C-fos gene expression in rat brain around birth: effect of asphyxia and catecholamines

Brain Volumes in Mice are Smaller at Birth After Term or Preterm Cesarean Section Delivery

The rate of cesarean section (CS) delivery has steadily increased over the past decades despite epidemiological studies reporting higher risks of neonatal morbidity and neurodevelopmental disorders. Yet, little is known about the immediate impact of CS birth on the brain, hence the need of experimental studies to evaluate brain parameters following this mode of delivery. Using the solvent clearing method iDISCO and 3D imaging technique, we report that on the day of birth, whole-brain, hippocampus, and striatum volumes are reduced in CS-delivered as compared to vaginally-born mice, with a stronger effect observed in preterm CS pups. These results stress the impact of CS delivery, at term or preterm, during parturition and at birth. In contrast, cellular activity and apoptosis are reduced in mice born by CS preterm but not term, suggesting that these early-life processes are only impacted by the combination of preterm birth and CS delivery.

Birth elicits a conserved neuroendocrine response with implications for perinatal osmoregulation and neuronal cell death

Long-standing clinical findings report a dramatic surge of vasopressin in umbilical cord blood of the human neonate, but the neural underpinnings and function(s) of this phenomenon remain obscure. We studied neural activation in perinatal mice and rats, and found that birth triggers activation of the suprachiasmatic, supraoptic, and paraventricular nuclei of the hypothalamus. This was seen whether mice were born vaginally or via Cesarean section (C-section), and when birth timing was experimentally manipulated. Neuronal phenotyping showed that the activated neurons were predominantly vasopressinergic, and vasopressin mRNA increased fivefold in the hypothalamus during the 2–3 days before birth. Copeptin, a surrogate marker of vasopressin, was elevated 30-to 50-fold in plasma of perinatal mice, with higher levels after a vaginal than a C-section birth. We also found an acute decrease in plasma osmolality after a vaginal, but not C-section birth, suggesting that the difference in vasopressin release between birth modes is functionally meaningful. When vasopressin was administered centrally to newborns, we found an ~ 50% reduction in neuronal cell death in specific brain areas. Collectively, our results identify a conserved neuroendocrine response to birth that is sensitive to birth mode, and influences peripheral physiology and neurodevelopment.

Vasopressin excites interneurons to suppress hippocampal network activity across a broad span of brain maturity at birth

During birth in mammals, a pronounced surge of fetal peripheral stress hormones takes place to promote survival in the transition to the extrauterine environment. However, it is not known whether the hormonal signaling involves central pathways with direct protective effects on the perinatal brain. Here, we show that arginine vasopressin specifically activates interneurons to suppress spontaneous network events in the perinatal hippocampus. Experiments done on the altricial rat and precocial guinea pig neonate demonstrated that the effect of vasopressin is not dependent on the level of maturation (depolarizing vs. hyperpolarizing) of postsynaptic GABA_A receptor actions. Thus, the fetal mammalian brain is equipped with an evolutionarily conserved mechanism well-suited to suppress energetically expensive correlated network events under conditions of reduced oxygen supply at birth.

25 years of research on global asphyxia in the immature rat brain

Hypoxic-ischemic encephalopathy remains a common cause of brain damage in neonates. Preterm infants have additional complications, as prematurity by itself increases the risk of encephalopathy. Currently, therapy for this subset of asphyxiated infants is limited to supportive care. There is an urgent need for therapies in preterm infants - and for representative animal models for preclinical drug development. In 1991, a novel rodent model of global asphyxia in the preterm infant was developed in Sweden. This method was based on the induction of asphyxia during the birth processes itself by submerging pups, still in the uterine horns, in a water bath followed by C-section. This insult occurs at a time-point when the rodent brain maturity resembles the brain of a 22-32 week old human fetus. This model has developed over the past 25 years as an established model of perinatal global asphyxia in the early preterm brain. Here we summarize the knowledge gained on the short- and long-term neuropathological and behavioral effects of asphyxia on the immature central nervous system.

Critical periods for the role of oxidative stress in the developmental neurotoxicity of chlorpyrifos and terbutaline, alone or in combination

The developmental neurotoxicity of chlorpyrifos (CPF) involves mechanisms other than inhibition of cholinesterase. In the current study, we examined the ability of CPF to evoke lipid peroxidation in the developing brain of fetal and neonatal rats. CPF given to pregnant rats on gestational days 17-20 or to neonatal rats on postnatal days 1-4, failed to elicit increases in thiobarbituric acid-reactive species (TBARS) in brain regions even when the dose was raised above the threshold for systemic toxicity and hepatic damage. In contrast, CPF administration during the second postnatal week, the peak period of neuronal cell differentiation and synaptogenesis, did evoke significant increases in TBARS even at a dose devoid of systemic toxicity. Terbutaline, which is chemically unrelated to CPF and which stimulates neuronal cell metabolism through direct actions on beta-adrenoceptors, also elicited oxidative damage in the developing brain with greater sensitivity in the second postnatal week. These results indicate that diverse compounds can exert convergent effects on brain development through their shared potential to elicit oxidative stress, and that the net outcome is dependent upon specific developmental stages in which metabolic demand is especially high. Furthermore, given the common use of terbutaline in the therapy of preterm labor, and the nearly ubiquitous exposure of the human population to organophosphorus pesticides, the combined oxidative burden of exposure to both agents may contribute to the worsened neurodevelopmental outcomes noted in animal models of such dual exposures.

