BMAA selectively injures motor neurons via AMPA/kainate receptor activation Shyam D. Rao a , Sandra Anne Banack b,c , Paul Alan Cox c , John H. Weiss a,d, ⁎ a Department of Anatomy and Neurobiology, 2101 Gillespie Building, University of California, Irvine, Irvine, CA 92697-4292, USA b Department of Biological Science, California State University, Fullerton, 800 N State College, Fullerton, CA 92834-6850, USA c Institute for Ethnomedicine, PO Box 3464, Jackson, WY 83001, USA d Department of Neurology, University of California, Irvine, CA 92697, USA Received 3 February 2006; revised 6 April 2006; accepted 8 April 2006 Available online 9 June 2006 Abstract The toxin beta-methylamino-L-alanine (BMAA) has been proposed to contribute to amyotrophic lateral sclerosis–Parkinsonism Dementia Complex of Guam (ALS/PDC) based on its ability to induce a similar disease phenotype in primates and its presence in cycad seeds, which constituted a dietary item in afflicted populations. Concerns about the apparent low potency of this toxin in relation to estimated levels of human ingestion led to a slowing of BMAA research. However, recent reports identifying potential new routes of exposure compel a re-examination of the BMAA/cycad hypothesis. BMAA was found to induce selective motor neuron (MN) loss in dissociated mixed spinal cord cultures at concentrations (∼ 30 μM) significantly lower than those previously found to induce widespread neuronal degeneration. The glutamate receptor antagonist NBQX prevented BMAA-induced death, implicating excitotoxic activation of AMPA/kainate receptors. Using microfluorimetric techniques, we further found that BMAA induced preferential [Ca 2+ ] i rises and selective reactive oxygen species (ROS) generation in MNs with minimal effect on other spinal neurons. Cycad seed extracts also triggered preferential AMPA/kainate-receptor-dependent MN injury, consistent with the idea that BMAA is a crucial toxic component in this plant. Present findings support the hypothesis that BMAA may contribute to the selective MN loss in ALS/PDC. © 2006 Elsevier Inc. All rights reserved. Keywords: ALS; Amyotrophic lateral sclerosis; ALS/PDC; ALS–PDC; Guam; Motor neuron; Cell culture; Glutamate; AMPA; Ca 2+ ; ROS; Cycad Amyotrophic lateral sclerosis (ALS) is an adult onset neuro- degenerative disease characterized by the selective loss of upper and lower motor neurons (MNs). Through the course of the disease, the clinical features of weakness, spasticity and muscu- lar atrophy progress to paralysis and ultimately death (Rowland and Shneider, 2001). Despite much research, its cause remains poorly understood. One of the earliest and most promising paths of scientific investigation focused on a rare form of the disease known as Guam ALS–Parkinsonism Dementia Complex (ALS/ PDC). In the 1950s, the ALS incidence and death rate among the indigenous Chamorro people of Guam were fifty to one hundred times that found in the continental United States and other industrialized countries (Koerner, 1952; Arnold et al., 1953; Mulder et al., 1954). The Guam form of ALS shows the same pattern of selective MN death with the additional feature of neurofibrillary tangles similar to those found in Alzheimer's disease (Malamud et al., 1961; Guiroy et al., 1987). Variant forms often exhibit Parkinsonism and an Alzheimer's-like de- mentia (PDC), but typically onset is 10 years later in life than ALS (Mulder et al., 1954; Kurland, 1988). Thus, understanding this syndrome might provide important insight into all three diseases. Epidemiological studies excluded a genetic or infectious ori- gin and implicated environmental exposures (Garruto and Yase, 1986; Spencer, 1987). One candidate cause was the seed of the cycad Cycas micronesia Hill (Hill, 1994), which was known to be acutely toxic but was consumed as food after repetitive washing and cooking (Whiting, 1963; Kurland, 1972). Several Experimental Neurology 201 (2006) 244 – 252 www.elsevier.com/locate/yexnr ⁎ Corresponding author. Fax: +1 949 824 1668. E-mail address: jweiss@uci.edu (J.H. Weiss). 0014-4886/$ - see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.expneurol.2006.04.017