[Show abstract][Hide abstract] ABSTRACT: The role of the cyclic nucleotide-gated (CNG) channel CNGA3 is well established in cone photoreceptors and guanylyl cyclase-D-expressing olfactory neurons. To assess a potential function of CNGA3 in the mouse amygdala and hippocampus, we examined synaptic plasticity and performed a comparative analysis of spatial learning, fear conditioning and step-down avoidance in wild-type mice and CNGA3 null mutants (CNGA3(-/-) ). CNGA3(-/-) mice showed normal basal synaptic transmission in the amygdala and the hippocampus. However, cornu Ammonis (CA1) hippocampal long-term potentiation (LTP) induced by a strong tetanus was significantly enhanced in CNGA3(-/-) mice as compared with their wild-type littermates. Unlike in the hippocampus, LTP was not significantly altered in the amygdala of CNGA3(-/-) mice. Enhanced hippocampal LTP did not coincide with changes in hippocampus-dependent learning, as both wild-type and mutant mice showed a similar performance in water maze tasks and contextual fear conditioning, except for a trend toward higher step-down latencies in a passive avoidance task. In contrast, CNGA3(-/-) mice showed markedly reduced freezing to the conditioned tone in the amygdala-dependent cued fear conditioning task. In conclusion, our study adds a new entry on the list of physiological functions of the CNGA3 channel. Despite the dissociation between physiological and behavioral parameters, our data describe a so far unrecognized role of CNGA3 in modulation of hippocampal plasticity and amygdala-dependent fear memory.
[Show abstract][Hide abstract] ABSTRACT: Neuronal hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are known to modulate spontaneous activity, resting membrane potential, input resistance, afterpotential, rebound activity, and dendritic integration. To evaluate the role of HCN2 for hippocampal synaptic plasticity, we recorded long-term potentiation (LTP) in the direct perforant path (PP) to CA1 pyramidal cells. LTP was enhanced in mice carrying a global deletion of the channel (HCN2(-/-)) but not in a pyramidal neuron-restricted knockout. This precludes an influence of HCN2 located in postsynaptic pyramidal neurons. Additionally, the selective HCN blocker zatebradine reduced the activity of oriens-lacunosum moleculare interneurons in wild-type but not HCN2(-/-) mice and decreased the frequency of spontaneous inhibitory currents in postsynaptic CA1 pyramidal cells. Finally, we found amplified LTP in the PP of mice carrying an interneuron-specific deletion of HCN2. We conclude that HCN2 channels in inhibitory interneurons modulate synaptic plasticity in the PP by facilitating the GABAergic output onto pyramidal neurons.
Cellular and Molecular Life Sciences CMLS 01/2011; 68(1):125-37. DOI:10.1007/s00018-010-0446-z · 5.81 Impact Factor