Nicotinic activity stabilizes convergence of nicotinic and GABAergic synapses on rilopodia of hippocampal interneurons

Nicotinic acetylcholine receptors containing alpha 7 subunits occupy pre- and postsynaptic sites in the adult hippocampus. We rind that embryonic hippocampal slices in culture display the receptors most prominently on interneurons where they form clusters localized in part on filopodia. The receptors often co-distribute specifically with GABA(A) receptors. In septal-hippocampal co-cultures, the filopodia become coinnervated by cholinergic and GABAergic terminals abutting the receptor clusters. Nicotinic transmission appears to stabilize the cholinergic contacts: pharmacological blockade of the alpha 7-containing nicotinic receptors increases the rate of filopodia movement and decreases the incidence of the clusters being adjacent to cholinergic terminals. Immunostaining fresh hippocampal slices from neonatal rat pups confirms that cholinergic and GABAergic terminals contact alpha 7-containing nicotinic receptor clusters in vivo, and the clusters appear to include filopodial sites. The results indicate a convergence of nicotinic and GABAergic input at specific sites on developing hippocampal interneurons and suggest that synaptic activity helps stabilize the nicotinic contribution. (c) 2005 Elsevier Inc. All rights reserved.