The serotonergic anatomy of the developing human medulla oblongata: implications for pediatric disorders of homeostasis

The medullary serotonergic centres involved in cardiorespiratory control are disrupted by fetal growth restriction

Fetal growth restriction (FGR) is associated with cardiovascular and respiratory complications after birth and beyond. Despite research showing a range of neurological changes following FGR, little is known about how FGR affects the brainstem cardiorespiratory control centres. The primary neurons that release serotonin reside in the brainstem cardiorespiratory control centres and may be affected by FGR. At two time points in the last trimester of sheep brain development, 110 and 127 days of gestation (0.74 and 0.86 of gestation), we assessed histopathological alterations in the brainstem cardiorespiratory control centres of the pons and medulla in early-onset FGR versus control fetal sheep. The FGR cohort were hypoxaemic and asymmetrically growth restricted. Compared to the controls, the brainstem of FGR fetuses exhibited signs of neuropathology, including elevated cell death and reduced cell proliferation, grey and white matter deficits, and evidence of oxidative stress and neuroinflammation. FGR brainstem pathology was predominantly observed in the medullary raphé nuclei, hypoglossal nucleus, nucleus ambiguous, solitary tract and nucleus of the solitary tract. The FGR groups showed imbalanced brainstem serotonin and serotonin 1A receptor abundance in the medullary raphé nuclei, despite evidence of increased serotonin staining within vascular regions of placentomes collected from FGR fetuses. Our findings demonstrate both early and adaptive brainstem neuropathology in response to placental insufficiency. KEY POINTS: Early-onset fetal growth restriction (FGR) was induced in fetal sheep, resulting in chronic fetal hypoxaemia. Growth-restricted fetuses exhibit persistent neuropathology in brainstem nuclei, characterised by disrupted cell proliferation and reduced neuronal cell number within critical centres responsible for the regulation of cardiovascular and respiratory functions. Elevated brainstem inflammation and oxidative stress suggest potential mechanisms contributing to the observed neuropathological changes. Both placental and brainstem levels of 5-HT were found to be impaired following FGR.

Perinatal asphyxia and hypothermic treatment from the endocrine perspective

Introduction

Perinatal asphyxia is one of the three most important causes of neonatal mortality and morbidity. Therapeutic hypothermia represents the standard treatment for infants with moderate-severe perinatal asphyxia, resulting in reduction in the mortality and major neurodevelopmental disability. So far, data in the literature focusing on the endocrine aspects of both asphyxia and hypothermia treatment at birth are scanty, and many aspects are still debated. Aim of this narrative review is to summarize the current knowledge regarding the short- and long-term effects of perinatal asphyxia and of hypothermia treatment on the endocrine system, thus providing suggestions for improving the management of asphyxiated children.

Results

Involvement of the endocrine system (especially glucose and electrolyte disturbances, adrenal hemorrhage, non-thyroidal illness syndrome) can occur in a variable percentage of subjects with perinatal asphyxia, potentially affecting mortality as well as neurological outcome. Hypothermia may also affect endocrine homeostasis, leading to a decreased incidence of hypocalcemia and an increased risk of dilutional hyponatremia and hypercalcemia.

Conclusions

Metabolic abnormalities in the context of perinatal asphyxia are important modifiable factors that may be associated with a worse outcome. Therefore, clinicians should be aware of the possible occurrence of endocrine complication, in order to establish appropriate screening protocols and allow timely treatment.

[Stress during prenatal and early postnatal period when everything begins]

Early severe stresses are known to affect the biological and psychological development in childhood. Good and adaptable stress during prenatal and early postnatal period can switch to traumatic during these highly susceptible developmental stages. These different stresses modulate genetic/epigenetic processes and the setting up of connectome during these highly plastic and adaptable time periods. The polyvagal processes control the base of the security/well-being perception of the newborn by the onset of synchronized interactions between the mother/parent/nurse and the baby. These positive adjustments in mirror lead to attachment and social links and to implicit learning processes leading to a balanced emotional and cognitive development.

Conformationally Flexible Dimeric-Serotonin-Based Sensitive and Selective Electrochemical Biosensing Strategy for Serotonin Recognition

A novel electrochemical sensor was constructed based on an enzyme-mediated physiological reaction between neurotransmitter serotonin per-oxidation to reconstruct dual-molecule 4,4'-dimeric-serotonin self-assembled derivative, and the potential biomedical application of the multi-functional nano-platform was explored. Serotonin accelerated the catalytic activity to form a dual molecule at the C4 position and created phenolic radical-radical coupling intermediates in a peroxidase reaction system. Here, 4,4' dimeric-serotonin possessed the capability to recognize intermolecular interactions between amine groups. The excellent quenching effects on top of the gold surface electrode system archive logically inexpensive and straightforward analytical demands. In biochemical sensing analysis, the serotonin dimerization concept demonstrated a robust, low-cost, and highly sensitive immunosensor, presenting the potential of quantifying serotonin at point-of-care (POC) testing. The high-specificity serotonin electrochemical sensor had a limit of detection (LOD) of 0.9 nM in phosphate buffer and 1.4 nM in human serum samples and a linear range of 10 to 400 with a sensitivity of 2.0 × 10^-2 nM. The bivalent 4,4'-dimer-serotonin interaction strategy provides a promising platform for serotonin biosensing with high specificity, sensitivity, selectivity, stability, and reproducibility. The self-assembling gold surface electrochemical system presents a new analytical method for explicitly detecting tiny neurotransmitter-responsive serotonin neuromolecules.

Neuroanatomy of the Will

Questions regarding the nature and source of consciousness and individual agency to make decisions have enormous practical implications that include human health and wellbeing, social policy, and economics. Ethical issues involving the ability for patients to make conscious, informed choices, such as in cases of dementia or coma, abound, and the health implications of individual choice on public wellbeing are becoming increasingly important as population densities increase. Furthermore, the use of animals for drug testing presents moral dilemmas related to our concepts of consciousness, pain, and consent. While philosophers have long debated aspects of consciousness, the means to scientifically address specific questions regarding regional and cellular functions of the brain are constantly emerging, as are new theories of physical laws and particle interactions which allow for the formation of new hypotheses of the source of consciousness. These emerging capabilities and hypotheses are increasingly able to be subjected to methodological scrutiny by the scientific community. To facilitate open discussion and advances in investigations regarding the nature of consciousness, this Topical Collection is intended to provide a peer-reviewed space to discuss or propose falsifiable hypotheses of consciousness in a full range of systems, using methods across disciplines of biology, physics, computer science, and philosophy of science that can inform such a discussion, while emphasizing the role that our conception of consciousness has on human health, society, and policy.

