Sub-neurotoxic neonatal anoxia induces subtle behavioural changes and specific abnormalities in brain group-I metabotropic glutamate receptors in rats

Perinatal Brain Injury and Inflammation: Lessons from Experimental Murine Models

Perinatal brain injury or neonatal encephalopathy (NE) is a state of disturbed neurological function in neonates, caused by a number of different aetiologies. The most prominent cause of NE is hypoxic ischaemic encephalopathy, which can often induce seizures. NE and neonatal seizures are both associated with poor neurological outcomes, resulting in conditions such as cerebral palsy, epilepsy, autism, schizophrenia and intellectual disability. The current treatment strategies for NE and neonatal seizures have suboptimal success in effectively treating neonates. Therapeutic hypothermia is currently used to treat NE and has been shown to reduce morbidity and has neuroprotective effects. However, its success varies between developed and developing countries, most likely as a result of lack of sufficient resources. The first-line pharmacological treatment for NE is phenobarbital, followed by phenytoin, fosphenytoin and lidocaine as second-line treatments. While these drugs are mostly effective at halting seizure activity, they are associated with long-lasting adverse neurological effects on development. Over the last years, inflammation has been recognized as a trigger of NE and seizures, and evidence has indicated that this inflammation plays a role in the long-term neuronal damage experienced by survivors. Researchers are therefore investigating the possible neuroprotective effects that could be achieved by using anti-inflammatory drugs in the treatment of NE. In this review we will highlight the current knowledge of the inflammatory response after perinatal brain injury and what we can learn from animal models.

Animal models for neonatal brain injury induced by hypoxic ischemic conditions in rodents

Neonatal hypoxia-ischemia and resulting encephalopathies are of significant concern. Intrapartum asphyxia is a leading cause of neonatal death globally. Among surviving infants, there remains a high incidence of hypoxic-ischemic encephalopathy due to neonatal hypoxic-ischemic brain injury, manifesting as mild conditions including attention deficit hyperactivity disorder, and debilitating disorders such as cerebral palsy. Various animal models of neonatal hypoxic brain injury have been implemented to explore cellular and molecular mechanisms, assess the potential of novel therapeutic strategies, and characterize the functional and behavioural correlates of injury. Each of the animal models has individual advantages and limitations. The present review looks at several widely-used and alternative rodent models of neonatal hypoxia and hypoxia-ischemia; it highlights their strengths and limitations, and their potential for continued and improved use.

Perinatal Hypoxia and Ischemia in Animal Models of Schizophrenia

Intrauterine or perinatal complications constitute a major risk for psychiatric diseases. Infants who suffered from hypoxia-ischemia (HI) are at twofold risk to develop schizophrenia in later life. Several animal models attempt to reproduce these complications to study the yet unknown steps between an insult in early life and outbreak of the disease decades later. However, it is very challenging to find the right type and severity of insult leading to a disease-like phenotype in the animal, but not causing necrosis and focal neurological deficits. By contrast, too mild, repetitive insults may even be protective via conditioning effects. Thus, it is not surprising that animal models of hypoxia lead to mixed results. To achieve clinically translatable findings, better protocols are urgently needed. Therefore, we compare widely used models of hypoxia and HI and propose future directions for the field.

Cerebral Hypoxia can lead to Personality Changes: A Review

The term ‘Cerebral hypoxia’ refers to reduced supply of oxygen to the brain tissues. If a brain cell becomes completely deprived of oxygen, the condition is referred to as cerebral anoxia. Since brain needs constant supply of oxygen for its vital functioning, cerebral hypoxia can have major impact of cerebral hemispheres, leading to cognitive, behavioural as well as personality changes including anxiety, depression and memory loss.

Neonatal Hypoxia Ischaemia: Mechanisms, Models, and Therapeutic Challenges

Neonatal hypoxia-ischaemia (HI) is the most common cause of death and disability in human neonates, and is often associated with persistent motor, sensory, and cognitive impairment. Improved intensive care technology has increased survival without preventing neurological disorder, increasing morbidity throughout the adult population. Early preventative or neuroprotective interventions have the potential to rescue brain development in neonates, yet only one therapeutic intervention is currently licensed for use in developed countries. Recent investigations of the transient cortical layer known as subplate, especially regarding subplate's secretory role, opens up a novel set of potential molecular modulators of neonatal HI injury. This review examines the biological mechanisms of human neonatal HI, discusses evidence for the relevance of subplate-secreted molecules to this condition, and evaluates available animal models. Neuroserpin, a neuronally released neuroprotective factor, is discussed as a case study for developing new potential pharmacological interventions for use post-ischaemic injury.

