Abstract: PURPOSE: The primary visual cortex (V1) undergoes plastic changes following associative learning, resulting in specific responses to visual stimuli. Classical fear conditioning is a model of associative learning. Simultaneously, color vision is a crucial component of visual perception. However, it is still unclear how color-related fear learning causes plastic changes in mouse V1.
METHODS: Firstly, we successfully established a fear conditioning model using blue light as a visual cue. We used two-photon calcium imaging to record light-evoked responses of the same neurons of layer II/III of V1 from anesthetized mice before and after learning. Using correlation-based graph theory analysis, we examined ensembles induced by blue light (cue) or green light (non-cue) before and after training. We employed in vivo whole-cell patch clamp technique to investigate the synaptic mechanisms of visual information processing in mouse V1 neurons before and after learning. We used bulk RNA-seq to find the differential gene. Finally, we used patch-seq to analyze the relationship between gene expression and electrophysiology.
RESULTS: Our findings showed that fear conditioning resulted in a notable increase in the strength of connections solely within the blue-light ensembles. In subgroups within these ensembles, our results revealed that newly generated neurons within the blue ensembles exhibited a higher clustering coefficient, and comparable relative degree and connectivity strength compared to stable neurons present in the same ensemble. Through patch-clamp experiments, we observed that fear conditioning resulted in an elevation in input resistance of V1 neurons, as well as an enhancement in the postsynaptic membrane potential response to blue-light stimulation. During light-off periods, we detected a higher difference between the responses to blue and green light. Furthermore, we observed a decrease in the power of the low-frequency signals following fear conditioning. We found some differentially expressed genes before and after learning, such as Fkbp5 and Kcnj3. Notably, we observed a significant correlation between the expression of certain genes and neuronal functions.
CONCLUSIONS: Our findings indicated that fear learning induced plasticity changes in mice, specifically in response to blue light stimulation, affecting the overall and individual activities of V1 neurons as well as the molecular level. Furthermore, we observed a high correlation between the electrophysiological features of V1 neurons after learning and their transcriptome expression.

Key words: associative memory, V1, ensembles, RNA-seq, patch-seq