Deep hypothermia reverses behavioral and histological alterations in a rat model of perinatal asphyxia

Lasting mesothalamic dopamine imbalance and altered exploratory behavior in rats after a mild neonatal hypoxic event

Introduction

Adversities during the perinatal period can decrease oxygen supply to the fetal brain, leading to various hypoxic brain injuries, which can compromise the regularity of brain development in different aspects. To examine the catecholaminergic contribution to the link between an early-life hypoxic insult and adolescent behavioral aberrations, we used a previously established rat model of perinatal hypoxia but altered the hypobaric to normobaric conditions.

Methods

Exploratory and social behavior and learning abilities were tested in 70 rats of both sexes at adolescent age. Inherent vertical locomotion, sensory-motor functions and spatial learning abilities were explored in a subset of animals to clarify the background of altered exploratory behavior. Finally, the concentrations of dopamine (DA) and noradrenaline in midbrain and pons, and the relative expression of genes for DA receptors D1 and D2, and their down-stream targets (DA- and cAMP-regulated phosphoprotein, Mr 32 kDa, the regulatory subunit of protein kinase A, and inhibitor-5 of protein phosphatase 1) in the hippocampus and thalamus were investigated in 31 rats.

Results

A lesser extent of alterations in exploratory and cognitive aspects of behavior in the present study suggests that normobaric conditions mitigate the hypoxic injury compared to the one obtained under hypobaric conditions. Increased exploratory rearing was the most prominent consequence, with impaired spatial learning in the background. In affected rats, increased midbrain/pons DA content, as well as mRNA levels for DA receptors and their down-stream elements in the thalamus, but not the hippocampus, were found.

Conclusion

We can conclude that a mild hypoxic event induced long-lasting disbalances in mesothalamic DA signaling, contributing to the observed behavioral alterations. The thalamus was thereby indicated as another structure, besides the well-established striatum, involved in mediating hypoxic effects on behavior through DA signaling.

The neurobiology of social play behaviour: Past, present and future

Social play behaviour is a highly energetic and rewarding activity that is of great importance for the development of brain and behaviour. Social play is abundant during the juvenile and early adolescent phases of life, and it occurs in most mammalian species, as well as in certain birds and reptiles. To date, the majority of research into the neural mechanisms of social play behaviour has been performed in male rats. In the present review we summarize studies on the neurobiology of social play behaviour in rats, including work on pharmacological and genetic models for autism spectrum disorders, early life manipulations and environmental factors that influence play in rats. We describe several recent developments that expand the field, and highlight outstanding questions that may guide future studies.

Treatments for Social Interaction Impairment in Animal Models of Schizophrenia: A Critical Review and Meta-analysis

BACKGROUND

While pharmacological treatments for positive symptoms of schizophrenia are widely used, their beneficial effect on negative symptoms, particularly social impairment, is insufficiently studied. Therefore, there is an increasing interest in preclinical research of potentially beneficial treatments, with mixed results. The current review aims to evaluate the efficacy of available treatments for social deficits in different animal models of schizophrenia.

STUDY DESIGN

A systematic literature search generated 145 outcomes for the measures "total time" and "number" of social interactions. Standardized mean differences (SMD) and 95% confidence interval (CI) were calculated, and heterogeneity was tested using Q statistics in a random-effect meta-analytic model. Given the vast heterogeneity in effect sizes, the animal model, treatment group, and sample size were all examined as potential moderators.

STUDY RESULTS

The results showed that in almost all models, treatment significantly improved social deficit (total time: SMD = 1.24; number: SMD = 1.1). The moderator analyses discovered significant subgroup differences across models and treatment subgroups. Perinatal and adult pharmacological models showed the most substantial influence of treatments on social deficits, reflecting relative pharmacological validity. Furthermore, atypical antipsychotic drugs had the highest SMD within each model subgroup.

