectrum of pathological manifestations and that maternal smoking during pregnancy can exert an adverse influence on this complex, even leading to sudden death in vulnerable periods of perinatal or infant development.

Biopathology of the dentate-olivary complex in sudden unexplained perinatal death and sudden infant death syndrome related to maternal cigarette smoking

OBJECTIVES

The present study was aimed to evaluate the possible presence of cytohistologic and/or biologic modifications of the human dentate-olivary complex in sudden unexplained perinatal and infant deaths.

METHODS

We investigated the histologic morphology of the dentate and inferior olivary nuclei, the glial index, the c-fos and apoptotic immunopositivity, as well as the possible effects elicited by maternal cigarette smoking, in 44 cases of perinatal and infant death victims, aged from the 26th gestational week to 10 months of life.

RESULTS

We observed subtle alterations of both the medullary inferior olivary nucleus and of the cerebellar dentate nucleus, represented by a significant increase in the reactive astrocyte density and in the neuronal c-fos and apoptotic expression in unexplained death victims, compared with age-matched controls. These alterations were closely related to a maternal cigarette smoking habit.

DISCUSSION

We postulate that maternal smoking, besides inducing the previously demonstrated morpho-functional alterations of the autonomic central nervous system, could also exert an adverse influence on the dentate-olivary complex, leading to sudden death in vulnerable periods of perinatal development or early infancy.

Active caspase-3 in the sudden infant death syndrome (SIDS) brainstem

In a retrospective postmortem study, we examined the neuronal expression of active caspase-3, a specific apoptotic marker, in the brainstem of 67 infants dying from sudden infant death syndrome (SIDS), and 25 age-matched control infants (non-SIDS). Neuronal immunostaining for active caspase-3 was semi-quantitatively scored in nuclei from five brainstem levels: rostral, mid and caudal pons, and rostral and caudal medulla. Regardless of the cause of death (SIDS vs. non-SIDS), age-related differences in active caspase-3 expression were identified, predominantly in the medulla. No gender-related differences were identified. Comparing SIDS to non-SIDS cases, increased active caspase-3 expression was restricted to four nuclei in the caudal pons (abducens, facial, superior olivary, and pontine nuclei) and two nuclei in the rostral medulla (hypoglossal and dorsal motor nucleus of the vagus). We conclude that neuronal apoptosis is increased in the brainstem of SIDS compared to non-SIDS infants.

Postnatal nicotine and/or intermittent hypercapnic hypoxia effects on apoptotic markers in the developing piglet brainstem medulla

The most important risk factors currently identified for the sudden infant death syndrome (SIDS) are prone sleeping and cigarette smoke exposure. In this study, we investigated the neuropathological sequelae of these risk factors by exposing piglets to intermittent hypercapnic-hypoxia (IHH) and/or nicotine (nic) in the early postnatal period. Our hypothesis was that either nic or IHH exposure could increase neuronal cell death, and that combined exposure (nic+IHH) would be additive. Four exposure patterns were studied: controls (n=14), IHH (n=10), nic (n=14), and nic+IHH (n=14). All groups had equal gender ratios. Nic exposure via an implanted osmotic minipump commenced within 48 h of birth and continued until age 13-14 days when animals were killed and brains collected. A total of 48 min of hypercapnic-hypoxia was delivered on the day immediately prior to killing in a pattern comprising 6 min of HH (8% O(2), 7% CO(2), balance N(2)) alternating with 6 min of air. Immunohistochemistry was performed to identify neurons positive for active caspase-3 and DNA fragmentation (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling, TUNEL) in seven nuclei of the caudal medulla. Staining quantification showed that: 1. IHH induced neuronal death (increased both TUNEL and casapse-3) in more brainstem nuclei than nicotine. 2. Females were more severely affected by IHH than males. 3. Where IHH and nicotine were combined, TUNEL expression was approximately 5% less than IHH alone, but changes in caspase-3 were variable. We conclude that acute exposure to IHH in the postnatal period is more neurotoxic than exposure to nicotine alone. Combined exposure to IHH and nicotine produced variable responses with some results suggesting that nicotine can be neuroprotective. These results indicate that environmental insults attributable to prone sleeping can produce neurotoxic sequelae in SIDS, with some regional specificity in the response. However, no consistent relationship is evident when combining the two insults.

Histological and biological developmental characterization of the human cerebellar cortex

The aim of this study was to investigate the histological and biological features of the human cerebellar cortex development and differentiation. We analyzed 52 brains of fetal and infant death victims, aged from 17 gestational weeks to 12th postnatal month. In particular, in the cerebellar cortex at different ages we evaluated, besides the structural aspects, the expression of several biomarkers implicated in proliferative processes (c-fos, PCNA and apoptosis). We observed morphological patterns progressively evolving every month, from the indefinite structure of the second gestational trimester to the four-layered structure (external granular layer, molecular layer, Purkinje cell layer, internal granular layer) of the late fetal cortex and subsequently to the three-layered postnatal definitive morphology, due to involution of the external granular layer. The evaluation of the biological features of the cerebellar cortex showed high proliferative activity mainly confined to the transient external granular layer in prenatal life, and high apoptotic index after birth. Thus, the histological examination, better with the support of biomarker investigations, allows with accuracy to describe the dynamic sequence of steps that occur in human cerebellar cortex development and to establish in each case the age, namely the pre- or postnatal month of life. Consequently, we can diagnose delayed or altered processes of differentiation during the development of the human cerebellar cortex.