Sudden infant death syndrome: Melatonin, serotonin, and CD34 factor as possible diagnostic markers and prophylactic targets

Sudden infant death syndrome (SIDS) is one of the primary causes of death of infants in the first year of life. According to the WHO's data, the global infant mortality rate is 0.64-2 per 1,000 live-born children. Molecular and cellular aspects of SIDS development have not been identified so far. The purpose of this paper is to verify and analyze the expression of melatonin 1 and 2 receptors, serotonin (as a melatonin precursor), and CD34 molecules (as hematopoietic and endothelial markers of cardiovascular damage) in the medulla, heart, and aorta in infants who died from SIDS. An immunohistochemical method was used to investigate samples of medulla, heart, and aorta tissues of infants 3 to 9 months of age who died from SIDS. The control group included children who died from accidents. It has been shown that the expression of melatonin receptors as well as serotonin and CD34 angiogenesis markers in tissues of the medulla, heart, and aorta of infants who died from SIDS is statistically lower as compared with their expression in the same tissues in children who died from accidents. The obtained data help to clarify in detail the role of melatonin and such signaling molecules as serotonin and CD34 in SIDS pathogenesis, which can open new prospects for devising novel methods for predictive diagnosis of development and targeted prophylaxis of SIDS.

Nicotinic Receptors in the Brainstem Ascending Arousal System in SIDS With Analysis of Pre-natal Exposures to Maternal Smoking and Alcohol in High-Risk Populations of the Safe Passage Study

Pre-natal exposures to nicotine and alcohol are known risk factors for sudden infant death syndrome (SIDS), the leading cause of post-neonatal infant mortality. Here, we present data on nicotinic receptor binding, as determined by 125I-epibatidine receptor autoradiography, in the brainstems of infants dying of SIDS and of other known causes of death collected from the Safe Passage Study, a prospective, multicenter study with clinical sites in Cape Town, South Africa and 5 United States sites, including 2 American Indian Reservations. We examined 15 pons and medulla regions related to cardiovascular control and arousal in infants dying of SIDS (n = 12) and infants dying from known causes (n = 20, 10 pre-discharge from time of birth, 10 post-discharge). Overall, there was a developmental decrease in 125I-epibatidine binding with increasing postconceptional age in 5 medullary sites [raphe obscurus, gigantocellularis, paragigantocellularis, centralis, and dorsal accessory olive (p = 0.0002-0.03)], three of which are nuclei containing serotonin cells. Comparing SIDS with post-discharge known cause of death (post-KCOD) controls, we found significant decreased binding in SIDS in the nucleus pontis oralis (p = 0.02), a critical component of the cholinergic ascending arousal system of the rostral pons (post-KCOD, 12.1 ± 0.9 fmol/mg and SIDS, 9.1 ± 0.78 fmol/mg). In addition, we found an effect of maternal smoking in SIDS (n = 11) combined with post-KCOD controls (n = 8) on the raphe obscurus (p = 0.01), gigantocellularis (p = 0.02), and the paragigantocellularis (p = 0.002), three medullary sites found in this study to have decreased binding with age and found in previous studies to have abnormal indices of serotonin neurotransmission in SIDS infants. At these sites, 125I-epibatidine binding increased with increasing cigarettes per week. We found no effect of maternal drinking on 125I-epibatidine binding at any site measured. Taken together, these data support changes in nicotinic receptor binding related to development, cause of death, and exposure to maternal cigarette smoking. These data present new evidence in a prospective study supporting the roles of developmental factors, as well as adverse exposure on nicotinic receptors, in serotonergic nuclei of the rostral medulla-a finding that highlights the interwoven and complex relationship between acetylcholine (via nicotinic receptors) and serotonergic neurotransmission in the medulla.

The Serotonin Brainstem Hypothesis for the Sudden Infant Death Syndrome

The sudden infant death syndrome (SIDS) is the leading cause of postneonatal infant mortality in the United States today, with an overall rate of 0.39/1000 live births. It is defined as the sudden and unexpected death of an infant <12 months of age that remains unexplained after a complete autopsy, death scene investigation, and review of the clinical history. The serotonin brainstem hypothesis has been a leading hypothesis for SIDS over the last 2 decades. Our laboratory has studied this hypothesis over time with a variety of tissue techniques, including tissue receptor autoradiography, high performance liquid chromatography, Western blot analysis, immunocytochemistry, and proteomics. The purpose of this article is to review the progress in our laboratory toward supporting this hypothesis. We conclude that an important subset of SIDS infants has serotonergic abnormalities resulting from a "core lesion" in the medullary reticular formation comprised of nuclei that contain serotonin neurons. This lesion could lead to a failure of protective brainstem responses to homeostatic challenges during sleep in a critical developmental period which cause sleep-related sudden death.

The effects of perinatal SSRI exposure on anxious behavior and neurobiology in rodent and human offspring

While the postpartum period is typically associated with increased positive affect, many women will develop a depressive- or anxiety-related disorder during this time, which can degrade the mother-infant bond and lead to detrimental consequences for the infant. Given the potential for negative consequences, effective treatments have been critical, with selective serotonin reuptake inhibitors (SSRIs) being the most commonly-prescribed pharmaceutical agents to treat postpartum depression and anxiety. However, SSRIs can readily cross the placenta and are present in breast milk, so they might, therefore, unintentionally interact with the developing fetus/infant. There is already experimental evidence that perinatal SSRI exposure has a number of long-term effects on offspring, but this review focuses on the current literature examining the timing and consequences of perinatal SSRI exposure specifically on anxiety-like behaviors in rodents and humans, with an emphasis on the anxiety-related brain regions of the amygdala and hippocampus. This review also discusses discrepancies between the rodent and human literatures and how they might inform future studies. Finally, some key factors to consider when examining the role of perinatal SSRIs on offspring anxiety will be discussed, such as the duration of SSRI exposure and the potential neuroprotective effects of SSRIs. Given the extensive prescribing of SSRIs, the potential health consequences of perinatal SSRI exposure, and the discrepancies in the literature, it will be necessary to critically examine the factors underlying offspring anxiety outcomes.

