Effects of the Selective Serotonin Reuptake Inhibitor Fluoxetine on Developing Neural Circuits in a Model of the Human Fetal Cortex

Abstract

The developing prenatal brain is particularly susceptible to environmental disturbances. During prenatal brain development, synapses form between neurons, resulting in neural circuits that support complex cognitive functions. In utero exposure to environmental factors such as pharmaceuticals that alter the process of synapse formation increases the risk of neurodevelopmental abnormalities. However, there is a lack of research into how specific environmental factors directly impact the developing neural circuitry of the human brain. For example, selective serotonin reuptake inhibitors are commonly used throughout pregnancy to treat depression, yet their impact on the developing fetal brain remains unclear. Recently, human brain models have provided unprecedented access to the critical window of prenatal brain development. In the present study, we used human neurons and cortical spheroids to determine whether the selective serotonin reuptake inhibitor fluoxetine alters neurite and synapse formation and the development of spontaneous activity within neural circuits. We demonstrate that cortical spheroids express serotonin transporter, thus recapitulating the early developmental expression of serotonin transporter associated with cortical pyramidal neurons. Cortical spheroids also appropriately express serotonin receptors, such as synaptic 5-HT2A and glial 5-HT5A. To determine whether fluoxetine can affect developing neural circuits independent of serotonergic innervation from the dorsal and medial raphe nuclei, we treated cortical neurons and spheroids with fluoxetine. Fluoxetine alters neurite formation in a dose-dependent fashion. Intriguingly, in cortical spheroids, neither acute nor chronic fluoxetine significantly altered excitatory synapse formation. However, only acute, but not chronic fluoxetine exposure altered inhibitory synaptogenesis. Finally, fluoxetine reversibly suppresses neuronal activity in a dose-dependent manner. These results demonstrate that fluoxetine can acutely alter synaptic function in developing neural circuits, but the effects were not long-lasting. This work provides a foundation for future studies to combine serotonergic innervation with cortical spheroids and assess the contributions of fluoxetine-induced alterations in serotonin levels to brain development.

Molecular and Functional Characterization of Different BrainSphere Models for Use in Neurotoxicity Testing on Microelectrode Arrays

“…Human in vitro models for acute neurotoxicity testing that examine neurotransmission mainly refer to effects of total neural networks by measuring spike-, burst-, and network-related parameters. While these parameters provide valuable information, they do not necessarily account for a large variety of neurotoxic MoA [31,37,[96][97][98][99][100]. The low granularity of the classical MEA evaluation by studying integrated signals over single electrodes is accompanied by a high dependence on the NN composition.…”

Molecular and functional characterization of different BrainSphere models for use in neurotoxicity testing on microelectrode arrays

“…Human in vitro models for acute neurotoxicity testing that examine neurotransmission mainly refer to effects of total neural networks by measuring spike-, burst-, and network-related parameters. While these parameters provide valuable information, they do not necessarily account for a large variety of neurotoxic MoA [29,35,[92][93][94][95][96]. The low granularity of the classical MEA evaluation by studying integrated signals over single electrodes is accompanied by high dependence on the NN composition.…”

Systems biology approaches to identify potential targets and inhibitors of the intestinal microbiota to treat depression

“…During prenatal brain development, synapses form between neurons, resulting in neural circuits that support complex cognitive functions. Selective serotonin reuptake inhibitors are commonly used throughout pregnancy to treat depression 51 . Dysregulation of the serotonergic system has been reported to have a significant role in several neurological disorders, including depression, autism and substance abuse disorders 52 .…”