Up-regulation of heat shock protein HSP 20 in the hippocampus as an early response to hypoxia of the newborn

Hypoxia is an important challenge for newborn mammals. Stress generated at the brain level under low oxygenation conditions results in up-regulation of heat shock proteins (HSPs) and other stress proteins. The aim of the present work was to determine the effect of hypoxia in the newborn on some newly described small molecular weight HSPs (HSP 20 and B8) in the hippocampus, cortex and cerebellum of newborn piglets. These effects will be compared with those of other closely related proteins such as alphaB crystallin, HSP 27, heme oxygenase (HO)-1, HO-2, cyclooxygenase (COX)-1 and COX-2. The piglets were submitted to hypoxia (5% O(2); 95% N(2)) over either 1 or 4 h, with recovery periods ranging from 0 to 68 h. Western blot analysis showed that HSP 20 was rapidly induced only in the hippocampus, long before hypoxia-inducible transcription factor HIF-1alpha, while HSP 27 was rapidly induced in the cortex and cerebellum. Vascular epithelial growth factor was increased simultaneously in the three regions. Moreover, an increase in the expression of, respectively, HO-1 and COX-2 was observed later, but at the same time, in the three regions tested. It appears that HSP 20 can be an early marker of hypoxia in the hippocampus. The other small HSPs or stress proteins display different temporal patterns of up-regulation (HSP 27 and HO-1, COX-2) or do not show changes in their expressions (alphaB crystallin, HSP B8, HO-2 and COX-1).

Apoptosis and necrosis in developing cerebellum and brainstem induced after focal cerebral hypoxic-ischemic injury

Focal cerebral hypoxia-ischemia due to isolated vascular insufficiency is well known to cause ipsilateral, but not contralateral, cerebral apoptosis. Hypoxic-ischemic damage to the cerebellum and brainstem in such a model has not been established. This experimental rodent study demonstrates, through deoxyribonucleic acid fragmentation and terminal deoxynucleotidyl transferase-mediated deoxyuridine 5'-triphosphate-digoxigenin nick end labeling analysis, that neuronal cells in these infratentorial regions also suffer mild apoptosis and necrosis after focal cerebral hypoxic-ischemic injury in the newborn rat. These data provide additional insight into the mechanisms of neurological injury in the cerebellum and brainstem areas resulting from a focal cerebral hypoxic-ischemic insult and demonstrate that future therapeutic interventions for hypoxic-ischemic encephalopathy system should deal with the entire central nervous system.

Effects of hypoxia on stress proteins in the piglet heart at birth

Hypoxia at birth represents a very stressful event that can result in severe lifelong consequences in different tissues, including those of the heart. Heat shock and other associated stress proteins are involved in cellular protection, but their roles are not clearly defined at the time of birth. Newborn piglets were subjected to 5% oxygen and 95% nitrogen for either 1 or 4 hours. They were allowed to recover over periods of 1 to 68 hours. The relative levels of alphaB-crystallin, HspB8, Hsp20, Hsp27, Hsp60, and Hsp70 as well as nitric oxide synthases (NOS) (endothelial NOS, inducible NOS, neuronal NOS) were examined by Western blot analysis. Surprisingly, alphaB-crystallin expression was drastically increased in animals submitted to hypoxia. The hypoxia-associated factor HIFlalpha was also strongly and rapidly overexpressed. Heme oxygenase 1 was also increased. To a lesser extent, neuronal NOS was also increased in the left ventricle of animals submitted to hypoxia. This work clearly shows that the Hsp chaperone alphaB-crystallin is strongly overexpressed in the left ventricle of animals submitted to hypoxia. This observation dissociates the response to low oxygenation of alphaB-crystallin and other stress-associated proteins including Hsp27, and it indicates that heme oxygenase is not alone among HSPs in its oxygen-related gene expression.

