α2* Nicotinic acetylcholine receptors influence hippocampus-dependent learning and memory in adolescent mice.

The absence of alpha 2* nicotinic acetylcholine receptors (nAChRs) in oriens lacunosum moleculare (OLM) GABAergic interneurons ablate the facilitation of nicotine-induced hippocampal CA1 long-term potentiation and impair memory. The current study delineated whether genetic mutations of alpha 2* nAChRs (Chrn alpha 2(L9'S/L9'S) and Chrna2(KO)) influence hippocampus- dependent learning and memory and CA1 synaptic plasticity. We substituted a serine for a leucine (L9'S) in the alpha 2 subunit (encoded by the Chrna2 gene) to make a hypersensitive nAChR. Using a dorsal hippocampus-dependent task of preexposure-dependent contextual fear conditioning, adolescent hypersensitive Chrna2(L9'S/L9'S) male mice exhibited impaired learning and memory. The deficit was rescued by low-dose nicotine exposure. Electrophysiological studies demonstrated that hypersensitive alpha 2 nAChRs potentiate acetylcholine-induced ion channel flux in oocytes and acute nicotine-induced facilitation of dorsal/intermediate CA1 hippocampal long-term potentiation in Chrna2(L9'S/L9'S) mice. Adolescent male mice null for the alpha 2 nAChR subunit exhibited a baseline deficit in learning that was not reversed by an acute dose of nicotine. These effects were not influenced by locomotor, sensory or anxiety-related measures. Our results demonstrated that alpha 2* nAChRs influenced hippocampus-dependent learning and memory, as well as nicotine-facilitated CA1 hippocampal synaptic plasticity.