Striatal cholinergic functional alterations in hypoxic neonatal rats: Role of glucose, oxygen, and epinephrine resuscitation

Molecular processes regulating cholinergic functions play an important role in the control of respiration under hypoxia. Cholinergic alterations and its further complications in respiration due to hypoxic insult in neonatal rats and the effect of glucose, oxygen, and epinephrine resuscitation was evaluated in the present study. Receptor binding and gene expression studies were done in the corpus striatum to analyse the changes in total muscarinic receptors, muscarinic M1, M2, M3 receptors, and the enzymes involved in acetylcholine metabolism, choline acetyltransferase and acetylcholinesterase. Neonatal hypoxia decreased total muscarinic receptors with reduced expression of muscarinic M1, M2, and M3 receptor genes. The reduction in acetylcholine metabolism is indicated by the downregulated choline acetyltransferase and upregulated acetyl cholinesterase expression. These cholinergic disturbances were reversed to near control in glucose-resuscitated hypoxic neonates. The adverse effects of immediate oxygenation and epinephrine administration are also reported. The present findings points to the cholinergic alterations due to neonatal hypoxic shock and suggests a proper resuscitation method to ameliorate these striatal changes.

Hypoxic-ischemic injury decreases anxiety-like behavior in rats when associated with loss of tyrosine-hydroxylase immunoreactive neurons of the substantia nigra

Neonatal Sprague-Dawley rats were randomly divided into normal control, mild hypoxia-ischemia (HI), and severe HI groups (N = 10 in each group at each time) on postnatal day 7 (P7) to study the effect of mild and severe HI on anxiety-like behavior and the expression of tyrosine hydroxylase (TH) in the substantia nigra (SN). The mild and severe HI groups were exposed to hypoxia (8% O2/92% N2) for 90 and 150 min, respectively. The elevated plus-maze (EPM) test was performed to assess anxiety-like behavior by measuring time spent in the open arms (OAT) and OAT%, and immunohistochemistry was used to determine the expression of TH in the SN at P14, P21, and P28. OAT and OAT% in the EPM were significantly increased in both the mild (1.88-, 1.99-, and 2.04-fold, and 1.94-, 1.51-, and 1.46-fold) and severe HI groups (1.69-, 1.68-, and 1.87-fold, and 1.83-, 1.43-, and 1.39-fold, respectively; P < 0.05). The percent of TH-positive cells occupying the SN area was significantly and similarly decreased in both the mild (17.7, 40.2, and 47.2%) and severe HI groups (16.3, 32.2, and 43.8%, respectively; P < 0.05). The decrease in the number of TH-positive cells in the SN and the level of protein expression were closely associated (Pearson correlation analysis: r = 0.991, P = 0.000 in the mild HI group and r = 0.974, P = 0.000 in the severe HI group) with the impaired anxiety-like behaviors. We conclude that neonatal HI results in decreased anxiety-like behavior during the juvenile period of Sprague-Dawley rats, which is associated with the decreased activity of TH in the SN. The impairment of anxiety and the expression of TH are not likely to be dependent on the severity of HI.

Effect of maternal administration of allopregnanolone before birth asphyxia on neonatal hippocampal function in the spiny mouse

Clinically, treatment options where fetal distress is anticipated or identified are limited. Allopregnanolone is an endogenous steroid, that positively modulates the GABA(A) receptor, and that has anti-apoptotic and anti-excitotoxic actions, reducing brain damage in adult animal models of brain injury. We sought to determine if prophylactic treatment of the pregnant female with a single dose of this steroid could reduce birth asphyxia-induced losses in hippocampal function at 5 days of age (P5) in spiny mouse neonates (Acomys cahirinus). At 37 days gestation (term=39 days) and 1h before inducing birth asphyxia, spiny mice dams were injected subcutaneously (0.2 ml) with either 3mg/kg allopregnanolone or 20% w/v β-cyclodextrin vehicle. One hour later, fetuses were either delivered immediately by caesarean section (control group) or exposed to 7.5 min of in utero asphyxia, causing acidosis and hypoxia. At P5, ex vivo hippocampal plasticity was assessed, or brains collected to determine cell proliferation (proliferating cell nuclear antigen; PCNA) or calcium channel expression (inositol trisphosphate receptor type 1; IP(3)R1) using immunohistochemistry. Allopregnanolone partially prevented the decrease in long term potentiation at P5, and the asphyxia-induced increase in IP(3)R1 expression in CA1 pyramidal neurons. There was no effect of allopregnanolone on the asphyxia induced impairment of the input/output (I/O) curve and paired-pulse facilitation (PPF). In control birth pups, maternal allopregnanolone treatment caused significant changes in short term post-synaptic plasticity and also reduced hippocampal proliferation at P5. These findings show that allopregnanolone can modulate hippocampal development and synaptic function in a normoxic or hypoxic environment, possibly by modifying calcium metabolism. Best practice for treatment dose and timing of treatment will need to be carefully considered.

