Effects of birth insult and stress at adulthood on in vivo tyrosine hydroxylase and tryptophan hydroxylase activities in rat brain

Animal Models for Assessing Impact of C-Section Delivery on Biological Systems

There has been a significant increase in Caesarean section (C-section) births worldwide over the past two decades and although it is can be a life-saving procedure, the enduring effects on host physiology are now undergoing further scrutiny. Indeed, epidemiological data have linked C-section birth with multiple immune, metabolic and neuropsychiatric diseases. Birth by C-section is known to alter the colonisation of the neonatal gut microbiota (with C-section delivered infants lacking vaginal microbiota associated with passing along the birth canal), which in turn can impact the development and maintenance of many important biological systems. Appropriate animal models are key to disentangling the role of missing microbes in brain health and disease in C-section births. In this review of preclinical studies, we interrogate the effects of C-section birth on the development (and maintenance) of several biological systems and we discuss the involvement of the gut microbiome on C-section-related alterations.

Perinatal Asphyxia in Rat Alters Expression of Novel Schizophrenia Risk Genes

Epidemiological studies suggest that obstetric complications, particularly those related to hypoxia during labor and delivery, are a risk factor for development of schizophrenia. The impact of perinatal asphyxia on postnatal life has been studied in a rodent model of global hypoxia, which is accompanied by cesarean section birth. This asphyxia model shows several behavioral, pharmacological, neurochemical, and neuroanatomical abnormalities in adulthood that have relevance to schizophrenia. Further, it is suggested that schizophrenia has a strong genetic component, and indeed novel candidate genes were recently identified by a genome-wide association study. Here, we examined alteration in the novel schizophrenia risk genes, CNNM2, CSMD1, and MMP16 in the brains of rats undergoing cesarean section with or without global hypoxia. The brain regions studied were the prefrontal cortex, striatum, and hippocampus, which are all relevant to schizophrenia. Risk gene expression was measured at three time periods: neonatal, adolescence, and adulthood. We also performed an in vitro analysis to determine involvement of these genes in CNS maturation during differentiation of human neuronal and glial cell lines. Cnnm2 expression was altered in the brains of asphyxia model rats. However, Csmd1 and Mmp16 showed altered expression by exposure to cesarean section only. These findings suggest that altered expression of these risk genes via asphyxia and cesarean section may be associated, albeit through distinct pathways, with the pathobiology of schizophrenia.

Bridging the gap between research into biological and psychosocial models of psychosis

Summary

Paul Bebbington’s recent Special Article provides an excellent synthesis of recent advances in psychosocial research on psychosis. However, we doubt that a model based solely on social epidemiology and cognitive theory can totally describe psychosis, and to be fair, Bebbington does not suggest that it does. A complete model must also incorporate what we have learned from non-social epidemiology, neuroscience, and genetics. Evidence indicates that both the social risk factors that interest Bebbington and biological risk factors, such as abuse of stimulants and cannabis, can provoke psychotic symptoms by dysregulating striatal dopamine. The role of neurodevelopmental deviance also needs to be considered in the etiology of schizophrenia-like psychosis. Moreover, the striking advances in our understanding of the genetic architecture of psychosis open an exciting door into studies examining gene-environment correlation and gene-environment interaction. In short, Bebbington demonstrates the value of cognitive and social researchers talking to each other, but the occasional chat with the more biologically inclined could produce a more comprehensive model.

 

 

Schizophrenia: an integrated sociodevelopmental-cognitive model

Schizophrenia remains a major burden on patients and society. The dopamine hypothesis attempts to explain the pathogenic mechanisms of the disorder, and the neurodevelopmental hypothesis the origins. In the past 10 years an alternative, the cognitive model, has gained popularity. However, the first two theories have not been satisfactorily integrated, and the most influential iteration of the cognitive model makes no mention of dopamine, neurodevelopment, or indeed the brain. In this Review we show that developmental alterations secondary to variant genes, early hazards to the brain, and childhood adversity sensitise the dopamine system, and result in excessive presynaptic dopamine synthesis and release. Social adversity biases the cognitive schema that the individual uses to interpret experiences towards paranoid interpretations. Subsequent stress results in dysregulated dopamine release, causing the misattribution of salience to stimuli, which are then misinterpreted by the biased cognitive processes. The resulting paranoia and hallucinations in turn cause further stress, and eventually repeated dopamine dysregulation hardwires the psychotic beliefs. Finally, we consider the implications of this model for understanding and treatment of schizophrenia.

Epinephrine administration at birth prevents long-term changes in dopaminergic parameters caused by Cesarean section birth in the rat

RATIONALE

Obstetric complications involving birth hypoxia are implicated in the etiology of disorders with dopaminergic dysfunction, such as schizophrenia. Cesarean section (C-section) birth in both humans and rats is associated with increased mild respiratory distress and with reduced levels of circulating catecholamines at birth, which normally serve to prime the lungs and activate other processes promoting extrauterine adaptation. Using a rat model, it has been found that C-section birth can produce long-term changes in central nervous system (CNS) dopamine function, compared to vaginal birth.

