Winston, S. | Search bioRxiv

bioRxiv2024

Deconstruction of a memory engram reveals distinct ensembles recruited at learning

How are associative memories formed? Which cells represent a memory, and when are they engaged? By visualizing and tagging cells based on their calcium influx with unparalleled temporal precision, we identified non-overlapping dorsal CA1 neuronal ensembles that are differentially active during associative fear memory acquisition. We dissected the acquisition experience into periods during which salient stimuli were presented or certain mouse behaviors occurred and found that cells associated with specific acquisition periods are sufficient alone to drive memory expression and contribute to fear engram formation. This study delineated the different identities of the cell ensembles active during learning, and revealed, for the first time, which ones form the core engram and are essential for memory formation and recall.

neuroscience↗

bioRxiv2020

Characterization of basal forebrain glutamate neurons suggests a role in control of arousal and avoidance behavior

The basal forebrain (BF) is involved in arousal, attention, and reward processing but the role of individual BF subtypes is still being uncovered. Glutamatergic neurons are the least well-understood of the three major BF neurotransmitter phenotypes. Here we analyzed the distribution, size, calcium-binding protein content and projections of the major group of BF glutamate neurons expressing the vesicular glutamate transporter subtype 2 (vGluT2) and tested the functional effect of activating them. Mice expressing Cre recombinase under control of the vGluT2 promoter were crossed with a reporter strain expressing the red fluorescent protein, tdTomato, to generate vGluT2-cre-tdTomato mice. Immunohistochemical staining for choline acetyltransferase and a cross with mice expressing green fluorescent protein selectively in GABAergic neurons confirmed cholinergic, GABAergic and vGluT2+ neurons represent separate BF subpopulations. Subsets of BF vGluT2+ neurons expressed the calcium binding proteins calbindin or calretinin, suggesting that multiple subtypes of BF vGluT2+ neurons exist. Anterograde tracing using adeno-associated viral vectors expressing channelrhodopsin2- enhanced yellow fluorescent fusion proteins revealed major projections of BF vGluT2+ neurons to neighboring BF cholinergic and parvalbumin neurons, as well as to extra-BF areas involved in the control of arousal and regions responding to aversive or rewarding stimuli such as the lateral habenula and ventral tegmental area. Optogenetic activation of BF vGluT2 neurons in a place preference paradigm elicited a striking avoidance of the area where stimulation was given. Together with previous optogenetic findings suggesting an arousal-promoting role, our findings suggest BF vGluT2 neurons play a dual role in promoting wakefulness and avoidance behavior.

neuroscience↗