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

Neuroinflammation in intrauterine growth restriction

Disruption to the maternal environment during pregnancy from events such as hypoxia, stress, toxins, inflammation, and reduced placental blood flow can affect fetal development. Intrauterine growth restriction (IUGR) is commonly caused by chronic placental insufficiency, interrupting supply of oxygen and nutrients to the fetus resulting in abnormal fetal growth. IUGR is a major cause of perinatal morbidity and mortality, occurring in approximately 5-10% of pregnancies. The fetal brain is particularly vulnerable in IUGR and there is an increased risk of long-term neurological disorders including cerebral palsy, epilepsy, learning difficulties, behavioural difficulties and psychiatric diagnoses. Few studies have focused on how growth restriction interferes with normal brain development in the IUGR neonate but recent studies in growth restricted animal models demonstrate increased neuroinflammation. This review describes the role of neuroinflammation in the progression of brain injury in growth restricted neonates. Identifying the mediators responsible for alterations in brain development in the IUGR infant is key to prevention and treatment of brain injury in these infants

GABAA receptor expression and white matter disruption in intrauterine growth restricted piglets

Intrauterine growth restriction (IUGR) is one of the most common causes of perinatal mortality and morbidity. White matter and neuronal injury are major pathophysiological features of the IUGR neonatal brain. GABA (γ-aminobutyric acid type A) receptors have been shown to play a role in oligodendrocyte differentiation and proliferation in the neonatal brain and may be a key factor in white matter injury and myelination in IUGR neonates. Whether there are impairments to the GABAergic system and neuronal cytoskeleton in IUGR brain has yet to be elucidated. This study aims to examine GABA receptor α and α subunit protein expression and distribution in parietal cortex and hippocampus of the IUGR piglet at four different ages (term = 115 d – days gestational age), 100 d, 104 d, birth (postnatal day 0–P0) and P7 and to examine neuronal and myelination patterns. Significant alterations to GABA receptor α and α protein expression levels were observed in the IUGR piglet brain of P7 IUGR piglets with significantly greater α expression compared to α expression in the hippocampus while there was virtually no difference between the two subunits in the parietal cortex. However a significantly lower α/α ratio was evident in P7 IUGR cortex when compared with P7 NG cortex. Neuronal somatodendrites studied using MAP2 immunohistochemistry showed reduced and disrupted somatodendrites while MBP immunolabelling showed loss of axonal fibres from gestational day 104 d through to P7. These findings provide insights into the effects of IUGR on the development of the GABA system, altered developmental maturation of GABA receptor subunit expression in the IUGR brain may influence myelination and may partly explain the cognitive disabilities observed in IUGR. Understanding the mechanisms behind grey and white matter injury in the IUGR infant is essential to identifying targets for treatments to improve long-term outcomes for IUGR infants

Evidence that the serotonin transporter does not shift into the cytosol of remaining neurons after neonatal brain injury

Following neonatal hypoxia-ischemia (HI) serotonin (5-hydroxytryptamine, 5-HT) levels are decreased in the brain. The regulation of brain 5-HT is dependent on the serotonin transporter (SERT) localised at the neuronal pre-synaptic cell membrane. However SERT can also traffic away from the cell membrane into the cytosol and, after injury, may contribute to the cell's inability to maintain 5-HT levels. Whether this occurs after neonatal HI brain injury is not known. In addition, there is contradictory evidence that glial cells may also contribute to the clearance of 5-HT in the brain. Using a postnatal day 3 (P3) HI rat pup model (right carotid ligation + 30 min 6% O-2), we found, in both control and P3 HI animals, that SERT is retained on the cell membrane and is not internalised in the cytosol. In addition, SERT was only detected on neurons. We found no evidence of SERT co-localisation on microglia or astrocytes. We conclude that neuronal SERT is the primary regulator of synaptic 5-HT availability in the intact and P3 HI-injured neonatal brain. Furthermore, since concomitant reductions in 5-HT, SERT and serotonergic neurons occur after neonatal HI, it is plausible that the decrease in brain 5-HT is a consequence of SEAT being lost as neurons degenerate as opposed to remaining neurons internalising SERT or clearance by glial cells. (C) 2012 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved

Disruption to the 5-HT7 Receptor Following Hypoxia-Ischemia in the Immature Rodent Brain