Decreased GABAB receptor function in the cerebellum and brain stem of hypoxic neonatal rats: role of glucose, oxygen and epinephrine resuscitation

Background-

Hypoxia during the first week of life can induce neuronal death in vulnerable brain regions usually associated with an impairment of cognitive function that can be detected later in life. The neurobiological changes mediated through neurotransmitters and other signaling molecules associated with neonatal hypoxia are an important aspect in establishing a proper neonatal care.

Methods-

The present study evaluated total GABA, GABA_B receptor alterations, gene expression changes in GABA_B receptor and glutamate decarboxylase in the cerebellum and brain stem of hypoxic neonatal rats and the resuscitation groups with glucose, oxygen and epinephrine. Radiolabelled GABA and baclofen were used for receptor studies of GABA and GABA_B receptors respectively and Real Time PCR analysis using specific probes for GABA_B receptor and GAD mRNA was done for gene expression studies.

Results-

The adaptive response of the body to hypoxic stress resulted in a reduction in total GABA and GABA_B receptors along with decreased GABA_B receptor and GAD gene expression in the cerebellum and brain stem. Hypoxic rats supplemented with glucose alone and with oxygen showed a reversal of the receptor alterations and changes in GAD. Resuscitation with oxygen alone and epinephrine was less effective in reversing the receptor alterations.

Conclusions-

Being a source of immediate energy, glucose can reduce the ATP-depletion-induced changes in GABA and oxygenation, which helps in encountering hypoxia. The present study suggests that reduction in the GABA_B receptors functional regulation during hypoxia plays an important role in central nervous system damage. Resuscitation with glucose alone and glucose and oxygen to hypoxic neonatal rats helps in protecting the brain from severe hypoxic damage.

Alterations in cortical GABAB receptors in neonatal rats exposed to hypoxic stress: role of glucose, oxygen, and epinephrine resuscitation

Hypoxia in neonates can cause permanent brain damage by gene and receptor level alterations mediated through changes in neurotransmitters. The present study evaluated GABA(B) receptor alterations, gene expression changes in glutamate decarboxylase and hypoxia-inducible factor 1A in the cerebral cortex of hypoxic neonatal rats and the resuscitation groups with glucose, oxygen, and epinephrine. Under hypoxic stress, a significant decrease in total GABA and GABA(B) receptors, GABA(B) and GAD gene expression was observed in the cerebral cortex, which accounts for the respiratory inhibition. Hypoxia-inducible factor 1A was upregulated under hypoxia to maintain body homeostasis. Hypoxic rats supplemented with glucose alone and with oxygen showed a reversal of the receptor alterations and changes in GAD and HIF-1A to near control. Being a source of immediate energy, glucose can reduce the ATP-depletion-induced changes in GABA and oxygenation, which helps in encountering hypoxia. Resuscitation with oxygen alone and epinephrine was less effective in reversing the receptor alterations. Thus, our study suggests that reduction in the GABA(B) receptors functional regulation during hypoxia plays an important role in cortical damage. Resuscitation with glucose alone and glucose and oxygen to hypoxic neonatal rats helps in protecting the brain from severe hypoxic damage.

Owner reports of attention, activity, and impulsivity in dogs: a replication study

Background

When developing behaviour measurement tools that use third party assessments, such as parent report, it is important to demonstrate reliability of resulting scales through replication using novel cohorts. The domestic dog has been suggested as a model to investigate normal variation in attention, hyperactivity, and impulsive behaviours impaired in Attention Deficit Hyperactive Disorder (ADHD). The human ADHD Rating Scale, modified for dogs and using owner-directed surveys, was applied in a European sample. We asked whether findings would be replicated utilizing an Internet survey in a novel sample, where unassisted survey completion, participant attitudes and breeds might affect previous findings.

Methods

Using a slightly modified version of the prior survey, we collected responses (n = 1030, 118 breeds representing 7 breed groups) primarily in the United States and Canada. This study was conducted using an Internet survey mechanism.

Results

Reliability analyses confirmed two scales previously identified for dogs (inattention [IA], hyperactivity-impulsivity [HA-IM]). Models including age, training status, and breed group accounted for very little variance in subscales, with no effect of gender.

