Developmental and Activity-Dependent Regulation of ARMS/Kidins220 in Cultured Rat Hippocampal Neurons Rosa Y. Corte ´ s, 1* Juan Carlos Are ´ valo, 2{ Jason P. Magby, 1{ Moses V. Chao, 2 Mark R. Plummer 1 1 Department of Cell Biology and Neuroscience, Rutgers University, Nelson Laboratories, Piscataway, New Jersey 2 Molecular Neurobiology Program, Department of Cell Biology, Physiology and Neuroscience, Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York Received 9 March 2007; revised 4 May 2007; accepted 18 May 2007 ABSTRACT: Neurotrophin activation of Trk receptors elicits diverse effects on neuronal survival, dif- ferentiation, and synaptic plasticity. One of the central questions is how specificity is encoded in neurotrophin receptor signaling and actions. A unique downstream protein is the Ankyrin-Repeat Rich Membrane Span- ning (ARMS)/Kinase D-interacting substrate-220 kDa (Kidins220), a very abundant scaffold protein in the hip- pocampus. To determine the roles of ARMS/Kidins220 in hippocampal neurons, we have analyzed the effects of synaptic activity upon the regulation and distribution of ARMS/Kidins220. At early times in vitro (<7 DIV), syn- aptic activity was low and ARMS/Kidins220 levels were high. As synaptic activity and markers for synapse mat- uration, such as PSD-95, increased, ARMS/Kidins220 significantly decreased to a plateau by later times in vitro (>12 DIV). Immunocytochemistry showed ARMS/ Kidins220 to be concentrated at the tips of growing processes in immature cultures, and more diffusely dis- tributed in older cultures. To examine the apparent inverse relationship between activity and ARMS/ Kidins220 levels, neuronal firing was manipulated phar- macologically. Chronic exposure to TTX increased ARMS/Kidins220 levels, whereas bicuculline caused the opposite effect. Moreover, using shRNA to decrease ARMS/Kidins220 levels produced a corresponding increase in synaptic activity. We find that ARMS/ Kidins220 may function in neuronal development as an indicator and potentially as a homeostatic regulator of overall synaptic strength in hippocampal neurons. ' 2007 Wiley Periodicals, Inc. Develop Neurobiol 00: 000–000, 2007 Keywords: ARMS; Kidins220; neurotrophins; synaptic plasticity; synaptic development INTRODUCTION Neurotrophins mediate diverse effects via Trk recep- tor signaling, including survival, process outgrowth, differentiation, synaptogenesis, and synaptic plastic- ity (Bibel and Barde, 2000; Huang and Reichardt, 2001; Poo, 2001; Chao, 2003). Brain-derived neuro- trophic factor (BDNF) has been shown to function in processes ranging from formation of ocular domi- nance pathways (Cabelli et al., 1997) to regulation of hippocampal long-term potentiation (Kang and Schu- *Present address: Redpoint Bio Corp. 2005 Eastpark Boule- vard, Cranbury, NJ 08512-3515. { Present address: Avda. Alfonso X el Sabio, INCYL-Facultad de Medicina, Salamanca 37007, Spain. { Present address: Rutgers University, Environmental and Occupational Health Sciences Institute, Piscataway, NJ 08854. Correspondence to: M.R. Plummer (mplummer@rci.rutgers. edu). Contract grant sponsors: Spanish Ministry of Education, NIH HD023315, NIH NS41310, NIH NS21072. ' 2007 Wiley Periodicals, Inc. Published online in Wiley InterScience(www.interscience. wiley.com). DOI 10.1002/dneu.20542 1