Scientists find new evidence of links between schizophrenia and dopamine

The study supports the emerging hypothesis that schizophrenia is a developmental dopaminergic disorder.
Sejal Sharma
Representational image
Representational image

Cinefootage Visuals/iStock 

Our body gets regular hits of the ‘feel-good’ hormone, dopamine, when we engage in certain pleasurable activities, like sex, or even when we open social media apps like Instagram. The human brain is hard-wired to seek behaviors that release dopamine in our reward system.

While the specific cause of schizophrenia is unknown, there is strong evidence to suggest that the disorder can be caused by abnormal dopamine signaling. 

In their previous research, a team of scientists had shown that low levels of maternal vitamin D increase the risk of schizophrenia in offspring. The same University of Queensland’s Brain Institute team dug deeper into their previously published work. It used molecular imaging technology to confirm the role played by a mother’s vitamin D levels in developing the baby’s dopamine-producing brain cells.

In the new study, the scientists created dopamine-like neurons to replicate the cell differentiation process during an embryo’s development. Cell differentiation is the process by which dividing cells change their functional or phenotypical type. 

The neurons were cultured with and without the hormone calcitriol, the active form of Vitamin D, and bind to its receptor in the cell’s nucleus.

The researchers discovered that not only cell differentiation but the neuron structure was affected by vitamin D. 

“What we found was the altered differentiation process in the presence of vitamin D not only makes the cells grow differently but recruits machinery to release dopamine differently,” said Darryl Eyles, corresponding author of the study.

The ‘machinery’ that Eyles mentioned are neurites, which are information messengers. They are projections growing from the body of a neuron, essential in the formation of complex neuronal circuits. As information messengers, neurites send and receive signals to and from other parts of the nervous system. The researchers found that the number of neurites was markedly increased, and within those neurites, the distribution of the proteins responsible for releasing dopamine was altered, explained the NewAtlas.

The team then used new imaging technology called false fluorescent neurotransmitters (FFNs) to observe how the release of dopamine is affected by the presence or absence of calcitriol. They found that the dopamine release was enhanced in neurons grown in the presence of calcitriol.

“This is conclusive evidence that vitamin D affects the structural differentiation of dopaminergic neurons,” added Eyles.

The study's results open new avenues for new research to investigate the connection between vitamin D and dopamine-neuron function.

Study abstract:

Vitamin D has been identified as a key factor in dopaminergic neurogenesis and differentiation. Consequently, developmental vitamin D (DVD) deficiency has been linked to disorders of abnormal dopamine signalling with a neurodevelopmental basis such as schizophrenia. Here we provide further evidence of vitamin D's role as a mediator of dopaminergic development by showing that it increases neurite outgrowth, neurite branching, presynaptic protein re-distribution, dopamine production and functional release in various in vitro models of developing dopaminergic cells including SH-SY5Y cells, primary mesencephalic cultures and mesencephalic/striatal explant co-cultures. This study continues to establish vitamin D as an important differentiation agent for developing dopamine neurons, and now for the first time shows chronic exposure to the active vitamin D hormone increases the capacity of developing neurons to release dopamine. This study also has implications for understanding mechanisms behind the link between DVD deficiency and schizophrenia.

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