The development of the serotonergic and dopaminergic systems during chicken mid-late embryogenesis

Serotonin (5-HT) acts as a morphogen influencing embryonic brain development, and as a neurotransmitter regulating multiple biological functions with lifelong effects on animal physical, physiological and mental health, especially during the rapid growth phase prior to birth when embryos face many challenges to reach structural and functional completion. In this study, the development of the serotoninergic (5-HTergic) system and its modulatory effect on the dopaminergic (DAergic) system and related neural circuits were investigated during the mid-late embryogenesis, embryonic day (E)12-E20, in the chicken's brain. During 5-HTergic neuronal maturation, a growth-related anatomical and functional remodeling was highlighted: the 5-HT neurons continuously grew during E12-E20 except for a remarkable regression during E14-E16. Correspondingly, there was a time-dependent change in the 5-HT synthetic capacity. Specifically, 5-HT concentrations in the raphe nuclei increased from E12 to E14, reaching a first plateau during E14-E16, then continuously increased up to E19, and reaching a second plateau between E19-E20. The second plateau of the 5-HT concentration was in correspondence with the establishment of the 5-HTergic autoregulatory loop during E19-E20 and the development of the DAergic system. The DA concentrations remained unchanged from E12 to E16, then started to increase at E16, reaching a maximum at E19, and diminished before hatching. The unique developing time sequence between the 5-HTergic and DAergic systems suggests that the 5-HTergic system may play a critical role in forming the 5-HT - DA neural circuit during chicken embryogenesis. These results provide new insights for understanding the functional organization of the 5-HTergic system during embryonic development and raise the possibility that prenatally modulating the 5-HTergic system may lead to long-lasting brain structural and functional alterations.

The ventrolateral medulla and medullary raphe in sudden unexpected death in epilepsy

Sudden unexpected death in epilepsy (SUDEP) is a leading cause of premature death in patients with epilepsy. One hypothesis proposes that sudden death is mediated by post-ictal central respiratory depression, which could relate to underlying pathology in key respiratory nuclei and/or their neuromodulators. Our aim was to investigate neuronal populations in the ventrolateral medulla (which includes the putative human pre-Bötzinger complex) and the medullary raphe. Forty brainstems were studied comprising four groups: 14 SUDEP, six epilepsy controls, seven Dravet syndrome cases and 13 non-epilepsy controls. Serial sections through the medulla (from obex 1 to 10 mm) were stained for Nissl, somatostatin, neurokinin 1 receptor (for pre-Bötzinger complex neurons) and galanin, tryptophan hydroxylase and serotonin transporter (neuromodulatory systems). Using stereology total neuronal number and densities, with respect to obex level, were measured. Whole slide scanning image analysis was used to quantify immunolabelling indices as well as co-localization between markers. Significant findings included reduction in somatostatin neurons and neurokinin 1 receptor labelling in the ventrolateral medulla in sudden death in epilepsy compared to controls (P < 0.05). Galanin and tryptophan hydroxylase labelling was also reduced in sudden death cases and more significantly in the ventrolateral medulla region than the raphe (P < 0.005 and P < 0.05). With serotonin transporter, reduction in labelling in cases of sudden death in epilepsy was noted only in the raphe (P ≤ 0.01); however, co-localization with tryptophan hydroxylase was significantly reduced in the ventrolateral medulla. Epilepsy controls and cases with Dravet syndrome showed less significant alterations with differences from non-epilepsy controls noted only for somatostatin in the ventrolateral medulla (P < 0.05). Variations in labelling with respect to obex level were noted of potential relevance to the rostro-caudal organization of respiratory nuclear groups, including tryptophan hydroxylase, where the greatest statistical difference noted between all epilepsy cases and controls was at obex 9-10 mm (P = 0.034), the putative level of the pre-Bötzinger complex. Furthermore, there was evidence for variation with duration of epilepsy for somatostatin and neurokinin 1 receptor. Our findings suggest alteration to neuronal populations in the medulla in SUDEP with evidence for greater reduction in neuromodulatory neuropeptidergic and mono-aminergic systems, including for galanin, and serotonin. Other nuclei need to be investigated to evaluate if this is part of more widespread brainstem pathology. Our findings could be a result of previous seizures and may represent a pathological risk factor for SUDEP through impaired respiratory homeostasis during a seizure.

Variability of the medullary arcuate nucleus in humans

INTRODUCTION

The arcuate nucleus is a component of the ventral medullary surface involved in chemoreception and breathing control. The hypoplasia of this nucleus is a very frequent finding in victims of sudden unexplained fetal and infant death (from the last weeks of pregnancy to the first year of life). On the contrary, this developmental alteration is rarely present in age-matched controls who died of defined causes. These observations lead to hypothesize that a well-developed and functional arcuate nucleus is generally required to sustain life. The aim of this study was to investigate whether the arcuate nucleus maintains the same supposed function throughout life.

METHODS

We carried out neuropathological examinations of brainstems obtained from 25 adult subjects, 18 males and 7 females, aged between 34 and 89 years, who died from various causes.

RESULTS

For almost half of the cases (44%) microscopic examinations of serial histological sections of medulla oblongata showed a normal cytoarchitecture of the arcuate nucleus, extending along the pyramids. For the remaining 56% of cases, various degrees of hypodevelopment of this nucleus were observed, validated through the application of quantitative morphometric investigations, from decreased area, neuron number and volume, to full aplasia.

CONCLUSIONS

These unexpected findings indicate that the involvement of the arcuate nucleus in chemoreception in adulthood is questionable, given the possibility of living until late age without this nucleus. This opens new perspectives for researchers on the role and function of the arcuate nucleus in humans from birth to old age.

Serotonin neuron development: shaping molecular and structural identities

The continuing fascination with serotonin (5-hydroxytryptamine, 5-HT) as a nervous system chemical messenger began with its discovery in the brains of mammals in 1953. Among the many reasons for this decades-long interest is that the small numbers of neurons that make 5-HT influence the excitability of neural circuits in nearly every region of the brain and spinal cord. A further reason is that 5-HT dysfunction has been linked to a range of psychiatric and neurological disorders many of which have a neurodevelopmental component. This has led to intense interest in understanding 5-HT neuron development with the aim of determining whether early alterations in their generation lead to brain disease susceptibility. Here, we present an overview of the neuroanatomical organization of vertebrate 5-HT neurons, their neurogenesis, and prodigious axonal architectures, which enables the expansive reach of 5-HT neuromodulation in the central nervous system. We review recent findings that have revealed the molecular basis for the tremendous diversity of 5-HT neuron subtypes, the impact of environmental factors on 5-HT neuron development, and how 5-HT axons are topographically organized through disparate signaling pathways. We summarize studies of the gene regulatory networks that control the differentiation, maturation, and maintenance of 5-HT neurons. These studies show that the regulatory factors controlling acquisition of 5-HT-type transmitter identity continue to play critical roles in the functional maturation and the maintenance of 5-HT neurons. New insights are presented into how continuously expressed 5-HT regulatory factors control 5-HT neurons at different stages of life and how the regulatory networks themselves are maintained. WIREs Dev Biol 2018, 7:e301. doi: 10.1002/wdev.301 This article is categorized under: Nervous System Development > Vertebrates: General Principles Gene Expression and Transcriptional Hierarchies > Gene Networks and Genomics Gene Expression and Transcriptional Hierarchies > Cellular Differentiation Nervous System Development > Secondary: Vertebrates: Regional Development.

