Astrocytes make long-term fear memories fade before they form

Amazing stuff!

"Manipulating important non-neuronal brain cells called astrocytes using light prevented fear memories from being retained long-term, according to new research. The findings add to growing evidence about astrocytes’ role in memory and open the door to potential treatments for conditions like PTSD, which is characterized by abnormal fear memory.

Astrocytes, the long-tailed, star-shaped cells that make up the majority of cells in the central nervous system, are known to perform metabolic, structural, and neuroprotective tasks in the brain. But scientists have started discovering that these cells play an important role in memory, too. ..."

"... Researchers ... discovered that part of the memory selection process depends on the function of astrocytes, a special type of cell that surrounds neurons in the brain. They showed that artificially acidifying the astrocytes did not affect short-term memory but prevented memories from being remembered long-term. ...

A mild electrical shock was delivered to mice in an experiment chamber. When placed back in the same chamber, the mice remembered the shock and froze as a natural response. In comparison, the mice who had their astrocytes acidified immediately after the mild shock were able to temporarily hold onto the fear memory, but they forgot it by the next day. This shows that acidifying the astrocytes did not affect short-term memory but prevented the memories from being remembered long-term.

A different effect was seen for mice who had their astrocytes alkalinized. When tested three weeks later, control mice typically showed signs of forgetting, demonstrated by a decrease in freezing responses. However, mice whose astrocytes were alkalinized immediately after a strong shock still displayed strong fear responses even after three weeks. This suggests that astrocytes play a key role in determining whether memories are erased or preserved for a long time, immediately after a traumatic event. ..."

From the abstract:

"While some vivid memories are unyielding and unforgettable, others fade with time. Astrocytes are recognized for their role in modulating the brain's environment and have recently been considered integral to the brain's information processing and memory formation. This suggests their potential roles in emotional perception and memory formation. In this study, we delve into the impact of amygdala astrocytes on fear behaviors and memory, employing astrocyte-specific optogenetic manipulations in mice. Our findings reveal that astrocytic photoactivation with channelrhodopsin-2 (ChR2) provokes aversive behavioral responses, while archaerhodopsin-T (ArchT) photoactivation diminishes fear perception. ChR2 photoactivation amplifies fear perception and fear memory encoding but obstructs its consolidation. On the other hand, ArchT photoactivation inhibits memory formation during intense aversive stimuli, possibly due to weakened fear perception. However, it prevents the decay of remote fear memory over three weeks. Crucially, these memory effects were observed when optogenetic manipulations coincided with the aversive experience, indicating a deterministic role of astrocytic states at the exact moment of fear experiences in shaping long-term memory. This research underscores the significant and multifaceted role of astrocytes in emotional perception, fear memory formation, and modulation, suggesting a sophisticated astrocyte-neuron communication mechanism underlying basic emotional state transitions of information processing in the brain."

'Star cells' make long-term fear memories fade before they form

Saying Goodbye to Traumatic Memories: Astrocytic Manipulation of the Fate of Memory (original news release)

Astrocytic determinant of the fate of long-term memory (open access)

Selective suppression of long-term memory formation through ChR2 photoactivation of amygdala astrocytes. The experiments suggest the presence of parallel processes governing short-term and long-term memory formation, respectively.

Mice inherently possess a selective filtering mechanism that enhances the memory of intense experiences; however, this filtering function was inhibited by ArchT photoactivation of astrocytes in the amygdala. Additionally, the natural forgetting process over three weeks was suppressed by the light stimulation of ArchT-expressing astrocytes.