nAChR-Mediated Calcium Responses and Plasticity in Drosophila Kenyon Cells Jorge M. Campusano, 1,2 Hailing Su, 1,2 Shaojuan A. Jiang, 1,2 Beatriz Sicaeros, 1,2 Diane K. O’Dowd 1,2 1 Department of Anatomy and Neurobiology, University of California—Irvine, Irvine CA 92697-1280 2 Department of Developmental and Cell Biology, University of California—Irvine, Irvine CA 92697-1280 Received 12 January 2007; revised 14 March 2007; accepted 2 April 2007 ABSTRACT: In Drosophila, nicotinic acetylcholine receptors (nAChRs) mediate fast excitatory synaptic transmission in mushroom body Kenyon cells, a neuro- nal population involved in generation of complex behav- iors, including responses to drugs of abuse. To deter- mine whether activation of nAChRs can induce cellular changes that contribute to functional plasticity in these neurons, we examined nicotine-evoked responses in cells cultured from brains of late stage OK107-GAL4 pupae. Kenyon cells can be identified by expression of green flu- orescent protein (GFPþ). Nicotine activates a-bungaro- toxin-sensitive nAChRs, causing a rapid increase in in- tracellular calcium levels in over 95% of the Kenyon cells. The nicotine-evoked calcium increase has a volt- age-gated calcium channel (VGCC) dependent compo- nent and a VGCC-independent component that involves calcium influx directly through nAChRs. Thapsigargin treatment reduces the nicotine response consistent with amplification by calcium release from intracellular stores. The response to nicotine is experience-depend- ent: a short conditioning pulse of nicotine causes a tran- sient 50% reduction in the magnitude of the response to a test pulse of nicotine when the interpulse interval is 4 h. This cellular plasticity is dependent on activation of the VGCC-component of the nicotine response and on cAMP-signaling, but not on protein synthesis. These data demonstrate that activation of nAChRs induces a calcium-dependent plasticity in Kenyon cells that could contribute to adult behaviors involving information processing in the mushroom bodies including responses to nicotine. ' 2007 Wiley Periodicals, Inc. Develop Neurobiol 67: 1520–1532, 2007 Keywords: calcium imaging; mushroom bodies; nicotine; Kenyon cells; nAChR INTRODUCTION Behavioral plasticity relies on the ability of experi- ence to cause persistent alterations in central neural circuits in all animals. In the mammalian brain, where glutamate is the major excitatory neurotransmitter, activation of calcium permeable glutamate receptors is important in mediating long-lasting changes in syn- aptic efficacy that contribute to memory formation (Malenka and Bear, 2004; Cull-Candy et al., 2006). Like mammals, insects are capable of learning and remembering information but acetylcholine as opposed to glutamate is the primary excitatory euro- transmitter in the central nervous system (CNS) (Breer and Sattelle, 1987; Gundelfinger, 1992). While previous studies have demonstrated that nicotinic ac- etylcholine receptors (nAChRs) in some insect neu- rons are calcium permeable (Goldberg et al., 1999; Oertner et al., 1999, 2001; Single and Borst, 2002), it Correspondence to: D.K. O’Dowd (dkodowd@uci.edu). Contract grant sponsor: NIH; contract grant numbers: DA14960, NS27501. Contract grant sponsor: The Howard Hughes Medical Institute. ' 2007 Wiley Periodicals, Inc. Published online 24 May 2007 in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/dneu.20527 1520