Some Autonomic Deficits of Acute or Chronic Cervical Spinal Contusion Reversed by Interim Brainstem Stimulation

Prolonged electrical stimulation of the hindbrain's nucleus raphe magnus (NRM) or of its major midbrain input region, the periaqueductal gray (PAG), was previously found in rats to promote recovery from sensory-motor and histological deficits of acute thoracic spinal cord injury (SCI). Here, some visceral deficits of acute and chronic midline cervical (C5) contusion are similarly examined. Cranially implanted wireless stimulators delivered intermittent 8 Hz, 30-70 μA cathodal pulse trains to a brainstem microelectrode. Injured controls were given inactive stimulators; rats without injuries or implants were also compared. Rectal distension or squeezing of the forepaws caused an exaggerated rise in mean arterial pressure in injured, untreated rats under anesthesia on post-injury week 6, probably reflecting autonomic dysreflexia (AD). These pressor responses became normal when 7 days of unilateral PAG stimulation was started on the injury day. Older untreated injuries (weeks 18-19) showed normal pressor responses, but unexpectedly had significant resting and nociceptive bradycardia, which was reversed by 3 weeks of PAG stimulation started on weeks 7 or 12. Subsequent chronic studies examined gastric emptying (GE), as indicated by intestinal transit of gavaged dye, and serum chemistry. GE and fasting serum insulin were reduced on injury weeks 14-15, and were both normalized by ∼5 weeks of PAG stimulation begun in weeks 7-8. Increases in calcitonin gene-related peptide, a prominent visceral afferent neurotransmitter, measured near untreated injuries (first thoracic segment) in superficial dorsal laminae were reversed by acutely or chronically initiated PAG stimulation. The NRM, given 2-3 weeks of stimulation beginning 2 days after SCI, prevented abnormalities in both pressor responses and GE on post-injury week 9, consistent with its relaying of repair commands from the PAG. The descending PAG-NRM axis thus exhibits broadly restorative influences on visceral as well as sensory-motor deficits, improving chronic as well as acute signs of injury.

Necdin shapes serotonergic development and SERT activity modulating breathing in a mouse model for Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a genetic neurodevelopmental disorder that presents with hypotonia and respiratory distress in neonates. The Necdin-deficient mouse is the only model that reproduces the respiratory phenotype of PWS (central apnea and blunted response to respiratory challenges). Here, we report that Necdin deletion disturbs the migration of serotonin (5-HT) neuronal precursors, leading to altered global serotonergic neuroarchitecture and increased spontaneous firing of 5-HT neurons. We show an increased expression and activity of 5-HT Transporter (SERT/Slc6a4) in 5-HT neurons leading to an increase of 5-HT uptake. In Necdin-KO pups, the genetic deletion of Slc6a4 or treatment with Fluoxetine, a 5-HT reuptake inhibitor, restored normal breathing. Unexpectedly, Fluoxetine administration was associated with respiratory side effects in wild-type animals. Overall, our results demonstrate that an increase of SERT activity is sufficient to cause the apneas in Necdin-KO pups, and that fluoxetine may offer therapeutic benefits to PWS patients with respiratory complications.

Prader-Willi syndrome results from the disruption of a cluster of neighboring genes, including one called Necdin. Symptoms begin in early infancy and worsen with age. Affected children tend to develop an insatiable appetite, which often leads to obesity. They also experience serious problems with their breathing. Chest infections, high altitude and intense physical activity can be dangerous for children with Prader-Willi syndrome. This is because a slight shortage of oxygen may trigger breathing difficulties that could prove fatal.

The brain cells that produce a chemical messenger called serotonin help to control breathing. Several lines of evidence suggest that loss of Necdin may trigger breathing difficulties in Prader-Willi syndrome via effects on the serotonin system. First, serotonin neurons produce the Necdin protein. Second, laboratory mice that lack the gene for Necdin have abnormally shaped serotonin neurons. Third, these mice show breathing difficulties like those of individuals with Prader-Willi syndrome. But while this implies a connection between serotonin, Necdin and breathing difficulties, it falls short of establishing a causal link.

Matarazzo et al. now reveal an increase in the quantity and activity of a protein called the serotonin transporter in mutant mice that lacked the gene for Necdin compared to normal mice. Serotonin transporter proteins mop up the serotonin that neurons release when they signal to one another. Neurons in the mutant mice take up more serotonin than their counterparts in normal mice; this means they have less serotonin available for signaling. This may make it harder for the mutant mice to regulate their breathing.

Drugs called selective serotonin-reuptake inhibitors (or SSRIs for short) can block the serotonin transporter. These drugs, which include Fluoxetine (also called Prozac), are antidepressants. Matarazzo et al. show that SSRIs temporarily restore normal breathing in young mice that lack the gene for Necdin. However, these drugs have harmful long-term effects on breathing in non-mutant mice. Further studies should test whether short-term use of SSRIs could offer immediate relief for breathing difficulties in infants and children with Prader-Willi syndrome.

Medullary Serotonin Neuron Abnormalities in an Australian Cohort of Sudden Infant Death Syndrome

Serotonin (5-hydroxytryptamine [5-HT]) neurons in the medulla oblongata project extensively to key autonomic and respiratory nuclei in the brainstem and spinal cord regulating critical homeostatic functions. Multiple abnormalities in markers of 5-HT function in the medulla in sudden infant death syndrome (SIDS) have been reported, informing the hypothesis that at least a subset of SIDS cases is caused by deficits in 5-HT function resulting in impaired homeostatic responses to potentially life-threatening events during sleep. To investigate medullary 5-HT defects in SIDS further, we undertook qualitative analysis immunohistochemical assessment of 5-HT neuron expression within the medulla of SIDS infants (n41) and nonSIDS controls (n = 28) in an independent cohort from Forensic Science South Australia. Compared with controls SIDS cases had significantly higher 5-HT neuron numbers and density in addition to significantly altered 5-HT neuron morphology. Thus, for the first time, we replicated and corroborated previous observations of a significant abnormality in medullary 5-HT neuron expression in SIDS in a separate independent SIDS cohort. This study further supports the hypothesis that medullary 5-HT defects contribute to the pathogenesis of a subset of SIDS victims and provides additional evidence of a more complex abnormality in 5-HT neuron dysfunction specifically within the different caudal and rostral medullary 5-HT domains.

