New Mechanism to Maintain Astrocyte-Neuron Communication

Neurons and astrocytes are the two types of cells required by the brain to enjoy the scent of morning coffee and freshly baked cookies or to discern the warning smell of something burning. This happens when the two cells work closely with each other.

Although scientists have shown that many different things occur in neurons when olfactory, or smell, perception occurs, what are the astrocyte responses and how they add up to the sensory experience is yet to be understood.

At the Baylor College of Medicine, scientists and collaborating institutions report in the journal Science that the responses of astrocytes to olfactory stimulation disclose a new mechanism that is needed to retain astrocyte-neuron communication and further process olfactory sensation.

Previous studies have shown that under natural conditions in a living animal, olfactory stimulation of the brain activates neurons first, which changes the genes these neurons express to be able to mediate the olfactory sensation.”

Dr. Debosmita Sardar, Study First Author and Postdoctoral Associate, Baylor School of Medicine

Sardar added, “In this study, we investigated what occurred to astrocytes following neural activity during olfactory stimulation and uncovered changes that had not been described before.”

Olfactory stimulation activated an increase of serotonin transporter Slc22a3 on the astrocytes, which facilitated serotonin transport into the cells.

We followed serotonin inside the astrocytes and were surprised to discover that it traveled to the cell nucleus, where it bound to histones, proteins attached to the DNA that help regulate astrocyte gene expression. Serotonin bound to DNA acted as a switch, which controlled gene expression.”

Dr. Debosmita Sardar, Study First Author and Postdoctoral Associate, Baylor School of Medicine

Fascinatingly, serotonin controls the expression of astrocyte genes involved in the production of the neurotransmitter GABA, which further feeds back to neurons that regulates the neural circuit that is fundamental to sensory perception.

We showed that losing transporter Slc22a3 in astrocytes reduced serotonin levels in the cells and led to alterations in serotonin-bound DNA. In turn, this reduced the expression of genes involved in the synthesis of GABA and decreased astrocytic GABA release, which disturbed the neural circuits of olfactory sensation.”

Dr. Debosmita Sardar, Study First Author and Postdoctoral Associate, Baylor School of Medicine

Serotonin is famous for its contribution to normal brain function and being involved in addiction and depression.

Sardar stated, “Here we discovered a new function of serotonin in astrocytes. Serotonin triggers changes in astrocyte gene expression patterns, turning astrocytes into a hub of olfactory sensation processing.”

“This project has uncovered novel aspects of astrocyte function,” stated Deneen, Professor and Dr. Russell J. and Marian K. Blattner Chair in the Department of Neurosurgery and Director of the Center for Cancer Neuroscience at Baylor. He also is the study’s corresponding author.

Deneen added, “We are learning that astrocytes are very plastic, just as neurons are, meaning that astrocytes can change their characteristics and functions in response to environmental stimuli. They listen to neurons and respond, and their two-way communication is at the core of sensory processing and ultimately, animal behavior.”