The Effects of Maternal Cortisol on the Amygdala and Internalizing Behaviours

What's the science?

Cortisol is a hormone involved in the body’s physical and psychological stress response. During pregnancy, the hormone can reach the neonate either directly or via fetal corticotropin-releasing hormone. Some cortisol is critical for fetal brain development, but abnormal levels are associated with psychiatric disorders in offspring. The amygdala is a brain region that has many cortisol receptors, and in animal models, high levels of maternal cortisol have been found to result in high negative emotion and stress reactivity in offspring. Sex differences in the effects of maternal cortisol have also been found; negative emotionality may be more likely to be present in female offspring. This week in Biological Psychiatry, Graham and colleagues assessed the effects of in utero cortisol exposure on the amygdala shortly after birth.

How did they do it?

A total of 70 mother-infant dyads participated in the study. Each mother collected 5 saliva samples of cortisol over the course of a day for a 4 day period during each of her 3 trimesters of pregnancy (60 samples per mother total). The area under the curve (similar to assessing overall cortisol output) was calculated for each trimester, resulting in reliable indicators of cortisol levels representative of each of the three trimesters. These values were also log-transformed for normalization purposes. Infants underwent brain functional magnetic resonance imaging (fMRI) at 4 weeks of age. Resting state functional connectivity (a measure of the synchrony of brain activity at rest) was calculated between the right and left amygdala and the rest of the brain, and the relationship between maternal cortisol and these connections was assessed. At 24 months of age, mothers reported on their child's internalizing behavior (e.g. depression or anxiety symptoms) using the Internalizing Behavior Scale of the Children's Behavioral Checklist.

What did they find?

There was an interaction between sex and maternal cortisol in predicting connectivity between the bilateral amygdala and the left supramarginal gyrus and superior temporal gyrus. Probing the interaction revealed that in females, amygdala connectivity with the aforementioned cortical regions was generally stronger with higher maternal cortisol, while it was weaker in males. The results suggest that the relationships between cortisol and connectivity of the amygdala to various regions of the cortex were opposite for males versus females. Further, connectivity between the right amygdala and the supramarginal gyrus was positively correlated with internalizing behaviour in children (not dependent on sex). This association remained even after considering levels of maternal depressive symptoms, another important potential influence on child internalizing behavior. Upon mediation analysis, the authors found that connectivity between the right amygdala and supramarginal gyrus mediated the relationship between maternal cortisol and child internalizing. Therefore, cortisol exposure during pregnancy is associated with higher internalizing behaviors in females through a pathway involving stronger right amygdala connectivity.

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What's the impact?

Cortisol levels have been assessed in utero in animals models and at single time points during pregnancy in humans. However, this is the first study to demonstrate a relationship between connectivity of amygdala and maternal cortisol (which differs by sex) using a robust measure for cortisol levels over multiple key time points. The results suggest that this hormone involved in the stress response may alter integration of the amygdala with cortical brain regions during an early phase of brain development.


Graham et al., Maternal Cortisol Concentrations During Pregnancy and Sex Specific Associations with Neonatal Amygdala Connectivity and Emerging Internalizing Behaviors. Biological Psychiatry (2018). Access the original scientific publication here.

Autoregulatory Gene Therapy as a Treatment for Focal Epilepsy

What's the science?

Patients with epilepsy often do not respond to anti-epileptic drugs and continue to experience seizures. Drug-resistance is especially common when seizures arise from a specific region of the brain (focal epilepsy). Further, anti-epileptic drugs are not selective for the neurons which cause seizures. Viral mediated gene therapy, where new DNA is carried by a viral vector and inserted into cells, could potentially be used to selectively modify neuron populations that cause seizures. Gene therapy has shown promise in animal models; however, most therapies have been irreversible. This week in Nature Medicine, Lieb and colleagues use an autoregulating viral-mediated gene therapy treatment in rats to test whether it is tolerated and reduces seizures.

How did they do it?

They designed a viral plasmid containing a gene encoding a glutamate-gated chloride channel that detects excessive glutamate (an excitatory neurotransmitter) release from neurons and inhibits neurons in a self-regulating manner. Glutamate release is increased in epilepsy resulting in heightened neural activity, so inhibiting this process can reduce seizures. Adult rats were injected with pilocarpine, a seizure inducing drug, before injection of the viral vector containing the glutamate sensitive channel or a control vector, and then again two weeks later. Both of these were administered to the primary motor cortex of the rats. An electrode was also placed in the motor cortex to record the electroencephalogram (EEG) to detect seizure activity. Comparing the effect of pilocarpine before and after treatment revealed the effect of gene therapy on seizure activity. They then tested the effect of gene therapy on a model of chronic focal epilepsy where seizures occur spontaneously for several weeks after injecting tetanus toxin into the visual cortex of rats. They did this by comparing the frequency of seizures before and after treatment. Finally, they performed a series of behavioral experiments to test whether motor coordination was altered by the gene therapy treatment administered to the primary motor cortex (i.e. whether it was well tolerated).