Key Brainstem Structures Activated during Hypoxic Exposure in One-day-old Mice Highlight Characteristics for Modeling Breathing Network in Premature Infants

We mapped and characterized changes in the activity of brainstem cell groups under hypoxia in one-day-old newborn mice, an animal model in which the central nervous system at birth is particularly immature. The classical biphasic respiratory response characterized by transient hyperventilation, followed by severe ventilation decline, was associated with increased c-FOS immunoreactivity in brainstem cell groups: the nucleus of the solitary tract, ventral reticular nucleus of the medulla, retrotrapezoid/parafacial region, parapyramidal group, raphe magnus nucleus, lateral, and medial parabrachial nucleus, and dorsal subcoeruleus nucleus. In contrast, the hypoglossal nucleus displayed decreased c-FOS immunoreactivity. There were fewer or no activated catecholaminergic cells activated in the medulla oblongata, whereas ~45% of the c-FOS-positive cells in the dorsal subcoeruleus were co-labeled. Approximately 30% of the c-FOS-positive cells in the parapyramidal group were serotoninergic, whereas only a small portion were labeled for serotonin in the raphe magnus nucleus. None of the c-FOS-positive cells in the retrotrapezoid/parafacial region were co-labeled for PHOX2B. Thus, the hypoxia-activated brainstem neuronal network of one-day-old mice is characterized by (i) the activation of catecholaminergic cells of the dorsal subcoeruleus nucleus, a structure implicated in the strong depressive pontine influence previously reported in the fetus but not in newborns, (ii) the weak activation of catecholaminergic cells of the ventral reticular nucleus of the medulla, an area involved in hypoxic hyperventilation, and (iii) the absence of PHOX2B-positive cells activated in the retrotrapezoid/parafacial region. Based on these results, one-day-old mice could highlight characteristics for modeling the breathing network of premature infants.

Infants dying suddenly and unexpectedly share demographic features with infants who die with retinal and dural bleeding: a review of neural mechanisms

The cause of death in infants who die suddenly and unexpectedly (sudden unexpected death in infancy [SUDI]) remains a diagnostic challenge. Some infants have identified diseases (explained SUDI); those without explanation are called sudden infant death syndrome (SIDS). Demographic data indicate subgroups among SUDI and SIDS cases, such as unsafe sleeping and apparent life-threatening events. Infants dying suddenly with retinal and dural bleeding are often classified as abused, but in many there is no evidence of trauma. Demographic features suggest that they may represent a further subgroup of SUDI. This review examines the neuropathological hypotheses to explain SIDS and highlights the interaction of infant oxygen-conserving reflexes with the brainstem networks considered responsible for SIDS. We consider sex- and age-specific vulnerabilities related to dural bleeding and how sensitization of the dural innervation by bleeding may influence these reflexes, potentially leading to collapse or even death after otherwise trivial insults.

Serotonin Receptors in the Medulla Oblongata of the Human Fetus and Infant: The Analytic Approach of the International Safe Passage Study

The Safe Passage Study is an international, prospective study of approximately 12 000 pregnancies to determine the effects of prenatal alcohol exposure (PAE) upon stillbirth and the sudden infant death syndrome (SIDS). A key objective of the study is to elucidate adverse effects of PAE upon binding to serotonin (5-HT) 1A receptors in brainstem homeostatic networks postulated to be abnormal in unexplained stillbirth and/or SIDS. We undertook a feasibility assessment of 5-HT_1A receptor binding using autoradiography in the medulla oblongata (6 nuclei in 27 cases). 5-HT_1A binding was compared to a reference dataset from the San Diego medical examiner’s system. There was no adverse effect of postmortem interval ≤100 h. The distribution and quantitated values of 5-HT_1A binding in Safe Passage Study cases were essentially identical to those in the reference dataset, and virtually identical between stillbirths and live born fetal cases in grossly non-macerated tissues. The pattern of binding was present at mid-gestation with dramatic changes in binding levels in the medullary 5-HT nuclei over the second half of gestation; there was a plateau at lower levels in the neonatal period and into infancy. This study demonstrates feasibility of 5-HT_1A binding analysis in the medulla in the Safe Passage Study.

Synaptogenesis and Myelination in the Nucleus/Tractus Solitarius: Potential Role in Apnea of Prematurity, Congenital Central Hypoventilation, and Sudden Infant Death Syndrome

Fetuses as early as 15 weeks' gestation exhibit rhythmical respiratory movements shown by real-time ultrasonography. The nucleus/tractus solitarius is the principal brainstem respiratory center; other medullary nuclei also participate. The purpose was to determine temporal maturation of synaptogenesis. Delayed synaptic maturation may explain neurogenic apnea or hypoventilation of prematurity and some cases of sudden infant death syndrome. Sections of medulla oblongata were studied from 30 human fetal and neonatal brains 9 to 41 weeks' gestation. Synaptophysin demonstrated the immunocytochemical sequence of synaptogenesis. Other neuronal markers and myelin stain also were applied. The nucleus/tractus solitarius was similarly studied in fetuses with chromosomopathies, metabolic encephalopathies, and brain malformations. Synapse formation in the nucleus solitarius begins at about 12 weeks' gestation and matures by 15 weeks; myelination initiated at 33 weeks. Synaptogenesis was delayed in 3 fetuses with different conditions, but was not specific for only nucleus solitarius. Delayed synaptogenesis or myelination in the nucleus solitarius may play a role in neonatal hypoventilation, especially in preterm infants and in some sudden infant death syndrome cases.

Pediatric Sudden Unexpected Death in Epilepsy

BACKGROUND

Epilepsy is a common neurological disorder among children and adolescents that is associated with increased mortality for numerous reasons. Sudden unexpected death in epilepsy is a critically important entity for physicians who treat patients with epilepsy. Many pediatric neurologists are hesitant to discuss this condition with patients and families because of the lower risk in the pediatric age group.

METHODS

We searched for studies published between January 2000 and June 2015 by means of a PubMed search and a cumulative review of reference lists of all relevant publications, using the keywords "sudden unexpected death in epilepsy patients," "pediatric SUDEP," "sudden unexpected death in epilepsy patients and children," "sudden unexpected death in children" and "sudden infant death syndrome."

RESULTS

SUDEP is a rare condition in children. Its mechanism is poorly understood and may have a distinct pathogenesis from adult sudden unexpected death in epilepsy. Limited comfort, experience, and knowledge to provide appropriate education about sudden unexpected death in epilepsy leads to fewer physicians discussing this subject leading to less informed and less prepared patients and families.

CONCLUSION

We provide a detailed review of the literature on pediatric SUDEP, including the definition, classification, and proposed mechanisms of sudden unexpected death in epilepsy in children, as well as discuss the incidence in the pediatric population and risk factors in children, concluding with possible prevention strategies.