It has become increasingly evident the serotonergic (5-hydroxytryptamine, 5-HT) system is an important central neuronal network disrupted following neonatal hypoxic-ischemic (HI) insults. Serotonin acts via a variety of receptor subtypes that are differentially associated with behavioural and cognitive mechanisms. The 5-HT7 receptor is purported to play a key role in epilepsy, anxiety, learning and memory and neuropsychiatric disorders. Furthermore, the 5-HT7 receptor is highly localized in brain regions damaged following neonatal HI insults. Utilising our well-established neonatal HI model in the postnatal day 3 (P3) rat pup we demonstrated a significant decrease in levels of the 5-HT7 protein in the frontal cortex, thalamus and brainstem one week after insult. We also observed a relative decrease in both the cytosolic and membrane fractions of 5-HT7. The 5-HT7 receptor was detected on neurons throughout the cortex and thalamus, and 5-HT cell bodies in the brainstem. However we found no evidence of 5-HT7 co-localisation on microglia or astrocytes. Moreover, minocycline treatment did not significantly prevent the HI-induced reductions in 5-HT7. In conclusion, neonatal HI injury caused significant disruption to 5-HT7 receptors in the forebrain and brainstem. Yet the use of minocycline to inhibit activated microglia, did not prevent the HI-induced changes in 5-HT7 expression

Therapeutic potential to reduce brain injury in growth restricted newborns

Brain injury in intrauterine growth restricted (IUGR) infants is a major contributing factor to morbidity and mortality worldwide. Adverse outcomes range from mild learning difficulties, to attention difficulties, neurobehavioral issues, cerebral palsy, epilepsy, and other cognitive and psychiatric disorders. While the use of medication to ameliorate neurological deficits in IUGR neonates have been identified as warranting urgent research for several years, few trials have been reported. This review summarises clinical trials focusing on brain protection in the IUGR newborn as well as therapeutic interventions trialled in animal models of IUGR. Therapeutically targeting mechanisms of brain injury in the IUGR neonate is fundamental to improving long-term neurodevelopmental outcomes. Inflammation is a key mechanism in neonatal brain injury; and therefore an appealing target. Ibuprofen, an anti-inflammatory drug currently used in the preterm neonate, may be a potential therapeutic candidate to treat brain injury in the IUGR neonate. To better understand the potential of ibuprofen and other therapeutic agents to be neuroprotective in the IUGR neonate, long-term follow up information of neurodevelopmental outcomes must be studied. Where agents are shown to be effective, have a good safety profile and are relatively inexpensive, such as ibuprofen, they can be widely adopted and lead to improved outcomes

Differential effects of neonatal hypoxic-ischemic brain injury on brainstem serotonergic raphe nuclei

Serotonergic fibres have a pervasive innervation of hypoxic-ischemic (HI)-affected areas in the neonatal brain and serotonin (5-HT) is pivotal in numerous neurobehaviours that match many HI-induced deficits. However, little is known about how neonatal HI affects the serotonergic system. We therefore examined whether neonatal HI can alter numbers of serotonergic raphe neurons in specific sub-divisions of the midbrain and brainstem since these nuclei are the primary sources of serotonin throughout the central nervous system (CNS). We utilised an established neonatal HI model in the postnatal day 3 (P3) rat pup (right common carotid artery ligation + 30 min 6% O(2)) and determined the effects of P3 HI on 5-HT counts in 5 raphe sub-divisions in the midbrain and brainstem one and six weeks later. After P3 HI, numbers of 5-HT-positive neurons were significantly decreased in the dorsal raphe dorsal, dorsal raphe ventrolateral and dorsal raphe caudal nuclei on P10 but only in the dorsal raphe dorsal and dorsal raphe ventrolateral nuclei on P45. In contrast, P3 HI did not alter counts in the dorsal raphe interfascicular and raphe magnus nuclei. We also discovered that P3 HI significantly reduces brainstem SERT protein expression; the key regulator of 5-HT in the CNS. In conclusion, neonatal HI injury caused significant disruption of the brainstem serotonergic system that can persist for up to six weeks after the insult. The different vulnerabilities of serotonergic populations in specific raphe nuclei suggest that certain raphe nuclei may underpin neurological deficits in HI-affected neonates through to adulthood. (C) 2010 Elsevier B.V. All rights reserved

Transient liver elastography in unsedated control children: Impact of age and intercurrent illness

Transient elastography (TE) is a rapid, non-invasive, reproducible assessment of liver fibrosis by liver stiffness measurement (LSM). Uncertainty remains regarding utility in children, unsedated an