OBJECTIVE

The present experiments tested if administering exogenous epinephrine at birth could reverse long-term changes in dopaminergic parameters in C-sectioned rats.

RESULTS

In the absence of stress at adulthood, no differences were observed between C-sectioned and vaginally born rats in levels of in vivo tyrosine hydroxylase (TH) activity and dopamine transporter (DAT) binding. However, after repeated mild stress at adulthood, C-sectioned rats showed increased TH activity in nucleus accumbens and increased DAT in dorsal striatum and accumbens, compared to vaginally born controls. A single injection of epinephrine to C-sectioned rats just after birth prevented the increased TH activity and DAT binding seen in C-sectioned rats after repeated mild stress at adulthood. There was also a trend for epinephrine at birth to partially reverse an increase in amphetamine-induced locomotion seen in C-sectioned rats at adulthood.

CONCLUSIONS

These results suggest that variations in levels of circulating catecholamines in the neonate at the time of birth could contribute to subtle long-term changes in CNS function.

Vacuum extraction and autonomic balance in human infants

The impact of delivery mode on the cardiac autonomic balance was studied in a sample of 101 full term appropriate for gestational age (AGA) human infants. Cardiac autonomic balance was measured by assessing basic heart rate, and two indicators of vagal tone, the Root Mean Square of Successive Differences (RMSSD) and Standard Deviation of NN-intervals (SDNN) as two different measures of short-term heart rate variability at 2, 6, and 16 weeks postnatal age. Sixty-seven infants were delivered spontaneously, 29 by cesarean section and five by vacuum extraction. Children delivered by vacuum extraction had a significantly lower basic heart rate (P=0.01), higher RMSSD (P=0.0003) and higher SDNN (P=0.0001) at two, but not at six and sixteen weeks, indicating a temporary elevation of cardiac vagal tone in these infants. These data indicate a potential transitory impact of vacuum extraction on autonomic balance persisting until at least two weeks postnatal age.

Acute global anoxia during C-section birth affects dopamine-mediated behavioural responses and reactivity to stress

Perinatal asphyxia may induce major neurological deficits shortly after birth as well as neurological/behavioural disorders later in development. We used a rat model of global perinatal asphyxia to model acute intrauterine asphyxia around the time of birth. Caesarean section was performed in rats and their pups, still in uterus horns, were placed into a water bath at 37 degrees C for periods of 0, 10 or 20 min. Pups were then given to surrogate mothers, and examined for long-term behavioural effects of the perinatal asphyctic insult. Behavioural assessment included analysis of novelty seeking behaviour at adolescence, while spatial discrimination abilities, response to both an acute and a chronic stress, and the effects of the full D1 receptor agonist SKF 82958 on open field behaviour were assessed at adulthood. Overall, no marked abnormalities were found in the novelty seeking test, in the ability to discriminate spatial changes in the test environment and in physiological response to stress. However, adult rats subjected to severe perinatal asphyxia (20 min) showed lower activity level and lower stereotyped behaviour after the administration of SKF 82958 in an open field test. These results support the observations from human and animal studies that perinatal insult can produce long-term dysfunction of dopaminergic neurotransmission, and points to the need of more thorough examination of the potential effects of perinatal asphyxia on hypothalamic-pituitary-adrenal (HPA) axis. Altogether, the present findings suggest that the present 20 min perinatal asphyxia model might serve for the study of neurodevelopmental disorders associated with perinatal insults.

Birth insult interacts with stress at adulthood to alter dopaminergic function in animal models: possible implications for schizophrenia and other disorders

Altered subcortical dopaminergic activity is thought to be involved in the pathophysiology of several disorders including schizophrenia, substance abuse and attention deficit hyperactivity disorder. Epidemiological studies have implicated perinatal insults, particularly obstetric complications involving fetal or neonatal hypoxia, as etiological risk factors for schizophrenia. This suggests the possibility that perinatal hypoxia might have lasting effects on dopaminergic function. In animal models, dopaminergic systems appears to be particularly vulnerable to a wide range of perinatal insults, resulting in persistent alterations in function of mesolimbic and mesostriatal pathways. This review summarizes recent work characterizing long-term changes in dopaminergic function and biochemistry in models of Caesarean section (C-section) birth and of C-section birth with added global anoxia in the rat and guinea pig. C-section birth and C-section with anoxia appear to be two distinct hypoxic birth insults, with somewhat differing patterns of lasting effects on dopamine systems. In addition, birth insult alters the manner in which dopaminergic function is regulated by stress at adulthood. The possible relevance of these finding to effects of human birth procedures is discussed.