Self-transcendence trait and its relationship with in vivo serotonin transporter availability in brainstem raphe nuclei: An ultra-high resolution PET-MRI study

Self-transcendence is an inherent human personality trait relating to the experience of spiritual aspects of the self. We examined the relationship between self-transcendence and serotonin transporter (SERT) availability in brainstem raphe nuclei, which are collections of five different serotonergic nuclei with rostro-caudal extension, using ultra-high resolution magnetic resonance imaging (MRI) and positron emission tomography (PET) with (11)C-3-amino-4-(2-dimethylaminomethylphenylthio)benzonitrile ([(11)C]DASB) to elucidate potential roles of serotonergic neuronal activities in this personality trait. Sixteen healthy subjects completed 7.0T MRI and High Resolution Research Tomograph (HRRT) PET. The regions of interest (ROIs) included the dorsal raphe nucleus (R1), median raphe nucleus (R2), raphe pontis (R3), and the caudal raphe nuclei (R4 and R5). For the estimation of SERT availability, the binding potential (BPND) was derived using the simplified reference tissue model (SRTM2). The Temperament and Character Inventory was used to measure self-transcendence. The analysis revealed that the self-transcendence total score had a significant negative correlation with the [(11)C]DASB BPND in the caudal raphe (R5). The subscale score for spiritual acceptance was significantly negatively correlated with the [(11)C]DASB BPND in the median raphe nucleus (R2). The results indicate that the self-transcendence trait is associated with SERT availability in specific raphe subnuclei, suggesting that the serotonin system may serve as an important biological basis for human self-transcendence. Based on the connections of these nuclei with cortico-limbic and visceral autonomic structures, the functional activity of these nuclei and their related neural circuitry may play a crucial role in the manifestation of self-transcendence.

Developmental exposure to paracetamol causes biochemical alterations in medulla oblongata

The effect and safety of prenatal and early life administration of paracetamol - routinely used over-the-counter antipyretic and analgesic medication on monoamines content and balance of amino acids in the medulla oblongata is still unknown. In this study we have determined the level of neurotransmitters in this structure in two-month old Wistar male rats exposed to paracetamol in the dose of 5 (P5, n=10) or 15mg/kg b.w. (P15, n=10) during prenatal period, lactation and till the end of the second month of life. Control group received drinking water (Con, n=10). Monoamines, their metabolites and amino acids concentration in medulla oblongata of rats were determined using high performance liquid chromatography (HPLC) in 60 postnatal day (PND60). This experiment shows that prenatal and early life paracetamol exposure modulates neurotransmission associated with serotonergic, noradrenergic and dopaminergic system in medulla oblongata. Reduction of alanine and taurine levels has also been established.

Sudden infant death syndrome, sleep, and seizures

benign febrile seizures seen in 7% of infants before 6 months play a role in the terminal pathway in a subset of sudden infant death syndrome victims. Supporting evidence: (1) lack of 5-hydroxitryptamine, one consistent finding in sudden infant death syndrome that Kinney et al coined a developmental serotonopathy, is consistent with risk for seizures. (2) Non-rapid eye movement sleep increasing during the age of highest risk for sudden infant death syndrome facilitates some seizures (seizure gate). (3) Sudden unexpected death in epilepsy is associated with severe hypoxemia and hypercapnia during postictal generalized electroencephalographic (EEG) suppression. In toddlers, sudden unexplained deaths are associated with hippocampal abnormalities and some seizures. (4) The sudden nature of both deaths warrants an exploration of similarities in the terminal pathway. Moreover, sudden infant death syndrome, febrile seizures, sudden unexplained death in childhood, and sudden unexpected death in epilepsy share some of the following risk factors: prone sleeping, infections, hyperthermia, preterm birth, male gender, maternal smoking, and mutations in genes that regulate sodium channels. State-of-the-art molecular studies can be exploited to test this hypothesis.

Complex brain malformations associated with chromosome 6q27 gain that includes THBS2, which encodes thrombospondin 2, an astrocyte-derived protein of the extracellular matrix

This case describes the autopsy findings of a 2-month-old male infant with extensive and severe developmental brain abnormalities, including microcephaly, neocortical neuronal layering abnormalities, leptomeningeal heterotopias, commissural agenesis, and cerebellar and brainstem hypoplasia. Microarray analysis identified a gain in chromosome band 6q27, which includes the entire coding region of THBS2. THSB2 encodes thrombospondin 2 (TSP2), an astrocyte secreted protein of the extracellular matrix that promotes synaptogenesis, neurite outgrowth, and cerebellar granule cell migration. Thrombospondin 2 is not a matrix structural protein; instead it serves as an extracellular modulator of cell function, so it is considered a matricellular protein. The neuropathological findings at autopsy are compatible with perturbations in several known functions of TSP2 and demonstrate that TSP2 dysregulation can have a significant negative impact on human brain development. Furthermore, this case demonstrates the important role of astrocytes in human brain development.

Deficits of brainstem and spinal cord functions after neonatal hypoxia-ischemia in mice

BACKGROUND

Perinatal cerebral hypoxia-ischemia (HI) can lead to severe neurodevelopmental disorders. Studies in humans and animal models mainly focused on cerebral outcomes, and little is known about the mechanisms that may affect the brainstem and the spinal cord. Dysfunctions of neuromodulatory systems, such as the serotonergic (5-HT) projections, critical for the development of neural networks, have been postulated to underlie behavioral and motor deficits, as well as metabolic changes.

METHODS

The aim of this study was to investigate brainstem and spinal cord functions by means of plethysmography and sensorimotor tests in a neonatal Rice-Vanucci model of HI in mice. We also evaluated bioaminergic contents in central regions dedicated to the motor control of autonomic functions.

RESULTS

Mice with cerebral infarct expressed motor disturbances and had a lower body weight and a decreased respiratory frequency than SHAM, suggesting defects of brainstem neural network involved in the motor control of feeding, suckling, swallowing, and respiration. Moreover, our study revealed changes of monoamine and amino acid contents in the brainstem and the spinal cord of HI mice.

CONCLUSION

Our results suggest that monoaminergic neuromodulation plays an important role in the physiopathology of HI brain injury that may represent a good therapeutic target.

