Synaptotagmin1 synthesis induced by synaptic plasticity in mouse hippocampus through activation of nicotinic acetylcholine receptors

We have reported that systemic application of nicotinic agonists expresses a long-term potentiation (LTP)-like facilitation, a model of synaptic plasticity, in vivo in the mouse hippocampus. The present study conducted to clarify the involvement of synaptotagmin1 in synaptic plasticity by investigating the time-dependent change of the mRNA and protein levels of synaptotagmin1 during LIP-like facilitation in the mouse hippocampus. The mRNA expression of synaptotagmin1 increased during 2- to 8-h period by intraperitoneal application of nicotine (3 mg/kg), returning to the basal level in 12-h. Also, the protein level of synaptotagmin1, but not synaptophysin, in a total fraction from hippocampus increased during 4- to 12-h period by the same treatment, returning to the basal level in 24-h. The protein level of synaptotagmin1 in a membrane fraction from hippocampus also increased during 4- to 8-h period by nicotine, returning to the basal level in 12-h. This nicotine-enhanced synaptotagmin1 protein in a membrane fraction was inhibited by pretreatment of mecamylamine (0.3 mg/kg, i.p.), a nonselective nicotinic acetylcholine receptors (nAChRs) antagonist. Furthermore, choline (30 mg/kg, i.p.), a selective alpha 7 nAChR agonist, or ABT-418 (10 mg/kg, i.p.), a selective alpha 4 beta 2 nAChR agonist, enhanced the level of synaptotagmin1 in a membrane fraction. Our findings demonstrate that synaptotagmin1 protein following mRNA which is enhanced without increasing the number of synapse gathers around pre-synaptic membrane during hippocampal LIP-like facilitation through activation of alpha 7 and/or alpha 4 beta 2 nAChRs in the brain. These results suggest that new-synthesized synaptotagmin1 following synaptic plasticity may contribute to long-lasting synaptic plasticity via positive, feedfoward mechanisms. (C) 2010 Elsevier Ireland Ltd. All rights reserved.