Effects of hypoxia on stress proteins in the piglet brain at birth

Newborn piglets were submitted to normobaric hypoxia (5% O2, 95% N2) for either 1 or 4 h. The effects of hypoxia on the neonatal brain were characterized through a time-course analysis of levels of various proteins such as heat shock proteins (HSP27, 70, and 90), hypoxia inducible factor-1alpha (HIF-1alpha), neuronal nitric oxide synthase (nNOS), hemeoxygenase-2 (HO-2), and caspase-3. The expression of these proteins was determined at different stages of recovery up to 72 h in cerebellum, cortex, and hippocampus by Western blot analysis in hypoxic maintained animals that were made hypoxic at either 20 or 37 degrees C. In all regions of the brain, HIF-1alpha and HSP27 expression were strongly increased until 22 h of recovery. No significant changes were observed for HSP70, HSP90, and HO-2. A small elevation of expression of nNOS was observed at early stages in the cerebellum and the cortex with no change in the hippocampus. Expression of caspase 3 was strongly increased in the cortex 24 and 48 h after hypoxia but unchanged in the hippocampus. These results are presented in terms of the porcine model of nonischemic hypoxia and its delayed neuronal effects on the cerebral outcome. Because of their recently established biochemical and functional interactions, the expression of the main HSPs, HIF-1alpha, nNOS, and caspase-3 after hypoxia are delineated.

Increased neuronal cell death after intermittent hypercapnic hypoxia in the developing piglet brainstem

We examined the immunohistochemical expression of caspase-3 (CASP3), active caspase-3 and TUNEL in the normal piglet brainstem at 13-14 days of age and evaluated the effects of exposure to 2 vs. 4 days of intermittent hypercapnic hypoxia (IHH) on their expression. Eight nuclei from the level of the caudal medulla were studied. In control piglets, CASP3 was present in approximately 45% of neurons while active caspase-3 and TUNEL were present in approximately 5%, indicating that approximately half the neuronal population of the piglet medulla express caspase-3 in a latent state and that only approximately 5% undergo 'normal' programmed cell death. After 2 days of IHH, CASP3 increased in the nucleus of the solitary tract (NTS), gracile and cuneate nuclei (P<0.05 for all). Active caspase-3 increased in the dorsal motor nucleus of the vagus (DMNV) (P<0.05) but decreased in the lateral reticular nucleus (LRt) (P<0.05), while TUNEL increased in both the DMNV and LRt (P<0.05 for both). After 4 days of IHH, CASP3 remained elevated in the cuneate nucleus (P<0.01) but decreased in the hypoglossal and DMNV (P<0.05) when compared to controls. Active caspase-3 levels were not changed, whereas TUNEL was increased in the DMNV, LRt, and inferior olivary nucleus (P<0.05 for all). These results show that IHH induces neuronal cell death within certain nuclei in the piglet caudal medulla that are functionally important in cardiorespiratory, sleep and arousal control. This could have important implications for clinical conditions including obstructive apnea and prone sleeping as a risk for SIDS.

Correlations between brainstem NMDA receptor changes and active neuronal cell death after intermittent hypercapnic hypoxia in the developing piglet

The role of the N-methyl-D-aspartate (NMDA) receptor in cell death was evaluated in the piglet brainstem after exposure to intermittent hypercapnic hypoxia (IHH). Study groups comprised controls (n=6) and piglets exposed to IHH on 2 (n=6) or 4 (n=5) successive days prior to euthanasia. All piglets had the caudal medulla evaluated at 13-14 days of age using double immunohistochemistry for TUNEL and the NMDA receptor 1 (NR1) subunit. The percent of TUNEL positive neurons amongst NR1 (% TUN in NR1) and non-NR1 neurons (% TUN in non-NR1) was determined in eight nuclei. After 2 days of IHH, %TUN in NR1 was increased in the dorsal motor nucleus of the vagus (DMNV, P=0.007) and the inferior olivary nucleus (ION, P=0.05). After 2 days IHH, %TUN in non-NR1 neurons was increased in the lateral reticular nucleus (LRt, P=0.05), nucleus of the solitary tract (NTS, P=0.004) and gracile nucleus (P=0.05). After 4days IHH, the increase of %TUN in NR1 was sustained in the ION (P=0.05), while %TUN in non-NR1 neurons was sustained in NTS (P=0.04) and LRt (P=0.006). Daily IHH exposure induces neuronal death within NR1 and non-NR1 neurons, but the neuronal phenotype is consistent within affected brainstem nuclei. Involvement of the NMDA receptor tended to occur in nuclei with higher basal NR1 expression, and thus occurred in nuclei relevant to cardiorespiratory function. We speculate that IHH exposures, such as occurs during obstructive apnea or facial entrapment in prone sleeping during infancy, can induce abnormalities of cardiorespiratory control.

Perinatal expression of heat shock proteins HSC 70 and HSP 70 in neural and non neural tissues of the piglet

Stress of different kinds during early perinatal life can result in severe consequences for further development. To determine possible involvement of heat shock proteins in brain development, the expression of HSC 70 and HSP 70 was determined in brain regions (cerebellum, cortex, hippocampus, hypothalamus and striatum) and non neural tissues (liver, lungs and kidneys) at birth and during early development of the piglet. In brain regions, HSC 70 expression was decreased during the few hours following birth. With the exception of cortex, hippocampus and kidney where a decrease of expression was observed, HSP 70 did not show significant changes during early development. These results are discussed in terms of using the piglet model of development to study the effect of different kinds of stress like hypoxia or temperature changes on brain development.