Serotonin metabolites in the cerebrospinal fluid in sudden infant death syndrome

Forensic biomarkers are needed in sudden infant death syndrome (SIDS) to help identify this group among other sudden unexpected deaths in infancy. Previously, we reported multiple serotonergic (5-HT) abnormalities in nuclei of the medulla oblongata that help mediate protective responses to homeostatic stressors. As a first step toward their assessment as forensic biomarkers of medullary pathology, here we test the hypothesis that 5-HT-related measures are abnormal in the cerebrospinal fluid (CSF) of SIDS infants compared with those of autopsy controls. Levels of CSF 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA), the degradative products of 5-HT and dopamine, respectively, were measured by high-performance liquid chromatography in 52 SIDS and 29 non-SIDS autopsy cases. Tryptophan (Trp) and tyrosine (Tyr), the substrates of 5-HT and dopamine, respectively, were also measured. There were no significant differences in 5-HIAA, Trp, HVA, or Tyr levels between the SIDS and non-SIDS groups. These data preclude the use of 5-HIAA, HVA, Trp, or Tyr measurements as CSF autopsy biomarkers of 5-HT medullary pathology in infants who have died suddenly and unexpectedly. They do, however, provide important information about monoaminergic measurements in human CSF at autopsy and their developmental profile in infancy that is applicable to multiple pediatric disorders beyond SIDS.

Lasting neurobehavioral abnormalities in rats after neonatal activation of serotonin 1A and 1B receptors: possible mechanisms for serotonin dysfunction in autistic spectrum disorders

RATIONALE

Perinatal exposure of rats to selective serotonin reuptake inhibitors (SSRIs) produces sensory and social abnormalities paralleling those seen in autistic spectrum disorders (ASDs). However, the possible mechanism(s) by which this exposure produces behavioral abnormalities is unclear.

OBJECTIVE

We hypothesized that the lasting effects of neonatal SSRI exposure are a consequence of abnormal stimulation of 5-HT1A and/or 5-HT1B receptors during brain development. We examined whether such stimulation would result in lasting sensory and social deficits in rats in a manner similar to SSRIs using both direct agonist stimulation of receptors as well as selective antagonism of these receptors during SSRI exposure.

METHODS

Male and female rat pups were treated from postnatal days 8 to 21. In Experiment 1, pups received citalopram (20 mg/kg/day), saline, (±)-8-hydroxy-dipropylaminotetralin hydrobromide (8-OH-DPAT; 0.5 mg/kg/day) or 7-trifluoromethyl-4(4-methyl-1-piperazinyl)-pyrrolo[1,2-a]-quinoxaline dimaleate (CGS-12066B; 10 mg/kg/day). In Experiment 2, a separate cohort of pups received citalopram (20 mg/kg/day), or saline which was combined with either N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinylcyclo-hexanecarboxamide maleate (WAY-100635; 0.6 mg/kg/day) or N-[4-methoxy-3-(4-methyl-1-piperazinyl)phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)-1-1'-biphenyl-4-carboxamide (GR-127935; 6 mg/kg/day) or vehicle. Rats were then tested in paradigms designed to assess sensory and social response behaviors at different time points during development.

RESULTS

Direct and indirect neonatal stimulation of 5-HT1A or 5-HT1B receptors disrupts sensory processing, produces neophobia, increases stereotypic activity, and impairs social interactions in manner analogous to that observed in ASD.

CONCLUSION

Increased stimulation of 5-HT1A and 5-HT1B receptors plays a significant role in the production of lasting social and sensory deficits in adult animals exposed as neonates to SSRIs.

Potential asphyxia and brainstem abnormalities in sudden and unexpected death in infants

OBJECTIVE

Sudden and unexplained death is a leading cause of infant mortality. Certain characteristics of the sleep environment increase the risk for sleep-related sudden and unexplained infant death. These characteristics have the potential to generate asphyxial conditions. We tested the hypothesis that infants may be exposed to differing degrees of asphyxia in sleep environments, such that vulnerable infants with a severe underlying brainstem deficiency in serotonergic, γ-aminobutyric acid-ergic, or 14-3-3 transduction proteins succumb even without asphyxial triggers (e.g., supine), whereas infants with intermediate or borderline brainstem deficiencies require asphyxial stressors to precipitate death.

METHODS

We classified cases of sudden infant death into categories relative to a "potential asphyxia" schema in a cohort autopsied at the San Diego County Medical Examiner's Office. Controls were infants who died with known causes of death established at autopsy. Analysis of covariance tested for differences between groups.

RESULTS

Medullary neurochemical abnormalities were present in both infants dying suddenly in circumstances consistent with asphyxia and infants dying suddenly without obvious asphyxia-generating circumstances. There were no differences in the mean neurochemical measures between these 2 groups, although mean measures were both significantly lower (P < .05) than those of controls dying of known causes.

CONCLUSIONS

We found no direct relationship between the presence of potentially asphyxia conditions in the sleep environment and brainstem abnormalities in infants dying suddenly and unexpectedly. Brainstem abnormalities were associated with both asphyxia-generating and non-asphyxia generating conditions. Heeding safe sleep messages is essential for all infants, especially given our current inability to detect underlying vulnerabilities.

Medullary serotonin neurons are CO2 sensitive in situ

Brainstem central chemoreceptors are critical to the hypercapnic ventilatory response, but their location and identity are poorly understood. When studied in vitro, serotonin-synthesizing (5-HT) neurons within the rat medullary raphé are intrinsically stimulated by CO2/acidosis. The contributions of these neurons to central chemosensitivity in vivo, however, are controversial. Lacking is documentation of CO2-sensitive 5-HT neurons in intact experimental preparations and understanding of their spatial and proportional distribution. Here we test the hypothesis that 5-HT neurons in the rat medullary raphé are sensitive to arterial hypercapnia. We use extracellular recording and hypercapnic challenge of spontaneously active medullary raphé neurons in the unanesthetized in situ perfused decerebrate brainstem preparation to assess chemosensitivity of individual cells. Juxtacellular labeling of a subset of recorded neurons and subsequent immunohistochemistry for the 5-HT-synthesizing enzyme tryptophan hydroxylase (TPH) identify or exclude this neurotransmitter phenotype in electrophysiologically characterized chemosensitive and insensitive cells. We show that the medullary raphé houses a heterogeneous population, including chemosensitive and insensitive 5-HT neurons. Of 124 recorded cells, 16 cells were juxtacellularly filled, visualized, and immunohistochemically identified as 5-HT synthesizing, based on TPH-immunoreactivity. Forty-four percent of 5-HT cells were CO2 stimulated (increased firing rate with hypercapnia), while 56% were unstimulated. Our results demonstrate that medullary raphé neurons are heterogeneous and clearly include a subset of 5-HT neurons that are excited by arterial hypercapnia. Together with data identifying intrinsically CO2-sensitive 5-HT neurons in vitro, these results support a role for such cells as central chemoreceptors in the intact system.

