Astrocytes Integrate Information from Dendrites for Spatial Memory

A new study led by researchers at the University of Bonn has found that astrocytes, a glial cell subtype, play an essential role in spatial learning in the brain. The study was conducted in collaboration with the German Center for Neurodegenerative Diseases (DZNE) and published in the journal Nature Communications.

The study looked closely at neurons in rodents' hippocampus, which is a region of the brain that plays a central role in memory processes, particularly spatial memory. "In the hippocampus, there are neurons that specialize in just that - place cells," says senior author Prof. Dr. Christian Henneberger from the Institute of Cellular Neuroscience at the University Hospital Bonn.

The researchers found that in the hippocampus, there are about one million neurons called place cells, each responding to a specific combination of environmental characteristics. To further analyze this area, the researchers utilized several techniques such as whole-cell patch clamp, iontophoretic glutamate application, two-photon excitation fluorescence microscopy, and glutamate uncaging in acute rat and mouse brain slices.

They found that exogenous D-serine reduced the threshold of dendritic spikes and increased their amplitude. They also found that triggering an astrocytic mechanism controlling endogenous D-serine supply via endocannabinoid receptors (CBRs) also increased dendritic spiking.

Interestingly, the team found this pathway activated by pyramidal cell activity primarily in the theta range, which required HCN channels and astrocytic CB1Rs. This suggests that astrocytes form a positive and frequency-dependent feedback loop between pyramidal cell activity and their integration of dendritic input. Disrupting this feedback loop in mice resulted in spatial memory impairment, demonstrating its behavioral relevance.

The researchers also found that if they inhibit the assistance provided by astrocytes in mice, they are less likely to remember new locations. These findings suggest that astrocytes play a critical role in amplifying the signals in the dendrites of hippocampal CA1 pyramidal cells through the release of D-serine. This process allows for efficient integration of inputs arriving at the dendrites, which is essential for spatial learning and memory.