Conclusions

The factor invariance demonstrated in these findings confirms that owner report, using this modified human questionnaire, provides dog scores according to "inattention" and "hyperactivity-impulsivity" axes. Further characterization of naturally occurring variability of attention, activity, and impulsivity in domestic dogs may provide insight into genetic backgrounds underlying behaviours impaired in attention and associated disorders.

Neuroprotective role of Bacopa monnieri extract in epilepsy and effect of glucose supplementation during hypoxia: glutamate receptor gene expression

The experiments were designed to study the glutamate gene expression during epilepsy in adult and hypoxic insult to brain during the neonatal period and the therapeutic role of neuroprotective supplements. We investigated the role of metabotropic glutamate-8 receptor (mGluR8) gene expression in cerebellum during epilepsy and neuroprotective role of Bacopa monnieri extract in epilepsy. We also studied the effect of NMDA receptor 1 (NMDAR1) gene expression during neonatal hypoxia and therapeutic role of glucose, oxygen and epinephrine supplementation. During epilepsy a significant down-regulation (P < 0.01) of mGluR8 gene expression was observed which was up-regulated (P < 0.05) near control level after B. monnieri treatment which is supported by Morris water maze experiment. In hypoxic neonates we observed up-regulation (P < 0.001) of the NMDAR1 gene expression whereas glucose and glucose + oxygen was able to significantly reverse (P < 0.001) the gene expression to near control level when compared to hypoxia and epinephrine treatment which was supported by open field test. Our results showed that B. monnieri treatment to epileptic rats significantly brought the reversal of the down-regulated mgluR8 gene expression toward control level. In neonatal rats, hypoxia induced expressional and functional changes in the NMDAR1 receptors of neuronal cells which is corrected by supplementation of glucose alone or glucose followed by oxygen during the resuscitation to prevent the glutamate related neuronal damage. Thus, the results suggest the clinical significance of corrective measures for epileptic and hypoxic management.

Acute perinatal asphyxia at birth has long-term effects on behavioural arousal and maternal behaviour in lactating rats

This study analysed the long-term consequences of an asphyctic event at birth on maternal behaviour and emotionality in rats. Pregnant Wistar rats were delivered by Caesarean section and the pups, still in the uterus horns, were placed into a water bath at 37 degrees C for periods of 0 (Caesarean delivery, CD) or 20 min (asphyxia, CD+20). Control subjects were born by vaginal delivery (VD). Subsequently, pups were given to surrogate mothers, weaned at 21 days, and mated at adulthood. After giving birth, differences in maternal competence and behavioural arousal were assessed observing: (i) maternal behaviour after reunion with the pups following a 3h separation, on postpartum day (PPD) 4; (ii) behaviour in an elevated plus-maze test, on postpartum day 7; and (iii) performance in a fear conditioning test, in which subjects learned to associate a conditional stimulus with an aversive unconditioned stimulus (postpartum days 7-8). Results indicate that subjects in the CD+20 group showed a deficit in maternal care, taking a longer time to retrieve the whole litter and often failing to retrieve all pups. Both CD and CD+20 groups showed higher behavioural activity in the plus-maze. In addition, when tested in the fear conditioning paradigm, the CD+20 group showed a lower latency to perform freezing behaviour in the auditory cue trial. The changes in behavioural arousal described suggest that the dopaminergic system may be a potential neurochemical target for an early hypoxic insult and indicate maternal behaviour as a useful endpoint to study the effects of early birth insult on brain function.

Response to novelty, social and self-control behaviors, in rats exposed to neonatal anoxia: modulatory effects of an enriched environment

Perinatal asphyxia is a concern for public health and may promote subtle and long-lasting neuropsychiatric disorders. In the present study, newborn Wistar rat pups underwent a repeated 20-min exposure to a 100% N2 atmosphere (or air) on postnatal days (pnd) 1, 3, 5, and 7. Half of the animals were housed during adolescence (pnd 21-35) in an enriched environment. The consequences on behavior were assessed throughout adolescence to adulthood. When scored for social performance, adolescent rats exposed to neonatal asphyxia exhibited exaggerated levels of anogenital sniffing behavior, which was normalized by enriched living. In air-exposed controls, enriched living increased the expression of affiliative and novelty-seeking behaviors, as compared to standard housing. However, this enrichment-induced behavioral plasticity was not found in rats neonatally exposed to asphyxia. At adulthood, levels of impulsivity and 5-HT2A receptors in the striatum were markedly increased in neonatal-asphyxia rats kept in standard-housing conditions. Interestingly, impulsivity and receptor density were normalized by enriched rearing during adolescence. These findings indicate profound long-lasting behavioral alterations as a consequence of repeated neonatal asphyxia in rats. Beneficial effects of stimulation by an enriched environment during the still-plastic window of adolescence are suggested in these animals.