Serotonin gene variants are unlikely to play a significant role in the pathogenesis of the sudden infant death syndrome

Sudden infant death syndrome (SIDS) is defined as the sudden and unexpected death of an infant less than 12 months of age that is related to a sleep period and remains unexplained after a complete autopsy, death scene investigation, and review of the clinical history. The cause of SIDS is unknown, but a major subset of SIDS is proposed to result from abnormalities in serotonin (5-HT) and related neurotransmitters in regions of the lower brainstem that result in failure of protective homeostatic responses to life-threatening challenges during sleep. Multiple studies have implicated gene variants that affect different elements of 5-HT neurotransmission in the pathogenesis of these abnormalities in SIDS. In this review I discuss the data from these studies together with some new data correlating genotype with brainstem 5-HT neurochemistry in the same SIDS cases and conclude that these gene variants are unlikely to play a major role in the pathogenesis of the medullary 5-HT abnormalities observed in SIDS.

Development of brainstem 5-HT1A receptor-binding sites in serotonin-deficient mice

The sudden infant death syndrome is associated with a reduction in brainstem serotonin 5-hydroxytryptamine (5-HT) and 5-HT(1A) receptor binding, yet it is unknown if and how these findings are linked. In this study, we used quantitative tissue autoradiography to determine if post-natal development of brainstem 5-HT(1A) receptors is altered in two mouse models where the development of 5-HT neurons is defective, the Lmx1b(f/f/p) , and the Pet-1⁻/⁻ mouse. 5-HT(1A) receptor agonist-binding sites were examined in both 5-HT-source nuclei (autoreceptors) and in sites that receive 5-HT innervation (heteroreceptors). In control mice between post-natal day (P) 3 and 10, 5-HT(1A) receptor binding increased in several brainstem sites; by P25, there were region-specific increases and decreases, refining the overall binding pattern. In the Lmx1b(f/f/p) and Pet-1⁻/⁻ mice, 5-HT(1A)-autoreceptor binding was significantly lower than in control mice at P3, and remained low at P10 and P25. In contrast, 5-HT(1A) heteroreceptor levels were comparable between control and 5-HT-deficient mice. These data define the post-natal development of 5-HT(1A)-receptor binding in the mouse brainstem. Furthermore, the data suggest that 5-HT(1A)-heteroreceptor deficits detected in sudden infant death syndrome are not a direct consequence of a 5-HT neuron dysfunction nor reduced brain 5-HT levels. To elucidate the developmental relationship between serotonin (5-HT) levels and 5-HT(1A) receptors in the brainstem, we examined 5-HT(1A) binding in two 5-HT-deficient mouse models. In nuclei containing 5-HT neurons, 5-HT(1A) binding was decreased (autoreceptors), while binding was maintained in projection sites (heteroreceptors). Thus, brainstem 5-HT(1A)-heteroreceptor-binding sites do not appear developmentally sensitive to reduced brain 5-HT levels.

The physiological determinants of sudden infant death syndrome

It is well-established that environmental and biological risk factors contribute to Sudden Infant Death Syndrome (SIDS). There is also growing consensus that SIDS requires the intersection of multiple risk factors that result in the failure of an infant to overcome cardio-respiratory challenges. Thus, the critical next steps in understanding SIDS are to unravel the physiological determinants that actually cause the sudden death, to synthesize how these determinants are affected by the known risk factors, and to develop novel ideas for SIDS prevention. In this review, we will examine current and emerging perspectives related to cardio-respiratory dysfunctions in SIDS. Specifically, we will review: (1) the role of the preBötzinger complex (preBötC) as a multi-functional network that is critically involved in the failure to adequately respond to hypoxic and hypercapnic challenges; (2) the potential involvement of the preBötC in the gender and age distributions that are characteristic for SIDS; (3) the link between SIDS and prematurity; and (4) the potential relationship between SIDS, auditory function, and central chemosensitivity. Each section underscores the importance of marrying the epidemiological and pathological data to experimental data in order to understand the physiological determinants of this syndrome. We hope that a better understanding will lead to novel ways to reduce the risk to succumb to SIDS.

Disruption of the serotonergic system after neonatal hypoxia-ischemia in a rodent model

Identifying which specific neuronal phenotypes are vulnerable to neonatal hypoxia-ischemia, where in the brain they are damaged, and the mechanisms that produce neuronal losses are critical to determine the anatomical substrates responsible for neurological impairments in hypoxic-ischemic brain-injured neonates. Here we describe our current work investigating how the serotonergic network in the brain is disrupted in a rodent model of preterm hypoxia-ischemia. One week after postnatal day 3 hypoxia-ischemia, losses of serotonergic raphé neurons, reductions in serotonin levels in the brain, and reduced serotonin transporter expression are evident. These changes can be prevented using two anti-inflammatory interventions; the postinsult administration of minocycline or ibuprofen. However, each drug has its own limitations and benefits for use in neonates to stem damage to the serotonergic network after hypoxia-ischemia. By understanding the fundamental mechanisms underpinning hypoxia-ischemia-induced serotonergic damage we will hopefully move closer to developing a successful clinical intervention to treat neonatal brain injury.

The "Shaken Baby" syndrome: pathology and mechanisms

The "Shaken Baby" syndrome (SBS) is the subject of intense controversy; the diagnosis has in the past depended on the triad of subdural haemorrhage (SDH), retinal haemorrhage and encephalopathy. While there is no doubt that infants do suffer abusive injury at the hands of their carers and that impact can cause catastrophic intracranial damage, research has repeatedly undermined the hypothesis that shaking per se can cause this triad. The term non-accidental head injury has therefore been widely adopted. This review will focus on the pathology and mechanisms of the three physiologically associated findings which constitute the "triad" and are seen in infants suffering from a wide range of non-traumatic as well as traumatic conditions. "Sub" dural bleeding in fact originates within the deep layers of the dura. The potential sources of SDH include: the bridging veins, small vessels within the dura itself, a granulating haemorrhagic membrane and ruptured intracranial aneurysm. Most neuropathologists do not routinely examine eyes, but the significance of this second arm of the triad in the diagnosis of Shaken Baby syndrome is such that it merits consideration in the context of this review. While retinal haemorrhage can be seen clinically, dural and subarachnoid optic nerve sheath haemorrhage is usually seen exclusively by the pathologist and only rarely described by the neuroradiologist. The term encephalopathy is used loosely in the context of SBS. It may encompass anything from vomiting, irritability, feeding difficulties or floppiness to seizures, apnoea and fulminant brain swelling. The spectrum of brain pathology associated with retinal and subdural bleeding from a variety of causes is described. The most important cerebral pathology is swelling and hypoxic-ischaemic injury. Mechanical shearing injury is rare and contusions, the hallmark of adult traumatic brain damage, are vanishingly rare in infants under 1 year of age. Clefts and haemorrhages in the immediate subcortical white matter have been assumed to be due to trauma but factors specific to this age group offer other explanations. Finally, examples of the most common causes of the triad encountered in clinical diagnostic and forensic practice are briefly annotated.