Abstract
Mice deficient in the extracellular matrix glycoprotein tenascin-C (TNC
−/−
) express a deficit in specific forms of hippocampal synaptic plasticity, which involve the L-type voltage-gated Ca
2+
channels (L-VGCCs). The mechanisms underlying this deficit and its functional implications for learning and memory have not been investigated. In line with previous findings, we report on impairment in theta-burst stimulation (TBS)-induced long-term potentiation (LTP) in TNC
−/−
mice in the CA1 hippocampal region and its rescue by the L-VGCC activator Bay K-8644. We further found that the overall pattern of L-VGCC expression in the hippocampus in TNC
−/−
mice was normal, but Western blot analysis results uncovered upregulated expression of the Ca
v
1.2 and Ca
v
1.3 α-subunits of L-VGCCs. However, these L-VGCCs were not fully functional in TNC
−/−
mice, as demonstrated by Ca
2+
imaging, which revealed a reduction of nifedipine-sensitive Ca
2+
transients in CA1 pyramidal neurons. TNC
−/−
mice showed normal learning and memory in the contextual fear conditioning paradigm but impaired extinction of conditioned fear responses. Systemic injection of the L-VGCC blockers nifedipine and diltiazem into wild-type mice mimicked the impairment of fear extinction observed in TNC
−/−
mice. The deficiency in TNC
−/−
mice substantially occluded the effects of these drugs. Our results suggest that TNC-mediated modulation of L-VGCC activity is essential for fear extinction.