Synaptic plasticity deficits in a mouse model of Timothy syndrome: LTP saturation and its pharmacological rescue by nifedipine

Abstract

Timothy syndrome (TS) is a multisystem disorder characterized by cardiovascular abnormalities and a spectrum of neuropsychiatric symptoms, including language impairment, seizure, cognitive disability and autism. TS is caused by gain of function mutations in the CACNA1C gene that encodes the CaV1.2 L-type calcium channel. TS mutations have been reported to disrupt hippocampal long-term potentiation (LTP), a process implicated in memory formation. Here, we compared wild type (WT) and heterozygous G406R CaV1.2 mutant TS2-neo model mice using a LTP saturation protocol consisting of two successive theta burst stimuli. While WT mice showed potentiated synaptic strength in response to both theta-burst stimuli, TS2-neo mutants exhibited a smaller initial LTP and minimal responses to the second stimulus. The dihydropyridine L-type calcium channel blocker, nifedipine, inhibited LTP in WT mice, but enhanced both the initial and the second LTP in TS2-neo mutants. By measuring the phosphorylation activation of ERK, CREB and glutamate receptor GluR1, steps required for hippocampal LTP, we found that all were abnormally high at baseline in the mutant mice. Nifedipine blocked LTP-related phosphorylation in WT mice, but normalized baseline phosphorylation of ERK, CREB and GluR1 in TS2-neo mice, allowing their subsequent activity-dependent induction. Thus, while nifedipine inhibits LTP in WT mice, the drug reinstates LTP and normal synaptic plasticity in a TS model, suggesting potential therapeutic approaches for synaptic deficits in channelopathies such as TS.