What did they find?

Rats injected with the viral DNA encoding the glutamate sensitive channel showed a reduction in frequency and amplitude of seizure-related activity (induced by pilocarpine in the motor cortex), when compared to rats injected with the control virus. The frequency of spontaneous seizures was also reduced after introducing the glutamate sensitive channel in a chronic model of focal epilepsy. However, there was no effect on seizure duration or intensity in the chronic epilepsy model, or on the background EEG. These results suggest that the gene therapy was effective in inhibiting both pilocarpine-evoked seizure-related activity and the number of spontaneous seizures in a chronic focal seizure model. After testing for effects of gene therapy on motor coordination, there was no difference between control rats and those rats treated with the viral injection of the glutamate sensitive channel, demonstrating that the gene therapy was well tolerated.

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What's the impact?

This is the first study to demonstrate how gene therapy can be used to express an autoregulating channel that responds to excessive glutamate release to reduce seizures. This gene therapy was well-tolerated and able to inhibit neurons to reduce seizure related activity and reduce the number of seizures in a chronic model of focal epilepsy. This study shows that gene therapy could potentially be used to apply selective treatment to specific brain regions causing seizures. Further research will be needed to ensure that this gene therapy can be well tolerated in humans.

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Lieb et al., Biochemical autoregulatory gene therapy for focal epilepsy. Nature Medicine (2018). Access the original scientific publication here.

MicroRNAs Cause Astrocyte Dysfunction in ALS

What's the science?

ALS is a devastating disease where motor neurons degenerate over time. Astrocytes which normally support neurons function abnormally in ALS and play a role in ongoing cell death. MicroRNAs are naturally occurring small pieces of non-coding RNA that regulate (and often inhibit) the production of proteins in cells. One type of microRNA called miR-218 has recently been shown to be higher in motor neurons in ALS and is released from the neuron into the cerebrospinal fluid. This microRNA, which is released from dying neurons, could communicate with astrocytes to cause dysfunction. This week in Brain Hoye and colleagues examine whether microRNA released from neurons are taken up by astrocytes and regulate their protein expression.

How did they do it?

They identified potential targets that microRNA miR-218 might bind to or regulate in astrocytes to affect their function. They did this by looking for genes with enriched (i.e. higher) expression in astrocytes. They identified EAAT2, a glutamate reuptake transporter that is enriched in healthy astrocytes but lost in ALS. They injected cells with either random microRNA or miR-218 (specifically released from motor neurons in ALS) to see whether it would affect EAAT2 expression. They then assessed whether miR-218 is taken up by astrocytes using a sensor they developed and whether it is free, protein bound, or encapsulated in vesicles. Finally, they tested whether any potentially pathological effects of miR-218 on astrocyte EAAT2 expression could be altered using antisense oligonucleotide therapy.

What did they find?

They found that miR-218 infected cells had reduced production of EAAT2 (measured with western blot) demonstrating that it can repress translation of this glutamate transporter in astrocytes. They then developed a ‘sensor’ to confirm that miR-218 is taken up by astrocytes. They found that the majority of miR-218 is protein bound in the cerebrospinal fluid (after it is released from the cell). They then tested whether they could block the miR-218 induced repression of EAAT2 expression in astrocytes using antisense oligonucleotides. They applied media from sporadic ALS patient iPSC-derived motor neurons to primary astrocytes that contained miR-218 with and without antisense oligonucleotides (a type of therapy for regulating protein production), and found that EAAT2 repression was blocked by antisense oligonucleotides. They then followed up by testing in a mouse model of ALS whether inhibiting miR-218 would block EAAT2 suppression. SOD1 mice (a mouse model of ALS) were treated with either antisense oligonucleotides or saline, and they found that the mice treated with the antisense oligonucleotides had less miR-218 activity in their brains. It also reduced astrogliosis (an abnormal increase in number of astrocytes) in ALS model mice.

                                      Astrocyte,  S  ervier Medical Art,  image by BrainPost,  CC BY-SA 3.0

                                     Astrocyte, Servier Medical Art, image by BrainPost, CC BY-SA 3.0

What's the impact?

This is the first study to demonstrate that a microRNA (miR-218) release from dying motor neurons results in the repression of glutamate transporter (EAAT2) expression. Further, this study shows that blocking this repression using antisense oligonucleotides can reverse the effects of this microRNA on causing potentially damaging effects on astrocytes. Importantly, this study suggests that microRNAs play an important role in affecting astrocytes that contribute to ongoing neurodegeneration in ALS.

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Hoye et al., Motor neuron-derived microRNAs cause astrocyte dysfunction in amyotrophic lateral sclerosis. Brain (2018). Access the original scientific publication here.