Neurotransmitters, Neuroregulators and Neurotoxins in Plants - Communication in Plants: Neuronal Aspects of Plant Life - page 147

paralysis, and damaged neurons in the striatum and cortex producing
parkinsonian and behavioral changes. However, Duncan et al. (1988) ar-
gued that humans would need to eat massive amounts of cycad seed flour
on a daily basis to generate a similar progressive neurological disease and
as a result the BMAA hypothesis was largely discounted. In 2002, Cox and
Sachs hypothesized that biomagnification of BMAA through the Guam
ecosystem could effectively concentrate cycad neurotoxins and increase
the exposure of the Chamorro people. The hypothesis suggested that fly-
ing foxes ( Pteropus mariannus mariannus ), large indigenous bats that feed
on cycad seeds, biomagnified cycad neurotoxins in the Chamorro diet.
In interviews many Chamorros identified flying foxes as the most prized
food item. The population of flying foxes dramatically declined from about
70,000 in the 1920s to just 58 individuals currently alive in Guam (Monson
et al. 2003). Flying foxes consume the outermost integument of cycad seeds,
whereBMAAispresentatthehighestconcentrations,masticatethetissueto
extract the juices and spit out the pulp as “ejectapellets,” thereby effectively
concentrating the neurotoxin (Banack and Cox 2003b).Varying concentra-
tions of BMAA in individual flying foxes, related to individual foraging
patterns, might have resulted in different cumulative doses of neurotox-
ins among Chamorros who consumed equivalent numbers of flying foxes
(Banack and Cox 2003b). Ecological surveys of cycads on Guam revealed
that cycads have modified root structures that are positively geotropic and
house a cyanobacterial symbiont (Cox et al. 2003). Axenic cultures of nos-
tocisolatedfrom“coralloid”rootsofcycadsproducedabout0.3µg / gof

BMAA (Cox et al. 2003) and BMAA was found in the roots with heavy
cyanobacterial infections at concentrations up to 37 µg

/ g(Murchetal.

2004c). Recently, BMAA was also found in diverse taxa of cyanobacteria
collected worldwide (Cox et al. 2005). Further, BMAA was detected in the
brain tissues of Chamorro patients who died of ALS/PDC and in the brain
tissues of two Canadians who died of Alzheimer's disease (Murch et al.
2004d) and chemical analysis of the Chamorro flour and flying fox samples
from Guam revealed that although BMAA is a non-protein amino acid,
it is accumulated into proteins in cyanobacteria, cycads, flying foxes and
humans (Murch et al. 2004c). These data are fascinating as together they
describe the biomagnification and persistence of a naturally occurring neu-
rotoxin through various trophic levels of the ecosystem culminating with
human exposure.