Role of TRPC6 in conditioning and extinction of contextual fear memory in mice

Abstract

Objective To explore the role of transient receptor potential canonical 6 (TRPC6) on conditioning and extinction in contextual fear memory. Methods A total of 32 male C57BL/6J mice (6~8 weeks old) were randomized into fear conditioning (Cond group, n=16) and fear extinction (Ext group, n=16). Both groups were further divided into sh-TRPC6 subgroup (n=8) and GFP subgroup (n=8). Stereotaxic injection of adeno-associated virus (AAV)-TRPC6 or AAV-green fluorescent protein (AAV-GFP) was performed into the hippocampus of the corresponding mice bilaterally for intervention of fear. Immunofluorescence assay and Western blotting were used to detect the expression of TRPC6 in hippocampus of each sub-group in 20 d after stereotaxic injection. On day 21, fear conditioning was established though inescapable foot shock (footshock of 0.7 mA for 2 s and intertrial interval for 58 s, totally 5 cycles), and fear test was carried out on day 22. For the mice from the Ext group, fear conditioning begun in 4 d after stereotaxic injection, fear extinction training started on day 21, and fear test was also carried out on day 22. Results At 20 d after injection, massive GFP-positive cells were observed in the pyramidal layer of hippocampal CA1 region, and Western blotting showed AAV-TRPC6 injection significantly reduced the hippocampal TRPC6 expression in the sh-TRPC6 subgroup than the GFP subgroup (P < 0.01). In the experiment of fear conditioning, the upward trend of the Freezing% levels in sh-TRPC6 subgroup was obviously slower (P < 0.05), and its Freezing% levels were notably lower in fear test when compared with the GFP subgroup (P < 0.05). In the experiment of fear extinction, the downward trend of the Freezing% levels in sh-TRPC6 subgroup was significantly slower (P < 0.05) and its Freezing% levels were significantly higher in fear test when compared with the GFP subgroup (P < 0.05). Conclusion Hippocampal TRPC6 participates in the conditioning and extinction in contextual fear memory, and suppression of its expression can destroy the processes.

Keywords

• transient receptor potential canonical 6
• fear conditioning
• fear extinction