Choi, D. I., Kim, J., Lee, H., Kim, J. I., Sung, Y., Choi, J. E., … & Kaang, B. K. (2021). Synaptic correlates of associative fear memory in the lateral amygdala. Neuron, 109(17), 2717-2726. https://doi.org/10.1016/j.neuron.2021.07.003
dual-eGRASP, Auditory Fear Conditioning
Mouse Auditory Cortex and Lateral Amygdala
Authors use the dual-eGRASP technique (which they developed in Choi et al. 2018) to tag engram populations in both auditory cortex (AC) and lateral amygdala (LA) during an auditory fear conditioning (AFC) experiment. Engram cells in the LA were labeled red (mScarlet) and expressed the post-eGRASP protein. Engram cells in AC (presumed to encode the auditory tone) expressed the Yellow pre-eGRASP protein. As such, synapses from AC engram cell axons onto LA engram dendrites would appear as yellow PSDs onto red dendritic spines (E-E synapses). A random subset of AC cells (non-engram) expressed the Blue pre-eGRASP protein and these AC non-engram to LA engram synapses could be visualized as blue PSDs onto red dendritic spines (N-E synapses). E-E synapses were found to be larger than N-E synapses after AFC. This difference disappeared after AFC extinction but returned after AFC re-conditioning, providing strong evidence that these synaptic changes encode the fear memory in LA.
“Our findings demonstrate the physical substrate of memory at the synaptic scale.”