Effect of perinatal asphyxia on tyrosine hydroxylase and D2 and D1 dopamine receptor mRNA levels expressed during early postnatal development in rat brain

This study was designed to investigate the postnatal developmental plasticity of the mesostriatal and mesolimbic dopamine systems that occurs following perinatal asphyxia. The time course and patterning of the changes in levels of tyrosine hydroxylase (TH), and D1 and D2 dopamine receptor (R) mRNA in the cell body region, substantia nigra and ventral tegmental area (SN/VTA), and projection fields, striatum and limbic regions at the age of 6 and 24 h, and 1 week after asphyxia were studied with a quantitative reverse transcription polymerase chain reaction method with appropriate internal cRNA standard. In Caesarean-delivered control rats (Sprague-Dawley), TH, D2R and D1R mRNA levels showed regional and temporal specificity in both absolute levels and developmental kinetics during the first week of life. TH mRNA levels were >10-fold higher in SN/VTA than in striatum and limbic regions. Compared to Caesarean delivered controls, severe asphyxia (15-20 min) induced an increase of TH and D2R mRNA in SN/VTA 6 h and 1 week after birth. In addition, asphyxia induced an increase of TH mRNA in the projection fields, striatum and limbic regions, at 1 week. Perinatal asphyxia did not appear to exert any effect on D1R mRNA levels. No differences in any of the parameters were observed between spontaneous- and Caesarean-delivered animals. The present results indicate that perinatal asphyxia triggers coordinated changes in the expression of TH, and dopamine receptor mRNA in SN/VTA, striatum and limbic regions. These changes may affect differently dopamine D2R and D1R expression along development, contributing to long-term neurocircuitry imbalances.

Identification of neurons responding to hypoxia in sudden infant death syndrome

The pathogenesis of sudden infant death syndrome (SIDS) is still not understood, although one of the most credited current hypotheses is the respiratory theory. Considerable evidence has been assembled suggesting that hypoxia in human infants produces an initial increase in ventilation, after which respiration is rapidly inhibited. We investigated the expression of the c-fos proto-oncogene, a marker of activated neurons, particularly by hypoxia, in the medulla oblongata nuclei involved in breathing after birth, with special reference to SIDS. We utilized c-fos protein immunohistochemistry on serial transverse sections of medulla oblongata from 22 SIDS victims. In 60% of the analyzed cases, we observed numerous positive c-fos neurons in the dorsal motor nucleus of the vagal nerve. In control cases, the immunohistochemical labeling was negative or very low. The c-fos protein was expressed in the rostral-intermediate portion of the dorsal motor vagal nucleus, where motoneurons with respiratory-related activity are located. The positive c-fos immunoreactivity observed in SIDS suggests that the neurons of the dorsal motor vagal nucleus involved in the regulation of breathing are able to yield an intense, immediate ventilatory response to hypoxia. Our results support the respiratory theory of SIDS.

Postnatal regulation of ZnT-1 expression in the mouse brain

We have characterized the postnatal development of ZnT-1, a putative zinc transporter, in the mouse brain with respect to chelatable zinc in four distinct brain areas: cerebral cortex, hippocampus, olfactory bulb and cerebellum. At birth, both zinc and ZnT-1 immunoreactivity were nearly undetectable. Beginning at the end of the first postnatal week, ZnT-1 expression increased significantly in all areas examined except the cerebellum, which contains virtually no synaptic zinc. Moreover, neurons immunoreactive for ZnT-1 were typically present in areas rich in synaptic zinc, which increased in parallel with ZnT-1. In the cerebellum, in contrast, Purkinje cells exhibited robust immunoreactivity for ZnT-1 only in the second postnatal week. While the parallel development of zinc and ZnT-1 in forebrain regions supports a direct role for synaptic zinc in regulating ZnT-1 expression, ZnT-1 in cerebellar Purkinje cells could indicate that expression of this zinc transporter may also be regulated by a non-synaptic pool of zinc or by other mechanism(s). The striking developmental regulation of ZnT-1 expression together with synaptic zinc indicates that ZnT-1 may play a key role in protecting developing neurons against potentially toxic zinc.