CONCLUSIONS

Our findings indicate that the improvement in social interaction behaviors is dependent on the animal model and treatment family used. Implications for the preclinical and clinical fields are discussed.

Early Postnatal Exposure to Intermittent Hypercapnic Hypoxia (IHH), but Not Nicotine, Decreases Reelin in the Young Piglet Hippocampus

This study evaluated the expression of reelin, an extracellular protein involved in lamination and migration of neurons, in the hippocampus of young piglets, and quantified to examine the following: (i) baseline levels within layers of the hippocampus and dentate gyrus (DG); (ii) differences between ventral and dorsal hippocampi; and (iii) changes attributable to postnatal exposure to continuous nicotine for 12 days, or intermittent hypercapnic hypoxia (IHH), with further analysis according to duration of IHH (1 vs 4 days). Additionally, we analysed whether any exposure altered DG morphology and whether it is related to altered reelin expression. Reelin was visualised via immunohistochemistry, and the number of positive reelin cells/mm² was measured in the CA4/Hilus, layers of the DG, and the CA1. The dorsal DG had significantly more reelin within the subgranular zone compared to the ventral DG (p < 0.01). There was no difference in reelin between nicotine (n = 5) and controls (n = 5). IHH exposed piglets (n = 10) had significantly lowered reelin in the CA1 (p = 0.05), specifically the stratum pyramidale (p = 0.04) and the hippocampal fissure (p = 0.02), compared to their controls (n = 7); the duration of IHH had no effect. No exposure was associated with an alteration in DG morphology. This study shows that postnatal IHH exposure decreased reelin expression in the developing piglet hippocampal CA1, suggesting that IHH may result in altered neuronal migration.

Deep hypothermia prevents striatal alterations produced by perinatal asphyxia: Implications for the prevention of dyskinesia and psychosis

GABAergic medium spiny neurons are the main neuronal population in the striatum. Calbindin is preferentially expressed in medium spiny neurons involved in the indirect pathway. The aim of the present work is to analyze the effect of perinatal asphyxia on different subpopulations of GABAergic neurons in the striatum and to assess the outcome of deep therapeutic hypothermia. The uterus of pregnant rats was removed by cesarean section and the fetuses were exposed to hypoxia by immersion in water (19 min) at 37°C (perinatal asphyxia). The hypothermic group was exposed to 10°C during 30 min after perinatal asphyxia. The rats were euthanized at the age of one month (adolescent/adult rats), their brains were dissected out and coronal sections were immunolabeled for calbindin, calretinin, NeuN, and reelin. Reelin+ cells showed no staining in the striatum besides subventricular zone. The perinatal asphyxia (PA) group showed a significant decrease in calbindin neurons and a paradoxical increase in neurons estimated by NeuN staining. Moreover, calretinin+ cells, a specific subpopulation of GABAergic neurons, showed an increase caused by PA. Deep hypothermia reversed most of these alterations probably by protecting calbindin neurons. Similarly, there was a reduction of the diameter of the anterior commissure produced by the asphyxia that was prevented by hypothermic treatment.

Clinical Implications of Epigenetic Dysregulation in Perinatal Hypoxic-Ischemic Brain Damage

Placental and fetal hypoxia caused by perinatal hypoxic-ischemic events are major causes of stillbirth, neonatal morbidity, and long-term neurological sequelae among surviving neonates. Brain hypoxia and associated pathological processes such as excitotoxicity, apoptosis, necrosis, and inflammation, are associated with lasting disruptions in epigenetic control of gene expression contributing to neurological dysfunction. Recent studies have pointed to DNA (de)methylation, histone modifications, and non-coding RNAs as crucial components of hypoxic-ischemic encephalopathy (HIE). The understanding of epigenetic dysregulation in HIE is essential in the development of new clinical interventions for perinatal HIE. Here, we summarize our current understanding of epigenetic mechanisms underlying the molecular pathology of HI brain damage and its clinical implications in terms of new diagnostic, prognostic, and therapeutic tools.